➢ The diagnosis of greater trochanteric pain syndrome encompasses a broad category of disorders, including trochanteric bursitis, gluteus medius or minimus tears, and external coxa saltans, all of which are associated with a common complaint of lateral-sided hip pain.
➢ Magnetic resonance imaging (MRI) and ultrasonography are the primary imaging modalities used to diagnose gluteus tendon abnormalities, with sensitivities of 73% and 79%, respectively.
➢ Nonoperative treatment, including rest, activity modification (including avoidance of exacerbating activities), nonsteroidal anti-inflammatory drugs (NSAIDs), weight loss (if indicated), and physical therapy are effective for the majority of patients; often, an injection of cortisone and local anesthetic is performed as both a diagnostic and therapeutic modality.
➢ Operative options include iliotibial band z-lengthening, longitudinal iliotibial band release with subgluteal bursal excision, gluteus medius tendon repair, trochanteric reduction osteotomy, and partial excision of the iliotibial band with removal of the trochanteric bursa. Although these options are generally effective, they subject the patient to substantial surgical site morbidity and a long recovery process.
Endoscopic techniques for the treatment of greater trochanteric pain syndrome have become increasingly popular with evolving indications and advances in instrumentation; the majority of abnormalities associated with greater trochanteric pain syndrome can now be effectively treated with these minimally invasive techniques. The indications for hip arthroscopy have expanded greatly over the past decade and remain an area of tremendous growth in orthopaedic surgery. With improvements in surgical technique and instrument design, there are increasing opportunities to treat peritrochanteric hip conditions endoscopically and intra-articular hip disorders arthroscopically. Greater trochanteric pain syndrome is a relatively common clinical entity that is seen in 10% to 25% of the general population1. It encompasses disorders of the lateral, peritrochanteric space of the hip and includes trochanteric bursitis, gluteus medius and minimus tendon tears, and external coxa saltans (snapping hip). Endoscopy provides improved visualization of extra-articular abnormalities that previously required large open incisions to adequately treat. The purpose of the present report is to critically review the anatomy and diagnosis of greater trochanteric pain syndrome disorders and the endoscopic approach to treatment when nonoperative treatment has failed.
Greater Trochanteric Pain Syndrome
The diagnosis of greater trochanteric pain syndrome encompasses a broad category of disorders, all of which are associated with lateral-sided hip pain. Specific disorders include trochanteric bursitis, gluteus medius or minimus tears, and external coxa saltans2-5. Trochanteric bursitis refers to inflammation of at least one of the three trochanteric bursae and is thought to result from gait abnormalities, trauma, or repetitive activity6-8. The typical pathogenesis involves repetitive friction between the iliotibial band and the greater trochanter with hip flexion and extension, causing pain that is localized to the greater trochanter and that radiates down the lateral aspect of the thigh or into the buttocks. Patients often present with other associated abnormalities, such as osteoarthritis of the ipsilateral hip or lumbar spine7, but the disease is now more common in younger patient populations without concomitant intra-articular abnormalities9,10.
In patients with recalcitrant trochanteric bursitis, gluteus medius and/or minimus tears are the most common underlying finding11,12. Recent studies have suggested that tears occur in 25% of middle-aged women and 10% of middle-aged men13. This increased prevalence in women may be secondary to the wider female pelvis. The natural progression of hip abductor tendinopathy is similar to the pathogenesis of tendon degeneration elsewhere in the body and generally begins with bursitis before progressing down the spectrum of tendinitis, tendinopathy, partial-thickness tears, full-thickness tears, and massive tears.
External snapping hip syndrome results from thickening of the posterior third of the iliotibial band that lies posterior to the greater trochanter when the hip is in a neutral position14. Repeated flexion and extension of an overly taut iliotibial band (e.g., while walking) will result in mechanical symptoms (e.g., snapping) as the iliotibial band catches on the greater trochanter. Subsequent tightening of the iliotibial band and its resultant snapping is exacerbated by hip adduction and extension at the knee15. Women with excessively prominent greater trochanters or a larger pelvis have predilection for external snapping hip, and this syndrome is commonly seen in women who adduct beyond the midline during gait15. Interestingly, the snapping of the iliotibial band itself is usually not painful14, but the repetitive nature of the disorder can lead to inflammation of the trochanteric bursa due to abrasive friction and wear16. Kingzett-Taylor et al.3 suggested that both abductor tendinopathy and trochanteric bursitis could be secondary to frictional trauma caused by high iliotibial band tension.
