➢ Pincer impingement involves abnormal osseous contact between the prominent acetabular rim and the femoral head-neck junction, causing damage to the acetabular labrum and the chondrolabral junction.
➢ Pincer impingement exists in a variety of acetabular morphologies, including focal (anterosuperior) acetabular overcoverage, global acetabular overcoverage, acetabular retroversion, and subspine impingement. Accurate identification of existing morphology is necessary for appropriate surgical intervention.
➢ The labral seal, the water-tight junction of the labrum with the femoral head, is crucial to the proper functioning of the labrum, and treatment of the damaged labrum should focus on restoring this seal.
➢ Recent research has supported the use of labral repair or refixation rather than labral debridement for the treatment of labral tears, whenever possible, as evidenced by improved patient outcome scores.
➢ Patients with Outerbridge grade-III to IV changes at the time of hip arthroscopy are known to have poor outcomes following operative intervention and a high risk of failure requiring subsequent conversion to hip arthroplasty.
➢ A growing body of information supports the role of hip arthroscopy in the treatment of symptomatic femoroacetabular impingement for relieving pain and improving function in patients without osteoarthritis.
The concepts of hip arthroscopy and femoroacetabular impingement both date back to the 1930s, although their clinical association in hip-preservation surgery took decades to emerge1-4. As the technique has evolved to allow better maneuverability and tissue management, the indications for hip arthroscopy have expanded to include a variety of hip abnormalities3,5.
The two patterns of femoroacetabular impingement are cam impingement and pincer impingement, although the majority of patients present with a combination of both deformities6,7. Cam impingement is the result of asphericity and/or loss of offset of the femoral head-neck junction. Pincer impingement is characterized by focal or global acetabular retroversion or global overcoverage6-8 (Fig. 1). Both types of impingement cause damage to the acetabular labrum and chondrolabral junction.
With improvement of minimally invasive surgical techniques and our understanding of femoroacetabular impingement as a source of pre-arthritic hip pain, arthroscopy has become a successful and frequently utilized treatment for femoroacetabular impingement. The prevalence of hip arthroscopy has grown over the past decade, with a 365% increase between 2004 and 20093. This review will address the arthroscopic techniques that are currently used to treat abnormalities of the central compartment, with a focus on focal pincer-type impingement and acetabular labral tears.
In hip arthroscopy, the joint is divided into two compartments—central and peripheral. The central compartment, also called the iliofemoral compartment, is a potential space between the acetabular and femoral articular surfaces that becomes accessible with traction9. The capsule, articular surfaces, acetabular labrum, ligamentum teres, acetabular rim, and subspine region can be visualized and accessed within the central compartment (Fig. 2). The peripheral compartment contains the lateral aspect of the femoral head, the intracapsular region of the femoral neck, and the capsular surface of the labrum. Typically, correction of pincer-type lesions and chondrolabral abnormalities occurs within the central compartment.
The fibrocartilaginous labrum is similar to the meniscus of the knee, being triangular in cross-section and vascularized only in its periphery, such that tears near the chondrolabral junction have the highest healing potential following repair10,11. The labrum contributes to hip stability, shock absorption, pressure distribution, lubrication, and nutrition6,12-16. The labral seal, the water-tight junction of the labrum with the femoral head, is crucial to the proper functioning of the labrum12,13. Therefore, treatments of the damaged labrum should focus on restoring this seal whenever possible (Fig. 3).
Pathophysiology of Pincer Impingement and Labral Tears
In pincer-type femoroacetabular impingement, the labrum is damaged as it is repetitively crushed between the overhanging acetabular rim and the femoral head-neck junction during hip flexion and rotation (Video 1). The labral seal may be compromised, leading to increased contact pressures and microinstability with joint-loading12,13,17. Contact forces may increase by as much as 92% in the presence of labral tears18. Many experts believe that, over time, these abnormal hip biomechanics may accelerate joint degradation and progression to osteoarthritis10,12,13,18,19. However, the current literature does not provide any definitive evidence that asymptomatic labral tears cause osteoarthritis or that the treatment of labral tears will delay the development of osteoarthritis7,20.
The articular cartilage may be affected in a so-called contrecoup pattern. When the hip flexes beyond the point of engagement with the overhanging rim, the femoral head levers and creates a shear force on the articular cartilage directly opposite the site of rim overcoverage. This force may erode the articular cartilage on the femoral head, the acetabulum, or both6,9,21 (Fig. 4).
