Hip arthroscopy is commonly performed in patients with

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1 JOANNE L. KEMP, PT, PhD 1,2 MAY ARNA RISBERG, PT, PhD 3 ANTHONY G. SCHACHE, PT, PhD 4 MICHAEL MAKDISSI, MD, PhD 5 MICHAEL G. PRITCHARD, MD, FRACS 6 KAY M. CROSSLEY, PT, PhD 2 Patients With Chondrolabral Pathology Have Bilateral Functional Impairments 12 to 24 Months After Unilateral Hip Arthroscopy: A Cross-sectional Study Hip arthroscopy is commonly performed in patients with hip pain attributable to intra-articular conditions, such as chondrolabral pathology. 20 Hip arthroscopy rates are growing rapidly, with a 50% increase in Australia since and an 18-fold increase in the United States in the past decade. 32 Despite this growth in hip arthroscopy, there TTSTUDY DESIGN: Cross-sectional study. TTBACKGROUND: Functional task performance in patients with chondrolabral pathology following hip arthroscopy is unknown. TTOBJECTIVES: To investigate in people with chondrolabral pathology following hip arthroscopy (1) the bilateral differences in functional task performance compared to controls, (2) the association of hip muscle strength with functional task performance, and (3) the association of functional task performance scores with good outcome, as measured by International Hip Outcome Tool score. TTMETHODS: Seventy-one patients who had unilateral hip arthroscopy for hip pain and 60 controls were recruited. Patient-reported outcomes included the 4 subscales of the International Hip Outcome Tool. Hip muscle strength measures included abduction, adduction, extension, flexion, external rotation, and internal rotation. Functional tasks assessed included the single hop test, the side bridge test, and the single-leg rise test. For aim 1, analyses of covariance tests were used. For aim 2, stepwise multiple linear regression analyses were used. For aim 3, receiver operating characteristic curve analyses were used. TTRESULTS: Compared to controls, the chondrolabral pathology group had significantly worse performance on both legs for each of the functional tasks (P<.001). Greater hip abduction strength was moderately associated with better performance on functional tasks in the chondrolabral pathology group (adjusted R 2 range, ; P<.001). Cutoff values associated with good outcome were 0.37 (hop distance/height) for the single hop, 16 repetitions for the single-leg rise, and 34 seconds for the side bridge test. TTCONCLUSION: Patients with hip chondrolabral pathology had reduced functional task performance bilaterally 12 to 24 months after unilateral hip arthroscopy when compared to controls. TTLEVEL OF EVIDENCE: Therapy/symptom prevalence, level 3b. J Orthop Sports Phys Ther 2016;46(11): doi: /jospt TTKEY WORDS: chondropathy, femoroacetabular impingement, functional task performance, labral pathology, patient-reported outcomes is limited evidence to underpin the development of rehabilitation programs following hip arthroscopy. 11 It is therefore difficult for clinicians to provide appropriate rehabilitation programs that are targeted to improve performance of functional tasks in this patient group. We recently demonstrated that patients with chondrolabral pathology have impairments in hip joint range of motion and hip muscle strength, and reduced single-leg balance on the operated leg, compared to controls for at least 18 months following hip arthroscopy. 18,24 Moreover, patients with chondrolabral pathology have reduced patient-reported outcomes (PROs) for up to 3 years post hip arthroscopy. 23 Impairments of physical function in this postoperative patient group may also be present postoperatively but have never been evaluated. In addition, our previous studies have shown that age and chondropathy severity affect PRO scores, 22,23 and these factors should be considered when examining outcomes and impairments in patients with chondrolabral pathology. As impairments in functional tasks, such as hopping distance and endurance in rising to standing on 1 leg, may ex- 1 Australian Collaboration for Research Into Injury in Sport and Its Prevention, Federation University Australia, Ballarat, Australia. 2 La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Bundoora, Australia. 3 Department of Sport Medicine, Norwegian School of Sport Sciences, Oslo, Norway. 4 Department of Mechanical Engineering, University of Melbourne, Parkville, Australia. 5 Department of Physiotherapy, University of Melbourne, Parkville, Australia. 6 Hip Arthroscopy Australia, Hobart, Australia. The study was approved by the University of Melbourne Human Research Ethics Committee (number ) and the University of Queensland Medical Research Ethics Committee (number ). Dr Kemp was a recipient of the Australian Physiotherapy Research Foundation Beryl Haynes Memorial Grant (T09-BH026). The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article. Address correspondence to Dr Joanne Kemp, Latrobe Sport and Exercise Medicine Research Centre, La Trobe University, Bundoora, VIC 3083 Australia. j.kemp@latrobe.edu.au t Copyright 2016 Journal of Orthopaedic & Sports Physical Therapy journal of orthopaedic & sports physical therapy volume 46 number 11 november

