Multicenter Analysis of Midterm Clinical Outcomes of Arthroscopic Labral Repair in the Hip
Minimum 5-Year Follow-up
Mario Hevesi,* MD, Aaron J. Krych,*y MD, Nick R. Johnson,* BS, John M. Redmond,z MD, David E. Hartigan,§ MD, Bruce A. Levy,* MD, and Benjamin G. Domb,II MD
Investigation performed at Mayo Clinic, Rochester, Minnesota, USA; Mayo Clinic, Phoenix, Arizona, USA; Southeast Orthopedic Specialists, Jacksonville, Florida, USA;
and American Hip Institute, Westmont, Illinois, USA
Background: The technique of hip arthroscopic surgery is advancing and becoming more commonly performed. However, most current reported results are limited to short-term follow-up, and therefore, the durability of the procedure is largely unknown.
Purpose: To perform a multicenter analysis of mid-term clinical outcomes of arthroscopic hip labral repair and determine the risk factors for patient outcomes.
Study Design: Cohort study; Level of evidence, 3.
Methods: Prospectively collected data of primary hip arthroscopic labral repair performed at 4 high-volume centers between 2008 and 2011 were reviewed retrospectively. Patients were assessed preoperatively and postoperatively with the visual analog scale (VAS), modified Harris Hip Score (mHHS), and Hip Outcome Score–Sports-Specific Subscale (HOS-SSS) at a minimum of 5 years’ follow-up. Factors including age, body mass index (BMI), To¨ nnis grade, and cartilage grade were analyzed in relation to outcome scores, and revision rates were determined. Failure was defined as subsequent ipsilateral hip surgery, including revision arthroscopic surgery and open hip surgery.
Results: A total of 303 patients (101 male, 202 female) with a mean age of 32.0 years (range, 10.7-58.9 years) were followed for a mean of 5.7 years (range, 5.0-7.9 years). Patients achieved mean improvements in VAS of 3.5 points, mHHS of 20.1 points, and HOS-SSS of 29.3 points. Thirty-seven patients (12.2%) underwent revision arthroscopic surgery, and 12 (4.0%) underwent peri- acetabular osteotomy, resurfacing, or total hip arthroplasty during the study period. Patients with a BMI .30 kg/m2 had a mean mHHS score 9.5 points lower and a mean HOS-SSS score 15.9 points lower than those with a BMI :::30 kg/m2 (P \ .01). Patients aged .35 years at surgery had a mean mHHS score 4.5 points lower and a HOS-SSS score 6.7 points lower than those aged :::35 years (P = .03). Patients with To¨ nnis grade 2 radiographs demonstrated a 12.5-point worse mHHS score (P = .02) and a 23.0-point worse HOS-SSS score (P \ .01) when compared with patients with To¨ nnis grade 0.
Conclusion: Patients demonstrated significant improvements in VAS, mHHS, and HOS-SSS scores after arthroscopic labral repair. However, those with To¨ nnis grade 2 changes preoperatively, BMI .30 kg/m2, and age .35 years at the time of surgery demonstrated significantly decreased mHHS and HOS-SSS scores at final follow-up.
Keywords: hip arthroscopic surgery; midterm; labral repair; clinical outcomes; VAS; mHHS; HOS-SSS
Hip pain and the development of osteoarthritis have been strongly associated with structural abnormalities of the hip joint including chondral injuries, labral tears, and fem- oroacetabular impingement (FAI).4,24,35,42 Traditionally, the treatment of hip disorders required open approaches; however, there has been a contemporary shift to less inva- sive management of these lesions.6 Hip arthroscopic surgery was popularized in the late 2000s, and there has been a dramatic increase in its recent use, as it has been shown to be safe and efficacious in short-term studies.7,28 Initial arthroscopic management of acetabular labral injuries was in the form of debridement, and this has been shown to have modest outcomes at mid-term follow- up, with 20% of hips requiring subsequent surgery and an additional 25% of hips rating function as abnormal or severely abnormal at 5 years’ follow-up. Subsequent efforts to preserve the labrum through repair have demon- strated promising short-term outcomes, with significantly greater improvements in the Hip Outcome Score–Activities of Daily Living (HOS-ADL) and HOS–Sports-Specific Subscale (HOS-SSS) when compared with isolated debridement.37 However, longer follow-up is currently underreported. As such, it is largely unknown whether early improvements after labral repair will be durable over time.
