Clinical Review

The chaos of a busy ED can test the cognitive reserve of even the most focused practitioner. To streamline the challenge of serial diagnosis and treatment, clinicians employ heuristics while honing the skills of pattern recognition. However, by definition, heuristics employs shortcuts, leaving out information for the sake of efficiency—sometimes at the expense of accuracy. Whether a patient presents with chest pain, abdominal pain, headache, or (the dreaded) dizziness, emergency physicians (EPs) employ algorithms based on a combination of education and prior experience.

Most of the time, these models lead the EP along the correct path, but not always. For example, when a clinician evaluating a patient presenting with psychotic behavior assumes the patient has schizophrenia, he or she will be correct eight or nine times out of 10. However, in some cases, a patient’s bizarre behavior may not be due to a true psychiatric disorder but, for example, from ingestion of an illicit substance.

In addition, in such patients, psychiatric symptoms may be masking a serious acute, organic condition—one requiring prompt intervention and therapy to avoid morbidity or death. To help prevent diagnostic errors, this 2-part series reviews several of the most common medical mimics of psychiatric conditions. Part 1 of this series reviews the psychiatric presentations associated with medical conditions of an infectious, pharmacological withdrawal, metabolic, autoimmune, traumatic, or central nervous system etiology (Table 1). This article also discusses clinical signs and symptoms that suggest an increased likelihood that a patient’s psychiatric symptoms are from an underlying medical condition (Table 2).

Case Scenarios

Case 1

A 58-year-old woman with a history of smoking 40 packs of cigarettes per year presented to the ED 1 hour after onset of intermittent chest pain. Upon arrival at the ED, the patient stated that she had trouble catching her breath on and off throughout the day. The patient’s vital signs, electrocardiogram (ECG), and chest X-ray were all normal. The physical examination was unremarkable except for mild diaphoresis. The patient denied experiencing palpitations, recent travel, or previous episodes; she further stated that she was currently not on any medications. There was no previous history of visits to this hospital. The patient’s husband, who accompanied her to the ED, noted that his wife’s behavior had been atypical for approximately 1 week.

After receiving aspirin, the patient appeared symptom-free. Pending the results of another chest radiograph and laboratory evaluation, the EP anticipated moving her to the chest-pain observation unit.

Case 2

A 36-year-old woman presented with altered mental status to the ED via emergency medical services (EMS). Her vital signs, including temperature, were normal. Despite intermittently appearing to be asleep, the patient was alternatingly cooperative and combative. She repetitively whispered, “Who am I?” and randomly shouted at staff members as they walked by her room.

Her neurological examination was nonfocal. The hospital’s electronic medical record (EMR) for this patient showed nearly monthly ED visits for behavioral symptoms. Precipitating events noted in the EMR included job loss and separation from her husband. While waiting for the results of the basic laboratory work-up and toxicology screening to medically clear the patient for psychiatric evaluation, the EP contemplated a computed tomography (CT) study. Realizing the patient would not be able to remain still for the scan, the EP ordered 10 mg of intramuscular ziprasidone for sedation. When the patient’s husband arrived, the EP placed the CT scan on hold until she could obtain additional history from him.

Infections

Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is a serious but treatable disease—one that requires early detection and treatment to avoid severe morbidity. While the classic symptoms are fever and altered mental status, recent literature has noted that afebrile patients with HSE may present with behavioral changes, cognitive decline, aggression, and disinhibition. Therefore, diagnosis of a functional psychiatric complaint, if made initially, could delay appropriate treatment with acyclovir.¹

Human Immunodeficiency Virus

Progression of human immunodeficiency virus (HIV) is a well-known cause of various neurocognitive disorders, including early-onset dementia. Since the availability of highly active antiretroviral therapy, the incidence of HIV dementia has decreased, but HIV remains the most common preventable cause of dementia in persons younger than age 50 years. Recent literature has described HIV dementia presenting as an early-onset, rapidly progressing dementia in a young person. Thus, the EP should consider early HIV testing in any young patient who presents with dementia, especially one with a history of fever of unknown origin.²

Progressive Multifocal Encephalopathy

Caused by reactivation of the John Cunningham virus, progressive multifocal encephalopathy has been classically described as a potentially lethal complication of a severely immunocompromised state, often presenting with clumsiness, weakness, visual changes, speech difficulty, and behavioral changes. Though typically described as occurring in the context of acquired immunodeficiency disease syndrome, hematological malignancy, or organ transplant, the condition can occur in the setting of minimal or occult immunosuppression—especially in patients with a history of cirrhosis. If the condition is detected early, immunotherapy can result in significant clinical improvement.³

Syphilis

Late stages of syphilis can present with a wide variety of psychiatric symptoms, including personality disorder, psychosis, delirium, and dementia. As with HIV, there has been a resurgence of syphilis cases, and screening is now often a routine part of a neuropsychiatric work-up. The EP should consider syphilis in the differential for any new-onset psychiatric complaint.^4,5

Typhoid Fever

Although this severe febrile illness is uncommon in the United States, it is endemic to many tropical countries within Africa, Southeast Asia, and Central and South America. Typhoid is characterized by a stepwise fever that can progress to abdominal distension, toxemia, and potentially bowel perforation. It is also known to present with psychiatric symptoms such as acute confusion, psychosis, generalized anxiety disorder, and, though rare, depressive disorder. Physicians traveling to rural endemic areas should be aware of these neuropsychiatric presentations to avoid misdiagnosis and delay of treatment.⁶ Other infectious endemic diseases with reports of neuropsychiatric components are neurocystercercosis, Lyme disease, and African trypanosomiasis.

Pharmacological Withdrawal Syndromes

Alcohol

Alcohol withdrawal is a common presentation in the ED, and up to 24% of US adults brought to the ED by EMS suffer from alcoholism. Typically characterized by tachycardia, hypertension, and tremors, alcohol withdrawal syndrome can also feature psychiatric components such as agitation, hallucinations, persecutory delusions, and even self-mutilation.⁷ Evidence-based protocols indicate loading doses of benzodiazepines as a mainstay of treatment, with supplemental barbiturates or propofol in cases of treatment failure.⁸

Benzodiazepines

Withdrawal from therapeutic doses of benzodiazepines can potentially cause psychiatric symptoms, including sleep disturbances, irritability, anxiety, panic attacks, tremor, and perceptual changes. Withdrawal from higher doses of benzodiazepines can lead to more serious presentations, such as seizures and acute psychosis.⁹ Withdrawal symptoms can develop from discontinuation of the drug and with non-tapered switching between benzodiazepines.¹⁰

Opiates

Opiate withdrawal is an unpleasant experience characterized by generalized pain, nausea and vomiting, sweating, and tachycardia. Neuropsychiatric complaints such as anxiety, agitation, and irritability can also be present. More severe agitation has been described in naltrexone-accelerated detoxification^.11

Cannabis

Recent literature on cannabis use indicates a high prevalence and clinical significance of associated withdrawal symptoms in frequent users. There appear to be two subsets of cannabis withdrawal—one characterized by weakness and hypersomnia, and the other by anxiety, depression, restlessness, and insomnia.¹²

Estrogen

Withdrawal from endogenous estrogen has been hypothesized as a possible cause of puerperal psychosis.¹³ Estrogen withdrawal outside of this setting, however, can and does occur, and recent literature has shown episodes of reversible psychosis associated with the discontinuation of both oral contraceptive regimens and hormonal therapy for menopausal symptoms.

Acute Metabolic Conditions

Hypoglycemia

Hypoglycemia, most often encountered as a side effect of insulin or oral hypoglycemic therapies, is a potentially lethal cause of confusion, anxiety, nervousness, and seizures. Nocturnal hypoglycemia can manifest as nightmares, crying out, and confusion upon awakening. A fingerstick blood-glucose test is an absolutely vital part of the initial work-up of any patient with an altered mental status or overt psychiatric complaint.¹⁴

Central Pontine Myelinolysis

A potentially devastating neurological condition associated with malnourishment and alcohol dependence, central pontine myelinolysis (CPM) is classically exacerbated by rapid overcorrection of hyponatremia. While the disease can manifest primarily with quadriplegia or pseudobulbar palsy and eventual progress to the dreaded “locked-in” syndrome, early presentations can include psychiatric symptoms such as behavioral changes, psychosis, and cognitive disturbances. Patients with early signs and symptoms of CPM have been misdiagnosed as having schizophrenia with catatonia, leading to delayed treatment and poor outcomes. The EP should remain vigilant when evaluating for this condition and consider a magnetic resonance imaging study in patients with psychiatric symptoms in the setting of fluctuating hyponatremia.¹⁵

Autoimmune Disorders

Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is one of the most common autoimmune disorders, and has a higher incidence in young women. The disease affects multiple organ systems. Though the classic initial presentation of SLE is fever, joint pain, and rash, the associated neuropsychiatric syndromes of this disease are diverse and surprisingly common, and can be the initial manifestation of the disease. Common psychiatric manifestations of SLE include cognitive dysfunction, anxiety, mood disorders such as depression, acute confusion, psychosis, paranoia, and auditory or visual hallucinations.¹⁶

Anti-N-methyl-D-Aspartate Receptor Encephalitis

Initially described as a paraneoplastic effect of ovarian teratomas, anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is actually an autoimmune disorder that can occur even in the absence of a primary tumor. As with SLE, the condition primarily occurs in young women. Antibodies in the cerebrospinal fluid cause prominent psychiatric symptoms such as acute psychosis, delusional thinking, hallucinations, agitation, and confusion. Although the disease can progress to seizures, movement disorders, autonomic dysregulation, and ultimately death, early recognition and treatment can lead to positive outcomes in up to 80% of cases.¹⁷ While the prevalence of anti-NMDAR antibodies in new-onset psychosis remains unclear, recent literature has suggested widespread screening for the disease in all first presentations of psychotic episodes.^18,19

Multiple Sclerosis

Multiple sclerosis (MS) is another autoimmune disorder that has a higher prevalence in young women. The disease is characterized by central nervous system involvement that occurs over a period of months to years, with symptoms corresponding to different anatomic locations. Though the classic presenting symptom of MS is optic neuritis, neuropsychiatric syndromes are a common co-occurrence and can be the initial presenting symptom. The most commonly associated psychiatric complaints are anxiety, depression, and bipolar disorder, though case reports of SLE have described acute psychosis, psychotic depression, and adult-onset tic disorder.²⁰

Trauma

Subarachnoid Hemorrhage

Long-term psychiatric sequelae from subarachnoid hemorrhage, either traumatic or aneurysmal, manifest most commonly as personality changes, intellectual impairment, depression, and anxiety. This condition is also known to cause a host of more bizarre psychiatric presentations, such as new-onset kleptomania, akinetic mutism, confabulatory amnesia, acute psychosis, and Capgras syndrome (the delusion that familiar individuals have been replaced by imposters). These symptoms can occur at initial presentation, and may show variable improvement with shunt surgery.²¹

Subdural Hematoma

Acute or chronic subdural hematoma can result from major head trauma, or even quite minor head trauma in an elderly or coagulopathic patient. Some common psychiatric manifestations of subdural hematoma include cognitive impairment, withdrawn behavior, blunted affect otherwise mimicking schizophrenic psychosis, and catatonia. The EP should consider early imaging studies in patients with new-onset psychotic symptoms—especially when they are refractory to typical antipsychotics.²²

Central Nervous Symptom Diseases

Huntington Disease

Huntington disease (HD) is an autosomal dominant inherited, progressive neurodegenerative disorder characterized by mental decline, mood disorder, and muscle coordination problems that eventually become the classic involuntary writhing termed chorea. Due to its progressive nature, precise onset of the disease is difficult to describe; however, HD can manifest initially as schizophrenia-like psychotic episodes with only minimal apparent motor difficulty. Family history, including movement disorders and suicide, is important to obtain when available.²³

Parkinson Disease

A progressive and disabling neurodegenerative disorder, Parkinson disease (PD) is classically characterized by fine resting tremor, cogwheeling rigidity, akinesia and mask-like facies, and postural instability. Comorbidity of psychiatric disorders is high, both as a result of the underlying disease process and as a side effect of dopaminergic treatment regimes. Common presentations of psychiatric disorders in PD include schizophrenia-like psychosis with visual hallucinations and mood disorders with prominent apathy and executive dysfunction. Recognition of the comorbidity is important because psychiatric disorders in PD respond differently to treatment than classic psychiatric disorders.²⁴

Temporal Lobe Epilepsy

Epilepsy is a complex group of related neurological disorders involving unregulated nerve cell firing with a large variability in clinical presentation. Characteristically there is recurrent seizure activity. Temporal lobe epilepsy (TLE) is a subset of epilepsy known to present as a number of behavioral and neuropsychiatric complaints. Most presentations of TLE involve auras of emotional phenomena such as depression, fear, or anxiety, which can occur alone or with subsequent progression to complex partial or secondary generalized seizures.²⁵ Many other bizarre presentations of TLE have been reported, including recurrent, potentially debilitating déjà vu, vivid recollection of past traumatic events mimicking posttraumatic stress disorder, paranoid delusions following olfactory triggers; and unprovoked attacks of depersonalization, derealization, anxiety, and dyspnea originally misdiagnosed as panic attack.

Stroke

The term “stroke chameleon” refers to presentations suggestive of other diseases that actually represent underlying strokes. Altered mental status is by far the largest block of these chameleons, with up to 30% of misdiagnosed strokes being misdiagnosed as altered mental status. The positive predictive value of altered mental status alone (ie, the chance that the diagnosis of altered mental status actually represents an undiagnosed acute stroke) is 7%.²⁶

Case Scenarios Continued

Case 1

[The 58-year-old woman with intermittent chest pain.]

The patient’s D-dimer and troponin I levels were normal. Before the EP had an opportunity to discuss the results and next steps with the patient, the nurse asked him to see the patient immediately. Upon entering her room, the EP noted that the patient appeared anxious. The patient said the shortness of breath had returned, and also that she felt as if she were “floating” off the gurney, outside of her body. A check of her vital signs revealed a heart rate of 106 beats/minute and blood pressure of 160/100 mm Hg. A repeat ECG was significant only for sinus tachycardia. In an effort to calm the patient, the EP reassured her that the ECG, chest X-ray, and screening laboratory studies were normal, and that there was no evidence of a heart attack. Relieved, the patient asked for an Ativan to calm her nerves. Upon further questioning, the patient sheepishly reported that she had been taking 3 to 6 mg lorazepam for about 10 years, as prescribed by her family physician (FP) for anxiety. She further admitted that she abruptly discontinued taking the drug about one week before this ED visit after she’d heard on a daytime TV show that the medication was addictive.

After receiving lorazepam, the patient showed marked improvement. The EP’s final impressions were atypical chest pain and acute panic attack precipitated by abrupt benzodiazepine withdrawal. After discussing the case with the patient’s FP, the EP discharged the patient home with instructions to complete the cardiac evaluation as an outpatient. The EP also recommended that the patient resume taking lorazepam and follow-up with her FP within one week to discuss a benzodiazepine taper and alternative therapy for anxiety.

Case 2

[The 36-year-old woman with altered mental status.]

When the EP entered the patient’s room, he witnessed the patient staring at her husband and striking him repetitively with her right arm. When the EP asked the patient to stop hitting, her husband told the EP that everything was alright and that the patient’s neurologist had previously told them this behavior was caused by a seizure. While in the next examination room, one of the EP’s colleagues had overheard some of the patient’s history and recognized the name of the patient’s neurologist as a specialist in partial complex seizures—one who had retired from the local medical school about 10 years ago.

After records from the local university hospital confirmed the patient’s diagnosis of partial complex seizures, she was given intravenous lorazepam 2 mg; she became alert, conversational, and stopped flailing her right arm. She was then admitted to the hospital for medical stabilization of her frequent seizures.

Editor’s Note: Part 2 of this article will appear in the June 2016 issue of Emergency Medicine and will cover psychiatric presentations related to dementia, cancer, cardiac disease, nutritional deficiencies, endocrine disorders, and toxins.

The chaos of a busy ED can test the cognitive reserve of even the most focused practitioner. To streamline the challenge of serial diagnosis and treatment, clinicians employ heuristics while honing the skills of pattern recognition. However, by definition, heuristics employs shortcuts, leaving out information for the sake of efficiency—sometimes at the expense of accuracy. Whether a patient presents with chest pain, abdominal pain, headache, or (the dreaded) dizziness, emergency physicians (EPs) employ algorithms based on a combination of education and prior experience.

Most of the time, these models lead the EP along the correct path, but not always. For example, when a clinician evaluating a patient presenting with psychotic behavior assumes the patient has schizophrenia, he or she will be correct eight or nine times out of 10. However, in some cases, a patient’s bizarre behavior may not be due to a true psychiatric disorder but, for example, from ingestion of an illicit substance.

In addition, in such patients, psychiatric symptoms may be masking a serious acute, organic condition—one requiring prompt intervention and therapy to avoid morbidity or death. To help prevent diagnostic errors, this 2-part series reviews several of the most common medical mimics of psychiatric conditions. Part 1 of this series reviews the psychiatric presentations associated with medical conditions of an infectious, pharmacological withdrawal, metabolic, autoimmune, traumatic, or central nervous system etiology (Table 1). This article also discusses clinical signs and symptoms that suggest an increased likelihood that a patient’s psychiatric symptoms are from an underlying medical condition (Table 2).

Case Scenarios

Case 1

A 58-year-old woman with a history of smoking 40 packs of cigarettes per year presented to the ED 1 hour after onset of intermittent chest pain. Upon arrival at the ED, the patient stated that she had trouble catching her breath on and off throughout the day. The patient’s vital signs, electrocardiogram (ECG), and chest X-ray were all normal. The physical examination was unremarkable except for mild diaphoresis. The patient denied experiencing palpitations, recent travel, or previous episodes; she further stated that she was currently not on any medications. There was no previous history of visits to this hospital. The patient’s husband, who accompanied her to the ED, noted that his wife’s behavior had been atypical for approximately 1 week.

After receiving aspirin, the patient appeared symptom-free. Pending the results of another chest radiograph and laboratory evaluation, the EP anticipated moving her to the chest-pain observation unit.

Case 2

A 36-year-old woman presented with altered mental status to the ED via emergency medical services (EMS). Her vital signs, including temperature, were normal. Despite intermittently appearing to be asleep, the patient was alternatingly cooperative and combative. She repetitively whispered, “Who am I?” and randomly shouted at staff members as they walked by her room.

Her neurological examination was nonfocal. The hospital’s electronic medical record (EMR) for this patient showed nearly monthly ED visits for behavioral symptoms. Precipitating events noted in the EMR included job loss and separation from her husband. While waiting for the results of the basic laboratory work-up and toxicology screening to medically clear the patient for psychiatric evaluation, the EP contemplated a computed tomography (CT) study. Realizing the patient would not be able to remain still for the scan, the EP ordered 10 mg of intramuscular ziprasidone for sedation. When the patient’s husband arrived, the EP placed the CT scan on hold until she could obtain additional history from him.

Infections

Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is a serious but treatable disease—one that requires early detection and treatment to avoid severe morbidity. While the classic symptoms are fever and altered mental status, recent literature has noted that afebrile patients with HSE may present with behavioral changes, cognitive decline, aggression, and disinhibition. Therefore, diagnosis of a functional psychiatric complaint, if made initially, could delay appropriate treatment with acyclovir.¹

Human Immunodeficiency Virus

Progression of human immunodeficiency virus (HIV) is a well-known cause of various neurocognitive disorders, including early-onset dementia. Since the availability of highly active antiretroviral therapy, the incidence of HIV dementia has decreased, but HIV remains the most common preventable cause of dementia in persons younger than age 50 years. Recent literature has described HIV dementia presenting as an early-onset, rapidly progressing dementia in a young person. Thus, the EP should consider early HIV testing in any young patient who presents with dementia, especially one with a history of fever of unknown origin.²

Progressive Multifocal Encephalopathy

Caused by reactivation of the John Cunningham virus, progressive multifocal encephalopathy has been classically described as a potentially lethal complication of a severely immunocompromised state, often presenting with clumsiness, weakness, visual changes, speech difficulty, and behavioral changes. Though typically described as occurring in the context of acquired immunodeficiency disease syndrome, hematological malignancy, or organ transplant, the condition can occur in the setting of minimal or occult immunosuppression—especially in patients with a history of cirrhosis. If the condition is detected early, immunotherapy can result in significant clinical improvement.³

Syphilis

Late stages of syphilis can present with a wide variety of psychiatric symptoms, including personality disorder, psychosis, delirium, and dementia. As with HIV, there has been a resurgence of syphilis cases, and screening is now often a routine part of a neuropsychiatric work-up. The EP should consider syphilis in the differential for any new-onset psychiatric complaint.^4,5

Typhoid Fever

Although this severe febrile illness is uncommon in the United States, it is endemic to many tropical countries within Africa, Southeast Asia, and Central and South America. Typhoid is characterized by a stepwise fever that can progress to abdominal distension, toxemia, and potentially bowel perforation. It is also known to present with psychiatric symptoms such as acute confusion, psychosis, generalized anxiety disorder, and, though rare, depressive disorder. Physicians traveling to rural endemic areas should be aware of these neuropsychiatric presentations to avoid misdiagnosis and delay of treatment.⁶ Other infectious endemic diseases with reports of neuropsychiatric components are neurocystercercosis, Lyme disease, and African trypanosomiasis.

Pharmacological Withdrawal Syndromes

Alcohol

Alcohol withdrawal is a common presentation in the ED, and up to 24% of US adults brought to the ED by EMS suffer from alcoholism. Typically characterized by tachycardia, hypertension, and tremors, alcohol withdrawal syndrome can also feature psychiatric components such as agitation, hallucinations, persecutory delusions, and even self-mutilation.⁷ Evidence-based protocols indicate loading doses of benzodiazepines as a mainstay of treatment, with supplemental barbiturates or propofol in cases of treatment failure.⁸

Benzodiazepines

Withdrawal from therapeutic doses of benzodiazepines can potentially cause psychiatric symptoms, including sleep disturbances, irritability, anxiety, panic attacks, tremor, and perceptual changes. Withdrawal from higher doses of benzodiazepines can lead to more serious presentations, such as seizures and acute psychosis.⁹ Withdrawal symptoms can develop from discontinuation of the drug and with non-tapered switching between benzodiazepines.¹⁰

Opiates

Opiate withdrawal is an unpleasant experience characterized by generalized pain, nausea and vomiting, sweating, and tachycardia. Neuropsychiatric complaints such as anxiety, agitation, and irritability can also be present. More severe agitation has been described in naltrexone-accelerated detoxification^.11

Cannabis

Recent literature on cannabis use indicates a high prevalence and clinical significance of associated withdrawal symptoms in frequent users. There appear to be two subsets of cannabis withdrawal—one characterized by weakness and hypersomnia, and the other by anxiety, depression, restlessness, and insomnia.¹²

Estrogen

Withdrawal from endogenous estrogen has been hypothesized as a possible cause of puerperal psychosis.¹³ Estrogen withdrawal outside of this setting, however, can and does occur, and recent literature has shown episodes of reversible psychosis associated with the discontinuation of both oral contraceptive regimens and hormonal therapy for menopausal symptoms.

Acute Metabolic Conditions

Hypoglycemia

Hypoglycemia, most often encountered as a side effect of insulin or oral hypoglycemic therapies, is a potentially lethal cause of confusion, anxiety, nervousness, and seizures. Nocturnal hypoglycemia can manifest as nightmares, crying out, and confusion upon awakening. A fingerstick blood-glucose test is an absolutely vital part of the initial work-up of any patient with an altered mental status or overt psychiatric complaint.¹⁴

Central Pontine Myelinolysis

A potentially devastating neurological condition associated with malnourishment and alcohol dependence, central pontine myelinolysis (CPM) is classically exacerbated by rapid overcorrection of hyponatremia. While the disease can manifest primarily with quadriplegia or pseudobulbar palsy and eventual progress to the dreaded “locked-in” syndrome, early presentations can include psychiatric symptoms such as behavioral changes, psychosis, and cognitive disturbances. Patients with early signs and symptoms of CPM have been misdiagnosed as having schizophrenia with catatonia, leading to delayed treatment and poor outcomes. The EP should remain vigilant when evaluating for this condition and consider a magnetic resonance imaging study in patients with psychiatric symptoms in the setting of fluctuating hyponatremia.¹⁵

Autoimmune Disorders

Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is one of the most common autoimmune disorders, and has a higher incidence in young women. The disease affects multiple organ systems. Though the classic initial presentation of SLE is fever, joint pain, and rash, the associated neuropsychiatric syndromes of this disease are diverse and surprisingly common, and can be the initial manifestation of the disease. Common psychiatric manifestations of SLE include cognitive dysfunction, anxiety, mood disorders such as depression, acute confusion, psychosis, paranoia, and auditory or visual hallucinations.¹⁶

Anti-N-methyl-D-Aspartate Receptor Encephalitis

Initially described as a paraneoplastic effect of ovarian teratomas, anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is actually an autoimmune disorder that can occur even in the absence of a primary tumor. As with SLE, the condition primarily occurs in young women. Antibodies in the cerebrospinal fluid cause prominent psychiatric symptoms such as acute psychosis, delusional thinking, hallucinations, agitation, and confusion. Although the disease can progress to seizures, movement disorders, autonomic dysregulation, and ultimately death, early recognition and treatment can lead to positive outcomes in up to 80% of cases.¹⁷ While the prevalence of anti-NMDAR antibodies in new-onset psychosis remains unclear, recent literature has suggested widespread screening for the disease in all first presentations of psychotic episodes.^18,19

Multiple Sclerosis

Multiple sclerosis (MS) is another autoimmune disorder that has a higher prevalence in young women. The disease is characterized by central nervous system involvement that occurs over a period of months to years, with symptoms corresponding to different anatomic locations. Though the classic presenting symptom of MS is optic neuritis, neuropsychiatric syndromes are a common co-occurrence and can be the initial presenting symptom. The most commonly associated psychiatric complaints are anxiety, depression, and bipolar disorder, though case reports of SLE have described acute psychosis, psychotic depression, and adult-onset tic disorder.²⁰

Trauma

Subarachnoid Hemorrhage

Long-term psychiatric sequelae from subarachnoid hemorrhage, either traumatic or aneurysmal, manifest most commonly as personality changes, intellectual impairment, depression, and anxiety. This condition is also known to cause a host of more bizarre psychiatric presentations, such as new-onset kleptomania, akinetic mutism, confabulatory amnesia, acute psychosis, and Capgras syndrome (the delusion that familiar individuals have been replaced by imposters). These symptoms can occur at initial presentation, and may show variable improvement with shunt surgery.²¹

Subdural Hematoma

Acute or chronic subdural hematoma can result from major head trauma, or even quite minor head trauma in an elderly or coagulopathic patient. Some common psychiatric manifestations of subdural hematoma include cognitive impairment, withdrawn behavior, blunted affect otherwise mimicking schizophrenic psychosis, and catatonia. The EP should consider early imaging studies in patients with new-onset psychotic symptoms—especially when they are refractory to typical antipsychotics.²²

Central Nervous Symptom Diseases

Huntington Disease

Huntington disease (HD) is an autosomal dominant inherited, progressive neurodegenerative disorder characterized by mental decline, mood disorder, and muscle coordination problems that eventually become the classic involuntary writhing termed chorea. Due to its progressive nature, precise onset of the disease is difficult to describe; however, HD can manifest initially as schizophrenia-like psychotic episodes with only minimal apparent motor difficulty. Family history, including movement disorders and suicide, is important to obtain when available.²³

Parkinson Disease

A progressive and disabling neurodegenerative disorder, Parkinson disease (PD) is classically characterized by fine resting tremor, cogwheeling rigidity, akinesia and mask-like facies, and postural instability. Comorbidity of psychiatric disorders is high, both as a result of the underlying disease process and as a side effect of dopaminergic treatment regimes. Common presentations of psychiatric disorders in PD include schizophrenia-like psychosis with visual hallucinations and mood disorders with prominent apathy and executive dysfunction. Recognition of the comorbidity is important because psychiatric disorders in PD respond differently to treatment than classic psychiatric disorders.²⁴

Temporal Lobe Epilepsy

Epilepsy is a complex group of related neurological disorders involving unregulated nerve cell firing with a large variability in clinical presentation. Characteristically there is recurrent seizure activity. Temporal lobe epilepsy (TLE) is a subset of epilepsy known to present as a number of behavioral and neuropsychiatric complaints. Most presentations of TLE involve auras of emotional phenomena such as depression, fear, or anxiety, which can occur alone or with subsequent progression to complex partial or secondary generalized seizures.²⁵ Many other bizarre presentations of TLE have been reported, including recurrent, potentially debilitating déjà vu, vivid recollection of past traumatic events mimicking posttraumatic stress disorder, paranoid delusions following olfactory triggers; and unprovoked attacks of depersonalization, derealization, anxiety, and dyspnea originally misdiagnosed as panic attack.

Stroke

The term “stroke chameleon” refers to presentations suggestive of other diseases that actually represent underlying strokes. Altered mental status is by far the largest block of these chameleons, with up to 30% of misdiagnosed strokes being misdiagnosed as altered mental status. The positive predictive value of altered mental status alone (ie, the chance that the diagnosis of altered mental status actually represents an undiagnosed acute stroke) is 7%.²⁶

Case Scenarios Continued

Case 1

[The 58-year-old woman with intermittent chest pain.]

The patient’s D-dimer and troponin I levels were normal. Before the EP had an opportunity to discuss the results and next steps with the patient, the nurse asked him to see the patient immediately. Upon entering her room, the EP noted that the patient appeared anxious. The patient said the shortness of breath had returned, and also that she felt as if she were “floating” off the gurney, outside of her body. A check of her vital signs revealed a heart rate of 106 beats/minute and blood pressure of 160/100 mm Hg. A repeat ECG was significant only for sinus tachycardia. In an effort to calm the patient, the EP reassured her that the ECG, chest X-ray, and screening laboratory studies were normal, and that there was no evidence of a heart attack. Relieved, the patient asked for an Ativan to calm her nerves. Upon further questioning, the patient sheepishly reported that she had been taking 3 to 6 mg lorazepam for about 10 years, as prescribed by her family physician (FP) for anxiety. She further admitted that she abruptly discontinued taking the drug about one week before this ED visit after she’d heard on a daytime TV show that the medication was addictive.

After receiving lorazepam, the patient showed marked improvement. The EP’s final impressions were atypical chest pain and acute panic attack precipitated by abrupt benzodiazepine withdrawal. After discussing the case with the patient’s FP, the EP discharged the patient home with instructions to complete the cardiac evaluation as an outpatient. The EP also recommended that the patient resume taking lorazepam and follow-up with her FP within one week to discuss a benzodiazepine taper and alternative therapy for anxiety.

Case 2

[The 36-year-old woman with altered mental status.]

When the EP entered the patient’s room, he witnessed the patient staring at her husband and striking him repetitively with her right arm. When the EP asked the patient to stop hitting, her husband told the EP that everything was alright and that the patient’s neurologist had previously told them this behavior was caused by a seizure. While in the next examination room, one of the EP’s colleagues had overheard some of the patient’s history and recognized the name of the patient’s neurologist as a specialist in partial complex seizures—one who had retired from the local medical school about 10 years ago.

After records from the local university hospital confirmed the patient’s diagnosis of partial complex seizures, she was given intravenous lorazepam 2 mg; she became alert, conversational, and stopped flailing her right arm. She was then admitted to the hospital for medical stabilization of her frequent seizures.

Editor’s Note: Part 2 of this article will appear in the June 2016 issue of Emergency Medicine and will cover psychiatric presentations related to dementia, cancer, cardiac disease, nutritional deficiencies, endocrine disorders, and toxins.

The chaos of a busy ED can test the cognitive reserve of even the most focused practitioner. To streamline the challenge of serial diagnosis and treatment, clinicians employ heuristics while honing the skills of pattern recognition. However, by definition, heuristics employs shortcuts, leaving out information for the sake of efficiency—sometimes at the expense of accuracy. Whether a patient presents with chest pain, abdominal pain, headache, or (the dreaded) dizziness, emergency physicians (EPs) employ algorithms based on a combination of education and prior experience.

Most of the time, these models lead the EP along the correct path, but not always. For example, when a clinician evaluating a patient presenting with psychotic behavior assumes the patient has schizophrenia, he or she will be correct eight or nine times out of 10. However, in some cases, a patient’s bizarre behavior may not be due to a true psychiatric disorder but, for example, from ingestion of an illicit substance.

In addition, in such patients, psychiatric symptoms may be masking a serious acute, organic condition—one requiring prompt intervention and therapy to avoid morbidity or death. To help prevent diagnostic errors, this 2-part series reviews several of the most common medical mimics of psychiatric conditions. Part 1 of this series reviews the psychiatric presentations associated with medical conditions of an infectious, pharmacological withdrawal, metabolic, autoimmune, traumatic, or central nervous system etiology (Table 1). This article also discusses clinical signs and symptoms that suggest an increased likelihood that a patient’s psychiatric symptoms are from an underlying medical condition (Table 2).

Case Scenarios

Case 1

A 58-year-old woman with a history of smoking 40 packs of cigarettes per year presented to the ED 1 hour after onset of intermittent chest pain. Upon arrival at the ED, the patient stated that she had trouble catching her breath on and off throughout the day. The patient’s vital signs, electrocardiogram (ECG), and chest X-ray were all normal. The physical examination was unremarkable except for mild diaphoresis. The patient denied experiencing palpitations, recent travel, or previous episodes; she further stated that she was currently not on any medications. There was no previous history of visits to this hospital. The patient’s husband, who accompanied her to the ED, noted that his wife’s behavior had been atypical for approximately 1 week.

After receiving aspirin, the patient appeared symptom-free. Pending the results of another chest radiograph and laboratory evaluation, the EP anticipated moving her to the chest-pain observation unit.

Case 2

A 36-year-old woman presented with altered mental status to the ED via emergency medical services (EMS). Her vital signs, including temperature, were normal. Despite intermittently appearing to be asleep, the patient was alternatingly cooperative and combative. She repetitively whispered, “Who am I?” and randomly shouted at staff members as they walked by her room.

Her neurological examination was nonfocal. The hospital’s electronic medical record (EMR) for this patient showed nearly monthly ED visits for behavioral symptoms. Precipitating events noted in the EMR included job loss and separation from her husband. While waiting for the results of the basic laboratory work-up and toxicology screening to medically clear the patient for psychiatric evaluation, the EP contemplated a computed tomography (CT) study. Realizing the patient would not be able to remain still for the scan, the EP ordered 10 mg of intramuscular ziprasidone for sedation. When the patient’s husband arrived, the EP placed the CT scan on hold until she could obtain additional history from him.

Infections

Herpes Simplex Encephalitis

Herpes simplex encephalitis (HSE) is a serious but treatable disease—one that requires early detection and treatment to avoid severe morbidity. While the classic symptoms are fever and altered mental status, recent literature has noted that afebrile patients with HSE may present with behavioral changes, cognitive decline, aggression, and disinhibition. Therefore, diagnosis of a functional psychiatric complaint, if made initially, could delay appropriate treatment with acyclovir.¹

Human Immunodeficiency Virus

Progression of human immunodeficiency virus (HIV) is a well-known cause of various neurocognitive disorders, including early-onset dementia. Since the availability of highly active antiretroviral therapy, the incidence of HIV dementia has decreased, but HIV remains the most common preventable cause of dementia in persons younger than age 50 years. Recent literature has described HIV dementia presenting as an early-onset, rapidly progressing dementia in a young person. Thus, the EP should consider early HIV testing in any young patient who presents with dementia, especially one with a history of fever of unknown origin.²

Progressive Multifocal Encephalopathy

Caused by reactivation of the John Cunningham virus, progressive multifocal encephalopathy has been classically described as a potentially lethal complication of a severely immunocompromised state, often presenting with clumsiness, weakness, visual changes, speech difficulty, and behavioral changes. Though typically described as occurring in the context of acquired immunodeficiency disease syndrome, hematological malignancy, or organ transplant, the condition can occur in the setting of minimal or occult immunosuppression—especially in patients with a history of cirrhosis. If the condition is detected early, immunotherapy can result in significant clinical improvement.³

Syphilis

Late stages of syphilis can present with a wide variety of psychiatric symptoms, including personality disorder, psychosis, delirium, and dementia. As with HIV, there has been a resurgence of syphilis cases, and screening is now often a routine part of a neuropsychiatric work-up. The EP should consider syphilis in the differential for any new-onset psychiatric complaint.^4,5

Typhoid Fever

Although this severe febrile illness is uncommon in the United States, it is endemic to many tropical countries within Africa, Southeast Asia, and Central and South America. Typhoid is characterized by a stepwise fever that can progress to abdominal distension, toxemia, and potentially bowel perforation. It is also known to present with psychiatric symptoms such as acute confusion, psychosis, generalized anxiety disorder, and, though rare, depressive disorder. Physicians traveling to rural endemic areas should be aware of these neuropsychiatric presentations to avoid misdiagnosis and delay of treatment.⁶ Other infectious endemic diseases with reports of neuropsychiatric components are neurocystercercosis, Lyme disease, and African trypanosomiasis.