Pincer impingement exists in a variety of acetabular morphologies. Most commonly, a focal rim lesion is present as a result of relative retroversion of the cephalad portion of the acetabulum, also described as anterosuperior acetabular overcoverage6,7,22. Impingement occurs in cases of true acetabular retroversion because the femoral head/neck junction contacts the anterior acetabular rim at lower degrees of hip flexion and rotation. Global acetabular overcoverage (i.e., coxa profunda and protrusio acetabuli) is an uncommon but dramatic type of pincer impingement5-7,22. In such cases, the labral injury can be more extensive and even circumferential. Finally, subspine impingement is a variation of extra-articular pincer impingement that involves prominence of the anterior inferior iliac spine at or below the level of the acetabular rim. It may be developmental, a sequela of prior anterior inferior iliac spine or rectus femoris avulsion, or an iatrogenic consequence of periacetabular osteotomy7. This abnormal morphology may result in abutment of the femoral head-neck junction against the anterior inferior iliac spine during terminal hip flexion and internal rotation (Fig. 5).
Clinical Manifestations of Pincer Impingement and Labral Tears
The typical history given by a patient with symptomatic pincer-type impingement is anterior groin pain, particularly with hip flexion and/or internal rotation. Activities such as getting out of a car, putting on shoes, climbing stairs, or sitting for prolonged periods tend to provoke the pain6,22,23. Athletes who participate in sports that involve the extremes of hip motion may be unable to compete secondary to the symptoms6,10,24. Patients may report clicking, catching, or giving-way with hip range of motion related to secondary labral or soft-tissue injury8,22,25.
Physical examination of the hip should include observation of gait, range-of-motion testing, strength testing, and provocative maneuvers for femoroacetabular impingement. Limitation of hip internal rotation in 90° of hip flexion is characteristic of anterosuperior femoroacetabular impingement deformity22. Common provocative maneuvers are flexion-adduction-internal rotation (FADIR), flexion-abduction-external rotation (FABER), and the straight-leg raise. The lateral impingement test (extension-abduction) and the butterfly test (flexion-abduction-internal rotation) are useful for the evaluation of lateral and posterolateral impingement, respectively.
Radiographic evaluation should consist of anteroposterior pelvic radiographs, frog-leg lateral and/or 45° or 90° Dunn lateral radiographs, and false-profile radiographs of the involved hip. The lateral images provide the most information regarding anteriorly and anterolaterally based femoral head asphericity8. The anteroposterior pelvic radiograph is examined for evidence of (1) a crossover sign, suggesting focal anterior overcoverage; (2) a posterior wall sign or a prominent ischial spine, suggesting acetabular retroversion; and (3) coxa profunda and protrusio acetabuli, suggesting global overcoverage7,8,10,21,26. The lateral center-edge angle27 and Tönnis angle28 should be calculated to assess for lateral overcoverage (i.e., profunda), undercoverage (i.e., dysplasia), and acetabular inclination29. The false-profile radiograph depicts anterior acetabular coverage as well as the status of the anterior and posterior aspects of the joint space and the morphology of the anterior inferior iliac spine and subspine22.
Three-dimensional computed tomography (CT) is a valuable imaging modality for the evaluation of femoroacetabular impingement. Specialized computer software is available for use with three-dimensional CT to provide reproducible measurements of the size and location of deformity and to perform dynamic analyses of zones of contact before and after virtual surgery30,31. This tool can assist with designing an intraoperative plan that is customized to the pathoanatomy31 (Video 2). Proper application of this template should be verified at the time of the operation with intermittent fluoroscopy and dynamic arthroscopic examination31.
Magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA) enhance evaluation of the soft-tissue lesions of femoroacetabular impingement, such as labral and paralabral cysts. Reurink et al.25 reported that MRA had 86% sensitivity, 50% to 75% specificity, and 98% to 99% positive predictive value for the detection of labral tears. However, the negative predictive value was <20%, classifying MRA as a useful tool for confirming suspected labral tears but not for ruling them out25.
A trial of nonoperative therapy is appropriate for the initial treatment of femoroacetabular impingement. This treatment consists of activity modification, anti-inflammatory medications, and physical therapy focused on core strengthening, abductor strengthening, and hip range of motion7,8,32. These modalities may allow the patient to avoid the extremes of motion that cause impingement and may limit impingement by improved control of pelvic position and tilt. Because nonoperative treatment does not alter the underlying osseous abnormality, it is often not successful in the long term when activity modification is not possible, as in athletes10,22,33.