Short-term studies have additionally established that body mass index (BMI) and increased patient age are risk factors for decreased patient-reported outcomes postoperatively.27,30,39,53 However, the preoperative Tonnis grade, which had previously been postulated to be a negative predictor of outcomes, has not been shown to have significant postoperative effects in large, matched cohorts.13,14
Therefore, the purpose of this study was to (1) outline the clinical mid-term patient-reported outcomes of arthroscopic hip labral repair at a minimum 5 years of follow-up, (2) determine the applicability of short-term risk factors on mid- to long-term outcomes, and (3) establish novel risk fac- tors as patient groups differentiate over time. Our hypothe- ses were that (1) patients would demonstrate durable improvements in patient-reported outcome scores at mid- term follow-up, (2) previously established short-term risk factors such as increased BMI and patient age would predict worse mid-term outcomes, and (3) an increased preoperative To¨nnis grade would negatively affect mid- to long-term out- comes as patients with varying degrees of pre-existing oste- oarthritis differentiate over time.
Study Population and Design
This retrospective clinical and radiographic study included all eligible patients undergoing hip arthroscopic surgery after the failure of nonoperative management at 4 high- volume hip arthroscopic surgery centers (Mayo Clinic, Rochester, Minnesota; Mayo Clinic, Phoenix, Arizona; Southeast Orthopedic Specialists, Jacksonville, Florida; and American Hip Institute, Westmont, Illinois). Patients consented to participate in research after institutional review board approval of the study design (#08-002259). Inclusion criteria consisted of all patients undergoing primary hip arthroscopic surgery between February 2008 and December 2011 who consented to research participation with labral repair performed at the time of surgery. Exclusion criteria consisted of less than 5 years of clinical follow-up, patients choosing not to participate in outcome surveys, labral debridement, labral reconstruction, and previous hip surgery. Patients with bilateral hip arthroscopic surgery, both simultaneous and staged, were included and noted in our database. Indications for arthroscopic surgery included labral tears, chondral injuries, and FAI that had failed nonoperative management. The prospectively collected institutional databases contained the records of 449 primary hip arthroscopic procedures with labral repair performed during the study period for potential inclusion. Of these, 146 patients were excluded because they had less than 5 years of clinical follow-up, resulting in 303 patients for inclusion in this study.
Arthroscopic hip surgery was performed by experienced arthroscopic surgeons (A.J.K., J.M.R., D.E.H., B.A.L., B.G.D.) in an operative setting. Patients were positioned in a modified supine position, and 2 or more portals were employed, including the anterolateral and midanterior portals. Positioning and approaches have been previously described in detail.8,40,54 Diagnostic arthroscopic surgery was performed to directly evaluate the articular and labral status. Correction of cam and pincer lesions was per- formed when present.16,17 All patients underwent labral repair with concurrent debridement as indicated, employing standard techniques.18,23,34 Psoas release was performed in the setting of clinically painful iliopsoas snapping reproduced on physical examination. Capsular repair was performed at the discretion of the operating surgeon, with its use favored in the setting of young patients participating in high-demand activities, patients demonstrating hip or generalized laxity such as that easily translated under femoral head traction, and those with dysplastic radiographic features.
Patients underwent standard postoperative rehabilitation and pain relief protocols, which were consistent between physicians at the same institution and similar between institutions. Patients were placed on crutches for 2 to 4 weeks with foot-flat partial weightbearing. Passive motion was started at 0 weeks. As crutches were gradually discontinued, patients progressed through institutional rehabilitation protocols, which have been previously outlined in detail for the centers involved.21,50 Jogging exercises began at 3 months, as tolerated, and return to sport was allowed at 5 to 6 months.
Demographic data such as age at the time of surgery, BMI, and sex were collected. In addition, preoperative radiographic measures such as Tonnis grade,51 alpha angle,2 and lateral center edge angle (LCEA)41 were noted. Hips with an LCEA \25° were classified as dysplastic. Surgical diagnoses such as the presence of cam and/or pincer lesions, femoral and acetabular chondromalacia as defined by the Outerbridge45 and acetabular labrum articular disruption (ALAD)9 classification systems, and surgical techniques such as ligamentum teres debridement and psoas release were documented using a standardized data form. Subjective preoperative and postoperative outcomes were documented using the visual analog scale (VAS),38 modi- fied Harris Hip Score (mHHS),29 and HOS-SSS.43 The completion rate for each individual outcome scale was 2:89.3%. Failure was defined as subsequent ipsilateral hip surgery, including revision arthroscopic surgery, open hip surgery, and conversion to hip replacement.