Pharmacological Withdrawal Syndromes

Alcohol

Alcohol withdrawal is a common presentation in the ED, and up to 24% of US adults brought to the ED by EMS suffer from alcoholism. Typically characterized by tachycardia, hypertension, and tremors, alcohol withdrawal syndrome can also feature psychiatric components such as agitation, hallucinations, persecutory delusions, and even self-mutilation.⁷ Evidence-based protocols indicate loading doses of benzodiazepines as a mainstay of treatment, with supplemental barbiturates or propofol in cases of treatment failure.⁸

Benzodiazepines

Withdrawal from therapeutic doses of benzodiazepines can potentially cause psychiatric symptoms, including sleep disturbances, irritability, anxiety, panic attacks, tremor, and perceptual changes. Withdrawal from higher doses of benzodiazepines can lead to more serious presentations, such as seizures and acute psychosis.⁹ Withdrawal symptoms can develop from discontinuation of the drug and with non-tapered switching between benzodiazepines.¹⁰

Opiates

Opiate withdrawal is an unpleasant experience characterized by generalized pain, nausea and vomiting, sweating, and tachycardia. Neuropsychiatric complaints such as anxiety, agitation, and irritability can also be present. More severe agitation has been described in naltrexone-accelerated detoxification^.11

Cannabis

Recent literature on cannabis use indicates a high prevalence and clinical significance of associated withdrawal symptoms in frequent users. There appear to be two subsets of cannabis withdrawal—one characterized by weakness and hypersomnia, and the other by anxiety, depression, restlessness, and insomnia.¹²

Estrogen

Withdrawal from endogenous estrogen has been hypothesized as a possible cause of puerperal psychosis.¹³ Estrogen withdrawal outside of this setting, however, can and does occur, and recent literature has shown episodes of reversible psychosis associated with the discontinuation of both oral contraceptive regimens and hormonal therapy for menopausal symptoms.

Acute Metabolic Conditions

Hypoglycemia

Hypoglycemia, most often encountered as a side effect of insulin or oral hypoglycemic therapies, is a potentially lethal cause of confusion, anxiety, nervousness, and seizures. Nocturnal hypoglycemia can manifest as nightmares, crying out, and confusion upon awakening. A fingerstick blood-glucose test is an absolutely vital part of the initial work-up of any patient with an altered mental status or overt psychiatric complaint.¹⁴

Central Pontine Myelinolysis

A potentially devastating neurological condition associated with malnourishment and alcohol dependence, central pontine myelinolysis (CPM) is classically exacerbated by rapid overcorrection of hyponatremia. While the disease can manifest primarily with quadriplegia or pseudobulbar palsy and eventual progress to the dreaded “locked-in” syndrome, early presentations can include psychiatric symptoms such as behavioral changes, psychosis, and cognitive disturbances. Patients with early signs and symptoms of CPM have been misdiagnosed as having schizophrenia with catatonia, leading to delayed treatment and poor outcomes. The EP should remain vigilant when evaluating for this condition and consider a magnetic resonance imaging study in patients with psychiatric symptoms in the setting of fluctuating hyponatremia.¹⁵

Autoimmune Disorders

Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is one of the most common autoimmune disorders, and has a higher incidence in young women. The disease affects multiple organ systems. Though the classic initial presentation of SLE is fever, joint pain, and rash, the associated neuropsychiatric syndromes of this disease are diverse and surprisingly common, and can be the initial manifestation of the disease. Common psychiatric manifestations of SLE include cognitive dysfunction, anxiety, mood disorders such as depression, acute confusion, psychosis, paranoia, and auditory or visual hallucinations.¹⁶

Anti-N-methyl-D-Aspartate Receptor Encephalitis

Initially described as a paraneoplastic effect of ovarian teratomas, anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is actually an autoimmune disorder that can occur even in the absence of a primary tumor. As with SLE, the condition primarily occurs in young women. Antibodies in the cerebrospinal fluid cause prominent psychiatric symptoms such as acute psychosis, delusional thinking, hallucinations, agitation, and confusion. Although the disease can progress to seizures, movement disorders, autonomic dysregulation, and ultimately death, early recognition and treatment can lead to positive outcomes in up to 80% of cases.¹⁷ While the prevalence of anti-NMDAR antibodies in new-onset psychosis remains unclear, recent literature has suggested widespread screening for the disease in all first presentations of psychotic episodes.^18,19

Multiple Sclerosis

Multiple sclerosis (MS) is another autoimmune disorder that has a higher prevalence in young women. The disease is characterized by central nervous system involvement that occurs over a period of months to years, with symptoms corresponding to different anatomic locations. Though the classic presenting symptom of MS is optic neuritis, neuropsychiatric syndromes are a common co-occurrence and can be the initial presenting symptom. The most commonly associated psychiatric complaints are anxiety, depression, and bipolar disorder, though case reports of SLE have described acute psychosis, psychotic depression, and adult-onset tic disorder.²⁰

Trauma

Subarachnoid Hemorrhage

Long-term psychiatric sequelae from subarachnoid hemorrhage, either traumatic or aneurysmal, manifest most commonly as personality changes, intellectual impairment, depression, and anxiety. This condition is also known to cause a host of more bizarre psychiatric presentations, such as new-onset kleptomania, akinetic mutism, confabulatory amnesia, acute psychosis, and Capgras syndrome (the delusion that familiar individuals have been replaced by imposters). These symptoms can occur at initial presentation, and may show variable improvement with shunt surgery.²¹

Subdural Hematoma

Acute or chronic subdural hematoma can result from major head trauma, or even quite minor head trauma in an elderly or coagulopathic patient. Some common psychiatric manifestations of subdural hematoma include cognitive impairment, withdrawn behavior, blunted affect otherwise mimicking schizophrenic psychosis, and catatonia. The EP should consider early imaging studies in patients with new-onset psychotic symptoms—especially when they are refractory to typical antipsychotics.²²

Central Nervous Symptom Diseases

Huntington Disease

Huntington disease (HD) is an autosomal dominant inherited, progressive neurodegenerative disorder characterized by mental decline, mood disorder, and muscle coordination problems that eventually become the classic involuntary writhing termed chorea. Due to its progressive nature, precise onset of the disease is difficult to describe; however, HD can manifest initially as schizophrenia-like psychotic episodes with only minimal apparent motor difficulty. Family history, including movement disorders and suicide, is important to obtain when available.²³

Parkinson Disease

A progressive and disabling neurodegenerative disorder, Parkinson disease (PD) is classically characterized by fine resting tremor, cogwheeling rigidity, akinesia and mask-like facies, and postural instability. Comorbidity of psychiatric disorders is high, both as a result of the underlying disease process and as a side effect of dopaminergic treatment regimes. Common presentations of psychiatric disorders in PD include schizophrenia-like psychosis with visual hallucinations and mood disorders with prominent apathy and executive dysfunction. Recognition of the comorbidity is important because psychiatric disorders in PD respond differently to treatment than classic psychiatric disorders.²⁴

Temporal Lobe Epilepsy

Epilepsy is a complex group of related neurological disorders involving unregulated nerve cell firing with a large variability in clinical presentation. Characteristically there is recurrent seizure activity. Temporal lobe epilepsy (TLE) is a subset of epilepsy known to present as a number of behavioral and neuropsychiatric complaints. Most presentations of TLE involve auras of emotional phenomena such as depression, fear, or anxiety, which can occur alone or with subsequent progression to complex partial or secondary generalized seizures.²⁵ Many other bizarre presentations of TLE have been reported, including recurrent, potentially debilitating déjà vu, vivid recollection of past traumatic events mimicking posttraumatic stress disorder, paranoid delusions following olfactory triggers; and unprovoked attacks of depersonalization, derealization, anxiety, and dyspnea originally misdiagnosed as panic attack.

Stroke

The term “stroke chameleon” refers to presentations suggestive of other diseases that actually represent underlying strokes. Altered mental status is by far the largest block of these chameleons, with up to 30% of misdiagnosed strokes being misdiagnosed as altered mental status. The positive predictive value of altered mental status alone (ie, the chance that the diagnosis of altered mental status actually represents an undiagnosed acute stroke) is 7%.²⁶

Case Scenarios Continued

Case 1

[The 58-year-old woman with intermittent chest pain.]

The patient’s D-dimer and troponin I levels were normal. Before the EP had an opportunity to discuss the results and next steps with the patient, the nurse asked him to see the patient immediately. Upon entering her room, the EP noted that the patient appeared anxious. The patient said the shortness of breath had returned, and also that she felt as if she were “floating” off the gurney, outside of her body. A check of her vital signs revealed a heart rate of 106 beats/minute and blood pressure of 160/100 mm Hg. A repeat ECG was significant only for sinus tachycardia. In an effort to calm the patient, the EP reassured her that the ECG, chest X-ray, and screening laboratory studies were normal, and that there was no evidence of a heart attack. Relieved, the patient asked for an Ativan to calm her nerves. Upon further questioning, the patient sheepishly reported that she had been taking 3 to 6 mg lorazepam for about 10 years, as prescribed by her family physician (FP) for anxiety. She further admitted that she abruptly discontinued taking the drug about one week before this ED visit after she’d heard on a daytime TV show that the medication was addictive.

After receiving lorazepam, the patient showed marked improvement. The EP’s final impressions were atypical chest pain and acute panic attack precipitated by abrupt benzodiazepine withdrawal. After discussing the case with the patient’s FP, the EP discharged the patient home with instructions to complete the cardiac evaluation as an outpatient. The EP also recommended that the patient resume taking lorazepam and follow-up with her FP within one week to discuss a benzodiazepine taper and alternative therapy for anxiety.

Case 2

[The 36-year-old woman with altered mental status.]

When the EP entered the patient’s room, he witnessed the patient staring at her husband and striking him repetitively with her right arm. When the EP asked the patient to stop hitting, her husband told the EP that everything was alright and that the patient’s neurologist had previously told them this behavior was caused by a seizure. While in the next examination room, one of the EP’s colleagues had overheard some of the patient’s history and recognized the name of the patient’s neurologist as a specialist in partial complex seizures—one who had retired from the local medical school about 10 years ago.

After records from the local university hospital confirmed the patient’s diagnosis of partial complex seizures, she was given intravenous lorazepam 2 mg; she became alert, conversational, and stopped flailing her right arm. She was then admitted to the hospital for medical stabilization of her frequent seizures.

Editor’s Note: Part 2 of this article will appear in the June 2016 issue of Emergency Medicine and will cover psychiatric presentations related to dementia, cancer, cardiac disease, nutritional deficiencies, endocrine disorders, and toxins.

Interpreting continuous fetal heart rate (FHR) monitoring is one of the most common tasks obstetricians perform during the course of intrapartum care. Notably, many providers do not seek ongoing training to optimize their ability to reliably and accurately interpret the FHR. Yet FHR interpretation is one of the most frequent causes of litigation in the modern obstetric practice. Failure to interpret continuous FHR monitoring appropriately is estimated to account for 75% of obstetric-related litigation.¹

Continuous FHR monitoring during labor was introduced to identify infants at risk for  developing hypoxic-ischemic encephalopathy (HIE). The rate of HIE has not declined, however, despite almost universal adoption of continuous FHR monitoring.² Numerous reasons account for this failure, including ad hoc interpretation of terminology, lack of standardized protocols for management and intervention, and the oftentimes challenging patterns that must be interpreted.³ The confusion about and dissatisfaction with the current state of FHR monitoring has led to attempts to enhance our ability to identify infants at risk with additional approaches (such as fetal pulse oximetry and fetal ST-segment evaluation), and some have called for a complete overhaul of our approach to interpreting the FHR. Clark and colleagues stated recently, "It is time to start over and establish some common language, standard interpretation, and reasonable management principles and guidelines."³

We must recognize that, as a stand-alone tool, continuous FHR monitoring is ineffective for avoiding preventable adverse outcomes. It is most likely to be effective when used in accordance with published standard guidelines by professionals skilled in interpretation and when timely, appropriate interventions are performed based on that interpretation. Optimal FHR monitoring requires a collaborative perinatal team that performs the monitoring correctly, interprets it appropriately, and communicates the findings effectively, and in a timely fashion, to all members of the care team when a high-risk pattern is detected.

In this article we review some common challenges that clinicians encounter during intrapartum FHR monitoring and we offer 10 simple tips to help overcome these challenges. The clinical scenarios described are derived from published reports in the medical literature, published malpractice claims, and from our personal experience working in a major health care system as part of a team charged with overseeing ongoing certification and training of labor and delivery nurses.

Challenge: Signal ambiguity
CASE 1  Young woman in labor with first pregnancy
A 19-year-old woman presents in spontaneous labor with her first pregnancy, which has been uncomplicated. During the course of her care, it is noted that the FHR changes to a lower baseline than previously recorded. Evaluation reveals that the external monitor is tracking the maternal heart rate and not the FHR (FIGURE 1). After the monitor is adjusted, both the fetal and maternal rates are documented for a short period. Ultimately, continuous monitoring of the maternal heart rate is discontinued. After delivery of the infant several hours later, it is noted that the FHR continues to register on the monitor, and it is determined that for the last few hours the maternal heart rate has been traced.

FIGURE 1 FHR tracing indicates signal ambiguity

As described in Case 1, the upper panel of this tracing demonstrates the maternal heart rate confused as the fetal heart rate, while the segment in the lower panel shows a clear distinction between the maternal and fetal heart rates.

TIP #10: Ensure the FHR monitor is tracking the fetal, not the maternal, heart rate
Confusing the maternal and the fetal heart rate with external cardiotocography is common. When the mix-up is noted and corrected expeditiously, it is unlikely to result in an adverse outcome. Signal ambiguity may arise from faulty Doppler equipment or the inability of the cardiotocograph to differentiate between maternal and fetal heart rates. It commonly occurs after repositioning the patient, after fetal movement, or during pushing in the second stage when the maternal heart rate may increase to a baseline that is similar to that of the fetus.

Signal ambiguity should be suspected when the FHR runs in the low-normal range or when FHR accelerations are noted with greater than 50% of contractions (especially when pushing).⁴ Signal ambiguity also should be ruled out when there is an apparent FHR deceleration to the maternal range that does not recover.

Evaluating for suspected signal ambiguity involves 2 key steps: (1) documentation and verification of the maternal heart rate and (2) definitive documentation of the true FHR. To document the maternal heart rate, manually count the radial pulse for 1 minute or use a pulse oximeter for continuous monitoring. Using a pulse oximeter is a less labor-intensive approach and has the advantage of allowing continuous assessment of the maternal heart rate for comparison. Recording the maternal pulse continuously on the same screen as the FHR enables ongoing differentiation of the mother and fetus in difficult cases, particularly if internal fetal monitoring is not an option (because of maternal infectious disease, low suspicion for an abnormal FHR pattern, or strong maternal preference against internal monitoring, for example).

When clinically appropriate, use of a fetal scalp electrode (FSE) can document the FHR. If intrauterine fetal death has occurred, however, the FSE may transmit the maternal heart rate.⁵ Using ultrasonography to confirm the FHR prior to placing the FSE is a reliable method of definitive differentiation. If a newly placed FSE shows a clear differentiation of 5 to 10 beats per minute from a continuously assessed maternal pulse rate, then this is also a reliable way to assure that the FHR monitoring represents the fetus, particularly if ultrasonography is not immediately available.

Ultimately, before intervening based on an abnormal FHR tracing, it is paramount to confirm that the data are adequate for interpretation and represent the actual FHR. If signal ambiguity is identified or suspected, correct it by using ultrasonography to locate the FHR and replace the external monitor until a rate that is at least 5 to 10 beats per minute different from the maternal rate is obtained. Alternatively, this is an indication for internal fetal monitoring with an FSE.

Challenge: Inadequate FHR tracing, poor communication, lack of clinical context
CASE 2  Woman with uncomplicated postdates pregnancy presents for induction
A 28-year-old woman (G3P2) at 41 weeks 0 days of gestation presents to labor and delivery for induction of labor for the indication of postdates. There have been no complications with the current pregnancy. The initial cervical exam reveals 1+ cm dilation, 90% effacement, and −3 station, and the patient is started on oxytocin per the hospital protocol. What is your interpretation of the continuous FHR tracing shown in FIGURE 2?

FIGURE 2 Inadequate, uninterpretable FHR tracing

This FHR tracing, from the patient described in Case 2, is unusable because of the absence of data.

TIP #9: Check that the monitors are providing useful data
The ability to accurately interpret a continuous FHR tracing depends on the quality of data recorded. Unfortunately, the absence of data makes interpretation impossible. This includes both FHR and tocometry data, since both pieces of information are required for appropriate interpretation of a continuous FHR tracing.

Prolonged periods of uninterpretable FHR and uterine activity tracings imply that no one was attending the mother and fetus.⁶ If it is difficult to obtain an interpretable FHR tracing, document in the medical record that you made ongoing efforts to maintain an adequate tracing, including the amount of time spent holding the external monitor, use of ultrasonography to document the FHR, and plans for potential internal monitoring.

CASE 2  Continued
After several hours, the patient requests an epidural for pain management and one is placed without difficulty. She reports adequate pain relief and is comfortable for the next 1 to 2 hours. Subsequently, the patient reports a sudden onset of increasing pain that does not respond to additional patient-administered doses of anesthesia over a 30-minute period. The labor and delivery nurse becomes concerned about the patient's pain level and contacts the attending physician to discuss her concerns. The physician, who is currently attending to patients in clinic, listens to the nurse and asks her to contact the anesthesia department with her concerns (FIGURE 3).

FIGURE 3 FHR tracing reveals recurrent variables in a patient with evolving clinical concerns

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #8: Clearly communicate an urgent situation to the care team
Poor communication underlies many preventable adverse outcomes in medicine.⁷ Effective communication requires an adequate description of the clinical scenario or problem. A root cause analysis of a series of intrapartum adverse events involving fetal death or injury showed that poor communication about a concerning FHR tracing played a role in 72% of cases.¹

In this clinical scenario, the nurse believed that the patient's pain level was unusual or more than anticipated. The person who is communicating his or her concern (the sender) must be sure that the person receiving the message (the responder) clearly understands the sender's level of concern. In this case, it would have been appropriate for the sender to state clearly that she felt the patient's pain was outside of normal expectations and to request that the attending physician come to evaluate the patient.

Clear and effective communication includes (1) an appropriate description of the urgency of the situation and (2) an indication by the sender as to the desired response to this information ("please come evaluate the patient").⁸ In all cases, both steps are necessary to elicit an appropriate response.

CASE 2  Continued
Over the next 2 hours, recurrent variable decelerations develop, and then sudden, prolonged fetal bradycardia leads to urgent cesarean delivery. At delivery, a uterine rupture is diagnosed and a fetal hand is observed protruding through a lower-uterine segment defect into the maternal abdomen.

TIP #7: Always consider the entire clinical scenario
In this case, the team caring for the patient was not aware that her previous pregnancy had ended with a low transverse cesarean delivery. How does this information change your interpretation of the clinical scenario? The importance of understanding the entire clinical context when interpreting individual characteristics of cardiotocography cannot be overstated. For example, the sudden onset of recurrent, significant variable decelerations is more concerning in the context of a prior cesarean delivery, and late decelerations are more concerning in a patient with placental abruption, fetal growth restriction, or poorly controlled maternal diabetes.

An estimated 70% of fetuses will have an indeterminate FHR pattern (category II) at some time during labor.⁹ To appropriately interpret the FHR tracing, it is crucial to know the a priori risk for fetal hypoxia and metabolic acidosis (the precursor of fetal injury) due to such identified clinical risk factors as placental insufficiency, medical comorbidities (hypertension, diabetes), or postdates gestational age.

It is well established that cardiotocography has a good negative predictive value for the absence of fetal metabolic acidosis when there is moderate variability and spontaneous or induced accelerations. When attempting to risk stratify the fetus with a category II (indeterminate) FHR tracing, consider these 3 important questions:

1. What are the risk factors for this particular patient and her fetus?
2. What is the state of the fetus right now, and when was the last time metabolic acidosis could be excluded reasonably (by the presence of moderate variability and accelerations)?
3. What is the risk that the fetus will develop acidemia prior to delivery?

The presence of decelerations indicates interruption of oxygen delivery to the fetus, and recurrent decelerations may indicate an evolving process of accumulated oxygen deprivation, hypoxia, and eventually, metabolic acidosis. Most authorities agree that, for the fetus with a previously normal FHR tracing, the onset of significant, recurrent decelerations with slowly cumulative oxygen deficit can lead to fetal acidemia over the course of approximately 1 hour.¹⁰ Of course, acidosis also can occur much more quickly with acute events, such as placental abruption or uterine rupture. In deciding whether or not to intervene based on an FHR tracing, the clinician must take into account the clinical context to determine if delivery is likely to occur before significant acidemia develops.

Challenge: Lack of situational awareness, failure to address nursing concerns, reluctance to initiate the chain of command
CASE 3  Spontaneous labor in a second pregnancy
A 28-year-old woman (G2P1) at 40 weeks' gestation presents in spontaneous labor. She has a history of a previous uncomplicated vaginal delivery. After 6 hours she reaches complete dilation with the fetus at −1 station and begins pushing. After 60 minutes, the patient has only progressed to +1 station. She is contracting every 1 to 2 minutes with recurrent variable decelerations (FIGURE 4).

FIGURE 4 FHR tracing shows time points for initiation and continuation of pushing

This tracing, from the patient described in Case 3, documents contraction frequency every 1-2 minutes for more than 60 minutes while the patient continues to push. The fetal heart rate demonstrates repetitive moderate variable decelerations with every push.

TIP #6: Maintain situational awareness
A state of situational awareness exists when caregivers have a clear understanding of all of the factors at play in a clinical situation.¹¹ This can be lost when caregivers focus too intensely on one aspect of care. It often happens when the patient is pushing in the second stage and the provider, focused on the progress of fetal descent, loses track of the amount of time that has passed without reassuring features (such as variability and induced or spontaneous accelerations) in the FHR tracing. The nurse, seeing the physician at the bedside, presumes he or she is aware of the tracing and is thus reluctant to point out the concerning features for fear of appearing insubordinate.

Situational awareness also may be lost at the time of patient hand off between providers wherein critical information, such as a history of previous cesarean delivery, is not communicated to the next care team. When receiving an intrapartum patient hand off, providers must have heightened vigilance to ensure they quickly reach situational awareness and are cognizant of the entire clinical context. Maintaining an environment in which all members of the care team, regardless of their training level, are encouraged to voice their concerns is another way to promote ongoing situational awareness.

CASE 3  Continued
The patient continues pushing for another 20 minutes without delivery, and the nurse raises a concern about the FHR tracing to the physician, who remains in the room but does not respond (FIGURE 5).

FIGURE 5 FHR tracing reveals ongoing repetitive variable decelerations

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #5: Acknowledge and respond to other caregivers' concerns
A team approach to patient care is essential in all areas of medicine, perhaps none more so than in obstetrics. Each member of the team is engaged in trying to provide optimal patient care and the concerns of every team member--regardless of title or level of training--must be acknowledged and addressed. Good communication requires creating a safe environment wherein each member of the team feels comfortable raising concerns without fear of reprisal. Rather than becoming angry or frustrated when questioned, providers should remain cognizant that these are ongoing efforts to maintain situational awareness and ensure the best possible outcome for mother and baby.

CASE 3  Continued
Pushing continues for another 30 minutes despite the nurse's repeated effort to express concern to the physician about the FHR tracing. After more than 2 hours of pushing, the infant is delivered; Apgar scores are 1, 5, and 7. No cord gas is obtained.

TIP #4: Initiate the chain of command when necessary
Any caregiver, regardless of job title, has a duty to initiate the institution's chain-of-command policy and procedure if he or she has a concern about patient well-being that is not being addressed adequately. It can be uncomfortable for a nurse, midwife, or resident physician to question an attending physician, particularly if that person responds in a dismissive, condescending, or angry manner. If a caregiver has made several attempts to engage the attending physician and feels the concerns are being inadequately addressed, then he or she must respectfully initiate the chain of command to seek additional objective review of the clinical situation.

Failure to follow oxytocin protocols, inadequate surveillance, poor documentation
CASE 4  Induction of an uncomplicated pregnancy due to postdates
A 20-year-old woman (G1P0) at 42 weeks' gestation with an otherwise uncomplicated first pregnancy presents for postdates induction with oxytocin. After 6 hours, she develops uterine tachysystole with recurrent variable decelerations but the oxytocin infusion is continued at the same rate (FIGURE 6).

FIGURE 6 FHR tracing indicates uterine tachysystole

The patient in Case 4 received oxytocin for induction of postdates pregnancy. The red arrow shown on the FHR tracing points out that oxytocin augmentation continues despite the presence of uterine contractions that are too frequent and initial changes, including subtle late decelerations in the FHR, that suggest early fetal compromise.

TIP #3: Manage oxytocin infusion according to protocol
Inappropriate use of oxytocin is common, including the improper management of oxytocin infusion in the setting of uterine tachysystole (defined as the presence of >5 contractions over a 10-minute period averaged over 30 minutes) and/or an abnormal FHR tracing. The mismanagement of uterine tachysystole is cited in more than two-thirds of obstetric malpractice cases.¹²

Uterine contractions alter blood flow through the spiral arteries and transiently reduce placental perfusion. Prolonged uterine tachysystole can lead to fetal oxygen debt and early signs of hypoxia, including the loss of spontaneous accelerations, tachycardia, and reduced variability. Continuing or increasing the oxytocin in the setting of such changes is hard to justify. One study found that the use of oxytocin in the setting of tachysystole was significantly associated with signs of fetal asphyxia (odds ratio [OR], 5.6).¹³ When the FHR pattern suggests significant interruption of fetal oxygen delivery and possible hypoxia, continuing or increasing an oxytocin infusion suggests a lack of understanding of the physiology that is the basis for FHR interpretation.

Appropriate management of tachysystole depends on the accompanying FHR.¹⁴ In the setting of a category I (normal) FHR tracing, tachysystole can be treated first with maternal repositioning (left or right lateral) and administration of a 500-cm3 maternal IV fluid bolus. If uterine activity does not return to normal after 10 to 15 minutes, decrease the oxytocin rate by at least half. If it does not return to normal after another 10 to 15 minutes, discontinue oxytocin until the tachysystole has resolved.

In the setting of a concerning category IIFHR tracing, discontinuation of oxytocin should be the first step along with maternal repositioning and administration of a fluid bolus. If these measures do not improve the FHR tracing and tachysystole persists, administration of an acute uterine relaxant, such as terbutaline, should be considered to slow contraction frequency.

If interventions result in normalization of the FHR tracing and resolution of tachysystole for 20 to 30 minutes, then oxytocin may be restarted if necessary for labor progress at no more than half the rate that produced tachysystole.

TIP #2: Recognize an abnormal FHR tracing--and what it means
Misinterpretation of the FHR tracing occurs when there is a failure to recognize characteristics that should raise concern about fetal well-being. Failure to recognize an abnormal FHR tracing occurred in 77% of sentinel cases involving intrapartum birth injury or death.^1,12,13 To limit misinterpretation of the FHR tracing, it is critical for nurses and physicians to use standardized terminology for clear, effective communication.

In 2008, the Eunice Kennedy Schriver National Institute of Child Health and Human Development (NICHD) published guidelines standardizing the terminology used to describe cardiotocography and to create consensus around its interpretation.15 Any description of an intrapartum FHR tracing should include a designation of category (I, II, or III). Fetal well-being is reasonably established with a category I FHR tracing.  A category III tracing indicates the high likelihood of fetal acidemia and the need for immediate intervention. A category II FHR tracing is considered indeterminate, and further characterization is required to reasonably exclude fetal metabolic acidosis and a risk of fetal injury.

The presence of moderate variability and fetal response to scalp stimulation are considered reassuring findings that reasonably exclude significant metabolic acidosis. In assessing variability, one pitfall is mistaking the appearance of "variability" within a deceleration (including during return to baseline) for baseline FHR variability. In the event of a persistent category II FHR tracing (>30 minutes), nursing staff should request direct physician review of the FHR tracing. In any case in which fetal well-being is uncertain, nursing staff should request direct physician evaluation of the mother in person and also the FHR tracing, with clear documentation of the findings, interpretation, and plan of care.¹⁶

TIP #1: Document, document, document
Nursing and physician documentation about the FHR tracing within the patient-specific clinical context is crucial for effective caregiver communication and patient safety. Thoughtful documentation also reduces liability exposure for providers by demonstrating maternal-fetal surveillance, early identification and treatment of an abnormal or indeterminate FHR tracing, and timely intervention on fetal behalf when necessary.

When the medical record aligns with the electronic FHR tracing and includes appropriate descriptions, interpretations, and interventions in line with national guidelines and institutional policy, the record demonstrates that the providers have a thorough understanding of the physiology behind cardiotocography and, more importantly, that they are able to apply that knowledge in clinical practice.⁶

Minimizing missteps
Several straightforward interventions can help clinicians overcome the most common pitfalls during FHR monitoring. These include accurate and high-quality cardiotocography, a collaborative team-based approach to patient care, and sustained situational awareness among providers. The consistent use of common language for the description and interpretation of FHR monitoring, adherence to hospital oxytocin protocols, and well-defined expectations for fetal surveillance and provider communication are critical to overcoming these challenges. Regularly scheduled nursing and physician education sessions and interdisciplinary case review can promote the adoption and sustained incorporation of these simple techniques into daily practice.³

Some have advocated for an "electronic fetal monitoring bundle," which would serve as a checklist of clinical evaluation steps that should occur every time a given process occurs.¹⁷ This approach would ensure that all providers on labor and delivery are qualified to read, accurately interpret, and respond to FHR tracings. It would require a credentialing process to confirm the competency of team members and reinforce the presence of a common language. It would also include an explicit escalation policy for rapid initiation of the chain of command in cases wherein there is a disagreement among team members about the FHR interpretation. Finally, each patient would be required to have, at all times, an identified responsible provider capable of a rapid response.

Although continuous FHR monitoring may not effectively reduce intrapartum fetal asphyxia, it is clearly here to stay. Recognizing--and addressing--the most common challenges encountered during intrapartum FHR monitoring may reduce unnecessary morbidity and potential liability for caregivers.

Share your thoughts! Send your Letter to the Editor to [email protected]. Please include your name and the city and state in which you practice.

Interpreting continuous fetal heart rate (FHR) monitoring is one of the most common tasks obstetricians perform during the course of intrapartum care. Notably, many providers do not seek ongoing training to optimize their ability to reliably and accurately interpret the FHR. Yet FHR interpretation is one of the most frequent causes of litigation in the modern obstetric practice. Failure to interpret continuous FHR monitoring appropriately is estimated to account for 75% of obstetric-related litigation.¹

Continuous FHR monitoring during labor was introduced to identify infants at risk for  developing hypoxic-ischemic encephalopathy (HIE). The rate of HIE has not declined, however, despite almost universal adoption of continuous FHR monitoring.² Numerous reasons account for this failure, including ad hoc interpretation of terminology, lack of standardized protocols for management and intervention, and the oftentimes challenging patterns that must be interpreted.³ The confusion about and dissatisfaction with the current state of FHR monitoring has led to attempts to enhance our ability to identify infants at risk with additional approaches (such as fetal pulse oximetry and fetal ST-segment evaluation), and some have called for a complete overhaul of our approach to interpreting the FHR. Clark and colleagues stated recently, "It is time to start over and establish some common language, standard interpretation, and reasonable management principles and guidelines."³

We must recognize that, as a stand-alone tool, continuous FHR monitoring is ineffective for avoiding preventable adverse outcomes. It is most likely to be effective when used in accordance with published standard guidelines by professionals skilled in interpretation and when timely, appropriate interventions are performed based on that interpretation. Optimal FHR monitoring requires a collaborative perinatal team that performs the monitoring correctly, interprets it appropriately, and communicates the findings effectively, and in a timely fashion, to all members of the care team when a high-risk pattern is detected.

In this article we review some common challenges that clinicians encounter during intrapartum FHR monitoring and we offer 10 simple tips to help overcome these challenges. The clinical scenarios described are derived from published reports in the medical literature, published malpractice claims, and from our personal experience working in a major health care system as part of a team charged with overseeing ongoing certification and training of labor and delivery nurses.

Challenge: Signal ambiguity
CASE 1  Young woman in labor with first pregnancy
A 19-year-old woman presents in spontaneous labor with her first pregnancy, which has been uncomplicated. During the course of her care, it is noted that the FHR changes to a lower baseline than previously recorded. Evaluation reveals that the external monitor is tracking the maternal heart rate and not the FHR (FIGURE 1). After the monitor is adjusted, both the fetal and maternal rates are documented for a short period. Ultimately, continuous monitoring of the maternal heart rate is discontinued. After delivery of the infant several hours later, it is noted that the FHR continues to register on the monitor, and it is determined that for the last few hours the maternal heart rate has been traced.

FIGURE 1 FHR tracing indicates signal ambiguity

As described in Case 1, the upper panel of this tracing demonstrates the maternal heart rate confused as the fetal heart rate, while the segment in the lower panel shows a clear distinction between the maternal and fetal heart rates.

TIP #10: Ensure the FHR monitor is tracking the fetal, not the maternal, heart rate
Confusing the maternal and the fetal heart rate with external cardiotocography is common. When the mix-up is noted and corrected expeditiously, it is unlikely to result in an adverse outcome. Signal ambiguity may arise from faulty Doppler equipment or the inability of the cardiotocograph to differentiate between maternal and fetal heart rates. It commonly occurs after repositioning the patient, after fetal movement, or during pushing in the second stage when the maternal heart rate may increase to a baseline that is similar to that of the fetus.

Signal ambiguity should be suspected when the FHR runs in the low-normal range or when FHR accelerations are noted with greater than 50% of contractions (especially when pushing).⁴ Signal ambiguity also should be ruled out when there is an apparent FHR deceleration to the maternal range that does not recover.

Evaluating for suspected signal ambiguity involves 2 key steps: (1) documentation and verification of the maternal heart rate and (2) definitive documentation of the true FHR. To document the maternal heart rate, manually count the radial pulse for 1 minute or use a pulse oximeter for continuous monitoring. Using a pulse oximeter is a less labor-intensive approach and has the advantage of allowing continuous assessment of the maternal heart rate for comparison. Recording the maternal pulse continuously on the same screen as the FHR enables ongoing differentiation of the mother and fetus in difficult cases, particularly if internal fetal monitoring is not an option (because of maternal infectious disease, low suspicion for an abnormal FHR pattern, or strong maternal preference against internal monitoring, for example).

When clinically appropriate, use of a fetal scalp electrode (FSE) can document the FHR. If intrauterine fetal death has occurred, however, the FSE may transmit the maternal heart rate.⁵ Using ultrasonography to confirm the FHR prior to placing the FSE is a reliable method of definitive differentiation. If a newly placed FSE shows a clear differentiation of 5 to 10 beats per minute from a continuously assessed maternal pulse rate, then this is also a reliable way to assure that the FHR monitoring represents the fetus, particularly if ultrasonography is not immediately available.

Ultimately, before intervening based on an abnormal FHR tracing, it is paramount to confirm that the data are adequate for interpretation and represent the actual FHR. If signal ambiguity is identified or suspected, correct it by using ultrasonography to locate the FHR and replace the external monitor until a rate that is at least 5 to 10 beats per minute different from the maternal rate is obtained. Alternatively, this is an indication for internal fetal monitoring with an FSE.

