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Background: The role of hip arthroscopy in the treatment of patients with borderline hip dysplasia is controversial and evolving. Purpose: To evaluate outcomes at a minimum 10-year follow-up in patients who underwent hip arthroscopy for femoroacetabular impingement in a hip with borderline dysplasia. Study Design: Case series; Level of evidence, 4. Methods: All hips that underwent labral repair between June 2006 and March 2009 for femoroacetabular impingement with borderline dysplasia were included if they had a lateral center-edge angle of 20° to 25°, had primary hip arthroscopy for the diagnosis of femoroacetabular impingement, and were aged 18 to 70 years. Patients were excluded if they had previous hip surgery, avascular necrosis, or fracture. Kaplan-Meier survivorship was performed, with survivorship defined as avoidance of conversion to total hip arthroplasty (THA). Results: A total of 45 patients met the inclusion criteria, and 38 were contacted at a minimum 10 years postoperatively (84%; mean ± SD, 12 ± 1.3 years). There were 23 women and 15 men with an average age of 41 ± 9.6 years (range, 25-69). Twenty patients were ≥40 years of age. In this patient cohort, survivorship was 87% at 5 years and 79% at 10 years for conversion to THA. Of the 38 patients included, 9 were converted to THA (24%), and 3 required revision hip arthroscopy (7%). Patient age, Tönnis grade, microfracture of cartilage lesions, and Tönnis angle >15° were associated with conversion to THA. No statistically significant differences were found between those who underwent conversion to THA and those who did not regarding lateral center-edge angle, Sharp angle, or alpha angle. Significant improvements were seen at follow-up of 12 years (range, 10-13) for the modified Harris Hip Score (58 to 83; P = .002), Hip Outcome Score–Activities of Daily Living (70 to 87; P = .003), Hip Outcome Score–Sport (47 to 76; P = .004), and Western Ontario and McMaster Universities Osteoarthritis Index (31 to 10; P = .001). At follow-up, >80% maintained the minimal clinically important difference for the Hip Outcome Score (Activities of Daily Living and Sport) with no differences between patients aged Conclusion: Risk factors for conversion to THA after hip arthroscopy in the borderline dysplastic hip included older age, higher Tönnis grades, grade 4 chondral lesions that were microfractures, and Tönnis angle >15°. In those patients who did not convert to THA, improvement in outcome measures was seen at 10 years. Careful patient selection is critical to the success of this procedure.

Return-to-sport rates following arthroscopic treatment of femoroacetabular impingement are high; however, the predictors of failure to return to sport must be elucidated. Recent data suggest that the postoperative alpha angle may be a significant predictor of return to sport in athletes, despite the fact that the role of radiographic measurements on postoperative outcomes is debated in the literature. Nonetheless, it is incumbent on surgeons to fully understand the unique biomechanics of the hip in each sport and consider each patient's unique anatomy when undertaking cam resection. Recreation of the motion at-risk during a careful intraoperative dynamic examination is imperative to ensure that all areas of impingement have been eradicated while attentively avoiding over-resection. While the postoperative alpha angle is an important metric for surgeons to keep in mind, it may only represent one piece of the puzzle.