The greater trochanter lies at the junction of the femoral neck and shaft and is the site of attachment of the gluteal, obturator, and piriformis tendons. The area around the greater trochanter, the peritrochanteric space17, consists of the gluteus medius and minimus tendons, iliotibial band, and greater trochanter with its associated bursa. A fibromuscular sheath composed of the gluteus maximus, the tensor fasciae latae, and the iliotibial band lies superficial to the medius and minimus tendons. The posterior border of the iliotibial band can become thickened and, as the hip moves from extension to flexion while the iliotibial band passes over the greater trochanter from posterior to anterior, a snapping sensation (external coxa saltans) may result. In addition to the snapping of the posterior portion of the iliotibial band, thickening of the tensor fasciae latae or gluteus maximus as they slide over the greater trochanter during hip flexion also can cause a snapping sensation. Rarely, snapping of the long head of the biceps femoris tendon over the ischial tuberosity with hip flexion and extension also can cause a snapping sensation18. Table I provides a summary of the relevant soft-tissue anatomy13,16,19,20.
The subgluteus medius bursa, the subgluteus minimus bursa, and the trochanteric (subgluteus maximus) bursa located around the greater trochanter serve to cushion the gluteal tendons, the iliotibial band, and the tensor fasciae latae. The subgluteus medius bursa lays over the lateral facet and the subgluteus minimus bursa lays deep to the tendon around the anterior facet and anterior hip capsule. The subgluteus maximus bursa is the largest bursa and lays deep to the fibers of the gluteus maximus and tensor fasciae latae as they form the iliotibial band. This bursa sits on top of the posterior facet of the greater trochanter, the distal-lateral aspect of the gluteus medius tendon at the lateral facet, and the proximal vastus lateralis insertion21. The gluteus medius and minimus tendons function in a similar manner to the rotator cuff, helping to stabilize the hip joint and initiate abduction22. Tears generally occur in the footprint on the greater trochanter and can be intrasubstance, partial, or complete23.
Abnormality in the greater trochanteric region often results in vague discomfort in the lateral aspect of the thigh and buttock that radiates down the limb and can be associated with paresthesias24,25 and a constellation of buttock, lateral hip, and groin pain. These symptoms may be caused, at least in part, by the varying neurological supply of the peritrochanteric compartment26. Patients may complain of lateral hip pain that is exacerbated by direct pressure, prolonged standing or upright activity, and activities that engage the hip abductors, such as getting up from a seated position or climbing stairs. Patients also may report night pain as a result of lying on the affected hip. In the majority of patients, the onset of symptoms is insidious, but some patients report an acute exacerbation of symptoms after a specific event27. Patients presenting with external snapping hip syndrome may describe a snapping sensation that occurs with exercise or routine daily activities as the hip moves from extension to flexion. These findings may be seen with increased frequency in patients who have previously undergone hip surgery.
A careful and thorough physical examination of both hips must be performed for every patient who presents with greater trochanteric pain syndrome. Clinicians also must be certain to rule out spine abnormality as a cause of symptoms24,28. Patients with gluteus medius avulsion may present with an obvious limp29,30 resulting from the loss of abductor function. In addition, several anatomic abnormalities such as high valgus knee angles and limb-length discrepancies are known to cause mechanical abrasion and subsequent abductor tears as a result of increased iliotibial band tension31.
Hip-specific examination begins with observation for Trendelenburg gait followed by the Trendelenburg fatigue test25,32,33. A distinct drop of the unsupported side of the pelvis indicates weakness or loss of function of the abductors. Next, a systematic evaluation of both hips, including inspection, palpation, range of motion, strength, sensation, stability, and provocative testing, is performed. With the patient in the lateral decubitus position with the painful hip up, the anterior, lateral, and posterior aspects of the greater trochanter are palpated for tenderness. Abductor strength testing can be performed with the knee in both flexion and extension to enable gravity strength testing.
The evaluation can include provocative maneuvers such as the trochanteric pain test, which is performed with the patient in a supine position. With the hip flexed to 90°, abduction and externally rotation is performed (Fig. 1). Pain with external rotation indicates a positive test. Flexion, abduction, external rotation, and extension (FABERE) testing may also elicit pain in patients with greater trochanteric pain syndrome (Fig. 2). Resisted external rotation should also be performed while the patient is in the supine position with the hip flexed at 90°23,34.