Challenge: Inadequate FHR tracing, poor communication, lack of clinical context
CASE 2  Woman with uncomplicated postdates pregnancy presents for induction
A 28-year-old woman (G3P2) at 41 weeks 0 days of gestation presents to labor and delivery for induction of labor for the indication of postdates. There have been no complications with the current pregnancy. The initial cervical exam reveals 1+ cm dilation, 90% effacement, and −3 station, and the patient is started on oxytocin per the hospital protocol. What is your interpretation of the continuous FHR tracing shown in FIGURE 2?

FIGURE 2 Inadequate, uninterpretable FHR tracing

This FHR tracing, from the patient described in Case 2, is unusable because of the absence of data.

TIP #9: Check that the monitors are providing useful data
The ability to accurately interpret a continuous FHR tracing depends on the quality of data recorded. Unfortunately, the absence of data makes interpretation impossible. This includes both FHR and tocometry data, since both pieces of information are required for appropriate interpretation of a continuous FHR tracing.

Prolonged periods of uninterpretable FHR and uterine activity tracings imply that no one was attending the mother and fetus.⁶ If it is difficult to obtain an interpretable FHR tracing, document in the medical record that you made ongoing efforts to maintain an adequate tracing, including the amount of time spent holding the external monitor, use of ultrasonography to document the FHR, and plans for potential internal monitoring.

CASE 2  Continued
After several hours, the patient requests an epidural for pain management and one is placed without difficulty. She reports adequate pain relief and is comfortable for the next 1 to 2 hours. Subsequently, the patient reports a sudden onset of increasing pain that does not respond to additional patient-administered doses of anesthesia over a 30-minute period. The labor and delivery nurse becomes concerned about the patient's pain level and contacts the attending physician to discuss her concerns. The physician, who is currently attending to patients in clinic, listens to the nurse and asks her to contact the anesthesia department with her concerns (FIGURE 3).

FIGURE 3 FHR tracing reveals recurrent variables in a patient with evolving clinical concerns

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #8: Clearly communicate an urgent situation to the care team
Poor communication underlies many preventable adverse outcomes in medicine.⁷ Effective communication requires an adequate description of the clinical scenario or problem. A root cause analysis of a series of intrapartum adverse events involving fetal death or injury showed that poor communication about a concerning FHR tracing played a role in 72% of cases.¹

In this clinical scenario, the nurse believed that the patient's pain level was unusual or more than anticipated. The person who is communicating his or her concern (the sender) must be sure that the person receiving the message (the responder) clearly understands the sender's level of concern. In this case, it would have been appropriate for the sender to state clearly that she felt the patient's pain was outside of normal expectations and to request that the attending physician come to evaluate the patient.

Clear and effective communication includes (1) an appropriate description of the urgency of the situation and (2) an indication by the sender as to the desired response to this information ("please come evaluate the patient").⁸ In all cases, both steps are necessary to elicit an appropriate response.

CASE 2  Continued
Over the next 2 hours, recurrent variable decelerations develop, and then sudden, prolonged fetal bradycardia leads to urgent cesarean delivery. At delivery, a uterine rupture is diagnosed and a fetal hand is observed protruding through a lower-uterine segment defect into the maternal abdomen.

TIP #7: Always consider the entire clinical scenario
In this case, the team caring for the patient was not aware that her previous pregnancy had ended with a low transverse cesarean delivery. How does this information change your interpretation of the clinical scenario? The importance of understanding the entire clinical context when interpreting individual characteristics of cardiotocography cannot be overstated. For example, the sudden onset of recurrent, significant variable decelerations is more concerning in the context of a prior cesarean delivery, and late decelerations are more concerning in a patient with placental abruption, fetal growth restriction, or poorly controlled maternal diabetes.

An estimated 70% of fetuses will have an indeterminate FHR pattern (category II) at some time during labor.⁹ To appropriately interpret the FHR tracing, it is crucial to know the a priori risk for fetal hypoxia and metabolic acidosis (the precursor of fetal injury) due to such identified clinical risk factors as placental insufficiency, medical comorbidities (hypertension, diabetes), or postdates gestational age.

It is well established that cardiotocography has a good negative predictive value for the absence of fetal metabolic acidosis when there is moderate variability and spontaneous or induced accelerations. When attempting to risk stratify the fetus with a category II (indeterminate) FHR tracing, consider these 3 important questions:

1. What are the risk factors for this particular patient and her fetus?
2. What is the state of the fetus right now, and when was the last time metabolic acidosis could be excluded reasonably (by the presence of moderate variability and accelerations)?
3. What is the risk that the fetus will develop acidemia prior to delivery?

The presence of decelerations indicates interruption of oxygen delivery to the fetus, and recurrent decelerations may indicate an evolving process of accumulated oxygen deprivation, hypoxia, and eventually, metabolic acidosis. Most authorities agree that, for the fetus with a previously normal FHR tracing, the onset of significant, recurrent decelerations with slowly cumulative oxygen deficit can lead to fetal acidemia over the course of approximately 1 hour.¹⁰ Of course, acidosis also can occur much more quickly with acute events, such as placental abruption or uterine rupture. In deciding whether or not to intervene based on an FHR tracing, the clinician must take into account the clinical context to determine if delivery is likely to occur before significant acidemia develops.

Challenge: Lack of situational awareness, failure to address nursing concerns, reluctance to initiate the chain of command
CASE 3  Spontaneous labor in a second pregnancy
A 28-year-old woman (G2P1) at 40 weeks' gestation presents in spontaneous labor. She has a history of a previous uncomplicated vaginal delivery. After 6 hours she reaches complete dilation with the fetus at −1 station and begins pushing. After 60 minutes, the patient has only progressed to +1 station. She is contracting every 1 to 2 minutes with recurrent variable decelerations (FIGURE 4).

FIGURE 4 FHR tracing shows time points for initiation and continuation of pushing

This tracing, from the patient described in Case 3, documents contraction frequency every 1-2 minutes for more than 60 minutes while the patient continues to push. The fetal heart rate demonstrates repetitive moderate variable decelerations with every push.

TIP #6: Maintain situational awareness
A state of situational awareness exists when caregivers have a clear understanding of all of the factors at play in a clinical situation.¹¹ This can be lost when caregivers focus too intensely on one aspect of care. It often happens when the patient is pushing in the second stage and the provider, focused on the progress of fetal descent, loses track of the amount of time that has passed without reassuring features (such as variability and induced or spontaneous accelerations) in the FHR tracing. The nurse, seeing the physician at the bedside, presumes he or she is aware of the tracing and is thus reluctant to point out the concerning features for fear of appearing insubordinate.

Situational awareness also may be lost at the time of patient hand off between providers wherein critical information, such as a history of previous cesarean delivery, is not communicated to the next care team. When receiving an intrapartum patient hand off, providers must have heightened vigilance to ensure they quickly reach situational awareness and are cognizant of the entire clinical context. Maintaining an environment in which all members of the care team, regardless of their training level, are encouraged to voice their concerns is another way to promote ongoing situational awareness.

CASE 3  Continued
The patient continues pushing for another 20 minutes without delivery, and the nurse raises a concern about the FHR tracing to the physician, who remains in the room but does not respond (FIGURE 5).

FIGURE 5 FHR tracing reveals ongoing repetitive variable decelerations

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #5: Acknowledge and respond to other caregivers' concerns
A team approach to patient care is essential in all areas of medicine, perhaps none more so than in obstetrics. Each member of the team is engaged in trying to provide optimal patient care and the concerns of every team member--regardless of title or level of training--must be acknowledged and addressed. Good communication requires creating a safe environment wherein each member of the team feels comfortable raising concerns without fear of reprisal. Rather than becoming angry or frustrated when questioned, providers should remain cognizant that these are ongoing efforts to maintain situational awareness and ensure the best possible outcome for mother and baby.

CASE 3  Continued
Pushing continues for another 30 minutes despite the nurse's repeated effort to express concern to the physician about the FHR tracing. After more than 2 hours of pushing, the infant is delivered; Apgar scores are 1, 5, and 7. No cord gas is obtained.

TIP #4: Initiate the chain of command when necessary
Any caregiver, regardless of job title, has a duty to initiate the institution's chain-of-command policy and procedure if he or she has a concern about patient well-being that is not being addressed adequately. It can be uncomfortable for a nurse, midwife, or resident physician to question an attending physician, particularly if that person responds in a dismissive, condescending, or angry manner. If a caregiver has made several attempts to engage the attending physician and feels the concerns are being inadequately addressed, then he or she must respectfully initiate the chain of command to seek additional objective review of the clinical situation.

Failure to follow oxytocin protocols, inadequate surveillance, poor documentation
CASE 4  Induction of an uncomplicated pregnancy due to postdates
A 20-year-old woman (G1P0) at 42 weeks' gestation with an otherwise uncomplicated first pregnancy presents for postdates induction with oxytocin. After 6 hours, she develops uterine tachysystole with recurrent variable decelerations but the oxytocin infusion is continued at the same rate (FIGURE 6).

FIGURE 6 FHR tracing indicates uterine tachysystole

The patient in Case 4 received oxytocin for induction of postdates pregnancy. The red arrow shown on the FHR tracing points out that oxytocin augmentation continues despite the presence of uterine contractions that are too frequent and initial changes, including subtle late decelerations in the FHR, that suggest early fetal compromise.

TIP #3: Manage oxytocin infusion according to protocol
Inappropriate use of oxytocin is common, including the improper management of oxytocin infusion in the setting of uterine tachysystole (defined as the presence of >5 contractions over a 10-minute period averaged over 30 minutes) and/or an abnormal FHR tracing. The mismanagement of uterine tachysystole is cited in more than two-thirds of obstetric malpractice cases.¹²

Uterine contractions alter blood flow through the spiral arteries and transiently reduce placental perfusion. Prolonged uterine tachysystole can lead to fetal oxygen debt and early signs of hypoxia, including the loss of spontaneous accelerations, tachycardia, and reduced variability. Continuing or increasing the oxytocin in the setting of such changes is hard to justify. One study found that the use of oxytocin in the setting of tachysystole was significantly associated with signs of fetal asphyxia (odds ratio [OR], 5.6).¹³ When the FHR pattern suggests significant interruption of fetal oxygen delivery and possible hypoxia, continuing or increasing an oxytocin infusion suggests a lack of understanding of the physiology that is the basis for FHR interpretation.

Appropriate management of tachysystole depends on the accompanying FHR.¹⁴ In the setting of a category I (normal) FHR tracing, tachysystole can be treated first with maternal repositioning (left or right lateral) and administration of a 500-cm3 maternal IV fluid bolus. If uterine activity does not return to normal after 10 to 15 minutes, decrease the oxytocin rate by at least half. If it does not return to normal after another 10 to 15 minutes, discontinue oxytocin until the tachysystole has resolved.

In the setting of a concerning category IIFHR tracing, discontinuation of oxytocin should be the first step along with maternal repositioning and administration of a fluid bolus. If these measures do not improve the FHR tracing and tachysystole persists, administration of an acute uterine relaxant, such as terbutaline, should be considered to slow contraction frequency.

If interventions result in normalization of the FHR tracing and resolution of tachysystole for 20 to 30 minutes, then oxytocin may be restarted if necessary for labor progress at no more than half the rate that produced tachysystole.

TIP #2: Recognize an abnormal FHR tracing--and what it means
Misinterpretation of the FHR tracing occurs when there is a failure to recognize characteristics that should raise concern about fetal well-being. Failure to recognize an abnormal FHR tracing occurred in 77% of sentinel cases involving intrapartum birth injury or death.^1,12,13 To limit misinterpretation of the FHR tracing, it is critical for nurses and physicians to use standardized terminology for clear, effective communication.

In 2008, the Eunice Kennedy Schriver National Institute of Child Health and Human Development (NICHD) published guidelines standardizing the terminology used to describe cardiotocography and to create consensus around its interpretation.15 Any description of an intrapartum FHR tracing should include a designation of category (I, II, or III). Fetal well-being is reasonably established with a category I FHR tracing.  A category III tracing indicates the high likelihood of fetal acidemia and the need for immediate intervention. A category II FHR tracing is considered indeterminate, and further characterization is required to reasonably exclude fetal metabolic acidosis and a risk of fetal injury.

The presence of moderate variability and fetal response to scalp stimulation are considered reassuring findings that reasonably exclude significant metabolic acidosis. In assessing variability, one pitfall is mistaking the appearance of "variability" within a deceleration (including during return to baseline) for baseline FHR variability. In the event of a persistent category II FHR tracing (>30 minutes), nursing staff should request direct physician review of the FHR tracing. In any case in which fetal well-being is uncertain, nursing staff should request direct physician evaluation of the mother in person and also the FHR tracing, with clear documentation of the findings, interpretation, and plan of care.¹⁶

TIP #1: Document, document, document
Nursing and physician documentation about the FHR tracing within the patient-specific clinical context is crucial for effective caregiver communication and patient safety. Thoughtful documentation also reduces liability exposure for providers by demonstrating maternal-fetal surveillance, early identification and treatment of an abnormal or indeterminate FHR tracing, and timely intervention on fetal behalf when necessary.

When the medical record aligns with the electronic FHR tracing and includes appropriate descriptions, interpretations, and interventions in line with national guidelines and institutional policy, the record demonstrates that the providers have a thorough understanding of the physiology behind cardiotocography and, more importantly, that they are able to apply that knowledge in clinical practice.⁶

Minimizing missteps
Several straightforward interventions can help clinicians overcome the most common pitfalls during FHR monitoring. These include accurate and high-quality cardiotocography, a collaborative team-based approach to patient care, and sustained situational awareness among providers. The consistent use of common language for the description and interpretation of FHR monitoring, adherence to hospital oxytocin protocols, and well-defined expectations for fetal surveillance and provider communication are critical to overcoming these challenges. Regularly scheduled nursing and physician education sessions and interdisciplinary case review can promote the adoption and sustained incorporation of these simple techniques into daily practice.³

Some have advocated for an "electronic fetal monitoring bundle," which would serve as a checklist of clinical evaluation steps that should occur every time a given process occurs.¹⁷ This approach would ensure that all providers on labor and delivery are qualified to read, accurately interpret, and respond to FHR tracings. It would require a credentialing process to confirm the competency of team members and reinforce the presence of a common language. It would also include an explicit escalation policy for rapid initiation of the chain of command in cases wherein there is a disagreement among team members about the FHR interpretation. Finally, each patient would be required to have, at all times, an identified responsible provider capable of a rapid response.

Although continuous FHR monitoring may not effectively reduce intrapartum fetal asphyxia, it is clearly here to stay. Recognizing--and addressing--the most common challenges encountered during intrapartum FHR monitoring may reduce unnecessary morbidity and potential liability for caregivers.

Share your thoughts! Send your Letter to the Editor to [email protected]. Please include your name and the city and state in which you practice.

Interpreting continuous fetal heart rate (FHR) monitoring is one of the most common tasks obstetricians perform during the course of intrapartum care. Notably, many providers do not seek ongoing training to optimize their ability to reliably and accurately interpret the FHR. Yet FHR interpretation is one of the most frequent causes of litigation in the modern obstetric practice. Failure to interpret continuous FHR monitoring appropriately is estimated to account for 75% of obstetric-related litigation.¹

Continuous FHR monitoring during labor was introduced to identify infants at risk for  developing hypoxic-ischemic encephalopathy (HIE). The rate of HIE has not declined, however, despite almost universal adoption of continuous FHR monitoring.² Numerous reasons account for this failure, including ad hoc interpretation of terminology, lack of standardized protocols for management and intervention, and the oftentimes challenging patterns that must be interpreted.³ The confusion about and dissatisfaction with the current state of FHR monitoring has led to attempts to enhance our ability to identify infants at risk with additional approaches (such as fetal pulse oximetry and fetal ST-segment evaluation), and some have called for a complete overhaul of our approach to interpreting the FHR. Clark and colleagues stated recently, "It is time to start over and establish some common language, standard interpretation, and reasonable management principles and guidelines."³

We must recognize that, as a stand-alone tool, continuous FHR monitoring is ineffective for avoiding preventable adverse outcomes. It is most likely to be effective when used in accordance with published standard guidelines by professionals skilled in interpretation and when timely, appropriate interventions are performed based on that interpretation. Optimal FHR monitoring requires a collaborative perinatal team that performs the monitoring correctly, interprets it appropriately, and communicates the findings effectively, and in a timely fashion, to all members of the care team when a high-risk pattern is detected.

In this article we review some common challenges that clinicians encounter during intrapartum FHR monitoring and we offer 10 simple tips to help overcome these challenges. The clinical scenarios described are derived from published reports in the medical literature, published malpractice claims, and from our personal experience working in a major health care system as part of a team charged with overseeing ongoing certification and training of labor and delivery nurses.

Challenge: Signal ambiguity
CASE 1  Young woman in labor with first pregnancy
A 19-year-old woman presents in spontaneous labor with her first pregnancy, which has been uncomplicated. During the course of her care, it is noted that the FHR changes to a lower baseline than previously recorded. Evaluation reveals that the external monitor is tracking the maternal heart rate and not the FHR (FIGURE 1). After the monitor is adjusted, both the fetal and maternal rates are documented for a short period. Ultimately, continuous monitoring of the maternal heart rate is discontinued. After delivery of the infant several hours later, it is noted that the FHR continues to register on the monitor, and it is determined that for the last few hours the maternal heart rate has been traced.

FIGURE 1 FHR tracing indicates signal ambiguity

As described in Case 1, the upper panel of this tracing demonstrates the maternal heart rate confused as the fetal heart rate, while the segment in the lower panel shows a clear distinction between the maternal and fetal heart rates.

TIP #10: Ensure the FHR monitor is tracking the fetal, not the maternal, heart rate
Confusing the maternal and the fetal heart rate with external cardiotocography is common. When the mix-up is noted and corrected expeditiously, it is unlikely to result in an adverse outcome. Signal ambiguity may arise from faulty Doppler equipment or the inability of the cardiotocograph to differentiate between maternal and fetal heart rates. It commonly occurs after repositioning the patient, after fetal movement, or during pushing in the second stage when the maternal heart rate may increase to a baseline that is similar to that of the fetus.

Signal ambiguity should be suspected when the FHR runs in the low-normal range or when FHR accelerations are noted with greater than 50% of contractions (especially when pushing).⁴ Signal ambiguity also should be ruled out when there is an apparent FHR deceleration to the maternal range that does not recover.

Evaluating for suspected signal ambiguity involves 2 key steps: (1) documentation and verification of the maternal heart rate and (2) definitive documentation of the true FHR. To document the maternal heart rate, manually count the radial pulse for 1 minute or use a pulse oximeter for continuous monitoring. Using a pulse oximeter is a less labor-intensive approach and has the advantage of allowing continuous assessment of the maternal heart rate for comparison. Recording the maternal pulse continuously on the same screen as the FHR enables ongoing differentiation of the mother and fetus in difficult cases, particularly if internal fetal monitoring is not an option (because of maternal infectious disease, low suspicion for an abnormal FHR pattern, or strong maternal preference against internal monitoring, for example).

When clinically appropriate, use of a fetal scalp electrode (FSE) can document the FHR. If intrauterine fetal death has occurred, however, the FSE may transmit the maternal heart rate.⁵ Using ultrasonography to confirm the FHR prior to placing the FSE is a reliable method of definitive differentiation. If a newly placed FSE shows a clear differentiation of 5 to 10 beats per minute from a continuously assessed maternal pulse rate, then this is also a reliable way to assure that the FHR monitoring represents the fetus, particularly if ultrasonography is not immediately available.

Ultimately, before intervening based on an abnormal FHR tracing, it is paramount to confirm that the data are adequate for interpretation and represent the actual FHR. If signal ambiguity is identified or suspected, correct it by using ultrasonography to locate the FHR and replace the external monitor until a rate that is at least 5 to 10 beats per minute different from the maternal rate is obtained. Alternatively, this is an indication for internal fetal monitoring with an FSE.

Challenge: Inadequate FHR tracing, poor communication, lack of clinical context
CASE 2  Woman with uncomplicated postdates pregnancy presents for induction
A 28-year-old woman (G3P2) at 41 weeks 0 days of gestation presents to labor and delivery for induction of labor for the indication of postdates. There have been no complications with the current pregnancy. The initial cervical exam reveals 1+ cm dilation, 90% effacement, and −3 station, and the patient is started on oxytocin per the hospital protocol. What is your interpretation of the continuous FHR tracing shown in FIGURE 2?

FIGURE 2 Inadequate, uninterpretable FHR tracing

This FHR tracing, from the patient described in Case 2, is unusable because of the absence of data.

TIP #9: Check that the monitors are providing useful data
The ability to accurately interpret a continuous FHR tracing depends on the quality of data recorded. Unfortunately, the absence of data makes interpretation impossible. This includes both FHR and tocometry data, since both pieces of information are required for appropriate interpretation of a continuous FHR tracing.

Prolonged periods of uninterpretable FHR and uterine activity tracings imply that no one was attending the mother and fetus.⁶ If it is difficult to obtain an interpretable FHR tracing, document in the medical record that you made ongoing efforts to maintain an adequate tracing, including the amount of time spent holding the external monitor, use of ultrasonography to document the FHR, and plans for potential internal monitoring.

CASE 2  Continued
After several hours, the patient requests an epidural for pain management and one is placed without difficulty. She reports adequate pain relief and is comfortable for the next 1 to 2 hours. Subsequently, the patient reports a sudden onset of increasing pain that does not respond to additional patient-administered doses of anesthesia over a 30-minute period. The labor and delivery nurse becomes concerned about the patient's pain level and contacts the attending physician to discuss her concerns. The physician, who is currently attending to patients in clinic, listens to the nurse and asks her to contact the anesthesia department with her concerns (FIGURE 3).

FIGURE 3 FHR tracing reveals recurrent variables in a patient with evolving clinical concerns

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #8: Clearly communicate an urgent situation to the care team
Poor communication underlies many preventable adverse outcomes in medicine.⁷ Effective communication requires an adequate description of the clinical scenario or problem. A root cause analysis of a series of intrapartum adverse events involving fetal death or injury showed that poor communication about a concerning FHR tracing played a role in 72% of cases.¹

In this clinical scenario, the nurse believed that the patient's pain level was unusual or more than anticipated. The person who is communicating his or her concern (the sender) must be sure that the person receiving the message (the responder) clearly understands the sender's level of concern. In this case, it would have been appropriate for the sender to state clearly that she felt the patient's pain was outside of normal expectations and to request that the attending physician come to evaluate the patient.

Clear and effective communication includes (1) an appropriate description of the urgency of the situation and (2) an indication by the sender as to the desired response to this information ("please come evaluate the patient").⁸ In all cases, both steps are necessary to elicit an appropriate response.

CASE 2  Continued
Over the next 2 hours, recurrent variable decelerations develop, and then sudden, prolonged fetal bradycardia leads to urgent cesarean delivery. At delivery, a uterine rupture is diagnosed and a fetal hand is observed protruding through a lower-uterine segment defect into the maternal abdomen.

TIP #7: Always consider the entire clinical scenario
In this case, the team caring for the patient was not aware that her previous pregnancy had ended with a low transverse cesarean delivery. How does this information change your interpretation of the clinical scenario? The importance of understanding the entire clinical context when interpreting individual characteristics of cardiotocography cannot be overstated. For example, the sudden onset of recurrent, significant variable decelerations is more concerning in the context of a prior cesarean delivery, and late decelerations are more concerning in a patient with placental abruption, fetal growth restriction, or poorly controlled maternal diabetes.

An estimated 70% of fetuses will have an indeterminate FHR pattern (category II) at some time during labor.⁹ To appropriately interpret the FHR tracing, it is crucial to know the a priori risk for fetal hypoxia and metabolic acidosis (the precursor of fetal injury) due to such identified clinical risk factors as placental insufficiency, medical comorbidities (hypertension, diabetes), or postdates gestational age.

It is well established that cardiotocography has a good negative predictive value for the absence of fetal metabolic acidosis when there is moderate variability and spontaneous or induced accelerations. When attempting to risk stratify the fetus with a category II (indeterminate) FHR tracing, consider these 3 important questions:

1. What are the risk factors for this particular patient and her fetus?
2. What is the state of the fetus right now, and when was the last time metabolic acidosis could be excluded reasonably (by the presence of moderate variability and accelerations)?
3. What is the risk that the fetus will develop acidemia prior to delivery?

The presence of decelerations indicates interruption of oxygen delivery to the fetus, and recurrent decelerations may indicate an evolving process of accumulated oxygen deprivation, hypoxia, and eventually, metabolic acidosis. Most authorities agree that, for the fetus with a previously normal FHR tracing, the onset of significant, recurrent decelerations with slowly cumulative oxygen deficit can lead to fetal acidemia over the course of approximately 1 hour.¹⁰ Of course, acidosis also can occur much more quickly with acute events, such as placental abruption or uterine rupture. In deciding whether or not to intervene based on an FHR tracing, the clinician must take into account the clinical context to determine if delivery is likely to occur before significant acidemia develops.

Challenge: Lack of situational awareness, failure to address nursing concerns, reluctance to initiate the chain of command
CASE 3  Spontaneous labor in a second pregnancy
A 28-year-old woman (G2P1) at 40 weeks' gestation presents in spontaneous labor. She has a history of a previous uncomplicated vaginal delivery. After 6 hours she reaches complete dilation with the fetus at −1 station and begins pushing. After 60 minutes, the patient has only progressed to +1 station. She is contracting every 1 to 2 minutes with recurrent variable decelerations (FIGURE 4).

FIGURE 4 FHR tracing shows time points for initiation and continuation of pushing

This tracing, from the patient described in Case 3, documents contraction frequency every 1-2 minutes for more than 60 minutes while the patient continues to push. The fetal heart rate demonstrates repetitive moderate variable decelerations with every push.

TIP #6: Maintain situational awareness
A state of situational awareness exists when caregivers have a clear understanding of all of the factors at play in a clinical situation.¹¹ This can be lost when caregivers focus too intensely on one aspect of care. It often happens when the patient is pushing in the second stage and the provider, focused on the progress of fetal descent, loses track of the amount of time that has passed without reassuring features (such as variability and induced or spontaneous accelerations) in the FHR tracing. The nurse, seeing the physician at the bedside, presumes he or she is aware of the tracing and is thus reluctant to point out the concerning features for fear of appearing insubordinate.

Situational awareness also may be lost at the time of patient hand off between providers wherein critical information, such as a history of previous cesarean delivery, is not communicated to the next care team. When receiving an intrapartum patient hand off, providers must have heightened vigilance to ensure they quickly reach situational awareness and are cognizant of the entire clinical context. Maintaining an environment in which all members of the care team, regardless of their training level, are encouraged to voice their concerns is another way to promote ongoing situational awareness.

CASE 3  Continued
The patient continues pushing for another 20 minutes without delivery, and the nurse raises a concern about the FHR tracing to the physician, who remains in the room but does not respond (FIGURE 5).

FIGURE 5 FHR tracing reveals ongoing repetitive variable decelerations

This tracing, from the patient described in Case 2, shows variables in the FHR while the patient experiences increasing discomfort. Each of the red arrows indicates documentation by the nurse of increasing pain reported by the patient. The black bars are used to cover names of caregivers.

TIP #5: Acknowledge and respond to other caregivers' concerns
A team approach to patient care is essential in all areas of medicine, perhaps none more so than in obstetrics. Each member of the team is engaged in trying to provide optimal patient care and the concerns of every team member--regardless of title or level of training--must be acknowledged and addressed. Good communication requires creating a safe environment wherein each member of the team feels comfortable raising concerns without fear of reprisal. Rather than becoming angry or frustrated when questioned, providers should remain cognizant that these are ongoing efforts to maintain situational awareness and ensure the best possible outcome for mother and baby.

CASE 3  Continued
Pushing continues for another 30 minutes despite the nurse's repeated effort to express concern to the physician about the FHR tracing. After more than 2 hours of pushing, the infant is delivered; Apgar scores are 1, 5, and 7. No cord gas is obtained.

TIP #4: Initiate the chain of command when necessary
Any caregiver, regardless of job title, has a duty to initiate the institution's chain-of-command policy and procedure if he or she has a concern about patient well-being that is not being addressed adequately. It can be uncomfortable for a nurse, midwife, or resident physician to question an attending physician, particularly if that person responds in a dismissive, condescending, or angry manner. If a caregiver has made several attempts to engage the attending physician and feels the concerns are being inadequately addressed, then he or she must respectfully initiate the chain of command to seek additional objective review of the clinical situation.

Failure to follow oxytocin protocols, inadequate surveillance, poor documentation
CASE 4  Induction of an uncomplicated pregnancy due to postdates
A 20-year-old woman (G1P0) at 42 weeks' gestation with an otherwise uncomplicated first pregnancy presents for postdates induction with oxytocin. After 6 hours, she develops uterine tachysystole with recurrent variable decelerations but the oxytocin infusion is continued at the same rate (FIGURE 6).

FIGURE 6 FHR tracing indicates uterine tachysystole

The patient in Case 4 received oxytocin for induction of postdates pregnancy. The red arrow shown on the FHR tracing points out that oxytocin augmentation continues despite the presence of uterine contractions that are too frequent and initial changes, including subtle late decelerations in the FHR, that suggest early fetal compromise.

TIP #3: Manage oxytocin infusion according to protocol
Inappropriate use of oxytocin is common, including the improper management of oxytocin infusion in the setting of uterine tachysystole (defined as the presence of >5 contractions over a 10-minute period averaged over 30 minutes) and/or an abnormal FHR tracing. The mismanagement of uterine tachysystole is cited in more than two-thirds of obstetric malpractice cases.¹²

Uterine contractions alter blood flow through the spiral arteries and transiently reduce placental perfusion. Prolonged uterine tachysystole can lead to fetal oxygen debt and early signs of hypoxia, including the loss of spontaneous accelerations, tachycardia, and reduced variability. Continuing or increasing the oxytocin in the setting of such changes is hard to justify. One study found that the use of oxytocin in the setting of tachysystole was significantly associated with signs of fetal asphyxia (odds ratio [OR], 5.6).¹³ When the FHR pattern suggests significant interruption of fetal oxygen delivery and possible hypoxia, continuing or increasing an oxytocin infusion suggests a lack of understanding of the physiology that is the basis for FHR interpretation.

Appropriate management of tachysystole depends on the accompanying FHR.¹⁴ In the setting of a category I (normal) FHR tracing, tachysystole can be treated first with maternal repositioning (left or right lateral) and administration of a 500-cm3 maternal IV fluid bolus. If uterine activity does not return to normal after 10 to 15 minutes, decrease the oxytocin rate by at least half. If it does not return to normal after another 10 to 15 minutes, discontinue oxytocin until the tachysystole has resolved.

In the setting of a concerning category IIFHR tracing, discontinuation of oxytocin should be the first step along with maternal repositioning and administration of a fluid bolus. If these measures do not improve the FHR tracing and tachysystole persists, administration of an acute uterine relaxant, such as terbutaline, should be considered to slow contraction frequency.

If interventions result in normalization of the FHR tracing and resolution of tachysystole for 20 to 30 minutes, then oxytocin may be restarted if necessary for labor progress at no more than half the rate that produced tachysystole.

TIP #2: Recognize an abnormal FHR tracing--and what it means
Misinterpretation of the FHR tracing occurs when there is a failure to recognize characteristics that should raise concern about fetal well-being. Failure to recognize an abnormal FHR tracing occurred in 77% of sentinel cases involving intrapartum birth injury or death.^1,12,13 To limit misinterpretation of the FHR tracing, it is critical for nurses and physicians to use standardized terminology for clear, effective communication.

In 2008, the Eunice Kennedy Schriver National Institute of Child Health and Human Development (NICHD) published guidelines standardizing the terminology used to describe cardiotocography and to create consensus around its interpretation.15 Any description of an intrapartum FHR tracing should include a designation of category (I, II, or III). Fetal well-being is reasonably established with a category I FHR tracing.  A category III tracing indicates the high likelihood of fetal acidemia and the need for immediate intervention. A category II FHR tracing is considered indeterminate, and further characterization is required to reasonably exclude fetal metabolic acidosis and a risk of fetal injury.

The presence of moderate variability and fetal response to scalp stimulation are considered reassuring findings that reasonably exclude significant metabolic acidosis. In assessing variability, one pitfall is mistaking the appearance of "variability" within a deceleration (including during return to baseline) for baseline FHR variability. In the event of a persistent category II FHR tracing (>30 minutes), nursing staff should request direct physician review of the FHR tracing. In any case in which fetal well-being is uncertain, nursing staff should request direct physician evaluation of the mother in person and also the FHR tracing, with clear documentation of the findings, interpretation, and plan of care.¹⁶

TIP #1: Document, document, document
Nursing and physician documentation about the FHR tracing within the patient-specific clinical context is crucial for effective caregiver communication and patient safety. Thoughtful documentation also reduces liability exposure for providers by demonstrating maternal-fetal surveillance, early identification and treatment of an abnormal or indeterminate FHR tracing, and timely intervention on fetal behalf when necessary.

When the medical record aligns with the electronic FHR tracing and includes appropriate descriptions, interpretations, and interventions in line with national guidelines and institutional policy, the record demonstrates that the providers have a thorough understanding of the physiology behind cardiotocography and, more importantly, that they are able to apply that knowledge in clinical practice.⁶

Minimizing missteps
Several straightforward interventions can help clinicians overcome the most common pitfalls during FHR monitoring. These include accurate and high-quality cardiotocography, a collaborative team-based approach to patient care, and sustained situational awareness among providers. The consistent use of common language for the description and interpretation of FHR monitoring, adherence to hospital oxytocin protocols, and well-defined expectations for fetal surveillance and provider communication are critical to overcoming these challenges. Regularly scheduled nursing and physician education sessions and interdisciplinary case review can promote the adoption and sustained incorporation of these simple techniques into daily practice.³

Some have advocated for an "electronic fetal monitoring bundle," which would serve as a checklist of clinical evaluation steps that should occur every time a given process occurs.¹⁷ This approach would ensure that all providers on labor and delivery are qualified to read, accurately interpret, and respond to FHR tracings. It would require a credentialing process to confirm the competency of team members and reinforce the presence of a common language. It would also include an explicit escalation policy for rapid initiation of the chain of command in cases wherein there is a disagreement among team members about the FHR interpretation. Finally, each patient would be required to have, at all times, an identified responsible provider capable of a rapid response.

Although continuous FHR monitoring may not effectively reduce intrapartum fetal asphyxia, it is clearly here to stay. Recognizing--and addressing--the most common challenges encountered during intrapartum FHR monitoring may reduce unnecessary morbidity and potential liability for caregivers.

Share your thoughts! Send your Letter to the Editor to [email protected]. Please include your name and the city and state in which you practice.

The rate of total hip arthroplasty (THA) is rising and demand is expected to increase by 174% to 572,000 by 2030.¹ The rate of periprosthetic fracture around primary THA is frequently reported at around 1%,^2-4 though a recent study of over 32,000 THAs quotes the 20-year probability of periprosthetic fracture at 3.5%.⁵ Revision THA is also increasing in frequency and associated rates of periprosthetic fracture range from 1.5% to 7.8% following revision THA,^3,4,6 with the probability of fracture at 20 years of 11%.⁷ Projection models predict that the number of periprosthetic fractures will rise by 4.6% per decade over the next 30 years.⁸

Broadly, treatment options include open reduction internal fixation (ORIF), revision THA, and combined approaches. The Vancouver classification, based on fracture location, stem stability, and bone loss, is often used to guide fracture treatment, with stable implants treated with ORIF and unstable implants requiring revision arthroplasty.

Fixation strategies for treatment of periprosthetic fracture around a well-fixed arthroplasty stem have evolved over time, and there continue to be a variety of available internal fixation options with no clear consensus on the optimal strategy.⁹ Rates of reoperation following ORIF of periprosthetic femur fracture are reported from 13% to 23%,^8,10-12 confirming that there remains room for improvement in management of these injuries.