2 FIGURE 1. Flow chart of participant recruitment. Patients who underwent arthroscopy by a single surgeon between January 2009 and July 2011, n = 355 Patients who fulfilled age criteria and were invited to participate in the study 12 to 24 months postsurgery, n = 334 Patients who responded to invitation to participate, n = 152 Patients, n = 100 Patients with chondral pathology, n = 71 can be identified at the hip, then it may be prioritized in rehabilitation programs to improve PROs in this patient group. Furthermore, providing cutoff values for such impairments may enable clinicians to identify patients at risk of worse outcomes during clinical assessment. A cutoff value is a score on a functional task performance test above which a good outcome is assumed, and may provide a target score for clinicians and patients. 36 The aims of this study were 3-fold: (1) to evaluate differences in functional task performance between surgical and nonsurgical sides in those with chondrolabral pathology following unilateral hip arthroscopy and compare the performance on the surgical side to that of a control group, (2) to evaluate the relationship between functional task perist bilaterally in this group, the ability of patients to undertake functional tasks on both legs following hip arthroscopy needs to be determined. Functional task performance in other lower-limb joints such as the knee has been studied for decades. Reduced functional task performance is evident in many conditions, including knee osteoarthritis, 41 patellofemoral joint pain and osteoarthritis, 43 and anterior cruciate ligament tears. 34,37 Such impairments are associated with worse PROs, 37,41 including reduced hop distance and reduced sit-to-stand endurance during the single-leg rise task. 41 Functional retraining exercises are often targeted in rehabilitation programs in these patient groups to improve PROs. 2,3,10,14,15,34,44 Similarly, if reduced functional task performance Patients excluded, n = 52: Deceased, n = 1 Legal reasons, n = 2 Moved away, n = 9 Did not attend, n = 2 Total hip arthroscopy, n = 4 Other surgery, n = 3 Low back pain, n = 3 Time commitments, n = 28 No labral or chondral pathology, or had bilateral surgery, n = 29 Age-matched, healthy controls, n = 60 Participant characteristics, strength tests, functional performance tests, and patient-reported outcomes collected, n = 131 This cross-sectional study was undertaken in a clinical setting in Hobart, Tasmania, Australia. The study was approved by the University of Melbourne Human Research Ethics Committee (number ) and the University of Queensland Medical Research Ethics Committee (number ). All participants completed written informed consent prior to entering the study. All participant rights were protected, and subjects were free to withdraw at any time from the study. Seventy-one people who had undergone hip arthroscopy surgery between January 2009 and July 2011 for hip pain associated with intra-articular hip conditions were included (FIGURE 1). Eligible participants were contacted by letter 12 to 24 months following the surgical procedure and invited to take part. The recruitment procedure has been described in detail previously. 23 Sixty controls were recruited from the community. All participants completed written informed consent and fulfilled inclusion criteria. Participants were included in the chondrolabral pathology group if they (1) were aged between 18 and 60 years, (2) had undergone hip arthroscopy due to hip pain and clinical signs of femoroacetabular impingement (FAI) 12 to 24 months prior to inclusion, and (3) were diagnosed with labral pathology and/or chondropathy of at least Outerbridge grade I (softening and swelling of the articular cartilage 35 ). Participants were not excluded based on other hip morphology, and 30 of 71 participants (42%) also had coex- formance and hip strength in those with chondrolabral pathology following hip arthroscopy, and (3) to determine the cutoff values associated with good outcomes (a score of 91 points out of 100 for the International Hip Outcome Tool [ihot-33]) for functional task performance in people with chondrolabral pathology following hip arthroscopy. METHODS 948 november 2016 volume 46 number 11 journal of orthopaedic & sports physical therapy

