The American Journal of Orthopedics

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.

A transition is underway at AJO. As we discuss the future of the “new journal,” I often think about the future of orthopedics. I’ve decided my vision of the future is centered on 3 components. First, there will be a change in our training paradigm from an apprenticeship model to standardized training, where core competencies must be demonstrated for certification. Second, robots and computers will improve our diagnostic accuracy and will allow us to perform surgery with improved component positioning, while biologics and genetic analysis will accelerate nature’s ability to heal, and perhaps regenerate, injured tissue. Finally, computerized algorithms and technologically improved surgical outcomes will allow us to deliver high-quality healthcare at a lower cost, producing the value our current health systems are striving for, and leveling the playing field between high-volume centers and rural institutions forced to offer complete service lines.

In this issue, we examine robotic-assisted arthroplasty and its role in modern healthcare. I think the best argument for robots in the operating room might come from the airline industry. I’m sitting on a plane as I write this, without once thinking about how much experience my pilot has in the cockpit. I know our pilot has demonstrated the core competencies required to safely operate the plane, trained on emergency simulations, and logged the necessary hours before being handed the controls. I also know that the instrumentation is so good that the plane can essentially fly itself, making pilot skill and experience less relevant. In short, technology has, in all but rare circumstances, made our pilots virtually interchangeable.

Unfortunately, none of the above is true in orthopedics. Our residents are not required to demonstrate their skills before any licensing authority, simulator training is not available in all programs, and we’ve limited resident work hours. Yet it’s that same interchangeability that most healthcare models assume. No one argues that high-volume centers have better results when it comes to arthroplasty, but only a small percentage of total joints are currently performed at these centers. Surgeon training remains a virtual apprenticeship, lacking standardization, and resulting in a wide variation in skill and experience. Surgical residencies are not awarded based on dexterity, and work hour restrictions, Relative Value Unit-based academic contracts, patient expectations, and staffing pressures can lead to reduced hands-on experience for trainees. The results: an entire generation of surgeons with decreased repetitions in the operating room when compared to their predecessors.

That’s why I believe we are on the cusp of a transition in the operating room, and that computer-assisted surgery is here to stay. While studies exist showing robots have tighter control over virtually every identifiable metric, little data currently exists supporting enhanced long-term outcomes. But as long as component malposition remains a leading cause of early failure, there will be a place for technologies that enhance accuracy of component placement. At odds with the drive for increased technology is the necessity of cost containment, leading us to question the value of robotic-assisted surgery, and whether the improved metrics are clinically important and the additional potential complications are worth the risk.

In the articles in this issue, we will take a critical look at the benefits and drawbacks of robotic surgery. As you read, think about the future of orthopedics and how you will implement new technology into your practice. A transition is coming, and I invite each of you to consider leading it.

A transition is underway at AJO. As we discuss the future of the “new journal,” I often think about the future of orthopedics. I’ve decided my vision of the future is centered on 3 components. First, there will be a change in our training paradigm from an apprenticeship model to standardized training, where core competencies must be demonstrated for certification. Second, robots and computers will improve our diagnostic accuracy and will allow us to perform surgery with improved component positioning, while biologics and genetic analysis will accelerate nature’s ability to heal, and perhaps regenerate, injured tissue. Finally, computerized algorithms and technologically improved surgical outcomes will allow us to deliver high-quality healthcare at a lower cost, producing the value our current health systems are striving for, and leveling the playing field between high-volume centers and rural institutions forced to offer complete service lines.

In this issue, we examine robotic-assisted arthroplasty and its role in modern healthcare. I think the best argument for robots in the operating room might come from the airline industry. I’m sitting on a plane as I write this, without once thinking about how much experience my pilot has in the cockpit. I know our pilot has demonstrated the core competencies required to safely operate the plane, trained on emergency simulations, and logged the necessary hours before being handed the controls. I also know that the instrumentation is so good that the plane can essentially fly itself, making pilot skill and experience less relevant. In short, technology has, in all but rare circumstances, made our pilots virtually interchangeable.

Unfortunately, none of the above is true in orthopedics. Our residents are not required to demonstrate their skills before any licensing authority, simulator training is not available in all programs, and we’ve limited resident work hours. Yet it’s that same interchangeability that most healthcare models assume. No one argues that high-volume centers have better results when it comes to arthroplasty, but only a small percentage of total joints are currently performed at these centers. Surgeon training remains a virtual apprenticeship, lacking standardization, and resulting in a wide variation in skill and experience. Surgical residencies are not awarded based on dexterity, and work hour restrictions, Relative Value Unit-based academic contracts, patient expectations, and staffing pressures can lead to reduced hands-on experience for trainees. The results: an entire generation of surgeons with decreased repetitions in the operating room when compared to their predecessors.

That’s why I believe we are on the cusp of a transition in the operating room, and that computer-assisted surgery is here to stay. While studies exist showing robots have tighter control over virtually every identifiable metric, little data currently exists supporting enhanced long-term outcomes. But as long as component malposition remains a leading cause of early failure, there will be a place for technologies that enhance accuracy of component placement. At odds with the drive for increased technology is the necessity of cost containment, leading us to question the value of robotic-assisted surgery, and whether the improved metrics are clinically important and the additional potential complications are worth the risk.

In the articles in this issue, we will take a critical look at the benefits and drawbacks of robotic surgery. As you read, think about the future of orthopedics and how you will implement new technology into your practice. A transition is coming, and I invite each of you to consider leading it.

A transition is underway at AJO. As we discuss the future of the “new journal,” I often think about the future of orthopedics. I’ve decided my vision of the future is centered on 3 components. First, there will be a change in our training paradigm from an apprenticeship model to standardized training, where core competencies must be demonstrated for certification. Second, robots and computers will improve our diagnostic accuracy and will allow us to perform surgery with improved component positioning, while biologics and genetic analysis will accelerate nature’s ability to heal, and perhaps regenerate, injured tissue. Finally, computerized algorithms and technologically improved surgical outcomes will allow us to deliver high-quality healthcare at a lower cost, producing the value our current health systems are striving for, and leveling the playing field between high-volume centers and rural institutions forced to offer complete service lines.

In this issue, we examine robotic-assisted arthroplasty and its role in modern healthcare. I think the best argument for robots in the operating room might come from the airline industry. I’m sitting on a plane as I write this, without once thinking about how much experience my pilot has in the cockpit. I know our pilot has demonstrated the core competencies required to safely operate the plane, trained on emergency simulations, and logged the necessary hours before being handed the controls. I also know that the instrumentation is so good that the plane can essentially fly itself, making pilot skill and experience less relevant. In short, technology has, in all but rare circumstances, made our pilots virtually interchangeable.

Unfortunately, none of the above is true in orthopedics. Our residents are not required to demonstrate their skills before any licensing authority, simulator training is not available in all programs, and we’ve limited resident work hours. Yet it’s that same interchangeability that most healthcare models assume. No one argues that high-volume centers have better results when it comes to arthroplasty, but only a small percentage of total joints are currently performed at these centers. Surgeon training remains a virtual apprenticeship, lacking standardization, and resulting in a wide variation in skill and experience. Surgical residencies are not awarded based on dexterity, and work hour restrictions, Relative Value Unit-based academic contracts, patient expectations, and staffing pressures can lead to reduced hands-on experience for trainees. The results: an entire generation of surgeons with decreased repetitions in the operating room when compared to their predecessors.

That’s why I believe we are on the cusp of a transition in the operating room, and that computer-assisted surgery is here to stay. While studies exist showing robots have tighter control over virtually every identifiable metric, little data currently exists supporting enhanced long-term outcomes. But as long as component malposition remains a leading cause of early failure, there will be a place for technologies that enhance accuracy of component placement. At odds with the drive for increased technology is the necessity of cost containment, leading us to question the value of robotic-assisted surgery, and whether the improved metrics are clinically important and the additional potential complications are worth the risk.

In the articles in this issue, we will take a critical look at the benefits and drawbacks of robotic surgery. As you read, think about the future of orthopedics and how you will implement new technology into your practice. A transition is coming, and I invite each of you to consider leading it.

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.

Eating a Mediterranean diet full of fruits, vegetables, fish, nuts, legumes, and whole grains is associated with a slightly lower risk of hip fracture in women, according to a study published online ahead of print in JAMA Internal Medicine.

Researchers analyzed data on diet and fracture risk in more than 90,000 postmenopausal women (average age, 63.6 years) who were followed for an average of almost 16 years. Diet quality and adherence were assessed by scores on 4 scales: the alternate Mediterranean Diet (aMED); the Healthy Eating Index 2010 (HEI-2010); the Alternate Healthy Eating Index 2010 (AHEI-2010); and the Dietary Approaches to Stop Hypertension (DASH) diet.

Women who scored the highest for adherence to a Mediterranean diet were at lower risk for hip fractures, although the absolute risk reduction was 0.29%. There was no association between a Mediterranean diet and total fracture risk.

A higher HEI-2010 or DASH score was inversely related to the risk of hip fracture, but the finding was not statistically significant. There was no association between HEI-2010, DASH and total fracture risk. The highest scores for AHEI-2010 were not significantly associated with hip or total fracture risk.

Eating a Mediterranean diet full of fruits, vegetables, fish, nuts, legumes, and whole grains is associated with a slightly lower risk of hip fracture in women, according to a study published online ahead of print in JAMA Internal Medicine.

Researchers analyzed data on diet and fracture risk in more than 90,000 postmenopausal women (average age, 63.6 years) who were followed for an average of almost 16 years. Diet quality and adherence were assessed by scores on 4 scales: the alternate Mediterranean Diet (aMED); the Healthy Eating Index 2010 (HEI-2010); the Alternate Healthy Eating Index 2010 (AHEI-2010); and the Dietary Approaches to Stop Hypertension (DASH) diet.

Women who scored the highest for adherence to a Mediterranean diet were at lower risk for hip fractures, although the absolute risk reduction was 0.29%. There was no association between a Mediterranean diet and total fracture risk.

A higher HEI-2010 or DASH score was inversely related to the risk of hip fracture, but the finding was not statistically significant. There was no association between HEI-2010, DASH and total fracture risk. The highest scores for AHEI-2010 were not significantly associated with hip or total fracture risk.

Eating a Mediterranean diet full of fruits, vegetables, fish, nuts, legumes, and whole grains is associated with a slightly lower risk of hip fracture in women, according to a study published online ahead of print in JAMA Internal Medicine.

Researchers analyzed data on diet and fracture risk in more than 90,000 postmenopausal women (average age, 63.6 years) who were followed for an average of almost 16 years. Diet quality and adherence were assessed by scores on 4 scales: the alternate Mediterranean Diet (aMED); the Healthy Eating Index 2010 (HEI-2010); the Alternate Healthy Eating Index 2010 (AHEI-2010); and the Dietary Approaches to Stop Hypertension (DASH) diet.

Women who scored the highest for adherence to a Mediterranean diet were at lower risk for hip fractures, although the absolute risk reduction was 0.29%. There was no association between a Mediterranean diet and total fracture risk.

A higher HEI-2010 or DASH score was inversely related to the risk of hip fracture, but the finding was not statistically significant. There was no association between HEI-2010, DASH and total fracture risk. The highest scores for AHEI-2010 were not significantly associated with hip or total fracture risk.

An increasing number of adolescents are undergoing ulnar lateral ligament (UCL) surgery to repair a pitching-related elbow injury, according to a study published online ahead of print in the March issue of the American Journal of Sports Medicine.

Analyzing a database of all ambulatory discharges in New York state, researchers found that 444 patients underwent surgery to repair their UCL between 2002 and 2011. The median age of study participants was 21; most were male.