Locking Plate Fixation

Early fixation strategies included allograft and cables alone as well as nonlocked plate and cerclage constructs. In response to the complication and reoperation rate for nonlocked plate constructs, reported at 33%,¹³ locking plates were introduced as a treatment option, allowing for both improved osseous vascularity and added screw options.¹⁴ When compared to the traditional nonlocked Ogden construct, locking plate constructs are more resistant to axial and torsional load.¹⁵ Clinically, the relative risk of nonunion after nonlocking plate fixation is reported at 11.9 times that of fixation with locking plate technology.¹⁶

Successful use of lateral locking plate fixation for treatment of this injury has been reported on in several clinical series.^17-20 Froberg and colleagues¹² evaluated 60 Vancouver B1 and C fractures treated by locking plate osteosynthesis and reported no nonunions, an improvement from previous constructs. However, 8 out of 60 patients with 2-year follow-up required reoperation—4 for infection, 3 for refracture, and 1 for stem loosening—making it clear that the locking plate alone was not a panacea.

With locking plate fixation a mainstay of modern treatment of periprosthetic femur fractures, many questions still remain.

Proximal Fixation

Even with the introduction of locked plates, treatment success after ORIF of Vancouver B1 fractures relies on adequate proximal fixation. Options for proximal fixation around the stem include cerclage wires or cables, unicortical locked screws, obliquely directed bicortical screws, and use of the locking attachment plate to insert bicortical locked screws. These strategies can be used in the presence of cemented or uncemented stems, with biomechanical evidence that screw fixation through the cement mantle does not cause failure.²¹

Several biomechanical studies address the stiffness and strength of varying proximal fixation strategies. While early fixation relied heavily on cables, the use of cables alone as proximal fixation has been linked to significantly higher rates of failure when compared to other constructs in a large clinical series.¹¹ Multiple biomechanical studies have shown that newer methods of proximal fixation provide more rigid constructs.^22,23

Unicortical locked screws appear to outperform cables biomechanically. The use of unicortical screws in lieu of or in addition to cables provides added resistance to lateral bending as well as torsion when compared to cables alone.²⁴ A second group found that unicortical locked screws alone were superior to combined fixation with cerclage wires and unicortical locked screws.²⁵

Added stability can be demonstrated by bicortical fixation strategies, which offer increased rigidity when compared to cables or unicortical screws.²² In vitro work has shown enhanced fixation stability with bicortical screw fixation using the locking attachment plate when compared to cerclage wires alone.^23,26 Clinically, some authors have demonstrated success with the use of reversed distal femoral locking plates in order to enhance proximal locking options and allow for bicortical fixation around the stem.¹⁹ As noted above, the data favor the opinion that clinical failure rates with cerclage wires alone are high, and biomechanically, bicortical fixation around the femoral stem appears to be superior to unicortical locked screw fixation or cerclage wires. If rigid proximal fixation is desired, an effort should be made to obtain bicortical fixation around the femoral stem.

Allograft

Allograft strut, either alone or in addition to plate osteosynthesis, has long been used in treatment of periprosthetic fractures. Proponents of this technique cite improved biomechanical stability¹⁷ and allograft incorporation resulting in restoration of bone stock.

Early treatment of periprosthetic femur fractures consisted solely of allograft and cable fixation, but data on the technique is limited. A small series reported reasonable success, with only 2 out of 19 patients developing nonunion.²⁷ More recently Haddad and colleagues²⁸ reported malunions in 3 out of 19 patients treated with allograft and cables alone. Allograft alone has been largely abandoned in favor of plate fixation, and biomechanical evidence shows that plate and screw or cerclage constructs are more resistant to torsion and lateral bending than allograft with cables alone.²⁹

However, the role of allograft in treatment of periprosthetic femur fractures is not clearly defined. Some authors advocate routinely supplementing plate fixation with allograft^28,30 and others go as far as to suggest superior union rates of strut allograft augmented plate fixation when compared to plate fixation alone for periprosthetic fractures around a stable femoral stem.³¹ However, in that series, the failure rate of 5/11 patients treated with plate alone is higher than current series,¹² and others have demonstrated good success without allograft, even with nonlocked plates.³²

As recently as 2016, a lateral locking plate supplemented with allograft has been described as a successful technique, with no nonunions reported in a small series.³⁰ However, without a comparison group, it is unclear what role the allograft plays in success in that construct.

Despite some proposed benefits, the additional soft tissue stripping required to place allograft has raised the question of delayed healing and increased infection rate as a result of this technique. A systematic review by Moore and colleagues³³ looking at the use of allograft strut in Vancouver B1 fractures found increased time to union (4.4 vs 6.6 months) and deep infection rate (3.8% vs 8.3%) with the use of allograft strut, leading them to recommend cautious use of allograft when treating Vancouver B1 fractures.

With improved fixation strategies available, the role of allograft may be best reserved for patients with inadequate bone stock.

Dual Plate Fixation

Dual plate fixation has been proposed as one mechanism to increase construct strength. A periprosthetic fracture model has shown that, biomechanically, orthogonal plates have higher bending stiffness, torsional stiffness, cycles to failure, and load to failure when compared to a single lateral plate with use of a locking attachment plate proximally.³⁴ Choi and colleagues³⁵ compared lateral locking plates alone, lateral locking plates with allograft, and lateral locking plates with an orthogonal anterior plate and found the addition of an anterior plate resulted in the strongest construct.

Clinically, Müller and colleagues³⁶ reported on a series of 10 patients treated with orthogonal (anterior and lateral) plating for periprosthetic femur fractures, including 3 nonunions. In their series, there was 1 plate failure and they conclude that dual plating is not associated with an increased risk of complications, and can also be used as a salvage procedure.

While the evidence for dual plating is limited, it may provide needed additional stability in certain cases without the added cost and exposure required for allograft.

Minimally Invasive Plate Osteosynthesis

Contrary to the extensive exposure required to place allograft, minimally invasive plate osteosynthesis (MIPO) of periprosthetic femur fractures is advocated by some authors.^18,20 Ricci and colleagues¹⁸ reported no nonunions in 50 patients treated with indirect reduction techniques and laterally based plating alone without use of allograft. A combination of cables, locking, and nonlocking screws were used. Critical to their technique was preservation of the soft tissue envelope at the level of the fracture.

In further support of MIPO techniques, a systematic review of 1571 periprosthetic hip fractures reported significantly increased risk of nonunion with open approaches when compared to minimally invasive osteosynthesis,¹⁶ emphasizing the role of preservation of vascularity in treating these fractures.

Length of Fixation

For some time it was recommended that fixation of Vancouver B1 fractures end 2 cortical diameters below the level of the fracture.^37,38 More recently there has been interest in the potential benefits of increased length of fixation.

A biomechanical study comparing long (20-hole) and short (12-hole) plates for periprosthetic fracture with regard to failure found no difference in failure rates between groups.³⁹ While plate length did not appear to affect construct stiffness, the issue of subsequent fracture distal to the construct remains.

Moloney and colleagues⁴⁰ proposed fixation of Vancouver B1 fractures using plates that span the length of the femur to the level of the femoral condyles to minimize peri-implant failures in osteoporotic patients. In 36 patients treated with standard-length plates, there were 2 fractures distal to the previous fixation compared to no subsequent fractures in 21 patients treated with spanning fixation.

Similarly, in Vancouver C fractures there is some evidence that fixation should span the femoral stem, regardless of available bone for fixation proximal to the fracture. Kubiak and colleagues⁴¹ found increasing load to failure and decreased cortical strain in a biomechanical model comparing plates that stop short of the femoral stem with those that span the stem.

Clinically, this concept is supported by Froberg and colleagues.¹² In their series of 60 Vancouver B1 and C fractures treated with laterally based locked plating, 3 patients went on to refracture. All of these fractures occurred in patients with Vancouver C fractures treated with plates overlapping the preexisting stem by <50%. The fractures all occurred at the high stress area between the tip of the stem and the end of the plate.

Further support of extended plate length comes from Drew and colleagues,⁸ who demonstrated a significantly decreased risk of reoperation following ORIF of periprosthetic femur fracture when >75% of the length of the femur was spanned compared to <50%. Although in some settings short fixation may produce satisfactory results, consideration should be given to extending the length of fixation, especially in the osteoporotic population.

Interprosthetic Fractures

With a rising number of patients with ipsilateral hip and knee arthroplasty, the rate of interprosthetic fractures is rising. These fractures present additional challenges given preexisting implants above and below the level of the fracture. The use of a single precontoured laterally based locked plate has been reported with good union rates approaching 90%.^42,43 In one series, all nonunions occurred in Vancouver B1 fractures,⁴³ again bringing to light the challenging nature of the B1 fracture.

Nonunion

Success in treating periprosthetic femur fractures has improved with improved fixation methods and understanding of technique. However, current rates of nonunion are still reported up to 27% for B1 and C fractures.⁴⁴

There is limited evidence on the treatment of periprosthetic femur fracture nonunion. However, treatment is difficult and complication rates are high. Crockarell and colleagues⁴⁵ reported a 52% overall complication rate in their series of 23 periprosthetic femur fracture nonunions.

Nonunions of the femur near a prosthesis can be treated by revision of the fracture fixation using compression and grafting to achieve bone healing vs revision of the joint prosthesis to span the area of the nonunited bone. Case-by-case decision-making is based on the remaining bone stock and the type of revision prosthesis necessary to span the problem area. Given the challenges associated with their treatment, a focus on prevention of nonunion is of paramount importance.

Authors’ Preferred Treatment

Our treatment of periprosthetic femur fractures with a well-fixed hip arthroplasty stem adheres to the principles supported in the literature (Figures 1A-1D and Figures 2A, 2B).

• Soft tissue friendly dissection with limited exposure at the fracture site is preferred as the fracture allows, particularly in cases with comminution where a direct assessment of the reduction is not available.
• Plate fixation strategy is dictated by the characteristics of the fracture. Fracture patterns amenable to anatomic reduction receive interfragmentary compression and absolute stability constructs. Highly comminuted fractures receive relatively stable bridging constructs to encourage callous.
• Locking screws are used rarely in diaphyseal fracture patterns, and when employed, are applied to only one side of the fracture to limit “over stiffening” the construct.
• Liberal use of dual plating, both as a method of maintaining fracture reduction while a structural plate is applied and increasing construct rigidity.
• Proximal fixation relies heavily on bicortical screws placed through the holes of the lateral plate. Cerclage wires and unicortical screws are rarely used in our practice. In the case of larger stems, a bicortical 3.5-mm screw can be placed through a 4.5-mm plate using a reduction washer.

Summary

Techniques for treatment of periprosthetic femur fractures around a well-fixed hip arthroplasty stem are constantly evolving. Several principles have emerged to decrease rates of treatment failure and subsequent reoperation. While there are several methods to do so, it is critical to achieve stable proximal fixation. Long spanning fixation constructs are linked to lower failure and reoperation rates in both B1 and C type fractures. Additionally, the importance of soft tissue management and maintenance of local vascularity should not be underestimated.

The rate of total hip arthroplasty (THA) is rising and demand is expected to increase by 174% to 572,000 by 2030.¹ The rate of periprosthetic fracture around primary THA is frequently reported at around 1%,^2-4 though a recent study of over 32,000 THAs quotes the 20-year probability of periprosthetic fracture at 3.5%.⁵ Revision THA is also increasing in frequency and associated rates of periprosthetic fracture range from 1.5% to 7.8% following revision THA,^3,4,6 with the probability of fracture at 20 years of 11%.⁷ Projection models predict that the number of periprosthetic fractures will rise by 4.6% per decade over the next 30 years.⁸

Broadly, treatment options include open reduction internal fixation (ORIF), revision THA, and combined approaches. The Vancouver classification, based on fracture location, stem stability, and bone loss, is often used to guide fracture treatment, with stable implants treated with ORIF and unstable implants requiring revision arthroplasty.

Fixation strategies for treatment of periprosthetic fracture around a well-fixed arthroplasty stem have evolved over time, and there continue to be a variety of available internal fixation options with no clear consensus on the optimal strategy.⁹ Rates of reoperation following ORIF of periprosthetic femur fracture are reported from 13% to 23%,^8,10-12 confirming that there remains room for improvement in management of these injuries.

Locking Plate Fixation

Early fixation strategies included allograft and cables alone as well as nonlocked plate and cerclage constructs. In response to the complication and reoperation rate for nonlocked plate constructs, reported at 33%,¹³ locking plates were introduced as a treatment option, allowing for both improved osseous vascularity and added screw options.¹⁴ When compared to the traditional nonlocked Ogden construct, locking plate constructs are more resistant to axial and torsional load.¹⁵ Clinically, the relative risk of nonunion after nonlocking plate fixation is reported at 11.9 times that of fixation with locking plate technology.¹⁶

Successful use of lateral locking plate fixation for treatment of this injury has been reported on in several clinical series.^17-20 Froberg and colleagues¹² evaluated 60 Vancouver B1 and C fractures treated by locking plate osteosynthesis and reported no nonunions, an improvement from previous constructs. However, 8 out of 60 patients with 2-year follow-up required reoperation—4 for infection, 3 for refracture, and 1 for stem loosening—making it clear that the locking plate alone was not a panacea.

With locking plate fixation a mainstay of modern treatment of periprosthetic femur fractures, many questions still remain.

Proximal Fixation

Even with the introduction of locked plates, treatment success after ORIF of Vancouver B1 fractures relies on adequate proximal fixation. Options for proximal fixation around the stem include cerclage wires or cables, unicortical locked screws, obliquely directed bicortical screws, and use of the locking attachment plate to insert bicortical locked screws. These strategies can be used in the presence of cemented or uncemented stems, with biomechanical evidence that screw fixation through the cement mantle does not cause failure.²¹

Several biomechanical studies address the stiffness and strength of varying proximal fixation strategies. While early fixation relied heavily on cables, the use of cables alone as proximal fixation has been linked to significantly higher rates of failure when compared to other constructs in a large clinical series.¹¹ Multiple biomechanical studies have shown that newer methods of proximal fixation provide more rigid constructs.^22,23

Unicortical locked screws appear to outperform cables biomechanically. The use of unicortical screws in lieu of or in addition to cables provides added resistance to lateral bending as well as torsion when compared to cables alone.²⁴ A second group found that unicortical locked screws alone were superior to combined fixation with cerclage wires and unicortical locked screws.²⁵

Added stability can be demonstrated by bicortical fixation strategies, which offer increased rigidity when compared to cables or unicortical screws.²² In vitro work has shown enhanced fixation stability with bicortical screw fixation using the locking attachment plate when compared to cerclage wires alone.^23,26 Clinically, some authors have demonstrated success with the use of reversed distal femoral locking plates in order to enhance proximal locking options and allow for bicortical fixation around the stem.¹⁹ As noted above, the data favor the opinion that clinical failure rates with cerclage wires alone are high, and biomechanically, bicortical fixation around the femoral stem appears to be superior to unicortical locked screw fixation or cerclage wires. If rigid proximal fixation is desired, an effort should be made to obtain bicortical fixation around the femoral stem.

Allograft

Allograft strut, either alone or in addition to plate osteosynthesis, has long been used in treatment of periprosthetic fractures. Proponents of this technique cite improved biomechanical stability¹⁷ and allograft incorporation resulting in restoration of bone stock.

Early treatment of periprosthetic femur fractures consisted solely of allograft and cable fixation, but data on the technique is limited. A small series reported reasonable success, with only 2 out of 19 patients developing nonunion.²⁷ More recently Haddad and colleagues²⁸ reported malunions in 3 out of 19 patients treated with allograft and cables alone. Allograft alone has been largely abandoned in favor of plate fixation, and biomechanical evidence shows that plate and screw or cerclage constructs are more resistant to torsion and lateral bending than allograft with cables alone.²⁹

However, the role of allograft in treatment of periprosthetic femur fractures is not clearly defined. Some authors advocate routinely supplementing plate fixation with allograft^28,30 and others go as far as to suggest superior union rates of strut allograft augmented plate fixation when compared to plate fixation alone for periprosthetic fractures around a stable femoral stem.³¹ However, in that series, the failure rate of 5/11 patients treated with plate alone is higher than current series,¹² and others have demonstrated good success without allograft, even with nonlocked plates.³²

As recently as 2016, a lateral locking plate supplemented with allograft has been described as a successful technique, with no nonunions reported in a small series.³⁰ However, without a comparison group, it is unclear what role the allograft plays in success in that construct.

Despite some proposed benefits, the additional soft tissue stripping required to place allograft has raised the question of delayed healing and increased infection rate as a result of this technique. A systematic review by Moore and colleagues³³ looking at the use of allograft strut in Vancouver B1 fractures found increased time to union (4.4 vs 6.6 months) and deep infection rate (3.8% vs 8.3%) with the use of allograft strut, leading them to recommend cautious use of allograft when treating Vancouver B1 fractures.

With improved fixation strategies available, the role of allograft may be best reserved for patients with inadequate bone stock.

Dual Plate Fixation

Dual plate fixation has been proposed as one mechanism to increase construct strength. A periprosthetic fracture model has shown that, biomechanically, orthogonal plates have higher bending stiffness, torsional stiffness, cycles to failure, and load to failure when compared to a single lateral plate with use of a locking attachment plate proximally.³⁴ Choi and colleagues³⁵ compared lateral locking plates alone, lateral locking plates with allograft, and lateral locking plates with an orthogonal anterior plate and found the addition of an anterior plate resulted in the strongest construct.

Clinically, Müller and colleagues³⁶ reported on a series of 10 patients treated with orthogonal (anterior and lateral) plating for periprosthetic femur fractures, including 3 nonunions. In their series, there was 1 plate failure and they conclude that dual plating is not associated with an increased risk of complications, and can also be used as a salvage procedure.

While the evidence for dual plating is limited, it may provide needed additional stability in certain cases without the added cost and exposure required for allograft.

Minimally Invasive Plate Osteosynthesis

Contrary to the extensive exposure required to place allograft, minimally invasive plate osteosynthesis (MIPO) of periprosthetic femur fractures is advocated by some authors.^18,20 Ricci and colleagues¹⁸ reported no nonunions in 50 patients treated with indirect reduction techniques and laterally based plating alone without use of allograft. A combination of cables, locking, and nonlocking screws were used. Critical to their technique was preservation of the soft tissue envelope at the level of the fracture.

In further support of MIPO techniques, a systematic review of 1571 periprosthetic hip fractures reported significantly increased risk of nonunion with open approaches when compared to minimally invasive osteosynthesis,¹⁶ emphasizing the role of preservation of vascularity in treating these fractures.

Length of Fixation

For some time it was recommended that fixation of Vancouver B1 fractures end 2 cortical diameters below the level of the fracture.^37,38 More recently there has been interest in the potential benefits of increased length of fixation.

A biomechanical study comparing long (20-hole) and short (12-hole) plates for periprosthetic fracture with regard to failure found no difference in failure rates between groups.³⁹ While plate length did not appear to affect construct stiffness, the issue of subsequent fracture distal to the construct remains.

Moloney and colleagues⁴⁰ proposed fixation of Vancouver B1 fractures using plates that span the length of the femur to the level of the femoral condyles to minimize peri-implant failures in osteoporotic patients. In 36 patients treated with standard-length plates, there were 2 fractures distal to the previous fixation compared to no subsequent fractures in 21 patients treated with spanning fixation.

Similarly, in Vancouver C fractures there is some evidence that fixation should span the femoral stem, regardless of available bone for fixation proximal to the fracture. Kubiak and colleagues⁴¹ found increasing load to failure and decreased cortical strain in a biomechanical model comparing plates that stop short of the femoral stem with those that span the stem.

Clinically, this concept is supported by Froberg and colleagues.¹² In their series of 60 Vancouver B1 and C fractures treated with laterally based locked plating, 3 patients went on to refracture. All of these fractures occurred in patients with Vancouver C fractures treated with plates overlapping the preexisting stem by <50%. The fractures all occurred at the high stress area between the tip of the stem and the end of the plate.

Further support of extended plate length comes from Drew and colleagues,⁸ who demonstrated a significantly decreased risk of reoperation following ORIF of periprosthetic femur fracture when >75% of the length of the femur was spanned compared to <50%. Although in some settings short fixation may produce satisfactory results, consideration should be given to extending the length of fixation, especially in the osteoporotic population.

Interprosthetic Fractures

With a rising number of patients with ipsilateral hip and knee arthroplasty, the rate of interprosthetic fractures is rising. These fractures present additional challenges given preexisting implants above and below the level of the fracture. The use of a single precontoured laterally based locked plate has been reported with good union rates approaching 90%.^42,43 In one series, all nonunions occurred in Vancouver B1 fractures,⁴³ again bringing to light the challenging nature of the B1 fracture.

Nonunion

Success in treating periprosthetic femur fractures has improved with improved fixation methods and understanding of technique. However, current rates of nonunion are still reported up to 27% for B1 and C fractures.⁴⁴

There is limited evidence on the treatment of periprosthetic femur fracture nonunion. However, treatment is difficult and complication rates are high. Crockarell and colleagues⁴⁵ reported a 52% overall complication rate in their series of 23 periprosthetic femur fracture nonunions.

Nonunions of the femur near a prosthesis can be treated by revision of the fracture fixation using compression and grafting to achieve bone healing vs revision of the joint prosthesis to span the area of the nonunited bone. Case-by-case decision-making is based on the remaining bone stock and the type of revision prosthesis necessary to span the problem area. Given the challenges associated with their treatment, a focus on prevention of nonunion is of paramount importance.

Authors’ Preferred Treatment

Our treatment of periprosthetic femur fractures with a well-fixed hip arthroplasty stem adheres to the principles supported in the literature (Figures 1A-1D and Figures 2A, 2B).

• Soft tissue friendly dissection with limited exposure at the fracture site is preferred as the fracture allows, particularly in cases with comminution where a direct assessment of the reduction is not available.
• Plate fixation strategy is dictated by the characteristics of the fracture. Fracture patterns amenable to anatomic reduction receive interfragmentary compression and absolute stability constructs. Highly comminuted fractures receive relatively stable bridging constructs to encourage callous.
• Locking screws are used rarely in diaphyseal fracture patterns, and when employed, are applied to only one side of the fracture to limit “over stiffening” the construct.
• Liberal use of dual plating, both as a method of maintaining fracture reduction while a structural plate is applied and increasing construct rigidity.
• Proximal fixation relies heavily on bicortical screws placed through the holes of the lateral plate. Cerclage wires and unicortical screws are rarely used in our practice. In the case of larger stems, a bicortical 3.5-mm screw can be placed through a 4.5-mm plate using a reduction washer.

Summary

Techniques for treatment of periprosthetic femur fractures around a well-fixed hip arthroplasty stem are constantly evolving. Several principles have emerged to decrease rates of treatment failure and subsequent reoperation. While there are several methods to do so, it is critical to achieve stable proximal fixation. Long spanning fixation constructs are linked to lower failure and reoperation rates in both B1 and C type fractures. Additionally, the importance of soft tissue management and maintenance of local vascularity should not be underestimated.

The rate of total hip arthroplasty (THA) is rising and demand is expected to increase by 174% to 572,000 by 2030.¹ The rate of periprosthetic fracture around primary THA is frequently reported at around 1%,^2-4 though a recent study of over 32,000 THAs quotes the 20-year probability of periprosthetic fracture at 3.5%.⁵ Revision THA is also increasing in frequency and associated rates of periprosthetic fracture range from 1.5% to 7.8% following revision THA,^3,4,6 with the probability of fracture at 20 years of 11%.⁷ Projection models predict that the number of periprosthetic fractures will rise by 4.6% per decade over the next 30 years.⁸

Broadly, treatment options include open reduction internal fixation (ORIF), revision THA, and combined approaches. The Vancouver classification, based on fracture location, stem stability, and bone loss, is often used to guide fracture treatment, with stable implants treated with ORIF and unstable implants requiring revision arthroplasty.

Fixation strategies for treatment of periprosthetic fracture around a well-fixed arthroplasty stem have evolved over time, and there continue to be a variety of available internal fixation options with no clear consensus on the optimal strategy.⁹ Rates of reoperation following ORIF of periprosthetic femur fracture are reported from 13% to 23%,^8,10-12 confirming that there remains room for improvement in management of these injuries.

Locking Plate Fixation

Early fixation strategies included allograft and cables alone as well as nonlocked plate and cerclage constructs. In response to the complication and reoperation rate for nonlocked plate constructs, reported at 33%,¹³ locking plates were introduced as a treatment option, allowing for both improved osseous vascularity and added screw options.¹⁴ When compared to the traditional nonlocked Ogden construct, locking plate constructs are more resistant to axial and torsional load.¹⁵ Clinically, the relative risk of nonunion after nonlocking plate fixation is reported at 11.9 times that of fixation with locking plate technology.¹⁶

Successful use of lateral locking plate fixation for treatment of this injury has been reported on in several clinical series.^17-20 Froberg and colleagues¹² evaluated 60 Vancouver B1 and C fractures treated by locking plate osteosynthesis and reported no nonunions, an improvement from previous constructs. However, 8 out of 60 patients with 2-year follow-up required reoperation—4 for infection, 3 for refracture, and 1 for stem loosening—making it clear that the locking plate alone was not a panacea.

With locking plate fixation a mainstay of modern treatment of periprosthetic femur fractures, many questions still remain.

Proximal Fixation

Even with the introduction of locked plates, treatment success after ORIF of Vancouver B1 fractures relies on adequate proximal fixation. Options for proximal fixation around the stem include cerclage wires or cables, unicortical locked screws, obliquely directed bicortical screws, and use of the locking attachment plate to insert bicortical locked screws. These strategies can be used in the presence of cemented or uncemented stems, with biomechanical evidence that screw fixation through the cement mantle does not cause failure.²¹

Several biomechanical studies address the stiffness and strength of varying proximal fixation strategies. While early fixation relied heavily on cables, the use of cables alone as proximal fixation has been linked to significantly higher rates of failure when compared to other constructs in a large clinical series.¹¹ Multiple biomechanical studies have shown that newer methods of proximal fixation provide more rigid constructs.^22,23

Unicortical locked screws appear to outperform cables biomechanically. The use of unicortical screws in lieu of or in addition to cables provides added resistance to lateral bending as well as torsion when compared to cables alone.²⁴ A second group found that unicortical locked screws alone were superior to combined fixation with cerclage wires and unicortical locked screws.²⁵

Added stability can be demonstrated by bicortical fixation strategies, which offer increased rigidity when compared to cables or unicortical screws.²² In vitro work has shown enhanced fixation stability with bicortical screw fixation using the locking attachment plate when compared to cerclage wires alone.^23,26 Clinically, some authors have demonstrated success with the use of reversed distal femoral locking plates in order to enhance proximal locking options and allow for bicortical fixation around the stem.¹⁹ As noted above, the data favor the opinion that clinical failure rates with cerclage wires alone are high, and biomechanically, bicortical fixation around the femoral stem appears to be superior to unicortical locked screw fixation or cerclage wires. If rigid proximal fixation is desired, an effort should be made to obtain bicortical fixation around the femoral stem.

Allograft

Allograft strut, either alone or in addition to plate osteosynthesis, has long been used in treatment of periprosthetic fractures. Proponents of this technique cite improved biomechanical stability¹⁷ and allograft incorporation resulting in restoration of bone stock.

Early treatment of periprosthetic femur fractures consisted solely of allograft and cable fixation, but data on the technique is limited. A small series reported reasonable success, with only 2 out of 19 patients developing nonunion.²⁷ More recently Haddad and colleagues²⁸ reported malunions in 3 out of 19 patients treated with allograft and cables alone. Allograft alone has been largely abandoned in favor of plate fixation, and biomechanical evidence shows that plate and screw or cerclage constructs are more resistant to torsion and lateral bending than allograft with cables alone.²⁹

However, the role of allograft in treatment of periprosthetic femur fractures is not clearly defined. Some authors advocate routinely supplementing plate fixation with allograft^28,30 and others go as far as to suggest superior union rates of strut allograft augmented plate fixation when compared to plate fixation alone for periprosthetic fractures around a stable femoral stem.³¹ However, in that series, the failure rate of 5/11 patients treated with plate alone is higher than current series,¹² and others have demonstrated good success without allograft, even with nonlocked plates.³²

As recently as 2016, a lateral locking plate supplemented with allograft has been described as a successful technique, with no nonunions reported in a small series.³⁰ However, without a comparison group, it is unclear what role the allograft plays in success in that construct.

Despite some proposed benefits, the additional soft tissue stripping required to place allograft has raised the question of delayed healing and increased infection rate as a result of this technique. A systematic review by Moore and colleagues³³ looking at the use of allograft strut in Vancouver B1 fractures found increased time to union (4.4 vs 6.6 months) and deep infection rate (3.8% vs 8.3%) with the use of allograft strut, leading them to recommend cautious use of allograft when treating Vancouver B1 fractures.

With improved fixation strategies available, the role of allograft may be best reserved for patients with inadequate bone stock.

Dual Plate Fixation

Dual plate fixation has been proposed as one mechanism to increase construct strength. A periprosthetic fracture model has shown that, biomechanically, orthogonal plates have higher bending stiffness, torsional stiffness, cycles to failure, and load to failure when compared to a single lateral plate with use of a locking attachment plate proximally.³⁴ Choi and colleagues³⁵ compared lateral locking plates alone, lateral locking plates with allograft, and lateral locking plates with an orthogonal anterior plate and found the addition of an anterior plate resulted in the strongest construct.

Clinically, Müller and colleagues³⁶ reported on a series of 10 patients treated with orthogonal (anterior and lateral) plating for periprosthetic femur fractures, including 3 nonunions. In their series, there was 1 plate failure and they conclude that dual plating is not associated with an increased risk of complications, and can also be used as a salvage procedure.

While the evidence for dual plating is limited, it may provide needed additional stability in certain cases without the added cost and exposure required for allograft.

Minimally Invasive Plate Osteosynthesis

Contrary to the extensive exposure required to place allograft, minimally invasive plate osteosynthesis (MIPO) of periprosthetic femur fractures is advocated by some authors.^18,20 Ricci and colleagues¹⁸ reported no nonunions in 50 patients treated with indirect reduction techniques and laterally based plating alone without use of allograft. A combination of cables, locking, and nonlocking screws were used. Critical to their technique was preservation of the soft tissue envelope at the level of the fracture.

In further support of MIPO techniques, a systematic review of 1571 periprosthetic hip fractures reported significantly increased risk of nonunion with open approaches when compared to minimally invasive osteosynthesis,¹⁶ emphasizing the role of preservation of vascularity in treating these fractures.

Length of Fixation

For some time it was recommended that fixation of Vancouver B1 fractures end 2 cortical diameters below the level of the fracture.^37,38 More recently there has been interest in the potential benefits of increased length of fixation.

A biomechanical study comparing long (20-hole) and short (12-hole) plates for periprosthetic fracture with regard to failure found no difference in failure rates between groups.³⁹ While plate length did not appear to affect construct stiffness, the issue of subsequent fracture distal to the construct remains.

Moloney and colleagues⁴⁰ proposed fixation of Vancouver B1 fractures using plates that span the length of the femur to the level of the femoral condyles to minimize peri-implant failures in osteoporotic patients. In 36 patients treated with standard-length plates, there were 2 fractures distal to the previous fixation compared to no subsequent fractures in 21 patients treated with spanning fixation.

Similarly, in Vancouver C fractures there is some evidence that fixation should span the femoral stem, regardless of available bone for fixation proximal to the fracture. Kubiak and colleagues⁴¹ found increasing load to failure and decreased cortical strain in a biomechanical model comparing plates that stop short of the femoral stem with those that span the stem.

Clinically, this concept is supported by Froberg and colleagues.¹² In their series of 60 Vancouver B1 and C fractures treated with laterally based locked plating, 3 patients went on to refracture. All of these fractures occurred in patients with Vancouver C fractures treated with plates overlapping the preexisting stem by <50%. The fractures all occurred at the high stress area between the tip of the stem and the end of the plate.

Further support of extended plate length comes from Drew and colleagues,⁸ who demonstrated a significantly decreased risk of reoperation following ORIF of periprosthetic femur fracture when >75% of the length of the femur was spanned compared to <50%. Although in some settings short fixation may produce satisfactory results, consideration should be given to extending the length of fixation, especially in the osteoporotic population.

Interprosthetic Fractures

With a rising number of patients with ipsilateral hip and knee arthroplasty, the rate of interprosthetic fractures is rising. These fractures present additional challenges given preexisting implants above and below the level of the fracture. The use of a single precontoured laterally based locked plate has been reported with good union rates approaching 90%.^42,43 In one series, all nonunions occurred in Vancouver B1 fractures,⁴³ again bringing to light the challenging nature of the B1 fracture.

Nonunion

Success in treating periprosthetic femur fractures has improved with improved fixation methods and understanding of technique. However, current rates of nonunion are still reported up to 27% for B1 and C fractures.⁴⁴

There is limited evidence on the treatment of periprosthetic femur fracture nonunion. However, treatment is difficult and complication rates are high. Crockarell and colleagues⁴⁵ reported a 52% overall complication rate in their series of 23 periprosthetic femur fracture nonunions.

Nonunions of the femur near a prosthesis can be treated by revision of the fracture fixation using compression and grafting to achieve bone healing vs revision of the joint prosthesis to span the area of the nonunited bone. Case-by-case decision-making is based on the remaining bone stock and the type of revision prosthesis necessary to span the problem area. Given the challenges associated with their treatment, a focus on prevention of nonunion is of paramount importance.

Authors’ Preferred Treatment

Our treatment of periprosthetic femur fractures with a well-fixed hip arthroplasty stem adheres to the principles supported in the literature (Figures 1A-1D and Figures 2A, 2B).

• Soft tissue friendly dissection with limited exposure at the fracture site is preferred as the fracture allows, particularly in cases with comminution where a direct assessment of the reduction is not available.
• Plate fixation strategy is dictated by the characteristics of the fracture. Fracture patterns amenable to anatomic reduction receive interfragmentary compression and absolute stability constructs. Highly comminuted fractures receive relatively stable bridging constructs to encourage callous.
• Locking screws are used rarely in diaphyseal fracture patterns, and when employed, are applied to only one side of the fracture to limit “over stiffening” the construct.
• Liberal use of dual plating, both as a method of maintaining fracture reduction while a structural plate is applied and increasing construct rigidity.
• Proximal fixation relies heavily on bicortical screws placed through the holes of the lateral plate. Cerclage wires and unicortical screws are rarely used in our practice. In the case of larger stems, a bicortical 3.5-mm screw can be placed through a 4.5-mm plate using a reduction washer.

Summary

Techniques for treatment of periprosthetic femur fractures around a well-fixed hip arthroplasty stem are constantly evolving. Several principles have emerged to decrease rates of treatment failure and subsequent reoperation. While there are several methods to do so, it is critical to achieve stable proximal fixation. Long spanning fixation constructs are linked to lower failure and reoperation rates in both B1 and C type fractures. Additionally, the importance of soft tissue management and maintenance of local vascularity should not be underestimated.

Total hip arthroplasty (THA) is a successful surgery with positive clinical outcomes and over 95% survivorship at 10-year follow-up and 80% survivorship at 25-year follow-up.^1,2 A hip replacement requires strong osteointegration^3,4 to prevent femoral osteolysis, and correct implant alignment has been shown to correlate with prolonged implant survivorship and reduced dislocation.^5,6 Robotics and computer-assisted navigation have been developed to increase the accuracy of implant placement and reduce outliers with the overall goal of improving long-term results. These technologies have shown significant improvements in implant positioning when compared to conventional techniques.⁷

The first active robotic system for use in orthopedic procedures, Robodoc (Think Surgical, Inc.), was based on a traditional computer-aided design/computer-aided manufacturing system. Currently, only 3 robotic systems for THA have clearance in the US: The Mako System (Stryker), Robodoc, and TSolution One (Think Surgical, Inc.). The TSolution One system is based on the legacy technology developed as Robodoc and currently provides assistance during preparation of the femoral canal as well as guidance and positioning assistance during acetabular cup reaming and implanting. The following is a summary of the author’s (DSD) preferred technique for robotic-assisted THA using TSolution One.

How It Works

The process begins with preoperative planning (Figure 1). A computed tomography (CT) scan is used to create a detailed 3-dimensional (3D) reconstruction of the patient’s pathologic hip anatomy. The CT scan images are uploaded to TPLAN, a preoperative planning station.