3 FIGURE 2. Single hop test. isting FAI that was addressed through osteochondroplasty at arthroscopy. Participants were excluded from the chondrolabral pathology group if they had (1) concurrent lower back pain or other leg injuries, (2) an inability to walk without assistance, (3) an inability to speak or read English, and (4) undergone further hip or other surgery since the primary procedure (FIGURE 1). Participants were included in the control group if they (1) were aged between 18 and 60 years, (2) had not had hip pain in the previous 6 months or a history of hip surgery, (3) did not have concurrent lower back pain or other leg injuries, (4) could read and speak English, and (5) could walk without assistance. Collection of PROs, participant characteristic data, and measures of functional task performance occurred between 12 and 24 months postsurgery for the hip arthroscopy group. All data were collected in a private physical therapy clinic by a single investigator (J.L.K.). Patient-reported outcomes included the 4 subscales of the ihot This PRO has demonstrated good psychometric properties in individuals who have undergone hip arthroscopy. 21 The ihot-33 includes a total of 33 questions evaluating symptoms and functional activity (16 questions), job-related concerns (4 questions), sport and recreation (6 questions), and social and emotional concerns (7 questions). 31 Each subscale of the ihot-33 PRO has a minimum score of zero (worst possible outcome) and a maximum score of 100 points (best possible outcome). The data collected included the following participant characteristics: age, sex, height, weight, body mass index, months since surgery, and hours of physical activity per week. Hip muscle strength was tested using a handheld dynamometer, previously demonstrated to be a reliable measure of muscle strength. 25 Hip muscle strength (isometric peak torque normalized for body weight [Newton meters per kilogram]) was assessed using a Commander PowerTrack II handheld dynamometer (JTECH Medical, Midvale, UT). Strength measures collected included hip abduction, adduction, extension, flexion, external rotation, and internal rotation. Hip abduction and adduction strength were measured in supine, with the hips in neutral and the knees fully extended. Hip extension, external rotation, and internal rotation strength were measured in prone, with the knee flexed to 90 and the hip in neutral. Hip flexion strength was measured in the sitting position, with the knees and hips in 90 of flexion. The contralateral limb was stabilized for all tests. All strength measures were repeated 3 times, and the highest value (Newton meters) was used for all strength tests. 25 Functional performance was assessed using several tasks, including the single hop test, 3,9 the side bridge test, 29 and the single-leg rise test. 41 Chondropathy severity was graded by the surgeon (M.P.) at the time of surgery, and was graded according to the Outerbridge scale. 35 Grade I represents softening and swelling of the articular cartilage, grade II represents fragmenting and fissuring of articular cartilage in an area less than 15 mm, grade III represents fragmenting and fissuring of articular cartilage greater than 15 mm, and grade IV represents erosion of articular cartilage to the subchondral bone. 35 For the single hop test, participants were asked to stand barefoot on a standardized starting line, bearing weight on 1 foot. They were instructed to hop as far forward as possible, landing on the same foot. The distance was recorded from the starting line to the heel of the landing foot with an inflexible tape measure. Participants were given 1 practice trial, after which 3 trials were completed on each leg, alternating legs, with the greatest distance for each leg recorded (FIGURE 2). This distance was normalized for participant height and reported as a measure of hop distance divided by height. The single hop test has been described previously in the literature as a reliable measure of functional performance in controls, 25 in people with patellar tendinopathy, 9 and in people following anterior cruciate ligament reconstruction. 3 For the side bridge test, participants were positioned in sidelying journal of orthopaedic & sports physical therapy volume 46 number 11 november