The physical examination for external snapping hip syndrome generally reveals a reproducible palpable or visible snapping of the iliotibial band over the greater trochanter on flexion and subsequent extension of the involved hip35. A single-leg bicycle maneuver, performed with the patient in the lateral decubitus position, may reproduce iliotibial band snapping. The diagnosis can be confirmed if pressure applied over the superior aspect of the greater trochanter prevents snapping with repeated hip flexion. A positive Ober test resulting in substantial tightening of the iliotibial band (as indicated by the inability of the knee on the affected side to adduct past neutral with the patient in the lateral decubitus position with 90° of knee flexion and hip extension) would qualify the patient as a good candidate for iliotibial band release along with removal of the symptomatic bursa4.
For most patients presenting with symptoms of greater trochanteric pain syndrome, the diagnosis is often based on history and physical examination alone. However, a complete evaluation that includes radiographs can be helpful for evaluating the osseous anatomy of the hip joint. In addition, radiographs are helpful for evaluating for osteoarthritis and evidence of calcific tendinitis and/or intrabursal calcifications. Radiographs generally have a low yield with regard to the detection of gluteus medius and minimus tears but can identify trochanteric osteophytes over which the gluteal tendons may be draped. A generally acceptable imaging series would include anteroposterior pelvic and lateral hip radiographs to assess for osteoarthritis and osteophytes as well as false-profile and/or Dunn views of the hip to evaluate for femoroacetabular impingement36.
Magnetic resonance imaging (MRI) and ultrasonography are the primary imaging modalities used to diagnose gluteus tendon abnormality37,38. Specific findings in patients with greater trochanteric pain syndrome may include enthesopathic changes along the trochanteric insertion, subminimus and submedius bursitis, and fatty atrophy of the associated muscle bellies14. On T2-weighted MRI, hyperintensity superior and lateral to the greater trochanter is often seen as a result of thickened hip abductor tendons, tendinopathy, or tendon tears (Fig. 3). Tendon discontinuity may be seen on T1-weighted images. Although the overall specificity of MRI has been debated39, Kingzett-Taylor et al. found T2-weighted MRI of the superior greater trochanter to be diagnostic for partial abductor tendon tears, with high sensitivity (73%) and specificity (95%)3, but the rate of false-positive findings was reported to be as high as 88% in one series37. Ultrasound may be a reliable alternative to MRI for the diagnosis of gluteus medius and minimus tears, with a sensitivity of 79% and a positive predictive value of 100%38. Dynamic real-time ultrasound also can be used to visualize snapping hip and to identify inflamed trochanteric bursa6.
For the majority of patients with greater trochanteric pain syndrome, nonoperative measures are the first line of treatment4. Rest, activity modification, and physical therapy are generally recommended. Physical therapy protocols for the treatment of greater trochanteric pain syndrome should focus on stretching, flexibility, strengthening, and gait mechanics5,7. Low-energy shock-wave therapy has been found to be efficacious for some patients; however, the data are limited and additional research is needed before this treatment strategy can be universally recommended5,8,40,41. In the study by Rompe et al.40, thirty-three patients undergoing low-energy shock-wave therapy were compared with thirty-three control patients. The authors found comparatively superior clinical improvement in the treatment group at one, three, and twelve months following treatment.
Persistent pain despite noninvasive treatment can be treated with cortisone injection and local anesthetic as both a diagnostic and therapeutic modality. Shbeeb et al. followed seventy-five patients with trochanteric bursitis and showed that lidocaine and betamethasone injections were effective for relieving pain secondary to greater trochanteric pain syndrome in 77.1% of the patients at one week and in 61.3% of the patients at six months42. Walker et al.43 evaluated ninety-seven patients with greater trochanteric pain syndrome in an effort to find a correlation between trochanteric bursitis, gluteus medius tears, and spinal degenerative changes. Thirty (63%) of forty-eight patients responded to local anesthetic injections with corticosteroid. The authors noted that the recurrence of pain after the injection was predicted by the presence of moderate to severe lumbar degenerative disease. In the study by Brinks et al.44, 120 patients with greater trochanteric pain syndrome were randomized to local corticosteroid injection or expectant treatment. At three months, a clinically relevant improvement in terms of pain at rest and pain with activity was found in the injection group; however, these differences diminished at the time of the latest follow-up at twelve months. While the majority of cases of greater trochanteric pain syndrome are self-limiting in nature, the failure of nonoperative treatment to alleviate symptoms leads to consideration of operative treatment8.