Descriptive statistics were used to present demographic data, employing means and SDs, percentages, and medians with interquartile ranges (IQRs), as appropriate. Factors such as BMI, sex, laterality, and intraoperative cartilage grade were examined for their association with outcome measures such as VAS, mHHS, and HOS-SSS using the Spearman rank correlation coefficient for continuous variables, independent sample t tests for differences between nominal values, and analysis of variance for categorical variables such as Tonnis, femoral, and acetabular cartilage grades. After analysis of single-factor predictors, stepwise linear regression was performed employing the Akaike information criterion to identify the optimal set of explanatory variables for postoperative outcome scores.1 The Wilcoxon rank-sum test (Mann-Whitney U test) was used to compare ordinal variables such as preoperative and postoperative VAS, mHHS, and HOS-SSS scores. Cox proportional hazards regression was performed to determine predictors of postoperative failure.
A priori analysis was used to determine the mean group sample size needed to demonstrate the minimal clinically important difference (MCID) for patient-reported outcome scores at an alpha of 0.05 and power of 0.80. Using the study by Chahal et al,12 in which MCID cutoffs were determined for mHHS and HOS-SSS at 3, 6, and 12 months after hip arthroscopic labral repair for FAI, the most conservative MCID value presented for each outcome measure was selected, resulting in a cutoff of 9.0 points for mHHS and 25.0 points for HOS-SSS. Additionally, based on a study of arthritic hip pain in 211 patients, an MCID of 2.0 points was established for VAS.52 Employing these values and out- come score distributions derived from previous studies on hip arthroscopic labral repair, the mean group sample size needed to demonstrate the MCID was determined to be 48 for mHHS, 12 for HOS-SSS, and 21 for VAS.32 P values\.05 were considered significant. Analyses were conducted in R version 3.4.0 (R Core Team).
Using institutional databases comprising cases of hip arthroscopic surgery performed from February 2008 to December 2011 at 4 institutions, we identified 303 patients with 2:5 year
s of clinical follow-up. The mean age at the time of surgery was 32.0 years, the mean BMI was 24.4 kg/m2, and the mean duration of follow-up was 5.7 years (range, 5.0-7.9 years) (Table 1). In terms of preoperative radiographic measures, Tonnis grade 0 predominated (72.1%), followed by grade 1 (24.2%) and grade 2 (3.7%). The median alpha angle was 56.9° (IQR, 49.0°-67.0°), and the median LCEA was 30.0° (IQR, 26.5°-34.0°). Of note, right-sided surgery (58.1%) was significantly more com- mon than left-sided surgery (41.9%) (P \ .01), and women (66.7%) were represented to a greater proportion than men (33.3%) (P \ .001).
Four patients underwent bilateral hip surgery, with both hips included in the dataset with a minimum 5 years of follow-up. Of these, 1 pair of hips underwent surgery simultaneously, and another 3 pairs underwent surgery in a staged manner, with the 2 procedures separated by 4.5 to 24.6 months. An additional 5 patients underwent hip arthroscopic surgery performed in a staged manner, with the second hip performed after December 2011 and thus had less than 5 years of follow-up. In these cases, the first hip was included in the dataset.
Patients underwent hip arthroscopic surgery for a combination of hip dysplasia (n = 50), cam lesions (n = 200), pincer lesions (n = 66), and labral lesions (n = 303) in the setting of varied acetabular and femoral chondromalacia (Table 2). For patients with dysplasia, the mean LCEA was 21.5° (range, 13.0°-24.9°).
Ligamentum teres debridement was performed in 37.6% of the study population, psoas release in 38.3%, and capsular repair in 48.5%. The total failure rate was observed to be 16.2%, with 49 of 303 patients undergoing revision hip surgery during the course of follow-up. Of these, 7 went on to total hip arthroplasty, 2 underwent hip resurfacing, 2 underwent periacetabular osteotomy alone, 37 underwent revision arthroscopic management, and 1 patient underwent revision arthroscopic management, followed by periacetabular osteotomy, at a later time. All patients going on to periacetabular osteotomy did so in the setting of hip dysplasia.
A multivariable Cox proportional hazards model was constructed to evaluate preoperative and intraoperative findings predictive of subsequent failure and the progres- sion to ipsilateral hip surgery. No significant predictors of failure were noted (Table 3). Dysplasia did not predict subsequent ipsilateral hip surgery, whether defined as an LCEA \25° (P = .56) or an LCEA \20° (P = .60).
VAS, mHHS, and HOS-SSS scores were all observed to significantly improve (P \ .001) between preoperative values and final follow-up at 5.0 to 7.9 years postoperatively (Figure 1). VAS score decreased a mean of 3.5 points after surgery, whereas mHHS and HOS-SSS scores increased by 20.1 and 29.3 points, respectively. Analysis was conducted to explore whether the institution or performing surgeon had an effect on outcome scores. The location and provider were found to be nonsignificant in predicting VAS, mHHS, and HOS-SSS scores at final follow-up (P 2: .11) when accounting for patient age, BMI, and Tonnis grade.