The total volume of UCL surgeries increased nearly 200% during that time, while the number of UCL reconstructions per 100,000 people tripled from 0.15 to 0.45. Almost all of the growth occurred in two age groups, 17- to 18-year-olds and 19- to 20-year-olds. Patients who had private insurance were 25 times more likely to undergo UCL construction than those with Medicaid.

An increasing number of adolescents are undergoing ulnar lateral ligament (UCL) surgery to repair a pitching-related elbow injury, according to a study published online ahead of print in the March issue of the American Journal of Sports Medicine.

Analyzing a database of all ambulatory discharges in New York state, researchers found that 444 patients underwent surgery to repair their UCL between 2002 and 2011. The median age of study participants was 21; most were male.

The total volume of UCL surgeries increased nearly 200% during that time, while the number of UCL reconstructions per 100,000 people tripled from 0.15 to 0.45. Almost all of the growth occurred in two age groups, 17- to 18-year-olds and 19- to 20-year-olds. Patients who had private insurance were 25 times more likely to undergo UCL construction than those with Medicaid.

An increasing number of adolescents are undergoing ulnar lateral ligament (UCL) surgery to repair a pitching-related elbow injury, according to a study published online ahead of print in the March issue of the American Journal of Sports Medicine.

Analyzing a database of all ambulatory discharges in New York state, researchers found that 444 patients underwent surgery to repair their UCL between 2002 and 2011. The median age of study participants was 21; most were male.

The total volume of UCL surgeries increased nearly 200% during that time, while the number of UCL reconstructions per 100,000 people tripled from 0.15 to 0.45. Almost all of the growth occurred in two age groups, 17- to 18-year-olds and 19- to 20-year-olds. Patients who had private insurance were 25 times more likely to undergo UCL construction than those with Medicaid.

Children and adolescents who take medication for attention-deficit hyperactivity disorder (ADHD) show decreased bone density, according to a large cross-sectional study presented at the 2016 Annual Meeting of the American Academy of Orthopaedic Surgeons in Orlando.

Researchers identified 5,315 pediatric patients in the Center for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES) and compared children who were taking an ADHD medication (methylphenidate, desmethylphenidate, dextroamphetamine, atomoxetine, or lisdexamfetamine) with those who were not.

Children taking ADHD medication had lower bone mineral density in the femur, femoral neck, and lumbar spine. Approximately 25% of survey participants who were taking ADHD medication met criteria for osteopenia.

Researchers were able to rule out other potential causes of low bone density in these children, including age, sex, race/ethnicity, and poverty levels. However, the study did not include information on dose, duration of use, or changes in therapy because of the limitations of the NHANES survey data.

Children and adolescents who take medication for attention-deficit hyperactivity disorder (ADHD) show decreased bone density, according to a large cross-sectional study presented at the 2016 Annual Meeting of the American Academy of Orthopaedic Surgeons in Orlando.

Researchers identified 5,315 pediatric patients in the Center for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES) and compared children who were taking an ADHD medication (methylphenidate, desmethylphenidate, dextroamphetamine, atomoxetine, or lisdexamfetamine) with those who were not.

Children taking ADHD medication had lower bone mineral density in the femur, femoral neck, and lumbar spine. Approximately 25% of survey participants who were taking ADHD medication met criteria for osteopenia.

Researchers were able to rule out other potential causes of low bone density in these children, including age, sex, race/ethnicity, and poverty levels. However, the study did not include information on dose, duration of use, or changes in therapy because of the limitations of the NHANES survey data.

Children and adolescents who take medication for attention-deficit hyperactivity disorder (ADHD) show decreased bone density, according to a large cross-sectional study presented at the 2016 Annual Meeting of the American Academy of Orthopaedic Surgeons in Orlando.

Researchers identified 5,315 pediatric patients in the Center for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES) and compared children who were taking an ADHD medication (methylphenidate, desmethylphenidate, dextroamphetamine, atomoxetine, or lisdexamfetamine) with those who were not.

Children taking ADHD medication had lower bone mineral density in the femur, femoral neck, and lumbar spine. Approximately 25% of survey participants who were taking ADHD medication met criteria for osteopenia.

Researchers were able to rule out other potential causes of low bone density in these children, including age, sex, race/ethnicity, and poverty levels. However, the study did not include information on dose, duration of use, or changes in therapy because of the limitations of the NHANES survey data.

Patients are learning about health and disease more independently than before, but such self-education may pose a unique challenge for practicing physicians. Although educated patients can assist in the critical appraisal of treatment options,¹ misinformed patients may have preconceived treatment biases and unrealistic expectations. More than 66 million Americans use the Internet daily, and recent surveys have shown 86% have used the Internet for health-related information.^2,3 With Internet use increasing, the number of patients turning to the web for medical information is increasing as well.⁴ For many patients, this information can be useful in making decisions about their health and health care.⁵

Although accessing medical information from the Internet has grown exponentially, analysis of information quality has grown considerably slower.⁶ With no regulatory body monitoring content, there is easy circumvention of the peer review process, an essential feature of academic publishing.⁷ With no external regulation, the information retrieved may be incorrect, outdated, or misleading. Many orthopedic studies have analyzed Internet content about numerous diagnoses.^3-6,8-18 Most of these studies have found this information highly variable and of poor quality.

We conducted a study to evaluate and analyze rotator cuff repair information available to the general public through the Internet; to assess changes in the quality of information over time; to determine if sites sponsored by academic institutions offered higher-quality information; and to assess whether the readability of the material varied according to DISCERN scores.

Rotator cuff repairs are among the most common surgeries performed by orthopedic surgeons. To our knowledge, this is the first study to assess the quality of web information about rotator cuff repairs. We hypothesized that the quality of information would positively correlate with the reading level of the material presented, that academic institutions would present the highest-quality information, and that the type of information presented would change over time.

Materials and Methods

We used the search phrase rotator cuff repair on the 3 most popular search engines: Google, Yahoo!, and Bing. Google is the dominant engine, taking 83.06% of total market share, followed by Yahoo! (6.86%) and Bing (4.27%).5 The first 50 websites identified by each search engine were selected for evaluation, excluding duplicates or overlapping websites. Similarly, advertisements and strictly video results lacking text were excluded. After each engine was queried, a master list of 150 websites was created for individual evaluation and assessment. To assess changes in results over time, we performed 2 searches, on November 16, 2011, and May 18, 2014.

The content of each website was analyzed for authorship, ability to contact the author, discussion of disorder, surgical treatment, complications, surgical eligibility, rehabilitation, other treatment options, and use of peer-reviewed sources. Authorship was placed in 1 of 6 categories:

1. Academic—university-affiliated physician or research group.

2. Private—physician or group without stated affiliation to an academic organization.

3. Industry—manufacturing or marketing company advertising a product or service for profit.

4. News source—bulletin or article without affiliation to a hospital or an academic institution.

5. Public education—individual or organization with noncommercial website providing third-party information (eg, Wikipedia, About.com).

6. Blog—website publishing an individual’s personal experiences in diary or journal form.

Websites were also assessed for accuracy and validity based on presence or absence of Health On the Net code (HONcode) certification and DISCERN score. Designed by the Health On the Net Foundation in 1996, HONcode provides a framework for disseminating high-quality medical information over the web.¹⁹ Website owners can request that their sites be evaluated for HONcode certification; a site that qualifies can display the HONcode seal.²⁰ The DISCERN project, initially funded by the National Health Service in the United Kingdom, judges the quality of written information available on health-related websites.²¹ It determines the quality of a publication on the basis of 16 questions: The first 8 address the publication’s reliability, the next 7 involve specific details of treatment choices, and the last is an overall rating of the website.

Website readability was assessed with the Flesch-Kincaid test. This test, designed under contract with the US Navy in 1975, has been used in other orthopedic studies.¹⁹ Regression analysis was performed to check for correlation between website readability and DISCERN score. Analysis of variance was used to analyze differences between scores.

Results

We performed a comprehensive analysis of the top 50 websites from each of the 3 search engines (N = 150 websites) (Figures 1–5, Table). Regarding authorship, our 2 searches demonstrated similar values (Figure 1). In 2011, 21% of websites were associated with an academic institution, 38% were authored by private physicians or hospital or physician groups not associated with an academic institution, 11.5% were industry-sponsored, 5% were news bulletins or media reports, 21.5% were public education websites, and 3% were personal blogs. Our 2014 search found a similar distribution of contributors. Between 2011 and 2014, the largest change was in academic authors, which decreased by 7%, from 21% to 14%. Percentage of websites authored by private physicians remained constant from the first to the second search: 38%.

When the 2011 and 2014 website content was compared, several changes were noted. Percentage of websites providing an author contact method increased from 21% to 50% (Figure 2), percentage detailing rotator cuff repairs increased from 82% to 91%, and percentage introducing treatment options in addition to surgical management increased from 11.5% to 61%. Percentage discussing surgical eligibility, however, decreased from 43% to 18%. Percentage citing peer-reviewed sources remained relatively constant (28%, 26%), as did percentage discussing surgical technique for rotator cuff repair (55%, 59%) (Figure 3). A major decrease was found in percentage of websites discussing surgical complications, 42% in 2011 down to 25% in 2014, whereas a major increase was found in percentage discussing rehabilitation, from 39% in 2011 up to 73% in 2014. In 2014, no websites discussed double- versus single-row surgery—compared with 6% in 2011. False claims remained low between 2011 and 2014. In both searches, no website guaranteed a return to sport, and few made claims of painless or bloodless surgery.

DISCERN scores for websites found during the 2014 search were averaged for each of the 6 authorship groups (Figure 4). The highest DISCERN scores were given to academic institution websites (51.6) and public education websites (49). For the academic websites, this difference was significant relative to news, blog, and private physician websites (Ps = .012, .001, .001) The lowest DISCERN scores were given to news organization websites and personal blogs. DISCERN scores were 43.8 for industry sources and 40.7 for private physician groups; the difference was not significant (P = .229). Overall mean DISCERN score for all websites was 44. Eleven percent of websites were HONcode-certified.

No correlation was found between website readability and DISCERN score; correlation coefficient r was .01 (Figure 5). For the websites in 2014, mean Flesch-Kincaid readability score was 50.17, and mean grade level was 10.98; coefficient of determination r² was 0.00012.

The Table compares our data with data from other orthopedic studies that have analyzed the quality of Internet information about various orthopedic injuries, diseases, and procedures.^{3-6,8,9,11-18} With its mean DISCERN score of 44, the present rotator cuff tear study was ranked third of 6 studies that have used this scoring system to analyze website content. Of these 6 studies, those reviewing osteosarcoma and juvenile idiopathic arthritis were ranked highest (mean scores, 49.8 and 48.9, respectively), and the study reviewing scoliosis surgery was ranked lowest (38.9). Bruce-Brand and colleagues9 recently found a mean DISCERN score of 41 for anterior cruciate ligament (ACL) reconstruction. When considering HONcode-certified websites, our Internet search for rotator cuff tears found the third lowest percentage, 10.5%, compared with the other studies (Table); the highest percentage, 30%, was found for websites discussing concussions in athletes. When considering authorship, our rotator cuff study found the third highest percentage, 76%, authored by academic centers, physicians, and public education websites; the highest percentage was found in websites discussing ACL reconstruction. Websites discussing ACL reconstruction also had the highest percentage of websites authored by industry.⁹

Discussion

To our knowledge, this is the first study specifically analyzing the quality of Internet information about rotator cuff repairs. A similar study, conducted by Starman and colleagues¹⁵ in 2010, addressed the quality of web information about 10 common sports medicine diagnoses, one of which was rotator cuff tears. In that study, only 16 of the websites included discussed rotator cuff tears. In addition, the authors used a customized, HONcode-based grading system to analyze each website, making their data difficult to compare across studies.

