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Does the Hip Capsule Remain Closed After Hip Arthroscopy With Routine Capsular Closure for Femoroacetabular Impingement? A Magnetic Resonance Imaging Analysis in Symptomatic Postoperative Patients
Does the Hip Capsule Remain Closed After Hip Arthroscopy With Routine Capsular Closure for Femoroacetabular Impingement? A Magnetic Resonance Imaging Analysis in Symptomatic Postoperative Patients Alexander E. Weber, M.D., Benjamin D. Kuhns, M.S., Gregory L. Cvetanovich, M.D., Paul B. Lewis, M.D., Richard C. Mather, M.D., Michael J. Salata, M.D., and Shane J. Nho, M.D., M.S.
Purpose: The purpose of this study was to examine the hip capsule in a subset of symptomatic patients who underwent capsular closure during hip arthroscopy. Methods: All patients undergoing primary hip arthroscopy for femoroacetabular impingement (FAI) with routine capsular closure between January 1, 2012, and December 31, 2015, were eligible. Only patients with unilateral surgery and a postoperative magnetic resonance imaging (MRI; ordered for persistent symptoms) were included. Four independent reviewers evaluated each hip capsule for thickness and the absence or presence of defects. Results: During the study, 1,463 patients had hip arthroscopy for FAI with routine capsular closure, and 53 (3.6%) underwent a postoperative MRI. Fourteen of the 53 were excluded owing to revision status or additional procedures. The final study population included 39 patients (23 female patients and 16 male patients), with an average patient age of 31.7 11.4 years and an average body mass index of 23.3 2.9. There were 3 (7.5%) capsular defects, and the intraclass correlation coefficient (ICC) was 0.82. The operative hip capsule was significantly thicker in the zone of capsulotomy, and subsequent repair as compared with the unaffected, contralateral hip capsule (5.0 1.2 mm vs 4.6 1.4 mm; P ¼ .02), ICC 0.83. Additionally, males had thicker hip capsules as compared with their female counterparts, on the operative side (5.4 1.1 mm vs 4.5 1.2 mm; P ¼ .02) and the nonoperative side (4.8 1.6 mm vs 4.1 0.9 mm; P ¼ .08). Conclusions: In a subset of symptomatic patients after hip arthroscopy for FAI, the majority (92.5%) of the repaired hip capsules remained closed at greater than 1 year of follow-up. The hip capsule adjacent to the capsulotomy and subsequent repair is thickened compared with the same location on the contralateral, nonoperative hip. Aside from gender, patient-related and FAI-related factors do not correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect. Level of Evidence: Level IV, prognostic case series.
O
ver the past 2 decades, femoroacetabular impingement (FAI) has become a well recognized clinical entity that may contribute to the development of hip osteoarthritis.1 Ganz et al.2 were the first to
describe the concept of FAI and subsequently developed an open surgical approach for operative treatment. As part of the open posterior approach to FAI, Ganz and colleagues described performing a formal
From the Section of Young Adult Hip Surgery, Division of Sports Medicine, Department of Orthopedic Surgery, Rush Medical College of Rush University (A.E.W., B.D.K., G.L.C., S.J.N.), Chicago, Illinois; Department of Radiology, University of Illinois Hospital (P.B.L.), Chicago, Illinois; Section of Sports Medicine, Department of Orthopedic Surgery, Duke University Medical Center (R.C.M.), Durham, North Carolina; Division of Sports Medicine, Department of Orthopedics, University Hospital, Case Western Reserve University School of Medicine (M.J.S.), Cleveland, Ohio, U.S.A. The authors report the following potential conflicts of interest or sources of funding: R.C.M. receives support from KNG Consulting, Pivot Medical, Smith & Nephew, Stryker, and MD. S.J.N. receives support from the American Orthopaedic Society for Sports Medicine, the Arthroscopy Association of North
America, the Journal of Bone and Joint Surgery, AOSSM, AANA, Stryker; Ossur, Springer, Allosource, Arthrex, Athletico, DJ Orthopaedics, Linvatec, and Miomed. Received March 30, 2016; accepted July 14, 2016. Address correspondence to Alexander E. Weber, M.D., Hip Preservation Center, Midwest Orthopaedics at Rush, 1611 West Harrison Street, Suite 300, Chicago, IL 60612, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/16267/$36.00 http://dx.doi.org/10.1016/j.arthro.2016.07.022
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arthrotomy, which was repaired at the end of the procedure. In the United States, open approaches for FAI have largely been replaced with arthroscopic techniques.3 These arthroscopic techniques, in general, have not placed emphasis on the treatment of the capsule and mostly describe extended capsulotomies and even capsulectomies for adequate visualization of femoral-sided cam deformities.4 Only recently has more attention been paid to the capsule during arthroscopic treatment of hip conditions.5,6 With the growth in arthroscopic treatment of hip conditions, iatrogenic instability caused by nonrepaired capsulotomy or capsulectomy has become more of a concern.7-10 Recently, there have been case reports of hip dislocation and subluxation after arthroscopic surgery for FAI.11-13 Capsular defects after hip arthroscopy have now been reported as one of the leading causes necessitating revision surgery for continued pain and/or instability.7,14 Frank et al.6 reiterated the importance of capsule repair in hip stability as they demonstrated increased sports specific activity after hip arthroscopy for FAI with complete capsular repair compared with partial capsular repair. Lastly, Wylie and colleagues have recently reported on 33 cases of symptomatic instability after hip arthroscopy without capsular repair and improvement in patient-reported outcome (PRO) 2 years after revision surgery to repair the capsular insufficiency.15 These previous authors concluded that the contemporary treatment of FAI should include chondrolabral repair, surgical correction of FAI, and complete capsular closure to optimize hip functional outcome and return to athletic activity. The clinical evidence stressing the importance of hip capsule integrity has also been corroborated with biomechanical data.10,16-19 The purpose of the current study was to examine the integrity of the hip capsule in a population of patients who underwent capsular closure as a routine component of primary hip arthroscopy for FAI. We hypothesized that the hip capsule would appear morphologically normal and remain intact as determined by magnetic resonance imaging (MRI) at an average of 1 year after index hip arthroscopy.
office examinations and normal appearance of postoperative radiographs. The exclusion criteria included revision surgery, bilateral surgery, and hip arthroscopy for a diagnosis other than FAI. The surgical indications for the study enrollees included symptomatic FAI with radiographic evidence of cam, pincer, or mixed pathology and failure of nonoperative treatment. The indications for a postoperative MRI included persistence of symptoms, despite postoperative rehabilitation, normal postoperative physical examination, and normal appearance of radiographs. The senior author (S.J.N.) performed all surgeries. All clinical data were gathered in a secure repository.