4 FIGURE 3. Side bridge test. on a plinth, with one leg resting directly on top of the other. Participants were instructed to lift their hips off the plinth, supporting their weight through their feet and forearm, and to hold the position for as long as possible. Standardized encouragement was given at 30-second intervals throughout the test. The time was recorded from the start of the test until the participant s hips touched the plinth, when the test ended (FIGURE 3). The side bridge test is assumed to be a measure of trunk muscle strength endurance. 25,29 For the single-leg rise test, participants were seated on the edge of a plinth, with the test foot placed in a comfortable position on the floor in front of the plinth. The contralateral leg was held straight out in front of the body, with the arms resting by the participant s side. The height of the plinth was adjusted so the flexion angle of the knee was 90 (measured with a template). Participants were instructed to stand as many times as possible on 1 leg without moving their foot, trunk, or arms, and the number of repetitions achieved was recorded (FIGURE 4). All statistical analyses were performed using SPSS Version 21.0 software (IBM Corporation, Armonk, NY). Significance was set at P<.05 a priori. Based on an acceptable correlation between the dependent and independent variables of 0.4, an alpha level of.05, and power of 0.90, a sample of 62 participants was required. 7 Differences in performance on the 3 functional tasks between the surgi- cal and nonsurgical legs of the chondrolabral pathology group and the controls were evaluated using analysis of covariance tests. The surgical leg in the chondrolabral pathology group was compared to the dominant leg of the controls (the leg used to kick a ball), and the nonsurgical leg in the chondrolabral pathology group was compared to the nondominant leg in the controls. We have previously found no differences in measures of functional performance between dominant and nondominant legs in healthy people. 25 The covariates used in the analyses of covariance were age, sex, weight, and severity of chondropathy, based on the known age-related variability in functional task performance, the between-group differences in sex and weight in this study, and our previously published work outlining the impact of age and severity of chondropathy on PROs. 23 Between-group differences for hip muscle strength were not evaluated in the current study, as we have previously published these data, 24 with between-group mean differences ranging from 0.09 Nm kg 1 (95% confidence interval [CI]: 0.00, 0.17; P =.044) for external rotation strength to 0.31 Nm kg 1 (95% CI: 0.19, 0.42; P<.001) for flexion strength. Hip muscle strength tests and functional performance tasks were compared for the surgical leg only. First, Pearson s correlation coefficients (r) were calculated between hip muscle strength tests and functional performance tasks. Second, the adjusted associations between FIGURE 4. Single-leg rise test. hip muscle strength measures (independent variables) and functional performance tasks (dependent variables) were then established using stepwise multiple linear regression analyses (backward-elimination model). Independent variables displaying evidence of collinearity (r>0.90) and singularity were excluded prior to running the model. The 2 strength measures with the highest r value from the correlations were used in the regression analyses to ensure that an appropriate number of variables were entered into the models. In addition, covariates of age, sex, weight, and chondropathy severity were included in each model, as our previous studies have shown that these characteristics impact PRO scores. 22,23 The covariates could be eliminated in each model. Therefore, up to 6 independent variables (2 strength measures and 4 covariates) were used in total in each regression analysis. Due to the study sample size and the number of independent variables used, the adjusted R 2 value was reported as a measure of model fit. Receiver operating characteristic (ROC) curve analyses were conducted to determine the cutoff values for the 950 november 2016 volume 46 number 11 journal of orthopaedic & sports physical therapy

5 3 functional performance tasks against the ihot-33 PRO (predicted variable). The clinical cutoff score for the ihot- 33 was determined a priori as 91 points out of 100, as an ihot-33 score of 91 has previously been defined as being a good outcome, using the methods of Jacobson and Truax 19 : The level of functioning that places the client closer to the mean of the functional population than the mean of the dysfunctional population. This enabled us to determine the ihot-33 score whereby participants pain and function were considered closer to that of a control than of a patient. 