Reduced joint space at the time of joint-preserving hip arthroscopy has been shown to be correlated with higher rates of eventual conversion to total hip arthroplasty (THA). This study sought to determine if quantitative differences in joint space width (JSW) between the operative and non-operative hip predicted the likelihood of conversion to THA at the time of hip arthroscopy.
A retrospective review identified 106 patients who underwent arthroscopic acetabular labral repair by a single-surgeon with a minimum of 5-year follow-up. Patients were stratified into cohorts based on whether they received a subsequent THA. Preoperative, anteroposterior pelvic radiographs were obtained for each patient and semi-automated, quantitative JSW measurements were performed at 3 predefined fixed locations per hip (10°, 30° and 50° in a polar coordinate system). All measurements were obtained by an independent assessor blinded to other radiographic or clinical information, with high reliability (intra-class correlations >0.8), as previously described in literature. Differences in JSW at each prefixed angle were calculated by subtracting the width (millimeters) of each patient’s operative hip from the measurements obtained from their non-operative hip.
Mean [standard deviation (SD)] follow up was 8.23 [2.24] years, identifying 21 (19.8%) patients that converted to THA and 85 (80.2%) that did not. When comparing demographic and intraoperative characteristics between cohorts, THA patients were found to have higher mean [SD] age 40.4 [13.1; p=0.006], BMI 27.2 [3.9; p=0.016], Tönnis grade (p<0.002), and Outerbridge grade (p=0.012). THA patients were found to have a significantly greater difference in JSW at 10° (0.494 ± 0.985mm versus -0.064 ± 0.609mm, p=0.009), 30° (0.779 ± 0.839mm versus 0.029 ± 0.507mm, p<0.001), and 50° (0.358 ± 0.832mm versus -0.044 ± 0.527mm, p=0.045) compared to those that did not require subsequent hip arthroplasty. Upon adjusting for differences in JSW at all locations, only the difference at 30° remained significantly correlated with conversion to THA (p=0.001), so our final regression only included JSW difference at the 30° location. When adjusting for significantly different covariates, the difference in JSW at 30° was correlated with an increased likelihood of conversion to THA (Adjusted Odds Ratio [AOR]: 16.64; 95% Confidence Interval [CI]: 3.18 to 87.05; p < 0.001).
To best educate patients on the risk of THA following hip arthroscopy, identifying objective predictors of early failure is imperative during preoperative evaluation. This study identified that differences in JSW at 30° between the operative and non-operative hip were significantly associated with increased risk of conversion after controlling for demographic and intraoperative factors.
ACKNOWLEDGEMENTS: Conine Family Foundation for Joint Preservation; Dr. Jeff Duryea PhD from Brigham and Women’s Hospital – Department of Radiology