Tips

Although the number of total hip arthroplasties (THAs) being performed in the United States is increasing, revision THAs are more common.¹ Many acetabular revisions can be successfully performed with standard or jumbo cementless acetabular cups, but major osseous deficiencies typically require reconstruction with a cage or cup/cage that bridges gaps in the pelvis and obtains fixation of the arthroplasty components.^2,3 Cages and rings have been combined with all-polyethylene acetabular components (ie, all-polyethylene cups, or APCs) to reconstruct pelvic bone defects, but complications, including APC dissociation (Figure 1) and postoperative instability, can occur despite stable fixation of cage to pelvis.⁴ The incidence of dislocations with pelvic reconstruction rings using APCs has been reported to be 11%.⁴ If an APC has to be replaced because of wear, then major surgery may be required to extract the worn cup and cement a new cup in its place.

In this article, we describe a technique in which a metal, multihole acetabular shell is cemented into the cage or ring construct, avoiding some of the complications associated with traditional techniques by permitting use of a variety of liners.

Materials and Methods

We retrospectively reviewed the cases of all of Dr. Bolanos’ patients who underwent acetabular revision THA with cage reconstruction between February 1, 1998 and October 9, 2006. During this period, we were cementing a modular metal shell into the cage instead of an APC or polyethylene liner. All patients who underwent revision THA with cage reconstruction during the study period were included. Bone defects were treated with structural or morselized bone allograft. Every reconstruction involved use of an antiprotrusio cage or ring secured to the pelvis with screws, and a multihole acetabular shell cemented into place with a polyethylene liner applied. Elevated rims, lateralized liners, and constrained liners were used as needed to optimize stability. Femoral components were retained. Cage size was based on matching the osseous deficiencies. Shell size was determined by the inner diameter of the corresponding cage. Liner size was based on matching the shell and femoral head. During this period, none of the patients had other reconstructive techniques, such as trabecular metal augmentation, in combination with a modular acetabular shell, cup/cage reconstruction, or custom triflange components.

Patients engaged in protected weight-bearing ambulation for 3 months after surgery and were then permitted full, unrestricted activity. The primary outcome was mechanical failure of the reconstruction, or reoperation (Table). All reconstructions in this series consisted of acetabular revisions for aseptic loosening.

Surgical Technique

Six consecutive cases of pelvic discontinuity and 7 cases of segmental acetabular bone loss required use of cages or rings. Reconstruction cages were used to secure fixation to the ilium and ischium. With the technique described in this article, we used screws with rounded, prominent heads rather than flat heads between the cup and the cage or ring (Synthes, 6.5 mm) to ensure adequate cement mantle. The rounded screw heads were left prominent to approximate the function of cement pegs found on APCs. Screws were placed into the anterior, superior, medial, and posterior aspects of the cage to ensure adequate cement mantle between cup and cage. This was confirmed with trial placement of the cup into the cage before cementation and observation of the uniformity of the space between cup and cage. Trial placement also confirmed that the screws did not interfere with appropriate positioning of the cup. A multihole, metal acetabular cup was then cemented in the cage or ring such that cement extruded around the shell and into the holes of the cup and the cage, securing the cup to the cage. Use of a multihole, metal shell resulted in excellent cement fixation because the multiple holes created multiple circumferential cement pegs. Various liner options could then be used to optimize stability of the reconstruction. In some cases, excessive cement extruded into the interior aspect of the shell and hardened before curettage. If the excess cement could interfere with complete seating/locking of the liner, then a high-speed burr was used to easily remove cement (Figure 2). Polyethylene liners were then inserted into the shell. Femoral reconstruction was then performed, if needed, and stability of the arthroplasty checked. This technique allows the surgeon to then select from a variety of polyethylene liners as needed to optimize stability. Liners with elevated rims, lateralized liners, and constrained liners could be interchangeable options with this technique.

Results

Thirteen patients with major osseous deficiencies of the pelvis were treated using this technique. At mean follow-up of 64.2 months (range, 3-133 months), 10 of the 13 patients had favorable outcomes without further surgery. One patient developed recurrent aseptic loosening that required re-revision, another patient developed recurrent instability that required acetabular liner and femoral head exchange, and a third patient with poor balance fell multiple times. This patient’s ninth fall resulted in dissociation of the acetabular shell from the cage (Figure 3), treated with placement of another cemented multihole metal shell with a standard liner. As dislocations recurred, the liner was changed to a constrained liner (Figure 4). The patient did not have any further dislocations or other hip-related problems. Integrity of cemented shell-cage fixation was maintained in 12 of the 13 patients at final follow-up.

Discussion

We have described a novel technique that facilitates reconstruction of major osseous deficiencies of the pelvis. The technique involves cementation of a multihole, metal acetabular shell into a cage or ring, permitting use of modular liners. The modularity in this approach to major hip reconstruction provides stability-optimization options that are not available with APCs. So far, the technique has demonstrated more advantages than disadvantages, so the indications for its use would be whenever a cage is used for pelvic reconstruction. Traditional techniques involve cementing an APC into the cage or ring. Use of multihole, metal shells for this purpose has several theoretical advantages. Multiple holes and the textured surface allow more interdigitation of cement with cup than APCs do; this interdigitation may improve the durability of the cemented interface. Cement also extrudes through the holes of the cage to secure the cup to the pelvis, as is done with cementation of APCs. Introduction of trabecular metal shells may also provide an even more secure bond to the shell, compared with APCs, though durability of a cemented trabecular metal interface has not been established. In addition, mechanical alignment guides cannot fasten as securely onto some APCs.

Nonmodular, cemented, metal-backed acetabular components, which were commonly used in hip arthroplasties at one time, were abandoned because of their relatively high loosening rate and because of advantages noted with modular components.⁵ The nonmodular components had been developed because of their theoretical advantages of improved distribution of forces into the cement mantle.^5,6 However, those models had a relatively smooth metallic surface, which probably did not bond as well to cement as the shells used with the technique described in this article.

Dislocations can occur because of inadequately placed cups. Metallic cups can be improperly positioned, as can APCs. An advantage of the technique we have described over APCs is that liners with raised rims can be inserted with the apex placed wherever needed to best address instability. Dislocations can also occur because of factors such as inadequate offset and cognitive impairments. Our technique allows use of offset liners and constrained liners. Although these options may not prevent further dislocations, they often mitigate instability issues. Constrained liners and lateralized liners can be easily placed, and elevated rims can be swiveled as needed for stability. As use of cementless, metal-backed, modular acetabular components is common in primary THAs, most surgeons are familiar with the modular liner options available with use of the technique described in this article.

 In this setting, modular, metal acetabular shells have the advantage of allowing surgeons to use the alignment guides they are accustomed to using. Modularity is another significant advantage over APCs. When an APC wears down, the component must be extracted to permit implantation of a new APC. With metal shells, a worn liner can be exchanged relatively easily. Modularity also gives surgeons many more options for addressing instability. Elevated rims can be moved, head sizes can be changed, and lateralized or constrained liners can be implanted easily. By comparison, with APCs, stability can be addressed only by modifying the femoral component or taking hip precautions which restrict range of motion of the hip. Modification of the femoral component is not possible with nonmodular femoral components in place (Figure 5). A potential disadvantage of this technique is increased cost associated with use of another component.

This small series of patients has had an excellent rate of success with cementation of multihole, metal-backed acetabular components into a cage or ring. These components may offer more secure fixation than APCs to cement extruded into the multiple holes, and improved metallurgy, such as trabecular metal. Surgeons who want to use modular components may prefer this technique because it allows them to select from various liner options. Surgeons should consider this technique for patients who need major pelvic reconstruction, though a larger study with longer follow-up is needed to determine its long-term durability.

Although the novel technique we have described has been helpful in our experience, this study had several limitations—small series, retrospective study, relatively short follow-up, lack of control group and functional data—that may have affected its conclusions. Further study and follow-up are needed to better determine the utility of this technique in clinical practice.

Although the number of total hip arthroplasties (THAs) being performed in the United States is increasing, revision THAs are more common.¹ Many acetabular revisions can be successfully performed with standard or jumbo cementless acetabular cups, but major osseous deficiencies typically require reconstruction with a cage or cup/cage that bridges gaps in the pelvis and obtains fixation of the arthroplasty components.^2,3 Cages and rings have been combined with all-polyethylene acetabular components (ie, all-polyethylene cups, or APCs) to reconstruct pelvic bone defects, but complications, including APC dissociation (Figure 1) and postoperative instability, can occur despite stable fixation of cage to pelvis.⁴ The incidence of dislocations with pelvic reconstruction rings using APCs has been reported to be 11%.⁴ If an APC has to be replaced because of wear, then major surgery may be required to extract the worn cup and cement a new cup in its place.

In this article, we describe a technique in which a metal, multihole acetabular shell is cemented into the cage or ring construct, avoiding some of the complications associated with traditional techniques by permitting use of a variety of liners.

Materials and Methods

We retrospectively reviewed the cases of all of Dr. Bolanos’ patients who underwent acetabular revision THA with cage reconstruction between February 1, 1998 and October 9, 2006. During this period, we were cementing a modular metal shell into the cage instead of an APC or polyethylene liner. All patients who underwent revision THA with cage reconstruction during the study period were included. Bone defects were treated with structural or morselized bone allograft. Every reconstruction involved use of an antiprotrusio cage or ring secured to the pelvis with screws, and a multihole acetabular shell cemented into place with a polyethylene liner applied. Elevated rims, lateralized liners, and constrained liners were used as needed to optimize stability. Femoral components were retained. Cage size was based on matching the osseous deficiencies. Shell size was determined by the inner diameter of the corresponding cage. Liner size was based on matching the shell and femoral head. During this period, none of the patients had other reconstructive techniques, such as trabecular metal augmentation, in combination with a modular acetabular shell, cup/cage reconstruction, or custom triflange components.

Patients engaged in protected weight-bearing ambulation for 3 months after surgery and were then permitted full, unrestricted activity. The primary outcome was mechanical failure of the reconstruction, or reoperation (Table). All reconstructions in this series consisted of acetabular revisions for aseptic loosening.

Surgical Technique

Six consecutive cases of pelvic discontinuity and 7 cases of segmental acetabular bone loss required use of cages or rings. Reconstruction cages were used to secure fixation to the ilium and ischium. With the technique described in this article, we used screws with rounded, prominent heads rather than flat heads between the cup and the cage or ring (Synthes, 6.5 mm) to ensure adequate cement mantle. The rounded screw heads were left prominent to approximate the function of cement pegs found on APCs. Screws were placed into the anterior, superior, medial, and posterior aspects of the cage to ensure adequate cement mantle between cup and cage. This was confirmed with trial placement of the cup into the cage before cementation and observation of the uniformity of the space between cup and cage. Trial placement also confirmed that the screws did not interfere with appropriate positioning of the cup. A multihole, metal acetabular cup was then cemented in the cage or ring such that cement extruded around the shell and into the holes of the cup and the cage, securing the cup to the cage. Use of a multihole, metal shell resulted in excellent cement fixation because the multiple holes created multiple circumferential cement pegs. Various liner options could then be used to optimize stability of the reconstruction. In some cases, excessive cement extruded into the interior aspect of the shell and hardened before curettage. If the excess cement could interfere with complete seating/locking of the liner, then a high-speed burr was used to easily remove cement (Figure 2). Polyethylene liners were then inserted into the shell. Femoral reconstruction was then performed, if needed, and stability of the arthroplasty checked. This technique allows the surgeon to then select from a variety of polyethylene liners as needed to optimize stability. Liners with elevated rims, lateralized liners, and constrained liners could be interchangeable options with this technique.

Results

Thirteen patients with major osseous deficiencies of the pelvis were treated using this technique. At mean follow-up of 64.2 months (range, 3-133 months), 10 of the 13 patients had favorable outcomes without further surgery. One patient developed recurrent aseptic loosening that required re-revision, another patient developed recurrent instability that required acetabular liner and femoral head exchange, and a third patient with poor balance fell multiple times. This patient’s ninth fall resulted in dissociation of the acetabular shell from the cage (Figure 3), treated with placement of another cemented multihole metal shell with a standard liner. As dislocations recurred, the liner was changed to a constrained liner (Figure 4). The patient did not have any further dislocations or other hip-related problems. Integrity of cemented shell-cage fixation was maintained in 12 of the 13 patients at final follow-up.

Discussion

We have described a novel technique that facilitates reconstruction of major osseous deficiencies of the pelvis. The technique involves cementation of a multihole, metal acetabular shell into a cage or ring, permitting use of modular liners. The modularity in this approach to major hip reconstruction provides stability-optimization options that are not available with APCs. So far, the technique has demonstrated more advantages than disadvantages, so the indications for its use would be whenever a cage is used for pelvic reconstruction. Traditional techniques involve cementing an APC into the cage or ring. Use of multihole, metal shells for this purpose has several theoretical advantages. Multiple holes and the textured surface allow more interdigitation of cement with cup than APCs do; this interdigitation may improve the durability of the cemented interface. Cement also extrudes through the holes of the cage to secure the cup to the pelvis, as is done with cementation of APCs. Introduction of trabecular metal shells may also provide an even more secure bond to the shell, compared with APCs, though durability of a cemented trabecular metal interface has not been established. In addition, mechanical alignment guides cannot fasten as securely onto some APCs.

Nonmodular, cemented, metal-backed acetabular components, which were commonly used in hip arthroplasties at one time, were abandoned because of their relatively high loosening rate and because of advantages noted with modular components.⁵ The nonmodular components had been developed because of their theoretical advantages of improved distribution of forces into the cement mantle.^5,6 However, those models had a relatively smooth metallic surface, which probably did not bond as well to cement as the shells used with the technique described in this article.

Dislocations can occur because of inadequately placed cups. Metallic cups can be improperly positioned, as can APCs. An advantage of the technique we have described over APCs is that liners with raised rims can be inserted with the apex placed wherever needed to best address instability. Dislocations can also occur because of factors such as inadequate offset and cognitive impairments. Our technique allows use of offset liners and constrained liners. Although these options may not prevent further dislocations, they often mitigate instability issues. Constrained liners and lateralized liners can be easily placed, and elevated rims can be swiveled as needed for stability. As use of cementless, metal-backed, modular acetabular components is common in primary THAs, most surgeons are familiar with the modular liner options available with use of the technique described in this article.

 In this setting, modular, metal acetabular shells have the advantage of allowing surgeons to use the alignment guides they are accustomed to using. Modularity is another significant advantage over APCs. When an APC wears down, the component must be extracted to permit implantation of a new APC. With metal shells, a worn liner can be exchanged relatively easily. Modularity also gives surgeons many more options for addressing instability. Elevated rims can be moved, head sizes can be changed, and lateralized or constrained liners can be implanted easily. By comparison, with APCs, stability can be addressed only by modifying the femoral component or taking hip precautions which restrict range of motion of the hip. Modification of the femoral component is not possible with nonmodular femoral components in place (Figure 5). A potential disadvantage of this technique is increased cost associated with use of another component.

This small series of patients has had an excellent rate of success with cementation of multihole, metal-backed acetabular components into a cage or ring. These components may offer more secure fixation than APCs to cement extruded into the multiple holes, and improved metallurgy, such as trabecular metal. Surgeons who want to use modular components may prefer this technique because it allows them to select from various liner options. Surgeons should consider this technique for patients who need major pelvic reconstruction, though a larger study with longer follow-up is needed to determine its long-term durability.

Although the novel technique we have described has been helpful in our experience, this study had several limitations—small series, retrospective study, relatively short follow-up, lack of control group and functional data—that may have affected its conclusions. Further study and follow-up are needed to better determine the utility of this technique in clinical practice.

Although the number of total hip arthroplasties (THAs) being performed in the United States is increasing, revision THAs are more common.¹ Many acetabular revisions can be successfully performed with standard or jumbo cementless acetabular cups, but major osseous deficiencies typically require reconstruction with a cage or cup/cage that bridges gaps in the pelvis and obtains fixation of the arthroplasty components.^2,3 Cages and rings have been combined with all-polyethylene acetabular components (ie, all-polyethylene cups, or APCs) to reconstruct pelvic bone defects, but complications, including APC dissociation (Figure 1) and postoperative instability, can occur despite stable fixation of cage to pelvis.⁴ The incidence of dislocations with pelvic reconstruction rings using APCs has been reported to be 11%.⁴ If an APC has to be replaced because of wear, then major surgery may be required to extract the worn cup and cement a new cup in its place.

In this article, we describe a technique in which a metal, multihole acetabular shell is cemented into the cage or ring construct, avoiding some of the complications associated with traditional techniques by permitting use of a variety of liners.

Materials and Methods

We retrospectively reviewed the cases of all of Dr. Bolanos’ patients who underwent acetabular revision THA with cage reconstruction between February 1, 1998 and October 9, 2006. During this period, we were cementing a modular metal shell into the cage instead of an APC or polyethylene liner. All patients who underwent revision THA with cage reconstruction during the study period were included. Bone defects were treated with structural or morselized bone allograft. Every reconstruction involved use of an antiprotrusio cage or ring secured to the pelvis with screws, and a multihole acetabular shell cemented into place with a polyethylene liner applied. Elevated rims, lateralized liners, and constrained liners were used as needed to optimize stability. Femoral components were retained. Cage size was based on matching the osseous deficiencies. Shell size was determined by the inner diameter of the corresponding cage. Liner size was based on matching the shell and femoral head. During this period, none of the patients had other reconstructive techniques, such as trabecular metal augmentation, in combination with a modular acetabular shell, cup/cage reconstruction, or custom triflange components.

Patients engaged in protected weight-bearing ambulation for 3 months after surgery and were then permitted full, unrestricted activity. The primary outcome was mechanical failure of the reconstruction, or reoperation (Table). All reconstructions in this series consisted of acetabular revisions for aseptic loosening.

Surgical Technique

Six consecutive cases of pelvic discontinuity and 7 cases of segmental acetabular bone loss required use of cages or rings. Reconstruction cages were used to secure fixation to the ilium and ischium. With the technique described in this article, we used screws with rounded, prominent heads rather than flat heads between the cup and the cage or ring (Synthes, 6.5 mm) to ensure adequate cement mantle. The rounded screw heads were left prominent to approximate the function of cement pegs found on APCs. Screws were placed into the anterior, superior, medial, and posterior aspects of the cage to ensure adequate cement mantle between cup and cage. This was confirmed with trial placement of the cup into the cage before cementation and observation of the uniformity of the space between cup and cage. Trial placement also confirmed that the screws did not interfere with appropriate positioning of the cup. A multihole, metal acetabular cup was then cemented in the cage or ring such that cement extruded around the shell and into the holes of the cup and the cage, securing the cup to the cage. Use of a multihole, metal shell resulted in excellent cement fixation because the multiple holes created multiple circumferential cement pegs. Various liner options could then be used to optimize stability of the reconstruction. In some cases, excessive cement extruded into the interior aspect of the shell and hardened before curettage. If the excess cement could interfere with complete seating/locking of the liner, then a high-speed burr was used to easily remove cement (Figure 2). Polyethylene liners were then inserted into the shell. Femoral reconstruction was then performed, if needed, and stability of the arthroplasty checked. This technique allows the surgeon to then select from a variety of polyethylene liners as needed to optimize stability. Liners with elevated rims, lateralized liners, and constrained liners could be interchangeable options with this technique.

Results

Thirteen patients with major osseous deficiencies of the pelvis were treated using this technique. At mean follow-up of 64.2 months (range, 3-133 months), 10 of the 13 patients had favorable outcomes without further surgery. One patient developed recurrent aseptic loosening that required re-revision, another patient developed recurrent instability that required acetabular liner and femoral head exchange, and a third patient with poor balance fell multiple times. This patient’s ninth fall resulted in dissociation of the acetabular shell from the cage (Figure 3), treated with placement of another cemented multihole metal shell with a standard liner. As dislocations recurred, the liner was changed to a constrained liner (Figure 4). The patient did not have any further dislocations or other hip-related problems. Integrity of cemented shell-cage fixation was maintained in 12 of the 13 patients at final follow-up.

Discussion

We have described a novel technique that facilitates reconstruction of major osseous deficiencies of the pelvis. The technique involves cementation of a multihole, metal acetabular shell into a cage or ring, permitting use of modular liners. The modularity in this approach to major hip reconstruction provides stability-optimization options that are not available with APCs. So far, the technique has demonstrated more advantages than disadvantages, so the indications for its use would be whenever a cage is used for pelvic reconstruction. Traditional techniques involve cementing an APC into the cage or ring. Use of multihole, metal shells for this purpose has several theoretical advantages. Multiple holes and the textured surface allow more interdigitation of cement with cup than APCs do; this interdigitation may improve the durability of the cemented interface. Cement also extrudes through the holes of the cage to secure the cup to the pelvis, as is done with cementation of APCs. Introduction of trabecular metal shells may also provide an even more secure bond to the shell, compared with APCs, though durability of a cemented trabecular metal interface has not been established. In addition, mechanical alignment guides cannot fasten as securely onto some APCs.