Ideally, a high-quality medical website should be written by a credible source and should cover a disorder, treatment options, eligibility, rehabilitation, and complications. As there is no standard grading system for analyzing web content about rotator cuff repairs, we analyzed the websites for specific information we thought should be included in a high-quality website (Figures 2, 3). When considering authorship, we found academic centers, private physicians, and educational sources comprised 76% of the sources; industry sources made up only 12%. Similar findings were noted by investigators analyzing Internet information about other orthopedic topics, including ACL reconstruction, lumbar arthroplasty, osteosarcoma, and cervical spine surgery.^5,11,22 Studies analyzing websites for information on ACL tears and distal radius fractures found have a higher percentage of industry-sponsored websites.^9,10

DISCERN showed that the highest-quality information came from websites with academic affiliations, consistent with previous studies,^3,9,17 and its mean score (51.6) was significantly higher than the scores for private physician websites, news sites, and blogs (Ps = .001, .016, .001); the least reliable information was from personal blogs and news outlets. Of note, mean DISCERN score was higher for the industry websites we found than for private physician websites (43.8 vs 40.7), though the difference was not significant (P = .229). Previous investigators considered number of industry-sponsored websites as a marker of poor quality of information relating to a given topic; however, given the DISCERN scores in our study, this might not necessarily be true.⁶ Based on the present study’s data, websites affiliated with academic institutions would be recommended for patients searching for high-quality information about rotator cuff tears.

Given DISCERN scores across studies, information about rotator cuff tears ranked below information about osteosarcoma and juvenile idiopathic arthritis but above information about scoliosis, cervical spine surgery, and ACL reconstruction (Table). DISCERN scores must be compared across studies, as there are no definitions for good and poor DISCERN scores.

Of the 4 studies that analyzed percentage of websites citing peer-reviewed sources, only our study and the study of cervical spine surgery¹⁸ analyzed that percentage as well as DISCERN score. Percentage citing peer-reviewed sources was 26% for rotator cuff tears and 24% for cervical spine surgery; the respective DISCERN scores were 44 and 43.6. As only these 2 studies could be compared, no real correlation between percentage of websites citing peer-reviewed sources and the quality of the content on a given topic can be assessed. More research into this relationship is needed. One already delineated association is the correlation between HONcode-certified sites and high DISCERN scores.²¹ For high-quality medical information, physicians can direct their patients both to academic institution websites and to HONcode-certified websites.

When we compared the present study with previous investigations, we found a large difference between search results for a given topic. In 2013, Duncan and colleagues⁶ and Bruce-Brand and colleagues⁹ used similar study designs (eg, search terms, search engines) for their investigations of quality of web information. Their results, however, were widely different. For example, percentages of industry authorship were 4.5% (Duncan and colleagues⁶) and 64% (Bruce-Brand and colleagues⁹). This inconsistency between studies conducted during similar periods might be related to what appears at the top of the results queue for a search. Duncan and colleagues⁶ analyzed 200 websites, Bruce-Brand and colleagues⁹ only 45. Industries may have made financial arrangements and used search engine optimization techniques to have their websites listed first in search results.

In our study, we also analyzed how web information has changed over time. On the Internet, information changes daily, and we hypothesized that the content found during our 2 searches (2011, 2014) would yield different results. Surprisingly, the data were similar, particularly concerning authorship (Figures 1, 2). In both searches, the largest authorship source was private physician or physician groups (38% in 2011 and 2014). Other authorship sources showed little change in percentage between searches. As for content, we found both increases and decreases in specific web information. Ability to contact authors increased from 21% (2011) to 50% (2014). We think it is important that websites offer a communication channel to people who read the medical information the sites provide. Percentage of websites discussing nonoperative treatment options increased from 11.5% to 61%. Therefore, patients in 2014 were being introduced to more options (in addition to surgery) for managing shoulder pain—an improvement in quality of information between the searches. Percentage of websites discussing surgical eligibility, however, decreased from 43% to 18%—a negative development in information quality. Another decrease, from 42% to 25%, was found for websites discussing surgical complications. Given the data as a whole, and our finding both negative and positive changes, it appears the quality of web content has not improved significantly. Interestingly, no websites discussed double- versus single-row surgery in 2014, but 6% did so in 2011.

Lost in the discussion of quality and reliability of information is whether patients comprehend what they are reading.²³ Yi and colleagues¹⁹ recentlyassessed the readability level of arthroscopy information in articles published online by the American Academy of Orthopaedic Surgeons (AAOS) and the Arthroscopy Association of North America (AANA). The investigators used the Flesch-Kincaid readability test to determine readability level in terms of grade level. They found that the majority of the patient education articles on the AAOS and AANA sites had a readability level far above the national average; only 4 articles were written at or below the eighth-grade level, the current average reading level in the United States.²⁴ Information that is not comprehensible is of no use to patients, and information that physicians and researchers consider high-quality might not be what patients consider high-quality. As we pursue higher-quality web content, we need to consider that its audience includes nonmedical readers, our patients. In the present study, we found that the readability of a website had no correlation with the site’s DISCERN score (Figure 5). Therefore, for information about rotator cuff repairs, higher-quality websites are no harder than lower-quality sites for patients to comprehend. The Flesch-Kincaid readability test is flawed in that it considers only total number of syllables per word and words per sentence, not nontextual elements of patient education materials, such as illustrations on a website. The 10.98 mean grade level found in our study is higher than the levels found for most studies reviewed by Yi and colleagues.¹⁹

This study had several limitations. During an Internet search, the number of websites a user visits drops precipitously after the first page of results. Studies have shown the top 20 sites in a given search receive 97% of the views, and the top 3 receive 58.4%. Whether patients visit websites far down in the list of 150 we found in our given search is unknown. Last, the Flesch-Kincaid readability test is flawed in several ways but nevertheless is used extensively in research. Grading is based on number of words and syllables used in a given sentence; it does not take into account the complexity or common usage of a given word or definition. Therefore, websites may receive low Flesch-Kincaid scores—indicating ease of reading—despite their use of complex medical terminology and jargon that complicate patients’ comprehension of the material.

Conclusion

Numerous authors have evaluated orthopedic patients’ accessing of medical information from the Internet. Although the Internet makes access easier, unreliable content can lead patients to develop certain notions about the direction of their care and certain expectations regarding their clinical outcomes. With there being no regulatory body monitoring content, the peer review process, an essential feature of academic publishing, can be easily circumvented.²⁵

In this study, the highest-quality websites had academic affiliations. Quality of information about rotator cuff repairs was similar to what was found for other orthopedic topics in comparable studies. Surprisingly, there was little change in authorship and content of web information between our 2 search periods (2011, 2014). Although there has been a rapid increase in the number of medical websites, quality of content seems not to have changed significantly. Patients look to physicians for guidance but increasingly are accessing the Internet for additional information. It is essential that physicians understand the quality of information available on the Internet when counseling patients regarding surgery.

Patients are learning about health and disease more independently than before, but such self-education may pose a unique challenge for practicing physicians. Although educated patients can assist in the critical appraisal of treatment options,¹ misinformed patients may have preconceived treatment biases and unrealistic expectations. More than 66 million Americans use the Internet daily, and recent surveys have shown 86% have used the Internet for health-related information.^2,3 With Internet use increasing, the number of patients turning to the web for medical information is increasing as well.⁴ For many patients, this information can be useful in making decisions about their health and health care.⁵

Although accessing medical information from the Internet has grown exponentially, analysis of information quality has grown considerably slower.⁶ With no regulatory body monitoring content, there is easy circumvention of the peer review process, an essential feature of academic publishing.⁷ With no external regulation, the information retrieved may be incorrect, outdated, or misleading. Many orthopedic studies have analyzed Internet content about numerous diagnoses.^3-6,8-18 Most of these studies have found this information highly variable and of poor quality.

We conducted a study to evaluate and analyze rotator cuff repair information available to the general public through the Internet; to assess changes in the quality of information over time; to determine if sites sponsored by academic institutions offered higher-quality information; and to assess whether the readability of the material varied according to DISCERN scores.

Rotator cuff repairs are among the most common surgeries performed by orthopedic surgeons. To our knowledge, this is the first study to assess the quality of web information about rotator cuff repairs. We hypothesized that the quality of information would positively correlate with the reading level of the material presented, that academic institutions would present the highest-quality information, and that the type of information presented would change over time.

Materials and Methods

We used the search phrase rotator cuff repair on the 3 most popular search engines: Google, Yahoo!, and Bing. Google is the dominant engine, taking 83.06% of total market share, followed by Yahoo! (6.86%) and Bing (4.27%).5 The first 50 websites identified by each search engine were selected for evaluation, excluding duplicates or overlapping websites. Similarly, advertisements and strictly video results lacking text were excluded. After each engine was queried, a master list of 150 websites was created for individual evaluation and assessment. To assess changes in results over time, we performed 2 searches, on November 16, 2011, and May 18, 2014.

The content of each website was analyzed for authorship, ability to contact the author, discussion of disorder, surgical treatment, complications, surgical eligibility, rehabilitation, other treatment options, and use of peer-reviewed sources. Authorship was placed in 1 of 6 categories:

1. Academic—university-affiliated physician or research group.

2. Private—physician or group without stated affiliation to an academic organization.

3. Industry—manufacturing or marketing company advertising a product or service for profit.

4. News source—bulletin or article without affiliation to a hospital or an academic institution.

5. Public education—individual or organization with noncommercial website providing third-party information (eg, Wikipedia, About.com).

6. Blog—website publishing an individual’s personal experiences in diary or journal form.

Websites were also assessed for accuracy and validity based on presence or absence of Health On the Net code (HONcode) certification and DISCERN score. Designed by the Health On the Net Foundation in 1996, HONcode provides a framework for disseminating high-quality medical information over the web.¹⁹ Website owners can request that their sites be evaluated for HONcode certification; a site that qualifies can display the HONcode seal.²⁰ The DISCERN project, initially funded by the National Health Service in the United Kingdom, judges the quality of written information available on health-related websites.²¹ It determines the quality of a publication on the basis of 16 questions: The first 8 address the publication’s reliability, the next 7 involve specific details of treatment choices, and the last is an overall rating of the website.

Website readability was assessed with the Flesch-Kincaid test. This test, designed under contract with the US Navy in 1975, has been used in other orthopedic studies.¹⁹ Regression analysis was performed to check for correlation between website readability and DISCERN score. Analysis of variance was used to analyze differences between scores.

Results

We performed a comprehensive analysis of the top 50 websites from each of the 3 search engines (N = 150 websites) (Figures 1–5, Table). Regarding authorship, our 2 searches demonstrated similar values (Figure 1). In 2011, 21% of websites were associated with an academic institution, 38% were authored by private physicians or hospital or physician groups not associated with an academic institution, 11.5% were industry-sponsored, 5% were news bulletins or media reports, 21.5% were public education websites, and 3% were personal blogs. Our 2014 search found a similar distribution of contributors. Between 2011 and 2014, the largest change was in academic authors, which decreased by 7%, from 21% to 14%. Percentage of websites authored by private physicians remained constant from the first to the second search: 38%.

When the 2011 and 2014 website content was compared, several changes were noted. Percentage of websites providing an author contact method increased from 21% to 50% (Figure 2), percentage detailing rotator cuff repairs increased from 82% to 91%, and percentage introducing treatment options in addition to surgical management increased from 11.5% to 61%. Percentage discussing surgical eligibility, however, decreased from 43% to 18%. Percentage citing peer-reviewed sources remained relatively constant (28%, 26%), as did percentage discussing surgical technique for rotator cuff repair (55%, 59%) (Figure 3). A major decrease was found in percentage of websites discussing surgical complications, 42% in 2011 down to 25% in 2014, whereas a major increase was found in percentage discussing rehabilitation, from 39% in 2011 up to 73% in 2014. In 2014, no websites discussed double- versus single-row surgery—compared with 6% in 2011. False claims remained low between 2011 and 2014. In both searches, no website guaranteed a return to sport, and few made claims of painless or bloodless surgery.