Intra-articular injections are another option for the treatment of femoroacetabular impingement, although they are best suited as a diagnostic and temporizing measure. Local anesthetic with or without corticosteroid is instilled into the joint with image guidance, for example, at the time of MRA. This technique assists in distinguishing intra-articular from extra-articular sources of pain5,22,34 and gives an estimate of the potential symptomatic benefits of operative intervention. A negative response to injection correlates with a low probability of having a favorable outcome following arthroscopic surgery for the treatment of femoroacetabular impingement (negative predictive value = 0.50, likelihood ratio = 0.57), although a positive response is not a strong predictor of a good outcome following surgery (positive predictive value = 0.67, likelihood ratio = 1.15)35.
Surgical Indications and Contraindications
Candidates for arthroscopic treatment of femoroacetabular impingement are those who have had a failure of nonoperative treatment and who have substantial deformity with minimal or no radiographic evidence of osteoarthritis6,10. Patients with Outerbridge grade-III or IV changes36 are known to have poor outcomes following surgery, with a failure rate of as high as 25%, requiring subsequent conversion to hip arthroplasty7,26.
Coexisting hip dysplasia is a relative contraindication to the arthroscopic treatment of femoroacetabular impingement. Labral debridement or excision in patients with hip dysplasia can increase stress on the lateral aspect of the acetabulum and can further alter the biomechanics of the hip joint, leading to poor results and even iatrogenic subluxation or dislocation26,37.
Arthroscopic surgery and open surgical hip dislocation are equally effective for the correction of most typical femoroacetabular impingement deformities7,38. Deciding between open and arthroscopic surgery depends on the degree of deformity, the location of the abnormality, and the comfort level and experience of the surgeon22. Situations in which open surgery is preferable include severe hip dysplasia, severe acetabular retroversion, posterior instability, proximal femoral rotational abnormalities, severe global pincer impingement, and severe extra-articular ischiofemoral or trochanteric-pelvic impingement5,6,21,26,39. Surgical hip dislocation is associated with a higher rate of major complications but still remains an important tool for hip preservation in patients with complex deformities.
Positioning and Preparation for Hip Arthroscopy
Careful positioning of the patient prior to surgery and obtaining satisfactory fluoroscopic views and traction are critical in order to permit safe instrumentation and to allow for the intraoperative assessment of the quality of deformity correction. Hip arthroscopy is performed with the patient in either the supine or the lateral decubitus position, depending on surgeon preference. Complete relaxation of the hip musculature and capsular venting with a needle are helpful in cases of severe deformity to obtain sufficient distraction for safe initial access9.
Full assessment of osseous correction can be achieved with six fluoroscopic views at the start and conclusion of the operation40. These include three anteroposterior views of the hip in neutral flexion-extension with (1) maximal internal rotation, (2) neutral rotation, and (3) maximal external rotation and three anteroposterior views of the hip in 40° of hip flexion with (4) neutral rotation, (5) 40° of external rotation, and (6) 60° of external rotation41. These views offer comprehensive characterization of the acetabulum and the head-neck junction from the 11:45 to the 2:30 position in the typical anterosuperior zone of deformity (Fig. 6). Intermittent fluoroscopy may be used to evaluate progress and avoid over-resection during correction of the osseous impingement41,42.
Arthroscopy is typically initiated by establishing the proximal anterolateral portal. This portal is located directly anterior to the iliotibial band and proximal to the tip of the greater trochanter, in a safe zone with respect to the vessels and nerves9. The trajectory may require adjustment in patients with coxa vara or coxa valga deformity to minimize the risk of iatrogenic chondral injury with subsequent instrumentation. A second portal is then established in the anterior or mid-anterior location under direct visualization, staying lateral to a line drawn from the anterior superior iliac spine distally over the anterior aspect of the thigh to avoid injury to the lateral femoral cutaneous nerve6.
In some cases of severe cephalad retroversion or global coxa profunda deformity, gaining access to the central compartment may be challenging. In these cases, a posterolateral portal may prove to be helpful as an initial access point. If the central compartment cannot be accessed safely, instruments should not be forced to because of the risk of devastating chondral injury and needle or wire breakage. Rather, a peripheral-first approach may be employed in which the extra-articular rim is accessed, triangulated, and resected to permit subsequent safe visualization and instrumentation.