19,21 The threshold for sensitivity and specificity for the ROC curve was set at 70%. RESULTS Body weight (mean difference, 7.3 kg; 95% CI: 3.9, 10.8; P<.001) and body mass index (mean difference, 2.9 kg/m 2 ; 95% CI: 1.2, 4.5; P =.003) TABLE 1 were significantly lower in the control group than in the chondrolabral pathology group. The between-group differences in sex in this study approached statistical significance (P =.05). There were no other differences between the groups for participant characteristics (TABLE 1). The results for aim 1 indicate that the chondrolabral pathology group had significantly poorer performance on the single-leg rise test on both the surgical (mean difference, 13 rises; 95% CI: 7, 19; P<.001) and nonsurgical sides (mean difference, 13 rises; 95% CI: 8, 19; P<.001) compared to the controls (TABLE 2). The chondrolabral pathology group also had a significantly shorter normalized single hop distance on the surgical side (mean difference, 0.17 hop/ height; 95% CI: 0.10, 0.23; P<.001) and nonsurgical side (mean difference, 0.22 hop/height; 95% CI: 0.16, 0.27; P<.001) compared to controls (TABLE 2). Finally, the chondrolabral pathology group had significantly worse performance on the Participant Characteristics by Group Variable Chondrolabral Pathology (n = 71) Control (n = 60) P Value Age, y 36 ± ± Sex (women), % Height, m 1.74 ± ± Weight, kg 77.3 ± ± 11.9 <.001 Body mass index, kg/m ± ± Physical activity, h/wk 4.4 ± ± *Values are mean ± SD unless otherwise indicated. Covariate of sex used in analysis of covariance. side bridge test on both the surgical side (mean difference, 22 seconds; 95% CI: 6, 38; P<.001) and nonsurgical side (mean difference, 39 seconds; 95% CI: 14, 64; P<.001) compared to controls (TABLE 2). For aim 2, all hip muscle strength measurements were found to be significantly correlated with functional task performance (TABLE 3). Results for stepwise multiple regression analyses are presented both without covariates of age, sex, weight, and chondropathy severity (TABLE 4) and with covariates of age, sex, weight, and chondropathy severity (TABLE 5). When adjusted for covariates of age, sex, weight, and chondropathy severity, greater hip abduction strength was associated with better performance on the single-leg rise test (adjusted R 2 = 0.197, P<.001), the single hop test (normalized for height) (adjusted R 2 = 0.366, P<.001), and the side bridge test (adjusted R 2 = 0.407, P<.001). The results for aim 3 demonstrate that the ROC curve analyses determined the cutoff value for the single-leg rise test to be 16 rises (area under the curve, 0.683; 95% CI: 0.545, 0.821; sensitivity, 0.933; specificity, 0.672). The cutoff value for the single hop was 0.37 (hop distance/height) (area under the curve, 0.737; 95% CI: 0.583, 0.891; sensitivity, 0.909; specificity, 0.717). The cutoff value for the side bridge test was 34 seconds (area under the curve, 0.721; 95% CI: 0.576, 0.865; sensitivity, 0.867; specificity, 0.681). TABLE 2 Performance on the 3 Functional Tasks by Group Variable Surgical Side Nonsurgical Side Dominant Side Nondominant Side Single-leg rise, n 28 ± ± ± ± 13 Single hop 0.52 ± ± ± ± 0.19 Side bridge, s 59 ± ± ± ± 44 *Values are mean ± SD. Covariates of age, sex, weight, and chondropathy severity used in analysis of covariance. Normalized for height. Chondrolabral Pathology (n = 71) Control (n = 60) journal of orthopaedic & sports physical therapy volume 46 number 11 november

6 DISCUSSION Functional task performance was worse in people with chondrolabral pathology 12 to 24 months following hip arthroscopy on both the surgical and nonsurgical sides compared to controls. Greater hip abductor strength was associated with better functional task performance for participants with chondrolabral pathology. Furthermore, better performance on the single hop and single-leg rise tests was associated with better scores on PROs in people with chondrolabral pathology following hip arthroscopy. Finally, this study determined the cutoff value on functional task TABLE 3 performance that accurately predicted a score of at least 91 on the ihot-33. The cutoff value is a score for a functional task performance test above which a good outcome is assumed, demonstrating the potential utility of these measures in clinical practice. Compared to controls, participants with chondrolabral pathology had reduced performance on the surgical leg for the single hop test and bilaterally for the single-leg rise test. The cutoff values of the single hop and single-leg rise tests were found to be 0.37 (hop distance/height) and 16 rises, respectively. When executing these tests, the hip may move into a position of impingement Correlation Coefficients Between Hip Muscle Strength Tests and the Functional Task Performance Tests in the Chondrolabral Pathology Group (n = 71) Hip Strength Measure Single-Leg Rise* Single Hop* Side Bridge* Abduction Adduction Extension Flexion External rotation Internal rotation *Significant (P<.001). Normalized for height. TABLE 4 Functional Task Performance Measure (flexion, adduction, and internal rotation) on a repetitive basis, which might explain why patients with chondrolabral pathology did not perform as well as the controls. It has been suggested that repetitive activity involving impingement may contribute to the progression of hip degenerative disease. 