BMI was found to be significantly and negatively corre- lated to final mHHS (P \ .001) and HOS-SSS (P \ .001) scores. It was nonsignificant for predicting VAS scores (P = .33). This pattern was also present for age at the time of surgery, with a significant negative correlation with final mHHS (P = .02) and HOS-SSS (P \ .01) scores and nonsignificance in terms of VAS scores (P = .66).
On average, patients with a BMI .30 kg/m2 had a final mHHS score 9.5 points lower (mean mHHS score, 74.0) than those with a BMI :::30 kg/m2 (mean mHHS score,83.5) (P \ .01) and demonstrated a HOS-SSS score 15.9 points lower (mean HOS-SSS score, 57.0) than those with a BMI :::30 kg/m2 (mean HOS-SSS score, 72.9) (P \ .001) (Figure 2). Patients aged .35 years at the time of surgery had a final mHHS score 4.5 points lower (mean mHHS score, 79.8) than those aged :::35 years (mean mHHS score, 84.3) (P = .03) and similarly demonstrated a HOS-SSS score 6.7 points lower (mean HOS-SSS score, 67.1) than those aged :::35 years (mean HOS-SSS score, 73.8) (P =.03) (Figure 3). Patients with a BMI .30 kg/m2 achieved mean improvements in the VAS of 4.0, the mHHS of 19.1, and the HOS-SSS of 29.2 postoperatively, whereas patients aged .35 years had mean improvements of 3.2 in the VAS, 17.5 in the mHHS, and 27.3 in the HOS-SSS. As such, both groups, while statistically inferior in outcomes as compared with patients with a BMI :::30 kg/m2 and age :::35 years, surpassed the MCID for each patient-reported score (2.0, 9.0, and 25.0, respectively).
Additionally, patients with Tonnis grade 2 preoperatively were found to have a 12.5-point worse mHHS score (P = .02) and 23.0-point worse HOS-SSS score
(P \ .01) at the time of follow-up as compared with patients with Tonnis grade 0 (Figure 4). VAS demonstrated no significant association with the Tonnis grade. No significant differences in the mHHS or HOS-SSS were found when comparing patients with grade 0 and grade 1 radiographs preoperatively. Patients presenting with To¨nnis grade 2 changes achieved final mean improvements in the VAS of 3.7 points (P = .0.01), surpassing the MCID. However, the mean HOS-SSS score decreased nonsignificantly from 72.1 preoperatively to 71.0 postoperatively (P = .84), while the mean HOS-SSS score decreased from 68.8 preoperatively to 49.5 postoperatively (P = .66) in Tonnis grade 2 patients.
The preoperative alpha angle, LCEA, sex, laterality, intra- operative femoral and acetabular cartilage grades, ligamen- tum teres debridement, psoas release, and capsular repair were found to be nonsignificant at predicting VAS, mHHS, and HOS-SSS scores.
After univariate analysis, multifactorial analysis for predictors of each of the 3 patient-reported outcomes was performed using stepwise regression employing the Akaike information criterion. As previously observed in univariate analysis, no significant predictors of the final VAS score were found. It was determined that the optimum model for both the mHHS and HOS-SSS at final follow-up was through the combination of BMI and Tonnis grade. As such, patients with a BMI .30 kg/m2 and Tonnis grade 2 preoperatively were modeled to have the worst outcomes, whereas patients with a BMI :::30 kg/m2 and Tonnis grade 0 to 1 were predicted to experience the most favorable results after arthroscopic labral repair (Table 4).
The purpose of this study was to determine the clinical out- comes of arthroscopic hip labral repair at a minimum 5 years of follow-up as well as to determine the risk factors for worse patient outcomes. Our hypothesis was supported in that patients demonstrated durable improvements in VAS, mHHS, and HOS-SSS scores at mid-term follow-up. In addition, we found that increasing Tonnis grade, patient BMI, and age at the time of surgery significantly predicted worse outcomes.
Our finding that patient outcomes demonstrated significant and sustained improvement at 5 years after hip arthro- scopic surgery is an extension of the previous literature that has demonstrated well-established short-term efficacy and favorable outcomes in terms of VAS,13 mHHS,11,20,33 and HOS-SSS scores.20 As longer term outcomes become available for analysis, recent studies have demonstrated mid- term benefits of hip arthroscopic surgery in the setting of FAI and labral tears. However, the sample size for most studies has been relatively small, and we believe that this study is among the largest cohorts with the longest mean follow-up when reviewing the current literature.25,31,44,47,49 As such, we believe that this study supports the durable outcomes previously described at mid-term follow-up while adding statistical power and decreasing the propensity for type 2 errors present in smaller sample sizes.
