Joint Space Narrowing Relative to the Contralateral Side Predicts Early Conversion to Total Hip Arthroplasty After Primary Hip Arthroscopy.

Background: Reduced absolute joint space width (JSW) has been shown to correlate with higher rates of total hip arthroplasty (THA) after hip arthroscopy. Purpose: To determine if quantitative differences in JSW between the operative and contralateral hips at the time of hip arthroscopy affect the risk of conversion to THA. Study Design: Case-control study; Level of evidence, 3. Methods: This retrospective analysis queried patients with preserved JSW (>2 mm) who underwent arthroscopic acetabular labral repair with minimum 5-year follow-up, performed by a single surgeon. Patients were grouped based on whether they received subsequent THA. Preoperative anteroposterior supine pelvic radiographs were obtained for each patient, and quantitative JSW measurements were performed at 3 fixed locations (10°, 30°, and 50° in a polar coordinate system, relative to the 0° line drawn from the center of the femoral head to the lateral edge of the acetabular roof). Measurements were obtained by an independent, blinded assessor in a semiautomated fashion, with intraclass correlation for this approach >0.8. JSW differences at each angle were calculated by subtracting the width in the operative hip from that of the nonoperative hip. Cox proportional hazards modeling identified predictors of THA conversion. Results: A total of 106 patients with mean follow-up of 8.23 ± 2.24 years were included; 21 (19.8%) converted to THA and 85 (80.2%) did not. THA patients had higher mean age (40.4 ± 13.1 years; Conclusion: This study found that greater JSW reductions in the operative versus nonoperative hip were associated with increased risk of THA conversion. In conjunction with known predictors of failure after hip arthroscopy, preoperative JSW differences may be used as an adjunct to assess risk of early THA and counsel patients appropriately.