In TPLAN, the user creates a 3D template of the surgical plan for both the femoral and acetabular portions of the procedure. The system has an open platform, meaning that the user is not limited to a single implant design or manufacturer. The surgeon can control every aspect of implant positioning: rotation, anteversion, fit and fill on the femoral side and anteversion, inclination/lateral opening, and depth on the acetabular side. Additional features available to the surgeon include accurately defining bony deficits, identifying outlier implant sizes, and checking for excess native version. The system allows the surgeon to determine the native center of hip rotation, which can then be used during templating to give the patient a hip that feels natural because the native muscle tension is restored. Once the desired plan has been achieved, it is uploaded to the robot.The TCAT robot is an active system similar to those used in manufacturing assembly plants (eg, automobiles) in that it follows a predetermined path and can do so in an efficient manner. More specifically, once the user has defined the patient’s anatomy within its workspace, it will proceed with actively milling the femur as planned with sub-millimeter accuracy without the use of navigation. This is in contrast to a haptic system, where the user manually guides the robotic arm within a predefined boundary.

The acetabular portion of the procedure currently uses a standard reamer system and power tools, but the TCAT guides the surgeon to the planned cup orientation, which is maintained during reaming and impaction.

In the Operating Suite

Once in the operating suite, the plan is uploaded into TCAT. Confirmation of the plan and the patient are incorporated into the surgical “time out.” Currently, the system supports patient positioning in standard lateral decubitus using a posterior approach with a standard operating room table. A posterior approach is undertaken to expose and dislocate the hip, with retractors placed to protect the soft tissues and allow the robot its working space.

One procedural difference from the standard THA technique is that the femoral head is initially retained to fixate the femur relative to the robot. A 5-mm Schanz pin is placed in the femoral head and then rigidly attached to the base of the robot. During a process called registration, a series of points on the surface of the exposed bone are collected by the surgeon via a digitizer probe attached to the robot. The TCAT monitor will guide the surgeon through point collection using a map showing the patient’s 3D bone model generated from the CT scan. The software then “finds” the patient’s femur in space and matches it to the 3D CT plan. Milling begins with a burr spinning at 80,000 rpm and saline to irrigate and remove bone debris (Figure 2). The actual milling process takes 5 to 15 minutes, depending on the choice and size of the implant.

A bone motion monitor (BMM) is also attached to the femur, along with recovery markers (RM). The BMM immediately pauses the robot during any active bone milling if it senses femoral motion from the original position. The surgeon then touches the RM with the digitizer to re-register the bone’s position and resume the milling process.

Attention is then turned to the acetabular portion of the procedure. Again, the robot must be rigidly fixed to the patient’s pelvis, along with the RM. Once the surgeon has registered the acetabular position using the digitizer, the robotic arm moves into the preoperatively planned orientation. A universal quick-release allows the surgeon to attach a standard reamer to the robot arm and ream while the robot holds the reamer in place. Once the acetabular preparation is complete, the cup impactor is placed onto the robotic arm and the implant is impacted into the patient. Thereafter, the digitizer can be used to collect points on the surface of the cup and confirm the exact cup placement (Figure 3).

Outcomes

The legacy system, Robodoc, has been used in thousands of clinical cases for both THA and total knee arthroplasty. The Table represents a summary of the THA clinical studies during a time frame in which only the femoral portion of the procedure was available to surgeons.

Bargar and colleagues⁸ describe the first Robodoc clinical trial in the US, along with the first 900 THA procedures performed in Germany. In the US, researchers conducted a prospective, randomized control study with 65 robotic cases and 62 conventional control cases. In terms of functional outcomes, there were no differences between the 2 groups. The robot group had improved radiographic fit and component positioning but significantly increased surgical time and blood loss. There were no femoral fractures in the robot group but 3 cases in the control group. In Germany, they reported on 870 primary THAs and 30 revision THA cases. For the primary cases, Harris hip scores rose from 43.7 preoperatively to 91.5 postoperatively. Complication rates were similar to conventional techniques, except the robot cases had no intraoperative femoral fractures.

Several prospective randomized clinical studies compared use of the Robodoc system with a conventional technique. The group studied by Honl and colleagues⁹ included 61 robotic cases and 80 conventional cases. The robot group had significant improvements in limb-length equality and varus-valgus orientation of the stem. When the revision cases were excluded, the authors found the Harris hip scores, prosthetic alignment, and limb length differentials were better for the robotic group at both 6 and 12 months.

Nakamura and colleagues¹⁰ looked at 75 robotic cases and 71 conventional cases. The results showed that at 2 and 3 years postoperatively, the robotic group had better Japanese Orthopaedic Association (JOA) scores, but by 5 years postoperatively, the differences were no longer significant. The robotic group had a smaller range for leg length inequality (0-12 mm) compared to the conventional group (0-29 mm). The results also showed that at both 2 and 5 years postoperatively, there was more significant stress shielding of the proximal femur, suggesting greater bone loss in the conventional group.

Nishihara and colleagues¹¹ had 78 subjects in each of the robotic and conventional groups and found significantly better Merle d’Aubigné hip scores at 2 years postoperatively in the robotic group. The conventional group suffered 5 intraoperative fractures compared with none in the robotic group, along with greater estimated blood loss, an increased use of undersized stems, higher-than-expected vertical seating, and unexpected femoral anteversion. The robotic cases did, however, take 19 minutes longer than the conventional cases.

Hananouchi and colleagues¹² looked at periprosthetic bone remodeling in 31 robotic hips and 27 conventional hips to determine whether load was effectively transferred from implant to bone after using the Robodoc system to prepare the femoral canal. Using dual energy X-ray absorptiometry (DEXA) to measure bone density, they found significantly less bone loss in the proximal periprosthetic areas in the robotic group compared to the conventional group; however, there were no differences in the Merle d’Aubigné hip scores.

Lim and colleagues¹³ looked specifically at alignment accuracy and clinical outcomes specifically for short femoral stem implants. In a group of 24 robotic cases and 25 conventional cases, they found significantly improved stem alignment and leg length inequality and no differences in Harris Hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, or complications at 24 months.

In 2004, Nishihara and colleagues¹⁴ evaluated the accuracy of femoral canal preparation using postoperative CT images for 75 cases of THA performed with the original pin-based version of Robodoc. The results showed that the differences between the preoperative plan and the postoperative CT were <5% in terms of canal fill, <1 mm in gap, and <1° in mediolateral and anteroposterior alignment with no reported fractures or complications. They concluded that the Robodoc system resulted in a high degree of accuracy.

Schulz and colleagues¹⁵ reported on 97 of 143 consecutive cases performed from 1997 to 2002. Technical complications were described in 9 cases. Five of the reported complications included the BMM pausing cutting as designed for patient safety, which led to re-registration, and slightly prolonged surgery. The remaining 4 complications included 2 femoral shaft fissures requiring wire cerclage, 1 case of damage to the acetabular rim from the milling device, and 1 defect of the greater trochanter that was milled. In terms of clinical results, they found that the complications, functional outcomes, and radiographic outcomes were comparable to conventional techniques. The rate of femoral shaft fissures, which had been zero in all other studies with Robodoc, was comparable to conventional technique.

Conclusion

The most significant change in hip arthroplasty until now has been the transition from a cemented technique to a press-fit or ingrowth prosthesis.¹⁶ The first robotic surgery was performed in the US in 1992 using the legacy system upon which the current TSolution One was based. Since then, the use of surgical robots has seen a 30% increase annually over the last decade in a variety of surgical fields.¹⁷ In orthopedics, specifically THA, the results have shown that robotics clearly offers benefits in terms of accuracy, precision, and reproducibility. These benefits will likely translate into improved long-term outcomes and increased survivorship in future studies.

Total hip arthroplasty (THA) is a successful surgery with positive clinical outcomes and over 95% survivorship at 10-year follow-up and 80% survivorship at 25-year follow-up.^1,2 A hip replacement requires strong osteointegration^3,4 to prevent femoral osteolysis, and correct implant alignment has been shown to correlate with prolonged implant survivorship and reduced dislocation.^5,6 Robotics and computer-assisted navigation have been developed to increase the accuracy of implant placement and reduce outliers with the overall goal of improving long-term results. These technologies have shown significant improvements in implant positioning when compared to conventional techniques.⁷

The first active robotic system for use in orthopedic procedures, Robodoc (Think Surgical, Inc.), was based on a traditional computer-aided design/computer-aided manufacturing system. Currently, only 3 robotic systems for THA have clearance in the US: The Mako System (Stryker), Robodoc, and TSolution One (Think Surgical, Inc.). The TSolution One system is based on the legacy technology developed as Robodoc and currently provides assistance during preparation of the femoral canal as well as guidance and positioning assistance during acetabular cup reaming and implanting. The following is a summary of the author’s (DSD) preferred technique for robotic-assisted THA using TSolution One.

How It Works

The process begins with preoperative planning (Figure 1). A computed tomography (CT) scan is used to create a detailed 3-dimensional (3D) reconstruction of the patient’s pathologic hip anatomy. The CT scan images are uploaded to TPLAN, a preoperative planning station.

In TPLAN, the user creates a 3D template of the surgical plan for both the femoral and acetabular portions of the procedure. The system has an open platform, meaning that the user is not limited to a single implant design or manufacturer. The surgeon can control every aspect of implant positioning: rotation, anteversion, fit and fill on the femoral side and anteversion, inclination/lateral opening, and depth on the acetabular side. Additional features available to the surgeon include accurately defining bony deficits, identifying outlier implant sizes, and checking for excess native version. The system allows the surgeon to determine the native center of hip rotation, which can then be used during templating to give the patient a hip that feels natural because the native muscle tension is restored. Once the desired plan has been achieved, it is uploaded to the robot.The TCAT robot is an active system similar to those used in manufacturing assembly plants (eg, automobiles) in that it follows a predetermined path and can do so in an efficient manner. More specifically, once the user has defined the patient’s anatomy within its workspace, it will proceed with actively milling the femur as planned with sub-millimeter accuracy without the use of navigation. This is in contrast to a haptic system, where the user manually guides the robotic arm within a predefined boundary.

The acetabular portion of the procedure currently uses a standard reamer system and power tools, but the TCAT guides the surgeon to the planned cup orientation, which is maintained during reaming and impaction.

In the Operating Suite

Once in the operating suite, the plan is uploaded into TCAT. Confirmation of the plan and the patient are incorporated into the surgical “time out.” Currently, the system supports patient positioning in standard lateral decubitus using a posterior approach with a standard operating room table. A posterior approach is undertaken to expose and dislocate the hip, with retractors placed to protect the soft tissues and allow the robot its working space.

One procedural difference from the standard THA technique is that the femoral head is initially retained to fixate the femur relative to the robot. A 5-mm Schanz pin is placed in the femoral head and then rigidly attached to the base of the robot. During a process called registration, a series of points on the surface of the exposed bone are collected by the surgeon via a digitizer probe attached to the robot. The TCAT monitor will guide the surgeon through point collection using a map showing the patient’s 3D bone model generated from the CT scan. The software then “finds” the patient’s femur in space and matches it to the 3D CT plan. Milling begins with a burr spinning at 80,000 rpm and saline to irrigate and remove bone debris (Figure 2). The actual milling process takes 5 to 15 minutes, depending on the choice and size of the implant.

A bone motion monitor (BMM) is also attached to the femur, along with recovery markers (RM). The BMM immediately pauses the robot during any active bone milling if it senses femoral motion from the original position. The surgeon then touches the RM with the digitizer to re-register the bone’s position and resume the milling process.

Attention is then turned to the acetabular portion of the procedure. Again, the robot must be rigidly fixed to the patient’s pelvis, along with the RM. Once the surgeon has registered the acetabular position using the digitizer, the robotic arm moves into the preoperatively planned orientation. A universal quick-release allows the surgeon to attach a standard reamer to the robot arm and ream while the robot holds the reamer in place. Once the acetabular preparation is complete, the cup impactor is placed onto the robotic arm and the implant is impacted into the patient. Thereafter, the digitizer can be used to collect points on the surface of the cup and confirm the exact cup placement (Figure 3).

Outcomes

The legacy system, Robodoc, has been used in thousands of clinical cases for both THA and total knee arthroplasty. The Table represents a summary of the THA clinical studies during a time frame in which only the femoral portion of the procedure was available to surgeons.

Bargar and colleagues⁸ describe the first Robodoc clinical trial in the US, along with the first 900 THA procedures performed in Germany. In the US, researchers conducted a prospective, randomized control study with 65 robotic cases and 62 conventional control cases. In terms of functional outcomes, there were no differences between the 2 groups. The robot group had improved radiographic fit and component positioning but significantly increased surgical time and blood loss. There were no femoral fractures in the robot group but 3 cases in the control group. In Germany, they reported on 870 primary THAs and 30 revision THA cases. For the primary cases, Harris hip scores rose from 43.7 preoperatively to 91.5 postoperatively. Complication rates were similar to conventional techniques, except the robot cases had no intraoperative femoral fractures.

Several prospective randomized clinical studies compared use of the Robodoc system with a conventional technique. The group studied by Honl and colleagues⁹ included 61 robotic cases and 80 conventional cases. The robot group had significant improvements in limb-length equality and varus-valgus orientation of the stem. When the revision cases were excluded, the authors found the Harris hip scores, prosthetic alignment, and limb length differentials were better for the robotic group at both 6 and 12 months.

Nakamura and colleagues¹⁰ looked at 75 robotic cases and 71 conventional cases. The results showed that at 2 and 3 years postoperatively, the robotic group had better Japanese Orthopaedic Association (JOA) scores, but by 5 years postoperatively, the differences were no longer significant. The robotic group had a smaller range for leg length inequality (0-12 mm) compared to the conventional group (0-29 mm). The results also showed that at both 2 and 5 years postoperatively, there was more significant stress shielding of the proximal femur, suggesting greater bone loss in the conventional group.

Nishihara and colleagues¹¹ had 78 subjects in each of the robotic and conventional groups and found significantly better Merle d’Aubigné hip scores at 2 years postoperatively in the robotic group. The conventional group suffered 5 intraoperative fractures compared with none in the robotic group, along with greater estimated blood loss, an increased use of undersized stems, higher-than-expected vertical seating, and unexpected femoral anteversion. The robotic cases did, however, take 19 minutes longer than the conventional cases.

Hananouchi and colleagues¹² looked at periprosthetic bone remodeling in 31 robotic hips and 27 conventional hips to determine whether load was effectively transferred from implant to bone after using the Robodoc system to prepare the femoral canal. Using dual energy X-ray absorptiometry (DEXA) to measure bone density, they found significantly less bone loss in the proximal periprosthetic areas in the robotic group compared to the conventional group; however, there were no differences in the Merle d’Aubigné hip scores.

Lim and colleagues¹³ looked specifically at alignment accuracy and clinical outcomes specifically for short femoral stem implants. In a group of 24 robotic cases and 25 conventional cases, they found significantly improved stem alignment and leg length inequality and no differences in Harris Hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, or complications at 24 months.

In 2004, Nishihara and colleagues¹⁴ evaluated the accuracy of femoral canal preparation using postoperative CT images for 75 cases of THA performed with the original pin-based version of Robodoc. The results showed that the differences between the preoperative plan and the postoperative CT were <5% in terms of canal fill, <1 mm in gap, and <1° in mediolateral and anteroposterior alignment with no reported fractures or complications. They concluded that the Robodoc system resulted in a high degree of accuracy.

Schulz and colleagues¹⁵ reported on 97 of 143 consecutive cases performed from 1997 to 2002. Technical complications were described in 9 cases. Five of the reported complications included the BMM pausing cutting as designed for patient safety, which led to re-registration, and slightly prolonged surgery. The remaining 4 complications included 2 femoral shaft fissures requiring wire cerclage, 1 case of damage to the acetabular rim from the milling device, and 1 defect of the greater trochanter that was milled. In terms of clinical results, they found that the complications, functional outcomes, and radiographic outcomes were comparable to conventional techniques. The rate of femoral shaft fissures, which had been zero in all other studies with Robodoc, was comparable to conventional technique.

Conclusion

The most significant change in hip arthroplasty until now has been the transition from a cemented technique to a press-fit or ingrowth prosthesis.¹⁶ The first robotic surgery was performed in the US in 1992 using the legacy system upon which the current TSolution One was based. Since then, the use of surgical robots has seen a 30% increase annually over the last decade in a variety of surgical fields.¹⁷ In orthopedics, specifically THA, the results have shown that robotics clearly offers benefits in terms of accuracy, precision, and reproducibility. These benefits will likely translate into improved long-term outcomes and increased survivorship in future studies.

Total hip arthroplasty (THA) is a successful surgery with positive clinical outcomes and over 95% survivorship at 10-year follow-up and 80% survivorship at 25-year follow-up.^1,2 A hip replacement requires strong osteointegration^3,4 to prevent femoral osteolysis, and correct implant alignment has been shown to correlate with prolonged implant survivorship and reduced dislocation.^5,6 Robotics and computer-assisted navigation have been developed to increase the accuracy of implant placement and reduce outliers with the overall goal of improving long-term results. These technologies have shown significant improvements in implant positioning when compared to conventional techniques.⁷

The first active robotic system for use in orthopedic procedures, Robodoc (Think Surgical, Inc.), was based on a traditional computer-aided design/computer-aided manufacturing system. Currently, only 3 robotic systems for THA have clearance in the US: The Mako System (Stryker), Robodoc, and TSolution One (Think Surgical, Inc.). The TSolution One system is based on the legacy technology developed as Robodoc and currently provides assistance during preparation of the femoral canal as well as guidance and positioning assistance during acetabular cup reaming and implanting. The following is a summary of the author’s (DSD) preferred technique for robotic-assisted THA using TSolution One.

How It Works

The process begins with preoperative planning (Figure 1). A computed tomography (CT) scan is used to create a detailed 3-dimensional (3D) reconstruction of the patient’s pathologic hip anatomy. The CT scan images are uploaded to TPLAN, a preoperative planning station.

In TPLAN, the user creates a 3D template of the surgical plan for both the femoral and acetabular portions of the procedure. The system has an open platform, meaning that the user is not limited to a single implant design or manufacturer. The surgeon can control every aspect of implant positioning: rotation, anteversion, fit and fill on the femoral side and anteversion, inclination/lateral opening, and depth on the acetabular side. Additional features available to the surgeon include accurately defining bony deficits, identifying outlier implant sizes, and checking for excess native version. The system allows the surgeon to determine the native center of hip rotation, which can then be used during templating to give the patient a hip that feels natural because the native muscle tension is restored. Once the desired plan has been achieved, it is uploaded to the robot.The TCAT robot is an active system similar to those used in manufacturing assembly plants (eg, automobiles) in that it follows a predetermined path and can do so in an efficient manner. More specifically, once the user has defined the patient’s anatomy within its workspace, it will proceed with actively milling the femur as planned with sub-millimeter accuracy without the use of navigation. This is in contrast to a haptic system, where the user manually guides the robotic arm within a predefined boundary.

The acetabular portion of the procedure currently uses a standard reamer system and power tools, but the TCAT guides the surgeon to the planned cup orientation, which is maintained during reaming and impaction.

In the Operating Suite

Once in the operating suite, the plan is uploaded into TCAT. Confirmation of the plan and the patient are incorporated into the surgical “time out.” Currently, the system supports patient positioning in standard lateral decubitus using a posterior approach with a standard operating room table. A posterior approach is undertaken to expose and dislocate the hip, with retractors placed to protect the soft tissues and allow the robot its working space.

One procedural difference from the standard THA technique is that the femoral head is initially retained to fixate the femur relative to the robot. A 5-mm Schanz pin is placed in the femoral head and then rigidly attached to the base of the robot. During a process called registration, a series of points on the surface of the exposed bone are collected by the surgeon via a digitizer probe attached to the robot. The TCAT monitor will guide the surgeon through point collection using a map showing the patient’s 3D bone model generated from the CT scan. The software then “finds” the patient’s femur in space and matches it to the 3D CT plan. Milling begins with a burr spinning at 80,000 rpm and saline to irrigate and remove bone debris (Figure 2). The actual milling process takes 5 to 15 minutes, depending on the choice and size of the implant.

A bone motion monitor (BMM) is also attached to the femur, along with recovery markers (RM). The BMM immediately pauses the robot during any active bone milling if it senses femoral motion from the original position. The surgeon then touches the RM with the digitizer to re-register the bone’s position and resume the milling process.

Attention is then turned to the acetabular portion of the procedure. Again, the robot must be rigidly fixed to the patient’s pelvis, along with the RM. Once the surgeon has registered the acetabular position using the digitizer, the robotic arm moves into the preoperatively planned orientation. A universal quick-release allows the surgeon to attach a standard reamer to the robot arm and ream while the robot holds the reamer in place. Once the acetabular preparation is complete, the cup impactor is placed onto the robotic arm and the implant is impacted into the patient. Thereafter, the digitizer can be used to collect points on the surface of the cup and confirm the exact cup placement (Figure 3).

Outcomes

The legacy system, Robodoc, has been used in thousands of clinical cases for both THA and total knee arthroplasty. The Table represents a summary of the THA clinical studies during a time frame in which only the femoral portion of the procedure was available to surgeons.

Bargar and colleagues⁸ describe the first Robodoc clinical trial in the US, along with the first 900 THA procedures performed in Germany. In the US, researchers conducted a prospective, randomized control study with 65 robotic cases and 62 conventional control cases. In terms of functional outcomes, there were no differences between the 2 groups. The robot group had improved radiographic fit and component positioning but significantly increased surgical time and blood loss. There were no femoral fractures in the robot group but 3 cases in the control group. In Germany, they reported on 870 primary THAs and 30 revision THA cases. For the primary cases, Harris hip scores rose from 43.7 preoperatively to 91.5 postoperatively. Complication rates were similar to conventional techniques, except the robot cases had no intraoperative femoral fractures.

Several prospective randomized clinical studies compared use of the Robodoc system with a conventional technique. The group studied by Honl and colleagues⁹ included 61 robotic cases and 80 conventional cases. The robot group had significant improvements in limb-length equality and varus-valgus orientation of the stem. When the revision cases were excluded, the authors found the Harris hip scores, prosthetic alignment, and limb length differentials were better for the robotic group at both 6 and 12 months.

Nakamura and colleagues¹⁰ looked at 75 robotic cases and 71 conventional cases. The results showed that at 2 and 3 years postoperatively, the robotic group had better Japanese Orthopaedic Association (JOA) scores, but by 5 years postoperatively, the differences were no longer significant. The robotic group had a smaller range for leg length inequality (0-12 mm) compared to the conventional group (0-29 mm). The results also showed that at both 2 and 5 years postoperatively, there was more significant stress shielding of the proximal femur, suggesting greater bone loss in the conventional group.

Nishihara and colleagues¹¹ had 78 subjects in each of the robotic and conventional groups and found significantly better Merle d’Aubigné hip scores at 2 years postoperatively in the robotic group. The conventional group suffered 5 intraoperative fractures compared with none in the robotic group, along with greater estimated blood loss, an increased use of undersized stems, higher-than-expected vertical seating, and unexpected femoral anteversion. The robotic cases did, however, take 19 minutes longer than the conventional cases.

Hananouchi and colleagues¹² looked at periprosthetic bone remodeling in 31 robotic hips and 27 conventional hips to determine whether load was effectively transferred from implant to bone after using the Robodoc system to prepare the femoral canal. Using dual energy X-ray absorptiometry (DEXA) to measure bone density, they found significantly less bone loss in the proximal periprosthetic areas in the robotic group compared to the conventional group; however, there were no differences in the Merle d’Aubigné hip scores.

Lim and colleagues¹³ looked specifically at alignment accuracy and clinical outcomes specifically for short femoral stem implants. In a group of 24 robotic cases and 25 conventional cases, they found significantly improved stem alignment and leg length inequality and no differences in Harris Hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, or complications at 24 months.

In 2004, Nishihara and colleagues¹⁴ evaluated the accuracy of femoral canal preparation using postoperative CT images for 75 cases of THA performed with the original pin-based version of Robodoc. The results showed that the differences between the preoperative plan and the postoperative CT were <5% in terms of canal fill, <1 mm in gap, and <1° in mediolateral and anteroposterior alignment with no reported fractures or complications. They concluded that the Robodoc system resulted in a high degree of accuracy.

Schulz and colleagues¹⁵ reported on 97 of 143 consecutive cases performed from 1997 to 2002. Technical complications were described in 9 cases. Five of the reported complications included the BMM pausing cutting as designed for patient safety, which led to re-registration, and slightly prolonged surgery. The remaining 4 complications included 2 femoral shaft fissures requiring wire cerclage, 1 case of damage to the acetabular rim from the milling device, and 1 defect of the greater trochanter that was milled. In terms of clinical results, they found that the complications, functional outcomes, and radiographic outcomes were comparable to conventional techniques. The rate of femoral shaft fissures, which had been zero in all other studies with Robodoc, was comparable to conventional technique.

Conclusion

The most significant change in hip arthroplasty until now has been the transition from a cemented technique to a press-fit or ingrowth prosthesis.¹⁶ The first robotic surgery was performed in the US in 1992 using the legacy system upon which the current TSolution One was based. Since then, the use of surgical robots has seen a 30% increase annually over the last decade in a variety of surgical fields.¹⁷ In orthopedics, specifically THA, the results have shown that robotics clearly offers benefits in terms of accuracy, precision, and reproducibility. These benefits will likely translate into improved long-term outcomes and increased survivorship in future studies.

The concept of robotics is relatively new in medical practice. The term “robot” itself is less than 100 years old, having been first introduced to popular culture in 1917 by Joseph Capek in the science fiction story Opilec.^1,2 Robots eventually transitioned from this initial fictional literary setting to reality in 1958, when General Motors began adding automated machines to its assembly lines.¹ However, it was not until the 1980s that robotics and their exacting efficiencies would be introduced in the medical field, and it would take another decade before they would enter the specialty of orthopedics.^1-4

The first robotic-assisted orthopedic surgery was reportedly performed in 1992, when the Robodoc autonomous system was utilized for total hip arthroplasty.^2-4 A robotic system for total knee arthroplasty (TKA) was first described in 1993, but it would take several more years until a system for unicompartmental knee arthroplasty (UKA) would be commercialized and used clinically.^5,6 The rationale for advancement of robotic technology for isolated medial or lateral knee arthritis stems from the recognition that while UKA is effective and durable when components and limb are well aligned and soft tissues appropriately balanced, they are less forgiving of even slight component malalignment of as little as 2° to 3° and prone to premature loosening or wear in those circumstances.^7-13,14 In the mid 2000s, Cobb and colleagues⁶ reported using a semiautonomous robot for UKA. Since then, emergence of other semiautonomous robotic systems has led to greater market penetration and technology utilization.¹⁵

Currently, an estimated 15% to 20% of UKA surgeries are being performed with robotic assistance.¹⁶ Further, patent activity and peer-reviewed publications related to robotic technology in UKA (which can be considered surrogate measures of interest and evolving development and experience with robotic technologies) have increased dramatically over the past few years.^{2,6,14,17,18-34} To date, while the most dramatic growth of robotic utilization and case volumes has occurred in the subspecialty of UKA, semiautonomous robotic systems have been used with increasing frequency for patellofemoral and bicompartmental knee arthroplasty.^35,36 Robotics have been used sparingly for TKA, and limited to autonomous systems;^37,38 however, it is anticipated that emergence of semiautonomous platforms for TKA will further expand the role of robotics over the next decade, particularly as our focus shifts beyond component and limb alignment in TKA and more towards the role of robotics in soft tissue balancing, reduction in instrumentation and inventory and its attendant cost savings, and surgical efficiencies. One semiautonomous robotic technology first used in 2006 (Mako, Stryker) reported a 130% increase in robotic volume from 2011 to 2012; another, first used in 2013, reported growth of 480% between 2013 and 2014, due to its improved cost structure, ease of use, smaller footprint, image-free platform and applicability in ambulatory surgery centers (Navio, Smith & Nephew; data supplied by manufacturer), demonstrating the growing popularity of robotic technology.^17,39 Further, a recent analysis of potential market penetration over the next decade published by Medical Device and Diagnostic Industry (http://www.mddionline.com) projected that nearly 37% of UKAs and 23% of TKAs will be performed with robotics in 10 years.

Distinction Between Robotic-Assisted Technologies

Autonomous systems involve pre-programming the system with parameters that define the amount and orientation of bone to be removed, after which the system prepares the surfaces independent of surgeon control, other than having access to a “shutdown” switch. There are currently no autonomous robotic tools approved by the US Food and Drug Administration (FDA) for knee arthroplasty.

Semiautonomous systems involve the mapping of condylar landmarks and determination of alignment indices, which also defines the volume and orientation of bone to be removed. While the systems remove bone and cartilage within the pre-established parameters, the robotic tools are controlled and manipulated by the surgeon (Figure 1). The predetermined safe zones modulate and safeguard the surgical actions. These systems also provide real-time quantification of soft tissue balancing, which may contribute to the reported successful clinical and functional outcomes with semiautonomous systems (Figure 2).^2,4,19,22 There are several semiautonomous robotic systems that are approved for use by the FDA.

Each robotic-assisted surgery (RAS) system utilizes some sort of 3-dimensional digital map of the surgical surfaces after a process of surface mapping and landmark registration.² In the case of Mako, this planning process also requires a preoperative computed tomography (CT) scan. Over the past few years, the requirement of a CT scan has proven problematic and costly, as increasingly third-party payers and insurers are denying coverage for additional studies used for preoperative planning, leaving the burden of cost on the patients and/or hospitals. Additionally, in an era in which bundled payment arrangements are commonplace or in which providers are held accountable for costly care, the use of costly preoperative imaging is untenable. Furthermore, there is a growing concern regarding the risk of radiation exposure from CT scans that makes image-free technologies, such as Navio, an alternative for stakeholders.⁴⁰

At this time, the 2 semiautonomous systems in use for UKA employ different methods to safeguard against inadvertent bone preparation: one by providing haptic constraint beyond which movement of the bur is limited (Mako); the other by modulating the exposure or speed of the handheld robotic bur (Navio) (Figure 3).

Outcomes of RAS in UKA

Compared to conventional UKA, robotic assistance has consistently demonstrated improved surgical accuracy, even through minimally invasive incisions (Figures 4, 5).^6,20-28 Several studies have found substantial reduction in variability and error of component positioning with use of semiautonomous robotic tools.^6,21,25 In fact, precision appears to be comparable regardless of whether an image-free system or one requiring a preoperative CT scan is used (Table). Further, in addition to improving component and limb alignment, Plate and colleagues²² demonstrated that RAS-based UKA systems can help the surgeon precisely reproduce plans for soft-tissue balancing. The authors reported ligament balancing to be accurate up to .53 mm compared to the preoperative plan, with approximately 83% of cases balanced within 1 mm of the plan through a full range of flexion.²²

When evaluating advanced and novel technologies, there is undoubtedly concern that there will be increased operative time and a substantial learning curve with those technologies. Karia and colleagues³⁰ found that when inexperienced surgeons performed UKA on synthetic bone models using robotics, the mean compound rotational and translational errors were lower than when conventional techniques were used. Among those using conventional techniques, although surgical times improved during the learning period, positional inaccuracies persisted. On the other hand, robotic assistance enabled surgeons to achieve precision and accuracy when positioning UKA components irrespective of their learning experience.³⁰ Another study, by Coon,³¹ similarly suggested a shorter learning curve and greater accuracy with RAS using the Mako system compared to conventional techniques. A prospective, multicenter, observational study evaluated the operative times of 11 surgeons during their initial clinical cases using Navio robotic technology for medial UKA after a period of training using cadaver knees and sawbones.⁴¹ The learning curve for total surgical time (tracker placement to implant trial phase) indicates that it takes 8 cases to achieve 95% of total learning and maintain a steady state surgical time.

Potential Disadvantages of RAS in UKA

RAS for UKA has several potential disadvantages that must be weighed against their potential benefits. One major barrier to broader use of RAS is the increased cost associated with the technologies.^17,19,27,32 Capital and maintenance costs for these systems can be high, and those that require additional advanced imaging, such as CT scans, further challenge the return on investment.^17,19,32 In a Markov analysis of one robotic system (Mako), Moschetti and colleagues¹⁷ found that if one assumes a system cost of $1.362 million, value can be attained due to slightly better outcomes despite being more expensive than traditional methods. Nonetheless, their analysis of the Mako system estimated that each robot-assisted UKA case cost $19,219, compared to $16,476 with traditional UKA, and was associated with an incremental cost of $47,180 per quality-adjusted life-year. Their analysis further demonstrated that the cost-effectiveness was very sensitive to case volume, with lower costs realized once volumes surpassed 94 cases per year. On the other hand, costs (and thus value) will also obviously vary depending on the capital costs, annual service charges, and avoidance of unnecessary preoperative scans.¹⁹ For instance, assuming a cost of $500,000 for the image-free Navio robotic system, return on investment is achievable within 25 cases annually, roughly one-quarter of the cases necessary with the image-based system.

Another disadvantage of RAS systems in UKA is the unique complications associated with their use. Both RAS and conventional UKA can be complicated by similar problems such as component loosening, polyethylene wear, progressive arthritis, infection, stiffness, instability, and thromboembolism. RAS systems, however, carry the additional risk of specific robot-related issues.^19,27 Perhaps most notably, the pin tracts for the required optical tracking arrays can create a stress riser in the cortical bone,^19,27,33,42 highlighting the importance of inserting these pins in metaphyseal, and not diaphyseal, bone. Soft tissue complications have been reported during bone preparation with autonomous systems in total knee and hip arthroplasty;^37,38 however, the senior author (JHL) has not observed that in 1000 consecutive cases with either semiautonomous surgeon-driven robotic tool.¹⁹

Finally, systems that require a preoperative CT scan pose an increased radiation risk.⁴⁰ Ponzio and Lonner⁴⁰ recently reported that each preoperative CT scan for robotic-assisted knee arthroplasty (using a Mako protocol) is associated with a mean effective dose of radiation of 4.8 mSv, which is approximately equivalent to 48 chest radiographs.³⁴ Further, in that study, at least 25% of patients had been subjected to multiple scans, with some being exposed to cumulative effective doses of up to 103 mSv. This risk should not be considered completely negligible given that 10 mSv may be associated with an increase in the possibility of fatal cancer, and an estimated 29,000 excess cancer cases in the United States annually are reportedly caused by CT scans.^40,43,44 However, this increased radiation risk is not inherent to all RAS systems. Image-free systems, such as Navio, do not require CT scans and are thus not associated with this potential disadvantage.

Conclusion

Robotics has come a long way from its humble conceptual beginnings nearly a century ago. Rapid advances in medical technology over the past 10 years have led to the development and growing popularity of RAS in orthopedic surgery, particularly during UKA. Component placement, quantified soft tissue balance, and radiographic alignment appear to be improved and the incidence of outliers reduced with the use of RAS during UKA. Further assessment is needed to determine whether the improved alignment and balance will impact clinical function and/or durability. Early results are very promising, though, creating optimism that the full benefits of RAS in UKA will be further confirmed with additional time and research.