Many open surgical techniques have been proposed for the treatment of greater trochanteric pain syndrome5,8. Options include iliotibial band z-lengthening45, open longitudinal iliotibial band release with subgluteal bursal excision46, open gluteus medius tendon repair11,47, open trochanteric reduction osteotomy48, and open partial excision of the iliotibial band with removal of the trochanteric bursa49. Given the morbidity associated with open procedures, endoscopic techniques have become increasingly popular over the past decade.
Many endoscopic techniques for the treatment of greater trochanteric pain syndrome have been proposed, and several reports have described preferred approaches for these techniques27,31,50-59. In this section, we describe our endoscopic approach to the treatment of greater trochanteric pain syndrome.
The operative setup is similar to that for hip arthroscopy and can be performed with the patient either in the lateral position on a standard operating table or in the supine position on a fracture table. Our preference is to perform the procedure with the patient in the supine position. If the patient has external coxa saltans, the symptomatic area is marked in the preoperative area to guide the intraoperative release. The patient is positioned on a hip traction table, and approximately 1 cm of hip joint distraction is obtained. Preparation and draping is performed in the standard sterile fashion, ensuring that the anterior superior iliac spine and the greater trochanter are readily accessible. The tip of the greater trochanter is identified, and an anterolateral portal is established approximately 1 cm anterior and 1 cm proximal to the anterior aspect of the greater trochanter (Fig. 4). If there is no concern about intra-articular abnormality, the anterolateral portal can be made slightly more superiorly to allow for better visualization of the gluteus medius and minimus tendons. A spinal needle is introduced into the central compartment, followed by the insertion of a guidewire and a 4.5-mm metal cannula. Diagnostic arthroscopy is performed to evaluate intra-articular abnormality. If degenerative labral tears are identified, a mid-anterior portal is established over the vastus ridge and an arthroscopic shaver is introduced through the mid-anterior portal for selective labral debridement.
After evaluation of the central compartment, traction is released and the lower limb is placed in complete extension and 15° to 20° of abduction following removal of the perineal post. The peritrochanteric space is then entered with use of a 5.0-mm metal cannula through the mid-anterior portal; the cannula is directed between the iliotibial band and the lateral aspect of the proximal part of the greater trochanter and is then swept from proximal to distal, opening the potential space. Fluoroscopy can be used to ensure that the cannula is located directly adjacent to the greater trochanter. A 70° arthroscope is placed through the cannula and is used to visualize the distal aspect of the peritrochanteric space. With use of a Wissinger rod through the anterolateral portal, a 5.0-mm metal cannula is positioned between the tip of the greater trochanter and the iliotibial band. A 4.5-mm shaver is introduced through the cannula, and a thorough bursectomy is performed until the gluteus maximus tendon is identified distally, the iliotibial band is identified laterally, the undersurface of the gluteus maximus is identified proximally, and the longitudinal fibers of the vastus lateralis are identified medially. The gluteus medius and minimus insertions should then be easily visualized, with the arthroscope and the light source directed anterosuperiorly. The arthroscope is then placed in the anterolateral portal and the shaver is placed in the mid-anterior portal and is used to continue to debride any excessive bursal tissue (Fig. 5, A). Some surgeons may prefer to perform the aforementioned bursectomy with the patient in the lateral decubitus position by entering the lateral compartment through an anterior portal and using a distal posterior portal to access the peritrochanteric space. The posterior third of the iliotibial band should be visualized and inspected for any evidence of abrasive wear or erythema. Release of the posterior third of the iliotibial band may prove to be beneficial for patients with evidence of wear on the greater trochanter10. This release may be performed before10 or after the bursectomy42.
