Postoperative Alpha Angle and Patient-Reported Outcomes After Hip Arthroscopy for Cam-Type Femoroacetabular Impingement Syndrome: Associations Across Radiographic Views

DOI: 10.70885/hmsj.2026.09.003

Abstract

Background: Cam-type femoroacetabular impingement syndrome (FAIS) is characterized by a nonspherical femoral head, routinely corrected via arthroscopic cam resection. Although postoperative radiographic measurements are widely used to assess resection quality, whether these objective structural metrics translate into improved patient-reported outcomes (PROs) remains unclear.Purpose: To determine whether postoperative alpha angle is associated with PROs following arthroscopic surgery for cam-type FAIS.Methods: This retrospective case series included 95 patients undergoing hip arthroscopy for FAIS.  Alpha angles were measured on anteroposterior (AP), 45° Dunn, and frog-leg lateral views. PROs (iHOT-33, NAHS, HOS-SP, HOS-ADL) were collected preoperatively and at two-year follow-up. Postoperative alpha angle was analyzed continuously and categorically (<55° vs ≥55°). Bivariate correlations were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR). Nominally significant associations were evaluated in multivariable linear regression adjusting for baseline PROs, preoperative alpha angle, age, sex, and BMI.Results: Postoperative alpha angles decreased across all views (p<0.001, <55° achieved in 75-82%). All PROs improved significantly at two-year follow-up (p<0.001). Bivariate analyses showed weak-to-fair correlations between alpha angles on 45° Dunn and frog-leg views and selected PROs, but none on AP views. After adjustment, no bivariate correlations remained statistically significant (45° Dunn - NAHS was borderline, FDRp=0.050). In multivariable analyses, higher 45° Dunn alpha angle remained associated with lower NAHS (β=-0.483, p=0.037) and HOS-ADL (β=-0.471, p=0.037). Frog-leg associations did not persist after adjustment, and categorical analyses were not significant.Conclusion: Postoperative alpha angle showed weak-to-fair, unadjusted associations with selected two-year PROs, with the most consistent findings observed on 45° Dunn radiographs. These findings highlight the importance of radiographic projection when interpreting postoperative alpha-angle measurements and support considering alpha angle alongside clinical and patient-level factors rather than as an isolated indicator of outcome.What this study adds: This study identified view-specific associations between postoperative alpha angle and selected PROs, with the most consistent associations observed on 45° Dunn radiographs.How this study might affect research, practice or policy: Postoperative alpha angle should be interpreted in the context of the radiographic projection used and alongside other clinical and patient-level factors when evaluating postoperative outcomes.Study Design: Retrospective case seriesLevel of Evidence: Level IVKeywords: Hip arthroscopy; Alpha angle; Surgical outcomes; Patient-reported outcomes; FAIS; Cam morphology.https://doi.org/10.70885/hmsj.2026.09.003

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