Nonmodular, cemented, metal-backed acetabular components, which were commonly used in hip arthroplasties at one time, were abandoned because of their relatively high loosening rate and because of advantages noted with modular components.⁵ The nonmodular components had been developed because of their theoretical advantages of improved distribution of forces into the cement mantle.^5,6 However, those models had a relatively smooth metallic surface, which probably did not bond as well to cement as the shells used with the technique described in this article.

Dislocations can occur because of inadequately placed cups. Metallic cups can be improperly positioned, as can APCs. An advantage of the technique we have described over APCs is that liners with raised rims can be inserted with the apex placed wherever needed to best address instability. Dislocations can also occur because of factors such as inadequate offset and cognitive impairments. Our technique allows use of offset liners and constrained liners. Although these options may not prevent further dislocations, they often mitigate instability issues. Constrained liners and lateralized liners can be easily placed, and elevated rims can be swiveled as needed for stability. As use of cementless, metal-backed, modular acetabular components is common in primary THAs, most surgeons are familiar with the modular liner options available with use of the technique described in this article.

 In this setting, modular, metal acetabular shells have the advantage of allowing surgeons to use the alignment guides they are accustomed to using. Modularity is another significant advantage over APCs. When an APC wears down, the component must be extracted to permit implantation of a new APC. With metal shells, a worn liner can be exchanged relatively easily. Modularity also gives surgeons many more options for addressing instability. Elevated rims can be moved, head sizes can be changed, and lateralized or constrained liners can be implanted easily. By comparison, with APCs, stability can be addressed only by modifying the femoral component or taking hip precautions which restrict range of motion of the hip. Modification of the femoral component is not possible with nonmodular femoral components in place (Figure 5). A potential disadvantage of this technique is increased cost associated with use of another component.

This small series of patients has had an excellent rate of success with cementation of multihole, metal-backed acetabular components into a cage or ring. These components may offer more secure fixation than APCs to cement extruded into the multiple holes, and improved metallurgy, such as trabecular metal. Surgeons who want to use modular components may prefer this technique because it allows them to select from various liner options. Surgeons should consider this technique for patients who need major pelvic reconstruction, though a larger study with longer follow-up is needed to determine its long-term durability.

Although the novel technique we have described has been helpful in our experience, this study had several limitations—small series, retrospective study, relatively short follow-up, lack of control group and functional data—that may have affected its conclusions. Further study and follow-up are needed to better determine the utility of this technique in clinical practice.

Potassium hydroxide (KOH) preparations remain an important bedside test for prompt and accurate diagnosis of superficial fungal infections known as dermatophytoses. This tool has been used for at least 100 years, with early terminology referring to it as potash; for the last century, it has largely been a technique passed down as a skill from master technician to learning apprentice. The original pioneer of the KOH preparation remains a mystery.¹

Variations on techniques for performing the KOH preparation exist, and tips and tricks on the use of this test are a hot topic among dermatologists.² Although primary care and dermatology-specific publications espouse the importance of the KOH preparation,^3,4 it has unfortunately been identified and labeled as one of the forgotten diagnostic tools.⁵

It is incumbent on dermatologists to educate medical students and residents using a simple and specific method to ensure that this simple and effective technique, with sensitivity reported between 87% and 91% depending on the expertise of the examiner,⁶ remains part of the clinical armamentarium. One concern in the instruction of large groups of students and clinicians is the ready accessibility or availability of viable skin samples. This article describes a method of collecting and storing skin samples that will allow educators to train large groups of students on performing KOH preparations without having to repeatedly seek skin samples or patients with superficial skin infections. A detailed description of the pedagogy used to teach the preparation and interpretation of KOH slides to a large group of students also is reviewed.

Specimen Collection

The first step in teaching the KOH preparation to a large group is the collection of a suitable number of skin scrapings from patients with a superficial fungal skin infection (eg, tinea corporis, tinea versicolor). A common technique for obtaining skin samples is to use a no. 15 scalpel blade (Figure 1) to scrape the scale of the lesion at its scaly border once the area is moistened with an alcohol pad or soap and water.⁷ The moisture from the alcohol pad allows the scale to stick to the no. 15 blade, facilitating collection. Once a suitable amount of scale is collected, it is placed on a glass microscope slide by smearing the scale from the blade onto the slide. This process has been modified to facilitate a larger quantity of specimen as follows: dermatophyte-infected plaques with scale are rubbed with the no. 15 blade and the free scale drops into a standard urine specimen cup. This process is repeated multiple times from different sites to capture the displaced scale with the dermatophyte. We have found that as long as the specimen cups are sealed tightly and stored in a relatively dry and cool environment (room temperature), the samples can be used to construct KOH teaching slides for at least 3 years. We have not used them beyond 3 years but suspect that they would continue to be viable after this time.

Figure 1. Scraping at leading edge of lesion with a no. 15 scalpel blade after cleaning the area with an alcohol pad.

Preparation of Slides

Given that time for teaching often is limited, it is beneficial to fix many skin scrapings on a large number of glass slides prior to the session, which enables students to simply add KOH to the slides on the teaching day. To prepare the slides in advance, it is necessary to gather the following materials: a specimen cup with skin samples, glass slides, pickups or tweezers, a small pipette, a cup of water, protective gloves, and a pencil. After donning protective gloves, the pickups or tweezers are used to retrieve a few flakes of scale from the specimen cup and place them on the center of a glass slide. Using the pipette, 1 or 2 drops of water are added to the scale, and the slide is then allowed to dry. The slides are marked with the pencil to indicate the “up” side to prevent the students from applying KOH solution to the wrong side of the slide. The skin scale is fixed in place on the slide as the water evaporates and may be stored until needed for use in a standard slide box or folder.

Performing the KOH Preparation

On the day of teaching, it is helpful to engage the entire group of students with an introductory lecture on the purpose and use of the KOH preparation. Upon completion, students move to a workstation with all of the materials needed to prepare the slide. Additional items needed at this time are 10% KOH solution, coverslips, and a heating device (eg, lighter, Bunsen burner, match)(optional). Students are instructed to place 1 or 2 skin scales onto a glass slide or retrieve a slide with skin scales already fixed, and then add 1 drop of 10% KOH solution directly to the sample (Figure 2). Next, they should place a slide coverslip onto the KOH drop and skin sample using a side-to-side technique that will move the scale into a thin layer within the KOH solution and push away any excess solution to the periphery (Figure 3). Large amounts of excess KOH solution should be cleared away with a paper towel, lens paper, or tissue. The heat source can be used to gently heat the underside of the glass slide (Figure 4), but it often is sufficient to simply wait 3 to 5 minutes for the KOH solution to take effect. The heat accelerates the maceration of the scale and makes it easier to see the hyphae among the keratinocytes. Some physicians advocate the use of dimethyl sulfoxide in lieu of heating,⁸ but this solution may not be available in all primary care settings.

Figure 2. Adding 10% potassium hydroxide solution to skin samples.

Figure 3. Placing the slide coverslip.

Figure 4. Applying gentle heat to the potassium hydroxide preparations.

Microscopic Examination

Prior to examining the slides under the microscope, students may complete a self-guided tutorial (eg, digital or paper slide show) on the various features seen through the microscope that are indicative of dermatophytes, including branching hyphae and yeast buds. They also should be educated about the common appearance of artifacts that may resemble hyphae. Once the students have completed the tutorial, they may proceed to microscopic examination.

 While the students are viewing their slides under the microscope, we find it helpful to have at least 1 experienced faculty member for every group of 10 students. This instructor should encourage the students to lower the microscope condenser all the way to facilitate better observation. Students should start with low power (×4 or red band) and scan for areas that are rich in skin scale. Once a collection of scale is found, the student can switch to higher power (×10 or yellow band) and start scanning for hyphae. Students should be reminded to search for filamentous and branching tubes that are refractile. The term refractile may be confusing to some students, so we explain that shifting the focus up or down will show the hyphae to change in brightness and may reveal a greenish tint. Another helpful indicator to point out is the feature that hyphae will cross the border of epidermal skin cells, whereas artifacts will not  (Figure 5). Once the students have identified evidence of a dermatophyte infection, they must call the instructor to their station to verify the presence of hyphae or yeast buds, which helps confirm their understanding of the procedure. Once the  student accurately identifies these items, the session is complete.

Figure 5. Example of hyphum crossing epithelial cell borders. Figure 5. Example of hyphum crossing epithelial cell borders.

Comment

The use of a KOH preparation is a fast, simple, accurate, and cost-effective way to diagnose superficial fungal infections; however, because of insufficient familiarity with this tool, the technique often is replaced by initiation of empiric antifungal therapy in patients with suspected dermatophytosis. This empiric treatment has the potential to delay appropriate diagnosis and treatment (eg, in a patient with nummular dermatitis, which can clinically mimic tinea corporis). One way to encourage the use of the KOH preparation in the primary care and dermatologic setting is to educate large groups of next-generation physicians while in medical training. This article describes a teaching technique that allows for long-term storage of positive skin samples and a detailed description of the pedagogy used to train and educate a large group of students in a relatively short period of time.

All KOH preparations fall under the US federal government’s Clinical Laboratory Improvement Amendments and require proficiency testing.⁹ Although the teaching method presented here is designed for teaching medical students, it may be utilized to educate or refamiliarize experienced physicians with the procedure in an effort to improve proficiency in point-of-care testing programs used in many health care systems to comply with the Clinical Laboratories Improvement Amendments. Future analyses could assess whether the method described here improves provider performance on such proficiency measures and whether it ultimately helps ensure quality patient care.

Potassium hydroxide (KOH) preparations remain an important bedside test for prompt and accurate diagnosis of superficial fungal infections known as dermatophytoses. This tool has been used for at least 100 years, with early terminology referring to it as potash; for the last century, it has largely been a technique passed down as a skill from master technician to learning apprentice. The original pioneer of the KOH preparation remains a mystery.¹

Variations on techniques for performing the KOH preparation exist, and tips and tricks on the use of this test are a hot topic among dermatologists.² Although primary care and dermatology-specific publications espouse the importance of the KOH preparation,^3,4 it has unfortunately been identified and labeled as one of the forgotten diagnostic tools.⁵

It is incumbent on dermatologists to educate medical students and residents using a simple and specific method to ensure that this simple and effective technique, with sensitivity reported between 87% and 91% depending on the expertise of the examiner,⁶ remains part of the clinical armamentarium. One concern in the instruction of large groups of students and clinicians is the ready accessibility or availability of viable skin samples. This article describes a method of collecting and storing skin samples that will allow educators to train large groups of students on performing KOH preparations without having to repeatedly seek skin samples or patients with superficial skin infections. A detailed description of the pedagogy used to teach the preparation and interpretation of KOH slides to a large group of students also is reviewed.

Specimen Collection

The first step in teaching the KOH preparation to a large group is the collection of a suitable number of skin scrapings from patients with a superficial fungal skin infection (eg, tinea corporis, tinea versicolor). A common technique for obtaining skin samples is to use a no. 15 scalpel blade (Figure 1) to scrape the scale of the lesion at its scaly border once the area is moistened with an alcohol pad or soap and water.⁷ The moisture from the alcohol pad allows the scale to stick to the no. 15 blade, facilitating collection. Once a suitable amount of scale is collected, it is placed on a glass microscope slide by smearing the scale from the blade onto the slide. This process has been modified to facilitate a larger quantity of specimen as follows: dermatophyte-infected plaques with scale are rubbed with the no. 15 blade and the free scale drops into a standard urine specimen cup. This process is repeated multiple times from different sites to capture the displaced scale with the dermatophyte. We have found that as long as the specimen cups are sealed tightly and stored in a relatively dry and cool environment (room temperature), the samples can be used to construct KOH teaching slides for at least 3 years. We have not used them beyond 3 years but suspect that they would continue to be viable after this time.

Figure 1. Scraping at leading edge of lesion with a no. 15 scalpel blade after cleaning the area with an alcohol pad.

Preparation of Slides

Given that time for teaching often is limited, it is beneficial to fix many skin scrapings on a large number of glass slides prior to the session, which enables students to simply add KOH to the slides on the teaching day. To prepare the slides in advance, it is necessary to gather the following materials: a specimen cup with skin samples, glass slides, pickups or tweezers, a small pipette, a cup of water, protective gloves, and a pencil. After donning protective gloves, the pickups or tweezers are used to retrieve a few flakes of scale from the specimen cup and place them on the center of a glass slide. Using the pipette, 1 or 2 drops of water are added to the scale, and the slide is then allowed to dry. The slides are marked with the pencil to indicate the “up” side to prevent the students from applying KOH solution to the wrong side of the slide. The skin scale is fixed in place on the slide as the water evaporates and may be stored until needed for use in a standard slide box or folder.

Performing the KOH Preparation

On the day of teaching, it is helpful to engage the entire group of students with an introductory lecture on the purpose and use of the KOH preparation. Upon completion, students move to a workstation with all of the materials needed to prepare the slide. Additional items needed at this time are 10% KOH solution, coverslips, and a heating device (eg, lighter, Bunsen burner, match)(optional). Students are instructed to place 1 or 2 skin scales onto a glass slide or retrieve a slide with skin scales already fixed, and then add 1 drop of 10% KOH solution directly to the sample (Figure 2). Next, they should place a slide coverslip onto the KOH drop and skin sample using a side-to-side technique that will move the scale into a thin layer within the KOH solution and push away any excess solution to the periphery (Figure 3). Large amounts of excess KOH solution should be cleared away with a paper towel, lens paper, or tissue. The heat source can be used to gently heat the underside of the glass slide (Figure 4), but it often is sufficient to simply wait 3 to 5 minutes for the KOH solution to take effect. The heat accelerates the maceration of the scale and makes it easier to see the hyphae among the keratinocytes. Some physicians advocate the use of dimethyl sulfoxide in lieu of heating,⁸ but this solution may not be available in all primary care settings.

Figure 2. Adding 10% potassium hydroxide solution to skin samples.

Figure 3. Placing the slide coverslip.

Figure 4. Applying gentle heat to the potassium hydroxide preparations.

Microscopic Examination

Prior to examining the slides under the microscope, students may complete a self-guided tutorial (eg, digital or paper slide show) on the various features seen through the microscope that are indicative of dermatophytes, including branching hyphae and yeast buds. They also should be educated about the common appearance of artifacts that may resemble hyphae. Once the students have completed the tutorial, they may proceed to microscopic examination.

 While the students are viewing their slides under the microscope, we find it helpful to have at least 1 experienced faculty member for every group of 10 students. This instructor should encourage the students to lower the microscope condenser all the way to facilitate better observation. Students should start with low power (×4 or red band) and scan for areas that are rich in skin scale. Once a collection of scale is found, the student can switch to higher power (×10 or yellow band) and start scanning for hyphae. Students should be reminded to search for filamentous and branching tubes that are refractile. The term refractile may be confusing to some students, so we explain that shifting the focus up or down will show the hyphae to change in brightness and may reveal a greenish tint. Another helpful indicator to point out is the feature that hyphae will cross the border of epidermal skin cells, whereas artifacts will not  (Figure 5). Once the students have identified evidence of a dermatophyte infection, they must call the instructor to their station to verify the presence of hyphae or yeast buds, which helps confirm their understanding of the procedure. Once the  student accurately identifies these items, the session is complete.

Figure 5. Example of hyphum crossing epithelial cell borders. Figure 5. Example of hyphum crossing epithelial cell borders.

Comment

The use of a KOH preparation is a fast, simple, accurate, and cost-effective way to diagnose superficial fungal infections; however, because of insufficient familiarity with this tool, the technique often is replaced by initiation of empiric antifungal therapy in patients with suspected dermatophytosis. This empiric treatment has the potential to delay appropriate diagnosis and treatment (eg, in a patient with nummular dermatitis, which can clinically mimic tinea corporis). One way to encourage the use of the KOH preparation in the primary care and dermatologic setting is to educate large groups of next-generation physicians while in medical training. This article describes a teaching technique that allows for long-term storage of positive skin samples and a detailed description of the pedagogy used to train and educate a large group of students in a relatively short period of time.

All KOH preparations fall under the US federal government’s Clinical Laboratory Improvement Amendments and require proficiency testing.⁹ Although the teaching method presented here is designed for teaching medical students, it may be utilized to educate or refamiliarize experienced physicians with the procedure in an effort to improve proficiency in point-of-care testing programs used in many health care systems to comply with the Clinical Laboratories Improvement Amendments. Future analyses could assess whether the method described here improves provider performance on such proficiency measures and whether it ultimately helps ensure quality patient care.

Potassium hydroxide (KOH) preparations remain an important bedside test for prompt and accurate diagnosis of superficial fungal infections known as dermatophytoses. This tool has been used for at least 100 years, with early terminology referring to it as potash; for the last century, it has largely been a technique passed down as a skill from master technician to learning apprentice. The original pioneer of the KOH preparation remains a mystery.¹

Variations on techniques for performing the KOH preparation exist, and tips and tricks on the use of this test are a hot topic among dermatologists.² Although primary care and dermatology-specific publications espouse the importance of the KOH preparation,^3,4 it has unfortunately been identified and labeled as one of the forgotten diagnostic tools.⁵

It is incumbent on dermatologists to educate medical students and residents using a simple and specific method to ensure that this simple and effective technique, with sensitivity reported between 87% and 91% depending on the expertise of the examiner,⁶ remains part of the clinical armamentarium. One concern in the instruction of large groups of students and clinicians is the ready accessibility or availability of viable skin samples. This article describes a method of collecting and storing skin samples that will allow educators to train large groups of students on performing KOH preparations without having to repeatedly seek skin samples or patients with superficial skin infections. A detailed description of the pedagogy used to teach the preparation and interpretation of KOH slides to a large group of students also is reviewed.

Specimen Collection

The first step in teaching the KOH preparation to a large group is the collection of a suitable number of skin scrapings from patients with a superficial fungal skin infection (eg, tinea corporis, tinea versicolor). A common technique for obtaining skin samples is to use a no. 15 scalpel blade (Figure 1) to scrape the scale of the lesion at its scaly border once the area is moistened with an alcohol pad or soap and water.⁷ The moisture from the alcohol pad allows the scale to stick to the no. 15 blade, facilitating collection. Once a suitable amount of scale is collected, it is placed on a glass microscope slide by smearing the scale from the blade onto the slide. This process has been modified to facilitate a larger quantity of specimen as follows: dermatophyte-infected plaques with scale are rubbed with the no. 15 blade and the free scale drops into a standard urine specimen cup. This process is repeated multiple times from different sites to capture the displaced scale with the dermatophyte. We have found that as long as the specimen cups are sealed tightly and stored in a relatively dry and cool environment (room temperature), the samples can be used to construct KOH teaching slides for at least 3 years. We have not used them beyond 3 years but suspect that they would continue to be viable after this time.

Figure 1. Scraping at leading edge of lesion with a no. 15 scalpel blade after cleaning the area with an alcohol pad.

Preparation of Slides

Given that time for teaching often is limited, it is beneficial to fix many skin scrapings on a large number of glass slides prior to the session, which enables students to simply add KOH to the slides on the teaching day. To prepare the slides in advance, it is necessary to gather the following materials: a specimen cup with skin samples, glass slides, pickups or tweezers, a small pipette, a cup of water, protective gloves, and a pencil. After donning protective gloves, the pickups or tweezers are used to retrieve a few flakes of scale from the specimen cup and place them on the center of a glass slide. Using the pipette, 1 or 2 drops of water are added to the scale, and the slide is then allowed to dry. The slides are marked with the pencil to indicate the “up” side to prevent the students from applying KOH solution to the wrong side of the slide. The skin scale is fixed in place on the slide as the water evaporates and may be stored until needed for use in a standard slide box or folder.

Performing the KOH Preparation

On the day of teaching, it is helpful to engage the entire group of students with an introductory lecture on the purpose and use of the KOH preparation. Upon completion, students move to a workstation with all of the materials needed to prepare the slide. Additional items needed at this time are 10% KOH solution, coverslips, and a heating device (eg, lighter, Bunsen burner, match)(optional). Students are instructed to place 1 or 2 skin scales onto a glass slide or retrieve a slide with skin scales already fixed, and then add 1 drop of 10% KOH solution directly to the sample (Figure 2). Next, they should place a slide coverslip onto the KOH drop and skin sample using a side-to-side technique that will move the scale into a thin layer within the KOH solution and push away any excess solution to the periphery (Figure 3). Large amounts of excess KOH solution should be cleared away with a paper towel, lens paper, or tissue. The heat source can be used to gently heat the underside of the glass slide (Figure 4), but it often is sufficient to simply wait 3 to 5 minutes for the KOH solution to take effect. The heat accelerates the maceration of the scale and makes it easier to see the hyphae among the keratinocytes. Some physicians advocate the use of dimethyl sulfoxide in lieu of heating,⁸ but this solution may not be available in all primary care settings.

