The Femoral Impingement Index Predicts Inferior Clinical Outcomes in Men Undergoing Hip Arthroscopy for Femoroacetabular Impingement Syndrome

PURPOSE: To evaluate the association of femoral version, McKibbin index, and femoral impingement index (FII) on patient-reported outcomes after primary hip arthroscopy for femoroacetabular impingement syndrome. METHODS: We retrospectively reviewed prospectively collected data from a hip preservation registry. Inclusion criteria included Tönnis grade ≤1 and a minimum 2-year follow-up. Computed tomography-based morphologic parameters and validated patient-reported outcomes (modified Harris Hip Score, hip outcome score-activities of daily living, hip outcome score-sport-specific subscale, and International Hip Outcome Tool) were analyzed. Patients were stratified by femoral version, McKibbin index, and FII (low <45°, moderate 45°-75°, high >75°). Multivariable regression adjusted for age and preoperative scores was used to assess outcomes and achievement of the minimal clinically important difference. RESULTS: A total of 456 hips met inclusion criteria, with significant improvements across all outcome measures at a mean follow-up of 2.6 years (P < .001). No significant differences in outcomes were observed when stratified by femoral version or McKibbin index. However, patients with high FII (>75°), predominantly men, displayed lower net improvement in hip outcome score-sport-specific subscale scores (14.6 vs 28.1 and 33.4 in moderate and low FII groups, respectively; P = .024) and reduced odds of achieving the minimal clinically important difference (53% vs 75% in low FII group; P = .047). Among men, increasing FII was associated with significantly lower improvements in hip outcome score-activities of daily living and hip outcome score-sport-specific subscale scores and lower likelihood of achieving minimal clinically important difference (adjusted odds ratio 0.19; 95% confidence interval 0.04-0.83; P = .028). CONCLUSIONS: In this cohort, a high FII (>75°) was associated with significantly lower net patient-reported outcome measure improvement in male patients. LEVEL OF EVIDENCE: Level III, retrospective cohort study.