The concept of robotics is relatively new in medical practice. The term “robot” itself is less than 100 years old, having been first introduced to popular culture in 1917 by Joseph Capek in the science fiction story Opilec.^1,2 Robots eventually transitioned from this initial fictional literary setting to reality in 1958, when General Motors began adding automated machines to its assembly lines.¹ However, it was not until the 1980s that robotics and their exacting efficiencies would be introduced in the medical field, and it would take another decade before they would enter the specialty of orthopedics.^1-4

The first robotic-assisted orthopedic surgery was reportedly performed in 1992, when the Robodoc autonomous system was utilized for total hip arthroplasty.^2-4 A robotic system for total knee arthroplasty (TKA) was first described in 1993, but it would take several more years until a system for unicompartmental knee arthroplasty (UKA) would be commercialized and used clinically.^5,6 The rationale for advancement of robotic technology for isolated medial or lateral knee arthritis stems from the recognition that while UKA is effective and durable when components and limb are well aligned and soft tissues appropriately balanced, they are less forgiving of even slight component malalignment of as little as 2° to 3° and prone to premature loosening or wear in those circumstances.^7-13,14 In the mid 2000s, Cobb and colleagues⁶ reported using a semiautonomous robot for UKA. Since then, emergence of other semiautonomous robotic systems has led to greater market penetration and technology utilization.¹⁵

Currently, an estimated 15% to 20% of UKA surgeries are being performed with robotic assistance.¹⁶ Further, patent activity and peer-reviewed publications related to robotic technology in UKA (which can be considered surrogate measures of interest and evolving development and experience with robotic technologies) have increased dramatically over the past few years.^{2,6,14,17,18-34} To date, while the most dramatic growth of robotic utilization and case volumes has occurred in the subspecialty of UKA, semiautonomous robotic systems have been used with increasing frequency for patellofemoral and bicompartmental knee arthroplasty.^35,36 Robotics have been used sparingly for TKA, and limited to autonomous systems;^37,38 however, it is anticipated that emergence of semiautonomous platforms for TKA will further expand the role of robotics over the next decade, particularly as our focus shifts beyond component and limb alignment in TKA and more towards the role of robotics in soft tissue balancing, reduction in instrumentation and inventory and its attendant cost savings, and surgical efficiencies. One semiautonomous robotic technology first used in 2006 (Mako, Stryker) reported a 130% increase in robotic volume from 2011 to 2012; another, first used in 2013, reported growth of 480% between 2013 and 2014, due to its improved cost structure, ease of use, smaller footprint, image-free platform and applicability in ambulatory surgery centers (Navio, Smith & Nephew; data supplied by manufacturer), demonstrating the growing popularity of robotic technology.^17,39 Further, a recent analysis of potential market penetration over the next decade published by Medical Device and Diagnostic Industry (http://www.mddionline.com) projected that nearly 37% of UKAs and 23% of TKAs will be performed with robotics in 10 years.

Distinction Between Robotic-Assisted Technologies

Autonomous systems involve pre-programming the system with parameters that define the amount and orientation of bone to be removed, after which the system prepares the surfaces independent of surgeon control, other than having access to a “shutdown” switch. There are currently no autonomous robotic tools approved by the US Food and Drug Administration (FDA) for knee arthroplasty.

Semiautonomous systems involve the mapping of condylar landmarks and determination of alignment indices, which also defines the volume and orientation of bone to be removed. While the systems remove bone and cartilage within the pre-established parameters, the robotic tools are controlled and manipulated by the surgeon (Figure 1). The predetermined safe zones modulate and safeguard the surgical actions. These systems also provide real-time quantification of soft tissue balancing, which may contribute to the reported successful clinical and functional outcomes with semiautonomous systems (Figure 2).^2,4,19,22 There are several semiautonomous robotic systems that are approved for use by the FDA.

Each robotic-assisted surgery (RAS) system utilizes some sort of 3-dimensional digital map of the surgical surfaces after a process of surface mapping and landmark registration.² In the case of Mako, this planning process also requires a preoperative computed tomography (CT) scan. Over the past few years, the requirement of a CT scan has proven problematic and costly, as increasingly third-party payers and insurers are denying coverage for additional studies used for preoperative planning, leaving the burden of cost on the patients and/or hospitals. Additionally, in an era in which bundled payment arrangements are commonplace or in which providers are held accountable for costly care, the use of costly preoperative imaging is untenable. Furthermore, there is a growing concern regarding the risk of radiation exposure from CT scans that makes image-free technologies, such as Navio, an alternative for stakeholders.⁴⁰

At this time, the 2 semiautonomous systems in use for UKA employ different methods to safeguard against inadvertent bone preparation: one by providing haptic constraint beyond which movement of the bur is limited (Mako); the other by modulating the exposure or speed of the handheld robotic bur (Navio) (Figure 3).

Outcomes of RAS in UKA

Compared to conventional UKA, robotic assistance has consistently demonstrated improved surgical accuracy, even through minimally invasive incisions (Figures 4, 5).^6,20-28 Several studies have found substantial reduction in variability and error of component positioning with use of semiautonomous robotic tools.^6,21,25 In fact, precision appears to be comparable regardless of whether an image-free system or one requiring a preoperative CT scan is used (Table). Further, in addition to improving component and limb alignment, Plate and colleagues²² demonstrated that RAS-based UKA systems can help the surgeon precisely reproduce plans for soft-tissue balancing. The authors reported ligament balancing to be accurate up to .53 mm compared to the preoperative plan, with approximately 83% of cases balanced within 1 mm of the plan through a full range of flexion.²²

When evaluating advanced and novel technologies, there is undoubtedly concern that there will be increased operative time and a substantial learning curve with those technologies. Karia and colleagues³⁰ found that when inexperienced surgeons performed UKA on synthetic bone models using robotics, the mean compound rotational and translational errors were lower than when conventional techniques were used. Among those using conventional techniques, although surgical times improved during the learning period, positional inaccuracies persisted. On the other hand, robotic assistance enabled surgeons to achieve precision and accuracy when positioning UKA components irrespective of their learning experience.³⁰ Another study, by Coon,³¹ similarly suggested a shorter learning curve and greater accuracy with RAS using the Mako system compared to conventional techniques. A prospective, multicenter, observational study evaluated the operative times of 11 surgeons during their initial clinical cases using Navio robotic technology for medial UKA after a period of training using cadaver knees and sawbones.⁴¹ The learning curve for total surgical time (tracker placement to implant trial phase) indicates that it takes 8 cases to achieve 95% of total learning and maintain a steady state surgical time.

Potential Disadvantages of RAS in UKA

RAS for UKA has several potential disadvantages that must be weighed against their potential benefits. One major barrier to broader use of RAS is the increased cost associated with the technologies.^17,19,27,32 Capital and maintenance costs for these systems can be high, and those that require additional advanced imaging, such as CT scans, further challenge the return on investment.^17,19,32 In a Markov analysis of one robotic system (Mako), Moschetti and colleagues¹⁷ found that if one assumes a system cost of $1.362 million, value can be attained due to slightly better outcomes despite being more expensive than traditional methods. Nonetheless, their analysis of the Mako system estimated that each robot-assisted UKA case cost $19,219, compared to $16,476 with traditional UKA, and was associated with an incremental cost of $47,180 per quality-adjusted life-year. Their analysis further demonstrated that the cost-effectiveness was very sensitive to case volume, with lower costs realized once volumes surpassed 94 cases per year. On the other hand, costs (and thus value) will also obviously vary depending on the capital costs, annual service charges, and avoidance of unnecessary preoperative scans.¹⁹ For instance, assuming a cost of $500,000 for the image-free Navio robotic system, return on investment is achievable within 25 cases annually, roughly one-quarter of the cases necessary with the image-based system.

Another disadvantage of RAS systems in UKA is the unique complications associated with their use. Both RAS and conventional UKA can be complicated by similar problems such as component loosening, polyethylene wear, progressive arthritis, infection, stiffness, instability, and thromboembolism. RAS systems, however, carry the additional risk of specific robot-related issues.^19,27 Perhaps most notably, the pin tracts for the required optical tracking arrays can create a stress riser in the cortical bone,^19,27,33,42 highlighting the importance of inserting these pins in metaphyseal, and not diaphyseal, bone. Soft tissue complications have been reported during bone preparation with autonomous systems in total knee and hip arthroplasty;^37,38 however, the senior author (JHL) has not observed that in 1000 consecutive cases with either semiautonomous surgeon-driven robotic tool.¹⁹

Finally, systems that require a preoperative CT scan pose an increased radiation risk.⁴⁰ Ponzio and Lonner⁴⁰ recently reported that each preoperative CT scan for robotic-assisted knee arthroplasty (using a Mako protocol) is associated with a mean effective dose of radiation of 4.8 mSv, which is approximately equivalent to 48 chest radiographs.³⁴ Further, in that study, at least 25% of patients had been subjected to multiple scans, with some being exposed to cumulative effective doses of up to 103 mSv. This risk should not be considered completely negligible given that 10 mSv may be associated with an increase in the possibility of fatal cancer, and an estimated 29,000 excess cancer cases in the United States annually are reportedly caused by CT scans.^40,43,44 However, this increased radiation risk is not inherent to all RAS systems. Image-free systems, such as Navio, do not require CT scans and are thus not associated with this potential disadvantage.

Conclusion

Robotics has come a long way from its humble conceptual beginnings nearly a century ago. Rapid advances in medical technology over the past 10 years have led to the development and growing popularity of RAS in orthopedic surgery, particularly during UKA. Component placement, quantified soft tissue balance, and radiographic alignment appear to be improved and the incidence of outliers reduced with the use of RAS during UKA. Further assessment is needed to determine whether the improved alignment and balance will impact clinical function and/or durability. Early results are very promising, though, creating optimism that the full benefits of RAS in UKA will be further confirmed with additional time and research.

The concept of robotics is relatively new in medical practice. The term “robot” itself is less than 100 years old, having been first introduced to popular culture in 1917 by Joseph Capek in the science fiction story Opilec.^1,2 Robots eventually transitioned from this initial fictional literary setting to reality in 1958, when General Motors began adding automated machines to its assembly lines.¹ However, it was not until the 1980s that robotics and their exacting efficiencies would be introduced in the medical field, and it would take another decade before they would enter the specialty of orthopedics.^1-4

The first robotic-assisted orthopedic surgery was reportedly performed in 1992, when the Robodoc autonomous system was utilized for total hip arthroplasty.^2-4 A robotic system for total knee arthroplasty (TKA) was first described in 1993, but it would take several more years until a system for unicompartmental knee arthroplasty (UKA) would be commercialized and used clinically.^5,6 The rationale for advancement of robotic technology for isolated medial or lateral knee arthritis stems from the recognition that while UKA is effective and durable when components and limb are well aligned and soft tissues appropriately balanced, they are less forgiving of even slight component malalignment of as little as 2° to 3° and prone to premature loosening or wear in those circumstances.^7-13,14 In the mid 2000s, Cobb and colleagues⁶ reported using a semiautonomous robot for UKA. Since then, emergence of other semiautonomous robotic systems has led to greater market penetration and technology utilization.¹⁵

Currently, an estimated 15% to 20% of UKA surgeries are being performed with robotic assistance.¹⁶ Further, patent activity and peer-reviewed publications related to robotic technology in UKA (which can be considered surrogate measures of interest and evolving development and experience with robotic technologies) have increased dramatically over the past few years.^{2,6,14,17,18-34} To date, while the most dramatic growth of robotic utilization and case volumes has occurred in the subspecialty of UKA, semiautonomous robotic systems have been used with increasing frequency for patellofemoral and bicompartmental knee arthroplasty.^35,36 Robotics have been used sparingly for TKA, and limited to autonomous systems;^37,38 however, it is anticipated that emergence of semiautonomous platforms for TKA will further expand the role of robotics over the next decade, particularly as our focus shifts beyond component and limb alignment in TKA and more towards the role of robotics in soft tissue balancing, reduction in instrumentation and inventory and its attendant cost savings, and surgical efficiencies. One semiautonomous robotic technology first used in 2006 (Mako, Stryker) reported a 130% increase in robotic volume from 2011 to 2012; another, first used in 2013, reported growth of 480% between 2013 and 2014, due to its improved cost structure, ease of use, smaller footprint, image-free platform and applicability in ambulatory surgery centers (Navio, Smith & Nephew; data supplied by manufacturer), demonstrating the growing popularity of robotic technology.^17,39 Further, a recent analysis of potential market penetration over the next decade published by Medical Device and Diagnostic Industry (http://www.mddionline.com) projected that nearly 37% of UKAs and 23% of TKAs will be performed with robotics in 10 years.

Distinction Between Robotic-Assisted Technologies

Autonomous systems involve pre-programming the system with parameters that define the amount and orientation of bone to be removed, after which the system prepares the surfaces independent of surgeon control, other than having access to a “shutdown” switch. There are currently no autonomous robotic tools approved by the US Food and Drug Administration (FDA) for knee arthroplasty.

Semiautonomous systems involve the mapping of condylar landmarks and determination of alignment indices, which also defines the volume and orientation of bone to be removed. While the systems remove bone and cartilage within the pre-established parameters, the robotic tools are controlled and manipulated by the surgeon (Figure 1). The predetermined safe zones modulate and safeguard the surgical actions. These systems also provide real-time quantification of soft tissue balancing, which may contribute to the reported successful clinical and functional outcomes with semiautonomous systems (Figure 2).^2,4,19,22 There are several semiautonomous robotic systems that are approved for use by the FDA.

Each robotic-assisted surgery (RAS) system utilizes some sort of 3-dimensional digital map of the surgical surfaces after a process of surface mapping and landmark registration.² In the case of Mako, this planning process also requires a preoperative computed tomography (CT) scan. Over the past few years, the requirement of a CT scan has proven problematic and costly, as increasingly third-party payers and insurers are denying coverage for additional studies used for preoperative planning, leaving the burden of cost on the patients and/or hospitals. Additionally, in an era in which bundled payment arrangements are commonplace or in which providers are held accountable for costly care, the use of costly preoperative imaging is untenable. Furthermore, there is a growing concern regarding the risk of radiation exposure from CT scans that makes image-free technologies, such as Navio, an alternative for stakeholders.⁴⁰

At this time, the 2 semiautonomous systems in use for UKA employ different methods to safeguard against inadvertent bone preparation: one by providing haptic constraint beyond which movement of the bur is limited (Mako); the other by modulating the exposure or speed of the handheld robotic bur (Navio) (Figure 3).

Outcomes of RAS in UKA

Compared to conventional UKA, robotic assistance has consistently demonstrated improved surgical accuracy, even through minimally invasive incisions (Figures 4, 5).^6,20-28 Several studies have found substantial reduction in variability and error of component positioning with use of semiautonomous robotic tools.^6,21,25 In fact, precision appears to be comparable regardless of whether an image-free system or one requiring a preoperative CT scan is used (Table). Further, in addition to improving component and limb alignment, Plate and colleagues²² demonstrated that RAS-based UKA systems can help the surgeon precisely reproduce plans for soft-tissue balancing. The authors reported ligament balancing to be accurate up to .53 mm compared to the preoperative plan, with approximately 83% of cases balanced within 1 mm of the plan through a full range of flexion.²²

When evaluating advanced and novel technologies, there is undoubtedly concern that there will be increased operative time and a substantial learning curve with those technologies. Karia and colleagues³⁰ found that when inexperienced surgeons performed UKA on synthetic bone models using robotics, the mean compound rotational and translational errors were lower than when conventional techniques were used. Among those using conventional techniques, although surgical times improved during the learning period, positional inaccuracies persisted. On the other hand, robotic assistance enabled surgeons to achieve precision and accuracy when positioning UKA components irrespective of their learning experience.³⁰ Another study, by Coon,³¹ similarly suggested a shorter learning curve and greater accuracy with RAS using the Mako system compared to conventional techniques. A prospective, multicenter, observational study evaluated the operative times of 11 surgeons during their initial clinical cases using Navio robotic technology for medial UKA after a period of training using cadaver knees and sawbones.⁴¹ The learning curve for total surgical time (tracker placement to implant trial phase) indicates that it takes 8 cases to achieve 95% of total learning and maintain a steady state surgical time.

Potential Disadvantages of RAS in UKA

RAS for UKA has several potential disadvantages that must be weighed against their potential benefits. One major barrier to broader use of RAS is the increased cost associated with the technologies.^17,19,27,32 Capital and maintenance costs for these systems can be high, and those that require additional advanced imaging, such as CT scans, further challenge the return on investment.^17,19,32 In a Markov analysis of one robotic system (Mako), Moschetti and colleagues¹⁷ found that if one assumes a system cost of $1.362 million, value can be attained due to slightly better outcomes despite being more expensive than traditional methods. Nonetheless, their analysis of the Mako system estimated that each robot-assisted UKA case cost $19,219, compared to $16,476 with traditional UKA, and was associated with an incremental cost of $47,180 per quality-adjusted life-year. Their analysis further demonstrated that the cost-effectiveness was very sensitive to case volume, with lower costs realized once volumes surpassed 94 cases per year. On the other hand, costs (and thus value) will also obviously vary depending on the capital costs, annual service charges, and avoidance of unnecessary preoperative scans.¹⁹ For instance, assuming a cost of $500,000 for the image-free Navio robotic system, return on investment is achievable within 25 cases annually, roughly one-quarter of the cases necessary with the image-based system.

Another disadvantage of RAS systems in UKA is the unique complications associated with their use. Both RAS and conventional UKA can be complicated by similar problems such as component loosening, polyethylene wear, progressive arthritis, infection, stiffness, instability, and thromboembolism. RAS systems, however, carry the additional risk of specific robot-related issues.^19,27 Perhaps most notably, the pin tracts for the required optical tracking arrays can create a stress riser in the cortical bone,^19,27,33,42 highlighting the importance of inserting these pins in metaphyseal, and not diaphyseal, bone. Soft tissue complications have been reported during bone preparation with autonomous systems in total knee and hip arthroplasty;^37,38 however, the senior author (JHL) has not observed that in 1000 consecutive cases with either semiautonomous surgeon-driven robotic tool.¹⁹

Finally, systems that require a preoperative CT scan pose an increased radiation risk.⁴⁰ Ponzio and Lonner⁴⁰ recently reported that each preoperative CT scan for robotic-assisted knee arthroplasty (using a Mako protocol) is associated with a mean effective dose of radiation of 4.8 mSv, which is approximately equivalent to 48 chest radiographs.³⁴ Further, in that study, at least 25% of patients had been subjected to multiple scans, with some being exposed to cumulative effective doses of up to 103 mSv. This risk should not be considered completely negligible given that 10 mSv may be associated with an increase in the possibility of fatal cancer, and an estimated 29,000 excess cancer cases in the United States annually are reportedly caused by CT scans.^40,43,44 However, this increased radiation risk is not inherent to all RAS systems. Image-free systems, such as Navio, do not require CT scans and are thus not associated with this potential disadvantage.

Conclusion

Robotics has come a long way from its humble conceptual beginnings nearly a century ago. Rapid advances in medical technology over the past 10 years have led to the development and growing popularity of RAS in orthopedic surgery, particularly during UKA. Component placement, quantified soft tissue balance, and radiographic alignment appear to be improved and the incidence of outliers reduced with the use of RAS during UKA. Further assessment is needed to determine whether the improved alignment and balance will impact clinical function and/or durability. Early results are very promising, though, creating optimism that the full benefits of RAS in UKA will be further confirmed with additional time and research.

Total knee arthroplasty (TKA) continues to be a widely utilized treatment option for end-stage knee osteoarthritis, and the number of patients undergoing TKA is projected to continually increase over the next decade.¹ Although TKA is highly successful for many patients, studies continue to report that approximately 20% of patients are dissatisfied after undergoing TKA, and nearly 25% of knee revisions are performed for instability or malalignment.^2,3 Technological advances have been developed to help improve clinical outcomes and implant survivorship. Over the past decade, computer navigation and intraoperative guides have been introduced to help control surgical variables and overcome the limitations and inaccuracies of traditional mechanical instrumentation. Currently, there are a variety of technologies available to assist surgeons with component alignment, including extramedullary devices, computer-assisted navigation systems (CAS), and patient-specific instrumentation (PSI) that help achieve desired alignment goals.^4,5

Computer-assisted navigation tools were introduced in an effort to improve implant alignment and clinical outcomes compared to traditional mechanical guides. Some argue that the use of computer-assisted surgery has a steep learning curve and successful use is dependent on the user’s experience; however, studies have suggested computer-assisted surgery may allow less experienced surgeons to reliably achieve anticipated intraoperative alignment goals with a low complication rate.^6,7 Various studies have looked at computer-assisted TKA at short to mid-term follow-up, but few studies have reported long-term outcomes.^6-9 de Steiger and colleagues¹⁰ recently found that computer-assisted TKA reduced the overall revision rate for aseptic loosening following TKA in patients younger than age 65 years, which suggests benefit of CAS for younger patients. Short-term follow-up has also shown the benefit of CAS TKA in patients with severe extra-articular deformity, where traditional instrumentation cannot be utilized.¹¹ Currently, there is no consensus that computer-assisted TKA leads to improved postoperative patient reported outcomes, because many studies are limited by study design or small cohorts; however, current literature does show an improvement in component alignment as compared to mechanical instrumentation.^9,12,13 As future implant and position targets are defined to improve implant survivorship and clinical outcomes in total joint arthroplasty, computer-assisted devices will be useful to help achieve more precise and accurate component positioning.

In addition to CAS devices, some companies have sought to improve TKA surgery by introducing PSI. PSI was introduced to improve component alignment in TKA, with the purported advantages of a shorter surgical time, decrease in the number of instruments needed, and improved clinical outcomes. PSI accuracy remains variable, which may be attributed to the various systems and implant designs in each study.^14-17 In addition, advanced preoperative imaging is necessary, which further adds to the overall cost.¹⁷ While the recent advancement in technology may provide decreased costs at the time of surgery, the increased cost and time incurred by the patient preoperatively has not resulted in significantly better clinical outcomes.^18,19 Additionally, recent work has not shown PSI to have superior accuracy as compared to currently available CAS devices.¹⁴ These findings suggest that the additional cost and time incurred by patients may limit the widespread use of PSI.

Although computer navigation has been shown to be more accurate than conventional instrumentation and PSI, the lack of improvement in long-term clinical outcome data has limited its use. In a meta-analysis, Bauwens and colleagues²⁰ suggested that while navigated TKAs have improved component alignment outcomes as compared to conventional surgery, the clinical benefit remains unclear. Less than 5% of surgeons are currently using navigation systems due to the perceived learning curve, cost, additional surgical time, and imaging required to utilize these systems. Certain navigation systems can be seemingly cumbersome, with large consoles, increased number of instruments required, and optical instruments with line-of-sight issues. Recent technological advances have worked to decrease this challenge by using accelerometer- and gyroscope-based electronic components, which combine the accuracy of computer-assisted technology with the ease of use of mechanical guides.

Accelerometer and gyroscope technology systems, such as the iAssist system, are portable devices that do not require a large computer console or navigation arrays. This technology relies on accelerator-based navigation without additional preoperative imaging. A recent study demonstrated the iAssist had reproducible accuracy in component alignment that could be easily incorporated into the operating room without optical trackers.²¹ The use of portable computer-assisted devices provides a more compact and easily accessible technology that can be used to achieve accurate component alignment without additional large equipment in the operating room.²² These new handheld intraoperative tools have been introduced to place implants according to a preoperative plan in order to minimize failure due to preoperative extra-articular deformity or intraoperative technical miscues.²³ Nam and colleagues²⁴ used an accelerometer-based surgical navigation system to perform tibial resections in cadaveric models, and found that the accelerometer-based guide was accurate for tibial resection in both the coronal and sagittal planes. In a prospective randomized controlled trial evaluating 100 patients undergoing a TKA using either an accelerometer-based guide or conventional alignment methods, the authors showed that the accelerometer-based guide decreased outliers in tibial component alignment compared to conventional guides.²⁵ In the accelerometer-based guide cohort, 95.7% of tibial components were within 2° of perpendicular to the tibial mechanical axis, compared to 68.1% in the conventional group (P < .001). These results suggested that portable accelerometer-based navigation allows surgeons to achieve satisfactory tibial component alignment with a decrease in the number of potential outliers.^24,25 Similarly, Bugbee and colleagues²⁶ found that accelerometer-based handheld navigation was accurate for tibial coronal and sagittal alignment and no additional surgical time was required compared to conventional techniques.

The relationship between knee alignment and clinical outcomes for TKA remains controversial. Regardless of the surgeon’s alignment preference, it is important to reliably and accurately execute the preoperative plan in a reproducible fashion. Advances in technology that assist with intraoperative component alignment can be useful, and may help decrease the incidence of implant malalignment in clinical practice.

Preoperative Planning and Intraoperative Technique

Preoperative planning is carried out in a manner identical to the use of conventional mechanical guides. Long leg films are taken for evaluation of overall limb alignment, and calibrated lateral images are taken for templating implant sizes. Lines are drawn on the images to determine the difference between the mechanical and anatomic axis of the femur, and a line drawn perpendicular to the mechanical axis is placed to show the expected bone cut. In similar fashion a perpendicular line to the tibial mechanical axis is also drawn to show the expected tibial resection. This preoperative plan allows the surgeon to have an additional intraoperative guide to ensure accuracy of the computer-assisted device.

After standard exposure, the distal femoral or proximal tibial cut can be made based on surgeon preference. The system being demonstrated in the accompanying photos is the KneeAlign 2 system (OrthAlign).

Distal Femoral Cut

The KneeAlign 2 femoral cutting guide is attached to the distal femur with a central pin that is placed in the middle of the distal femur measured from medial to lateral, and 1 cm anterior to the intercondylar notch. It is important to note that this spot is often more medial than traditionally used for insertion of an intramedullary rod. This central point sets the distal point of the femoral mechanical axis. The device is then held in place with 2 oblique pins, and is solidly fixed to the bone. Using a rotating motion, the femur is rotated around the hip joint. The accelerometer and gyroscope in the unit are able to determine the center of the hip joint from this motion, creating the proximal point of the mechanical axis of the femur. Once the mechanical axis of the femur is determined, varus/valgus and flexion/extension can be adjusted on the guide. One adjustment screw is available for varus/valgus, and a second is available for flexion/extension. Numbers on the device screen show real-time alignment, and are easily adjusted to set the desired alignment (Figure 1). Once alignment is obtained, a mechanical stylus is used to determine depth of resection, and the distal femoral cutting block is pinned. After pinning the block, the 3 pins in the device are removed, and the device is removed from the bone. This leaves only the distal femoral cutting block in place. In experienced hands, this part of the procedure takes less than 3 minutes.

Proximal Tibial Cut

The KneeAlign 2 proximal tibial guide is similar in appearance to a standard mechanical tibial cutting guide. It is attached to the proximal tibia with a spring around the calf and 2 pins that hold the device aligned with the medial third of the tibial tubercle. A stylus is then centered on the anterior cruciate ligament (ACL) footprint, which sets the proximal mechanical axis point of the tibia (Figure 2). An offset number is read off the stylus on the ACL footprint, and this number is matched on the ankle offset portion of the guide. The device has 2 sensors. One sensor is on the chassis of the device, and the other is on a mobile arm. Movements between the 2 are monitored by the accelerometers, allowing for accurate maintenance of alignment position even with motion in the leg. A point is taken from the lateral malleolus and then a second point is taken from the medial malleolus. These points are used to determine the center of the ankle joint, which sets the distal mechanical axis point. Once mechanical axis of the tibia is determined, the tibial cutting guide is pinned in place, and can be adjusted with real-time guidance of the varus/valgus and posterior slope values seen on the device (Figure 3). Cut depth is once again determined with a mechanical stylus.

Limitations

Although these devices have proven to be very accurate, surgeons must continue to recognize that all tools can have errors. With computerized guides of any sort, these errors are usually user errors that cannot be detected by the device. Surgeons need to be able to recognize this and always double-check bone cuts for accuracy. Templating the bone cuts prior to surgery is an effective double-check. In addition, many handheld accelerometer devices do not currently assist with the rotational alignment of the femoral component. This is still performed using the surgeon’s preferred technique, and is a limitation of these systems.

Discussion

Currently, TKA provides satisfactory 10-year results with modern implant designs and survival rates as high as 90% to 95%.^27,28 Even with good survival rates, a percentage of patients fail within the first 5 years.³ At a single institution, 50% of revision TKAs were related to instability, malalignment, or failure of fixation that occurred less than 2 years after the index procedure.²⁹ In general, TKA with mechanical instrumentation provides satisfactory pain relief and postoperative knee function; however, studies have consistently shown that the use of advanced technology decreases the risk of implant malalignment, which may decrease early implant failure rates as compared to mechanical and some PSI.^13,14,22 While there is a paucity of literature that has shown better clinical outcomes with the use of advanced technology, there are studies supporting the notion that proper limb alignment and component positioning improves implant survivorship.^23,30

CAS may have additional advantages if the surgeon chooses to place the TKA in an alignment other than a neutral mechanical axis. Kinematic alignment for TKA has gained increasing popularity, where the target of a neutral mechanical axis alignment is not always the goal.^31,32 The reported benefit is a more natural ligament tension with the hope of improving patient satisfaction. One concern with this technique is that it is a departure from the long-held teaching that a TKA aligned to a neutral mechanical axis is necessary for long-term implant survivorship.^33,34 In addition, if the goal of surgery is to cut the tibia and femur at a specific varus/valgus cut, standard instrumentation may not allow for this level of accuracy. This in turn increases the risk of having a tibial or femoral cut that is outside the commonly accepted standards of alignment, which may lead to early implant failure. If further research suggests alignment is a variable that differs from patient to patient, the use of precise tools to ensure accuracy of executing the preoperatively templated alignment becomes even more important.

As the number of TKAs continues to rise each year, even a small percentage of malaligned knees that go on to revision surgery will create a large burden on the healthcare system.^1,3 Although the short-term clinical benefits of CAS have not shown substantial differences as compared to conventional TKA, the number of knees aligned outside of a desired neutral mechanical axis alignment has been shown in multiple studies to be decreased with the use of advanced technology.^7,12,34 Although CAS is an additional cost to a primary TKA, if the orthopedic community can decrease the number of TKA revisions due to malalignment from 6.6% to nearly zero, this may decrease the revision burden and overall cost to the healthcare system.^1,3

TKA technology continues to evolve, and we must continue to assess each new advance not only to understand how it works, but also to ensure it addresses a specific clinical problem, and to be aware of the costs associated before incorporating it into routine practice. Some argue that the use of advanced technology requires increased surgical time, which in turn ultimately increases costs; however, one study has documented no increase in surgical time with handheld navigation while maintaining the accuracy of the device.³⁴ In addition, no significant radiographic or clinical differences have been found between handheld navigation and larger console CAS systems, but large console systems have been associated with increased surgical times.²² The use of handheld accelerometer- and gyroscope-based guides has proven to provide reliable coronal and sagittal implant alignment that can easily be incorporated into the operating room. More widespread use of such technology will help decrease alignment outliers for TKA, and future long-term clinical outcome studies will be necessary to assess functional outcomes.

Conclusion

Advanced computer based technology offers an additional tool to the surgeon for reliably improving component positioning during TKA. The use of handheld accelerometer- and gyroscope-based guides increases the accuracy of component placement while decreasing the incidence of outliers compared to standard mechanical guides, without the need for a large computer console. Long-term radiographic and patient-reported outcomes are necessary to further validate these devices.

Total knee arthroplasty (TKA) continues to be a widely utilized treatment option for end-stage knee osteoarthritis, and the number of patients undergoing TKA is projected to continually increase over the next decade.¹ Although TKA is highly successful for many patients, studies continue to report that approximately 20% of patients are dissatisfied after undergoing TKA, and nearly 25% of knee revisions are performed for instability or malalignment.^2,3 Technological advances have been developed to help improve clinical outcomes and implant survivorship. Over the past decade, computer navigation and intraoperative guides have been introduced to help control surgical variables and overcome the limitations and inaccuracies of traditional mechanical instrumentation. Currently, there are a variety of technologies available to assist surgeons with component alignment, including extramedullary devices, computer-assisted navigation systems (CAS), and patient-specific instrumentation (PSI) that help achieve desired alignment goals.^4,5

Computer-assisted navigation tools were introduced in an effort to improve implant alignment and clinical outcomes compared to traditional mechanical guides. Some argue that the use of computer-assisted surgery has a steep learning curve and successful use is dependent on the user’s experience; however, studies have suggested computer-assisted surgery may allow less experienced surgeons to reliably achieve anticipated intraoperative alignment goals with a low complication rate.^6,7 Various studies have looked at computer-assisted TKA at short to mid-term follow-up, but few studies have reported long-term outcomes.^6-9 de Steiger and colleagues¹⁰ recently found that computer-assisted TKA reduced the overall revision rate for aseptic loosening following TKA in patients younger than age 65 years, which suggests benefit of CAS for younger patients. Short-term follow-up has also shown the benefit of CAS TKA in patients with severe extra-articular deformity, where traditional instrumentation cannot be utilized.¹¹ Currently, there is no consensus that computer-assisted TKA leads to improved postoperative patient reported outcomes, because many studies are limited by study design or small cohorts; however, current literature does show an improvement in component alignment as compared to mechanical instrumentation.^9,12,13 As future implant and position targets are defined to improve implant survivorship and clinical outcomes in total joint arthroplasty, computer-assisted devices will be useful to help achieve more precise and accurate component positioning.

In addition to CAS devices, some companies have sought to improve TKA surgery by introducing PSI. PSI was introduced to improve component alignment in TKA, with the purported advantages of a shorter surgical time, decrease in the number of instruments needed, and improved clinical outcomes. PSI accuracy remains variable, which may be attributed to the various systems and implant designs in each study.^14-17 In addition, advanced preoperative imaging is necessary, which further adds to the overall cost.¹⁷ While the recent advancement in technology may provide decreased costs at the time of surgery, the increased cost and time incurred by the patient preoperatively has not resulted in significantly better clinical outcomes.^18,19 Additionally, recent work has not shown PSI to have superior accuracy as compared to currently available CAS devices.¹⁴ These findings suggest that the additional cost and time incurred by patients may limit the widespread use of PSI.

Although computer navigation has been shown to be more accurate than conventional instrumentation and PSI, the lack of improvement in long-term clinical outcome data has limited its use. In a meta-analysis, Bauwens and colleagues²⁰ suggested that while navigated TKAs have improved component alignment outcomes as compared to conventional surgery, the clinical benefit remains unclear. Less than 5% of surgeons are currently using navigation systems due to the perceived learning curve, cost, additional surgical time, and imaging required to utilize these systems. Certain navigation systems can be seemingly cumbersome, with large consoles, increased number of instruments required, and optical instruments with line-of-sight issues. Recent technological advances have worked to decrease this challenge by using accelerometer- and gyroscope-based electronic components, which combine the accuracy of computer-assisted technology with the ease of use of mechanical guides.

Accelerometer and gyroscope technology systems, such as the iAssist system, are portable devices that do not require a large computer console or navigation arrays. This technology relies on accelerator-based navigation without additional preoperative imaging. A recent study demonstrated the iAssist had reproducible accuracy in component alignment that could be easily incorporated into the operating room without optical trackers.²¹ The use of portable computer-assisted devices provides a more compact and easily accessible technology that can be used to achieve accurate component alignment without additional large equipment in the operating room.²² These new handheld intraoperative tools have been introduced to place implants according to a preoperative plan in order to minimize failure due to preoperative extra-articular deformity or intraoperative technical miscues.²³ Nam and colleagues²⁴ used an accelerometer-based surgical navigation system to perform tibial resections in cadaveric models, and found that the accelerometer-based guide was accurate for tibial resection in both the coronal and sagittal planes. In a prospective randomized controlled trial evaluating 100 patients undergoing a TKA using either an accelerometer-based guide or conventional alignment methods, the authors showed that the accelerometer-based guide decreased outliers in tibial component alignment compared to conventional guides.²⁵ In the accelerometer-based guide cohort, 95.7% of tibial components were within 2° of perpendicular to the tibial mechanical axis, compared to 68.1% in the conventional group (P < .001). These results suggested that portable accelerometer-based navigation allows surgeons to achieve satisfactory tibial component alignment with a decrease in the number of potential outliers.^24,25 Similarly, Bugbee and colleagues²⁶ found that accelerometer-based handheld navigation was accurate for tibial coronal and sagittal alignment and no additional surgical time was required compared to conventional techniques.

The relationship between knee alignment and clinical outcomes for TKA remains controversial. Regardless of the surgeon’s alignment preference, it is important to reliably and accurately execute the preoperative plan in a reproducible fashion. Advances in technology that assist with intraoperative component alignment can be useful, and may help decrease the incidence of implant malalignment in clinical practice.

Preoperative Planning and Intraoperative Technique

Preoperative planning is carried out in a manner identical to the use of conventional mechanical guides. Long leg films are taken for evaluation of overall limb alignment, and calibrated lateral images are taken for templating implant sizes. Lines are drawn on the images to determine the difference between the mechanical and anatomic axis of the femur, and a line drawn perpendicular to the mechanical axis is placed to show the expected bone cut. In similar fashion a perpendicular line to the tibial mechanical axis is also drawn to show the expected tibial resection. This preoperative plan allows the surgeon to have an additional intraoperative guide to ensure accuracy of the computer-assisted device.