To correct anterior and anterosuperior pincer lesions from the 1 o’clock to 3 o’clock positions, the anterior or modified anterior portal is best suited for working while viewing from the anterolateral portal. The capsule is stripped to define the extra-articular rim in the plane below the indirect head of the rectus tendon. For more lateral lesions at the 12 o’clock position, the arthroscope may be moved to the anterior or modified anterior portal and the proximal anterolateral portal should be used as the working portal6.
Creating an interportal capsulotomy facilitates movement of the arthroscopic instruments, exposes the extracapsular rim for resection and labral refixation or reconstruction, and limits the number of portals needed to access the areas of abnormality9,21,43. This step also reduces the risk of iatrogenic injury associated with the repetitive insertion and removal of instruments during the operation5. Using an arthroscopic Beaver blade (Smith and Nephew, Andover, Massachusetts), the surgeon creates the interportal capsulotomy between the labrum and the femoral head by starting in one portal and then switching the arthroscope and the scalpel to opposite portals to complete the capsulotomy parallel to the labrum. Care is taken to preserve capsular tissue on both the femoral and acetabular sides to permit later repair of the capsule and the iliofemoral ligament (Video 3). Capsulectomy or extensive capsulotomy without repair should be avoided because of the risk of destabilizing the hip joint, particularly in cases of known instability or dysplasia21,24.
Acetabular Rim Osteoplasty
Treatment of pincer-type impingement begins with localizing the deformity and assessing the condition of the adjacent labrum. This step, combined with preoperative radiographic evaluation, will help to determine the appropriate intervention: labral debridement with rim resection, capsular elevation with rim resection and labral repair, or labral detachment with rim resection and labral refixation6. Focal rim retroversion and subspine impingement can both result in a crossover sign and anterosuperior labral injury, but they require different corrective osteoplasties to treat the femoroacetabular impingement.
When labral tissue is well preserved and securely attached, the rim may be resected without detaching the labrum6. Capsular tissue is elevated with use of the arthroscopic shaver and radiofrequency probe to expose the appropriate zones of the anterosuperior rim (Video 4). With use of a motorized burr, the excess bone is removed until the chondrolabral junction is visible6,43. Switching between working portals facilitates the resection of bone at the far lateral, anterior, and posterior regions. The labrum is often torn in the region of the pincer impingement, and, if not torn, may be destabilized by the rim resection. Therefore, labral refixation or stabilization with suture anchors may be necessary after complete resection of the pincer lesion (Fig. 7).
In cases of coxa profunda or substantial overhanging bone, thorough resection of the pincer lesion may not be possible without labral detachment. An arthroscopic Beaver blade is used to cleanly separate the labrum from the rim at its attachment. The pincer lesion is resected with the motorized burr, and the labrum is reattached to the recessed acetabular rim9,43,44.
Resecting the appropriate amount of bone from the rim requires precision in that too little resection fails to comprehensively address the impingement, whereas overzealous resection can lead to instability and iatrogenic dysplasia6,45-47. The most common location of the pincer lesion, the anterosuperior rim, is the primary weight-bearing region. Therefore, resection of bone in this region will increase joint-reactive forces on the weight-bearing zone48. In studies correlating the amount of bone resection with the decrease in the center-edge angle, it has been estimated that each millimeter of bone resection corresponds with a 1° to 2° decrease in the center-edge angle9,49. Philippon et al.49 found that the largest change in center-edge angle of 2.4° occurred with the first millimeter of bone resected, with smaller increments of 0.6° occurring with each additional millimeter resected. In general, the lateral center-edge angle should not be decreased beyond 25o9. Ultimately, the amount of osseous resection is confirmed with dynamic assessment and a goal of impingement-free range of motion.
Cases of pincer impingement may involve os acetabuli or acetabular rim fractures. With care being taken to remain cognizant of the adjacent capsule and labrum, the lesion can be excised with the motorized burr after exposure or raised with an elevator and excised en toto. Both approaches should minimize injury to the adjacent labrum to permit repair when possible.
Osteoplasty of the acetabular rim may be carried superiorly into the subspine region in cases of extra-articular anterior inferior iliac spine impingement. The inferior and medial aspects of the anterior inferior iliac spine are exposed via capsular windows and are typically resected with the motorized burr.