Figure 2. Adding 10% potassium hydroxide solution to skin samples.

Figure 3. Placing the slide coverslip.

Figure 4. Applying gentle heat to the potassium hydroxide preparations.

Microscopic Examination

Prior to examining the slides under the microscope, students may complete a self-guided tutorial (eg, digital or paper slide show) on the various features seen through the microscope that are indicative of dermatophytes, including branching hyphae and yeast buds. They also should be educated about the common appearance of artifacts that may resemble hyphae. Once the students have completed the tutorial, they may proceed to microscopic examination.

 While the students are viewing their slides under the microscope, we find it helpful to have at least 1 experienced faculty member for every group of 10 students. This instructor should encourage the students to lower the microscope condenser all the way to facilitate better observation. Students should start with low power (×4 or red band) and scan for areas that are rich in skin scale. Once a collection of scale is found, the student can switch to higher power (×10 or yellow band) and start scanning for hyphae. Students should be reminded to search for filamentous and branching tubes that are refractile. The term refractile may be confusing to some students, so we explain that shifting the focus up or down will show the hyphae to change in brightness and may reveal a greenish tint. Another helpful indicator to point out is the feature that hyphae will cross the border of epidermal skin cells, whereas artifacts will not  (Figure 5). Once the students have identified evidence of a dermatophyte infection, they must call the instructor to their station to verify the presence of hyphae or yeast buds, which helps confirm their understanding of the procedure. Once the  student accurately identifies these items, the session is complete.

Figure 5. Example of hyphum crossing epithelial cell borders. Figure 5. Example of hyphum crossing epithelial cell borders.

Comment

The use of a KOH preparation is a fast, simple, accurate, and cost-effective way to diagnose superficial fungal infections; however, because of insufficient familiarity with this tool, the technique often is replaced by initiation of empiric antifungal therapy in patients with suspected dermatophytosis. This empiric treatment has the potential to delay appropriate diagnosis and treatment (eg, in a patient with nummular dermatitis, which can clinically mimic tinea corporis). One way to encourage the use of the KOH preparation in the primary care and dermatologic setting is to educate large groups of next-generation physicians while in medical training. This article describes a teaching technique that allows for long-term storage of positive skin samples and a detailed description of the pedagogy used to train and educate a large group of students in a relatively short period of time.

All KOH preparations fall under the US federal government’s Clinical Laboratory Improvement Amendments and require proficiency testing.⁹ Although the teaching method presented here is designed for teaching medical students, it may be utilized to educate or refamiliarize experienced physicians with the procedure in an effort to improve proficiency in point-of-care testing programs used in many health care systems to comply with the Clinical Laboratories Improvement Amendments. Future analyses could assess whether the method described here improves provider performance on such proficiency measures and whether it ultimately helps ensure quality patient care.

“The Burden of Craft in Arthroscopic Rotator Cuff Repair” is a summary of the annual Neer Lecture that was delivered by Stephen S. Burkhart, MD, at the 2014 annual meeting of American Shoulder and Elbow Surgeons. It is a fascinating personal story of the 35-year evolution of arthroscopic rotator cuff surgery presented by one of the most respected arthroscopic innovators of our times. I especially enjoyed his apt citations of classic leaders—Churchill and Gandhi—but 3 points I believe deserve special comment.

First, Steve describes the challenges he faced bringing new products to market in the 1980s. How do we resolve the inherent conflict between innovation that introduces new technology and the “tried and true” standards of established practice? Do the hard work that Steve has done over the years: pose a hypothesis, design a study to answer the question, publish results in peer-reviewed journals, and embrace the techniques that demonstrate better outcomes for patients.

My second point relates to surgeon–device industry relationships, a subject of great interest to The American Journal of Orthopedics dating back to 2006.^1-3 Dr. Burkhart learned early on that he could not fashion new arthroscopic instruments in his garage. Nor could a company develop useful instruments without a knowledgeable surgeon’s input. Hence, a partnership between the innovator-surgeon and the device industry is essential to bring new and effective “tools” to market. Dr. Burkhart’s partnership with Arthrex has benefited many thousands of patients.

The agreements announced in 2007 between the US Department of Justice and 5 orthopedic device manufacturers (interestingly, current presidential candidate and Governor of New Jersey Chris Christie was the lead US Attorney on the case!) dramatically altered the surgeon–industry interaction and established strict guidelines that governed these relationships.⁴ These were needed reforms. However, the changes did not preclude an entrepreneurial surgeon with great ideas and a device manufacturer from profiting from excellent products that advanced patient care, provided, quoting from my editorial of 2006, “that these partnerships comply with legal and ethical standards” and are transparent as well as fully disclosed.¹

Finally, Steve’s last point focuses on the “burden of craft,” a topic dear to all orthopedic surgeons and our professional societies. All of us are committed to improving our surgical skills and, as a profession, we are consistently engaged in learning from our talented colleagues, who are only too willing to share their expertise. The burden of craft requires eager students and dedicated teachers, all committed to the same goal—better outcomes for our patients. We are indeed fortunate that, as orthopedic surgeons, we fundamentally support a culture of continued learning.

I thank Steve for his eloquent paper on this important principle.

“The Burden of Craft in Arthroscopic Rotator Cuff Repair” is a summary of the annual Neer Lecture that was delivered by Stephen S. Burkhart, MD, at the 2014 annual meeting of American Shoulder and Elbow Surgeons. It is a fascinating personal story of the 35-year evolution of arthroscopic rotator cuff surgery presented by one of the most respected arthroscopic innovators of our times. I especially enjoyed his apt citations of classic leaders—Churchill and Gandhi—but 3 points I believe deserve special comment.

First, Steve describes the challenges he faced bringing new products to market in the 1980s. How do we resolve the inherent conflict between innovation that introduces new technology and the “tried and true” standards of established practice? Do the hard work that Steve has done over the years: pose a hypothesis, design a study to answer the question, publish results in peer-reviewed journals, and embrace the techniques that demonstrate better outcomes for patients.

My second point relates to surgeon–device industry relationships, a subject of great interest to The American Journal of Orthopedics dating back to 2006.^1-3 Dr. Burkhart learned early on that he could not fashion new arthroscopic instruments in his garage. Nor could a company develop useful instruments without a knowledgeable surgeon’s input. Hence, a partnership between the innovator-surgeon and the device industry is essential to bring new and effective “tools” to market. Dr. Burkhart’s partnership with Arthrex has benefited many thousands of patients.

The agreements announced in 2007 between the US Department of Justice and 5 orthopedic device manufacturers (interestingly, current presidential candidate and Governor of New Jersey Chris Christie was the lead US Attorney on the case!) dramatically altered the surgeon–industry interaction and established strict guidelines that governed these relationships.⁴ These were needed reforms. However, the changes did not preclude an entrepreneurial surgeon with great ideas and a device manufacturer from profiting from excellent products that advanced patient care, provided, quoting from my editorial of 2006, “that these partnerships comply with legal and ethical standards” and are transparent as well as fully disclosed.¹

Finally, Steve’s last point focuses on the “burden of craft,” a topic dear to all orthopedic surgeons and our professional societies. All of us are committed to improving our surgical skills and, as a profession, we are consistently engaged in learning from our talented colleagues, who are only too willing to share their expertise. The burden of craft requires eager students and dedicated teachers, all committed to the same goal—better outcomes for our patients. We are indeed fortunate that, as orthopedic surgeons, we fundamentally support a culture of continued learning.

I thank Steve for his eloquent paper on this important principle.

“The Burden of Craft in Arthroscopic Rotator Cuff Repair” is a summary of the annual Neer Lecture that was delivered by Stephen S. Burkhart, MD, at the 2014 annual meeting of American Shoulder and Elbow Surgeons. It is a fascinating personal story of the 35-year evolution of arthroscopic rotator cuff surgery presented by one of the most respected arthroscopic innovators of our times. I especially enjoyed his apt citations of classic leaders—Churchill and Gandhi—but 3 points I believe deserve special comment.

First, Steve describes the challenges he faced bringing new products to market in the 1980s. How do we resolve the inherent conflict between innovation that introduces new technology and the “tried and true” standards of established practice? Do the hard work that Steve has done over the years: pose a hypothesis, design a study to answer the question, publish results in peer-reviewed journals, and embrace the techniques that demonstrate better outcomes for patients.

My second point relates to surgeon–device industry relationships, a subject of great interest to The American Journal of Orthopedics dating back to 2006.^1-3 Dr. Burkhart learned early on that he could not fashion new arthroscopic instruments in his garage. Nor could a company develop useful instruments without a knowledgeable surgeon’s input. Hence, a partnership between the innovator-surgeon and the device industry is essential to bring new and effective “tools” to market. Dr. Burkhart’s partnership with Arthrex has benefited many thousands of patients.

The agreements announced in 2007 between the US Department of Justice and 5 orthopedic device manufacturers (interestingly, current presidential candidate and Governor of New Jersey Chris Christie was the lead US Attorney on the case!) dramatically altered the surgeon–industry interaction and established strict guidelines that governed these relationships.⁴ These were needed reforms. However, the changes did not preclude an entrepreneurial surgeon with great ideas and a device manufacturer from profiting from excellent products that advanced patient care, provided, quoting from my editorial of 2006, “that these partnerships comply with legal and ethical standards” and are transparent as well as fully disclosed.¹

Finally, Steve’s last point focuses on the “burden of craft,” a topic dear to all orthopedic surgeons and our professional societies. All of us are committed to improving our surgical skills and, as a profession, we are consistently engaged in learning from our talented colleagues, who are only too willing to share their expertise. The burden of craft requires eager students and dedicated teachers, all committed to the same goal—better outcomes for our patients. We are indeed fortunate that, as orthopedic surgeons, we fundamentally support a culture of continued learning.

I thank Steve for his eloquent paper on this important principle.

Gamekeeper’s or skier’s thumb is caused by an injury to the ulnar collateral ligament (UCL) of the metacarpophalangeal (MCP) joint of the thumb. The mechanism of injury is forced radial and palmar abduction and hyperextension.

This lesion was initially described in 1955 by Campbell.¹ It occurred in gamekeepers who worked in preserves in Scotland. The UCL was injured because of the way they killed rabbits—hence, gamekeeper’s thumb. Now these injuries are more common in skiers—skier’s thumb. In skiers, the mechanism of injury is the force exerted by the ski pole strap on the thumb during a fall. This injury is also seen in breakdancers.^1,2

Different lesions can result, the most common being that of the UCL. The UCL lesion may be partial, with no joint instability,^3,4 or total, with instability and subdislocation of the proximal phalanx.^5-9 Rupture of the thumb adductor aponeurosis and displacement of the long extensor have been described as the cause of thumb instability.^6-8

UCL rupture can occur in its extension or can cause a fracture-tearing in the proximal phalanx.^9-12 Intra-articular fractures are sometimes found. The essential problem in UCL injuries is the impossibility of spontaneous healing once the rupture is complete, because of the Stener effect. (When the UCL ruptures, its proximal part retracts and runs above the fibrous expansion of the adductor muscle, which is interposed between the 2 parts of the ruptured UCL and prevents healing, even if the thumb is immobilized.) In these cases, only surgery can repair the lesion.²

In any thumb injury, particularly one caused by hyperabduction, a UCL lesion should be considered. The main problem is diagnosing sprain severity, which is evidenced by the degree of joint hypermobility. Radiologic examination should be performed in all cases to rule out fracture with tear, posterior capsular tear, palmar plate tear, and palmar subdislocation of the proximal phalanx, all of which are associated with UCL tearing.^7-9

If the diagnosis is suspected, and radiographs show no fracture, comparative radiographs should be obtained in forced valgus.

Technique

We report on a simple, reliable, reproducible method that allows the patient’s thumbs to be compared, under the same force application conditions, on a single radiograph. This technique reduces the patient’s and examiner’s exposure to x-rays and is well tolerated by the patient. Anesthesia for the thumb is usually not necessary.

In each hand, the patient holds a cylindrical object, such as a drinking glass (standard diameter, 7.5-8.5 cm). We use an elastic crepe bandage roll (diameter, 7.5 cm; width, 10 cm). This roll is common in emergency departments (EDs) and easily accessible. The patient holds the rolls in his or her hands with the thumbs in the posteroanterior position (Figures 1–3) and places himself or herself on a 18×24-cm frame or directly on the radiography table.

Both thumbs are captured on a single functional radiograph for comparison of forced valgus of the MCP joints, as in our example cases. The patients provided written informed consent for print and electronic publication of these case reports.

Case Reports

Control Case

The single functional radiograph of both thumbs showed no evidence of joint laxity on the valgus stress test (Figure 4).

Case 1

A 72-year-old woman landed on her left hand when she fell backward while supporting the hand on a piece of furniture. She presented to the ED with pain in the region of the thumb and thenar eminence. Posteroanterior and lateral radiograph projections showed no significant bone injury (Figure 5). Given the patient’s persistent pain, the traumatologist suspected damage to the thumb UCL, so a simultaneous bilateral functional radiographic projection was obtained. The projection showed joint laxity, implying damage to the thumb UCL. Repair and reinsertion of the UCL were performed using a bone harpoon suture.

Case 2

A 58-year-old man sustained a left hand injury when, using both hands, he tried to catch hold of a falling wooden plank. When he presented to the ED the following week, he was given a diagnosis of thumb contusion and forced hyperabduction and was wearing a metal strap for immobilization. Radiographs showed no bone damage (Figure 6). Thumb UCL injury was suspected on the basis of the physical examination findings and the mechanism of injury. A bilateral simultaneous functional radiographic projection showed significant joint laxity. Surgical treatment with the pull-out technique was performed.

Case 3

A 44-year-old woman experienced forced traction from a dog leash and presented to the ED with pain in the right thumb region. Radiographs showed no bone damage (Figure 7). Thumb UCL injury was suspected. A bilateral simultaneous functional radiographic projection showed slight joint laxity, a sprain was diagnosed, and plaster bandaging was applied. Figures 8A–8D show the accurate thumb positions for performing the functional radiograph in forced valgus. We call the technique J.J.’s thumb radiographic projection.

Discussion

Examination using the stress test to cause joint tilt is crucial in making an accurate diagnosis and deciding on the most appropriate therapeutic approach.¹⁰ Most authors accept that surgical management is required in joint tilts over 30º, as these involve complete UCL rupture.^10-12

The MCP joint must be examined in flexion, when the main fascicle of the UCL is tight, and not in extension, when the main fascicle of the UCL is relaxed. If we examine the thumb in extension, radial deviations may occur that are not caused by joint instability. Tilt here must be compared with that of the healthy side.¹¹

Early diagnosis and adequate management are essential, as unnoticed or undervalued injuries can progress to painful sequelae, associated with stiffness, instability, and osteoarthritis, with evident harm to the grip and pinch functions of the hand. In many cases, clinical evidence of MCP joint instability is difficult. The radiologic diagnosis is usually obtained with comparative radiographs in forced valgus of both thumbs.

The forced valgus maneuver typically is performed by the examiner, who must stay with the patient in the radiography room and wear radiologic protection. Incredibly, some patients must force the valgus themselves.

The maneuver we have described clearly has complications, as it is painful, and some patients are uncooperative. Usually the thumb is anesthetized, and the examiner assumes the exposure to x-rays. The valgus deviation force that can be applied during stability testing may lead to further disruption of a partially torn ligament or displacement of a ruptured ligament if the overforced maneuver is performed.^13,14 That does not occur with our technique. On the other hand, the forces applied to the thumbs must be symmetrical for comparison purposes. The way to prevent these inconveniences is to perform the forced valgus maneuver over both thumbs simultaneously, under the same force application conditions and on a single radiograph, without requiring the examiner to remain with the patient in the radiography room.

Heim¹⁵ designed a system for simultaneous functional radiographs, but an apparatus must be built to adapt it to the frame of the radiography table, and the technique involves hyperpronating both hands and bandaging them to the forearm—which is uncomfortable and bothersome for patients and, in our opinion, has a poor application in high-volume EDs.

The technique of having the patient hold a bandage roll (J.J.’s thumb radiographic projection) offers several advantages:

1.  The thumb can be placed in flexion, tightening the main fascicle of the UCL, which is how the UCL must be examined.

2. Forced valgus is allowed. Holding a water glass involves opening the thumb and the necessary stability of the MCP joint of the thumb (grip function of thumb); this radiographic technique is functional.

3. The examiner need not stay with the patient in the radiography room or be exposed to x-rays.

4. The bandage roll is thick enough to generate forced valgus in a patient with large hands. The nonrigid roll makes the examination more tolerable and avoids overforced valgus, eliminating the need for anesthetic blockade.

5. The technique is accessible and simple. In fact, there is no need to remove the roll from its wrapping.

Gamekeeper’s or skier’s thumb is caused by an injury to the ulnar collateral ligament (UCL) of the metacarpophalangeal (MCP) joint of the thumb. The mechanism of injury is forced radial and palmar abduction and hyperextension.

This lesion was initially described in 1955 by Campbell.¹ It occurred in gamekeepers who worked in preserves in Scotland. The UCL was injured because of the way they killed rabbits—hence, gamekeeper’s thumb. Now these injuries are more common in skiers—skier’s thumb. In skiers, the mechanism of injury is the force exerted by the ski pole strap on the thumb during a fall. This injury is also seen in breakdancers.^1,2

Different lesions can result, the most common being that of the UCL. The UCL lesion may be partial, with no joint instability,^3,4 or total, with instability and subdislocation of the proximal phalanx.^5-9 Rupture of the thumb adductor aponeurosis and displacement of the long extensor have been described as the cause of thumb instability.^6-8

UCL rupture can occur in its extension or can cause a fracture-tearing in the proximal phalanx.^9-12 Intra-articular fractures are sometimes found. The essential problem in UCL injuries is the impossibility of spontaneous healing once the rupture is complete, because of the Stener effect. (When the UCL ruptures, its proximal part retracts and runs above the fibrous expansion of the adductor muscle, which is interposed between the 2 parts of the ruptured UCL and prevents healing, even if the thumb is immobilized.) In these cases, only surgery can repair the lesion.²

In any thumb injury, particularly one caused by hyperabduction, a UCL lesion should be considered. The main problem is diagnosing sprain severity, which is evidenced by the degree of joint hypermobility. Radiologic examination should be performed in all cases to rule out fracture with tear, posterior capsular tear, palmar plate tear, and palmar subdislocation of the proximal phalanx, all of which are associated with UCL tearing.^7-9

If the diagnosis is suspected, and radiographs show no fracture, comparative radiographs should be obtained in forced valgus.

Technique

We report on a simple, reliable, reproducible method that allows the patient’s thumbs to be compared, under the same force application conditions, on a single radiograph. This technique reduces the patient’s and examiner’s exposure to x-rays and is well tolerated by the patient. Anesthesia for the thumb is usually not necessary.

In each hand, the patient holds a cylindrical object, such as a drinking glass (standard diameter, 7.5-8.5 cm). We use an elastic crepe bandage roll (diameter, 7.5 cm; width, 10 cm). This roll is common in emergency departments (EDs) and easily accessible. The patient holds the rolls in his or her hands with the thumbs in the posteroanterior position (Figures 1–3) and places himself or herself on a 18×24-cm frame or directly on the radiography table.

Both thumbs are captured on a single functional radiograph for comparison of forced valgus of the MCP joints, as in our example cases. The patients provided written informed consent for print and electronic publication of these case reports.

Case Reports

Control Case

The single functional radiograph of both thumbs showed no evidence of joint laxity on the valgus stress test (Figure 4).

Case 1

A 72-year-old woman landed on her left hand when she fell backward while supporting the hand on a piece of furniture. She presented to the ED with pain in the region of the thumb and thenar eminence. Posteroanterior and lateral radiograph projections showed no significant bone injury (Figure 5). Given the patient’s persistent pain, the traumatologist suspected damage to the thumb UCL, so a simultaneous bilateral functional radiographic projection was obtained. The projection showed joint laxity, implying damage to the thumb UCL. Repair and reinsertion of the UCL were performed using a bone harpoon suture.

Case 2

A 58-year-old man sustained a left hand injury when, using both hands, he tried to catch hold of a falling wooden plank. When he presented to the ED the following week, he was given a diagnosis of thumb contusion and forced hyperabduction and was wearing a metal strap for immobilization. Radiographs showed no bone damage (Figure 6). Thumb UCL injury was suspected on the basis of the physical examination findings and the mechanism of injury. A bilateral simultaneous functional radiographic projection showed significant joint laxity. Surgical treatment with the pull-out technique was performed.

Case 3

A 44-year-old woman experienced forced traction from a dog leash and presented to the ED with pain in the right thumb region. Radiographs showed no bone damage (Figure 7). Thumb UCL injury was suspected. A bilateral simultaneous functional radiographic projection showed slight joint laxity, a sprain was diagnosed, and plaster bandaging was applied. Figures 8A–8D show the accurate thumb positions for performing the functional radiograph in forced valgus. We call the technique J.J.’s thumb radiographic projection.