DISCERN scores for websites found during the 2014 search were averaged for each of the 6 authorship groups (Figure 4). The highest DISCERN scores were given to academic institution websites (51.6) and public education websites (49). For the academic websites, this difference was significant relative to news, blog, and private physician websites (Ps = .012, .001, .001) The lowest DISCERN scores were given to news organization websites and personal blogs. DISCERN scores were 43.8 for industry sources and 40.7 for private physician groups; the difference was not significant (P = .229). Overall mean DISCERN score for all websites was 44. Eleven percent of websites were HONcode-certified.

No correlation was found between website readability and DISCERN score; correlation coefficient r was .01 (Figure 5). For the websites in 2014, mean Flesch-Kincaid readability score was 50.17, and mean grade level was 10.98; coefficient of determination r² was 0.00012.

The Table compares our data with data from other orthopedic studies that have analyzed the quality of Internet information about various orthopedic injuries, diseases, and procedures.^{3-6,8,9,11-18} With its mean DISCERN score of 44, the present rotator cuff tear study was ranked third of 6 studies that have used this scoring system to analyze website content. Of these 6 studies, those reviewing osteosarcoma and juvenile idiopathic arthritis were ranked highest (mean scores, 49.8 and 48.9, respectively), and the study reviewing scoliosis surgery was ranked lowest (38.9). Bruce-Brand and colleagues9 recently found a mean DISCERN score of 41 for anterior cruciate ligament (ACL) reconstruction. When considering HONcode-certified websites, our Internet search for rotator cuff tears found the third lowest percentage, 10.5%, compared with the other studies (Table); the highest percentage, 30%, was found for websites discussing concussions in athletes. When considering authorship, our rotator cuff study found the third highest percentage, 76%, authored by academic centers, physicians, and public education websites; the highest percentage was found in websites discussing ACL reconstruction. Websites discussing ACL reconstruction also had the highest percentage of websites authored by industry.⁹

Discussion

To our knowledge, this is the first study specifically analyzing the quality of Internet information about rotator cuff repairs. A similar study, conducted by Starman and colleagues¹⁵ in 2010, addressed the quality of web information about 10 common sports medicine diagnoses, one of which was rotator cuff tears. In that study, only 16 of the websites included discussed rotator cuff tears. In addition, the authors used a customized, HONcode-based grading system to analyze each website, making their data difficult to compare across studies.

Ideally, a high-quality medical website should be written by a credible source and should cover a disorder, treatment options, eligibility, rehabilitation, and complications. As there is no standard grading system for analyzing web content about rotator cuff repairs, we analyzed the websites for specific information we thought should be included in a high-quality website (Figures 2, 3). When considering authorship, we found academic centers, private physicians, and educational sources comprised 76% of the sources; industry sources made up only 12%. Similar findings were noted by investigators analyzing Internet information about other orthopedic topics, including ACL reconstruction, lumbar arthroplasty, osteosarcoma, and cervical spine surgery.^5,11,22 Studies analyzing websites for information on ACL tears and distal radius fractures found have a higher percentage of industry-sponsored websites.^9,10

DISCERN showed that the highest-quality information came from websites with academic affiliations, consistent with previous studies,^3,9,17 and its mean score (51.6) was significantly higher than the scores for private physician websites, news sites, and blogs (Ps = .001, .016, .001); the least reliable information was from personal blogs and news outlets. Of note, mean DISCERN score was higher for the industry websites we found than for private physician websites (43.8 vs 40.7), though the difference was not significant (P = .229). Previous investigators considered number of industry-sponsored websites as a marker of poor quality of information relating to a given topic; however, given the DISCERN scores in our study, this might not necessarily be true.⁶ Based on the present study’s data, websites affiliated with academic institutions would be recommended for patients searching for high-quality information about rotator cuff tears.

Given DISCERN scores across studies, information about rotator cuff tears ranked below information about osteosarcoma and juvenile idiopathic arthritis but above information about scoliosis, cervical spine surgery, and ACL reconstruction (Table). DISCERN scores must be compared across studies, as there are no definitions for good and poor DISCERN scores.

Of the 4 studies that analyzed percentage of websites citing peer-reviewed sources, only our study and the study of cervical spine surgery¹⁸ analyzed that percentage as well as DISCERN score. Percentage citing peer-reviewed sources was 26% for rotator cuff tears and 24% for cervical spine surgery; the respective DISCERN scores were 44 and 43.6. As only these 2 studies could be compared, no real correlation between percentage of websites citing peer-reviewed sources and the quality of the content on a given topic can be assessed. More research into this relationship is needed. One already delineated association is the correlation between HONcode-certified sites and high DISCERN scores.²¹ For high-quality medical information, physicians can direct their patients both to academic institution websites and to HONcode-certified websites.

When we compared the present study with previous investigations, we found a large difference between search results for a given topic. In 2013, Duncan and colleagues⁶ and Bruce-Brand and colleagues⁹ used similar study designs (eg, search terms, search engines) for their investigations of quality of web information. Their results, however, were widely different. For example, percentages of industry authorship were 4.5% (Duncan and colleagues⁶) and 64% (Bruce-Brand and colleagues⁹). This inconsistency between studies conducted during similar periods might be related to what appears at the top of the results queue for a search. Duncan and colleagues⁶ analyzed 200 websites, Bruce-Brand and colleagues⁹ only 45. Industries may have made financial arrangements and used search engine optimization techniques to have their websites listed first in search results.

In our study, we also analyzed how web information has changed over time. On the Internet, information changes daily, and we hypothesized that the content found during our 2 searches (2011, 2014) would yield different results. Surprisingly, the data were similar, particularly concerning authorship (Figures 1, 2). In both searches, the largest authorship source was private physician or physician groups (38% in 2011 and 2014). Other authorship sources showed little change in percentage between searches. As for content, we found both increases and decreases in specific web information. Ability to contact authors increased from 21% (2011) to 50% (2014). We think it is important that websites offer a communication channel to people who read the medical information the sites provide. Percentage of websites discussing nonoperative treatment options increased from 11.5% to 61%. Therefore, patients in 2014 were being introduced to more options (in addition to surgery) for managing shoulder pain—an improvement in quality of information between the searches. Percentage of websites discussing surgical eligibility, however, decreased from 43% to 18%—a negative development in information quality. Another decrease, from 42% to 25%, was found for websites discussing surgical complications. Given the data as a whole, and our finding both negative and positive changes, it appears the quality of web content has not improved significantly. Interestingly, no websites discussed double- versus single-row surgery in 2014, but 6% did so in 2011.

Lost in the discussion of quality and reliability of information is whether patients comprehend what they are reading.²³ Yi and colleagues¹⁹ recentlyassessed the readability level of arthroscopy information in articles published online by the American Academy of Orthopaedic Surgeons (AAOS) and the Arthroscopy Association of North America (AANA). The investigators used the Flesch-Kincaid readability test to determine readability level in terms of grade level. They found that the majority of the patient education articles on the AAOS and AANA sites had a readability level far above the national average; only 4 articles were written at or below the eighth-grade level, the current average reading level in the United States.²⁴ Information that is not comprehensible is of no use to patients, and information that physicians and researchers consider high-quality might not be what patients consider high-quality. As we pursue higher-quality web content, we need to consider that its audience includes nonmedical readers, our patients. In the present study, we found that the readability of a website had no correlation with the site’s DISCERN score (Figure 5). Therefore, for information about rotator cuff repairs, higher-quality websites are no harder than lower-quality sites for patients to comprehend. The Flesch-Kincaid readability test is flawed in that it considers only total number of syllables per word and words per sentence, not nontextual elements of patient education materials, such as illustrations on a website. The 10.98 mean grade level found in our study is higher than the levels found for most studies reviewed by Yi and colleagues.¹⁹

This study had several limitations. During an Internet search, the number of websites a user visits drops precipitously after the first page of results. Studies have shown the top 20 sites in a given search receive 97% of the views, and the top 3 receive 58.4%. Whether patients visit websites far down in the list of 150 we found in our given search is unknown. Last, the Flesch-Kincaid readability test is flawed in several ways but nevertheless is used extensively in research. Grading is based on number of words and syllables used in a given sentence; it does not take into account the complexity or common usage of a given word or definition. Therefore, websites may receive low Flesch-Kincaid scores—indicating ease of reading—despite their use of complex medical terminology and jargon that complicate patients’ comprehension of the material.

Conclusion

Numerous authors have evaluated orthopedic patients’ accessing of medical information from the Internet. Although the Internet makes access easier, unreliable content can lead patients to develop certain notions about the direction of their care and certain expectations regarding their clinical outcomes. With there being no regulatory body monitoring content, the peer review process, an essential feature of academic publishing, can be easily circumvented.²⁵

In this study, the highest-quality websites had academic affiliations. Quality of information about rotator cuff repairs was similar to what was found for other orthopedic topics in comparable studies. Surprisingly, there was little change in authorship and content of web information between our 2 search periods (2011, 2014). Although there has been a rapid increase in the number of medical websites, quality of content seems not to have changed significantly. Patients look to physicians for guidance but increasingly are accessing the Internet for additional information. It is essential that physicians understand the quality of information available on the Internet when counseling patients regarding surgery.

Patients are learning about health and disease more independently than before, but such self-education may pose a unique challenge for practicing physicians. Although educated patients can assist in the critical appraisal of treatment options,¹ misinformed patients may have preconceived treatment biases and unrealistic expectations. More than 66 million Americans use the Internet daily, and recent surveys have shown 86% have used the Internet for health-related information.^2,3 With Internet use increasing, the number of patients turning to the web for medical information is increasing as well.⁴ For many patients, this information can be useful in making decisions about their health and health care.⁵

Although accessing medical information from the Internet has grown exponentially, analysis of information quality has grown considerably slower.⁶ With no regulatory body monitoring content, there is easy circumvention of the peer review process, an essential feature of academic publishing.⁷ With no external regulation, the information retrieved may be incorrect, outdated, or misleading. Many orthopedic studies have analyzed Internet content about numerous diagnoses.^3-6,8-18 Most of these studies have found this information highly variable and of poor quality.

We conducted a study to evaluate and analyze rotator cuff repair information available to the general public through the Internet; to assess changes in the quality of information over time; to determine if sites sponsored by academic institutions offered higher-quality information; and to assess whether the readability of the material varied according to DISCERN scores.

Rotator cuff repairs are among the most common surgeries performed by orthopedic surgeons. To our knowledge, this is the first study to assess the quality of web information about rotator cuff repairs. We hypothesized that the quality of information would positively correlate with the reading level of the material presented, that academic institutions would present the highest-quality information, and that the type of information presented would change over time.

Materials and Methods

We used the search phrase rotator cuff repair on the 3 most popular search engines: Google, Yahoo!, and Bing. Google is the dominant engine, taking 83.06% of total market share, followed by Yahoo! (6.86%) and Bing (4.27%).5 The first 50 websites identified by each search engine were selected for evaluation, excluding duplicates or overlapping websites. Similarly, advertisements and strictly video results lacking text were excluded. After each engine was queried, a master list of 150 websites was created for individual evaluation and assessment. To assess changes in results over time, we performed 2 searches, on November 16, 2011, and May 18, 2014.

The content of each website was analyzed for authorship, ability to contact the author, discussion of disorder, surgical treatment, complications, surgical eligibility, rehabilitation, other treatment options, and use of peer-reviewed sources. Authorship was placed in 1 of 6 categories:

1. Academic—university-affiliated physician or research group.

2. Private—physician or group without stated affiliation to an academic organization.

3. Industry—manufacturing or marketing company advertising a product or service for profit.

4. News source—bulletin or article without affiliation to a hospital or an academic institution.

5. Public education—individual or organization with noncommercial website providing third-party information (eg, Wikipedia, About.com).