In terms of the VAS, our findings demonstrated a mean postoperative VAS score within the SD of the overall VAS score observed for 935 hips previously described at 2:2 years of follow-up.13 It is noteworthy that our mean VAS score fell below the point estimates for the Tonnis grade 0, 1, and 2 subgroups reported in the prior study; however, our population was 12.8 years younger at the time of surgery, making direct comparisons between study populations difficult. In terms of our findings associating increasing To¨nnis grade with decreasing outcome scores, it has been previously reported in large matched-cohort studies that VAS, mHHS, and HOS-SSS scores are not significantly affected by the preoperative Tonnis grade at 2 years of follow-up.13,14 Our findings are significant in that they suggest that preoperative osteoarthritis evolves over time, causing significant effects in mHHS and HOS-SSS at mid-term fol- low-up, which are not apparent earlier in patients’ clinical courses. This was especially noticeable in mHHS and HOS-SSS scores for patients with Tonnis grade 2 radio- graphs, which decreased nonsignificantly postoperatively, failing to meet the MCID. In comparison, patients with Tonnis grade 0 to 1 changes demonstrated significant postoperative improvements in mHHS and HOS-SSS as well as VAS, which surpassed the MCID. This highlights the importance of large cohorts with extended follow-up as outcomes can differentiate over the course of many years. Future studies should aim to investigate outcome score trends over time as well as correlate these outcomes to postoperative radiographic signs of arthritis.
In terms of mHHS, we observed postoperative scores that approximated the findings of Kamath et al,33 who demonstrated a mean mHHS score of 80.4 at 4.8 years in their sample of labral tears managed arthroscopically. When comparing our subgroup of patients aged .35 years to their sample, which had an average age of 42 years, the difference in the observed postoperative mHHS score is 0.6, suggesting relative homogeneity between our outcomes and those found at the university and private hospital included in their study. Similarly, our HOS-SSS scores are similar to values previously presented for both adolescents and recreational athletes at short-term follow-up.20,53
A meta-analysis comprising 107 study populations and 9044 hips at 2:1 year by Levy et al39 demonstrated that increasing patient age negatively predicts mHHS and HOS-SSS scores. Similarly, the study suggested that increasing BMI predicts worse HOS-SSS scores. In terms of age, there has been a significant amount of data associating age-related chondropathy with worse outcomes as well as identifying increasing age as an independent negative predictor of postoperative outcomes and as a risk factor for subsequent conversion to total hip arthroplasty, especially in those patients over 40 years of age.27,30 However, meta-analyses have focused on stratifying the risk of revision and have been limited by differences in outcome scores collected by various studies as well as by their combination of relatively dissimilar and individually small sample sizes. We believe that this cohort serves as the first single-study sample to describe the association between increased age and worsened mid-term outcomes after hip arthroscopic surgery.
Our finding of increased BMI being associated with worse patient outcome scores has also been described previously in the short-term literature. A recent work correlated increasing BMI and decreased mHHS and HOS-SSS values at 2 years’ follow-up in a population of relatively young recreational and amateur athletes.53 These findings have also been described in larger cross-sectional samples, such as the previously mentioned meta-analysis by Levy et al,39 which demonstrated a significant correlation between increasing BMI in 3149 hips and decreasing HOS-SSS and HOS-ADL scores. Finally, a 2-study meta-analysis associated BMI 2:30 kg/m2 with both decreased mHHS and Non-Arthritic Hip Score (NAHS) scores as compared with nonobese controls as well as an increased risk of revision arthroscopic surgery and total hip arthroplasty at 2.5 years of follow-up.3 The current study, however, remains the only study to extend these findings to mid-term follow-up, suggesting that increased BMI and patient age have lasting effects on patient outcomes. It is noteworthy that there is likely a considerable degree of interplay between age, BMI, and osteoarthritis for most patients; however, each has been established as an independent risk factor for failure after hip arthroscopic surgery.30,39,46 With the exception of the isolated VAS improvements observed in patients presenting with preoperative Tonnis grade 2 radiographs, patients at risk for poorer outcomes because of increased BMI and age achieved significant improvements in VAS, mHHS, and HOS-SSS, reaching the MCID in all 3 scales, albeit to a lower magnitude than their younger and lower BMI counterparts. As such, our findings suggest that while outcomes are com- promised in these patients, hip arthroscopic labral repair may still provide significant relief and improvement in function.