1 Our findings regarding the impairments with the single hop and single-leg rise tests may have important implications for people with intra-articular hip pathology. The ability to hop a greater distance and perform a greater number of single-leg rises is associated with better scores on PROs. It is possible that better performance on these tests reflects more coordinated pelvic, trunk, and leg muscles, and perhaps a lower likelihood for hip impingement during these tasks. As such, exercises aimed at improving performance on the various functional tasks so that achieved repetitions exceed our reported cutoff values may be an important component of rehabilitation programs for people with intra-articular hip pathology. The findings of this study indicate that patients with chondrolabral pathology have poor performance on the single hop test 12 to 24 months following hip arthroscopy compared to controls. Adequate performance of the single hop test is a criterion used to indicate readiness for return to sport in other conditions, such as anterior cruciate ligament The Unadjusted Relationship (Without Covariates) Between Hip Muscle Strength Tests and Performance on the Various Functional Tasks for the Surgical Side in People With Chondrolabral Pathology (n = 71) Functional Task Performance Test Model Independent Variable* β P Value Adjusted R 2 P Value Single-leg rise 1 Abduction < <.001 Single hop 1 Abduction < < Abduction < <.001 Extension Side bridge 1 Abduction < <.001 *Remaining in model. Standardized beta coefficient. Statistically significant (P<.05). Normalized for height. 952 november 2016 volume 46 number 11 journal of orthopaedic & sports physical therapy

7 TABLE 5 The Adjusted Relationship (With Covariates of Age, Sex, Weight, and Chondropathy Severity) Between Hip Muscle Strength Tests and Performance on the Various Functional Tasks for the Surgical Side in People With Chondrolabral Pathology (n = 71) Functional Task Performance Test Model Independent Variable/Covariate* β P Value Adjusted R 2 P Value Single-leg rise 1 Abduction < <.001 Single hop 1 Abduction < <.001 reconstruction, 14,16 although hopping tests do not yet have reported validity in a post hip arthroscopy population. 26 It has been reported that some patients have achieved return to sport between 12 and 20 weeks postsurgery, 12 while up to 75% of patients have returned to sport by 12 months. 4 Our study indicates that significant impairments still exist in single hopping on both sides 12 to 24 months following hip arthroscopy. It is also possible that the chondrolabral repair side influences the hop test for the nonsurgical side, because of the inability to get full range of motion or swing from the repair side. This may decrease the ability of the participant to perform the single hop on the nonsurgical side. Poor performance on the single hop test may indicate an inability to control motion and/or fear of impact loading following hip arthroscopy. Retraining hopping in a painfree fashion is likely to be an important target for patients with chondrolabral pathology following hip arthroscopy, particularly prior to return to sport. Importantly, the validity of hopping tests 2 Abduction < <.001 Sex Abduction <.001 Sex <.001 Age Abduction <.001 Sex <.001 Age <.001 Weight Side bridge 1 Abduction < <.001 *Remaining in model. Standardized beta coefficient. Statistically significant (P<.05). Normalized for height. 2 Abduction < <.001 Sex <.001 as a functional measure in this patient group needs to be determined. Performance on the side bridge test, a test of trunk muscle performance, was also reduced bilaterally in participants with chondrolabral pathology compared to controls. The cutoff value for the side bridge test was found to be 34 seconds. The ability of the trunk musculature to control the position of the pelvis has been evaluated in patients with FAI using 3-D modeling of pelvic computed tomography scans. 38 Increased anterior pelvic tilt was reported to result in increased acetabular retroversion, potentially exacerbating impingement pathologies within the hip. 38 We recently demonstrated that patients with chondrolabral pathology have hip flexion and extension weakness following hip arthroscopy surgery, 24 while patients with chronic hip pain also have similar impairments. 17 While the side bridge does not measure pelvic control in the sagittal plane, it may be a surrogate measure of overall trunk endurance, and our findings might suggest that trunk muscle performance bilaterally is an important target for rehabilitation programs in patients following hip arthroscopic surgery. Hip abduction strength was the only strength measure associated with performance on the various functional tasks. This association suggests that exercise programs targeting hip abduction strength gains may be an important focus when aiming to improve performance on these tasks, although longitudinal studies are needed to confirm a causal relationship between these factors. Hip abduction torque is primarily generated by the gluteus minimus and gluteus medius muscles. 33 The fiber alignment, 33 muscle cross-sectional area, 42 and activation pattern 39 of the gluteus minimus suggest that it acts primarily to compress the hip and prevent excessive anterior translation. A previous modeling study reported increased anterior hip joint forces when gluteal muscle weakness exists. 27 The 3 portions of the gluteus medius are considered to act synergistically throughout gait, 8,40 stabilizing the femoral head in the acetabulum 13 while maintaining an upright trunk and pelvis on the leg, 33,40,42 journal of orthopaedic & sports physical therapy volume 46 number 11 november