Discussion

Examination using the stress test to cause joint tilt is crucial in making an accurate diagnosis and deciding on the most appropriate therapeutic approach.¹⁰ Most authors accept that surgical management is required in joint tilts over 30º, as these involve complete UCL rupture.^10-12

The MCP joint must be examined in flexion, when the main fascicle of the UCL is tight, and not in extension, when the main fascicle of the UCL is relaxed. If we examine the thumb in extension, radial deviations may occur that are not caused by joint instability. Tilt here must be compared with that of the healthy side.¹¹

Early diagnosis and adequate management are essential, as unnoticed or undervalued injuries can progress to painful sequelae, associated with stiffness, instability, and osteoarthritis, with evident harm to the grip and pinch functions of the hand. In many cases, clinical evidence of MCP joint instability is difficult. The radiologic diagnosis is usually obtained with comparative radiographs in forced valgus of both thumbs.

The forced valgus maneuver typically is performed by the examiner, who must stay with the patient in the radiography room and wear radiologic protection. Incredibly, some patients must force the valgus themselves.

The maneuver we have described clearly has complications, as it is painful, and some patients are uncooperative. Usually the thumb is anesthetized, and the examiner assumes the exposure to x-rays. The valgus deviation force that can be applied during stability testing may lead to further disruption of a partially torn ligament or displacement of a ruptured ligament if the overforced maneuver is performed.^13,14 That does not occur with our technique. On the other hand, the forces applied to the thumbs must be symmetrical for comparison purposes. The way to prevent these inconveniences is to perform the forced valgus maneuver over both thumbs simultaneously, under the same force application conditions and on a single radiograph, without requiring the examiner to remain with the patient in the radiography room.

Heim¹⁵ designed a system for simultaneous functional radiographs, but an apparatus must be built to adapt it to the frame of the radiography table, and the technique involves hyperpronating both hands and bandaging them to the forearm—which is uncomfortable and bothersome for patients and, in our opinion, has a poor application in high-volume EDs.

The technique of having the patient hold a bandage roll (J.J.’s thumb radiographic projection) offers several advantages:

1.  The thumb can be placed in flexion, tightening the main fascicle of the UCL, which is how the UCL must be examined.

2. Forced valgus is allowed. Holding a water glass involves opening the thumb and the necessary stability of the MCP joint of the thumb (grip function of thumb); this radiographic technique is functional.

3. The examiner need not stay with the patient in the radiography room or be exposed to x-rays.

4. The bandage roll is thick enough to generate forced valgus in a patient with large hands. The nonrigid roll makes the examination more tolerable and avoids overforced valgus, eliminating the need for anesthetic blockade.

5. The technique is accessible and simple. In fact, there is no need to remove the roll from its wrapping.

Gamekeeper’s or skier’s thumb is caused by an injury to the ulnar collateral ligament (UCL) of the metacarpophalangeal (MCP) joint of the thumb. The mechanism of injury is forced radial and palmar abduction and hyperextension.

This lesion was initially described in 1955 by Campbell.¹ It occurred in gamekeepers who worked in preserves in Scotland. The UCL was injured because of the way they killed rabbits—hence, gamekeeper’s thumb. Now these injuries are more common in skiers—skier’s thumb. In skiers, the mechanism of injury is the force exerted by the ski pole strap on the thumb during a fall. This injury is also seen in breakdancers.^1,2

Different lesions can result, the most common being that of the UCL. The UCL lesion may be partial, with no joint instability,^3,4 or total, with instability and subdislocation of the proximal phalanx.^5-9 Rupture of the thumb adductor aponeurosis and displacement of the long extensor have been described as the cause of thumb instability.^6-8

UCL rupture can occur in its extension or can cause a fracture-tearing in the proximal phalanx.^9-12 Intra-articular fractures are sometimes found. The essential problem in UCL injuries is the impossibility of spontaneous healing once the rupture is complete, because of the Stener effect. (When the UCL ruptures, its proximal part retracts and runs above the fibrous expansion of the adductor muscle, which is interposed between the 2 parts of the ruptured UCL and prevents healing, even if the thumb is immobilized.) In these cases, only surgery can repair the lesion.²

In any thumb injury, particularly one caused by hyperabduction, a UCL lesion should be considered. The main problem is diagnosing sprain severity, which is evidenced by the degree of joint hypermobility. Radiologic examination should be performed in all cases to rule out fracture with tear, posterior capsular tear, palmar plate tear, and palmar subdislocation of the proximal phalanx, all of which are associated with UCL tearing.^7-9

If the diagnosis is suspected, and radiographs show no fracture, comparative radiographs should be obtained in forced valgus.

Technique

We report on a simple, reliable, reproducible method that allows the patient’s thumbs to be compared, under the same force application conditions, on a single radiograph. This technique reduces the patient’s and examiner’s exposure to x-rays and is well tolerated by the patient. Anesthesia for the thumb is usually not necessary.

In each hand, the patient holds a cylindrical object, such as a drinking glass (standard diameter, 7.5-8.5 cm). We use an elastic crepe bandage roll (diameter, 7.5 cm; width, 10 cm). This roll is common in emergency departments (EDs) and easily accessible. The patient holds the rolls in his or her hands with the thumbs in the posteroanterior position (Figures 1–3) and places himself or herself on a 18×24-cm frame or directly on the radiography table.

Both thumbs are captured on a single functional radiograph for comparison of forced valgus of the MCP joints, as in our example cases. The patients provided written informed consent for print and electronic publication of these case reports.

Case Reports

Control Case

The single functional radiograph of both thumbs showed no evidence of joint laxity on the valgus stress test (Figure 4).

Case 1

A 72-year-old woman landed on her left hand when she fell backward while supporting the hand on a piece of furniture. She presented to the ED with pain in the region of the thumb and thenar eminence. Posteroanterior and lateral radiograph projections showed no significant bone injury (Figure 5). Given the patient’s persistent pain, the traumatologist suspected damage to the thumb UCL, so a simultaneous bilateral functional radiographic projection was obtained. The projection showed joint laxity, implying damage to the thumb UCL. Repair and reinsertion of the UCL were performed using a bone harpoon suture.

Case 2

A 58-year-old man sustained a left hand injury when, using both hands, he tried to catch hold of a falling wooden plank. When he presented to the ED the following week, he was given a diagnosis of thumb contusion and forced hyperabduction and was wearing a metal strap for immobilization. Radiographs showed no bone damage (Figure 6). Thumb UCL injury was suspected on the basis of the physical examination findings and the mechanism of injury. A bilateral simultaneous functional radiographic projection showed significant joint laxity. Surgical treatment with the pull-out technique was performed.

Case 3

A 44-year-old woman experienced forced traction from a dog leash and presented to the ED with pain in the right thumb region. Radiographs showed no bone damage (Figure 7). Thumb UCL injury was suspected. A bilateral simultaneous functional radiographic projection showed slight joint laxity, a sprain was diagnosed, and plaster bandaging was applied. Figures 8A–8D show the accurate thumb positions for performing the functional radiograph in forced valgus. We call the technique J.J.’s thumb radiographic projection.

Discussion

Examination using the stress test to cause joint tilt is crucial in making an accurate diagnosis and deciding on the most appropriate therapeutic approach.¹⁰ Most authors accept that surgical management is required in joint tilts over 30º, as these involve complete UCL rupture.^10-12

The MCP joint must be examined in flexion, when the main fascicle of the UCL is tight, and not in extension, when the main fascicle of the UCL is relaxed. If we examine the thumb in extension, radial deviations may occur that are not caused by joint instability. Tilt here must be compared with that of the healthy side.¹¹

Early diagnosis and adequate management are essential, as unnoticed or undervalued injuries can progress to painful sequelae, associated with stiffness, instability, and osteoarthritis, with evident harm to the grip and pinch functions of the hand. In many cases, clinical evidence of MCP joint instability is difficult. The radiologic diagnosis is usually obtained with comparative radiographs in forced valgus of both thumbs.

The forced valgus maneuver typically is performed by the examiner, who must stay with the patient in the radiography room and wear radiologic protection. Incredibly, some patients must force the valgus themselves.

The maneuver we have described clearly has complications, as it is painful, and some patients are uncooperative. Usually the thumb is anesthetized, and the examiner assumes the exposure to x-rays. The valgus deviation force that can be applied during stability testing may lead to further disruption of a partially torn ligament or displacement of a ruptured ligament if the overforced maneuver is performed.^13,14 That does not occur with our technique. On the other hand, the forces applied to the thumbs must be symmetrical for comparison purposes. The way to prevent these inconveniences is to perform the forced valgus maneuver over both thumbs simultaneously, under the same force application conditions and on a single radiograph, without requiring the examiner to remain with the patient in the radiography room.

Heim¹⁵ designed a system for simultaneous functional radiographs, but an apparatus must be built to adapt it to the frame of the radiography table, and the technique involves hyperpronating both hands and bandaging them to the forearm—which is uncomfortable and bothersome for patients and, in our opinion, has a poor application in high-volume EDs.

The technique of having the patient hold a bandage roll (J.J.’s thumb radiographic projection) offers several advantages:

1.  The thumb can be placed in flexion, tightening the main fascicle of the UCL, which is how the UCL must be examined.

2. Forced valgus is allowed. Holding a water glass involves opening the thumb and the necessary stability of the MCP joint of the thumb (grip function of thumb); this radiographic technique is functional.

3. The examiner need not stay with the patient in the radiography room or be exposed to x-rays.

4. The bandage roll is thick enough to generate forced valgus in a patient with large hands. The nonrigid roll makes the examination more tolerable and avoids overforced valgus, eliminating the need for anesthetic blockade.

5. The technique is accessible and simple. In fact, there is no need to remove the roll from its wrapping.

Restoration of stability with return to activity is generally expected after anterior cruciate ligament (ACL) reconstruction; long-term success rates range from 75% to 95%.¹ However, graft failure occurs most frequently with soft-tissue grafts fixated only with interference screws.^2,3 Fixation failure also occurs more frequently at the tibial site.² This failure has been attributed to extensive graft slippage in cases of soft-tissue fixation with interference screws.² Interference screw fixation alone, with a double-looped hamstring tendon graft, fails at 350 N in young human tibiae.^4,5 However, failure is limited with use of a bone–tendon–bone graft or with backup fixation, particularly at the tibial site.³ The superiority of bicortical fixation has also been proven.^5-7

In addition, as shown in a goat model, ACL graft fixation is a major cause of failure in the immediate postoperative period, before biological incorporation of the graft.⁸ Fixation techniques for soft-tissue grafts must withstand stresses during the healing period (grafts may take up to 12 weeks to incorporate).⁹ Failures may result from forces exerted on the graft—forces that may be as high as 450 to 700 N during daily activities.^10,11 Within the tibial tunnel, various fixation devices are used, including interference screws, staples, pins, buttons, and interference screw/sheath constructs.^12,13 Primary fixation is commonly achieved with interference screws because of their ease of insertion and greater stiffness. However, fixation of the soft-tissue graft is influenced by several variables, including bone density, insertion torque, thread geometry, and interference screw material.^14-16 Many of these variables, which are a source of inconsistency and concern during the immediate postoperative period, have led surgeons to seek alternative methods of backup fixation at the tibial site. Nevertheless, good clinical and subjective results have been found after ACL reconstruction with a 4-stranded semitendinosus tendon at 10-year follow-up.¹⁷

An anchor used in rotator cuff repair is the SwiveLock system (Arthrex). Major advantages of this system include ease and speed of insertion, good strength, and reduced need for later hardware removal.

We conducted a study to biomechanically evaluate 3 methods of tibial-sided fixation for ACL reconstruction: fully threaded interference screw only, interference screw backed with 4.75-mm SwiveLock anchor, and fully threaded bio-interference screw backed with 4.5-mm bicortical screw. We hypothesized that a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanical strength no different from that provided by backup fixation with a bicortical post at the tibial site. We further hypothesized that SwiveLock backup fixation would provide more strength than fixation with bio-interference screw alone.

Materials and Methods

The design of this study was adapted from one used by Walsh and colleagues,³ who compared 3 fixation methods: retrograde interference screw, suture button, and combined fixation. Tibiae inspected before selection showed no signs of injury or abnormality. Bovine extensor tendons, which lacked any defects along their entire length, were stored in saline 0.9% solution. Both the tibiae and the extensor tendons were stored at –20°C before completion of the tibial-sided ACL reconstruction. Thirty fresh-frozen, skeletally mature porcine proximal tibiae were selected and thawed at 4°C before preparation. Specimens were prepared by potting the diaphysis in fiberglass resin, and a tunnel 9 mm in diameter was drilled through the anteromedial aspect of the tibia.

For consistency, one author (CAV) prepared all 30 specimens. Both tails of all 30 bovine extensor tendons were whip-stitched with No. 2 FiberLoop (Arthrex) 9 mm in diameter. Grafts and tibiae were randomly divided into 3 sample groups. The first group was prepared by antegrade graft fixation within the tibial tunnel using a fully threaded 9×28-mm BioComposite interference screw (Arthrex). The second and third groups used the same primary fixation within the tibial tunnel along with 2 types of secondary fixation. These backup fixation groups included a 4.5-mm titanium bicortical post (Arthrex) and a 4.75-mm BioComposite SwiveLock C anchor (Arthrex) (Figure 1). The FiberLoop at the ends of the distal graft tails for backup groups were fixated 1 cm distal to the tibial tunnel and tapped before insertion of backup devices (Figures 2A, 2B). Insertion was completed after 4.5-mm bicortical and 4.75-mm unicortical drilling and tapping of the anteromedial cortices for the titanium posts and SwiveLocks, respectively. The free ends of the whip-stitched No. 2 FiberLoop were tied to the proximal end of the titanium post with a single surgical knot followed by 5 square knots.³ The free ends of the No. 2 FiberLoop were inserted into the eyelet of the 4.75-mm SwiveLock and 1 cm directly inferior to the tibial tunnel. Interference fit of FiberLoop with SwiveLock was achieved within the corticocancellous bone of the tibiae. All samples retained a 30-mm tendon loop superior to the tibial plateau to simulate intra-articular ACL length. Specimens were then stored at –20°C and thawed at 4°C before biomechanical testing.

Each of the 30 tibiae was tested once. Each testing group consisted of 10 porcine tibiae. The tendons were kept moist during the entire testing procedure by spraying them thoroughly with saline 0.9% solution. Mechanical testing was performed with an Instron 8871 system with a 5-kN load cell secured to the crosshead. A fixed-angle aperture, attached to the testing surface, was adjusted so that the tendon would be pulled in line with the tibial tunnel. A hook fixture suspended from clevis and dowel was used to secure the tendon to the crosshead (Figure 3). A small preload of 5 N manually applied to each sample was followed by a precycling regimen of 10 cycles between 10 N and 50 N at 1 Hz. Precycling was performed to remove slack from the system. Mechanical testing consisted of 500 cycles between 50 N and 250 N at 1 Hz followed by pull to failure at 20 mm per minute. Load and displacement data were recorded at 500 Hz.

An a priori power analysis was not performed because 6 specimens per group in the study from which the testing protocol was adapted demonstrated sufficient power among 3 testing categories.³ In addition, other studies have demonstrated similar testing protocols using 10 specimens per testing group.^7,12,13,18 The data for each sample were analyzed with OriginPro 8.0 software (OriginLab). Ultimate load, yield load, stiffness, and cyclic displacement of the 3 sample groups were compared with 1-way analysis of variance (α = 0.05). Holm-Sidak tests were used for post hoc analysis.¹⁹P < .05 was statistically significant.

Results

None of the 30 specimens failed during preloading. Modes of failure were consistent among groups. All 10 specimens in the interference-screw-only group failed by graft slippage past the screw in the tibial tunnel. Nineteen of the 20 specimens in the backup-fixation groups failed by graft slippage past the screw and suture cutout through the distal graft tail. In the bicortical-post backup group, 1 failure was attributed to tendon tearing proximal to whip-stitching. There were no instances of hardware breakage or failure of either titanium screw or SwiveLock anchor.

Mean (SD) cyclic displacement was higher in the interference-screw-only group, 3.5 (2.2) mm, than in the SwiveLock backup group, 2.6 (0.5) mm, and the bicortical-post backup group, 2.1 (0.6) mm; no statistical significance was demonstrated between any 2 of these groups alone (P = .12) (Figure 4). Mean (SD) pullout stiff­ness was higher in the bicortical-post backup group, 192 (48) N/mm, than in the SwiveLock backup group, 164 (53) N/mm, and the screw-only group, 163 (64) N/mm (P = .42) (Figure 5). Mean (SD) initial load at 5 mm of displacement was higher in the bicortical-post backup group, 482 (156) N, and the SwiveLock backup group, 423 (94) N, than in the screw-only group, 381 (169) N (P = .30).

Mean (SD) yield load was higher in the bicortical-post backup group, 829 (253) N, than in the SwiveLock backup group, 642 (172) N, and the interference-screw-only group, 496 (133) N (P = .003). Statistical significance was demonstrated between the screw-only and bicortical-post groups (P = .002) and between the screw-only and SwiveLock groups (P = .048). There was no statistical difference between the bicortical-post and SwiveLock groups (P = .07).

Mean (SD) ultimate load to failure was higher in the bicortical-post backup group, 1148 (186) N, than in the SwiveLock backup group, 1007 (176) N, and the interference-screw-only group, 778 (139) N (Figure 6). The difference was statistically significant, whereby the screw-only group failed at a lower load compared with the bicortical-post group (P < .001) and the SwiveLock group (P = .005). The 2 backup groups were not statistically different (P = .1).

Discussion

We investigated whether a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanically equivalent pullout strength within the tibial tunnel during ACL reconstruction with soft-tissue allografts in comparison either with a fully threaded bio-interference screw backed with a bicortical post or with a fully threaded bio-interference screw without backup fixation. The results of the study support this hypothesis. With SwiveLock used for backup fixation, there was no significant difference in stiffness or cyclic load displacement between the screw-only, SwiveLock, and bicortical-post groups. However, adding backup fixation could particularly help improve fixation consistency. Specifically, although after only 500 cycles there was no statistically significant difference in cyclic displacement, continued cycling may be clinically relevant if graft slippage exceeded limits to allow for healing within the tibial tunnel. Conversely, a significantly larger difference was found between the SwiveLock, bicortical-post, and screw-only groups in yield load and ultimate load to failure. However, there was no significant difference between the SwiveLock and bicortical-post groups.

 In this study, interference screw with SwiveLock backup demonstrated a mean (SD) ultimate load to failure of 1007 (176) N, comparable to that found by Walsh and colleagues³ for retrograde bio-interference screw with suture button, 1027 (157.11) N. In a study comparing quadrupled hamstring tibial graft fixation, Intrafix (DePuy Mitek) and an 8×25-mm Bioscrew (Linvatec) demonstrated mean (SD) single-cycle yield loads of 1332 (304) N and 612 (176) N, respectively.¹³ These results are similar to the ultimate yield loads in the present study: bicortical-post group, 1148 (186) N; SwiveLock group, 1007 (176) N; screw-only group, 778 (139) N. Differences may be attributed to hamstring tendons used in a quadrupled manner in the aforementioned study.^12,13 Last, mean (SD) ultimate load to failure in a study that used only a retrograde bio-interference screw (9×20 mm) was 679.00 (109.44) N,³ similar to the 778 (139) N found for interference-screw-only in the present study. The difference is likely attributable to the longer screw (9×28 mm) in our study. Using SwiveLock C in cortical bone, Barber and colleagues¹⁸ found mean (SD) loads to failure up to 711.9 (89.1) N.

Clinically, it has been shown that a statistically significant increase in anterior laxity occurred between 4 months and 2 years in 10.7% of patients who underwent hamstring ACL reconstruction.²⁰ The knees were clinically categorized as unstable or severely abnormal. The authors concluded that the clinical outcome was more likely influenced by the methods used to fix the free ends of the graft, specifically with 2 staples or a washer. To simulate early postoperative rehabilitation in the present study, cyclic loading of the graft was performed. Ultimate load to failure was then determined in order to evaluate catastrophic failure strength of the backup fixation devices in comparison with the interference-screw-only group without supplementary fixation.