While the 4 institutions and use of 3 outcome scales (VAS, mHHS, and HOS-SSS) are relative strengths of our study, future investigations should aim to include additional arthroscopic surgery centers and outcome measures as the prior literature contains a variety of measurement tools, such as the NAHS,11,19 International Hip Outcome Tool (iHOT-12),22,26 and Functional Activity Assessment,5,48 for which further outcome research is merited. An associated limitation of our study is the inherent difficulty of mid-term to long-term clinical follow-up in a young and healthy patient popu- lation and ensuring that patients fill out multiple time-con- suming scales at each clinical visit. Although we believe that our data performed well at a 2:89.3% completion rate for each scale, future studies should aim to achieve near 100% response rates as relationships may exist between patient outcomes and patient propensity to complete surveys. Additionally, while Tonnis grade is a reasonable surrogate for degree of joint involvement and chondral damage, further studies may also consider noting the intraoperative surface area of chondral damage in addition to the Outerbridge grade. Our study also contains biases inherent to a retrospective review, namely, selection bias and reliance on accurate and complete record keeping.
In summary, our data suggest that improvements in VAS, mHHS, and HOS-SSS scores outlined in previous studies are durable through mid-term follow-up. Additionally, this study reinforces the association between increased BMI and patient age and worse patient outcomes after hip arthroscopic surgery. Our finding that patients with a higher preoperative Tonnis grade have worse outcomes at mid-term follow-up is novel in that this differentiation was not apparent in previous short-term studies, suggesting that patients grouped by preoperative radiographic arthritis clinically differentiate over the course of extended follow-up. As such, we believe that this study’s significance lies in its ability to support hip arthroscopic surgery in providing sustained relief for labral tears and FAI as well as in providing both univariate and multivariate preoperative measures that can serve as enduring predictors of clinical outcomes for the surgeon selecting and counseling patients for hip arthroscopic surgery.
Akaike Information Theory and an Extension of the Maximum Like- lihood Principle. 2nd International Symposium on Information Theory. Budapest: Akade´ miai Kiado´ ; 1973.
Barton C, Salineros MJ, Rakhra KS, Beaule Validity of the alpha angle measurement on plain radiographs in the evaluation of camtype femoroacetabular impingement. Clin Orthop Relat Res. 2011;469(2):464-469.
Bech NH, Kodde IF, Dusseldorp F, Druyts PA, Jansen SP, Haverkamp Hip arthroscopy in obese, a successful combination? J Hip Preserv Surg. 2016;3(1):37-42.
Beck M, Kalhor M, Leunig M, Ganz Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br. 2005;87(7):1012-1018.
Bennett AN, Nixon J, Roberts A, Barker-Davies R, Villar R, Houghton Prospective 12-month functional and vocational outcomes of hip arthroscopy for femoroacetabular impingement as part of an evi- dence-based hip pain rehabilitation pathway in an active military population. BMJ Open Sport Exerc Med. 2016;2(1):e000144.
Botser IB, Smith TW Jr, Nasser R, Domb Open surgical disloca- tion versus arthroscopy for femoroacetabular impingement: a com- parison of clinical outcomes. Arthroscopy. 2011;27(2):270-278.
Bozic KJ, Chan V, Valone FH 3rd, Feeley BT, Vail Trends in hip arthroscopy utilization in the United States. J Arthroplasty. 2013; 28(8 Suppl):140-143.
Byrd Hip arthroscopy: the supine position. Clin Sports Med. 2001;20(4):703-731.
Callaghan JJ, Rosenberg AG, Rubash The Adult Hip. 2nd ed. Philadelphia: Lippincott Williams & Wilkins; 2007.
Camp CL, Reardon PJ, Levy BA, Krych A simple technique for capsular repair after hip arthroscopy. Arthrosc Tech. 2015;4(6): e737-e740.
Capogna BM, Ryan MK, Begly JP, Chenard KE, Mahure SA, Youm Clinical outcomes of hip arthroscopy in patients 60 or older: a mini- mum of 2-year follow-up. Arthroscopy. 2016;32(12):2505-2510.
Chahal J, Thiel GSV, Mather RC, Lee S, Salata MJ, Nho The min- imal clinical important difference (MCID) and patient acceptable symptomatic state (PASS) for the modified Harris Hip Score and Hip Outcome Score among patients undergoing surgical treatment for femoroacetabular impingement. Orthop J Sports Med. 2014;2(2 Suppl):2325967114S2325900105.
Chandrasekaran S, Darwish N, Gui C, Lodhia P, Suarez-Ahedo C, Domb Outcomes of hip arthroscopy in patients with To¨ nnis grade-2 osteoarthritis at a mean 2-year follow-up: evaluation using a matched-pair analysis with To¨ nnis grade-0 and grade-1 cohorts. J Bone Joint Surg Am. 2016;98(12):973-982.