External coxa saltans can be addressed with iliotibial band lengthening once the trochanteric bursectomy is completed. The endoscope is placed in the anterolateral portal to visualize the iliotibial band (Fig. 5, B). A spinal needle is used to localize the posterior third of the iliotibial band at the level of the posterolateral portal. A number-11 scalpel is used to create a portal and then is passed deeper to lengthen the iliotibial band (Fig. 5, C). The blade is passed in line with the iliotibial band fibers approximately 2 to 3 cm. At the midpoint of the lengthened iliotibial band, a perpendicular incision is created and is extended anteriorly and posteriorly for approximately 1.5 cm in both directions. Next, a 4.5-mm shaver is passed through the posterolateral portal to debride the flaps of the iliotibial band so that a diamond configuration is visible at the conclusion of the iliotibial band lengthening (Fig. 5, D).
The gluteus medius and minimus are readily identifiable if a thorough bursectomy has been performed, and the tear pattern can be recognized with the use of a probe (Fig. 6). The tendons can be inspected for evidence of calcific tendinitis, for which endoscopic debridement has been described59. Partial-thickness tears are generally articular-sided and can be difficult to visualize because of overlying unaffected bursal-sided tissue. A shaver can be used to debride the tear edges, and high-grade partial tears may be needed to facilitate tendon repair. With use of a grasper, we check to ensure that the tendon can be approximated onto the gluteus medius footprint without excessive tension (Fig. 7, A). With use of a 5.0-mm cylindrical burr, the greater trochanter is decorticated to facilitate healing (Fig. 7, B). Suture anchor placement into the greater trochanter (Fig. 7, C) can be determined with use of a spinal needle, with the number of anchors being used depending on the size of the tear. For small and medium tears, a single-row repair with one or two suture anchors is preferred. For large and massive tears, a double-row suture bridge technique is the preferred fixation construct. Anchors are inserted percutaneously through a posterolateral portal, which is 1 cm posterior and 1 cm proximal to the tip of the posterolateral aspect of the greater trochanter. Next, two 5.5-mm biocomposite anchors, double-loaded with number-2 high-strength sutures (Bio-Corkscrew; Arthrex, Naples, Florida), are placed at the medial border of the gluteus medius footprint. Sutures are passed through the tendon with a tissue penetrator or suture shuttler and are grasped through the mid-anterior portal (Fig. 7, D). In general, two sets of horizontal mattress stitches are passed per anchor and are subsequently tied with use of reverse half-hitches and alternating posts. An 8.5-mm plastic cannula is placed in the posterolateral portal, and one limb from each stitch is retrieved (Fig. 7, E). The first lateral-row anchor (SwiveLock; Arthrex) and the remaining limb of the suture are retrieved for the second lateral-row anchor (SwiveLock; Arthrex). The final appearance should show anatomic repair of the torn gluteus medius over the anatomic footprint on the greater trochanter. The hip is rotated to ensure anatomic reduction and fixation of the torn gluteus medius tendon (Fig. 7, F). If there seems to be excessive contact from the iliotibial band on the repaired gluteus medius tendon, an iliotibial band release can be performed as described above.
Treatment of Chronic and/or Massive Tears
For patients with chronic abductor tears with fatty atrophy or acute massive tears that are not amenable to direct endoscopic repair, gluteus maximus transfers can be performed60-62. Alternatively, other techniques involving tensor fasciae latae transfers63 and allograft reconstruction58,64 have been described. These are open procedures that require a large approach for adequate exposure. Outcomes have generally been acceptable, but these procedures are not without limitations. Most recently, Whiteside60 reported on five patients undergoing gluteus maximus and tensor fasciae latae transfer for the treatment of primary deficiency of the hip abductors. At one year postoperatively, 60% of the patients had no pain, 40% had mild pain, and 60% had no limp.
Postoperative Rehabilitation Protocol
Following endoscopic treatment of greater trochanteric pain syndrome, postoperative rehabilitation is conducted in phases, beginning with an initial period of limited weight-bearing or non-weight-bearing. The final rehabilitation protocol is determined by the specific procedures performed in addition to the treatment of greater trochanteric pain syndrome. Our postoperative protocol consists of bracing with partial weight-bearing for six weeks after surgery, with gentle passive range of motion to prevent adhesions. From six to eight weeks postoperatively, patients will progress to full weight-bearing but will continue to use assistive devices. Patients may continue to use an assistive device until three months postoperatively. Miozzari et al., in a study of twelve patients for whom MRI was used to evaluate progress at the site of late abductor avulsion repair following total hip arthroplasty, found that fatty degeneration of the anterior aspect of the gluteus medius did not reverse or improve at one year following surgery65. This finding illustrates the limitation of late-stage abductor avulsion repairs and the possibility that fatty degeneration cannot be reversed.