It has been shown in autologous hamstring ACL reconstruction that a centrally placed polyethylene screw with sheath (Intrafix) performed as well as a standard, eccentrically placed metal interference screw with staple.¹⁰ It is therefore logical that backup fixation with use of a similar device (eg, SwiveLock, bicortical post) is necessary to ensure comparable clinical outcomes in relation to a screw/sheath device that has been shown to endure the highest yield loads.^{2,9,12,13,21-23} Potential benefits of using SwiveLock anchors for backup fixation include a statistically significant increased mean (SD) ultimate yield load of 229 (176) N over interference screw only. These results are similar to those in comparable studies: 218.3 (59.7) N²⁴ and 165 (24.15) N²⁵ in healthy bone with a reported bone mineral density (BMD) of 1.39 g/cm², similar to that of skeletally mature porcine tibia (1.220-1.675 g/cm²).³ In addition, ease of insertion of this device over a bicortical post was demonstrated. The titanium post required bicortical drilling as well as measurement with a depth gauge to ensure adequate screw length. This process appeared to require more time during specimen preparation and theoretically could prove to be more dangerous clinically.⁷ However, caution in using a SwiveLock anchor in osteoporotic bone is advised because of reduced pullout strength.²⁶ In this case, bicortical-post backup fixation may be more suitable. Moreover, although not demonstrated in this study, hardware prominence and irritation with a post may cause postoperative morbidity necessitating future removal.²⁰ Hardware removal was the most common reason for additional surgery using hamstring tendons as graft.²⁰ A second surgery for hardware removal was required in 21% of these patients.²⁰ This is unlikely to occur with a SwiveLock, as the anchor is buried within cortical bone.

Limitations

Regarding use of nonhuman tissues in a biomechanical model, porcine tibiae and bovine extensor tendons were used because of availability, consistency among specimens, and cost-effectiveness. However, bovine extensor tendons have been shown to exhibit stiffness and viscoelastic properties similar to those of a human hamstring graft.²⁷ In addition, the BMD of the porcine tibiae used in this study was not tested because of time involved and cost-efficiency. However, it has been shown that average BMD of porcine tibiae, 1.220-1.675 g/cm², is similar to that in a young athletic population, 1.24-1.62 g/cm².^3,28-31 We therefore assumed similarity to a young athletic population and uniformity of BMD of the porcine tibiae used in this study.

In addition, the biomechanical testing protocol did not simulate physiologic loading within the tibial tunnel. Moreover, the testing protocol used loads of only 250 N during cyclic testing for 500 cycles. This simulates only the early rehabilitation period and not the healing period, which may last up to 12 weeks.⁹ In addition, as previously mentioned, forces on the graft may be as high as 450 to 700 N.^11,32 Pullout testing in line with the long axis of the tibia was performed in order to compare mechanical testing results with those of similar studies.^3,12,13 Last, the P of .07 for the comparison of ultimate load to failure between the 2 backup fixation groups suggests that this study may have been underpowered.

Conclusion

This study demonstrated an effective, alternative, and equivalent backup fixation device that can help prevent graft slippage within the tibial tunnel during soft-tissue ACL reconstruction. Potential benefits of using SwiveLock anchors for backup fixation include a significantly increased ultimate yield load (229 N) when supplementing an interference screw, ease of insertion compared with a bicortical post, and the improbable need for future hardware removal. We support using SwiveLock for supplementary fixation at the tibial tunnel site when using soft-tissue grafts in ACL reconstruction.

Restoration of stability with return to activity is generally expected after anterior cruciate ligament (ACL) reconstruction; long-term success rates range from 75% to 95%.¹ However, graft failure occurs most frequently with soft-tissue grafts fixated only with interference screws.^2,3 Fixation failure also occurs more frequently at the tibial site.² This failure has been attributed to extensive graft slippage in cases of soft-tissue fixation with interference screws.² Interference screw fixation alone, with a double-looped hamstring tendon graft, fails at 350 N in young human tibiae.^4,5 However, failure is limited with use of a bone–tendon–bone graft or with backup fixation, particularly at the tibial site.³ The superiority of bicortical fixation has also been proven.^5-7

In addition, as shown in a goat model, ACL graft fixation is a major cause of failure in the immediate postoperative period, before biological incorporation of the graft.⁸ Fixation techniques for soft-tissue grafts must withstand stresses during the healing period (grafts may take up to 12 weeks to incorporate).⁹ Failures may result from forces exerted on the graft—forces that may be as high as 450 to 700 N during daily activities.^10,11 Within the tibial tunnel, various fixation devices are used, including interference screws, staples, pins, buttons, and interference screw/sheath constructs.^12,13 Primary fixation is commonly achieved with interference screws because of their ease of insertion and greater stiffness. However, fixation of the soft-tissue graft is influenced by several variables, including bone density, insertion torque, thread geometry, and interference screw material.^14-16 Many of these variables, which are a source of inconsistency and concern during the immediate postoperative period, have led surgeons to seek alternative methods of backup fixation at the tibial site. Nevertheless, good clinical and subjective results have been found after ACL reconstruction with a 4-stranded semitendinosus tendon at 10-year follow-up.¹⁷

An anchor used in rotator cuff repair is the SwiveLock system (Arthrex). Major advantages of this system include ease and speed of insertion, good strength, and reduced need for later hardware removal.

We conducted a study to biomechanically evaluate 3 methods of tibial-sided fixation for ACL reconstruction: fully threaded interference screw only, interference screw backed with 4.75-mm SwiveLock anchor, and fully threaded bio-interference screw backed with 4.5-mm bicortical screw. We hypothesized that a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanical strength no different from that provided by backup fixation with a bicortical post at the tibial site. We further hypothesized that SwiveLock backup fixation would provide more strength than fixation with bio-interference screw alone.

Materials and Methods

The design of this study was adapted from one used by Walsh and colleagues,³ who compared 3 fixation methods: retrograde interference screw, suture button, and combined fixation. Tibiae inspected before selection showed no signs of injury or abnormality. Bovine extensor tendons, which lacked any defects along their entire length, were stored in saline 0.9% solution. Both the tibiae and the extensor tendons were stored at –20°C before completion of the tibial-sided ACL reconstruction. Thirty fresh-frozen, skeletally mature porcine proximal tibiae were selected and thawed at 4°C before preparation. Specimens were prepared by potting the diaphysis in fiberglass resin, and a tunnel 9 mm in diameter was drilled through the anteromedial aspect of the tibia.

For consistency, one author (CAV) prepared all 30 specimens. Both tails of all 30 bovine extensor tendons were whip-stitched with No. 2 FiberLoop (Arthrex) 9 mm in diameter. Grafts and tibiae were randomly divided into 3 sample groups. The first group was prepared by antegrade graft fixation within the tibial tunnel using a fully threaded 9×28-mm BioComposite interference screw (Arthrex). The second and third groups used the same primary fixation within the tibial tunnel along with 2 types of secondary fixation. These backup fixation groups included a 4.5-mm titanium bicortical post (Arthrex) and a 4.75-mm BioComposite SwiveLock C anchor (Arthrex) (Figure 1). The FiberLoop at the ends of the distal graft tails for backup groups were fixated 1 cm distal to the tibial tunnel and tapped before insertion of backup devices (Figures 2A, 2B). Insertion was completed after 4.5-mm bicortical and 4.75-mm unicortical drilling and tapping of the anteromedial cortices for the titanium posts and SwiveLocks, respectively. The free ends of the whip-stitched No. 2 FiberLoop were tied to the proximal end of the titanium post with a single surgical knot followed by 5 square knots.³ The free ends of the No. 2 FiberLoop were inserted into the eyelet of the 4.75-mm SwiveLock and 1 cm directly inferior to the tibial tunnel. Interference fit of FiberLoop with SwiveLock was achieved within the corticocancellous bone of the tibiae. All samples retained a 30-mm tendon loop superior to the tibial plateau to simulate intra-articular ACL length. Specimens were then stored at –20°C and thawed at 4°C before biomechanical testing.

Each of the 30 tibiae was tested once. Each testing group consisted of 10 porcine tibiae. The tendons were kept moist during the entire testing procedure by spraying them thoroughly with saline 0.9% solution. Mechanical testing was performed with an Instron 8871 system with a 5-kN load cell secured to the crosshead. A fixed-angle aperture, attached to the testing surface, was adjusted so that the tendon would be pulled in line with the tibial tunnel. A hook fixture suspended from clevis and dowel was used to secure the tendon to the crosshead (Figure 3). A small preload of 5 N manually applied to each sample was followed by a precycling regimen of 10 cycles between 10 N and 50 N at 1 Hz. Precycling was performed to remove slack from the system. Mechanical testing consisted of 500 cycles between 50 N and 250 N at 1 Hz followed by pull to failure at 20 mm per minute. Load and displacement data were recorded at 500 Hz.

An a priori power analysis was not performed because 6 specimens per group in the study from which the testing protocol was adapted demonstrated sufficient power among 3 testing categories.³ In addition, other studies have demonstrated similar testing protocols using 10 specimens per testing group.^7,12,13,18 The data for each sample were analyzed with OriginPro 8.0 software (OriginLab). Ultimate load, yield load, stiffness, and cyclic displacement of the 3 sample groups were compared with 1-way analysis of variance (α = 0.05). Holm-Sidak tests were used for post hoc analysis.¹⁹P < .05 was statistically significant.

Results

None of the 30 specimens failed during preloading. Modes of failure were consistent among groups. All 10 specimens in the interference-screw-only group failed by graft slippage past the screw in the tibial tunnel. Nineteen of the 20 specimens in the backup-fixation groups failed by graft slippage past the screw and suture cutout through the distal graft tail. In the bicortical-post backup group, 1 failure was attributed to tendon tearing proximal to whip-stitching. There were no instances of hardware breakage or failure of either titanium screw or SwiveLock anchor.

Mean (SD) cyclic displacement was higher in the interference-screw-only group, 3.5 (2.2) mm, than in the SwiveLock backup group, 2.6 (0.5) mm, and the bicortical-post backup group, 2.1 (0.6) mm; no statistical significance was demonstrated between any 2 of these groups alone (P = .12) (Figure 4). Mean (SD) pullout stiff­ness was higher in the bicortical-post backup group, 192 (48) N/mm, than in the SwiveLock backup group, 164 (53) N/mm, and the screw-only group, 163 (64) N/mm (P = .42) (Figure 5). Mean (SD) initial load at 5 mm of displacement was higher in the bicortical-post backup group, 482 (156) N, and the SwiveLock backup group, 423 (94) N, than in the screw-only group, 381 (169) N (P = .30).

Mean (SD) yield load was higher in the bicortical-post backup group, 829 (253) N, than in the SwiveLock backup group, 642 (172) N, and the interference-screw-only group, 496 (133) N (P = .003). Statistical significance was demonstrated between the screw-only and bicortical-post groups (P = .002) and between the screw-only and SwiveLock groups (P = .048). There was no statistical difference between the bicortical-post and SwiveLock groups (P = .07).

Mean (SD) ultimate load to failure was higher in the bicortical-post backup group, 1148 (186) N, than in the SwiveLock backup group, 1007 (176) N, and the interference-screw-only group, 778 (139) N (Figure 6). The difference was statistically significant, whereby the screw-only group failed at a lower load compared with the bicortical-post group (P < .001) and the SwiveLock group (P = .005). The 2 backup groups were not statistically different (P = .1).

Discussion

We investigated whether a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanically equivalent pullout strength within the tibial tunnel during ACL reconstruction with soft-tissue allografts in comparison either with a fully threaded bio-interference screw backed with a bicortical post or with a fully threaded bio-interference screw without backup fixation. The results of the study support this hypothesis. With SwiveLock used for backup fixation, there was no significant difference in stiffness or cyclic load displacement between the screw-only, SwiveLock, and bicortical-post groups. However, adding backup fixation could particularly help improve fixation consistency. Specifically, although after only 500 cycles there was no statistically significant difference in cyclic displacement, continued cycling may be clinically relevant if graft slippage exceeded limits to allow for healing within the tibial tunnel. Conversely, a significantly larger difference was found between the SwiveLock, bicortical-post, and screw-only groups in yield load and ultimate load to failure. However, there was no significant difference between the SwiveLock and bicortical-post groups.

 In this study, interference screw with SwiveLock backup demonstrated a mean (SD) ultimate load to failure of 1007 (176) N, comparable to that found by Walsh and colleagues³ for retrograde bio-interference screw with suture button, 1027 (157.11) N. In a study comparing quadrupled hamstring tibial graft fixation, Intrafix (DePuy Mitek) and an 8×25-mm Bioscrew (Linvatec) demonstrated mean (SD) single-cycle yield loads of 1332 (304) N and 612 (176) N, respectively.¹³ These results are similar to the ultimate yield loads in the present study: bicortical-post group, 1148 (186) N; SwiveLock group, 1007 (176) N; screw-only group, 778 (139) N. Differences may be attributed to hamstring tendons used in a quadrupled manner in the aforementioned study.^12,13 Last, mean (SD) ultimate load to failure in a study that used only a retrograde bio-interference screw (9×20 mm) was 679.00 (109.44) N,³ similar to the 778 (139) N found for interference-screw-only in the present study. The difference is likely attributable to the longer screw (9×28 mm) in our study. Using SwiveLock C in cortical bone, Barber and colleagues¹⁸ found mean (SD) loads to failure up to 711.9 (89.1) N.

Clinically, it has been shown that a statistically significant increase in anterior laxity occurred between 4 months and 2 years in 10.7% of patients who underwent hamstring ACL reconstruction.²⁰ The knees were clinically categorized as unstable or severely abnormal. The authors concluded that the clinical outcome was more likely influenced by the methods used to fix the free ends of the graft, specifically with 2 staples or a washer. To simulate early postoperative rehabilitation in the present study, cyclic loading of the graft was performed. Ultimate load to failure was then determined in order to evaluate catastrophic failure strength of the backup fixation devices in comparison with the interference-screw-only group without supplementary fixation.

It has been shown in autologous hamstring ACL reconstruction that a centrally placed polyethylene screw with sheath (Intrafix) performed as well as a standard, eccentrically placed metal interference screw with staple.¹⁰ It is therefore logical that backup fixation with use of a similar device (eg, SwiveLock, bicortical post) is necessary to ensure comparable clinical outcomes in relation to a screw/sheath device that has been shown to endure the highest yield loads.^{2,9,12,13,21-23} Potential benefits of using SwiveLock anchors for backup fixation include a statistically significant increased mean (SD) ultimate yield load of 229 (176) N over interference screw only. These results are similar to those in comparable studies: 218.3 (59.7) N²⁴ and 165 (24.15) N²⁵ in healthy bone with a reported bone mineral density (BMD) of 1.39 g/cm², similar to that of skeletally mature porcine tibia (1.220-1.675 g/cm²).³ In addition, ease of insertion of this device over a bicortical post was demonstrated. The titanium post required bicortical drilling as well as measurement with a depth gauge to ensure adequate screw length. This process appeared to require more time during specimen preparation and theoretically could prove to be more dangerous clinically.⁷ However, caution in using a SwiveLock anchor in osteoporotic bone is advised because of reduced pullout strength.²⁶ In this case, bicortical-post backup fixation may be more suitable. Moreover, although not demonstrated in this study, hardware prominence and irritation with a post may cause postoperative morbidity necessitating future removal.²⁰ Hardware removal was the most common reason for additional surgery using hamstring tendons as graft.²⁰ A second surgery for hardware removal was required in 21% of these patients.²⁰ This is unlikely to occur with a SwiveLock, as the anchor is buried within cortical bone.

Limitations

Regarding use of nonhuman tissues in a biomechanical model, porcine tibiae and bovine extensor tendons were used because of availability, consistency among specimens, and cost-effectiveness. However, bovine extensor tendons have been shown to exhibit stiffness and viscoelastic properties similar to those of a human hamstring graft.²⁷ In addition, the BMD of the porcine tibiae used in this study was not tested because of time involved and cost-efficiency. However, it has been shown that average BMD of porcine tibiae, 1.220-1.675 g/cm², is similar to that in a young athletic population, 1.24-1.62 g/cm².^3,28-31 We therefore assumed similarity to a young athletic population and uniformity of BMD of the porcine tibiae used in this study.

In addition, the biomechanical testing protocol did not simulate physiologic loading within the tibial tunnel. Moreover, the testing protocol used loads of only 250 N during cyclic testing for 500 cycles. This simulates only the early rehabilitation period and not the healing period, which may last up to 12 weeks.⁹ In addition, as previously mentioned, forces on the graft may be as high as 450 to 700 N.^11,32 Pullout testing in line with the long axis of the tibia was performed in order to compare mechanical testing results with those of similar studies.^3,12,13 Last, the P of .07 for the comparison of ultimate load to failure between the 2 backup fixation groups suggests that this study may have been underpowered.

Conclusion

This study demonstrated an effective, alternative, and equivalent backup fixation device that can help prevent graft slippage within the tibial tunnel during soft-tissue ACL reconstruction. Potential benefits of using SwiveLock anchors for backup fixation include a significantly increased ultimate yield load (229 N) when supplementing an interference screw, ease of insertion compared with a bicortical post, and the improbable need for future hardware removal. We support using SwiveLock for supplementary fixation at the tibial tunnel site when using soft-tissue grafts in ACL reconstruction.

Restoration of stability with return to activity is generally expected after anterior cruciate ligament (ACL) reconstruction; long-term success rates range from 75% to 95%.¹ However, graft failure occurs most frequently with soft-tissue grafts fixated only with interference screws.^2,3 Fixation failure also occurs more frequently at the tibial site.² This failure has been attributed to extensive graft slippage in cases of soft-tissue fixation with interference screws.² Interference screw fixation alone, with a double-looped hamstring tendon graft, fails at 350 N in young human tibiae.^4,5 However, failure is limited with use of a bone–tendon–bone graft or with backup fixation, particularly at the tibial site.³ The superiority of bicortical fixation has also been proven.^5-7

In addition, as shown in a goat model, ACL graft fixation is a major cause of failure in the immediate postoperative period, before biological incorporation of the graft.⁸ Fixation techniques for soft-tissue grafts must withstand stresses during the healing period (grafts may take up to 12 weeks to incorporate).⁹ Failures may result from forces exerted on the graft—forces that may be as high as 450 to 700 N during daily activities.^10,11 Within the tibial tunnel, various fixation devices are used, including interference screws, staples, pins, buttons, and interference screw/sheath constructs.^12,13 Primary fixation is commonly achieved with interference screws because of their ease of insertion and greater stiffness. However, fixation of the soft-tissue graft is influenced by several variables, including bone density, insertion torque, thread geometry, and interference screw material.^14-16 Many of these variables, which are a source of inconsistency and concern during the immediate postoperative period, have led surgeons to seek alternative methods of backup fixation at the tibial site. Nevertheless, good clinical and subjective results have been found after ACL reconstruction with a 4-stranded semitendinosus tendon at 10-year follow-up.¹⁷

An anchor used in rotator cuff repair is the SwiveLock system (Arthrex). Major advantages of this system include ease and speed of insertion, good strength, and reduced need for later hardware removal.

We conducted a study to biomechanically evaluate 3 methods of tibial-sided fixation for ACL reconstruction: fully threaded interference screw only, interference screw backed with 4.75-mm SwiveLock anchor, and fully threaded bio-interference screw backed with 4.5-mm bicortical screw. We hypothesized that a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanical strength no different from that provided by backup fixation with a bicortical post at the tibial site. We further hypothesized that SwiveLock backup fixation would provide more strength than fixation with bio-interference screw alone.

Materials and Methods

The design of this study was adapted from one used by Walsh and colleagues,³ who compared 3 fixation methods: retrograde interference screw, suture button, and combined fixation. Tibiae inspected before selection showed no signs of injury or abnormality. Bovine extensor tendons, which lacked any defects along their entire length, were stored in saline 0.9% solution. Both the tibiae and the extensor tendons were stored at –20°C before completion of the tibial-sided ACL reconstruction. Thirty fresh-frozen, skeletally mature porcine proximal tibiae were selected and thawed at 4°C before preparation. Specimens were prepared by potting the diaphysis in fiberglass resin, and a tunnel 9 mm in diameter was drilled through the anteromedial aspect of the tibia.

For consistency, one author (CAV) prepared all 30 specimens. Both tails of all 30 bovine extensor tendons were whip-stitched with No. 2 FiberLoop (Arthrex) 9 mm in diameter. Grafts and tibiae were randomly divided into 3 sample groups. The first group was prepared by antegrade graft fixation within the tibial tunnel using a fully threaded 9×28-mm BioComposite interference screw (Arthrex). The second and third groups used the same primary fixation within the tibial tunnel along with 2 types of secondary fixation. These backup fixation groups included a 4.5-mm titanium bicortical post (Arthrex) and a 4.75-mm BioComposite SwiveLock C anchor (Arthrex) (Figure 1). The FiberLoop at the ends of the distal graft tails for backup groups were fixated 1 cm distal to the tibial tunnel and tapped before insertion of backup devices (Figures 2A, 2B). Insertion was completed after 4.5-mm bicortical and 4.75-mm unicortical drilling and tapping of the anteromedial cortices for the titanium posts and SwiveLocks, respectively. The free ends of the whip-stitched No. 2 FiberLoop were tied to the proximal end of the titanium post with a single surgical knot followed by 5 square knots.³ The free ends of the No. 2 FiberLoop were inserted into the eyelet of the 4.75-mm SwiveLock and 1 cm directly inferior to the tibial tunnel. Interference fit of FiberLoop with SwiveLock was achieved within the corticocancellous bone of the tibiae. All samples retained a 30-mm tendon loop superior to the tibial plateau to simulate intra-articular ACL length. Specimens were then stored at –20°C and thawed at 4°C before biomechanical testing.