6. Blog—website publishing an individual’s personal experiences in diary or journal form.

Websites were also assessed for accuracy and validity based on presence or absence of Health On the Net code (HONcode) certification and DISCERN score. Designed by the Health On the Net Foundation in 1996, HONcode provides a framework for disseminating high-quality medical information over the web.¹⁹ Website owners can request that their sites be evaluated for HONcode certification; a site that qualifies can display the HONcode seal.²⁰ The DISCERN project, initially funded by the National Health Service in the United Kingdom, judges the quality of written information available on health-related websites.²¹ It determines the quality of a publication on the basis of 16 questions: The first 8 address the publication’s reliability, the next 7 involve specific details of treatment choices, and the last is an overall rating of the website.

Website readability was assessed with the Flesch-Kincaid test. This test, designed under contract with the US Navy in 1975, has been used in other orthopedic studies.¹⁹ Regression analysis was performed to check for correlation between website readability and DISCERN score. Analysis of variance was used to analyze differences between scores.

Results

We performed a comprehensive analysis of the top 50 websites from each of the 3 search engines (N = 150 websites) (Figures 1–5, Table). Regarding authorship, our 2 searches demonstrated similar values (Figure 1). In 2011, 21% of websites were associated with an academic institution, 38% were authored by private physicians or hospital or physician groups not associated with an academic institution, 11.5% were industry-sponsored, 5% were news bulletins or media reports, 21.5% were public education websites, and 3% were personal blogs. Our 2014 search found a similar distribution of contributors. Between 2011 and 2014, the largest change was in academic authors, which decreased by 7%, from 21% to 14%. Percentage of websites authored by private physicians remained constant from the first to the second search: 38%.

When the 2011 and 2014 website content was compared, several changes were noted. Percentage of websites providing an author contact method increased from 21% to 50% (Figure 2), percentage detailing rotator cuff repairs increased from 82% to 91%, and percentage introducing treatment options in addition to surgical management increased from 11.5% to 61%. Percentage discussing surgical eligibility, however, decreased from 43% to 18%. Percentage citing peer-reviewed sources remained relatively constant (28%, 26%), as did percentage discussing surgical technique for rotator cuff repair (55%, 59%) (Figure 3). A major decrease was found in percentage of websites discussing surgical complications, 42% in 2011 down to 25% in 2014, whereas a major increase was found in percentage discussing rehabilitation, from 39% in 2011 up to 73% in 2014. In 2014, no websites discussed double- versus single-row surgery—compared with 6% in 2011. False claims remained low between 2011 and 2014. In both searches, no website guaranteed a return to sport, and few made claims of painless or bloodless surgery.

DISCERN scores for websites found during the 2014 search were averaged for each of the 6 authorship groups (Figure 4). The highest DISCERN scores were given to academic institution websites (51.6) and public education websites (49). For the academic websites, this difference was significant relative to news, blog, and private physician websites (Ps = .012, .001, .001) The lowest DISCERN scores were given to news organization websites and personal blogs. DISCERN scores were 43.8 for industry sources and 40.7 for private physician groups; the difference was not significant (P = .229). Overall mean DISCERN score for all websites was 44. Eleven percent of websites were HONcode-certified.

No correlation was found between website readability and DISCERN score; correlation coefficient r was .01 (Figure 5). For the websites in 2014, mean Flesch-Kincaid readability score was 50.17, and mean grade level was 10.98; coefficient of determination r² was 0.00012.

The Table compares our data with data from other orthopedic studies that have analyzed the quality of Internet information about various orthopedic injuries, diseases, and procedures.^{3-6,8,9,11-18} With its mean DISCERN score of 44, the present rotator cuff tear study was ranked third of 6 studies that have used this scoring system to analyze website content. Of these 6 studies, those reviewing osteosarcoma and juvenile idiopathic arthritis were ranked highest (mean scores, 49.8 and 48.9, respectively), and the study reviewing scoliosis surgery was ranked lowest (38.9). Bruce-Brand and colleagues9 recently found a mean DISCERN score of 41 for anterior cruciate ligament (ACL) reconstruction. When considering HONcode-certified websites, our Internet search for rotator cuff tears found the third lowest percentage, 10.5%, compared with the other studies (Table); the highest percentage, 30%, was found for websites discussing concussions in athletes. When considering authorship, our rotator cuff study found the third highest percentage, 76%, authored by academic centers, physicians, and public education websites; the highest percentage was found in websites discussing ACL reconstruction. Websites discussing ACL reconstruction also had the highest percentage of websites authored by industry.⁹

Discussion

To our knowledge, this is the first study specifically analyzing the quality of Internet information about rotator cuff repairs. A similar study, conducted by Starman and colleagues¹⁵ in 2010, addressed the quality of web information about 10 common sports medicine diagnoses, one of which was rotator cuff tears. In that study, only 16 of the websites included discussed rotator cuff tears. In addition, the authors used a customized, HONcode-based grading system to analyze each website, making their data difficult to compare across studies.

Ideally, a high-quality medical website should be written by a credible source and should cover a disorder, treatment options, eligibility, rehabilitation, and complications. As there is no standard grading system for analyzing web content about rotator cuff repairs, we analyzed the websites for specific information we thought should be included in a high-quality website (Figures 2, 3). When considering authorship, we found academic centers, private physicians, and educational sources comprised 76% of the sources; industry sources made up only 12%. Similar findings were noted by investigators analyzing Internet information about other orthopedic topics, including ACL reconstruction, lumbar arthroplasty, osteosarcoma, and cervical spine surgery.^5,11,22 Studies analyzing websites for information on ACL tears and distal radius fractures found have a higher percentage of industry-sponsored websites.^9,10

DISCERN showed that the highest-quality information came from websites with academic affiliations, consistent with previous studies,^3,9,17 and its mean score (51.6) was significantly higher than the scores for private physician websites, news sites, and blogs (Ps = .001, .016, .001); the least reliable information was from personal blogs and news outlets. Of note, mean DISCERN score was higher for the industry websites we found than for private physician websites (43.8 vs 40.7), though the difference was not significant (P = .229). Previous investigators considered number of industry-sponsored websites as a marker of poor quality of information relating to a given topic; however, given the DISCERN scores in our study, this might not necessarily be true.⁶ Based on the present study’s data, websites affiliated with academic institutions would be recommended for patients searching for high-quality information about rotator cuff tears.

Given DISCERN scores across studies, information about rotator cuff tears ranked below information about osteosarcoma and juvenile idiopathic arthritis but above information about scoliosis, cervical spine surgery, and ACL reconstruction (Table). DISCERN scores must be compared across studies, as there are no definitions for good and poor DISCERN scores.

Of the 4 studies that analyzed percentage of websites citing peer-reviewed sources, only our study and the study of cervical spine surgery¹⁸ analyzed that percentage as well as DISCERN score. Percentage citing peer-reviewed sources was 26% for rotator cuff tears and 24% for cervical spine surgery; the respective DISCERN scores were 44 and 43.6. As only these 2 studies could be compared, no real correlation between percentage of websites citing peer-reviewed sources and the quality of the content on a given topic can be assessed. More research into this relationship is needed. One already delineated association is the correlation between HONcode-certified sites and high DISCERN scores.²¹ For high-quality medical information, physicians can direct their patients both to academic institution websites and to HONcode-certified websites.

When we compared the present study with previous investigations, we found a large difference between search results for a given topic. In 2013, Duncan and colleagues⁶ and Bruce-Brand and colleagues⁹ used similar study designs (eg, search terms, search engines) for their investigations of quality of web information. Their results, however, were widely different. For example, percentages of industry authorship were 4.5% (Duncan and colleagues⁶) and 64% (Bruce-Brand and colleagues⁹). This inconsistency between studies conducted during similar periods might be related to what appears at the top of the results queue for a search. Duncan and colleagues⁶ analyzed 200 websites, Bruce-Brand and colleagues⁹ only 45. Industries may have made financial arrangements and used search engine optimization techniques to have their websites listed first in search results.

In our study, we also analyzed how web information has changed over time. On the Internet, information changes daily, and we hypothesized that the content found during our 2 searches (2011, 2014) would yield different results. Surprisingly, the data were similar, particularly concerning authorship (Figures 1, 2). In both searches, the largest authorship source was private physician or physician groups (38% in 2011 and 2014). Other authorship sources showed little change in percentage between searches. As for content, we found both increases and decreases in specific web information. Ability to contact authors increased from 21% (2011) to 50% (2014). We think it is important that websites offer a communication channel to people who read the medical information the sites provide. Percentage of websites discussing nonoperative treatment options increased from 11.5% to 61%. Therefore, patients in 2014 were being introduced to more options (in addition to surgery) for managing shoulder pain—an improvement in quality of information between the searches. Percentage of websites discussing surgical eligibility, however, decreased from 43% to 18%—a negative development in information quality. Another decrease, from 42% to 25%, was found for websites discussing surgical complications. Given the data as a whole, and our finding both negative and positive changes, it appears the quality of web content has not improved significantly. Interestingly, no websites discussed double- versus single-row surgery in 2014, but 6% did so in 2011.

Lost in the discussion of quality and reliability of information is whether patients comprehend what they are reading.²³ Yi and colleagues¹⁹ recentlyassessed the readability level of arthroscopy information in articles published online by the American Academy of Orthopaedic Surgeons (AAOS) and the Arthroscopy Association of North America (AANA). The investigators used the Flesch-Kincaid readability test to determine readability level in terms of grade level. They found that the majority of the patient education articles on the AAOS and AANA sites had a readability level far above the national average; only 4 articles were written at or below the eighth-grade level, the current average reading level in the United States.²⁴ Information that is not comprehensible is of no use to patients, and information that physicians and researchers consider high-quality might not be what patients consider high-quality. As we pursue higher-quality web content, we need to consider that its audience includes nonmedical readers, our patients. In the present study, we found that the readability of a website had no correlation with the site’s DISCERN score (Figure 5). Therefore, for information about rotator cuff repairs, higher-quality websites are no harder than lower-quality sites for patients to comprehend. The Flesch-Kincaid readability test is flawed in that it considers only total number of syllables per word and words per sentence, not nontextual elements of patient education materials, such as illustrations on a website. The 10.98 mean grade level found in our study is higher than the levels found for most studies reviewed by Yi and colleagues.¹⁹

This study had several limitations. During an Internet search, the number of websites a user visits drops precipitously after the first page of results. Studies have shown the top 20 sites in a given search receive 97% of the views, and the top 3 receive 58.4%. Whether patients visit websites far down in the list of 150 we found in our given search is unknown. Last, the Flesch-Kincaid readability test is flawed in several ways but nevertheless is used extensively in research. Grading is based on number of words and syllables used in a given sentence; it does not take into account the complexity or common usage of a given word or definition. Therefore, websites may receive low Flesch-Kincaid scores—indicating ease of reading—despite their use of complex medical terminology and jargon that complicate patients’ comprehension of the material.

Conclusion

Numerous authors have evaluated orthopedic patients’ accessing of medical information from the Internet. Although the Internet makes access easier, unreliable content can lead patients to develop certain notions about the direction of their care and certain expectations regarding their clinical outcomes. With there being no regulatory body monitoring content, the peer review process, an essential feature of academic publishing, can be easily circumvented.²⁵

In this study, the highest-quality websites had academic affiliations. Quality of information about rotator cuff repairs was similar to what was found for other orthopedic topics in comparable studies. Surprisingly, there was little change in authorship and content of web information between our 2 search periods (2011, 2014). Although there has been a rapid increase in the number of medical websites, quality of content seems not to have changed significantly. Patients look to physicians for guidance but increasingly are accessing the Internet for additional information. It is essential that physicians understand the quality of information available on the Internet when counseling patients regarding surgery.