Methods
Operative Procedures All arthroscopic procedures were performed under general anesthesia in the supine position on a standard traction table. The senior author’s technique has been described elsewhere.20 Briefly, the central compartment was accessed via the anterolateral and modified anterior portals. An interportal capsulotomy (approximately 2 to 4 cm) was performed to expose the acetabular rim. Once in the central compartment, a diagnostic arthroscopy was performed and the labrum, chondral surfaces, and acetabular rim were treated. After work in the central compartment was complete, traction was released and the peripheral compartment was accessed. All patients underwent T capsulotomy through the distal anterolateral accessory portal to assist with arthroscopic visualization of the femoral neck. A femoral osteochondroplasty was performed in the peripheral compartment to address cam-type FAI. Dynamic fluoroscopic examination was used to confirm complete bony resection and absence of residual deformity. At the conclusion of the case, the entire capsulotomy was repaired with high-strength mattress sutures. The longitudinal portion of the T capsulotomy was closed using 3 simple interrupted no. 2 high tensile strength sutures passed with a suture-shuttling device (Spectrum, Conmed Linvatec, Key Largo, FL). The interportal capsulotomy was subsequently closed with 2 simple interrupted no. 2 high tensile strength sutures in simple interrupted fashion using a capsular closure device (Injector, Stryker Sports Medicine, Greenwood Village, CO).
Patient Enrollment After Institutional Review Board approval (no. 120221080), we enrolled consenting patients who underwent hip arthroscopy for FAI with routine capsular closure between January 1, 2012, and December 31, 2015. The inclusion criteria included a diagnosis of FAI, unilateral hip arthroscopy with capsular closure for the treatment of FAI, and a postoperative MRI of the operative hip within 2 years of the day of surgery for persistent symptoms, despite normal
Rehabilitation After surgery, all patients were rehabilitated through the same 4-phase rehabilitation protocol lasting 32 weeks. Patients were kept on crutches for 3 weeks with a 20-pound, flatfoot weight-bearing restriction. A hip orthosis and night abduction pillow were used for the first 3 weeks, aiming to prevent active abduction, hip flexion beyond 90 , and extension with external rotation. All of the aforementioned motions may compromise the labral and capsular repair. Passive and
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gentle active motion, including circumduction, was encouraged to prevent stiffness. At 3 weeks, patients progress to weight bearing as tolerated without crutches or a brace. Also at 3 weeks we progressed hip range of motion including gentle stretching in all planes and progressed core and hip muscle strengthening. At 6 weeks, closed-chain exercises began and stretching was advanced. At 12 weeks, patients participated in running using an antigravity treadmill and performed plyometrics. Patients were typically cleared to return to sports at 4 to 6 months after surgery based on their individual milestones in therapy. Diagnostic Imaging Routine preoperative and postoperative radiographic views performed on all patients included an anteroposterior (AP) pelvis, false profile, and 90 Dunn lateral views of the affected hip. On the AP pelvis radiographs, the lateral center edge angle (LCEA) was measured, and on the 90 Dunn lateral radiograph, the alpha angle was measured.21,22 Patients with persistence of symptoms despite a normal examination and radiographs underwent MRI at least 4 months after surgery. The MRI was infrequently needed; however, it served as an exclusionary test to rule out any structural abnormalities. All MRIs were performed using the same technique on a 1.5 T magnet obtaining 0.25-mm slices with patients in the supine position. The routine protocols included a (1) coronal STIR (TR [Time to relaxation]/TE [Time to excitation], 3000 to 6000/34; slice thickness/gap, 4/1 mm; field of view [FOV], 350 to 380 mm; matrix, 172 320); (2) coronal T1 (TR/TE, 400 to 600/14; slice thickness/gap, 4/1 mm; FOV, 350 to 380 mm; matrix, 172 320); (3) axial T2 (TR/TE, 4000 to 6000/70; slice thickness/gap, 4/1 mm; FOV, 350 to 380 mm; matrix, 238 320); (4) sagittal T2 (TR/TE, 4000 to 6000/71; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 187 256); (5) coronal proton density (PD) (TR/TE, 2800 to 3800/32; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 192 256); and (6) axial PD (TR/TE, 2800 to 3800/32; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 256 256). MRI Analysis Each postoperative MRI was analyzed by 4 physicians including one fellowship-trained, high-volume hip arthroscopist (S.J.N.), one fellowship trained musculoskeletal radiologist (P.B.L.), one sports medicine fellow (A.E.W.), and one orthopaedic surgery resident (G.L.C.), who were provided information regarding the operative side but were blinded to the details of each clinical scenario and the results of the other MRI interpretations. All MRI reviewers were aware that only postoperative patients with symptoms received an MRI. All analysis was conducted on an imaging archiving and
communication system workstation (Opal-Rad, Viztek LLC, Garner, NC). Images were reviewed in a randomized order. Each reviewer, using the same measurement tool, made capsular thickness measurements for each patient. Each reviewer was permitted to adjust window width and level as well as size via zoom features. Each operative hip capsule was examined for the absence or presence of a capsular defect in any of the standard 3 planes analyzed (sagittal, coronal, axial). Each reviewer was permitted to evaluate all sequences in all planes to detect the presence of a capsular defect (Fig 1). A capsular defect was defined as any visual disruption in the iliofemoral ligament in the zone of capsulotomy or appearance of communication between the joint and the iliopsoas bursa. The zone of capsulotomy and subsequent repair through the iliofemoral ligament was examined for capsular thickness and compared to the same site on the healthy contralateral hip using similar methods to previous literature.23,24 In cases of disparity, the decisions were made by the senior surgeon and fellowship-trained musculoskeletal radiologist. Capsular thickness was determined based on the minimum distance in millimeters assessed on T2weighted fat-saturated coronal sections through the iliofemoral ligament at the site of routine capsulotomy and subsequent closure. In addition to capsular thickness and capsular integrity, one of the MRI evaluators (A.E.W.) reviewed each MRI for structural defects that may have explained the need for advanced imaging in the postoperative period. The structures and/or pathology evaluated included labral integrity, presence of residual osseous impingement, focal chondral injury, intraarticular adhesions, and presence of diffuse osteoarthrosis. Statistical Analysis Categorical demographic variables were compared to capsular thickness with bivariate regression, while continuous demographic variables were compared to capsular thickness with one-way analysis of variance. Capsular thickness comparisons between operative and nonoperative sides were compared using the Student t-test. Interobserver reliability was determined through the intraclass correlation coefficient (ICC) using the 2-way mixed model for absolute agreement. All data was analyzed using SPSS software (IBM Corporation, Armonk, NY). P < .05 was considered statistically significant.