Labral Debridement Versus Repair
Recent work has supported the role of labral repair or refixation rather than labral debridement for the treatment of labral tears whenever possible. Krych et al.17 performed a prospective, randomized controlled trial in which labral repair was compared with labral debridement in thirty-six women with labral tears related to femoroacetabular impingement. The results revealed better improvements in terms of the Hip Outcome Score50 (HOS) and subjective rating postoperatively in the labral repair group after a mean duration of follow-up of thirty-two months17. Larson et al.29 reported similar results in a study of patients with femoroacetabular impingement in which those managed with labral debridement during the early study period were compared with those who underwent labral take-down, rim resection, and labral refixation during the later study period. The labral refixation group had better modified Harris hip scores (HHS), Short Form-12 (SF-12) scores, and visual analog scores (VAS) for pain after a mean duration of follow-up of 3.5 years. Schilders et al.51 also reported greater improvement in the modified HHS in patients who were selected for labral repair rather than labral resection.
Despite this evidence, there are cases in which the labrum is irreparable. In patients with severe pincer lesions or coxa profunda, the labrum may be ossified, degenerative, or hypoplastic and thus may not be amenable to repair with suture anchors6,17,52. Complex degenerative labral tears also may preclude repair29. In such cases, the damaged portion of the labrum should be debrided with an arthroscopic shaver. Unstable labral tissue should be removed to prevent tear propagation while preserving as much normal labral tissue as possible in order to maintain labral function10. Labral debridement should be avoided in cases of hip dysplasia in order to prevent iatrogenic instability10,15.
Labral refixation involves placement of suture anchors in the acetabular rim following rim osteoplasty43. Given the depth of penetration needed for anchor placement, care must be taken to ensure a trajectory that minimizes the risk of iatrogenic joint penetration. The suture can be looped around the entire labrum or passed through the labral substance in a vertical or horizontal mattress fashion (Fig. 8, Video 5). The mattress configuration is less likely to evert the labrum and thus preserves the labral seal more reliably. However, a hypoplastic labrum or one with marginal tissue quality may only support a simple looped suture configuration10,43. The knot is always tied on the rim side away from the joint interface to prevent any risk of abrasion to the femoral head6.
Labral reconstruction has been described for situations of segmental and global labral deficiency in the setting of an otherwise well-preserved hip joint and is primarily indicated in the revision setting following prior labral debridement18,43. Domb et al.53 suggested consideration of labral reconstruction instead of debridement even in the setting of a primary segmental labral defect. A recent study by Larson et al.54 also confirmed that labral preservation and/or reconstruction is a predictor of improved outcome in cases of revision hip arthroscopy for the treatment of residual femoroacetabular impingement. Philippon et al.18 described a labral reconstruction technique involving the use of iliotibial band autograft in forty-seven patients and reported improvement in the mean HHS, a mean patient satisfaction score of 8 (of 10), and a 9% rate of conversion to hip arthroplasty. Joint-space narrowing to <2 mm is a contraindication to labral reconstruction18. Labral reconstruction with use of ligamentum teres and other autograft and allograft options also has been described in small case series6.
The incidence of complications following hip arthroscopy for the treatment of femoroacetabular impingement has been reported to be 0.5% to 7.7%, although these values likely underestimate iatrogenic chondral scuffing, labral penetration during portal establishment, and transient neurapraxias5,16,55,56. Larson et al. recently found a 16.5% incidence of transient postoperative sensory disturbance after 1615 hip arthroscopy procedures (unpublished data). The incidence of all other complications in that series totaled 7.4%, with perineal numbness (1.4%), iatrogenic chondral injury (1.2%), and superficial portal infection (1%) occurring most commonly.
Nerve injury, usually a temporary neurapraxia, may result from improper portal placement or prolonged traction. Insufficient padding of the perineal post or excessive traction also can cause pressure necrosis or trauma of the perineal region5. The guidelines for preventing traction-related complications advise ideally less than one and absolutely less than two hours of traction time, <50 lb (<22.7 kg) of traction, and a well-padded perineal post measuring at least 7 to 9 cm in diameter16.