After standard exposure, the distal femoral or proximal tibial cut can be made based on surgeon preference. The system being demonstrated in the accompanying photos is the KneeAlign 2 system (OrthAlign).

Distal Femoral Cut

The KneeAlign 2 femoral cutting guide is attached to the distal femur with a central pin that is placed in the middle of the distal femur measured from medial to lateral, and 1 cm anterior to the intercondylar notch. It is important to note that this spot is often more medial than traditionally used for insertion of an intramedullary rod. This central point sets the distal point of the femoral mechanical axis. The device is then held in place with 2 oblique pins, and is solidly fixed to the bone. Using a rotating motion, the femur is rotated around the hip joint. The accelerometer and gyroscope in the unit are able to determine the center of the hip joint from this motion, creating the proximal point of the mechanical axis of the femur. Once the mechanical axis of the femur is determined, varus/valgus and flexion/extension can be adjusted on the guide. One adjustment screw is available for varus/valgus, and a second is available for flexion/extension. Numbers on the device screen show real-time alignment, and are easily adjusted to set the desired alignment (Figure 1). Once alignment is obtained, a mechanical stylus is used to determine depth of resection, and the distal femoral cutting block is pinned. After pinning the block, the 3 pins in the device are removed, and the device is removed from the bone. This leaves only the distal femoral cutting block in place. In experienced hands, this part of the procedure takes less than 3 minutes.

Proximal Tibial Cut

The KneeAlign 2 proximal tibial guide is similar in appearance to a standard mechanical tibial cutting guide. It is attached to the proximal tibia with a spring around the calf and 2 pins that hold the device aligned with the medial third of the tibial tubercle. A stylus is then centered on the anterior cruciate ligament (ACL) footprint, which sets the proximal mechanical axis point of the tibia (Figure 2). An offset number is read off the stylus on the ACL footprint, and this number is matched on the ankle offset portion of the guide. The device has 2 sensors. One sensor is on the chassis of the device, and the other is on a mobile arm. Movements between the 2 are monitored by the accelerometers, allowing for accurate maintenance of alignment position even with motion in the leg. A point is taken from the lateral malleolus and then a second point is taken from the medial malleolus. These points are used to determine the center of the ankle joint, which sets the distal mechanical axis point. Once mechanical axis of the tibia is determined, the tibial cutting guide is pinned in place, and can be adjusted with real-time guidance of the varus/valgus and posterior slope values seen on the device (Figure 3). Cut depth is once again determined with a mechanical stylus.

Limitations

Although these devices have proven to be very accurate, surgeons must continue to recognize that all tools can have errors. With computerized guides of any sort, these errors are usually user errors that cannot be detected by the device. Surgeons need to be able to recognize this and always double-check bone cuts for accuracy. Templating the bone cuts prior to surgery is an effective double-check. In addition, many handheld accelerometer devices do not currently assist with the rotational alignment of the femoral component. This is still performed using the surgeon’s preferred technique, and is a limitation of these systems.

Discussion

Currently, TKA provides satisfactory 10-year results with modern implant designs and survival rates as high as 90% to 95%.^27,28 Even with good survival rates, a percentage of patients fail within the first 5 years.³ At a single institution, 50% of revision TKAs were related to instability, malalignment, or failure of fixation that occurred less than 2 years after the index procedure.²⁹ In general, TKA with mechanical instrumentation provides satisfactory pain relief and postoperative knee function; however, studies have consistently shown that the use of advanced technology decreases the risk of implant malalignment, which may decrease early implant failure rates as compared to mechanical and some PSI.^13,14,22 While there is a paucity of literature that has shown better clinical outcomes with the use of advanced technology, there are studies supporting the notion that proper limb alignment and component positioning improves implant survivorship.^23,30

CAS may have additional advantages if the surgeon chooses to place the TKA in an alignment other than a neutral mechanical axis. Kinematic alignment for TKA has gained increasing popularity, where the target of a neutral mechanical axis alignment is not always the goal.^31,32 The reported benefit is a more natural ligament tension with the hope of improving patient satisfaction. One concern with this technique is that it is a departure from the long-held teaching that a TKA aligned to a neutral mechanical axis is necessary for long-term implant survivorship.^33,34 In addition, if the goal of surgery is to cut the tibia and femur at a specific varus/valgus cut, standard instrumentation may not allow for this level of accuracy. This in turn increases the risk of having a tibial or femoral cut that is outside the commonly accepted standards of alignment, which may lead to early implant failure. If further research suggests alignment is a variable that differs from patient to patient, the use of precise tools to ensure accuracy of executing the preoperatively templated alignment becomes even more important.

As the number of TKAs continues to rise each year, even a small percentage of malaligned knees that go on to revision surgery will create a large burden on the healthcare system.^1,3 Although the short-term clinical benefits of CAS have not shown substantial differences as compared to conventional TKA, the number of knees aligned outside of a desired neutral mechanical axis alignment has been shown in multiple studies to be decreased with the use of advanced technology.^7,12,34 Although CAS is an additional cost to a primary TKA, if the orthopedic community can decrease the number of TKA revisions due to malalignment from 6.6% to nearly zero, this may decrease the revision burden and overall cost to the healthcare system.^1,3

TKA technology continues to evolve, and we must continue to assess each new advance not only to understand how it works, but also to ensure it addresses a specific clinical problem, and to be aware of the costs associated before incorporating it into routine practice. Some argue that the use of advanced technology requires increased surgical time, which in turn ultimately increases costs; however, one study has documented no increase in surgical time with handheld navigation while maintaining the accuracy of the device.³⁴ In addition, no significant radiographic or clinical differences have been found between handheld navigation and larger console CAS systems, but large console systems have been associated with increased surgical times.²² The use of handheld accelerometer- and gyroscope-based guides has proven to provide reliable coronal and sagittal implant alignment that can easily be incorporated into the operating room. More widespread use of such technology will help decrease alignment outliers for TKA, and future long-term clinical outcome studies will be necessary to assess functional outcomes.

Conclusion

Advanced computer based technology offers an additional tool to the surgeon for reliably improving component positioning during TKA. The use of handheld accelerometer- and gyroscope-based guides increases the accuracy of component placement while decreasing the incidence of outliers compared to standard mechanical guides, without the need for a large computer console. Long-term radiographic and patient-reported outcomes are necessary to further validate these devices.

Total knee arthroplasty (TKA) continues to be a widely utilized treatment option for end-stage knee osteoarthritis, and the number of patients undergoing TKA is projected to continually increase over the next decade.¹ Although TKA is highly successful for many patients, studies continue to report that approximately 20% of patients are dissatisfied after undergoing TKA, and nearly 25% of knee revisions are performed for instability or malalignment.^2,3 Technological advances have been developed to help improve clinical outcomes and implant survivorship. Over the past decade, computer navigation and intraoperative guides have been introduced to help control surgical variables and overcome the limitations and inaccuracies of traditional mechanical instrumentation. Currently, there are a variety of technologies available to assist surgeons with component alignment, including extramedullary devices, computer-assisted navigation systems (CAS), and patient-specific instrumentation (PSI) that help achieve desired alignment goals.^4,5

Computer-assisted navigation tools were introduced in an effort to improve implant alignment and clinical outcomes compared to traditional mechanical guides. Some argue that the use of computer-assisted surgery has a steep learning curve and successful use is dependent on the user’s experience; however, studies have suggested computer-assisted surgery may allow less experienced surgeons to reliably achieve anticipated intraoperative alignment goals with a low complication rate.^6,7 Various studies have looked at computer-assisted TKA at short to mid-term follow-up, but few studies have reported long-term outcomes.^6-9 de Steiger and colleagues¹⁰ recently found that computer-assisted TKA reduced the overall revision rate for aseptic loosening following TKA in patients younger than age 65 years, which suggests benefit of CAS for younger patients. Short-term follow-up has also shown the benefit of CAS TKA in patients with severe extra-articular deformity, where traditional instrumentation cannot be utilized.¹¹ Currently, there is no consensus that computer-assisted TKA leads to improved postoperative patient reported outcomes, because many studies are limited by study design or small cohorts; however, current literature does show an improvement in component alignment as compared to mechanical instrumentation.^9,12,13 As future implant and position targets are defined to improve implant survivorship and clinical outcomes in total joint arthroplasty, computer-assisted devices will be useful to help achieve more precise and accurate component positioning.

In addition to CAS devices, some companies have sought to improve TKA surgery by introducing PSI. PSI was introduced to improve component alignment in TKA, with the purported advantages of a shorter surgical time, decrease in the number of instruments needed, and improved clinical outcomes. PSI accuracy remains variable, which may be attributed to the various systems and implant designs in each study.^14-17 In addition, advanced preoperative imaging is necessary, which further adds to the overall cost.¹⁷ While the recent advancement in technology may provide decreased costs at the time of surgery, the increased cost and time incurred by the patient preoperatively has not resulted in significantly better clinical outcomes.^18,19 Additionally, recent work has not shown PSI to have superior accuracy as compared to currently available CAS devices.¹⁴ These findings suggest that the additional cost and time incurred by patients may limit the widespread use of PSI.

Although computer navigation has been shown to be more accurate than conventional instrumentation and PSI, the lack of improvement in long-term clinical outcome data has limited its use. In a meta-analysis, Bauwens and colleagues²⁰ suggested that while navigated TKAs have improved component alignment outcomes as compared to conventional surgery, the clinical benefit remains unclear. Less than 5% of surgeons are currently using navigation systems due to the perceived learning curve, cost, additional surgical time, and imaging required to utilize these systems. Certain navigation systems can be seemingly cumbersome, with large consoles, increased number of instruments required, and optical instruments with line-of-sight issues. Recent technological advances have worked to decrease this challenge by using accelerometer- and gyroscope-based electronic components, which combine the accuracy of computer-assisted technology with the ease of use of mechanical guides.

Accelerometer and gyroscope technology systems, such as the iAssist system, are portable devices that do not require a large computer console or navigation arrays. This technology relies on accelerator-based navigation without additional preoperative imaging. A recent study demonstrated the iAssist had reproducible accuracy in component alignment that could be easily incorporated into the operating room without optical trackers.²¹ The use of portable computer-assisted devices provides a more compact and easily accessible technology that can be used to achieve accurate component alignment without additional large equipment in the operating room.²² These new handheld intraoperative tools have been introduced to place implants according to a preoperative plan in order to minimize failure due to preoperative extra-articular deformity or intraoperative technical miscues.²³ Nam and colleagues²⁴ used an accelerometer-based surgical navigation system to perform tibial resections in cadaveric models, and found that the accelerometer-based guide was accurate for tibial resection in both the coronal and sagittal planes. In a prospective randomized controlled trial evaluating 100 patients undergoing a TKA using either an accelerometer-based guide or conventional alignment methods, the authors showed that the accelerometer-based guide decreased outliers in tibial component alignment compared to conventional guides.²⁵ In the accelerometer-based guide cohort, 95.7% of tibial components were within 2° of perpendicular to the tibial mechanical axis, compared to 68.1% in the conventional group (P < .001). These results suggested that portable accelerometer-based navigation allows surgeons to achieve satisfactory tibial component alignment with a decrease in the number of potential outliers.^24,25 Similarly, Bugbee and colleagues²⁶ found that accelerometer-based handheld navigation was accurate for tibial coronal and sagittal alignment and no additional surgical time was required compared to conventional techniques.

The relationship between knee alignment and clinical outcomes for TKA remains controversial. Regardless of the surgeon’s alignment preference, it is important to reliably and accurately execute the preoperative plan in a reproducible fashion. Advances in technology that assist with intraoperative component alignment can be useful, and may help decrease the incidence of implant malalignment in clinical practice.

Preoperative Planning and Intraoperative Technique

Preoperative planning is carried out in a manner identical to the use of conventional mechanical guides. Long leg films are taken for evaluation of overall limb alignment, and calibrated lateral images are taken for templating implant sizes. Lines are drawn on the images to determine the difference between the mechanical and anatomic axis of the femur, and a line drawn perpendicular to the mechanical axis is placed to show the expected bone cut. In similar fashion a perpendicular line to the tibial mechanical axis is also drawn to show the expected tibial resection. This preoperative plan allows the surgeon to have an additional intraoperative guide to ensure accuracy of the computer-assisted device.

After standard exposure, the distal femoral or proximal tibial cut can be made based on surgeon preference. The system being demonstrated in the accompanying photos is the KneeAlign 2 system (OrthAlign).

Distal Femoral Cut

The KneeAlign 2 femoral cutting guide is attached to the distal femur with a central pin that is placed in the middle of the distal femur measured from medial to lateral, and 1 cm anterior to the intercondylar notch. It is important to note that this spot is often more medial than traditionally used for insertion of an intramedullary rod. This central point sets the distal point of the femoral mechanical axis. The device is then held in place with 2 oblique pins, and is solidly fixed to the bone. Using a rotating motion, the femur is rotated around the hip joint. The accelerometer and gyroscope in the unit are able to determine the center of the hip joint from this motion, creating the proximal point of the mechanical axis of the femur. Once the mechanical axis of the femur is determined, varus/valgus and flexion/extension can be adjusted on the guide. One adjustment screw is available for varus/valgus, and a second is available for flexion/extension. Numbers on the device screen show real-time alignment, and are easily adjusted to set the desired alignment (Figure 1). Once alignment is obtained, a mechanical stylus is used to determine depth of resection, and the distal femoral cutting block is pinned. After pinning the block, the 3 pins in the device are removed, and the device is removed from the bone. This leaves only the distal femoral cutting block in place. In experienced hands, this part of the procedure takes less than 3 minutes.

Proximal Tibial Cut

The KneeAlign 2 proximal tibial guide is similar in appearance to a standard mechanical tibial cutting guide. It is attached to the proximal tibia with a spring around the calf and 2 pins that hold the device aligned with the medial third of the tibial tubercle. A stylus is then centered on the anterior cruciate ligament (ACL) footprint, which sets the proximal mechanical axis point of the tibia (Figure 2). An offset number is read off the stylus on the ACL footprint, and this number is matched on the ankle offset portion of the guide. The device has 2 sensors. One sensor is on the chassis of the device, and the other is on a mobile arm. Movements between the 2 are monitored by the accelerometers, allowing for accurate maintenance of alignment position even with motion in the leg. A point is taken from the lateral malleolus and then a second point is taken from the medial malleolus. These points are used to determine the center of the ankle joint, which sets the distal mechanical axis point. Once mechanical axis of the tibia is determined, the tibial cutting guide is pinned in place, and can be adjusted with real-time guidance of the varus/valgus and posterior slope values seen on the device (Figure 3). Cut depth is once again determined with a mechanical stylus.

Limitations

Although these devices have proven to be very accurate, surgeons must continue to recognize that all tools can have errors. With computerized guides of any sort, these errors are usually user errors that cannot be detected by the device. Surgeons need to be able to recognize this and always double-check bone cuts for accuracy. Templating the bone cuts prior to surgery is an effective double-check. In addition, many handheld accelerometer devices do not currently assist with the rotational alignment of the femoral component. This is still performed using the surgeon’s preferred technique, and is a limitation of these systems.

Discussion

Currently, TKA provides satisfactory 10-year results with modern implant designs and survival rates as high as 90% to 95%.^27,28 Even with good survival rates, a percentage of patients fail within the first 5 years.³ At a single institution, 50% of revision TKAs were related to instability, malalignment, or failure of fixation that occurred less than 2 years after the index procedure.²⁹ In general, TKA with mechanical instrumentation provides satisfactory pain relief and postoperative knee function; however, studies have consistently shown that the use of advanced technology decreases the risk of implant malalignment, which may decrease early implant failure rates as compared to mechanical and some PSI.^13,14,22 While there is a paucity of literature that has shown better clinical outcomes with the use of advanced technology, there are studies supporting the notion that proper limb alignment and component positioning improves implant survivorship.^23,30

CAS may have additional advantages if the surgeon chooses to place the TKA in an alignment other than a neutral mechanical axis. Kinematic alignment for TKA has gained increasing popularity, where the target of a neutral mechanical axis alignment is not always the goal.^31,32 The reported benefit is a more natural ligament tension with the hope of improving patient satisfaction. One concern with this technique is that it is a departure from the long-held teaching that a TKA aligned to a neutral mechanical axis is necessary for long-term implant survivorship.^33,34 In addition, if the goal of surgery is to cut the tibia and femur at a specific varus/valgus cut, standard instrumentation may not allow for this level of accuracy. This in turn increases the risk of having a tibial or femoral cut that is outside the commonly accepted standards of alignment, which may lead to early implant failure. If further research suggests alignment is a variable that differs from patient to patient, the use of precise tools to ensure accuracy of executing the preoperatively templated alignment becomes even more important.

As the number of TKAs continues to rise each year, even a small percentage of malaligned knees that go on to revision surgery will create a large burden on the healthcare system.^1,3 Although the short-term clinical benefits of CAS have not shown substantial differences as compared to conventional TKA, the number of knees aligned outside of a desired neutral mechanical axis alignment has been shown in multiple studies to be decreased with the use of advanced technology.^7,12,34 Although CAS is an additional cost to a primary TKA, if the orthopedic community can decrease the number of TKA revisions due to malalignment from 6.6% to nearly zero, this may decrease the revision burden and overall cost to the healthcare system.^1,3

TKA technology continues to evolve, and we must continue to assess each new advance not only to understand how it works, but also to ensure it addresses a specific clinical problem, and to be aware of the costs associated before incorporating it into routine practice. Some argue that the use of advanced technology requires increased surgical time, which in turn ultimately increases costs; however, one study has documented no increase in surgical time with handheld navigation while maintaining the accuracy of the device.³⁴ In addition, no significant radiographic or clinical differences have been found between handheld navigation and larger console CAS systems, but large console systems have been associated with increased surgical times.²² The use of handheld accelerometer- and gyroscope-based guides has proven to provide reliable coronal and sagittal implant alignment that can easily be incorporated into the operating room. More widespread use of such technology will help decrease alignment outliers for TKA, and future long-term clinical outcome studies will be necessary to assess functional outcomes.

Conclusion

Advanced computer based technology offers an additional tool to the surgeon for reliably improving component positioning during TKA. The use of handheld accelerometer- and gyroscope-based guides increases the accuracy of component placement while decreasing the incidence of outliers compared to standard mechanical guides, without the need for a large computer console. Long-term radiographic and patient-reported outcomes are necessary to further validate these devices.

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are 2 reliable treatment options for patients with primary osteoarthritis. Recently published systematic reviews of cohort studies have shown that 10-year survivorship of medial and lateral UKA is 92% and 91%, respectively,¹ while 10-year survivorship of TKA in cohort studies is 95%.² National and annual registries show a similar trend, although the reported survivorship is lower.^1,3-7

In order to improve these survivorship rates, the surgical variables that can intraoperatively be controlled by the orthopedic surgeon have been evaluated. These variables include lower leg alignment, soft tissue balance, joint line maintenance, and alignment, size, and fixation of the tibial and femoral component. Several studies have shown that tight control of lower leg alignment,^8-14 balancing of the soft tissues,^15-19 joint line maintenance,^20-23 component alignment,^24-28 component size,^29-34 and component fixation^35-40 can improve the outcomes of UKA and TKA. As a result, over the past 2 decades, several computer-assisted surgery systems have been developed with the goal of more accurate and reliable control of these factors, and thus improved outcomes of knee arthroplasty.

These systems differ with regard to the number and type of variables they control. Computer navigation systems aim to control one or more of these surgical variables, and several meta-analyses have shown that these systems, when compared to conventional surgery, improve mechanical axis accuracy, decrease the risk for mechanical axis outliers, and improve component positioning in TKA^41-49 and UKA surgery.^50,51 Interestingly, however, meta-analyses have failed to show the expected superiority in clinical outcomes following computer navigation compared to conventional knee arthroplasty.^48,52-55 Furthermore, authors have shown that, despite the fact that computer-navigated surgery increases the accuracy of mechanical alignment and surgical cutting, there is still room for improvement.⁵⁶ As a consequence, robotic-assisted systems have been developed.

Similar to computer navigation, these robotic-assisted systems aim to control the surgical variables; in addition, they aim to improve the surgical precision of the procedure. Interestingly, 2 recent studies have shown that robotic-assisted systems are superior to computer navigation systems with regard to less cutting time and less resection deviations in coronal and sagittal plane in a cadaveric study,⁵⁷ and shorter total surgery time, more accurate mechanical axis, and shorter hospital stay in a clinical study.⁵⁸ Although these results are promising, the exact role of robotic surgery in knee arthroplasty remains unclear. In this review, we aim to report the current state of robotic-assisted knee arthroplasty by discussing (1) the different robotic-assisted knee arthroplasty systems that are available for UKA and TKA surgery, (2) studies that assessed the role of robotic-assisted knee arthroplasty in controlling the aforementioned surgical variables, (3) cadaveric and clinical comparative studies that compared how accurate robotic-assisted and conventional knee surgery control these surgical variables, and (4) studies that assessed the cost-effectiveness of robotic-assisted knee arthroplasty surgery.

Robotic-Assisted Knee Arthroplasty Systems

Several systems have been developed over the years for knee arthroplasty, and these are usually defined as active, semi-active, or passive.⁵⁹ Active systems are capable of performing tasks or processes autonomously under the watchful eye of the surgeon, while passive systems do not perform actions independently but provide the surgeon with information. In semi-active systems, the surgical action is physically constrained in order to follow a predefined strategy.

In the United States, 3 robotic systems are FDA-approved for knee arthroplasty. The Stryker/Mako haptic guided robot (Mako Surgical Corp.) was introduced in 2005 and has been used for over 50,000 UKA procedures (Figure 1). There are nearly 300 robotic systems used nationally, as it has 20% of the market share for UKA in the United States. The Mako system is a semi-active tactile robotic system that requires preoperative imaging, after which a preoperative planning is performed. Intraoperatively, the robotic arm is under direct surgeon control and gives real-time tactile feedback during the procedure (Figure 2).

Furthermore, the surgeon can intraoperatively virtually adjust component positioning and alignment and move the knee through the range of motion, after which the system can provide information on alignment, component position, and balance of the soft tissue (eg, if the knee is overtight or lax through the flexion-arch).⁶⁰ This system has a burr that resects the bone and when the surgeon directs the burr outside the preplanned area, the burr stops and prevents unnecessary and unwanted resections (Figure 3).

The Navio Precision Free-Hand Sculptor (PFS) system (Blue Belt Technologies) has been used for 1500 UKA procedures, with 50 robots in use in the United States (Figure 4). This system is an image-free semi-active robotic system and has the same characteristics as the aforementioned Mako system.⁶¹ Finally, the OmniBotic robotic system (Omnilife Science) has been released for TKA and has been used for over 7300 procedures (Figure 5). This system has an automated cutting-guide technique in which the surgeon designs a virtual plan on the computer system. After this, the cutting-guides are placed by the robotic system at the planned location for all 5 femoral cuts (ie, distal, anterior chamfer, anterior, posterior chamfer, and posterior) and the surgeon then makes the final cuts.^57,62

Three robotic systems for knee arthroplasty surgery have been used in Europe. The Caspar system (URS Ortho) is an active robotic system in which a computed tomography (CT) scan is performed preoperatively, after which a virtual implantation is performed on the screen. The surgeon can then obtain information on lower leg alignment, gap balancing, and component positioning, and after an operative plan is made, the surgical resections are performed by the robot. Reflective markers are attached to the leg and all robotic movements are monitored using an infrared camera system. Any undesired motion will be detected by this camera system and will stop all movements.⁶³ A second and more frequently reported system in the literature is the active Robodoc surgical system (Curexo Technology Corporation). This system is designed for TKA and total hip arthroplasty (THA) surgery. Although initial studies reported a high incidence of system-related complications in THA,⁶⁴ the use of this system for TKA has frequently been reported in the literature.^56,63,65-69 A third robotic system that has been used in Europe is the Acrobot surgical system (Acrobot Company Ltd), which is an image-based semi-active robotic system⁷⁰ used for both UKA and TKA surgery.^70,71

Accuracy of Controlling Surgical Variables in Robotic-Assisted Knee Arthroplasty

Several studies have assessed the accuracy of robotic-assisted surgery in UKA surgery with regard to control of the aforementioned surgical variables. Pearle and colleagues⁷² assessed the mechanical axis accuracy of the Mako system in 10 patients undergoing medial UKA robotic-assisted surgery. They reported that the intraoperative registration lasted 7.5 minutes and the duration of time needed for robotic-assisted burring was 34.8 minutes. They compared the actual postoperative alignment at 6 weeks follow-up with the planned lower leg alignment and found that all measurements were within 1.6° of the planned lower leg alignment. Dunbar and colleagues⁷³ assessed the accuracy of component positioning of the Mako system in 20 patients undergoing medial UKA surgery by comparing preoperative and postoperative 3-dimensional CT scans. They found that the femoral component was within 0.8 mm and 0.9° in all directions and that the tibial component was within 0.9 mm and 1.7° in all directions. They concluded that the accuracy of component positioning with the Mako system was excellent. Finally, Plate and colleagues¹⁷ assessed the accuracy of soft tissue balancing in the Mako system in 52 patients undergoing medial UKA surgery. They compared the balance plan with the soft tissue balance after implantation and the Mako system quantified soft tissue balance as the amount of mm of the knee being tight or loose at 0°, 30°, 60°, 90°, and 110° of flexion. They found that at all flexion angles the ligament balancing was accurate up to 0.53 mm of the original plan. Furthermore, they noted that in 83% of cases the accuracy was within 1 mm at all flexion angles.

For the Navio system, Smith and colleagues⁷⁴ assessed the accuracy of component positioning using 20 synthetic femurs and tibia. They reported a maximum rotational error of 3.2°, an angular error of 1.46° in all orientations, and a maximum translational error of 1.18 mm for both the tibial and femoral implants. Lonner and colleagues⁷⁵ assessed the accuracy of component positioning in 25 cadaveric specimens. They found similar results as were found in the study of Smith and colleagues⁷⁴ and concluded that these results were similar to other semi-active robotic systems designed for UKA.

For TKA surgery, Ponder and colleagues⁷⁶ assessed the accuracy of the OmniBotic system and found that the average error in the anterior-posterior dimension between the targeted and measured cuts was -0.14 mm, and that the standard deviation in guide positioning for the distal, anterior chamfer, and posterior chamfer resections was 0.03° and 0.17 mm. Koenig and colleagues⁶² assessed the accuracy of the OmniBotic system in the first 100 cases and found that 98% of the cases were within 3° of the neutral mechanical axis. Furthermore, they found a learning curve with regard to tourniquet time between the first and second 10 patients in which they performed robotic-assisted TKA surgery. Siebert and colleagues⁶³ assessed the accuracy of mechanical alignment in the Caspar system in 70 patients treated with the robotic system. They found that the difference between preoperatively planned and postoperatively achieved mechanical alignment was 0.8°. Similarly, Bellemans and colleagues⁷⁷ assessed mechanical alignment and the positioning and rotation of the tibial and femoral components in a clinical study of 25 cases using the Caspar system. They noted that none of the patients had mechanical alignment, tibial or femoral component positioning, or rotation beyond 1° of the neutral axis. Liow and colleagues⁵⁶ assessed the accuracy of mechanical axis alignment and component sizing accuracy using the Robodoc system in 25 patients. They reported that the mean postoperative alignment was 0.4° valgus and that all cases were within 3° of the neutral mechanical axis. Furthermore, they reported a mean surgical time of 96 minutes and reported that preoperative planning yielded femoral and tibial component size accuracy of 100%.

These studies have shown that robotic systems for UKA and TKA are accurate in the surgical variables they aim to control. These studies validated tight control of mechanical axis alignment, decrease for outliers, and component positioning and rotation, and also found that the balancing of soft tissues was improved using robotic-assisted surgery.

Robotic-Assisted vs Conventional Knee Arthroplasty

Despite the fact that these systems are accurate in the variables they aim to control, these systems have to be compared to the gold standard of conventional knee arthroplasty. For UKA, Cobb and colleagues⁷⁰ performed a randomized clinical trial for patients treated undergoing UKA with robotic-assistance of the Acrobot systems compared to conventional UKA and assessed differences in mechanical accuracy. A total of 27 patients were randomly assigned to one of both treatments. They found that in the group of robotic-assisted surgery, 100% of the patients had a mechanical axis within 2° of neutral, while this was only 40% in the conventional UKA groups (difference P < .001). They also assessed the increase in functional outcomes and noted a trend towards improvement in performance with increasing accuracy at 6 weeks and 3 months postoperatively. Lonner and colleagues⁷⁸ also compared the tibial component positioning between robotic-assisted UKA surgery using the Mako system and conventional UKA surgery. The authors found that the variance in tibial slope, in coronal plane of the tibial component, and varus/valgus alignment were all larger with conventional UKA when compared to robotic-assisted UKA. Citak and colleagues⁷⁹ compared the accuracy of tibial and femoral implant positioning between robotic-assisted surgery using the Mako system and conventional UKA in a cadaveric study. They reported that the root mean square (RMS) error of femoral component was 1.9 mm and 3.7° in robotic-assisted surgery and 5.4 mm and 10.2° for conventional UKA, while the RMS error for tibial component were 1.4 mm and 5.0° for robotic-assisted surgery and 5.7 mm and 19.2° for conventional UKA surgery. MacCallum and colleagues⁸⁰ compared the tibial base plate position in a prospective clinical study of 177 patients treated with conventional UKA and 87 patients treated with robotic-assisted surgery using the Mako system. They found that surgery with robotic-assistance was more precise in the coronal and sagittal plane and was more accurate in coronal alignment when compared to conventional UKA. Finally, the first results of robotic-assisted UKA surgery have been presented. Coon and colleagues⁸¹ reported the preliminary results of a multicenter study of 854 patients and found a survivorship of 98.9% and satisfaction rate of 92% at minimum 2-year follow-up. Comparing these results to other large conventional UKA cohorts^82,83 suggests that robotic-assisted surgery may improve survivorship at short-term follow-up. However, comparative studies and studies with longer follow-up are necessary to assess the additional value of robotic-assisted UKA surgery. Due to the relatively new concept of robotic-assisted surgery, these studies have not been performed or published yet.

For TKA, several studies also have compared how these robotic-systems control the surgical variables compared to conventional TKA surgery. Siebert and colleagues⁶³ assessed mechanical axis accuracy and mechanical outliers following robotic-assisted TKA surgery using the Caspar system and conventional TKA surgery. They reported the difference between preoperative planned and postoperative achieved alignment was 0.8° for robotic-assisted surgery and 2.6° for conventional TKA surgery. Furthermore, they showed that 1 patient in the robotic-assisted group (1.4%) and 18 patients in the conventional TKA group (35%) had mechanical alignment greater than 3° from the neutral mechanical axis. Liow and colleagues⁵⁶ found similar differences in their prospective randomized study in which they reported that 0% outliers greater than 3° from the neutral mechanical axis were found in the robotic-assisted group while 19.4% of the patients in the conventional TKA group had mechanical axis outliers. They also assessed the joint-line outliers in both procedures and found that 3.2% had joint-line outliers greater than 5 mm in the robotic-assisted group compared to 20.6% in the conventional TKA group. Kim and colleagues⁶⁵ assessed implant accuracy in robotic-assisted surgery using the ROBODOC system and in conventional surgery and reported higher implant accuracy and fewer outliers using robotic-assisted surgery. Moon and colleagues⁶⁶ compared robotic-assisted TKA surgery using the Robodoc system with conventional TKA surgery in 10 cadavers. They found that robotic-assisted surgery had excellent precision in all planes and had better accuracy in femoral rotation alignment compared to conventional TKA surgery. Park and Lee⁶⁷ compared Robodoc robotic-assisted TKA surgery with conventional TKA surgery in a randomized clinical trial of 72 patients. They found that robotic-assisted surgery had definitive advantages in preoperative planning, accuracy of the procedure, and postoperative follow-up regarding femoral and tibial component flexion angles. Finally, Song and colleagues^68,69 performed 2 randomized clinical trials in which they compared mechanical axis alignment, component positioning, soft tissue balancing, and patient preference between conventional TKA surgery and robotic-assisted surgery using the Robodoc system. In the first study,⁶⁸ they simultaneously performed robotic-assisted surgery in one leg and conventional TKA surgery in the other leg. They found that robotic-assisted surgery resulted in less outlier in mechanical axis and component positioning. Furthermore, they found at latest follow-up of 2 years that 12 patients preferred the leg treated with robotic-assisted surgery while 6 preferred the conventional leg. Despite this finding, no significant differences in functional outcome scores were detected between both treatment options. Furthermore, they found that flexion-extension balance was achieved in 92% of patients treated with robotic-assisted TKA surgery and in 77% of patients treated with conventional TKA surgery. In the other study,⁶⁹ the authors found that more patients treated with robotic-assisted surgery had <2 mm flexion-extension gap and more satisfactory posterior cruciate ligament tension when compared to conventional surgery.

These studies have shown that robotic-assisted surgery is accurate in controlling surgical variables, such as mechanical lower leg alignment, maintaining joint-line, implant positioning, and soft tissue balancing. Furthermore, these studies have shown that controlling these variables is better than the current gold standard of manual knee arthroplasty. Until now, not many studies have assessed survivorship of robotic-assisted surgery. Furthermore, no studies have, to our knowledge, compared survivorship of robotic-assisted with conventional knee replacement surgery. Finally, studies comparing functional outcomes following robotic-assisted surgery and conventional knee arthroplasty surgery are frequently underpowered due to their small sample sizes.^68,70 Since many studies have shown that the surgical variables are more tightly controlled using robotic-assisted surgery when compared to conventional surgery, large comparative studies are necessary to assess the role of robotic-assisted surgery in functional outcomes and survivorship of UKA and TKA.

Cost-Effectiveness of Robotic-Assisted Surgery

High initial capital costs of robotic-assisted surgery is one of the factors that constitute a barrier to the widespread implementation of this technique. Multiple authors have suggested that improved implant survivorship afforded by robotic-assisted surgery may justify the expenditure from both societal and provider perspective.^84-86 Two studies have performed a cost-effectiveness analysis for UKA surgery. Swank and colleagues⁸⁴ reviewed the hospital expenditures and profits associated with robot-assisted knee arthroplasty, citing upfront costs of approximately $800,000. The authors estimated a mean per-case contribution profit of $5790 for robotic-assisted UKA, assuming an inpatient-to-outpatient ratio of 1 to 3. Based on this data, Swank and colleagues84 proposed that the capital costs of robotic-assisted UKA may be recovered in as little as 2 years when in the first 3 consecutive years 50, 70, and 90 cases were performed using robotic-assisted UKA. Moschetti and colleagues⁸⁵ recently published the first formal cost-effectiveness analysis of robotic-assisted compared to manual UKA. The authors used an annual revision risk of 0.55% for the first 2 years following robot-assisted UKA, based on the aforementioned presented data by Coon and colleagues.⁸¹ They based their data on the Mako system and assumed an initial capital expenditure of $934,728 with annual servicing costs of 10% (discounted annually) for 4 years thereafter, resulting in a total cost of the robotic system of $1.362 million. These costs were divided by the number of patients estimated to undergo robotic-assisted UKA per year, which was varied to estimate the effect of case volume on cost-effectiveness. The authors reported that robotic-assisted UKA was associated with higher lifetime costs and net utilities compared to manual UKA, at an incremental cost-effectiveness ratio of $47,180 per quality-adjusted life year (QALY) in a high-volume center. This falls well within the societal willingness-to-pay threshold of $100,000/QALY. Sensitivity analysis showed that robotic-assisted UKA is cost-effective under the following conditions: (1) centers performing at least 94 cases annually, (2) in patients younger than age 67 years, and (3) 2-year revision rate does not exceed 1.2%. While the results of this initial analysis are promising, follow-up cost-effectiveness analysis studies will be required as long-term survivorship data become available.

Conclusion

Tighter control of intraoperative surgical variables, such as lower leg alignment, soft tissue balance, joint-line maintenance, and component alignment and positioning, have been associated with improved survivorship and functional outcomes. Upon reviewing the available literature on robotic-assisted surgery, it becomes clear that this technique can improve the accuracy of these surgical variables and is superior to conventional manual UKA and TKA. Although larger and comparative survivorship studies are necessary to compare robotic-assisted knee arthroplasty to conventional techniques, the early results and cost-effectiveness analysis seem promising.