Results Population Demographics During the inclusion study period, 1,463 patients had hip arthroscopy for FAI performed by the senior surgeon. In that population, 53 (3.6%) underwent a postoperative MRI due to abnormal pain or symptoms in the
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Fig 1. Representative T2 magnetic resonance imaging after hip arthroscopy for femoroacetabular impingement with routine capsular closure. A and B demonstrate a defect in the operative hip capsule (red arrows) as compared with the unaffected, intact contralateral hip capsule (white arrows). C and D demonstrate an intact operative hip capsule (yellow arrows) as compared with the unaffected, intact contralateral hip capsule (white arrows).
postoperative period that were not explained by postoperative physical examination or radiographs. Fourteen of the 53 were excluded owing to a prior hip arthroscopy or hip arthroscopy that did not pertain to FAI. Thus, the final study population included 39 patients (23 female and 16 male) who underwent postoperative MRI after hip arthroscopy with capsular closure for a diagnosis of FAI (Table 1). Postoperative MRIs were performed on average 12.5 6.8 months after surgery. The average patient age was 31.7 11.4 years, and the average body mass index (BMI) was 23.3 2.9. The primary diagnosis was mixed-type FAI in 37 (95%) patients and isolated cam-type FAI in 2 (5%) patients. Based upon standardized preoperative and postoperative radiographs, the average preoperative alpha angle was 62.2 10.1 , which was significantly reduced with femoral osteochondroplasty to 32.2 4.3 (P < .001). The average preoperative LCEA was 39.7 5.9 , and this also was significantly reduced with acetabular rim trimming to 29 4.8 (P < .001). Labral tears were present in all patients, and repairs were performed in 95% of cases, whereas debridements were performed in the remaining 5% of cases.
Capsular Defects Of the 39 patients to undergo hip arthroscopy for FAI with routine capsular closure, MRI detected capsular defects in 3 patients (7.5%). The defect was found to be along the interportal capsulotomy line in all 3 cases (Fig 1). There were no cases of frank capsular repair failure. There were no statistically significant correlations between the presence of a capsular defect and patient age, gender, BMI, preoperative alpha angle, or preoperative LCEA. Across all 4 evaluators, the ICC for detecting a capsular defect was 0.82, signifying a high inter-rater reliability. Capsular Thickness The operative hip capsule was significantly thicker in the zone of capsulotomy and subsequent repair as compared with the unaffected, contralateral hip capsule (5.0 1.2 mm vs 4.6 1.4 mm; P ¼ .02; Fig 2). Additionally, males had significantly thicker hip capsules as compared with their female counterparts. The increase in capsular thickness for males included both the operative side after capsular repair (5.4 1.1 mm vs 4.5 1.2 mm; P ¼ .02) and the nonoperative side
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MRI OF HIP CAPSULE AFTER HIP ARTHROSCOPY Table 1. Demographic and Surgical Data Value Demographic data Gender, female/male (% female) Age, yr BMI Preoperative AA, Postoperative AA, Preoperative LCEA, Postoperative LCEA, Time from surgery to MRI, mo Surgical data, n (%) Labral repair Synovectomy Acetabular rim Trimming Femoral osteochondroplasty Capsular closure Trochanteric bursectomy
23/16 (59) 31.7 11.4 23.3 2.9 62.2 10.1 32.2 4.3 39.7 5.9 29 4.8 12.5 6.8 37 (95) 39 (100) 37 (95) 39 (100) 39 (100) 4 (10.2)
AA, alpha angle; BMI, body mass index; LCEA, lateral center edge angle; MRI, magnetic resonance imaging.
(4.8 1.6 mm vs 4.1 0.9 mm; P ¼ .08), although it reached statistical significance only on the operative side (Fig 2). There were no significant correlations between patient age, BMI, preoperative alpha angle, preoperative LCEA, or time from surgery to MRI and capsular thickness. The ICC for capsular thickness among all 4 evaluators was 0.83, again signifying high inter-rater agreement. Additional MRI Findings Aside from the 3 capsular defects without complete failure of repair, there were 7 cases of intrasubstance labral signal consistent with postoperative changes. There were no cases of overt labral tears. In addition, there were no cases of new focal chondral defects of either the femoral head or acetabulum and there were no cases of diffuse osteoarthrosis. There were no cases of residual femoral or acetabular osseous impingement.
There were 9 cases in which capsular adhesions were present. All of the pathology identified was successfully treated with improved or refocused rehabilitation. None of the pathology identified required revision hip arthroscopy.
Discussion At an average of 12.5 6.8 months after capsular closure we found MRI evidence that the majority of the capsular repairs (92.5%) remained intact, with a low percentage developing defects (7.5%) and no complete disruptions of the prior repair. Furthermore, the hip capsule adjacent to the capsulotomy and subsequent repair is significantly thickened compared with the same location on the contralateral hip. Males demonstrated thicker anterior capsules compared with their female counterparts, on both the operative side and nonoperative side and significantly so on the operative side. Aside from gender, patient-related and FAI-related factors do not seem to correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect. Prior studies have quantified hip capsular thickness after hip arthroscopy. Magerkurth et al.23 retrospectively reviewed the capsular thickness in 27 patients who had previously undergone hip arthroscopy without capsular repair. They found that the hip capsule adjacent to the capsulotomy site was on average 3.3 mm thick in patients with symptomatic capsular laxity and 2.5 mm thick in those patients without symptoms of laxity.23 Weidner et al.24 measured hip capsular thickness as it related to the acetabular clockface in a population of symptomatic preoperative FAI patients. Their results suggest that the hip capsule thickness varies in thickness from 1.8 mm posteriorly to 6.8 mm anterosuperiorly.24 They also found that males had significantly thicker hip capsules as compared with females, particularly in
Fig 2. Graphic representation of capsular thickness based on operative side and gender. *Statistically significant.