Chandrasekaran S, Gui C, Darwish N, Lodhia P, Suarez-Ahedo C, Domb Outcomes of hip arthroscopic surgery in patients with To¨nnis grade 1 osteoarthritis with a minimum 2-year follow-up: evaluation using a matched-pair analysis with a control group with Tonnis grade 0. Am J Sports Med. 2016;44(7):1781-1788.
Chow RM, Engasser WM, Krych AJ, Levy Arthroscopic capsular repair in the treatment of femoroacetabular impingement. Arthrosc Tech. 2014;3(1):e27-e30.
Chow RM, Krych AJ, Levy Arthroscopic acetabular rim resection in the treatment of femoroacetabular impingement. Arthrosc Tech. 2013;2(4):e327-e331.
Chow RM, Kuzma SA, Krych AJ, Levy Arthroscopic femoral neck osteoplasty in the treatment of femoroacetabular impingement. Arthrosc Tech. 2014;3(1):e21-e25.
Chow RM, Owens CJ, Krych AJ, Levy Arthroscopic labral repair in the treatment of femoroacetabular impingement. Arthrosc Tech. 2013;2(4):e333-e336.
Christensen CP, Althausen PL, Mittleman MA, Lee JA, McCarthy The Nonarthritic Hip Score: reliable and validated. Clin Orthop Relat Res. 2003;406:75-83.
Cvetanovich GL, Weber AE, Kuhns BD, et Clinically meaningful improvements after hip arthroscopy for femoroacetabular impinge- ment in adolescent and young adult patients regardless of gender [published online August 29, 2016]. J Pediatr Orthop. doi:10.1097/ BPO.0000000000000852.
Domb BG, Sgroi TA, VanDevender JC. Physical therapy protocol after hip arthroscopy: clinical guidelines supported by 2-year out- comes. Sports Health. 2016;8(4):347-354.
Filbay SR, Kemp JL, Ackerman IN, Crossley Quality of life impairments after hip arthroscopy in people with hip chondropathy. J Hip Preserv Surg. 2016;3(2):154-164.
Fry R, Domb Labral base refixation in the hip: rationale and tech- nique for an anatomic approach to labral repair. Arthroscopy. 2010;26(9 Suppl):S81-S89.
Ganz R, Parvizi J, Beck M, Leunig M, Notzli H, Siebenrock Fem- oroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003;417:112-120.
Gicquel T, Gedouin JE, Krantz N, May O, Gicquel P, Bonin Func- tion and osteoarthritis progression after arthroscopic treatment of femoro-acetabular impingement: a prospective study after a mean follow-up of 4.6 (4.2-5.5) years. Orthop Traumatol Surg Res. 2014;100(6):651-656.
Griffin DR, Parsons N, Mohtadi NG, Safran A short version of the International Hip Outcome Tool (iHOT-12) for use in routine clinical practice. Arthroscopy. 2012;28(5):611-616, quiz 616-618.
Griffin DW, Kinnard MJ, Formby PM, McCabe MP, Anderson Outcomes of hip arthroscopy in the older adult: a systematic review of the literature. Am J Sports Med. 2017;45(8):1928-1936.
Gupta A, Redmond JM, Stake CE, Dunne KF, Domb Does pri- mary hip arthroscopy result in improved clinical outcomes? 2-year clinical follow-up on a mixed group of 738 consecutive primary hip arthroscopies performed at a high-volume referral center. Am J Sports Med. 2016;44(1):74-82.
Harris WH. Traumatic arthritis of the hip after dislocation and acetab- ular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am. 1969;51(4):737-755.
Horner NS, Ekhtiari S, Simunovic N, Safran MR, Philippon MJ, Ayeni Hip arthroscopy in patients age 40 or older: a systematic review. Arthroscopy. 2017;33(2):464-475.
Hufeland M, Kruger D, Haas NP, Perka C, Schroder Arthroscopic treatment of femoroacetabular impingement shows persistent clinical improvement in the mid-term. Arch Orthop Trauma Surg. 2016; 136(5):687-691.
Jackson TJ, Hanypsiak B, Stake CE, Lindner D, El Bitar YF, Domb Arthroscopic labral base repair in the hip: clinical results of a described technique. Arthroscopy. 2014;30(2):208-213.
Kamath AF, Componovo R, Baldwin K, Israelite CL, Nelson Hip arthroscopy for labral tears: review of clinical outcomes with 4.8- year mean follow-up. Am J Sports Med. 2009;37(9):1721-1727.