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are 2 reliable treatment options for patients with primary osteoarthritis. Recently published systematic reviews of cohort studies have shown that 10-year survivorship of medial and lateral UKA is 92% and 91%, respectively,¹ while 10-year survivorship of TKA in cohort studies is 95%.² National and annual registries show a similar trend, although the reported survivorship is lower.^1,3-7

In order to improve these survivorship rates, the surgical variables that can intraoperatively be controlled by the orthopedic surgeon have been evaluated. These variables include lower leg alignment, soft tissue balance, joint line maintenance, and alignment, size, and fixation of the tibial and femoral component. Several studies have shown that tight control of lower leg alignment,^8-14 balancing of the soft tissues,^15-19 joint line maintenance,^20-23 component alignment,^24-28 component size,^29-34 and component fixation^35-40 can improve the outcomes of UKA and TKA. As a result, over the past 2 decades, several computer-assisted surgery systems have been developed with the goal of more accurate and reliable control of these factors, and thus improved outcomes of knee arthroplasty.

These systems differ with regard to the number and type of variables they control. Computer navigation systems aim to control one or more of these surgical variables, and several meta-analyses have shown that these systems, when compared to conventional surgery, improve mechanical axis accuracy, decrease the risk for mechanical axis outliers, and improve component positioning in TKA^41-49 and UKA surgery.^50,51 Interestingly, however, meta-analyses have failed to show the expected superiority in clinical outcomes following computer navigation compared to conventional knee arthroplasty.^48,52-55 Furthermore, authors have shown that, despite the fact that computer-navigated surgery increases the accuracy of mechanical alignment and surgical cutting, there is still room for improvement.⁵⁶ As a consequence, robotic-assisted systems have been developed.

Similar to computer navigation, these robotic-assisted systems aim to control the surgical variables; in addition, they aim to improve the surgical precision of the procedure. Interestingly, 2 recent studies have shown that robotic-assisted systems are superior to computer navigation systems with regard to less cutting time and less resection deviations in coronal and sagittal plane in a cadaveric study,⁵⁷ and shorter total surgery time, more accurate mechanical axis, and shorter hospital stay in a clinical study.⁵⁸ Although these results are promising, the exact role of robotic surgery in knee arthroplasty remains unclear. In this review, we aim to report the current state of robotic-assisted knee arthroplasty by discussing (1) the different robotic-assisted knee arthroplasty systems that are available for UKA and TKA surgery, (2) studies that assessed the role of robotic-assisted knee arthroplasty in controlling the aforementioned surgical variables, (3) cadaveric and clinical comparative studies that compared how accurate robotic-assisted and conventional knee surgery control these surgical variables, and (4) studies that assessed the cost-effectiveness of robotic-assisted knee arthroplasty surgery.

Robotic-Assisted Knee Arthroplasty Systems

Several systems have been developed over the years for knee arthroplasty, and these are usually defined as active, semi-active, or passive.⁵⁹ Active systems are capable of performing tasks or processes autonomously under the watchful eye of the surgeon, while passive systems do not perform actions independently but provide the surgeon with information. In semi-active systems, the surgical action is physically constrained in order to follow a predefined strategy.

In the United States, 3 robotic systems are FDA-approved for knee arthroplasty. The Stryker/Mako haptic guided robot (Mako Surgical Corp.) was introduced in 2005 and has been used for over 50,000 UKA procedures (Figure 1). There are nearly 300 robotic systems used nationally, as it has 20% of the market share for UKA in the United States. The Mako system is a semi-active tactile robotic system that requires preoperative imaging, after which a preoperative planning is performed. Intraoperatively, the robotic arm is under direct surgeon control and gives real-time tactile feedback during the procedure (Figure 2).

Furthermore, the surgeon can intraoperatively virtually adjust component positioning and alignment and move the knee through the range of motion, after which the system can provide information on alignment, component position, and balance of the soft tissue (eg, if the knee is overtight or lax through the flexion-arch).⁶⁰ This system has a burr that resects the bone and when the surgeon directs the burr outside the preplanned area, the burr stops and prevents unnecessary and unwanted resections (Figure 3).

The Navio Precision Free-Hand Sculptor (PFS) system (Blue Belt Technologies) has been used for 1500 UKA procedures, with 50 robots in use in the United States (Figure 4). This system is an image-free semi-active robotic system and has the same characteristics as the aforementioned Mako system.⁶¹ Finally, the OmniBotic robotic system (Omnilife Science) has been released for TKA and has been used for over 7300 procedures (Figure 5). This system has an automated cutting-guide technique in which the surgeon designs a virtual plan on the computer system. After this, the cutting-guides are placed by the robotic system at the planned location for all 5 femoral cuts (ie, distal, anterior chamfer, anterior, posterior chamfer, and posterior) and the surgeon then makes the final cuts.^57,62

Three robotic systems for knee arthroplasty surgery have been used in Europe. The Caspar system (URS Ortho) is an active robotic system in which a computed tomography (CT) scan is performed preoperatively, after which a virtual implantation is performed on the screen. The surgeon can then obtain information on lower leg alignment, gap balancing, and component positioning, and after an operative plan is made, the surgical resections are performed by the robot. Reflective markers are attached to the leg and all robotic movements are monitored using an infrared camera system. Any undesired motion will be detected by this camera system and will stop all movements.⁶³ A second and more frequently reported system in the literature is the active Robodoc surgical system (Curexo Technology Corporation). This system is designed for TKA and total hip arthroplasty (THA) surgery. Although initial studies reported a high incidence of system-related complications in THA,⁶⁴ the use of this system for TKA has frequently been reported in the literature.^56,63,65-69 A third robotic system that has been used in Europe is the Acrobot surgical system (Acrobot Company Ltd), which is an image-based semi-active robotic system⁷⁰ used for both UKA and TKA surgery.^70,71

Accuracy of Controlling Surgical Variables in Robotic-Assisted Knee Arthroplasty

Several studies have assessed the accuracy of robotic-assisted surgery in UKA surgery with regard to control of the aforementioned surgical variables. Pearle and colleagues⁷² assessed the mechanical axis accuracy of the Mako system in 10 patients undergoing medial UKA robotic-assisted surgery. They reported that the intraoperative registration lasted 7.5 minutes and the duration of time needed for robotic-assisted burring was 34.8 minutes. They compared the actual postoperative alignment at 6 weeks follow-up with the planned lower leg alignment and found that all measurements were within 1.6° of the planned lower leg alignment. Dunbar and colleagues⁷³ assessed the accuracy of component positioning of the Mako system in 20 patients undergoing medial UKA surgery by comparing preoperative and postoperative 3-dimensional CT scans. They found that the femoral component was within 0.8 mm and 0.9° in all directions and that the tibial component was within 0.9 mm and 1.7° in all directions. They concluded that the accuracy of component positioning with the Mako system was excellent. Finally, Plate and colleagues¹⁷ assessed the accuracy of soft tissue balancing in the Mako system in 52 patients undergoing medial UKA surgery. They compared the balance plan with the soft tissue balance after implantation and the Mako system quantified soft tissue balance as the amount of mm of the knee being tight or loose at 0°, 30°, 60°, 90°, and 110° of flexion. They found that at all flexion angles the ligament balancing was accurate up to 0.53 mm of the original plan. Furthermore, they noted that in 83% of cases the accuracy was within 1 mm at all flexion angles.

For the Navio system, Smith and colleagues⁷⁴ assessed the accuracy of component positioning using 20 synthetic femurs and tibia. They reported a maximum rotational error of 3.2°, an angular error of 1.46° in all orientations, and a maximum translational error of 1.18 mm for both the tibial and femoral implants. Lonner and colleagues⁷⁵ assessed the accuracy of component positioning in 25 cadaveric specimens. They found similar results as were found in the study of Smith and colleagues⁷⁴ and concluded that these results were similar to other semi-active robotic systems designed for UKA.

For TKA surgery, Ponder and colleagues⁷⁶ assessed the accuracy of the OmniBotic system and found that the average error in the anterior-posterior dimension between the targeted and measured cuts was -0.14 mm, and that the standard deviation in guide positioning for the distal, anterior chamfer, and posterior chamfer resections was 0.03° and 0.17 mm. Koenig and colleagues⁶² assessed the accuracy of the OmniBotic system in the first 100 cases and found that 98% of the cases were within 3° of the neutral mechanical axis. Furthermore, they found a learning curve with regard to tourniquet time between the first and second 10 patients in which they performed robotic-assisted TKA surgery. Siebert and colleagues⁶³ assessed the accuracy of mechanical alignment in the Caspar system in 70 patients treated with the robotic system. They found that the difference between preoperatively planned and postoperatively achieved mechanical alignment was 0.8°. Similarly, Bellemans and colleagues⁷⁷ assessed mechanical alignment and the positioning and rotation of the tibial and femoral components in a clinical study of 25 cases using the Caspar system. They noted that none of the patients had mechanical alignment, tibial or femoral component positioning, or rotation beyond 1° of the neutral axis. Liow and colleagues⁵⁶ assessed the accuracy of mechanical axis alignment and component sizing accuracy using the Robodoc system in 25 patients. They reported that the mean postoperative alignment was 0.4° valgus and that all cases were within 3° of the neutral mechanical axis. Furthermore, they reported a mean surgical time of 96 minutes and reported that preoperative planning yielded femoral and tibial component size accuracy of 100%.

These studies have shown that robotic systems for UKA and TKA are accurate in the surgical variables they aim to control. These studies validated tight control of mechanical axis alignment, decrease for outliers, and component positioning and rotation, and also found that the balancing of soft tissues was improved using robotic-assisted surgery.

Robotic-Assisted vs Conventional Knee Arthroplasty

Despite the fact that these systems are accurate in the variables they aim to control, these systems have to be compared to the gold standard of conventional knee arthroplasty. For UKA, Cobb and colleagues⁷⁰ performed a randomized clinical trial for patients treated undergoing UKA with robotic-assistance of the Acrobot systems compared to conventional UKA and assessed differences in mechanical accuracy. A total of 27 patients were randomly assigned to one of both treatments. They found that in the group of robotic-assisted surgery, 100% of the patients had a mechanical axis within 2° of neutral, while this was only 40% in the conventional UKA groups (difference P < .001). They also assessed the increase in functional outcomes and noted a trend towards improvement in performance with increasing accuracy at 6 weeks and 3 months postoperatively. Lonner and colleagues⁷⁸ also compared the tibial component positioning between robotic-assisted UKA surgery using the Mako system and conventional UKA surgery. The authors found that the variance in tibial slope, in coronal plane of the tibial component, and varus/valgus alignment were all larger with conventional UKA when compared to robotic-assisted UKA. Citak and colleagues⁷⁹ compared the accuracy of tibial and femoral implant positioning between robotic-assisted surgery using the Mako system and conventional UKA in a cadaveric study. They reported that the root mean square (RMS) error of femoral component was 1.9 mm and 3.7° in robotic-assisted surgery and 5.4 mm and 10.2° for conventional UKA, while the RMS error for tibial component were 1.4 mm and 5.0° for robotic-assisted surgery and 5.7 mm and 19.2° for conventional UKA surgery. MacCallum and colleagues⁸⁰ compared the tibial base plate position in a prospective clinical study of 177 patients treated with conventional UKA and 87 patients treated with robotic-assisted surgery using the Mako system. They found that surgery with robotic-assistance was more precise in the coronal and sagittal plane and was more accurate in coronal alignment when compared to conventional UKA. Finally, the first results of robotic-assisted UKA surgery have been presented. Coon and colleagues⁸¹ reported the preliminary results of a multicenter study of 854 patients and found a survivorship of 98.9% and satisfaction rate of 92% at minimum 2-year follow-up. Comparing these results to other large conventional UKA cohorts^82,83 suggests that robotic-assisted surgery may improve survivorship at short-term follow-up. However, comparative studies and studies with longer follow-up are necessary to assess the additional value of robotic-assisted UKA surgery. Due to the relatively new concept of robotic-assisted surgery, these studies have not been performed or published yet.

For TKA, several studies also have compared how these robotic-systems control the surgical variables compared to conventional TKA surgery. Siebert and colleagues⁶³ assessed mechanical axis accuracy and mechanical outliers following robotic-assisted TKA surgery using the Caspar system and conventional TKA surgery. They reported the difference between preoperative planned and postoperative achieved alignment was 0.8° for robotic-assisted surgery and 2.6° for conventional TKA surgery. Furthermore, they showed that 1 patient in the robotic-assisted group (1.4%) and 18 patients in the conventional TKA group (35%) had mechanical alignment greater than 3° from the neutral mechanical axis. Liow and colleagues⁵⁶ found similar differences in their prospective randomized study in which they reported that 0% outliers greater than 3° from the neutral mechanical axis were found in the robotic-assisted group while 19.4% of the patients in the conventional TKA group had mechanical axis outliers. They also assessed the joint-line outliers in both procedures and found that 3.2% had joint-line outliers greater than 5 mm in the robotic-assisted group compared to 20.6% in the conventional TKA group. Kim and colleagues⁶⁵ assessed implant accuracy in robotic-assisted surgery using the ROBODOC system and in conventional surgery and reported higher implant accuracy and fewer outliers using robotic-assisted surgery. Moon and colleagues⁶⁶ compared robotic-assisted TKA surgery using the Robodoc system with conventional TKA surgery in 10 cadavers. They found that robotic-assisted surgery had excellent precision in all planes and had better accuracy in femoral rotation alignment compared to conventional TKA surgery. Park and Lee⁶⁷ compared Robodoc robotic-assisted TKA surgery with conventional TKA surgery in a randomized clinical trial of 72 patients. They found that robotic-assisted surgery had definitive advantages in preoperative planning, accuracy of the procedure, and postoperative follow-up regarding femoral and tibial component flexion angles. Finally, Song and colleagues^68,69 performed 2 randomized clinical trials in which they compared mechanical axis alignment, component positioning, soft tissue balancing, and patient preference between conventional TKA surgery and robotic-assisted surgery using the Robodoc system. In the first study,⁶⁸ they simultaneously performed robotic-assisted surgery in one leg and conventional TKA surgery in the other leg. They found that robotic-assisted surgery resulted in less outlier in mechanical axis and component positioning. Furthermore, they found at latest follow-up of 2 years that 12 patients preferred the leg treated with robotic-assisted surgery while 6 preferred the conventional leg. Despite this finding, no significant differences in functional outcome scores were detected between both treatment options. Furthermore, they found that flexion-extension balance was achieved in 92% of patients treated with robotic-assisted TKA surgery and in 77% of patients treated with conventional TKA surgery. In the other study,⁶⁹ the authors found that more patients treated with robotic-assisted surgery had <2 mm flexion-extension gap and more satisfactory posterior cruciate ligament tension when compared to conventional surgery.

These studies have shown that robotic-assisted surgery is accurate in controlling surgical variables, such as mechanical lower leg alignment, maintaining joint-line, implant positioning, and soft tissue balancing. Furthermore, these studies have shown that controlling these variables is better than the current gold standard of manual knee arthroplasty. Until now, not many studies have assessed survivorship of robotic-assisted surgery. Furthermore, no studies have, to our knowledge, compared survivorship of robotic-assisted with conventional knee replacement surgery. Finally, studies comparing functional outcomes following robotic-assisted surgery and conventional knee arthroplasty surgery are frequently underpowered due to their small sample sizes.^68,70 Since many studies have shown that the surgical variables are more tightly controlled using robotic-assisted surgery when compared to conventional surgery, large comparative studies are necessary to assess the role of robotic-assisted surgery in functional outcomes and survivorship of UKA and TKA.

Cost-Effectiveness of Robotic-Assisted Surgery

High initial capital costs of robotic-assisted surgery is one of the factors that constitute a barrier to the widespread implementation of this technique. Multiple authors have suggested that improved implant survivorship afforded by robotic-assisted surgery may justify the expenditure from both societal and provider perspective.^84-86 Two studies have performed a cost-effectiveness analysis for UKA surgery. Swank and colleagues⁸⁴ reviewed the hospital expenditures and profits associated with robot-assisted knee arthroplasty, citing upfront costs of approximately $800,000. The authors estimated a mean per-case contribution profit of $5790 for robotic-assisted UKA, assuming an inpatient-to-outpatient ratio of 1 to 3. Based on this data, Swank and colleagues84 proposed that the capital costs of robotic-assisted UKA may be recovered in as little as 2 years when in the first 3 consecutive years 50, 70, and 90 cases were performed using robotic-assisted UKA. Moschetti and colleagues⁸⁵ recently published the first formal cost-effectiveness analysis of robotic-assisted compared to manual UKA. The authors used an annual revision risk of 0.55% for the first 2 years following robot-assisted UKA, based on the aforementioned presented data by Coon and colleagues.⁸¹ They based their data on the Mako system and assumed an initial capital expenditure of $934,728 with annual servicing costs of 10% (discounted annually) for 4 years thereafter, resulting in a total cost of the robotic system of $1.362 million. These costs were divided by the number of patients estimated to undergo robotic-assisted UKA per year, which was varied to estimate the effect of case volume on cost-effectiveness. The authors reported that robotic-assisted UKA was associated with higher lifetime costs and net utilities compared to manual UKA, at an incremental cost-effectiveness ratio of $47,180 per quality-adjusted life year (QALY) in a high-volume center. This falls well within the societal willingness-to-pay threshold of $100,000/QALY. Sensitivity analysis showed that robotic-assisted UKA is cost-effective under the following conditions: (1) centers performing at least 94 cases annually, (2) in patients younger than age 67 years, and (3) 2-year revision rate does not exceed 1.2%. While the results of this initial analysis are promising, follow-up cost-effectiveness analysis studies will be required as long-term survivorship data become available.

Conclusion

Tighter control of intraoperative surgical variables, such as lower leg alignment, soft tissue balance, joint-line maintenance, and component alignment and positioning, have been associated with improved survivorship and functional outcomes. Upon reviewing the available literature on robotic-assisted surgery, it becomes clear that this technique can improve the accuracy of these surgical variables and is superior to conventional manual UKA and TKA. Although larger and comparative survivorship studies are necessary to compare robotic-assisted knee arthroplasty to conventional techniques, the early results and cost-effectiveness analysis seem promising.

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are 2 reliable treatment options for patients with primary osteoarthritis. Recently published systematic reviews of cohort studies have shown that 10-year survivorship of medial and lateral UKA is 92% and 91%, respectively,¹ while 10-year survivorship of TKA in cohort studies is 95%.² National and annual registries show a similar trend, although the reported survivorship is lower.^1,3-7

In order to improve these survivorship rates, the surgical variables that can intraoperatively be controlled by the orthopedic surgeon have been evaluated. These variables include lower leg alignment, soft tissue balance, joint line maintenance, and alignment, size, and fixation of the tibial and femoral component. Several studies have shown that tight control of lower leg alignment,^8-14 balancing of the soft tissues,^15-19 joint line maintenance,^20-23 component alignment,^24-28 component size,^29-34 and component fixation^35-40 can improve the outcomes of UKA and TKA. As a result, over the past 2 decades, several computer-assisted surgery systems have been developed with the goal of more accurate and reliable control of these factors, and thus improved outcomes of knee arthroplasty.

These systems differ with regard to the number and type of variables they control. Computer navigation systems aim to control one or more of these surgical variables, and several meta-analyses have shown that these systems, when compared to conventional surgery, improve mechanical axis accuracy, decrease the risk for mechanical axis outliers, and improve component positioning in TKA^41-49 and UKA surgery.^50,51 Interestingly, however, meta-analyses have failed to show the expected superiority in clinical outcomes following computer navigation compared to conventional knee arthroplasty.^48,52-55 Furthermore, authors have shown that, despite the fact that computer-navigated surgery increases the accuracy of mechanical alignment and surgical cutting, there is still room for improvement.⁵⁶ As a consequence, robotic-assisted systems have been developed.

Similar to computer navigation, these robotic-assisted systems aim to control the surgical variables; in addition, they aim to improve the surgical precision of the procedure. Interestingly, 2 recent studies have shown that robotic-assisted systems are superior to computer navigation systems with regard to less cutting time and less resection deviations in coronal and sagittal plane in a cadaveric study,⁵⁷ and shorter total surgery time, more accurate mechanical axis, and shorter hospital stay in a clinical study.⁵⁸ Although these results are promising, the exact role of robotic surgery in knee arthroplasty remains unclear. In this review, we aim to report the current state of robotic-assisted knee arthroplasty by discussing (1) the different robotic-assisted knee arthroplasty systems that are available for UKA and TKA surgery, (2) studies that assessed the role of robotic-assisted knee arthroplasty in controlling the aforementioned surgical variables, (3) cadaveric and clinical comparative studies that compared how accurate robotic-assisted and conventional knee surgery control these surgical variables, and (4) studies that assessed the cost-effectiveness of robotic-assisted knee arthroplasty surgery.

Robotic-Assisted Knee Arthroplasty Systems

Several systems have been developed over the years for knee arthroplasty, and these are usually defined as active, semi-active, or passive.⁵⁹ Active systems are capable of performing tasks or processes autonomously under the watchful eye of the surgeon, while passive systems do not perform actions independently but provide the surgeon with information. In semi-active systems, the surgical action is physically constrained in order to follow a predefined strategy.

In the United States, 3 robotic systems are FDA-approved for knee arthroplasty. The Stryker/Mako haptic guided robot (Mako Surgical Corp.) was introduced in 2005 and has been used for over 50,000 UKA procedures (Figure 1). There are nearly 300 robotic systems used nationally, as it has 20% of the market share for UKA in the United States. The Mako system is a semi-active tactile robotic system that requires preoperative imaging, after which a preoperative planning is performed. Intraoperatively, the robotic arm is under direct surgeon control and gives real-time tactile feedback during the procedure (Figure 2).

Furthermore, the surgeon can intraoperatively virtually adjust component positioning and alignment and move the knee through the range of motion, after which the system can provide information on alignment, component position, and balance of the soft tissue (eg, if the knee is overtight or lax through the flexion-arch).⁶⁰ This system has a burr that resects the bone and when the surgeon directs the burr outside the preplanned area, the burr stops and prevents unnecessary and unwanted resections (Figure 3).

The Navio Precision Free-Hand Sculptor (PFS) system (Blue Belt Technologies) has been used for 1500 UKA procedures, with 50 robots in use in the United States (Figure 4). This system is an image-free semi-active robotic system and has the same characteristics as the aforementioned Mako system.⁶¹ Finally, the OmniBotic robotic system (Omnilife Science) has been released for TKA and has been used for over 7300 procedures (Figure 5). This system has an automated cutting-guide technique in which the surgeon designs a virtual plan on the computer system. After this, the cutting-guides are placed by the robotic system at the planned location for all 5 femoral cuts (ie, distal, anterior chamfer, anterior, posterior chamfer, and posterior) and the surgeon then makes the final cuts.^57,62

Three robotic systems for knee arthroplasty surgery have been used in Europe. The Caspar system (URS Ortho) is an active robotic system in which a computed tomography (CT) scan is performed preoperatively, after which a virtual implantation is performed on the screen. The surgeon can then obtain information on lower leg alignment, gap balancing, and component positioning, and after an operative plan is made, the surgical resections are performed by the robot. Reflective markers are attached to the leg and all robotic movements are monitored using an infrared camera system. Any undesired motion will be detected by this camera system and will stop all movements.⁶³ A second and more frequently reported system in the literature is the active Robodoc surgical system (Curexo Technology Corporation). This system is designed for TKA and total hip arthroplasty (THA) surgery. Although initial studies reported a high incidence of system-related complications in THA,⁶⁴ the use of this system for TKA has frequently been reported in the literature.^56,63,65-69 A third robotic system that has been used in Europe is the Acrobot surgical system (Acrobot Company Ltd), which is an image-based semi-active robotic system⁷⁰ used for both UKA and TKA surgery.^70,71

Accuracy of Controlling Surgical Variables in Robotic-Assisted Knee Arthroplasty

Several studies have assessed the accuracy of robotic-assisted surgery in UKA surgery with regard to control of the aforementioned surgical variables. Pearle and colleagues⁷² assessed the mechanical axis accuracy of the Mako system in 10 patients undergoing medial UKA robotic-assisted surgery. They reported that the intraoperative registration lasted 7.5 minutes and the duration of time needed for robotic-assisted burring was 34.8 minutes. They compared the actual postoperative alignment at 6 weeks follow-up with the planned lower leg alignment and found that all measurements were within 1.6° of the planned lower leg alignment. Dunbar and colleagues⁷³ assessed the accuracy of component positioning of the Mako system in 20 patients undergoing medial UKA surgery by comparing preoperative and postoperative 3-dimensional CT scans. They found that the femoral component was within 0.8 mm and 0.9° in all directions and that the tibial component was within 0.9 mm and 1.7° in all directions. They concluded that the accuracy of component positioning with the Mako system was excellent. Finally, Plate and colleagues¹⁷ assessed the accuracy of soft tissue balancing in the Mako system in 52 patients undergoing medial UKA surgery. They compared the balance plan with the soft tissue balance after implantation and the Mako system quantified soft tissue balance as the amount of mm of the knee being tight or loose at 0°, 30°, 60°, 90°, and 110° of flexion. They found that at all flexion angles the ligament balancing was accurate up to 0.53 mm of the original plan. Furthermore, they noted that in 83% of cases the accuracy was within 1 mm at all flexion angles.

For the Navio system, Smith and colleagues⁷⁴ assessed the accuracy of component positioning using 20 synthetic femurs and tibia. They reported a maximum rotational error of 3.2°, an angular error of 1.46° in all orientations, and a maximum translational error of 1.18 mm for both the tibial and femoral implants. Lonner and colleagues⁷⁵ assessed the accuracy of component positioning in 25 cadaveric specimens. They found similar results as were found in the study of Smith and colleagues⁷⁴ and concluded that these results were similar to other semi-active robotic systems designed for UKA.

For TKA surgery, Ponder and colleagues⁷⁶ assessed the accuracy of the OmniBotic system and found that the average error in the anterior-posterior dimension between the targeted and measured cuts was -0.14 mm, and that the standard deviation in guide positioning for the distal, anterior chamfer, and posterior chamfer resections was 0.03° and 0.17 mm. Koenig and colleagues⁶² assessed the accuracy of the OmniBotic system in the first 100 cases and found that 98% of the cases were within 3° of the neutral mechanical axis. Furthermore, they found a learning curve with regard to tourniquet time between the first and second 10 patients in which they performed robotic-assisted TKA surgery. Siebert and colleagues⁶³ assessed the accuracy of mechanical alignment in the Caspar system in 70 patients treated with the robotic system. They found that the difference between preoperatively planned and postoperatively achieved mechanical alignment was 0.8°. Similarly, Bellemans and colleagues⁷⁷ assessed mechanical alignment and the positioning and rotation of the tibial and femoral components in a clinical study of 25 cases using the Caspar system. They noted that none of the patients had mechanical alignment, tibial or femoral component positioning, or rotation beyond 1° of the neutral axis. Liow and colleagues⁵⁶ assessed the accuracy of mechanical axis alignment and component sizing accuracy using the Robodoc system in 25 patients. They reported that the mean postoperative alignment was 0.4° valgus and that all cases were within 3° of the neutral mechanical axis. Furthermore, they reported a mean surgical time of 96 minutes and reported that preoperative planning yielded femoral and tibial component size accuracy of 100%.

These studies have shown that robotic systems for UKA and TKA are accurate in the surgical variables they aim to control. These studies validated tight control of mechanical axis alignment, decrease for outliers, and component positioning and rotation, and also found that the balancing of soft tissues was improved using robotic-assisted surgery.

Robotic-Assisted vs Conventional Knee Arthroplasty

Despite the fact that these systems are accurate in the variables they aim to control, these systems have to be compared to the gold standard of conventional knee arthroplasty. For UKA, Cobb and colleagues⁷⁰ performed a randomized clinical trial for patients treated undergoing UKA with robotic-assistance of the Acrobot systems compared to conventional UKA and assessed differences in mechanical accuracy. A total of 27 patients were randomly assigned to one of both treatments. They found that in the group of robotic-assisted surgery, 100% of the patients had a mechanical axis within 2° of neutral, while this was only 40% in the conventional UKA groups (difference P < .001). They also assessed the increase in functional outcomes and noted a trend towards improvement in performance with increasing accuracy at 6 weeks and 3 months postoperatively. Lonner and colleagues⁷⁸ also compared the tibial component positioning between robotic-assisted UKA surgery using the Mako system and conventional UKA surgery. The authors found that the variance in tibial slope, in coronal plane of the tibial component, and varus/valgus alignment were all larger with conventional UKA when compared to robotic-assisted UKA. Citak and colleagues⁷⁹ compared the accuracy of tibial and femoral implant positioning between robotic-assisted surgery using the Mako system and conventional UKA in a cadaveric study. They reported that the root mean square (RMS) error of femoral component was 1.9 mm and 3.7° in robotic-assisted surgery and 5.4 mm and 10.2° for conventional UKA, while the RMS error for tibial component were 1.4 mm and 5.0° for robotic-assisted surgery and 5.7 mm and 19.2° for conventional UKA surgery. MacCallum and colleagues⁸⁰ compared the tibial base plate position in a prospective clinical study of 177 patients treated with conventional UKA and 87 patients treated with robotic-assisted surgery using the Mako system. They found that surgery with robotic-assistance was more precise in the coronal and sagittal plane and was more accurate in coronal alignment when compared to conventional UKA. Finally, the first results of robotic-assisted UKA surgery have been presented. Coon and colleagues⁸¹ reported the preliminary results of a multicenter study of 854 patients and found a survivorship of 98.9% and satisfaction rate of 92% at minimum 2-year follow-up. Comparing these results to other large conventional UKA cohorts^82,83 suggests that robotic-assisted surgery may improve survivorship at short-term follow-up. However, comparative studies and studies with longer follow-up are necessary to assess the additional value of robotic-assisted UKA surgery. Due to the relatively new concept of robotic-assisted surgery, these studies have not been performed or published yet.

For TKA, several studies also have compared how these robotic-systems control the surgical variables compared to conventional TKA surgery. Siebert and colleagues⁶³ assessed mechanical axis accuracy and mechanical outliers following robotic-assisted TKA surgery using the Caspar system and conventional TKA surgery. They reported the difference between preoperative planned and postoperative achieved alignment was 0.8° for robotic-assisted surgery and 2.6° for conventional TKA surgery. Furthermore, they showed that 1 patient in the robotic-assisted group (1.4%) and 18 patients in the conventional TKA group (35%) had mechanical alignment greater than 3° from the neutral mechanical axis. Liow and colleagues⁵⁶ found similar differences in their prospective randomized study in which they reported that 0% outliers greater than 3° from the neutral mechanical axis were found in the robotic-assisted group while 19.4% of the patients in the conventional TKA group had mechanical axis outliers. They also assessed the joint-line outliers in both procedures and found that 3.2% had joint-line outliers greater than 5 mm in the robotic-assisted group compared to 20.6% in the conventional TKA group. Kim and colleagues⁶⁵ assessed implant accuracy in robotic-assisted surgery using the ROBODOC system and in conventional surgery and reported higher implant accuracy and fewer outliers using robotic-assisted surgery. Moon and colleagues⁶⁶ compared robotic-assisted TKA surgery using the Robodoc system with conventional TKA surgery in 10 cadavers. They found that robotic-assisted surgery had excellent precision in all planes and had better accuracy in femoral rotation alignment compared to conventional TKA surgery. Park and Lee⁶⁷ compared Robodoc robotic-assisted TKA surgery with conventional TKA surgery in a randomized clinical trial of 72 patients. They found that robotic-assisted surgery had definitive advantages in preoperative planning, accuracy of the procedure, and postoperative follow-up regarding femoral and tibial component flexion angles. Finally, Song and colleagues^68,69 performed 2 randomized clinical trials in which they compared mechanical axis alignment, component positioning, soft tissue balancing, and patient preference between conventional TKA surgery and robotic-assisted surgery using the Robodoc system. In the first study,⁶⁸ they simultaneously performed robotic-assisted surgery in one leg and conventional TKA surgery in the other leg. They found that robotic-assisted surgery resulted in less outlier in mechanical axis and component positioning. Furthermore, they found at latest follow-up of 2 years that 12 patients preferred the leg treated with robotic-assisted surgery while 6 preferred the conventional leg. Despite this finding, no significant differences in functional outcome scores were detected between both treatment options. Furthermore, they found that flexion-extension balance was achieved in 92% of patients treated with robotic-assisted TKA surgery and in 77% of patients treated with conventional TKA surgery. In the other study,⁶⁹ the authors found that more patients treated with robotic-assisted surgery had <2 mm flexion-extension gap and more satisfactory posterior cruciate ligament tension when compared to conventional surgery.

These studies have shown that robotic-assisted surgery is accurate in controlling surgical variables, such as mechanical lower leg alignment, maintaining joint-line, implant positioning, and soft tissue balancing. Furthermore, these studies have shown that controlling these variables is better than the current gold standard of manual knee arthroplasty. Until now, not many studies have assessed survivorship of robotic-assisted surgery. Furthermore, no studies have, to our knowledge, compared survivorship of robotic-assisted with conventional knee replacement surgery. Finally, studies comparing functional outcomes following robotic-assisted surgery and conventional knee arthroplasty surgery are frequently underpowered due to their small sample sizes.^68,70 Since many studies have shown that the surgical variables are more tightly controlled using robotic-assisted surgery when compared to conventional surgery, large comparative studies are necessary to assess the role of robotic-assisted surgery in functional outcomes and survivorship of UKA and TKA.

Cost-Effectiveness of Robotic-Assisted Surgery

High initial capital costs of robotic-assisted surgery is one of the factors that constitute a barrier to the widespread implementation of this technique. Multiple authors have suggested that improved implant survivorship afforded by robotic-assisted surgery may justify the expenditure from both societal and provider perspective.^84-86 Two studies have performed a cost-effectiveness analysis for UKA surgery. Swank and colleagues⁸⁴ reviewed the hospital expenditures and profits associated with robot-assisted knee arthroplasty, citing upfront costs of approximately $800,000. The authors estimated a mean per-case contribution profit of $5790 for robotic-assisted UKA, assuming an inpatient-to-outpatient ratio of 1 to 3. Based on this data, Swank and colleagues84 proposed that the capital costs of robotic-assisted UKA may be recovered in as little as 2 years when in the first 3 consecutive years 50, 70, and 90 cases were performed using robotic-assisted UKA. Moschetti and colleagues⁸⁵ recently published the first formal cost-effectiveness analysis of robotic-assisted compared to manual UKA. The authors used an annual revision risk of 0.55% for the first 2 years following robot-assisted UKA, based on the aforementioned presented data by Coon and colleagues.⁸¹ They based their data on the Mako system and assumed an initial capital expenditure of $934,728 with annual servicing costs of 10% (discounted annually) for 4 years thereafter, resulting in a total cost of the robotic system of $1.362 million. These costs were divided by the number of patients estimated to undergo robotic-assisted UKA per year, which was varied to estimate the effect of case volume on cost-effectiveness. The authors reported that robotic-assisted UKA was associated with higher lifetime costs and net utilities compared to manual UKA, at an incremental cost-effectiveness ratio of $47,180 per quality-adjusted life year (QALY) in a high-volume center. This falls well within the societal willingness-to-pay threshold of $100,000/QALY. Sensitivity analysis showed that robotic-assisted UKA is cost-effective under the following conditions: (1) centers performing at least 94 cases annually, (2) in patients younger than age 67 years, and (3) 2-year revision rate does not exceed 1.2%. While the results of this initial analysis are promising, follow-up cost-effectiveness analysis studies will be required as long-term survivorship data become available.

Conclusion

Tighter control of intraoperative surgical variables, such as lower leg alignment, soft tissue balance, joint-line maintenance, and component alignment and positioning, have been associated with improved survivorship and functional outcomes. Upon reviewing the available literature on robotic-assisted surgery, it becomes clear that this technique can improve the accuracy of these surgical variables and is superior to conventional manual UKA and TKA. Although larger and comparative survivorship studies are necessary to compare robotic-assisted knee arthroplasty to conventional techniques, the early results and cost-effectiveness analysis seem promising.