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the anterosuperior and direct anterior locations.24 The current study’s findings of average capsular thickness along the iliofemoral ligament (anterosuperior and anterior locations) as well as thicker capsules in males are consistent with the current state of the literature. The finding of significantly thickened hip capsule on the operative, repaired side as compared with the unaffected hip has not been previously reported. In general, capsular thickening may suggest a normal healing response or an abnormal pathology such as synovitis. We postulate that the thickening seen in the current study was more likely due to the normal healing response owing to the fact that the thickening was isolated to the region surrounding the capsulotomy, whereas synovitis would affect the capsular tissue more systemically throughout the joint. Furthermore, tissue hypertrophy is a hallmark of healing and has been well documented in other body regions as a sign of remodeling associated with soft tissue and osseous healing.25-27 Atraumatic or iatrogenic instability have been the terms assigned to the clinical entity of continued pain or diminished function due to microinstability of the hip after hip arthroscopy.9,28 There are now defined preoperative, patient-related factors that may predispose the patient undergoing hip arthroscopy to postoperative instability. These patient-related factors include generalized ligamentous laxity, hyperflexible athletics, and borderline or true hip dysplasia.29 In addition to the patient-related factors, there are also intraoperative factors that may predispose to postoperative iatrogenic instability. Overzealous acetabular rim resection or labral debridement can induce iatrogenic instability postoperatively.11,30 Lastly, there has been a recent focus on the hip capsule’s contribution to postoperative hip stability and pain-free function.12,17,28,31 Capsular closure after hip arthroscopy for the treatment of FAI makes intuitive sense as surgeons are often attempting to restore normal anatomy or recapitulate the normal tissues to promote proper structure and function. This intuitive process is substantiated by the biomechanical data to date.10,16-19 Myers et al.16 examined the contributions of the iliofemoral ligament and the acetabular labrum to restriction in anterior translation and external rotation of the cadaveric hip. In 15 specimens, they found that the iliofemoral ligament provided a primary stabilization role in both anterior translation and external rotation, whereas the labrum served as a secondary stabilizer.16 Abrams and colleagues17 evaluated the external rotation of cadaveric hips in the intact state as compared to after a T capsulotomy and after a T capsulotomy repair. They found that the T capsulotomy promoted significantly increased external rotation of the hip as compared with the intact state and that the capsular repair restored the range of motion to the intact state.17 In the current study, the capsular defects were found to be along the
interportal capsulotomy and subsequent repair rather than along the T component of the capsulotomy and subsequent repair. Given the small sample size this may be coincidence; however, it is also possible to speculate that this region may be at greater stress given its orientation relative to hip motion. Furthermore, while the T component is inline with the iliofemoral ligament fibers, the interportal capsulotomy is across the capsule fibers, which may promote less of a healing response. Additional study of this topic will aid in delineating a cause for the current finding. The biomechanical importance of the hip capsule to normal hip structure and function has been corroborated in recent clinical studies.5-10,15,32 McCormick et al.7 were able to link postoperative pain to capsular defects in 9 of 25 (36%) patients requiring revision surgery after hip arthroscopy for FAI. Domb and colleagues32 evaluated 2-year PROs in 168 patients with and 235 patients without capsular repair. They found that the Hip Outcome Score-Activities of Daily Living and Non-Arthritic Hip Scores improved significantly in the capsular repair group compared with in the nonrepair group.28 Frank et al.6 reported a similar finding, favoring complete capsular repair versus partial repair. In this study, Frank et al. compared 32 partial repairs of just the T component of the capsulotomy with 32 complete repairs of both the T and interportal components. The authors found that patients with complete repair had improved Hip Outcome Score-Sports Specific subscale at the 6-month, 1-year, and 2-year time points. Additionally, the patients in the partial repair group had a higher revision rate at 13%, compared with 0% in the complete repair group. Finally, the importance of hip capsular stability to overall clinical outcomes was elegantly illustrated by examining a patient population that was in pain after index hip arthroscopy without capsular closure.15 Wylie and colleagues performed revision hip arthroscopy with routine capsular closure on this patient population and demonstrated significant improvements in all PROs at greater than 2 years of follow-up.15 While these clinical outcome studies are not without limitations, the overall body of literature to date demonstrates the importance of capsular closure to clinical outcomes after hip arthroscopy. Limitations Our study is not without limitations. The retrospective nature of the study introduces innate bias associated with the study design. Another limitation is the use of MRI rather than MR arthrography. MR arthrography is more sensitive and specific for detecting changes in the joint capsule as compared with MRI; however, arthrography is not without risks. For the needs of the current study, the invasive nature of arthrography and the infection risk outweighed the benefits. There are many methods for
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quantifying capsular thickness, and some methods are more sophisticated than the current study; however, the technique used for our study was replicated from prior studies of hip capsular thickness. In addition, the MRI readers were unblinded to the fact that only symptomatic patients underwent postoperative MRI. This study contains MRI analysis of symptomatic patients after hip arthroscopy and capsular repair. Studying a symptomatic patient population introduces selection bias into the current study and may limit the external validity of the current studies findings.
Conclusions In a subset of symptomatic patients after hip arthroscopy for FAI, the majority (92.5%) of the repaired hip capsules remained closed at greater than 1 year of follow-up. The hip capsule adjacent to the capsulotomy and subsequent repair is thickened compared with the same location on the contralateral, nonoperative hip. Aside from gender, patient-related and FAI-related factors do not correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect.
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fracture healing: influence of interfragmentary movement on the callus growth. J Biomech 2007;40:1467-1476. 27. Alemann G, Dietsch E, Gallinet D, Obert L, Kastler B, Aubry S. Repair of distal biceps brachii tendon assessed with 3-T magnetic resonance imaging and correlation with functional outcome. Skeletal Radiol 2015;44:629-639. 28. Domb BG, Philippon MJ, Giordano BD. Arthroscopic capsulotomy, capsular repair, and capsular plication of the hip: relation to atraumatic instability. Arthroscopy 2013;29: 162-173. 29. Weber AE, Bedi A, Tibor LM, Zaltz I, Larson CM. The hyperflexible hip: managing hip pain in the dancer and gymnast. Sports Health 2015;7:346-358.
30. Mei-Dan O, McConkey MO, Brick M. Catastrophic failure of hip arthroscopy due to iatrogenic instability: can partial division of the ligamentum teres and iliofemoral ligament cause subluxation? Arthroscopy 2012;28: 440-445. 31. Nepple JJ, Smith MV. Biomechanics of the hip capsule and capsule management strategies in hip arthroscopy. Sports Med Arthrosc 2015;23:164-168. 32. Domb BG, Stake CE, Finley ZJ, Chen T, Giordano BD. Influence of capsular repair versus unrepaired capsulotomy on 2-year clinical outcomes after arthroscopic hip preservation surgery. Arthroscopy 2015;31: 643-650.