Each of the 30 tibiae was tested once. Each testing group consisted of 10 porcine tibiae. The tendons were kept moist during the entire testing procedure by spraying them thoroughly with saline 0.9% solution. Mechanical testing was performed with an Instron 8871 system with a 5-kN load cell secured to the crosshead. A fixed-angle aperture, attached to the testing surface, was adjusted so that the tendon would be pulled in line with the tibial tunnel. A hook fixture suspended from clevis and dowel was used to secure the tendon to the crosshead (Figure 3). A small preload of 5 N manually applied to each sample was followed by a precycling regimen of 10 cycles between 10 N and 50 N at 1 Hz. Precycling was performed to remove slack from the system. Mechanical testing consisted of 500 cycles between 50 N and 250 N at 1 Hz followed by pull to failure at 20 mm per minute. Load and displacement data were recorded at 500 Hz.

An a priori power analysis was not performed because 6 specimens per group in the study from which the testing protocol was adapted demonstrated sufficient power among 3 testing categories.³ In addition, other studies have demonstrated similar testing protocols using 10 specimens per testing group.^7,12,13,18 The data for each sample were analyzed with OriginPro 8.0 software (OriginLab). Ultimate load, yield load, stiffness, and cyclic displacement of the 3 sample groups were compared with 1-way analysis of variance (α = 0.05). Holm-Sidak tests were used for post hoc analysis.¹⁹P < .05 was statistically significant.

Results

None of the 30 specimens failed during preloading. Modes of failure were consistent among groups. All 10 specimens in the interference-screw-only group failed by graft slippage past the screw in the tibial tunnel. Nineteen of the 20 specimens in the backup-fixation groups failed by graft slippage past the screw and suture cutout through the distal graft tail. In the bicortical-post backup group, 1 failure was attributed to tendon tearing proximal to whip-stitching. There were no instances of hardware breakage or failure of either titanium screw or SwiveLock anchor.

Mean (SD) cyclic displacement was higher in the interference-screw-only group, 3.5 (2.2) mm, than in the SwiveLock backup group, 2.6 (0.5) mm, and the bicortical-post backup group, 2.1 (0.6) mm; no statistical significance was demonstrated between any 2 of these groups alone (P = .12) (Figure 4). Mean (SD) pullout stiff­ness was higher in the bicortical-post backup group, 192 (48) N/mm, than in the SwiveLock backup group, 164 (53) N/mm, and the screw-only group, 163 (64) N/mm (P = .42) (Figure 5). Mean (SD) initial load at 5 mm of displacement was higher in the bicortical-post backup group, 482 (156) N, and the SwiveLock backup group, 423 (94) N, than in the screw-only group, 381 (169) N (P = .30).

Mean (SD) yield load was higher in the bicortical-post backup group, 829 (253) N, than in the SwiveLock backup group, 642 (172) N, and the interference-screw-only group, 496 (133) N (P = .003). Statistical significance was demonstrated between the screw-only and bicortical-post groups (P = .002) and between the screw-only and SwiveLock groups (P = .048). There was no statistical difference between the bicortical-post and SwiveLock groups (P = .07).

Mean (SD) ultimate load to failure was higher in the bicortical-post backup group, 1148 (186) N, than in the SwiveLock backup group, 1007 (176) N, and the interference-screw-only group, 778 (139) N (Figure 6). The difference was statistically significant, whereby the screw-only group failed at a lower load compared with the bicortical-post group (P < .001) and the SwiveLock group (P = .005). The 2 backup groups were not statistically different (P = .1).

Discussion

We investigated whether a fully threaded bio-interference screw backed with a 4.75-mm SwiveLock anchor would provide mechanically equivalent pullout strength within the tibial tunnel during ACL reconstruction with soft-tissue allografts in comparison either with a fully threaded bio-interference screw backed with a bicortical post or with a fully threaded bio-interference screw without backup fixation. The results of the study support this hypothesis. With SwiveLock used for backup fixation, there was no significant difference in stiffness or cyclic load displacement between the screw-only, SwiveLock, and bicortical-post groups. However, adding backup fixation could particularly help improve fixation consistency. Specifically, although after only 500 cycles there was no statistically significant difference in cyclic displacement, continued cycling may be clinically relevant if graft slippage exceeded limits to allow for healing within the tibial tunnel. Conversely, a significantly larger difference was found between the SwiveLock, bicortical-post, and screw-only groups in yield load and ultimate load to failure. However, there was no significant difference between the SwiveLock and bicortical-post groups.

 In this study, interference screw with SwiveLock backup demonstrated a mean (SD) ultimate load to failure of 1007 (176) N, comparable to that found by Walsh and colleagues³ for retrograde bio-interference screw with suture button, 1027 (157.11) N. In a study comparing quadrupled hamstring tibial graft fixation, Intrafix (DePuy Mitek) and an 8×25-mm Bioscrew (Linvatec) demonstrated mean (SD) single-cycle yield loads of 1332 (304) N and 612 (176) N, respectively.¹³ These results are similar to the ultimate yield loads in the present study: bicortical-post group, 1148 (186) N; SwiveLock group, 1007 (176) N; screw-only group, 778 (139) N. Differences may be attributed to hamstring tendons used in a quadrupled manner in the aforementioned study.^12,13 Last, mean (SD) ultimate load to failure in a study that used only a retrograde bio-interference screw (9×20 mm) was 679.00 (109.44) N,³ similar to the 778 (139) N found for interference-screw-only in the present study. The difference is likely attributable to the longer screw (9×28 mm) in our study. Using SwiveLock C in cortical bone, Barber and colleagues¹⁸ found mean (SD) loads to failure up to 711.9 (89.1) N.

Clinically, it has been shown that a statistically significant increase in anterior laxity occurred between 4 months and 2 years in 10.7% of patients who underwent hamstring ACL reconstruction.²⁰ The knees were clinically categorized as unstable or severely abnormal. The authors concluded that the clinical outcome was more likely influenced by the methods used to fix the free ends of the graft, specifically with 2 staples or a washer. To simulate early postoperative rehabilitation in the present study, cyclic loading of the graft was performed. Ultimate load to failure was then determined in order to evaluate catastrophic failure strength of the backup fixation devices in comparison with the interference-screw-only group without supplementary fixation.

It has been shown in autologous hamstring ACL reconstruction that a centrally placed polyethylene screw with sheath (Intrafix) performed as well as a standard, eccentrically placed metal interference screw with staple.¹⁰ It is therefore logical that backup fixation with use of a similar device (eg, SwiveLock, bicortical post) is necessary to ensure comparable clinical outcomes in relation to a screw/sheath device that has been shown to endure the highest yield loads.^{2,9,12,13,21-23} Potential benefits of using SwiveLock anchors for backup fixation include a statistically significant increased mean (SD) ultimate yield load of 229 (176) N over interference screw only. These results are similar to those in comparable studies: 218.3 (59.7) N²⁴ and 165 (24.15) N²⁵ in healthy bone with a reported bone mineral density (BMD) of 1.39 g/cm², similar to that of skeletally mature porcine tibia (1.220-1.675 g/cm²).³ In addition, ease of insertion of this device over a bicortical post was demonstrated. The titanium post required bicortical drilling as well as measurement with a depth gauge to ensure adequate screw length. This process appeared to require more time during specimen preparation and theoretically could prove to be more dangerous clinically.⁷ However, caution in using a SwiveLock anchor in osteoporotic bone is advised because of reduced pullout strength.²⁶ In this case, bicortical-post backup fixation may be more suitable. Moreover, although not demonstrated in this study, hardware prominence and irritation with a post may cause postoperative morbidity necessitating future removal.²⁰ Hardware removal was the most common reason for additional surgery using hamstring tendons as graft.²⁰ A second surgery for hardware removal was required in 21% of these patients.²⁰ This is unlikely to occur with a SwiveLock, as the anchor is buried within cortical bone.

Limitations

Regarding use of nonhuman tissues in a biomechanical model, porcine tibiae and bovine extensor tendons were used because of availability, consistency among specimens, and cost-effectiveness. However, bovine extensor tendons have been shown to exhibit stiffness and viscoelastic properties similar to those of a human hamstring graft.²⁷ In addition, the BMD of the porcine tibiae used in this study was not tested because of time involved and cost-efficiency. However, it has been shown that average BMD of porcine tibiae, 1.220-1.675 g/cm², is similar to that in a young athletic population, 1.24-1.62 g/cm².^3,28-31 We therefore assumed similarity to a young athletic population and uniformity of BMD of the porcine tibiae used in this study.

In addition, the biomechanical testing protocol did not simulate physiologic loading within the tibial tunnel. Moreover, the testing protocol used loads of only 250 N during cyclic testing for 500 cycles. This simulates only the early rehabilitation period and not the healing period, which may last up to 12 weeks.⁹ In addition, as previously mentioned, forces on the graft may be as high as 450 to 700 N.^11,32 Pullout testing in line with the long axis of the tibia was performed in order to compare mechanical testing results with those of similar studies.^3,12,13 Last, the P of .07 for the comparison of ultimate load to failure between the 2 backup fixation groups suggests that this study may have been underpowered.

Conclusion

This study demonstrated an effective, alternative, and equivalent backup fixation device that can help prevent graft slippage within the tibial tunnel during soft-tissue ACL reconstruction. Potential benefits of using SwiveLock anchors for backup fixation include a significantly increased ultimate yield load (229 N) when supplementing an interference screw, ease of insertion compared with a bicortical post, and the improbable need for future hardware removal. We support using SwiveLock for supplementary fixation at the tibial tunnel site when using soft-tissue grafts in ACL reconstruction.

Knotless suture anchor fixation techniques continue to evolve as efficient, low-profile options for arthroscopic rotator cuff repair (RCR).^1,2 Excellent outcomes have been reported for constructs that use knotless fixation laterally, typically in suture bridge-type configurations.^2-4 Early comparative biomechanical and clinical studies have also demonstrated equivalent results for all-knotless versus conventional constructs for arthroscopic RCR.^5-10 Given the increased use and availability of multiple implant designs, it is important to supplement our clinical knowledge of these devices with laboratory studies delineating the biomechanical properties of the anchors that are used to help guide appropriate clinical use of the implants in specific patient populations.

Several biomechanical studies have shown suture slippage to be the weak but crucial link in the design of knotless anchors and the most likely mode of in vivo failure.^11,12 Other studies have demonstrated frequent anchor dislodgement from bone, but these analyses involved use of elderly cadaveric specimens and relatively high-force testing protocols.^12,13 Because suture-retention force may have exceeded anchor resistance to pullout (imparted by weak cadaveric bone in such biomechanical settings), the focus on suture-retention properties was limited.¹¹ It is thought that, in clinical practice, the majority of patients who undergo RCR tend not to generate the high forces (relative to resistance to bone pullout) used to cause the anchor pullouts observed in biomechanical studies, particularly in the early postoperative setting.^11-15 Cadaveric testing, however, often involves use of specimens with diminished bone mineral density (BMD), relative to age, because of the illness and other factors leading to death and donation.

Using a novel testing apparatus, we isolated, analyzed, and compared suture slippage in 2 anchor designs, one with entirely press-fit suture clamping and the other reliant on an intrinsic suture-locking mechanism.

Materials and Methods

Six human cadaveric proximal humeri specimens were used for this biomechanical study. Mean (SD) age was 53.3 (5.7) years (range, 46-59 years). Middle-aged specimens were used in order to best represent the quality of bone typically encountered in RCR surgery. To approximate tissue in clinical use, we used fresh-frozen cadaver tissue. Specimens were maintained at –20°C until about 24 hours before use and then were thawed to room temperature for testing. Specimens were included only if they had a completely intact humeral head and no prior surgery or hardware placement. Before instrumentation, dual-energy x-ray absorptiometry with a QDR-1000 scanner (Hologic) was used to determine BMD of all proximal humeri.

Two knotless suture anchors were compared: PushLock (4.5×18.5 mm; Arthrex) and ReelX STT (5.5×19.4 mm; Stryker). These anchors have multiple surgical indications (including RCR), allow patient-specific tissue tensioning, and use polyetheretherketone eyelets. The clamping force for PushLock depends entirely on the interference fit achieved for the suture between the outside of the anchor and the surrounding trabecular/cortical bone after device insertion, whereas the suture in ReelX is secured within the anchor shaft entirely by an internal ratchet-locking mechanism.

For anchor insertion, shoulders were dissected down to the greater tuberosity of the proximal humerus, and all implants were inserted (by a fellowship-trained surgeon in accordance with manufacturer guidelines) at a 25° insertion angle with manufacturer-supplied instruments. One anchor of each type (Figure 1) was inserted into the center of the rotator cuff footprint on the greater tuberosity of each specimen. Anterior and posterior positions were randomized, and an anchor from the other group was inserted into the matching location on the contralateral matched-pair specimen. In all instances, distance between the anterior and posterior anchors was 2 cm, and anchors were placed midway between the articular margin and the lateral edge of the greater tuberosity (Figure 2). Two strands of size 2 ultrahigh-molecular-weight–polyethylene Force Fiber (Stryker) were loaded into all anchors.

A custom urethane fixture was secured over the center of each anchor to allow testing to focus on suture slippage by minimizing anchor migration (Figure 3). The small aperture of this device allowed suture tails to pass freely through the center of the fixture but prevented disengagement and proximal migration of the suture anchor from the underlying bone through contact of the urethane fixture with the anchor perimeter. Any system deformation observed during testing was restricted to the suture and/or the anchor’s suture-locking mechanism. Testing fixtures also oriented the suture anchor coaxial with the axis of tension, creating a worst-case loading scenario (Figure 3).

PushLock implants were inserted with 5 pounds of tension, as indicated, using a manufacturer-supplied suture tensioner, and ReelX devices were inserted and locked with 2 full rotations, as specified by the manufacturer. After one end of each suture was cut, as would be done in vivo, the 2 other suture ends, which would have been part of the RCR in vivo, were tied together to form an 8-cm circumference loop that was brought through the urethane fixture. Humeri were then mounted in a materials testing system (MTS 810; MTS Systems) servohydraulic load frame, and the suture loop was passed around a cross-bar on the actuator of the testing device. A mechanical testing protocol consisting of modest repetitive forces was carefully chosen to simulate expected activity during rehabilitation after RCR.¹⁵ In this protocol, a 60-second preload of 10 N was followed by tensile loading between 10 N and 90 N at a frequency of 0.5 Hz for 500 cycles.¹⁵ Cycle duration at 3 mm and 5 mm of suture slippage (threshold for clinical failure) was recorded.^12,16,17 In addition, suture slippage was measured after 1, 10, 50, 100, 200, 300, 400, and 500 cycles. The first 5 test cycles were not counted in the analysis to control for initial knot slippage. Finally, after completion of dynamic testing, samples were loaded at a displacement rate of 0.5 mm/s for tension-to-failure testing in the custom fixtures. Maximum failure load, stiffness, and failure mode were recorded. Ultimate failure was defined as suture breakage or gross suture slippage.

Paired Student t test was used to determine significant differences in suture slippage distance between the 2 groups at various cycle durations. In addition, Kaplan-Meier survival test was used to determine statistical differences in sample survival during the dynamic loading test.

Results

Mean (SD) BMD of the cadaveric shoulder specimens was 0.55 (0.13) g/cm² (range, 0.29-0.68 g/cm²). The testing fixtures isolated suture slippage from anchor–bone disengagement. All 6 PushLock implants demonstrated slippage of more than 3 mm, and 5 of the 6 demonstrated slippage of more than 5 mm. All 6 ReelX devices exhibited slippage of less than 3 mm. In addition, PushLock demonstrated more suture slippage at cycles 1, 10, and 100 (P < .05) and more maximum slippage after 500 cycles (mean, 11.2 mm; SD, 4.7 mm) compared with ReelX (mean, 1.9 mm; SD, 0.5 mm) (P = .004). Figure 4 shows mean suture slippage at each cycle.

 Kaplan-Meier analysis revealed significantly (λ² = 8.170; P = .0043) decreased survival after dynamic testing for PushLock versus ReelX (Figure 5). Survival was defined as suture slippage of less than 5 mm after completion of dynamic testing. Only 1 of the 6 PushLock anchors completed dynamic testing; the other 5 failed via complete suture slippage from the anchor before testing could be completed. All 6 ReelX devices survived dynamic testing.

Therefore, 1 PushLock implant and all 6 ReelX devices were available for subsequent load-to-failure testing. Failure in this setting was defined as suture slippage of more than 10 mm or suture breakage. The PushLock implant failed at a maximum force of 171.8 N with a stiffness of 74.4 N/mm and eventually exhibited gross suture slippage. All 6 ReelX devices failed at a mean (SD) maximum of 273.5 (20.2) N, with a mean (SD) stiffness of 74.1 (17) N/mm. Mechanism of failure for all ReelX devices was suture breakage during the tensile load-to-failure test.

Discussion

We evaluated a new technique designed to isolate suture slippage in knotless anchors used for RCR. The impetus for developing this new method was to provide a means for better analyzing the ability of a knotless anchor to resist suture slippage in the cadaveric biomechanical testing setting. Suture slippage is an important mode of failure during such analyses.^11,12 Significant slippage occurred in a range of implants before half the anchor–bone pullout strength was reached in a study using young bovine femoral heads.¹¹ In another study, using young, high-BMD cadaveric humeral heads, initial slippage and maximum failure loads were equivalent among numerous devices using various suture-retention mechanisms, and suture slippage was the most common failure mode.¹² Nevertheless, other biomechanical studies have demonstrated frequent failure caused by anchor pullout in elderly human cadaveric specimens with diminished BMD, often with high-force testing protocols.^12,13 In the more modest-force, in vivo rehabilitative environment, suture slippage rather than anchor dislodgement may be the main failure mode.^11-15

We compared the PushLock implant and its entirely press-fit suture clamping design with the ReelX device, which relies on an intrinsic suture-locking mechanism. Middle-aged (mean, 53.3 years; SD, 5.7 years) cadaveric humeri were tested under physiologically relevant biomechanical conditions to begin to help identify how relatively osteopenic bone may affect suture-retention properties for a given implant. The results showed that the study methodology prevented implant failure via anchor–bone pullout. To our knowledge, this was the first study to exclusively analyze suture slippage in knotless anchors. The findings indicated that implants that rely heavily on a tight interference fit of the suture between the anchor and the surrounding bone may exhibit early slippage and failure after RCR in middle-aged patients with relative osteopenia.^11,12 However, this study also demonstrated that devices with intrinsic clamping mechanisms that do not depend on the quality of surrounding bone may better resist suture slippage. It is not clear that all knotless anchors with intrinsic locking mechanisms function equivalently. For instance, Pietschmann and colleagues¹² found that 2 of 10 implants with a different internal clamping device were unable to resist failure via suture slippage, even in healthy bone. Similarly, in a study comparing ReelX devices with implants having a different internal suture-retention mechanism, ReelX failed at higher ultimate loads, and typically via anchor dislodgement, versus suture slippage in the other implants.¹⁸

It is important to note that, in the present study, the loads at which sutures broke in the intrinsic clamping anchors approached the maximum contractile force of the supraspinatus muscle (302 N).^19,20 In addition, these loads were above the resistance of the rotator cuff tendon to cut out with modern suture material.²¹

This study’s limitations include use of an in vitro human cadaveric model that precluded analysis of the effects of postoperative healing. Biomechanical testing was also performed in a single row-type suture configuration with the rotator cuff tendon removed. Fixtures used during testing oriented the load coaxially with the axis of tension, creating a worst-case loading scenario. Although this form of testing may limit its clinical applicability, its purpose was to critically isolate how well a knotless anchor could resist suture slippage. The methods we used were also limited because the stability of the bone–anchor interface was not assessed. For patients with osteopenia, anchor pullout rather than suture slippage could be the most limiting factor for knotless anchor construct failure, and therefore further testing of both failure modes is needed. Future biomechanical studies should compare various knotless anchors’ suture-slippage characteristics in other constructs in physiologic testing orientations, including double-row and suture-bridge configurations, as well as with intact rotator cuff tendons. In addition, use of labral tape as a substitute for polyblend suture has been suggested to limit suture slippage, and this technique theoretically could have changed the results of this study.²²

Conclusion

An implant with an internal ratcheting mechanism for suture retention demonstrated significantly less suture slippage in an axial tension evaluation protocol than a device reliant on interference fit of the suture between the anchor and surrounding bone. In the clinical setting, this may allow for less gap formation during the healing phase following RCR with a knotless anchor. There was also increased maximum load to failure, demonstrating an increased load until catastrophic failure using a device with a ratcheting internal locking mechanism.