While capsulotomy improves joint access and instrumentation, it increases the rate of fluid extravasation into the surrounding tissues5. The threat of abdominal or thigh compartment syndrome is real and should be assessed intraoperatively, particularly during long procedures. Extra-articular interventions, such as iliopsoas tenotomy, can increase the risk of fluid extravasation into the retroperitoneal compartment16. Failure to repair the capsulotomy site at the conclusion of the procedure can result in iatrogenic instability, especially in patients with ligamentous laxity or dysplasia5.
In cases involving substantial osseous resection, there is risk of heterotopic ossification; Bedi et al. reported that the rate of heterotopic ossification was 8% (twenty-three of 277) in the absence of prophylaxis57. The majority of patients in whom heterotopic ossification develops remain asymptomatic, but the potential for subsequent operative treatment with advanced cases is enough to warrant routine prophylaxis with postoperative nonsteroidal anti-inflammatory drugs5,9. Overresection of bone on either the femoral or acetabular side may lead to the rare but disastrous complications of femoral neck fracture and dislocation, respectively2.
Additional complications that have been reported following hip arthroscopy include infection, postoperative adhesions, and trochanteric bursitis11,16. Konan et al.58 reported a dramatic decrease in the overall complication rate following the first thirty hip arthroscopies in their series.
The growing body of literature supports the role of hip arthroscopy for relieving pain and improving function in patients with symptomatic femoroacetabular impingement without osteoarthritis5,52,59-61. The practice of hip arthroscopy has now matured to the point where long-term outcome data may be collected. Byrd and Jones62 presented the ten-year follow-up data on hip arthroscopy with isolated labral debridement in twenty-nine patients; although this study was reflective of earlier techniques, the authors reported a mean improvement in the modified HHS of 29 points with a 31% rate of conversion to hip arthroplasty at a mean of sixty-three months. A subset of athletes from that group had a mean improvement of 45 points in the modified HHS and an 87% rate of return to sports at three months postoperatively63.
Short and intermediate-term outcome studies are more representative of the current arthroscopic interventions, including osteoplasty and labral refixation. Patient satisfaction rates have ranged from 65% to 100%64, with mean improvements in the modified HHS from 9 to 27 points at two to three years postoperatively5,65. A systematic review of surgical treatment of femoroacetabular impingement in >1400 hips demonstrated the highest mean improvement in the modified HHS (24.6 points) in the group that was managed with arthroscopic surgery61. Rates of conversion to hip arthroplasty also have decreased to <10% with refinement in techniques and indications56,65.
A theme throughout the outcomes literature is that patients with any preexisting arthritis at the time of hip arthroscopy do poorly and have a substantial risk of failure requiring conversion to arthroplasty1,5,16,52,59,60,62,64-68. Other predictors of poor outcome include smoking, history of pain medication use, female sex, secondary gain, Workers’ Compensation, and lateral or traumatic labral tears55,69.
Positive predictors for good outcomes include young age, high preoperative activity level, well-defined radiographic deformity, presence of symptoms for longer than eighteen months, and labral refixation for the treatment of labral abnormality52,55,60,66. Studies focusing on athletes have demonstrated high rates of return to athletics, ranging from 79% to 90% at one year postoperatively70,71.
The most common reasons for revision hip arthroscopy are residual symptomatic impingement resulting from incomplete resection of osseous impingement lesions during the index procedure16,31 and postoperative adhesions66.
The ability of arthroscopic treatment of femoroacetabular impingement to prevent or delay hip osteoarthritis is yet unknown, but data suggest that delays as short as five years make hip arthroscopy a highly cost-effective treatment option65. There are currently no data to support the role of prophylactic hip arthroscopy for the treatment of asymptomatic femoroacetabular impingement5.
Arthroscopic treatment of femoroacetabular impingement has grown rapidly over the past few decades, and the body of research has concurrently expanded techniques and refined indications in an effort to improve patient outcomes and reduce failure rates. This review outlines the surgical steps for effective access to and treatment of central compartment abnormalities associated with femoroacetabular impingement. As long-term data become available for these newer techniques, our understanding of the disease process and proper treatment will evolve. Prospective and randomized studies would enhance the quality of evidence and help to quantify the value of these interventions. A discussion of cam-type impingement (http://reviews.jbjs.org/content/3/9/e3) will be published in a future issue of JBJS Reviews72.
Source of Funding: No external funds were received in support of this study.
Investigation performed at MedSport, University of Michigan, Ann Arbor, Michigan
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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