Systemic cobalt toxicity has been reported in the literature after hip arthroplasty revisions for failed ceramic components secondary to third-body abrasive wear of cobalt-chrome (CoCr) components, as well as with metal-on-metal (MOM) hip arthroplasty designs. There have been several cases of systemic cobalt toxicity after revision for fractured ceramic components.^1,2 Of these 7 reported cases, all patients had neurologic complaints and 4 patients developed cardiomyopathy secondary to toxic cobalt levels, with 1 case being fatal.¹ MOM hip prostheses have also been associated with local and systemic problems secondary to metal debris. Adverse local tissue reactions have been reported to occur in up to 59% of patients, and, in some registries, the failure rate of MOM arthroplasty caused by these soft-tissue reactions is 2 to 3 times that of conventional metal-on-polyethylene design failures.^3,4 The occurrence of systemic complications from MOM total hip arthroplasty (THA) wear debris is much less common. There have been 6 cases of systemic cobalt toxicity reported in the literature resulting from MOM total hip prosthesis design.^1,2

We present a case of biopsy-confirmed cardiomyopathy secondary to cobalt toxicity from a MOM THA design with subsequent requirement for left ventricular assist device (LVAD) implantation despite prosthesis removal. To our knowledge, this is the first report in the literature of this specific implant design causing systemic cobalt toxicity. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

The patient was a healthy nondiabetic man age 54 years who presented to our clinic 6 years after undergoing left THA and 5 years after undergoing right THA with the Biomet M2a-Magnum MOM prosthesis at an outside facility. The left-side components placed at the index procedure were a size 50 cup, 44 magnum head, 10 Taperloc stem (Biomet), and +9 neck. The right-side components were a size 52 cup, 46 magnum head, 10 Taperloc stem, and +3 neck. The patient emphasized that he was very happy with his hip prostheses and denied groin or thigh pain. His medical history was significant for exogenous obesity, and he denied any history of alcohol, tobacco, steroid, or recreational drug use.

The patient’s review of systems suggested that, approximately 11 months prior to presentation at our facility, he began having difficulty with his activities of daily living secondary to chest pressure with exertion, fatigue, and associated diaphoresis. He complained of decreased sensation in his feet bilaterally but denied any hearing loss, tinnitus, or vision changes. He underwent evaluation of the new-onset chest discomfort with a cardiac stress test that suggested no active cardiac ischemia. An echocardiogram revealed mitral regurgitation, stage II diastolic dysfunction with a left ventricular ejection fraction of 55%. Additionally, during this time period, the patient was being followed by his local orthopedic surgeon for an elevated cobalt level of 120 ppb and a chromium level of 109 ppb. The patient was referred to our clinic for recommendations regarding the elevated metal-ion levels. Upon initial evaluation, the patient denied any hip or groin pain. His physical examination revealed a nonantalgic gait with full range of motion and no signs of instability, tenderness, or masses. The patient was also noted to have no vibratory sensation in his feet bilaterally. The plain radiographs indicated bilateral MOM THA with acetabular inclination levels of 55º on the right and left sides. No cystic changes or other worrisome signs that would suggest implant loosening or failure were present (Figure 1). The serum metal levels were repeated and showed a cobalt level of 189 ppb and a chromium level of 71 ppb. Whole venous blood samples were drawn at our request using trace element tubes and were sent to Medtox Laboratories Inc. for analysis. Other pertinent laboratory values, including hematocrit and thyroid levels, were within normal limits. Because of concerns of systemic toxicity from significantly elevated cobalt and chromium levels, the patient elected to proceed with revision of the MOM components.

During the preoperative medical evaluation, the patient’s cardiac status was a concern, and the etiology of the cardiac dysfunction was unclear. Cardiac magnetic resonance imaging (MRI), which was performed to evaluate the extent and etiology of cardiac dysfunction, showed biventricular dysfunction. To evaluate the underlying myocardial tissue characteristics, delayed contrast imaging was performed and showed diffuse myocardial hyperenhancement of the anterior, lateral, and apical walls, with sparing of the base and midseptum. This type of extensive hyperenhancement is commonly seen with cardiac amyloidosis; however, the blood-pool kinetics during contrast administration is unusual for amyloidosis, as well as the diffuse edema noted on T2-weighted MRI. Importantly, cardiac MRI is very specific in excluding alternative diagnoses, such as postinfarct, infiltrative, acquired, viral, or alcoholic/drugs of abuse etiologies. In the absence of amyloidosis, the only other pattern that would be consistent with symptoms was diffuse, fulminant myocarditis of toxic origin lacking clinical evidence for an infectious origin. The patient’s prior exposure to cobalt was noted. Thus, the hyperenhancement and edema could be strong supportive evidence of cobalt infiltration, despite no reported cases in the literature of cobalt cardiomyopathy found on cardiac MRI.

Additional workup was initiated, and cardiac catheterization showed that the patient continued to decompensate, with worsening global left ventricular dysfunction with an ejection fraction of 30% without evidence of coronary artery disease. Also, he was noted to have mild renal impairment with a blood urea nitrogen level of 31 mg/dL and a creatinine level of 1.7 mg/dL. The etiology of the renal impairment was unknown and had not been established, according to the patient and his wife. The renal impairment was not thought to be caused by the elevated metal ions levels but likely resulted from prerenal azotemia secondary to decreased cardiac output. During catheterization, an endomyocardial biopsy was performed and the tissue sent to the Mayo Clinic pathology department for analysis. The sample showed myocyte hypertrophy and interstitial fibrosis with scattered myofibers containing large cytoplasmic vacuoles. Also present was karyomegaly consistent with myocyte hypertrophy (Figures 2A, 2B). Trichrome stain confirmed replacement of myofibers by collagen (Figure 2C). Electron microscopy performed on a paraffin block showed reduced contractile elements, vacuolar spaces, and increased lipofuscin. The findings were very consistent with, but not specific for, cardiomyopathy from cobalt toxicity. No evidence of an inflammatory infiltrate was identified. The diagnosis was cobalt cardiomyopathy based on biopsy, presentation, cobalt levels, and intraoperative findings.

The patient was admitted to the cardiac intensive care unit preoperatively and optimized with inotropic agents. A multidisciplinary consultation with the cardiology and anesthesia departments was obtained. Both recommended cardiac anesthesia with intraoperative Swan-Ganz catheter and transesophageal echo monitoring. Assuming that the patient remained hemodynamically stable with limited blood loss and the first hip was timely performed, the cardiology department recommended a single surgery, because fewer risks and complications could be expected than from a staged procedure. Subsequently, surgery was performed on the left hip via a conservative anterior approach on the fracture table. The patient remained stable with limited blood loss. During the same operating room time, revision of the right hip was performed using an anterior approach. The intraoperative findings showed evidence of pseudotumors in the adjacent soft tissues and abundant brown, creamy fluid upon entering the joint capsule, consistent with a metallic appearance. Both hips showed similar prosthetic findings. There was no significant visible wear of the large diameter metal heads or gross abnormality of the acetabular components. The trunnion area on both femoral implants was abnormal, revealing a black coating suggestive of marked corrosion. The components were all well fixed, without visible damage, and, because of his fragile cardiac status, the patient’s acetabular components were not revised. The trunnions were cleaned and the femoral heads were revised to active articulation dual-mobility metal-on-polyethylene constructs using 28-mm Biolox Option ceramic (CeramTec). The tissue specimens from the operation showed chronic inflammation with areas of fibroconnective tissue and bland fibrinoid necrosis with extensive brown pigment-laden macrophage reaction. The intraoperative cultures were negative.

The patient tolerated the surgery without complication, and his postoperative period was without incident. Nine months after surgery, the patient’s cobalt and chromium levels had declined to 16 ppb and 32 ppb, respectively (normal, <1 ppb). However, his cardiac status continued to worsen with significant shortness of breath and bilateral lower extremity edema despite diuresis. Follow-up cardiac MRI indicated progressive left and right dysfunction with ejection fractions of 23% and 25%, respectively. After progressive heart-failure symptoms, the patient was admitted to the hospital for severe congestive heart failure and underwent implantation of a HeartWare LVAD with tricuspid valve repair using an Edwards annuloplasty ring. He has since had a cardiac transplant and is doing well.

Discussion

To our knowledge, this is the first reported case of cardiomyopathy in a patient with elevated cobalt ion levels and a Biomet M2a-Magnum hip prosthesis. This is also the first reported case of cardiac MRI–defined cobalt cardiomyopathy. The cobalt levels seen in this patient were similar to those of other cases with systemic cobalt toxicity from a MOM hip construct. Mao and colleagues⁵ reported 2 cases of systemic cobalt toxicity in 2 patients with articular surface replacement hip prostheses.One patient presented with mild groin pain, neurologic symptoms, and a cobalt level of 410 ppb 5 years after her index procedure. The other patient presented with cardiac and neurologic symptoms but no hip complaints. The patient’s cobalt levels ranged from 185 ppb to 210 ppb. Both patients improved after their revision surgery, and their cobalt levels decreased. The 2 patients in Tower’s report⁶ were 49-year-old men who had articular surface replacement implants (DePuy). One patient who presented with progressive hip pain 11 months postoperatively developed neurologic symptoms and cardiomyopathy, with cobalt levels of 83 ppb before revision surgery 43 months after his index procedure. The other patient presented with hip pain and vertigo, headaches, fatigue, and dyspnea. He underwent hip revision 40 months postoperatively and required closed reduction under sedation for dislocation. Finally, and most recently, Allen and colleagues² reported a 59-year-old woman with a cobalt level of 287 ppb whose symptoms did not resolve after implantation of an LVAD or cardiac transplantation but only after removal of her bilateral hip prosthesis. Our case is most similar to this report but significantly adds to the literature in 2 distinct manners: (1) Biomet M2a-Magnum has not been implicated in cobalt toxicity; and (2) this is the first reported use of dedicated cardiac MRI to noninvasively define underlying cardiac pathology.

The cardiac manifestations secondary to systemic cobalt toxicity in this patient represent a frightening consequence of MOM prosthetic wear. The effects of cobalt toxicity on cardiac tissues were first described in a series of alcoholic patients from Manchester in 1900;⁷ however, it was not until 1967, in a series of patients in Quebec, that cobalt was found to be the inciting factor. In the modern era, hip arthroplasty techniques resulting in excessive cobalt and chromium wear have demonstrated the same findings of myocyte hypertrophy, interstitial fibrosis, and scattered myofibers containing large cytoplasmic inclusions.^8,9 The patient presented here has pathologic findings consistent with previous cases of cobalt cardiomyopathy; however, in the other cases of cardiomyopathy due to MOM total hip components, the patients’ cardiac conditions improved after the prostheses were revised and the cobalt levels began to diminish.^5,6In our case, the patient has sustained permanent damage to his myocardium and a progressive decline in his cardiac status, which is a deviation from reported cases as of 2014.

While there is no guideline to unequivocally diagnose cobalt cardiomyopathy, the constellation of findings, including pathologic, biologic, blood levels, imaging, and surgical, all uniformly indicate a unifying diagnosis. The lack of improvement after prosthetic device removal supports a diagnosis of permanent myocardial damage, which is consistent with cardiomyopathy of advanced toxic etiology.

Conclusion

This case presents a patient with bilateral MOM THAs, acetabular cup inclinations of greater than 55º, renal impairment, and cobalt levels greater than 60 ppb, with occult cardiac failure leading to LVAD implantation as a prelude to cardiac transplantation in order to avoid certain death. These factors have been shown, in prior case reports, to be associated with cardiac damage that may be reversible.⁶ However; it is important for orthopedic surgeons to recognize that certain hip prostheses can be associated or lead to irreversible cardiac damage.