Knotless suture anchor fixation techniques continue to evolve as efficient, low-profile options for arthroscopic rotator cuff repair (RCR).^1,2 Excellent outcomes have been reported for constructs that use knotless fixation laterally, typically in suture bridge-type configurations.^2-4 Early comparative biomechanical and clinical studies have also demonstrated equivalent results for all-knotless versus conventional constructs for arthroscopic RCR.^5-10 Given the increased use and availability of multiple implant designs, it is important to supplement our clinical knowledge of these devices with laboratory studies delineating the biomechanical properties of the anchors that are used to help guide appropriate clinical use of the implants in specific patient populations.

Several biomechanical studies have shown suture slippage to be the weak but crucial link in the design of knotless anchors and the most likely mode of in vivo failure.^11,12 Other studies have demonstrated frequent anchor dislodgement from bone, but these analyses involved use of elderly cadaveric specimens and relatively high-force testing protocols.^12,13 Because suture-retention force may have exceeded anchor resistance to pullout (imparted by weak cadaveric bone in such biomechanical settings), the focus on suture-retention properties was limited.¹¹ It is thought that, in clinical practice, the majority of patients who undergo RCR tend not to generate the high forces (relative to resistance to bone pullout) used to cause the anchor pullouts observed in biomechanical studies, particularly in the early postoperative setting.^11-15 Cadaveric testing, however, often involves use of specimens with diminished bone mineral density (BMD), relative to age, because of the illness and other factors leading to death and donation.

Using a novel testing apparatus, we isolated, analyzed, and compared suture slippage in 2 anchor designs, one with entirely press-fit suture clamping and the other reliant on an intrinsic suture-locking mechanism.

Materials and Methods

Six human cadaveric proximal humeri specimens were used for this biomechanical study. Mean (SD) age was 53.3 (5.7) years (range, 46-59 years). Middle-aged specimens were used in order to best represent the quality of bone typically encountered in RCR surgery. To approximate tissue in clinical use, we used fresh-frozen cadaver tissue. Specimens were maintained at –20°C until about 24 hours before use and then were thawed to room temperature for testing. Specimens were included only if they had a completely intact humeral head and no prior surgery or hardware placement. Before instrumentation, dual-energy x-ray absorptiometry with a QDR-1000 scanner (Hologic) was used to determine BMD of all proximal humeri.

Two knotless suture anchors were compared: PushLock (4.5×18.5 mm; Arthrex) and ReelX STT (5.5×19.4 mm; Stryker). These anchors have multiple surgical indications (including RCR), allow patient-specific tissue tensioning, and use polyetheretherketone eyelets. The clamping force for PushLock depends entirely on the interference fit achieved for the suture between the outside of the anchor and the surrounding trabecular/cortical bone after device insertion, whereas the suture in ReelX is secured within the anchor shaft entirely by an internal ratchet-locking mechanism.

For anchor insertion, shoulders were dissected down to the greater tuberosity of the proximal humerus, and all implants were inserted (by a fellowship-trained surgeon in accordance with manufacturer guidelines) at a 25° insertion angle with manufacturer-supplied instruments. One anchor of each type (Figure 1) was inserted into the center of the rotator cuff footprint on the greater tuberosity of each specimen. Anterior and posterior positions were randomized, and an anchor from the other group was inserted into the matching location on the contralateral matched-pair specimen. In all instances, distance between the anterior and posterior anchors was 2 cm, and anchors were placed midway between the articular margin and the lateral edge of the greater tuberosity (Figure 2). Two strands of size 2 ultrahigh-molecular-weight–polyethylene Force Fiber (Stryker) were loaded into all anchors.

A custom urethane fixture was secured over the center of each anchor to allow testing to focus on suture slippage by minimizing anchor migration (Figure 3). The small aperture of this device allowed suture tails to pass freely through the center of the fixture but prevented disengagement and proximal migration of the suture anchor from the underlying bone through contact of the urethane fixture with the anchor perimeter. Any system deformation observed during testing was restricted to the suture and/or the anchor’s suture-locking mechanism. Testing fixtures also oriented the suture anchor coaxial with the axis of tension, creating a worst-case loading scenario (Figure 3).

PushLock implants were inserted with 5 pounds of tension, as indicated, using a manufacturer-supplied suture tensioner, and ReelX devices were inserted and locked with 2 full rotations, as specified by the manufacturer. After one end of each suture was cut, as would be done in vivo, the 2 other suture ends, which would have been part of the RCR in vivo, were tied together to form an 8-cm circumference loop that was brought through the urethane fixture. Humeri were then mounted in a materials testing system (MTS 810; MTS Systems) servohydraulic load frame, and the suture loop was passed around a cross-bar on the actuator of the testing device. A mechanical testing protocol consisting of modest repetitive forces was carefully chosen to simulate expected activity during rehabilitation after RCR.¹⁵ In this protocol, a 60-second preload of 10 N was followed by tensile loading between 10 N and 90 N at a frequency of 0.5 Hz for 500 cycles.¹⁵ Cycle duration at 3 mm and 5 mm of suture slippage (threshold for clinical failure) was recorded.^12,16,17 In addition, suture slippage was measured after 1, 10, 50, 100, 200, 300, 400, and 500 cycles. The first 5 test cycles were not counted in the analysis to control for initial knot slippage. Finally, after completion of dynamic testing, samples were loaded at a displacement rate of 0.5 mm/s for tension-to-failure testing in the custom fixtures. Maximum failure load, stiffness, and failure mode were recorded. Ultimate failure was defined as suture breakage or gross suture slippage.

Paired Student t test was used to determine significant differences in suture slippage distance between the 2 groups at various cycle durations. In addition, Kaplan-Meier survival test was used to determine statistical differences in sample survival during the dynamic loading test.

Results

Mean (SD) BMD of the cadaveric shoulder specimens was 0.55 (0.13) g/cm² (range, 0.29-0.68 g/cm²). The testing fixtures isolated suture slippage from anchor–bone disengagement. All 6 PushLock implants demonstrated slippage of more than 3 mm, and 5 of the 6 demonstrated slippage of more than 5 mm. All 6 ReelX devices exhibited slippage of less than 3 mm. In addition, PushLock demonstrated more suture slippage at cycles 1, 10, and 100 (P < .05) and more maximum slippage after 500 cycles (mean, 11.2 mm; SD, 4.7 mm) compared with ReelX (mean, 1.9 mm; SD, 0.5 mm) (P = .004). Figure 4 shows mean suture slippage at each cycle.

 Kaplan-Meier analysis revealed significantly (λ² = 8.170; P = .0043) decreased survival after dynamic testing for PushLock versus ReelX (Figure 5). Survival was defined as suture slippage of less than 5 mm after completion of dynamic testing. Only 1 of the 6 PushLock anchors completed dynamic testing; the other 5 failed via complete suture slippage from the anchor before testing could be completed. All 6 ReelX devices survived dynamic testing.

Therefore, 1 PushLock implant and all 6 ReelX devices were available for subsequent load-to-failure testing. Failure in this setting was defined as suture slippage of more than 10 mm or suture breakage. The PushLock implant failed at a maximum force of 171.8 N with a stiffness of 74.4 N/mm and eventually exhibited gross suture slippage. All 6 ReelX devices failed at a mean (SD) maximum of 273.5 (20.2) N, with a mean (SD) stiffness of 74.1 (17) N/mm. Mechanism of failure for all ReelX devices was suture breakage during the tensile load-to-failure test.

Discussion

We evaluated a new technique designed to isolate suture slippage in knotless anchors used for RCR. The impetus for developing this new method was to provide a means for better analyzing the ability of a knotless anchor to resist suture slippage in the cadaveric biomechanical testing setting. Suture slippage is an important mode of failure during such analyses.^11,12 Significant slippage occurred in a range of implants before half the anchor–bone pullout strength was reached in a study using young bovine femoral heads.¹¹ In another study, using young, high-BMD cadaveric humeral heads, initial slippage and maximum failure loads were equivalent among numerous devices using various suture-retention mechanisms, and suture slippage was the most common failure mode.¹² Nevertheless, other biomechanical studies have demonstrated frequent failure caused by anchor pullout in elderly human cadaveric specimens with diminished BMD, often with high-force testing protocols.^12,13 In the more modest-force, in vivo rehabilitative environment, suture slippage rather than anchor dislodgement may be the main failure mode.^11-15

We compared the PushLock implant and its entirely press-fit suture clamping design with the ReelX device, which relies on an intrinsic suture-locking mechanism. Middle-aged (mean, 53.3 years; SD, 5.7 years) cadaveric humeri were tested under physiologically relevant biomechanical conditions to begin to help identify how relatively osteopenic bone may affect suture-retention properties for a given implant. The results showed that the study methodology prevented implant failure via anchor–bone pullout. To our knowledge, this was the first study to exclusively analyze suture slippage in knotless anchors. The findings indicated that implants that rely heavily on a tight interference fit of the suture between the anchor and the surrounding bone may exhibit early slippage and failure after RCR in middle-aged patients with relative osteopenia.^11,12 However, this study also demonstrated that devices with intrinsic clamping mechanisms that do not depend on the quality of surrounding bone may better resist suture slippage. It is not clear that all knotless anchors with intrinsic locking mechanisms function equivalently. For instance, Pietschmann and colleagues¹² found that 2 of 10 implants with a different internal clamping device were unable to resist failure via suture slippage, even in healthy bone. Similarly, in a study comparing ReelX devices with implants having a different internal suture-retention mechanism, ReelX failed at higher ultimate loads, and typically via anchor dislodgement, versus suture slippage in the other implants.¹⁸

It is important to note that, in the present study, the loads at which sutures broke in the intrinsic clamping anchors approached the maximum contractile force of the supraspinatus muscle (302 N).^19,20 In addition, these loads were above the resistance of the rotator cuff tendon to cut out with modern suture material.²¹

This study’s limitations include use of an in vitro human cadaveric model that precluded analysis of the effects of postoperative healing. Biomechanical testing was also performed in a single row-type suture configuration with the rotator cuff tendon removed. Fixtures used during testing oriented the load coaxially with the axis of tension, creating a worst-case loading scenario. Although this form of testing may limit its clinical applicability, its purpose was to critically isolate how well a knotless anchor could resist suture slippage. The methods we used were also limited because the stability of the bone–anchor interface was not assessed. For patients with osteopenia, anchor pullout rather than suture slippage could be the most limiting factor for knotless anchor construct failure, and therefore further testing of both failure modes is needed. Future biomechanical studies should compare various knotless anchors’ suture-slippage characteristics in other constructs in physiologic testing orientations, including double-row and suture-bridge configurations, as well as with intact rotator cuff tendons. In addition, use of labral tape as a substitute for polyblend suture has been suggested to limit suture slippage, and this technique theoretically could have changed the results of this study.²²

Conclusion

An implant with an internal ratcheting mechanism for suture retention demonstrated significantly less suture slippage in an axial tension evaluation protocol than a device reliant on interference fit of the suture between the anchor and surrounding bone. In the clinical setting, this may allow for less gap formation during the healing phase following RCR with a knotless anchor. There was also increased maximum load to failure, demonstrating an increased load until catastrophic failure using a device with a ratcheting internal locking mechanism.

Knotless suture anchor fixation techniques continue to evolve as efficient, low-profile options for arthroscopic rotator cuff repair (RCR).^1,2 Excellent outcomes have been reported for constructs that use knotless fixation laterally, typically in suture bridge-type configurations.^2-4 Early comparative biomechanical and clinical studies have also demonstrated equivalent results for all-knotless versus conventional constructs for arthroscopic RCR.^5-10 Given the increased use and availability of multiple implant designs, it is important to supplement our clinical knowledge of these devices with laboratory studies delineating the biomechanical properties of the anchors that are used to help guide appropriate clinical use of the implants in specific patient populations.

Several biomechanical studies have shown suture slippage to be the weak but crucial link in the design of knotless anchors and the most likely mode of in vivo failure.^11,12 Other studies have demonstrated frequent anchor dislodgement from bone, but these analyses involved use of elderly cadaveric specimens and relatively high-force testing protocols.^12,13 Because suture-retention force may have exceeded anchor resistance to pullout (imparted by weak cadaveric bone in such biomechanical settings), the focus on suture-retention properties was limited.¹¹ It is thought that, in clinical practice, the majority of patients who undergo RCR tend not to generate the high forces (relative to resistance to bone pullout) used to cause the anchor pullouts observed in biomechanical studies, particularly in the early postoperative setting.^11-15 Cadaveric testing, however, often involves use of specimens with diminished bone mineral density (BMD), relative to age, because of the illness and other factors leading to death and donation.

Using a novel testing apparatus, we isolated, analyzed, and compared suture slippage in 2 anchor designs, one with entirely press-fit suture clamping and the other reliant on an intrinsic suture-locking mechanism.

Materials and Methods

Six human cadaveric proximal humeri specimens were used for this biomechanical study. Mean (SD) age was 53.3 (5.7) years (range, 46-59 years). Middle-aged specimens were used in order to best represent the quality of bone typically encountered in RCR surgery. To approximate tissue in clinical use, we used fresh-frozen cadaver tissue. Specimens were maintained at –20°C until about 24 hours before use and then were thawed to room temperature for testing. Specimens were included only if they had a completely intact humeral head and no prior surgery or hardware placement. Before instrumentation, dual-energy x-ray absorptiometry with a QDR-1000 scanner (Hologic) was used to determine BMD of all proximal humeri.

Two knotless suture anchors were compared: PushLock (4.5×18.5 mm; Arthrex) and ReelX STT (5.5×19.4 mm; Stryker). These anchors have multiple surgical indications (including RCR), allow patient-specific tissue tensioning, and use polyetheretherketone eyelets. The clamping force for PushLock depends entirely on the interference fit achieved for the suture between the outside of the anchor and the surrounding trabecular/cortical bone after device insertion, whereas the suture in ReelX is secured within the anchor shaft entirely by an internal ratchet-locking mechanism.

For anchor insertion, shoulders were dissected down to the greater tuberosity of the proximal humerus, and all implants were inserted (by a fellowship-trained surgeon in accordance with manufacturer guidelines) at a 25° insertion angle with manufacturer-supplied instruments. One anchor of each type (Figure 1) was inserted into the center of the rotator cuff footprint on the greater tuberosity of each specimen. Anterior and posterior positions were randomized, and an anchor from the other group was inserted into the matching location on the contralateral matched-pair specimen. In all instances, distance between the anterior and posterior anchors was 2 cm, and anchors were placed midway between the articular margin and the lateral edge of the greater tuberosity (Figure 2). Two strands of size 2 ultrahigh-molecular-weight–polyethylene Force Fiber (Stryker) were loaded into all anchors.

A custom urethane fixture was secured over the center of each anchor to allow testing to focus on suture slippage by minimizing anchor migration (Figure 3). The small aperture of this device allowed suture tails to pass freely through the center of the fixture but prevented disengagement and proximal migration of the suture anchor from the underlying bone through contact of the urethane fixture with the anchor perimeter. Any system deformation observed during testing was restricted to the suture and/or the anchor’s suture-locking mechanism. Testing fixtures also oriented the suture anchor coaxial with the axis of tension, creating a worst-case loading scenario (Figure 3).

PushLock implants were inserted with 5 pounds of tension, as indicated, using a manufacturer-supplied suture tensioner, and ReelX devices were inserted and locked with 2 full rotations, as specified by the manufacturer. After one end of each suture was cut, as would be done in vivo, the 2 other suture ends, which would have been part of the RCR in vivo, were tied together to form an 8-cm circumference loop that was brought through the urethane fixture. Humeri were then mounted in a materials testing system (MTS 810; MTS Systems) servohydraulic load frame, and the suture loop was passed around a cross-bar on the actuator of the testing device. A mechanical testing protocol consisting of modest repetitive forces was carefully chosen to simulate expected activity during rehabilitation after RCR.¹⁵ In this protocol, a 60-second preload of 10 N was followed by tensile loading between 10 N and 90 N at a frequency of 0.5 Hz for 500 cycles.¹⁵ Cycle duration at 3 mm and 5 mm of suture slippage (threshold for clinical failure) was recorded.^12,16,17 In addition, suture slippage was measured after 1, 10, 50, 100, 200, 300, 400, and 500 cycles. The first 5 test cycles were not counted in the analysis to control for initial knot slippage. Finally, after completion of dynamic testing, samples were loaded at a displacement rate of 0.5 mm/s for tension-to-failure testing in the custom fixtures. Maximum failure load, stiffness, and failure mode were recorded. Ultimate failure was defined as suture breakage or gross suture slippage.

Paired Student t test was used to determine significant differences in suture slippage distance between the 2 groups at various cycle durations. In addition, Kaplan-Meier survival test was used to determine statistical differences in sample survival during the dynamic loading test.

Results

Mean (SD) BMD of the cadaveric shoulder specimens was 0.55 (0.13) g/cm² (range, 0.29-0.68 g/cm²). The testing fixtures isolated suture slippage from anchor–bone disengagement. All 6 PushLock implants demonstrated slippage of more than 3 mm, and 5 of the 6 demonstrated slippage of more than 5 mm. All 6 ReelX devices exhibited slippage of less than 3 mm. In addition, PushLock demonstrated more suture slippage at cycles 1, 10, and 100 (P < .05) and more maximum slippage after 500 cycles (mean, 11.2 mm; SD, 4.7 mm) compared with ReelX (mean, 1.9 mm; SD, 0.5 mm) (P = .004). Figure 4 shows mean suture slippage at each cycle.

 Kaplan-Meier analysis revealed significantly (λ² = 8.170; P = .0043) decreased survival after dynamic testing for PushLock versus ReelX (Figure 5). Survival was defined as suture slippage of less than 5 mm after completion of dynamic testing. Only 1 of the 6 PushLock anchors completed dynamic testing; the other 5 failed via complete suture slippage from the anchor before testing could be completed. All 6 ReelX devices survived dynamic testing.

Therefore, 1 PushLock implant and all 6 ReelX devices were available for subsequent load-to-failure testing. Failure in this setting was defined as suture slippage of more than 10 mm or suture breakage. The PushLock implant failed at a maximum force of 171.8 N with a stiffness of 74.4 N/mm and eventually exhibited gross suture slippage. All 6 ReelX devices failed at a mean (SD) maximum of 273.5 (20.2) N, with a mean (SD) stiffness of 74.1 (17) N/mm. Mechanism of failure for all ReelX devices was suture breakage during the tensile load-to-failure test.

Discussion

We evaluated a new technique designed to isolate suture slippage in knotless anchors used for RCR. The impetus for developing this new method was to provide a means for better analyzing the ability of a knotless anchor to resist suture slippage in the cadaveric biomechanical testing setting. Suture slippage is an important mode of failure during such analyses.^11,12 Significant slippage occurred in a range of implants before half the anchor–bone pullout strength was reached in a study using young bovine femoral heads.¹¹ In another study, using young, high-BMD cadaveric humeral heads, initial slippage and maximum failure loads were equivalent among numerous devices using various suture-retention mechanisms, and suture slippage was the most common failure mode.¹² Nevertheless, other biomechanical studies have demonstrated frequent failure caused by anchor pullout in elderly human cadaveric specimens with diminished BMD, often with high-force testing protocols.^12,13 In the more modest-force, in vivo rehabilitative environment, suture slippage rather than anchor dislodgement may be the main failure mode.^11-15

We compared the PushLock implant and its entirely press-fit suture clamping design with the ReelX device, which relies on an intrinsic suture-locking mechanism. Middle-aged (mean, 53.3 years; SD, 5.7 years) cadaveric humeri were tested under physiologically relevant biomechanical conditions to begin to help identify how relatively osteopenic bone may affect suture-retention properties for a given implant. The results showed that the study methodology prevented implant failure via anchor–bone pullout. To our knowledge, this was the first study to exclusively analyze suture slippage in knotless anchors. The findings indicated that implants that rely heavily on a tight interference fit of the suture between the anchor and the surrounding bone may exhibit early slippage and failure after RCR in middle-aged patients with relative osteopenia.^11,12 However, this study also demonstrated that devices with intrinsic clamping mechanisms that do not depend on the quality of surrounding bone may better resist suture slippage. It is not clear that all knotless anchors with intrinsic locking mechanisms function equivalently. For instance, Pietschmann and colleagues¹² found that 2 of 10 implants with a different internal clamping device were unable to resist failure via suture slippage, even in healthy bone. Similarly, in a study comparing ReelX devices with implants having a different internal suture-retention mechanism, ReelX failed at higher ultimate loads, and typically via anchor dislodgement, versus suture slippage in the other implants.¹⁸

It is important to note that, in the present study, the loads at which sutures broke in the intrinsic clamping anchors approached the maximum contractile force of the supraspinatus muscle (302 N).^19,20 In addition, these loads were above the resistance of the rotator cuff tendon to cut out with modern suture material.²¹

This study’s limitations include use of an in vitro human cadaveric model that precluded analysis of the effects of postoperative healing. Biomechanical testing was also performed in a single row-type suture configuration with the rotator cuff tendon removed. Fixtures used during testing oriented the load coaxially with the axis of tension, creating a worst-case loading scenario. Although this form of testing may limit its clinical applicability, its purpose was to critically isolate how well a knotless anchor could resist suture slippage. The methods we used were also limited because the stability of the bone–anchor interface was not assessed. For patients with osteopenia, anchor pullout rather than suture slippage could be the most limiting factor for knotless anchor construct failure, and therefore further testing of both failure modes is needed. Future biomechanical studies should compare various knotless anchors’ suture-slippage characteristics in other constructs in physiologic testing orientations, including double-row and suture-bridge configurations, as well as with intact rotator cuff tendons. In addition, use of labral tape as a substitute for polyblend suture has been suggested to limit suture slippage, and this technique theoretically could have changed the results of this study.²²

Conclusion

An implant with an internal ratcheting mechanism for suture retention demonstrated significantly less suture slippage in an axial tension evaluation protocol than a device reliant on interference fit of the suture between the anchor and surrounding bone. In the clinical setting, this may allow for less gap formation during the healing phase following RCR with a knotless anchor. There was also increased maximum load to failure, demonstrating an increased load until catastrophic failure using a device with a ratcheting internal locking mechanism.