Purpose: The purpose of this study was to examine the hip capsule in a subset of symptomatic patients who underwent capsular closure during hip arthroscopy. Methods: All patients undergoing primary hip arthroscopy for femoroacetabular impingement (FAI) with routine capsular closure between January 1, 2012, and December 31, 2015, were eligible. Only patients with unilateral surgery and a postoperative magnetic resonance imaging (MRI; ordered for persistent symptoms) were included. Four independent reviewers evaluated each hip capsule for thickness and the absence or presence of defects. Results: During the study, 1,463 patients had hip arthroscopy for FAI with routine capsular closure, and 53 (3.6%) underwent a postoperative MRI. Fourteen of the 53 were excluded owing to revision status or additional procedures. The final study population included 39 patients (23 female patients and 16 male patients), with an average patient age of 31.7 11.4 years and an average body mass index of 23.3 2.9. There were 3 (7.5%) capsular defects, and the intraclass correlation coefficient (ICC) was 0.82. The operative hip capsule was significantly thicker in the zone of capsulotomy, and subsequent repair as compared with the unaffected, contralateral hip capsule (5.0 1.2 mm vs 4.6 1.4 mm; P ¼ .02), ICC 0.83. Additionally, males had thicker hip capsules as compared with their female counterparts, on the operative side (5.4 1.1 mm vs 4.5 1.2 mm; P ¼ .02) and the nonoperative side (4.8 1.6 mm vs 4.1 0.9 mm; P ¼ .08). Conclusions: In a subset of symptomatic patients after hip arthroscopy for FAI, the majority (92.5%) of the repaired hip capsules remained closed at greater than 1 year of follow-up. The hip capsule adjacent to the capsulotomy and subsequent repair is thickened compared with the same location on the contralateral, nonoperative hip. Aside from gender, patient-related and FAI-related factors do not correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect. Level of Evidence: Level IV, prognostic case series.
O
ver the past 2 decades, femoroacetabular impingement (FAI) has become a well recognized clinical entity that may contribute to the development of hip osteoarthritis.1 Ganz et al.2 were the first to
describe the concept of FAI and subsequently developed an open surgical approach for operative treatment. As part of the open posterior approach to FAI, Ganz and colleagues described performing a formal
From the Section of Young Adult Hip Surgery, Division of Sports Medicine, Department of Orthopedic Surgery, Rush Medical College of Rush University (A.E.W., B.D.K., G.L.C., S.J.N.), Chicago, Illinois; Department of Radiology, University of Illinois Hospital (P.B.L.), Chicago, Illinois; Section of Sports Medicine, Department of Orthopedic Surgery, Duke University Medical Center (R.C.M.), Durham, North Carolina; Division of Sports Medicine, Department of Orthopedics, University Hospital, Case Western Reserve University School of Medicine (M.J.S.), Cleveland, Ohio, U.S.A. The authors report the following potential conflicts of interest or sources of funding: R.C.M. receives support from KNG Consulting, Pivot Medical, Smith & Nephew, Stryker, and MD. S.J.N. receives support from the American Orthopaedic Society for Sports Medicine, the Arthroscopy Association of North
America, the Journal of Bone and Joint Surgery, AOSSM, AANA, Stryker; Ossur, Springer, Allosource, Arthrex, Athletico, DJ Orthopaedics, Linvatec, and Miomed. Received March 30, 2016; accepted July 14, 2016. Address correspondence to Alexander E. Weber, M.D., Hip Preservation Center, Midwest Orthopaedics at Rush, 1611 West Harrison Street, Suite 300, Chicago, IL 60612, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/16267/$36.00 http://dx.doi.org/10.1016/j.arthro.2016.07.022
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arthrotomy, which was repaired at the end of the procedure. In the United States, open approaches for FAI have largely been replaced with arthroscopic techniques.3 These arthroscopic techniques, in general, have not placed emphasis on the treatment of the capsule and mostly describe extended capsulotomies and even capsulectomies for adequate visualization of femoral-sided cam deformities.4 Only recently has more attention been paid to the capsule during arthroscopic treatment of hip conditions.5,6 With the growth in arthroscopic treatment of hip conditions, iatrogenic instability caused by nonrepaired capsulotomy or capsulectomy has become more of a concern.7-10 Recently, there have been case reports of hip dislocation and subluxation after arthroscopic surgery for FAI.11-13 Capsular defects after hip arthroscopy have now been reported as one of the leading causes necessitating revision surgery for continued pain and/or instability.7,14 Frank et al.6 reiterated the importance of capsule repair in hip stability as they demonstrated increased sports specific activity after hip arthroscopy for FAI with complete capsular repair compared with partial capsular repair. Lastly, Wylie and colleagues have recently reported on 33 cases of symptomatic instability after hip arthroscopy without capsular repair and improvement in patient-reported outcome (PRO) 2 years after revision surgery to repair the capsular insufficiency.15 These previous authors concluded that the contemporary treatment of FAI should include chondrolabral repair, surgical correction of FAI, and complete capsular closure to optimize hip functional outcome and return to athletic activity. The clinical evidence stressing the importance of hip capsule integrity has also been corroborated with biomechanical data.10,16-19 The purpose of the current study was to examine the integrity of the hip capsule in a population of patients who underwent capsular closure as a routine component of primary hip arthroscopy for FAI. We hypothesized that the hip capsule would appear morphologically normal and remain intact as determined by magnetic resonance imaging (MRI) at an average of 1 year after index hip arthroscopy.
office examinations and normal appearance of postoperative radiographs. The exclusion criteria included revision surgery, bilateral surgery, and hip arthroscopy for a diagnosis other than FAI. The surgical indications for the study enrollees included symptomatic FAI with radiographic evidence of cam, pincer, or mixed pathology and failure of nonoperative treatment. The indications for a postoperative MRI included persistence of symptoms, despite postoperative rehabilitation, normal postoperative physical examination, and normal appearance of radiographs. The senior author (S.J.N.) performed all surgeries. All clinical data were gathered in a secure repository.
Methods
Operative Procedures All arthroscopic procedures were performed under general anesthesia in the supine position on a standard traction table. The senior author’s technique has been described elsewhere.20 Briefly, the central compartment was accessed via the anterolateral and modified anterior portals. An interportal capsulotomy (approximately 2 to 4 cm) was performed to expose the acetabular rim. Once in the central compartment, a diagnostic arthroscopy was performed and the labrum, chondral surfaces, and acetabular rim were treated. After work in the central compartment was complete, traction was released and the peripheral compartment was accessed. All patients underwent T capsulotomy through the distal anterolateral accessory portal to assist with arthroscopic visualization of the femoral neck. A femoral osteochondroplasty was performed in the peripheral compartment to address cam-type FAI. Dynamic fluoroscopic examination was used to confirm complete bony resection and absence of residual deformity. At the conclusion of the case, the entire capsulotomy was repaired with high-strength mattress sutures. The longitudinal portion of the T capsulotomy was closed using 3 simple interrupted no. 2 high tensile strength sutures passed with a suture-shuttling device (Spectrum, Conmed Linvatec, Key Largo, FL). The interportal capsulotomy was subsequently closed with 2 simple interrupted no. 2 high tensile strength sutures in simple interrupted fashion using a capsular closure device (Injector, Stryker Sports Medicine, Greenwood Village, CO).