Systemic cobalt toxicity has been reported in the literature after hip arthroplasty revisions for failed ceramic components secondary to third-body abrasive wear of cobalt-chrome (CoCr) components, as well as with metal-on-metal (MOM) hip arthroplasty designs. There have been several cases of systemic cobalt toxicity after revision for fractured ceramic components.^1,2 Of these 7 reported cases, all patients had neurologic complaints and 4 patients developed cardiomyopathy secondary to toxic cobalt levels, with 1 case being fatal.¹ MOM hip prostheses have also been associated with local and systemic problems secondary to metal debris. Adverse local tissue reactions have been reported to occur in up to 59% of patients, and, in some registries, the failure rate of MOM arthroplasty caused by these soft-tissue reactions is 2 to 3 times that of conventional metal-on-polyethylene design failures.^3,4 The occurrence of systemic complications from MOM total hip arthroplasty (THA) wear debris is much less common. There have been 6 cases of systemic cobalt toxicity reported in the literature resulting from MOM total hip prosthesis design.^1,2

We present a case of biopsy-confirmed cardiomyopathy secondary to cobalt toxicity from a MOM THA design with subsequent requirement for left ventricular assist device (LVAD) implantation despite prosthesis removal. To our knowledge, this is the first report in the literature of this specific implant design causing systemic cobalt toxicity. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

The patient was a healthy nondiabetic man age 54 years who presented to our clinic 6 years after undergoing left THA and 5 years after undergoing right THA with the Biomet M2a-Magnum MOM prosthesis at an outside facility. The left-side components placed at the index procedure were a size 50 cup, 44 magnum head, 10 Taperloc stem (Biomet), and +9 neck. The right-side components were a size 52 cup, 46 magnum head, 10 Taperloc stem, and +3 neck. The patient emphasized that he was very happy with his hip prostheses and denied groin or thigh pain. His medical history was significant for exogenous obesity, and he denied any history of alcohol, tobacco, steroid, or recreational drug use.

The patient’s review of systems suggested that, approximately 11 months prior to presentation at our facility, he began having difficulty with his activities of daily living secondary to chest pressure with exertion, fatigue, and associated diaphoresis. He complained of decreased sensation in his feet bilaterally but denied any hearing loss, tinnitus, or vision changes. He underwent evaluation of the new-onset chest discomfort with a cardiac stress test that suggested no active cardiac ischemia. An echocardiogram revealed mitral regurgitation, stage II diastolic dysfunction with a left ventricular ejection fraction of 55%. Additionally, during this time period, the patient was being followed by his local orthopedic surgeon for an elevated cobalt level of 120 ppb and a chromium level of 109 ppb. The patient was referred to our clinic for recommendations regarding the elevated metal-ion levels. Upon initial evaluation, the patient denied any hip or groin pain. His physical examination revealed a nonantalgic gait with full range of motion and no signs of instability, tenderness, or masses. The patient was also noted to have no vibratory sensation in his feet bilaterally. The plain radiographs indicated bilateral MOM THA with acetabular inclination levels of 55º on the right and left sides. No cystic changes or other worrisome signs that would suggest implant loosening or failure were present (Figure 1). The serum metal levels were repeated and showed a cobalt level of 189 ppb and a chromium level of 71 ppb. Whole venous blood samples were drawn at our request using trace element tubes and were sent to Medtox Laboratories Inc. for analysis. Other pertinent laboratory values, including hematocrit and thyroid levels, were within normal limits. Because of concerns of systemic toxicity from significantly elevated cobalt and chromium levels, the patient elected to proceed with revision of the MOM components.

During the preoperative medical evaluation, the patient’s cardiac status was a concern, and the etiology of the cardiac dysfunction was unclear. Cardiac magnetic resonance imaging (MRI), which was performed to evaluate the extent and etiology of cardiac dysfunction, showed biventricular dysfunction. To evaluate the underlying myocardial tissue characteristics, delayed contrast imaging was performed and showed diffuse myocardial hyperenhancement of the anterior, lateral, and apical walls, with sparing of the base and midseptum. This type of extensive hyperenhancement is commonly seen with cardiac amyloidosis; however, the blood-pool kinetics during contrast administration is unusual for amyloidosis, as well as the diffuse edema noted on T2-weighted MRI. Importantly, cardiac MRI is very specific in excluding alternative diagnoses, such as postinfarct, infiltrative, acquired, viral, or alcoholic/drugs of abuse etiologies. In the absence of amyloidosis, the only other pattern that would be consistent with symptoms was diffuse, fulminant myocarditis of toxic origin lacking clinical evidence for an infectious origin. The patient’s prior exposure to cobalt was noted. Thus, the hyperenhancement and edema could be strong supportive evidence of cobalt infiltration, despite no reported cases in the literature of cobalt cardiomyopathy found on cardiac MRI.

Additional workup was initiated, and cardiac catheterization showed that the patient continued to decompensate, with worsening global left ventricular dysfunction with an ejection fraction of 30% without evidence of coronary artery disease. Also, he was noted to have mild renal impairment with a blood urea nitrogen level of 31 mg/dL and a creatinine level of 1.7 mg/dL. The etiology of the renal impairment was unknown and had not been established, according to the patient and his wife. The renal impairment was not thought to be caused by the elevated metal ions levels but likely resulted from prerenal azotemia secondary to decreased cardiac output. During catheterization, an endomyocardial biopsy was performed and the tissue sent to the Mayo Clinic pathology department for analysis. The sample showed myocyte hypertrophy and interstitial fibrosis with scattered myofibers containing large cytoplasmic vacuoles. Also present was karyomegaly consistent with myocyte hypertrophy (Figures 2A, 2B). Trichrome stain confirmed replacement of myofibers by collagen (Figure 2C). Electron microscopy performed on a paraffin block showed reduced contractile elements, vacuolar spaces, and increased lipofuscin. The findings were very consistent with, but not specific for, cardiomyopathy from cobalt toxicity. No evidence of an inflammatory infiltrate was identified. The diagnosis was cobalt cardiomyopathy based on biopsy, presentation, cobalt levels, and intraoperative findings.

The patient was admitted to the cardiac intensive care unit preoperatively and optimized with inotropic agents. A multidisciplinary consultation with the cardiology and anesthesia departments was obtained. Both recommended cardiac anesthesia with intraoperative Swan-Ganz catheter and transesophageal echo monitoring. Assuming that the patient remained hemodynamically stable with limited blood loss and the first hip was timely performed, the cardiology department recommended a single surgery, because fewer risks and complications could be expected than from a staged procedure. Subsequently, surgery was performed on the left hip via a conservative anterior approach on the fracture table. The patient remained stable with limited blood loss. During the same operating room time, revision of the right hip was performed using an anterior approach. The intraoperative findings showed evidence of pseudotumors in the adjacent soft tissues and abundant brown, creamy fluid upon entering the joint capsule, consistent with a metallic appearance. Both hips showed similar prosthetic findings. There was no significant visible wear of the large diameter metal heads or gross abnormality of the acetabular components. The trunnion area on both femoral implants was abnormal, revealing a black coating suggestive of marked corrosion. The components were all well fixed, without visible damage, and, because of his fragile cardiac status, the patient’s acetabular components were not revised. The trunnions were cleaned and the femoral heads were revised to active articulation dual-mobility metal-on-polyethylene constructs using 28-mm Biolox Option ceramic (CeramTec). The tissue specimens from the operation showed chronic inflammation with areas of fibroconnective tissue and bland fibrinoid necrosis with extensive brown pigment-laden macrophage reaction. The intraoperative cultures were negative.

The patient tolerated the surgery without complication, and his postoperative period was without incident. Nine months after surgery, the patient’s cobalt and chromium levels had declined to 16 ppb and 32 ppb, respectively (normal, <1 ppb). However, his cardiac status continued to worsen with significant shortness of breath and bilateral lower extremity edema despite diuresis. Follow-up cardiac MRI indicated progressive left and right dysfunction with ejection fractions of 23% and 25%, respectively. After progressive heart-failure symptoms, the patient was admitted to the hospital for severe congestive heart failure and underwent implantation of a HeartWare LVAD with tricuspid valve repair using an Edwards annuloplasty ring. He has since had a cardiac transplant and is doing well.

Discussion

To our knowledge, this is the first reported case of cardiomyopathy in a patient with elevated cobalt ion levels and a Biomet M2a-Magnum hip prosthesis. This is also the first reported case of cardiac MRI–defined cobalt cardiomyopathy. The cobalt levels seen in this patient were similar to those of other cases with systemic cobalt toxicity from a MOM hip construct. Mao and colleagues⁵ reported 2 cases of systemic cobalt toxicity in 2 patients with articular surface replacement hip prostheses.One patient presented with mild groin pain, neurologic symptoms, and a cobalt level of 410 ppb 5 years after her index procedure. The other patient presented with cardiac and neurologic symptoms but no hip complaints. The patient’s cobalt levels ranged from 185 ppb to 210 ppb. Both patients improved after their revision surgery, and their cobalt levels decreased. The 2 patients in Tower’s report⁶ were 49-year-old men who had articular surface replacement implants (DePuy). One patient who presented with progressive hip pain 11 months postoperatively developed neurologic symptoms and cardiomyopathy, with cobalt levels of 83 ppb before revision surgery 43 months after his index procedure. The other patient presented with hip pain and vertigo, headaches, fatigue, and dyspnea. He underwent hip revision 40 months postoperatively and required closed reduction under sedation for dislocation. Finally, and most recently, Allen and colleagues² reported a 59-year-old woman with a cobalt level of 287 ppb whose symptoms did not resolve after implantation of an LVAD or cardiac transplantation but only after removal of her bilateral hip prosthesis. Our case is most similar to this report but significantly adds to the literature in 2 distinct manners: (1) Biomet M2a-Magnum has not been implicated in cobalt toxicity; and (2) this is the first reported use of dedicated cardiac MRI to noninvasively define underlying cardiac pathology.

The cardiac manifestations secondary to systemic cobalt toxicity in this patient represent a frightening consequence of MOM prosthetic wear. The effects of cobalt toxicity on cardiac tissues were first described in a series of alcoholic patients from Manchester in 1900;⁷ however, it was not until 1967, in a series of patients in Quebec, that cobalt was found to be the inciting factor. In the modern era, hip arthroplasty techniques resulting in excessive cobalt and chromium wear have demonstrated the same findings of myocyte hypertrophy, interstitial fibrosis, and scattered myofibers containing large cytoplasmic inclusions.^8,9 The patient presented here has pathologic findings consistent with previous cases of cobalt cardiomyopathy; however, in the other cases of cardiomyopathy due to MOM total hip components, the patients’ cardiac conditions improved after the prostheses were revised and the cobalt levels began to diminish.^5,6In our case, the patient has sustained permanent damage to his myocardium and a progressive decline in his cardiac status, which is a deviation from reported cases as of 2014.

While there is no guideline to unequivocally diagnose cobalt cardiomyopathy, the constellation of findings, including pathologic, biologic, blood levels, imaging, and surgical, all uniformly indicate a unifying diagnosis. The lack of improvement after prosthetic device removal supports a diagnosis of permanent myocardial damage, which is consistent with cardiomyopathy of advanced toxic etiology.

Conclusion

This case presents a patient with bilateral MOM THAs, acetabular cup inclinations of greater than 55º, renal impairment, and cobalt levels greater than 60 ppb, with occult cardiac failure leading to LVAD implantation as a prelude to cardiac transplantation in order to avoid certain death. These factors have been shown, in prior case reports, to be associated with cardiac damage that may be reversible.⁶ However; it is important for orthopedic surgeons to recognize that certain hip prostheses can be associated or lead to irreversible cardiac damage.