As the largest sesamoid bone in the human body, the patella acts as a fulcrum to enhance the biomechanical advantage of the quadriceps in extension.¹ It is subject to a variety of forces while improving distribution of forces along the extensor mechanism.² With sufficient force, the patella can be dislocated. Acute patellar dislocations are the most common knee injury, encompassing 2% to 3% of all knee injuries³ and occurring in 5.8 per 100,000 individuals.^4-5 These injuries are associated with acute trauma, frequently from sports and physical activities, occurring while in terminal extension with an axial-valgus stress on the knee during rotation.⁶

With acute patellar dislocations, patients are usually in significant discomfort. Often, the patella may spontaneously reduce; if not, closed reduction is usually successful with pressure applied anteromedially on the lateral patellar margin, while simultaneously attempting gentle extension of the leg.⁷ Closed reduction is almost universally successful, and there have only been case reports of irreducible, mainly fixed vertical axis patellar dislocations.^8-11 No reports in the literature have described subacute patellar dislocations because of their rarity. Patients present immediately after dislocation, spontaneously reduce, or have a painless, chronically dislocated patella.

We present a case of an elderly man with dementia and a subacute fixed irreducible patellar dislocation, which was reduced using a technique not described in the literature. The patient and the patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A 68-year-old nonambulatory man with a history of dementia and stroke presented to the emergency department with complaints of left knee pain and his knee locked in flexion. The patient’s knee had been in that fixed hyperflexed position for at least 10 days after he sustained a twisting injury to his knee while attempting to get out of bed. At baseline, the patient was mostly bedbound and could walk minimally with maximum support, but, given his dementia, he would often attempt to ambulate by himself. After the injury, the patient did not complain of much pain at rest, but attempts at his group home to straighten his leg had caused severe pain. As a result, the patient was brought to the emergency department to be evaluated for fractures. 

Physical examination in the emergency department revealed atrophy of the lower extremity musculature and a left knee fixed at 120º in flexion. The skin was intact, and there was minimal effusion of the knee joint. The patella was noted to be laterally subluxated and tender to palpation over the lateral and medial facets. He was neurovascularly intact distally and had painless range of motion of his hips. His contralateral right knee had full range of motion with good patellar tracking.

Radiographs of the patient’s knee confirmed a lateral dislocation of the patella (Figures 1A-1C). After oral and intravenous administration of pain medication, a reduction was attempted without success. Next, an intra-articular knee injection of 10 mL of 1% lidocaine was given. After waiting 15 minutes, another reduction was tried. While the pain control was sufficient, the reduction was again unsuccessful. The knee was insufflated with 120 mL of sterile saline and reduction attempted again. By extending the knee and applying a medially directed force to the patella, reduction was successful. The patient was placed into a knee immobilizer and postreduction radiographs were taken (Figures 2A, 2B). Saline was extracted from the knee. The patient was admitted to the hospital where repeat examination of his knees during the next week revealed markedly less pain. The patient was lost to follow-up.

Discussion

Our patient presumably had a low-energy mechanism of injury, resulting in an undiagnosed patellar dislocation with delayed treatment. This subacute patellar dislocation was irreducible using the standard techniques. Alternatively, insufflation of the joint with saline provided the necessary impetus to allow for successful patellar reduction. The history of the patient reveals clues about the mechanism of injury. It is likely that the patient’s nonambulatory status resulted in a weak vastus medialis muscle that placed the patella at risk for dislocation. While the exact mechanism of dislocation is unknown, the patella was unable to be reduced spontaneously because our patient’s knee was maintained in a state of flexion secondary to pain and muscle contraction. The combination of weak quadriceps musculature, increased Q angle, and forced hyperflexion of the knee prevented closed reduction of the patella.

Fixed, irreducible patellar dislocations are rare and discussed infrequently in the literature.^9,11-12 Reported mechanisms are mostly high energy, including blows during athletics and impacts from motor vehicle collisions.^9,13 Vertical axis rotation, as first described by Cooper,¹⁴ is commonly implicated in irreducible patellar dislocations. This occurs when the patella internally rotates 180º on its vertical axis, associated with a large tear of the medial retinaculum but intact quadriceps tendon. The patella is fixed over the lateral femoral condyle with the articular surface pointing anterolaterally. Despite adequate sedation and analgesia, these are notoriously difficult to close-reduce and may necessitate open reduction.³ Our patient, while having a fixed dislocation, did not have a vertical axis component and, therefore, was amenable to our closed reduction attempt.

Our first reduction attempts were unsuccessful, likely because the patient continued to be tense, firing his quadriceps. Even after injecting the knee with lidocaine and eliminating the pain component, the patella was still impinging on the lateral femoral condyle (Figure 3A). By insufflating the knee with saline, we were able to increase the distance from the patella to the trochlea (Figure 3B). This is comparable to a knee arthroscopy, in which joint fluid pressure allows passage of arthroscopic instruments into the patellofemoral joint. We postulate that the farther the patella is anterior to the trochlea, the higher the likelihood that the patella can be reduced to its anatomic position. 

Insufflation of the knee with sterile saline is a novel technique that involves minimal risk compared with the alternatives. Sometimes, for closed reduction to be successful, individuals need to be consciously sedated to relax their muscles and eliminate pain. While conscious sedation is generally considered low risk, complications have been noted, including hypotension, apnea, and retrograde amnesia.¹⁵ Manual closed reduction may also cause additional chondral damage when the medial patellar facet contacts the lateral femoral trochlea. When closed reduction of the patella fails, open reduction is required; this inherently includes all the risks of surgery, such as bleeding, infection, neurovascular injury, and wound complications.  

Our insufflation technique does not require sedation and is minimally invasive. The saline creates space and provides lubrication to allow for easier manipulation of the patella. This theoretically protects the cartilage as the patella passes over the lateral trochlea. In addition to the intended effect of providing more space and lubrication for the reduction of the patella, insufflation of the joint may also relax the vastus musculature.¹⁶ In their study, Torry and colleagues¹⁶ injected 13 knees with 20 mL sterile saline and noted reduction in electromyography readings in the vastus medialis and lateralis muscles. This inhibition of vastus musculature may provide enough relaxation to aid in the successful reduction of the patella.

Our study is limited by our sample size of 1. Because acute patellar dislocations are often easily reduced, our technical trick is not frequently used. Additionally, while we were able to monitor his progress during his inpatient stay, our patient was lost to follow-up after his discharge from the hospital.

 If successful, the insufflation technique eliminates the need for urgent open reduction in the operating room. As a result, we recommend attempting closed reduction using insufflation of the knee with sterile saline for irreducible patellar dislocations before proceeding with open reduction.

Conclusion

Saline insufflation of the knee can be safely and easily performed to aid in the reduction of subacute, difficult patellar dislocations.

As the largest sesamoid bone in the human body, the patella acts as a fulcrum to enhance the biomechanical advantage of the quadriceps in extension.¹ It is subject to a variety of forces while improving distribution of forces along the extensor mechanism.² With sufficient force, the patella can be dislocated. Acute patellar dislocations are the most common knee injury, encompassing 2% to 3% of all knee injuries³ and occurring in 5.8 per 100,000 individuals.^4-5 These injuries are associated with acute trauma, frequently from sports and physical activities, occurring while in terminal extension with an axial-valgus stress on the knee during rotation.⁶

With acute patellar dislocations, patients are usually in significant discomfort. Often, the patella may spontaneously reduce; if not, closed reduction is usually successful with pressure applied anteromedially on the lateral patellar margin, while simultaneously attempting gentle extension of the leg.⁷ Closed reduction is almost universally successful, and there have only been case reports of irreducible, mainly fixed vertical axis patellar dislocations.^8-11 No reports in the literature have described subacute patellar dislocations because of their rarity. Patients present immediately after dislocation, spontaneously reduce, or have a painless, chronically dislocated patella.

We present a case of an elderly man with dementia and a subacute fixed irreducible patellar dislocation, which was reduced using a technique not described in the literature. The patient and the patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A 68-year-old nonambulatory man with a history of dementia and stroke presented to the emergency department with complaints of left knee pain and his knee locked in flexion. The patient’s knee had been in that fixed hyperflexed position for at least 10 days after he sustained a twisting injury to his knee while attempting to get out of bed. At baseline, the patient was mostly bedbound and could walk minimally with maximum support, but, given his dementia, he would often attempt to ambulate by himself. After the injury, the patient did not complain of much pain at rest, but attempts at his group home to straighten his leg had caused severe pain. As a result, the patient was brought to the emergency department to be evaluated for fractures. 

Physical examination in the emergency department revealed atrophy of the lower extremity musculature and a left knee fixed at 120º in flexion. The skin was intact, and there was minimal effusion of the knee joint. The patella was noted to be laterally subluxated and tender to palpation over the lateral and medial facets. He was neurovascularly intact distally and had painless range of motion of his hips. His contralateral right knee had full range of motion with good patellar tracking.

Radiographs of the patient’s knee confirmed a lateral dislocation of the patella (Figures 1A-1C). After oral and intravenous administration of pain medication, a reduction was attempted without success. Next, an intra-articular knee injection of 10 mL of 1% lidocaine was given. After waiting 15 minutes, another reduction was tried. While the pain control was sufficient, the reduction was again unsuccessful. The knee was insufflated with 120 mL of sterile saline and reduction attempted again. By extending the knee and applying a medially directed force to the patella, reduction was successful. The patient was placed into a knee immobilizer and postreduction radiographs were taken (Figures 2A, 2B). Saline was extracted from the knee. The patient was admitted to the hospital where repeat examination of his knees during the next week revealed markedly less pain. The patient was lost to follow-up.

Discussion

Our patient presumably had a low-energy mechanism of injury, resulting in an undiagnosed patellar dislocation with delayed treatment. This subacute patellar dislocation was irreducible using the standard techniques. Alternatively, insufflation of the joint with saline provided the necessary impetus to allow for successful patellar reduction. The history of the patient reveals clues about the mechanism of injury. It is likely that the patient’s nonambulatory status resulted in a weak vastus medialis muscle that placed the patella at risk for dislocation. While the exact mechanism of dislocation is unknown, the patella was unable to be reduced spontaneously because our patient’s knee was maintained in a state of flexion secondary to pain and muscle contraction. The combination of weak quadriceps musculature, increased Q angle, and forced hyperflexion of the knee prevented closed reduction of the patella.

Fixed, irreducible patellar dislocations are rare and discussed infrequently in the literature.^9,11-12 Reported mechanisms are mostly high energy, including blows during athletics and impacts from motor vehicle collisions.^9,13 Vertical axis rotation, as first described by Cooper,¹⁴ is commonly implicated in irreducible patellar dislocations. This occurs when the patella internally rotates 180º on its vertical axis, associated with a large tear of the medial retinaculum but intact quadriceps tendon. The patella is fixed over the lateral femoral condyle with the articular surface pointing anterolaterally. Despite adequate sedation and analgesia, these are notoriously difficult to close-reduce and may necessitate open reduction.³ Our patient, while having a fixed dislocation, did not have a vertical axis component and, therefore, was amenable to our closed reduction attempt.

Our first reduction attempts were unsuccessful, likely because the patient continued to be tense, firing his quadriceps. Even after injecting the knee with lidocaine and eliminating the pain component, the patella was still impinging on the lateral femoral condyle (Figure 3A). By insufflating the knee with saline, we were able to increase the distance from the patella to the trochlea (Figure 3B). This is comparable to a knee arthroscopy, in which joint fluid pressure allows passage of arthroscopic instruments into the patellofemoral joint. We postulate that the farther the patella is anterior to the trochlea, the higher the likelihood that the patella can be reduced to its anatomic position. 

Insufflation of the knee with sterile saline is a novel technique that involves minimal risk compared with the alternatives. Sometimes, for closed reduction to be successful, individuals need to be consciously sedated to relax their muscles and eliminate pain. While conscious sedation is generally considered low risk, complications have been noted, including hypotension, apnea, and retrograde amnesia.¹⁵ Manual closed reduction may also cause additional chondral damage when the medial patellar facet contacts the lateral femoral trochlea. When closed reduction of the patella fails, open reduction is required; this inherently includes all the risks of surgery, such as bleeding, infection, neurovascular injury, and wound complications.  

Our insufflation technique does not require sedation and is minimally invasive. The saline creates space and provides lubrication to allow for easier manipulation of the patella. This theoretically protects the cartilage as the patella passes over the lateral trochlea. In addition to the intended effect of providing more space and lubrication for the reduction of the patella, insufflation of the joint may also relax the vastus musculature.¹⁶ In their study, Torry and colleagues¹⁶ injected 13 knees with 20 mL sterile saline and noted reduction in electromyography readings in the vastus medialis and lateralis muscles. This inhibition of vastus musculature may provide enough relaxation to aid in the successful reduction of the patella.

Our study is limited by our sample size of 1. Because acute patellar dislocations are often easily reduced, our technical trick is not frequently used. Additionally, while we were able to monitor his progress during his inpatient stay, our patient was lost to follow-up after his discharge from the hospital.

 If successful, the insufflation technique eliminates the need for urgent open reduction in the operating room. As a result, we recommend attempting closed reduction using insufflation of the knee with sterile saline for irreducible patellar dislocations before proceeding with open reduction.

Conclusion

Saline insufflation of the knee can be safely and easily performed to aid in the reduction of subacute, difficult patellar dislocations.

As the largest sesamoid bone in the human body, the patella acts as a fulcrum to enhance the biomechanical advantage of the quadriceps in extension.¹ It is subject to a variety of forces while improving distribution of forces along the extensor mechanism.² With sufficient force, the patella can be dislocated. Acute patellar dislocations are the most common knee injury, encompassing 2% to 3% of all knee injuries³ and occurring in 5.8 per 100,000 individuals.^4-5 These injuries are associated with acute trauma, frequently from sports and physical activities, occurring while in terminal extension with an axial-valgus stress on the knee during rotation.⁶

With acute patellar dislocations, patients are usually in significant discomfort. Often, the patella may spontaneously reduce; if not, closed reduction is usually successful with pressure applied anteromedially on the lateral patellar margin, while simultaneously attempting gentle extension of the leg.⁷ Closed reduction is almost universally successful, and there have only been case reports of irreducible, mainly fixed vertical axis patellar dislocations.^8-11 No reports in the literature have described subacute patellar dislocations because of their rarity. Patients present immediately after dislocation, spontaneously reduce, or have a painless, chronically dislocated patella.

We present a case of an elderly man with dementia and a subacute fixed irreducible patellar dislocation, which was reduced using a technique not described in the literature. The patient and the patient’s guardian provided written informed consent for print and electronic publication of this case report.

Case Report

A 68-year-old nonambulatory man with a history of dementia and stroke presented to the emergency department with complaints of left knee pain and his knee locked in flexion. The patient’s knee had been in that fixed hyperflexed position for at least 10 days after he sustained a twisting injury to his knee while attempting to get out of bed. At baseline, the patient was mostly bedbound and could walk minimally with maximum support, but, given his dementia, he would often attempt to ambulate by himself. After the injury, the patient did not complain of much pain at rest, but attempts at his group home to straighten his leg had caused severe pain. As a result, the patient was brought to the emergency department to be evaluated for fractures. 

Physical examination in the emergency department revealed atrophy of the lower extremity musculature and a left knee fixed at 120º in flexion. The skin was intact, and there was minimal effusion of the knee joint. The patella was noted to be laterally subluxated and tender to palpation over the lateral and medial facets. He was neurovascularly intact distally and had painless range of motion of his hips. His contralateral right knee had full range of motion with good patellar tracking.

Radiographs of the patient’s knee confirmed a lateral dislocation of the patella (Figures 1A-1C). After oral and intravenous administration of pain medication, a reduction was attempted without success. Next, an intra-articular knee injection of 10 mL of 1% lidocaine was given. After waiting 15 minutes, another reduction was tried. While the pain control was sufficient, the reduction was again unsuccessful. The knee was insufflated with 120 mL of sterile saline and reduction attempted again. By extending the knee and applying a medially directed force to the patella, reduction was successful. The patient was placed into a knee immobilizer and postreduction radiographs were taken (Figures 2A, 2B). Saline was extracted from the knee. The patient was admitted to the hospital where repeat examination of his knees during the next week revealed markedly less pain. The patient was lost to follow-up.

Discussion

Our patient presumably had a low-energy mechanism of injury, resulting in an undiagnosed patellar dislocation with delayed treatment. This subacute patellar dislocation was irreducible using the standard techniques. Alternatively, insufflation of the joint with saline provided the necessary impetus to allow for successful patellar reduction. The history of the patient reveals clues about the mechanism of injury. It is likely that the patient’s nonambulatory status resulted in a weak vastus medialis muscle that placed the patella at risk for dislocation. While the exact mechanism of dislocation is unknown, the patella was unable to be reduced spontaneously because our patient’s knee was maintained in a state of flexion secondary to pain and muscle contraction. The combination of weak quadriceps musculature, increased Q angle, and forced hyperflexion of the knee prevented closed reduction of the patella.

Fixed, irreducible patellar dislocations are rare and discussed infrequently in the literature.^9,11-12 Reported mechanisms are mostly high energy, including blows during athletics and impacts from motor vehicle collisions.^9,13 Vertical axis rotation, as first described by Cooper,¹⁴ is commonly implicated in irreducible patellar dislocations. This occurs when the patella internally rotates 180º on its vertical axis, associated with a large tear of the medial retinaculum but intact quadriceps tendon. The patella is fixed over the lateral femoral condyle with the articular surface pointing anterolaterally. Despite adequate sedation and analgesia, these are notoriously difficult to close-reduce and may necessitate open reduction.³ Our patient, while having a fixed dislocation, did not have a vertical axis component and, therefore, was amenable to our closed reduction attempt.

Our first reduction attempts were unsuccessful, likely because the patient continued to be tense, firing his quadriceps. Even after injecting the knee with lidocaine and eliminating the pain component, the patella was still impinging on the lateral femoral condyle (Figure 3A). By insufflating the knee with saline, we were able to increase the distance from the patella to the trochlea (Figure 3B). This is comparable to a knee arthroscopy, in which joint fluid pressure allows passage of arthroscopic instruments into the patellofemoral joint. We postulate that the farther the patella is anterior to the trochlea, the higher the likelihood that the patella can be reduced to its anatomic position. 

Insufflation of the knee with sterile saline is a novel technique that involves minimal risk compared with the alternatives. Sometimes, for closed reduction to be successful, individuals need to be consciously sedated to relax their muscles and eliminate pain. While conscious sedation is generally considered low risk, complications have been noted, including hypotension, apnea, and retrograde amnesia.¹⁵ Manual closed reduction may also cause additional chondral damage when the medial patellar facet contacts the lateral femoral trochlea. When closed reduction of the patella fails, open reduction is required; this inherently includes all the risks of surgery, such as bleeding, infection, neurovascular injury, and wound complications.  

Our insufflation technique does not require sedation and is minimally invasive. The saline creates space and provides lubrication to allow for easier manipulation of the patella. This theoretically protects the cartilage as the patella passes over the lateral trochlea. In addition to the intended effect of providing more space and lubrication for the reduction of the patella, insufflation of the joint may also relax the vastus musculature.¹⁶ In their study, Torry and colleagues¹⁶ injected 13 knees with 20 mL sterile saline and noted reduction in electromyography readings in the vastus medialis and lateralis muscles. This inhibition of vastus musculature may provide enough relaxation to aid in the successful reduction of the patella.

Our study is limited by our sample size of 1. Because acute patellar dislocations are often easily reduced, our technical trick is not frequently used. Additionally, while we were able to monitor his progress during his inpatient stay, our patient was lost to follow-up after his discharge from the hospital.

 If successful, the insufflation technique eliminates the need for urgent open reduction in the operating room. As a result, we recommend attempting closed reduction using insufflation of the knee with sterile saline for irreducible patellar dislocations before proceeding with open reduction.

Conclusion

Saline insufflation of the knee can be safely and easily performed to aid in the reduction of subacute, difficult patellar dislocations.