Patient Enrollment After Institutional Review Board approval (no. 120221080), we enrolled consenting patients who underwent hip arthroscopy for FAI with routine capsular closure between January 1, 2012, and December 31, 2015. The inclusion criteria included a diagnosis of FAI, unilateral hip arthroscopy with capsular closure for the treatment of FAI, and a postoperative MRI of the operative hip within 2 years of the day of surgery for persistent symptoms, despite normal
Rehabilitation After surgery, all patients were rehabilitated through the same 4-phase rehabilitation protocol lasting 32 weeks. Patients were kept on crutches for 3 weeks with a 20-pound, flatfoot weight-bearing restriction. A hip orthosis and night abduction pillow were used for the first 3 weeks, aiming to prevent active abduction, hip flexion beyond 90 , and extension with external rotation. All of the aforementioned motions may compromise the labral and capsular repair. Passive and
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gentle active motion, including circumduction, was encouraged to prevent stiffness. At 3 weeks, patients progress to weight bearing as tolerated without crutches or a brace. Also at 3 weeks we progressed hip range of motion including gentle stretching in all planes and progressed core and hip muscle strengthening. At 6 weeks, closed-chain exercises began and stretching was advanced. At 12 weeks, patients participated in running using an antigravity treadmill and performed plyometrics. Patients were typically cleared to return to sports at 4 to 6 months after surgery based on their individual milestones in therapy. Diagnostic Imaging Routine preoperative and postoperative radiographic views performed on all patients included an anteroposterior (AP) pelvis, false profile, and 90 Dunn lateral views of the affected hip. On the AP pelvis radiographs, the lateral center edge angle (LCEA) was measured, and on the 90 Dunn lateral radiograph, the alpha angle was measured.21,22 Patients with persistence of symptoms despite a normal examination and radiographs underwent MRI at least 4 months after surgery. The MRI was infrequently needed; however, it served as an exclusionary test to rule out any structural abnormalities. All MRIs were performed using the same technique on a 1.5 T magnet obtaining 0.25-mm slices with patients in the supine position. The routine protocols included a (1) coronal STIR (TR [Time to relaxation]/TE [Time to excitation], 3000 to 6000/34; slice thickness/gap, 4/1 mm; field of view [FOV], 350 to 380 mm; matrix, 172 320); (2) coronal T1 (TR/TE, 400 to 600/14; slice thickness/gap, 4/1 mm; FOV, 350 to 380 mm; matrix, 172 320); (3) axial T2 (TR/TE, 4000 to 6000/70; slice thickness/gap, 4/1 mm; FOV, 350 to 380 mm; matrix, 238 320); (4) sagittal T2 (TR/TE, 4000 to 6000/71; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 187 256); (5) coronal proton density (PD) (TR/TE, 2800 to 3800/32; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 192 256); and (6) axial PD (TR/TE, 2800 to 3800/32; slice thickness/gap, 4/1 mm; FOV, 200 to 250 mm; matrix, 256 256). MRI Analysis Each postoperative MRI was analyzed by 4 physicians including one fellowship-trained, high-volume hip arthroscopist (S.J.N.), one fellowship trained musculoskeletal radiologist (P.B.L.), one sports medicine fellow (A.E.W.), and one orthopaedic surgery resident (G.L.C.), who were provided information regarding the operative side but were blinded to the details of each clinical scenario and the results of the other MRI interpretations. All MRI reviewers were aware that only postoperative patients with symptoms received an MRI. All analysis was conducted on an imaging archiving and
communication system workstation (Opal-Rad, Viztek LLC, Garner, NC). Images were reviewed in a randomized order. Each reviewer, using the same measurement tool, made capsular thickness measurements for each patient. Each reviewer was permitted to adjust window width and level as well as size via zoom features. Each operative hip capsule was examined for the absence or presence of a capsular defect in any of the standard 3 planes analyzed (sagittal, coronal, axial). Each reviewer was permitted to evaluate all sequences in all planes to detect the presence of a capsular defect (Fig 1). A capsular defect was defined as any visual disruption in the iliofemoral ligament in the zone of capsulotomy or appearance of communication between the joint and the iliopsoas bursa. The zone of capsulotomy and subsequent repair through the iliofemoral ligament was examined for capsular thickness and compared to the same site on the healthy contralateral hip using similar methods to previous literature.23,24 In cases of disparity, the decisions were made by the senior surgeon and fellowship-trained musculoskeletal radiologist. Capsular thickness was determined based on the minimum distance in millimeters assessed on T2weighted fat-saturated coronal sections through the iliofemoral ligament at the site of routine capsulotomy and subsequent closure. In addition to capsular thickness and capsular integrity, one of the MRI evaluators (A.E.W.) reviewed each MRI for structural defects that may have explained the need for advanced imaging in the postoperative period. The structures and/or pathology evaluated included labral integrity, presence of residual osseous impingement, focal chondral injury, intraarticular adhesions, and presence of diffuse osteoarthrosis. Statistical Analysis Categorical demographic variables were compared to capsular thickness with bivariate regression, while continuous demographic variables were compared to capsular thickness with one-way analysis of variance. Capsular thickness comparisons between operative and nonoperative sides were compared using the Student t-test. Interobserver reliability was determined through the intraclass correlation coefficient (ICC) using the 2-way mixed model for absolute agreement. All data was analyzed using SPSS software (IBM Corporation, Armonk, NY). P < .05 was considered statistically significant.
Results Population Demographics During the inclusion study period, 1,463 patients had hip arthroscopy for FAI performed by the senior surgeon. In that population, 53 (3.6%) underwent a postoperative MRI due to abnormal pain or symptoms in the
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Fig 1. Representative T2 magnetic resonance imaging after hip arthroscopy for femoroacetabular impingement with routine capsular closure. A and B demonstrate a defect in the operative hip capsule (red arrows) as compared with the unaffected, intact contralateral hip capsule (white arrows). C and D demonstrate an intact operative hip capsule (yellow arrows) as compared with the unaffected, intact contralateral hip capsule (white arrows).
postoperative period that were not explained by postoperative physical examination or radiographs. Fourteen of the 53 were excluded owing to a prior hip arthroscopy or hip arthroscopy that did not pertain to FAI. Thus, the final study population included 39 patients (23 female and 16 male) who underwent postoperative MRI after hip arthroscopy with capsular closure for a diagnosis of FAI (Table 1). Postoperative MRIs were performed on average 12.5 6.8 months after surgery. The average patient age was 31.7 11.4 years, and the average body mass index (BMI) was 23.3 2.9. The primary diagnosis was mixed-type FAI in 37 (95%) patients and isolated cam-type FAI in 2 (5%) patients. Based upon standardized preoperative and postoperative radiographs, the average preoperative alpha angle was 62.2 10.1 , which was significantly reduced with femoral osteochondroplasty to 32.2 4.3 (P < .001). The average preoperative LCEA was 39.7 5.9 , and this also was significantly reduced with acetabular rim trimming to 29 4.8 (P < .001). Labral tears were present in all patients, and repairs were performed in 95% of cases, whereas debridements were performed in the remaining 5% of cases.