8 and possibly controlling anterior hip joint forces. 27 The loss of hip abduction strength adversely impacts performance on important functional tasks. Future research should evaluate the causal relationship between hip abduction strength and functional task performance, and whether this relationship influences PROs in this patient group. The present study found reduced performance on functional tasks bilaterally in participants with chondrolabral pathology, despite hip arthroscopy having been performed on 1 side only in these participants. There are several possible explanations for this finding. It is possible that the participants in this study had bilateral pathology, although surgery was performed unilaterally. Recent studies have reported the bilateral nature of hip morphology and associated pathology that may or may not be painful, and it is possible that the participants in this study may also have had pathology on the nonsurgical side. 28 The reported average duration of symptoms for participants with intra-articular hip pathology prior to surgery is 1 to 3 years, with 12% of patients having symptoms for more than 5 years. 5 It is possible that the long-standing duration of symptoms in the participants included in this study resulted in lack of use and subsequent deconditioning of both legs with respect to functional task performance. Finally, unilateral painful stimuli have been shown to activate the brain s cerebellum bilaterally, supplementary motor area contralaterally, and premotor area ipsilaterally. 6 This phenomenon suggests the potential for a bilateral motor response to a condition of unilateral pain, although it is well beyond the scope of this study to detect such central nervous system changes. Regardless of the mechanism, rehabilitation programs for patients with chondrolabral pathology after surgery should include the execution of functional tasks, trunk retraining, and impingement position avoidance strategies for both legs to obtain the best possible outcomes. The current study has some limitations that should be acknowledged. First, this study was cross-sectional in design, measuring the association between variables without examining the causal nature of these relationships. Therefore, it is not possible to make claims regarding the potential of functional task retraining programs to positively influence PROs. Second, we tested functional task performance at 1 postoperative time point only. It is not known whether these deficits existed preoperatively, and whether surgical intervention influenced functional task performance in our cohort. Third, we included all participants with hip chondrolabral pathology, regardless of the underlying morphology of the hip that may have included FAI. Fourth, the functional tests used in this study lack data on reliability for the post hip arthroscopy patient group. Fifth, we did not examine the relationship between hip muscle strength and functional task performance in the control group, and we did not examine pain levels during functional task performance in either group. Furthermore, less than half of eligible patients responded to the invitation to take part in the study, meaning that there is potential for selection bias in the included participants. Finally, we did not measure functional task performance in people with hip pain who did not undergo surgical intervention. Future studies may choose to include subgroups of people based on hip morphological variants, and may also group patients based on the severity of pathology, to determine whether these factors affect functional task performance. Future studies may examine the effect of pain on functional task performance in patients with chondrolabral pathology post hip arthroscopy. Further studies are required to examine the validity of functional task performance post hip arthroscopy, to examine functional task performance preoperatively and in nonoperatively treated subjects, and to follow performance over time to better understand the relationship with PROs. CONCLUSION People with hip chondrolabral pathology have impaired functional task performance bilaterally 