Kelly BT, Weiland DE, Schenker ML, Philippon Arthroscopic lab- ral repair in the hip: surgical technique and review of the literature. Arthroscopy. 2005;21(12):1496-1504.
Kemp JL, Makdissi M, Schache AG, Pritchard MG, Pollard TC, Crossley Hip chondropathy at arthroscopy: prevalence and relationship to labral pathology, femoroacetabular impingement and patient-reported outcomes. Br J Sports Med. 2014;48(14):1102- 1107.
Krych AJ, Kuzma SA, Kovachevich R, Hudgens JL, Stuart MJ, Levy Modest mid-term outcomes after isolated arthroscopic debridement of acetabular labral tears. Knee Surg Sports Traumatol Arthrosc. 2014;22(4):763-767.
Krych AJ, Thompson M, Knutson Z, Scoon J, Coleman Arthro- scopic labral repair versus selective labral debridement in female patients with femoroacetabular impingement: a prospective randomized study. Arthroscopy. 2013;29(1):46-53.
Langley GB, Sheppeard The visual analogue scale: its use in pain measurement. Rheumatol Int. 1985;5(4):145-148.
Levy DM, Kuhns BD, Chahal J, Philippon MJ, Kelly BT, Nho Hip arthroscopy outcomes with respect to patient acceptable symptom- atic state and minimal clinically important difference. Arthroscopy. 2016;32(9):1877-1886.
Mohan R, Johnson NR, Hevesi M, Gibbs CM, Levy BA, Krych Return to sport and clinical outcomes after hip arthroscopic labral repair in young amateur athletes: minimum 2-year follow-up. Arthros- copy. 2017;33(9):1679-1684.
Murphy SB, Kijewski PK, Millis MB, Harless Acetabular dysplasia in the adolescent and young adult. Clin Orthop Relat Res. 1990; 261:214-223.
Neumann G, Mendicuti AD, Zou KH, et Prevalence of labral tears and cartilage loss in patients with mechanical symptoms of the hip: evaluation using MR arthrography. Osteoarthritis Cartilage. 2007;15(8):909-917.
Nilsdotter AK, Lohmander LS, Klassbo M, Roos Hip Disability and Osteoarthritis Outcome Score (HOOS): validity and responsive- ness in total hip replacement. BMC Musculoskelet Disord. 2003;4:10.
Nwachukwu BU, Rebolledo BJ, McCormick F, Rosas S, Harris JD, Kelly Arthroscopic versus open treatment of femoroacetabular impingement: a systematic review of medium- to long-term out- comes. Am J Sports Med. 2016;44(4):1062-1068.
Outerbridge The etiology of chondromalacia patellae: 1961. Clin Orthop Relat Res. 2001;389:5-8.
Philippon MJ, Briggs KK, Carlisle JC, Patterson Joint space pre- dicts THA after hip arthroscopy in patients 50 years and older. Clin Orthop Relat Res. 2013;471(8):2492-2496.
Polesello GC, Lima FR, Guimaraes RP, Ricioli W, Queiroz Arthroscopic treatment of femoroacetabular impingement: minimum five-year follow-up. Hip Int. 2014;24(4):381-386.
Roberts AJ, Franklyn-Miller AD, Etherington A new functional out- come assessment tool for military musculoskeletal rehabilitation: a pilot validation study. PM R. 2011;3(6):527-532.
Skendzel JG, Philippon MJ, Briggs KK, Goljan P. The effect of joint space on midterm outcomes after arthroscopic hip surgery for femoroacetabular Am J Sports Med. 2014;42(5):1127-1133.
Spencer-Gardner L, Eischen JJ, Levy BA, Sierra RJ, Engasser WM, Krych A comprehensive five-phase rehabilitation programme after hip arthroscopy for femoroacetabular impingement. Knee Surg Sports Traumatol Arthrosc. 2014;22(4):848-859.
To¨ nnis D, Heinecke Acetabular and femoral anteversion: relation- ship with osteoarthritis of the hip. J Bone Joint Surg Am. 1999; 81(12):1747-1770.
Tubach F, Ravaud P, Baron G, et Evaluation of clinically relevant changes in patient reported outcomes in knee and hip osteoarthritis: the minimal clinically important improvement. Ann Rheum Dis. 2005;64(1):29-33.
Weber AE, Kuhns BD, Cvetanovich GL, Grzybowski JS, Salata MJ, Nho Amateur and recreational athletes return to sport at a high rate following hip arthroscopy for femoroacetabular impingement. Arthroscopy. 2017;33(4):748-755.
Weiland DE, Philippon Arthroscopic technique of femoroacetabular impingement. Oper Tech Orthop. 2005;15(3):256-260.