Capsular Defects Of the 39 patients to undergo hip arthroscopy for FAI with routine capsular closure, MRI detected capsular defects in 3 patients (7.5%). The defect was found to be along the interportal capsulotomy line in all 3 cases (Fig 1). There were no cases of frank capsular repair failure. There were no statistically significant correlations between the presence of a capsular defect and patient age, gender, BMI, preoperative alpha angle, or preoperative LCEA. Across all 4 evaluators, the ICC for detecting a capsular defect was 0.82, signifying a high inter-rater reliability. Capsular Thickness The operative hip capsule was significantly thicker in the zone of capsulotomy and subsequent repair as compared with the unaffected, contralateral hip capsule (5.0 1.2 mm vs 4.6 1.4 mm; P ¼ .02; Fig 2). Additionally, males had significantly thicker hip capsules as compared with their female counterparts. The increase in capsular thickness for males included both the operative side after capsular repair (5.4 1.1 mm vs 4.5 1.2 mm; P ¼ .02) and the nonoperative side
5
MRI OF HIP CAPSULE AFTER HIP ARTHROSCOPY Table 1. Demographic and Surgical Data Value Demographic data Gender, female/male (% female) Age, yr BMI Preoperative AA, Postoperative AA, Preoperative LCEA, Postoperative LCEA, Time from surgery to MRI, mo Surgical data, n (%) Labral repair Synovectomy Acetabular rim Trimming Femoral osteochondroplasty Capsular closure Trochanteric bursectomy
23/16 (59) 31.7 11.4 23.3 2.9 62.2 10.1 32.2 4.3 39.7 5.9 29 4.8 12.5 6.8 37 (95) 39 (100) 37 (95) 39 (100) 39 (100) 4 (10.2)
AA, alpha angle; BMI, body mass index; LCEA, lateral center edge angle; MRI, magnetic resonance imaging.
(4.8 1.6 mm vs 4.1 0.9 mm; P ¼ .08), although it reached statistical significance only on the operative side (Fig 2). There were no significant correlations between patient age, BMI, preoperative alpha angle, preoperative LCEA, or time from surgery to MRI and capsular thickness. The ICC for capsular thickness among all 4 evaluators was 0.83, again signifying high inter-rater agreement. Additional MRI Findings Aside from the 3 capsular defects without complete failure of repair, there were 7 cases of intrasubstance labral signal consistent with postoperative changes. There were no cases of overt labral tears. In addition, there were no cases of new focal chondral defects of either the femoral head or acetabulum and there were no cases of diffuse osteoarthrosis. There were no cases of residual femoral or acetabular osseous impingement.
There were 9 cases in which capsular adhesions were present. All of the pathology identified was successfully treated with improved or refocused rehabilitation. None of the pathology identified required revision hip arthroscopy.
Discussion At an average of 12.5 6.8 months after capsular closure we found MRI evidence that the majority of the capsular repairs (92.5%) remained intact, with a low percentage developing defects (7.5%) and no complete disruptions of the prior repair. Furthermore, the hip capsule adjacent to the capsulotomy and subsequent repair is significantly thickened compared with the same location on the contralateral hip. Males demonstrated thicker anterior capsules compared with their female counterparts, on both the operative side and nonoperative side and significantly so on the operative side. Aside from gender, patient-related and FAI-related factors do not seem to correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect. Prior studies have quantified hip capsular thickness after hip arthroscopy. Magerkurth et al.23 retrospectively reviewed the capsular thickness in 27 patients who had previously undergone hip arthroscopy without capsular repair. They found that the hip capsule adjacent to the capsulotomy site was on average 3.3 mm thick in patients with symptomatic capsular laxity and 2.5 mm thick in those patients without symptoms of laxity.23 Weidner et al.24 measured hip capsular thickness as it related to the acetabular clockface in a population of symptomatic preoperative FAI patients. Their results suggest that the hip capsule thickness varies in thickness from 1.8 mm posteriorly to 6.8 mm anterosuperiorly.24 They also found that males had significantly thicker hip capsules as compared with females, particularly in
Fig 2. Graphic representation of capsular thickness based on operative side and gender. *Statistically significant.
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the anterosuperior and direct anterior locations.24 The current study’s findings of average capsular thickness along the iliofemoral ligament (anterosuperior and anterior locations) as well as thicker capsules in males are consistent with the current state of the literature. The finding of significantly thickened hip capsule on the operative, repaired side as compared with the unaffected hip has not been previously reported. In general, capsular thickening may suggest a normal healing response or an abnormal pathology such as synovitis. We postulate that the thickening seen in the current study was more likely due to the normal healing response owing to the fact that the thickening was isolated to the region surrounding the capsulotomy, whereas synovitis would affect the capsular tissue more systemically throughout the joint. Furthermore, tissue hypertrophy is a hallmark of healing and has been well documented in other body regions as a sign of remodeling associated with soft tissue and osseous healing.25-27 Atraumatic or iatrogenic instability have been the terms assigned to the clinical entity of continued pain or diminished function due to microinstability of the hip after hip arthroscopy.9,28 There are now defined preoperative, patient-related factors that may predispose the patient undergoing hip arthroscopy to postoperative instability. These patient-related factors include generalized ligamentous laxity, hyperflexible athletics, and borderline or true hip dysplasia.29 In addition to the patient-related factors, there are also intraoperative factors that may predispose to postoperative iatrogenic instability. Overzealous acetabular rim resection or labral debridement can induce iatrogenic instability postoperatively.11,30 Lastly, there has been a recent focus on the hip capsule’s contribution to postoperative hip stability and pain-free function.12,17,28,31 Capsular closure after hip arthroscopy for the treatment of FAI makes intuitive sense as surgeons are often attempting to restore normal anatomy or recapitulate the normal tissues to promote proper structure and function. This intuitive process is substantiated by the biomechanical data to date.10,16-19 Myers et al.16 examined the contributions of the iliofemoral ligament and the acetabular labrum to restriction in anterior translation and external rotation of the cadaveric hip. In 15 specimens, they found that the iliofemoral ligament provided a primary stabilization role in both anterior translation and external rotation, whereas the labrum served as a secondary stabilizer.16 Abrams and colleagues17 evaluated the external rotation of cadaveric hips in the intact state as compared to after a T capsulotomy and after a T capsulotomy repair. They found that the T capsulotomy promoted significantly increased external rotation of the hip as compared with the intact state and that the capsular repair restored the range of motion to the intact state.17 In the current study, the capsular defects were found to be along the