Systemic cobalt toxicity has been reported in the literature after hip arthroplasty revisions for failed ceramic components secondary to third-body abrasive wear of cobalt-chrome (CoCr) components, as well as with metal-on-metal (MOM) hip arthroplasty designs. There have been several cases of systemic cobalt toxicity after revision for fractured ceramic components.^1,2 Of these 7 reported cases, all patients had neurologic complaints and 4 patients developed cardiomyopathy secondary to toxic cobalt levels, with 1 case being fatal.¹ MOM hip prostheses have also been associated with local and systemic problems secondary to metal debris. Adverse local tissue reactions have been reported to occur in up to 59% of patients, and, in some registries, the failure rate of MOM arthroplasty caused by these soft-tissue reactions is 2 to 3 times that of conventional metal-on-polyethylene design failures.^3,4 The occurrence of systemic complications from MOM total hip arthroplasty (THA) wear debris is much less common. There have been 6 cases of systemic cobalt toxicity reported in the literature resulting from MOM total hip prosthesis design.^1,2

We present a case of biopsy-confirmed cardiomyopathy secondary to cobalt toxicity from a MOM THA design with subsequent requirement for left ventricular assist device (LVAD) implantation despite prosthesis removal. To our knowledge, this is the first report in the literature of this specific implant design causing systemic cobalt toxicity. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

The patient was a healthy nondiabetic man age 54 years who presented to our clinic 6 years after undergoing left THA and 5 years after undergoing right THA with the Biomet M2a-Magnum MOM prosthesis at an outside facility. The left-side components placed at the index procedure were a size 50 cup, 44 magnum head, 10 Taperloc stem (Biomet), and +9 neck. The right-side components were a size 52 cup, 46 magnum head, 10 Taperloc stem, and +3 neck. The patient emphasized that he was very happy with his hip prostheses and denied groin or thigh pain. His medical history was significant for exogenous obesity, and he denied any history of alcohol, tobacco, steroid, or recreational drug use.

The patient’s review of systems suggested that, approximately 11 months prior to presentation at our facility, he began having difficulty with his activities of daily living secondary to chest pressure with exertion, fatigue, and associated diaphoresis. He complained of decreased sensation in his feet bilaterally but denied any hearing loss, tinnitus, or vision changes. He underwent evaluation of the new-onset chest discomfort with a cardiac stress test that suggested no active cardiac ischemia. An echocardiogram revealed mitral regurgitation, stage II diastolic dysfunction with a left ventricular ejection fraction of 55%. Additionally, during this time period, the patient was being followed by his local orthopedic surgeon for an elevated cobalt level of 120 ppb and a chromium level of 109 ppb. The patient was referred to our clinic for recommendations regarding the elevated metal-ion levels. Upon initial evaluation, the patient denied any hip or groin pain. His physical examination revealed a nonantalgic gait with full range of motion and no signs of instability, tenderness, or masses. The patient was also noted to have no vibratory sensation in his feet bilaterally. The plain radiographs indicated bilateral MOM THA with acetabular inclination levels of 55º on the right and left sides. No cystic changes or other worrisome signs that would suggest implant loosening or failure were present (Figure 1). The serum metal levels were repeated and showed a cobalt level of 189 ppb and a chromium level of 71 ppb. Whole venous blood samples were drawn at our request using trace element tubes and were sent to Medtox Laboratories Inc. for analysis. Other pertinent laboratory values, including hematocrit and thyroid levels, were within normal limits. Because of concerns of systemic toxicity from significantly elevated cobalt and chromium levels, the patient elected to proceed with revision of the MOM components.

During the preoperative medical evaluation, the patient’s cardiac status was a concern, and the etiology of the cardiac dysfunction was unclear. Cardiac magnetic resonance imaging (MRI), which was performed to evaluate the extent and etiology of cardiac dysfunction, showed biventricular dysfunction. To evaluate the underlying myocardial tissue characteristics, delayed contrast imaging was performed and showed diffuse myocardial hyperenhancement of the anterior, lateral, and apical walls, with sparing of the base and midseptum. This type of extensive hyperenhancement is commonly seen with cardiac amyloidosis; however, the blood-pool kinetics during contrast administration is unusual for amyloidosis, as well as the diffuse edema noted on T2-weighted MRI. Importantly, cardiac MRI is very specific in excluding alternative diagnoses, such as postinfarct, infiltrative, acquired, viral, or alcoholic/drugs of abuse etiologies. In the absence of amyloidosis, the only other pattern that would be consistent with symptoms was diffuse, fulminant myocarditis of toxic origin lacking clinical evidence for an infectious origin. The patient’s prior exposure to cobalt was noted. Thus, the hyperenhancement and edema could be strong supportive evidence of cobalt infiltration, despite no reported cases in the literature of cobalt cardiomyopathy found on cardiac MRI.

Additional workup was initiated, and cardiac catheterization showed that the patient continued to decompensate, with worsening global left ventricular dysfunction with an ejection fraction of 30% without evidence of coronary artery disease. Also, he was noted to have mild renal impairment with a blood urea nitrogen level of 31 mg/dL and a creatinine level of 1.7 mg/dL. The etiology of the renal impairment was unknown and had not been established, according to the patient and his wife. The renal impairment was not thought to be caused by the elevated metal ions levels but likely resulted from prerenal azotemia secondary to decreased cardiac output. During catheterization, an endomyocardial biopsy was performed and the tissue sent to the Mayo Clinic pathology department for analysis. The sample showed myocyte hypertrophy and interstitial fibrosis with scattered myofibers containing large cytoplasmic vacuoles. Also present was karyomegaly consistent with myocyte hypertrophy (Figures 2A, 2B). Trichrome stain confirmed replacement of myofibers by collagen (Figure 2C). Electron microscopy performed on a paraffin block showed reduced contractile elements, vacuolar spaces, and increased lipofuscin. The findings were very consistent with, but not specific for, cardiomyopathy from cobalt toxicity. No evidence of an inflammatory infiltrate was identified. The diagnosis was cobalt cardiomyopathy based on biopsy, presentation, cobalt levels, and intraoperative findings.

The patient was admitted to the cardiac intensive care unit preoperatively and optimized with inotropic agents. A multidisciplinary consultation with the cardiology and anesthesia departments was obtained. Both recommended cardiac anesthesia with intraoperative Swan-Ganz catheter and transesophageal echo monitoring. Assuming that the patient remained hemodynamically stable with limited blood loss and the first hip was timely performed, the cardiology department recommended a single surgery, because fewer risks and complications could be expected than from a staged procedure. Subsequently, surgery was performed on the left hip via a conservative anterior approach on the fracture table. The patient remained stable with limited blood loss. During the same operating room time, revision of the right hip was performed using an anterior approach. The intraoperative findings showed evidence of pseudotumors in the adjacent soft tissues and abundant brown, creamy fluid upon entering the joint capsule, consistent with a metallic appearance. Both hips showed similar prosthetic findings. There was no significant visible wear of the large diameter metal heads or gross abnormality of the acetabular components. The trunnion area on both femoral implants was abnormal, revealing a black coating suggestive of marked corrosion. The components were all well fixed, without visible damage, and, because of his fragile cardiac status, the patient’s acetabular components were not revised. The trunnions were cleaned and the femoral heads were revised to active articulation dual-mobility metal-on-polyethylene constructs using 28-mm Biolox Option ceramic (CeramTec). The tissue specimens from the operation showed chronic inflammation with areas of fibroconnective tissue and bland fibrinoid necrosis with extensive brown pigment-laden macrophage reaction. The intraoperative cultures were negative.

The patient tolerated the surgery without complication, and his postoperative period was without incident. Nine months after surgery, the patient’s cobalt and chromium levels had declined to 16 ppb and 32 ppb, respectively (normal, <1 ppb). However, his cardiac status continued to worsen with significant shortness of breath and bilateral lower extremity edema despite diuresis. Follow-up cardiac MRI indicated progressive left and right dysfunction with ejection fractions of 23% and 25%, respectively. After progressive heart-failure symptoms, the patient was admitted to the hospital for severe congestive heart failure and underwent implantation of a HeartWare LVAD with tricuspid valve repair using an Edwards annuloplasty ring. He has since had a cardiac transplant and is doing well.

Discussion

To our knowledge, this is the first reported case of cardiomyopathy in a patient with elevated cobalt ion levels and a Biomet M2a-Magnum hip prosthesis. This is also the first reported case of cardiac MRI–defined cobalt cardiomyopathy. The cobalt levels seen in this patient were similar to those of other cases with systemic cobalt toxicity from a MOM hip construct. Mao and colleagues⁵ reported 2 cases of systemic cobalt toxicity in 2 patients with articular surface replacement hip prostheses.One patient presented with mild groin pain, neurologic symptoms, and a cobalt level of 410 ppb 5 years after her index procedure. The other patient presented with cardiac and neurologic symptoms but no hip complaints. The patient’s cobalt levels ranged from 185 ppb to 210 ppb. Both patients improved after their revision surgery, and their cobalt levels decreased. The 2 patients in Tower’s report⁶ were 49-year-old men who had articular surface replacement implants (DePuy). One patient who presented with progressive hip pain 11 months postoperatively developed neurologic symptoms and cardiomyopathy, with cobalt levels of 83 ppb before revision surgery 43 months after his index procedure. The other patient presented with hip pain and vertigo, headaches, fatigue, and dyspnea. He underwent hip revision 40 months postoperatively and required closed reduction under sedation for dislocation. Finally, and most recently, Allen and colleagues² reported a 59-year-old woman with a cobalt level of 287 ppb whose symptoms did not resolve after implantation of an LVAD or cardiac transplantation but only after removal of her bilateral hip prosthesis. Our case is most similar to this report but significantly adds to the literature in 2 distinct manners: (1) Biomet M2a-Magnum has not been implicated in cobalt toxicity; and (2) this is the first reported use of dedicated cardiac MRI to noninvasively define underlying cardiac pathology.

The cardiac manifestations secondary to systemic cobalt toxicity in this patient represent a frightening consequence of MOM prosthetic wear. The effects of cobalt toxicity on cardiac tissues were first described in a series of alcoholic patients from Manchester in 1900;⁷ however, it was not until 1967, in a series of patients in Quebec, that cobalt was found to be the inciting factor. In the modern era, hip arthroplasty techniques resulting in excessive cobalt and chromium wear have demonstrated the same findings of myocyte hypertrophy, interstitial fibrosis, and scattered myofibers containing large cytoplasmic inclusions.^8,9 The patient presented here has pathologic findings consistent with previous cases of cobalt cardiomyopathy; however, in the other cases of cardiomyopathy due to MOM total hip components, the patients’ cardiac conditions improved after the prostheses were revised and the cobalt levels began to diminish.^5,6In our case, the patient has sustained permanent damage to his myocardium and a progressive decline in his cardiac status, which is a deviation from reported cases as of 2014.

While there is no guideline to unequivocally diagnose cobalt cardiomyopathy, the constellation of findings, including pathologic, biologic, blood levels, imaging, and surgical, all uniformly indicate a unifying diagnosis. The lack of improvement after prosthetic device removal supports a diagnosis of permanent myocardial damage, which is consistent with cardiomyopathy of advanced toxic etiology.

Conclusion

This case presents a patient with bilateral MOM THAs, acetabular cup inclinations of greater than 55º, renal impairment, and cobalt levels greater than 60 ppb, with occult cardiac failure leading to LVAD implantation as a prelude to cardiac transplantation in order to avoid certain death. These factors have been shown, in prior case reports, to be associated with cardiac damage that may be reversible.⁶ However; it is important for orthopedic surgeons to recognize that certain hip prostheses can be associated or lead to irreversible cardiac damage.