Clinical Outcomes of Endoscopic Treatment
Multiple authors have presented their preferred endoscopic approaches27,31,50-59. Baker et al.9 reported on twenty-five consecutive patients who underwent endoscopic trochanteric bursectomy and were followed for a mean of more than two years. The authors found significant improvements in visual analog scale pain scores (p = 0.001), Harris hip scores (p = 0.001), and all eight categories of the Short Form-36 (SF-36), particularly the physical function (p = 0.022) and pain (p = 0.001) scores, compared with preoperative values. Similarly, Fox66, in a retrospective review of the records of twenty-seven patients who had undergone endoscopic bursectomy, reported that twenty-three patients had a good or excellent result at one year postoperatively. Two of the twenty-seven patients experienced recurrence of symptoms at five years postoperatively.
Voos et al. prospectively followed ten patients who were managed with endoscopic gluteus minimus repair for the treatment of greater trochanteric pain syndrome27. After an average duration of follow-up of twenty-five months, the authors reported resolution of pain and return of abductor strength in 100% of the patients, with excellent postoperative modified Harris hip scores (mean, 94 points; range, 84 to 100 points) and hip outcomes scores (mean, 93 points; range, 85 to 100 points)27. Domb et al. prospectively followed fifteen patients undergoing endoscopic gluteus medius repair of high-grade partial-thickness or full-thickness tears55. After an average duration of follow-up of twenty-eight months, the authors reported improvement in all hip-specific outcome scores for fourteen of the fifteen patients, with satisfaction being rated as good to excellent. The one patient with a poor outcome was a smoker who was noted to have been noncompliant with postoperative weight-bearing restrictions and who ultimately was managed with spinal fusion six months postoperatively.
Multiple authors have demonstrated endoscopic treatment of external coxa saltans to be an acceptable treatment option with good to excellent results. Ilizaliturri et al. reported on eleven patients who underwent endoscopic treatment of external coxa saltans in the lateral position31. A diamond-shaped resection and release of the iliotibial band followed by debridement of the trochanteric bursa was performed, with ten of the eleven patients having relief of pain at the time of the minimum one-year follow-up. All patients returned to the preoperative level of activity, and no patient required revision surgery. Polesello et al. performed endoscopic gluteus maximus tenotomy in nine patients with refractory external snapping hip53. At the time of the latest follow-up, all patients had returned to the preoperative level of activity, with no complaints of weakness. Seven patients had relief of pain, and one patient required revision surgery. The successful outcomes in those studies parallel the excellent results that have been reported by multiple authors in association with open treatment of external snapping hip67-69.
Endoscopic treatment of extra-articular hip conditions is a relatively new frontier. Long-term outcome studies are not yet available, and it is difficult to fully appreciate any potential negative complications. Complications following endoscopic treatment of extra-articular hip conditions have not been well-described70 but are thought to be less frequent and less severe than those following hip arthroscopy71. The peritrochanteric space17,72 is outside the pelvis; thus, potentially severe complications such as fluid extravasation have not been reported, to our knowledge. Other major complications such as osteonecrosis, femoral neck fracture, postoperative instability, or adhesions also have not been reported, to our knowledge. Iatrogenic injury to the gluteal vessels or sciatic nerve is a possibility if entry into the space is either too proximal or too posterior.
Disorders such as trochanteric bursitis, gluteus medius and minimus tears, and external snapping hip represent a spectrum of sometimes overlapping abnormalities that are collectively referred to as greater trochanteric pain syndrome. The diagnosis of this syndrome and the indications for surgery are continuing to evolve as our understanding of the pathology improves. While greater trochanteric pain syndrome can often be successfully treated noninvasively, surgical intervention can lead to relief of pain and return to function in patients with refractory symptoms. Endoscopic techniques for the treatment of greater trochanteric pain syndrome are considered to be relatively safe, with few reported complications. Given the recent development of many of these techniques, additional clinical and scientific research in this area is required to determine if the reported short-term outcomes are maintained over time.
The authors would like to acknowledge the Hip Preservation Center, Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, for their support in completing this work.
Source of Funding: No external funding was required or used in the preparation of this manuscript.
Investigation performed at the Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
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