interportal capsulotomy and subsequent repair rather than along the T component of the capsulotomy and subsequent repair. Given the small sample size this may be coincidence; however, it is also possible to speculate that this region may be at greater stress given its orientation relative to hip motion. Furthermore, while the T component is inline with the iliofemoral ligament fibers, the interportal capsulotomy is across the capsule fibers, which may promote less of a healing response. Additional study of this topic will aid in delineating a cause for the current finding. The biomechanical importance of the hip capsule to normal hip structure and function has been corroborated in recent clinical studies.5-10,15,32 McCormick et al.7 were able to link postoperative pain to capsular defects in 9 of 25 (36%) patients requiring revision surgery after hip arthroscopy for FAI. Domb and colleagues32 evaluated 2-year PROs in 168 patients with and 235 patients without capsular repair. They found that the Hip Outcome Score-Activities of Daily Living and Non-Arthritic Hip Scores improved significantly in the capsular repair group compared with in the nonrepair group.28 Frank et al.6 reported a similar finding, favoring complete capsular repair versus partial repair. In this study, Frank et al. compared 32 partial repairs of just the T component of the capsulotomy with 32 complete repairs of both the T and interportal components. The authors found that patients with complete repair had improved Hip Outcome Score-Sports Specific subscale at the 6-month, 1-year, and 2-year time points. Additionally, the patients in the partial repair group had a higher revision rate at 13%, compared with 0% in the complete repair group. Finally, the importance of hip capsular stability to overall clinical outcomes was elegantly illustrated by examining a patient population that was in pain after index hip arthroscopy without capsular closure.15 Wylie and colleagues performed revision hip arthroscopy with routine capsular closure on this patient population and demonstrated significant improvements in all PROs at greater than 2 years of follow-up.15 While these clinical outcome studies are not without limitations, the overall body of literature to date demonstrates the importance of capsular closure to clinical outcomes after hip arthroscopy. Limitations Our study is not without limitations. The retrospective nature of the study introduces innate bias associated with the study design. Another limitation is the use of MRI rather than MR arthrography. MR arthrography is more sensitive and specific for detecting changes in the joint capsule as compared with MRI; however, arthrography is not without risks. For the needs of the current study, the invasive nature of arthrography and the infection risk outweighed the benefits. There are many methods for
MRI OF HIP CAPSULE AFTER HIP ARTHROSCOPY
quantifying capsular thickness, and some methods are more sophisticated than the current study; however, the technique used for our study was replicated from prior studies of hip capsular thickness. In addition, the MRI readers were unblinded to the fact that only symptomatic patients underwent postoperative MRI. This study contains MRI analysis of symptomatic patients after hip arthroscopy and capsular repair. Studying a symptomatic patient population introduces selection bias into the current study and may limit the external validity of the current studies findings.
Conclusions In a subset of symptomatic patients after hip arthroscopy for FAI, the majority (92.5%) of the repaired hip capsules remained closed at greater than 1 year of follow-up. The hip capsule adjacent to the capsulotomy and subsequent repair is thickened compared with the same location on the contralateral, nonoperative hip. Aside from gender, patient-related and FAI-related factors do not correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect.
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9. Weber AE, Harris JD, Nho SJ. Complications in hip arthroscopy: a systematic review and strategies for prevention. Sports Med Arthrosc 2015;23:187-193. 10. Bayne CO, Stanley R, Simon P, et al. Effect of capsulotomy on hip stabilityda consideration during hip arthroscopy. Am J Orthop 2014;43:160-165. 11. Matsuda DK. Acute iatrogenic dislocation following hip impingement arthroscopic surgery. Arthroscopy 2009;25: 400-404. 12. Ranawat AS, McClincy M, Sekiya JK. Anterior dislocation of the hip after arthroscopy in a patient with capsular laxity of the hip. A case report. J Bone Joint Surg Am 2009;91:192-197. 13. Benali Y, Katthagen BD. Hip subluxation as a complication of arthroscopic debridement. Arthroscopy 2009;25: 405-407. 14. Philippon MJ, Schenker ML, Briggs KK, Kuppersmith DA, Maxwell RB, Stubbs AJ. Revision hip arthroscopy. Am J Sports Med 2007;35:1918-1921. 15. Wylie JD, Beckmann JT, Maak TG, Aoki SK. Arthroscopic capsular repair for symptomatic hip instability after previous hip arthroscopic surgery. Am J Sports Med 2016;44: 39-45. 16. Myers CA, Register BC, Lertwanich P, et al. Role of the acetabular labrum and the iliofemoral ligament in hip stability: an in vitro biplane fluoroscopy study. Am J Sports Med 2011;39:85S-91S (suppl). 17. Abrams GD, Hart MA, Takami K, et al. Biomechanical evaluation of capsulotomy, capsulectomy, and capsular repair on hip rotation. Arthroscopy 2015;31:1511-1517. 18. Smith MV, Costic RS, Allaire R, Schilling PL, Sekiya JK. A biomechanical analysis of the soft tissue and osseous constraints of the hip joint. Knee Surg Sports Traumatol Arthrosc 2014;22:946-952. 19. van Arkel RJ, Amis AA, Cobb JP, Jeffers JR. The capsular ligaments provide more hip rotational restraint than the acetabular labrum and the ligamentum teres: an experimental study. Bone Joint J 2015;97-B:484-491. 20. Harris JD, Slikker W 3rd, Gupta AK, McCormick FM, Nho SJ. Routine complete capsular closure during hip arthroscopy. Arthrosc Tech 2013;2:e89-e94. 21. Clohisy JC, Carlisle JC, Beaule PE, et al. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am 2008;90:47-66 (suppl 4). 22. Notzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br 2002;84:556-560. 23. Magerkurth O, Jacobson JA, Morag Y, Caoili E, Fessell D, Sekiya JK. Capsular laxity of the hip: findings at magnetic resonance arthrography. Arthroscopy 2013;29:1615-1622. 24. Weidner J, Buchler L, Beck M. Hip capsule dimensions in patients with femoroacetabular impingement: a pilot study. Clin Orthop Relat Res 2012;470:3306-3312. 25. Ahn JH, Lee SH, Choi SH, Lim TK. Magnetic resonance imaging evaluation of anterior cruciate ligament reconstruction using quadrupled hamstring tendon autografts: comparison of remnant bundle preservation and standard technique. Am J Sports Med 2010;38:1768-1777. 26. Garcia-Aznar JM, Kuiper JH, Gomez-Benito MJ, Doblare M, Richardson JB. Computational simulation of
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