12 to 24 months after unilateral hip arthroscopy compared to controls. Greater hip abductor strength was associated with better functional task performance for participants with chondrolabral pathology. In addition, cutoff values for performance on the single-leg rise, single hop, and side bridge tests were reported as 16 repetitions, 0.37 (hop distance/height), and 34 seconds, respectively. These findings may guide clinicians in designing targeted rehabilitation programs that optimize PROs for these people. t KEY POINTS FINDINGS: People with hip chondrolabral pathology have impaired functional task performance bilaterally 12 to 24 months after unilateral hip arthroscopy compared to controls. Greater hip abductor strength was associated with better functional task performance for participants with chondrolabral pathology. Cutoff values for performance on the single-leg rise, single hop, and side bridge tests against a score of 91 points out of 100 on the ihot-33 were reported as 16 repetitions, 0.37 (hop distance/ height), and 34 seconds, respectively. IMPLICATIONS: People with hip chondrolabral pathology who have gone through hip arthroscopy may require rehabilitation programs to target hip abductor strength and functional task retraining to improve PROs. People with hip chondrolabral pathology who have gone through hip arthroscopy have bilateral impairments, and using the nonsurgical leg as a control may not be adequate. CAUTION: The cross-sectional study design does not confirm causal relationships between hip muscle strength, PROs, or functional task performance. 954 november 2016 volume 46 number 11 journal of orthopaedic & sports physical therapy

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10 36. Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. 3rd ed. Upper Saddle River, NJ: Pearson/Prentice Hall; Risberg MA, Holm I, Tjomsland O, Ljunggren E, Ekeland A. Prospective study of changes in impairments and disabilities after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther. 1999;29: org/ /jospt Ross JR, Nepple JJ, Philippon MJ, Kelly BT, Larson CM, Bedi A. Effect of changes in pelvic tilt on range of motion to impingement and radiographic parameters of acetabular morphologic characteristics. Am J Sports Med. 2014;42: org/ / Semciw A, Pizzari T, Green R. Are there functionally independent segments within gluteus minimus and gluteus medius? An EMG investigation [abstract]. In: Tucker K, Butler B, Hodges P, eds. XIX Biennial ISEK Congress. Brisbane, Australia: International Society of Electrophysiology and Kinesiology; 2012: Semciw AI, Pizzari T, Murley GS, Green RA. Gluteus medius: an intramuscular EMG investigation of anterior, middle and posterior segments during gait. J Electromyogr Kinesiol. 2013;23: jelekin Thorstensson CA, Petersson IF, Jacobsson LT, Boegard TL, Roos EM. Reduced functional performance in the lower extremity predicted radiographic knee osteoarthritis five years later. Ann Rheum Dis. 2004;63: dx.doi.org/ /ard Ward SR, Winters TM, Blemker SS. The architectural design of the gluteal muscle group: implications for movement and rehabilitation. J Orthop Sports Phys Ther. 2010;40: Witvrouw E, Callaghan MJ, Stefanik JJ, et al. Patellofemoral pain: consensus statement from the 3rd International Patellofemoral Pain Research Retreat held in Vancouver, September Br J Sports Med. 2014;48: bjsports Wondrasch B, Årøen A, Røtterud JH, Høysveen T, Bølstad K, Risberg MA. The feasibility of a 3-month active rehabilitation program for patients with knee full-thickness articular cartilage lesions: the Oslo Cartilage Active Rehabilitation and Education Study. J Orthop Sports Phys Ther. 2013;43: EARN CEUs With JOSPT s Read for Credit Program JOSPT s Read for Credit (RFC) program invites readers to study and analyze selected JOSPT articles and successfully complete online exams about them for continuing education credit. To participate in the program: 1. Go to and click on Read for Credit in the top blue navigation bar that runs throughout the site. 2. Log in to read and study an article and to pay for the exam by credit card. 3. When ready, click Take Exam to answer the exam questions for that article. 4. Evaluate the RFC experience and receive a personalized certificate of continuing education credits. The RFC program offers you 2 opportunities to pass the exam. You may review all of your answers including your answers to the questions you missed. You receive 0.2 CEUs, or 2 contact hours, for each exam passed. MORE INFORMATION JOSPT s website maintains a history of the exams you have taken and the credits and certificates you have been awarded in My CEUs and Your Exam Activity, located in the right rail of the Read for Credit page listing available exams. 956 november 2016 volume 46 number 11 journal of orthopaedic & sports physical therapy