Defining the postoperative alpha angle threshold for improved outcomes in posterolateral cam lesions

Femoroacetabular impingement syndrome (FAIS) is a common hip disorder that can lead to joint degeneration and osteoarthritis. Posterolateral (PL) cam lesions, characterised by an α angle >60° on anteroposterior (AP) pelvis and Dunn views, present significant surgical challenges due to their anatomical location and proximity to critical vascular structures. Effective surgical intervention relies on achieving optimal postoperative resection, yet clear radiographic thresholds for surgical success remain undefined.

This study aimed to investigate the relationship between postoperative α angle measurements on pelvis AP radiographs and clinical outcomes in patients undergoing hip arthroscopy for PL cam lesions. Additionally, it seeks to determine an optimal postoperative α angle threshold that correlates with improved patient-reported outcomes at 2 years.

A retrospective analysis was performed on a cohort of 117 patients (121 hips) who underwent hip arthroscopy for femoroacetabular impingement syndrome (FAIS) between the years 2013 and 2022, with a minimum follow-up period of 2 years. Preoperative and postoperative α angles were measured on the pelvis AP and Dunn views. Clinical outcomes were assessed using the Hip Outcome Score-Activities of Daily Living (HOS-ADL), the modified Harris Hip Score (mHHS), and the Non-Arthritic Hip Score (NAHS). Receiver operating characteristic (ROC) curve analysis was used to establish an α angle cutoff associated with better functional recovery.

Patients with a postoperative α angle below 55° demonstrated significantly better functional outcomes across all scoring systems. ROC analysis confirmed that α < 55° was a strong predictor of achieving a patient-acceptable symptomatic state (PASS), with an area under the curve (AUC) of 0.849 for mHHS, 0.741 for NAHS, and 0.721 for HOS-ADL (p < 0.001). Sensitivity and specificity values varied across scoring systems, with PASS-NAHS showing a sensitivity of 88.0% and specificity of 52.6%, PASS-HOS-ADL demonstrating a sensitivity of 88.0% and specificity of 52.6%, and PASS-mHHS revealing a sensitivity of 87.6% and specificity of 75%. Multivariate logistic regression further confirmed that a postoperative α angle below 55° was independently associated with improved hip function, reinforcing its significance as a key threshold for surgical success.

A postoperative pelvis AP α angle of less than 55° appears to be a key threshold for optimal recovery in patients with PL cam lesions. These findings highlight the importance of adequate resection during hip arthroscopy to enhance functional outcomes. Further research with larger patient cohorts and advanced imaging techniques may help refine postoperative evaluation criteria.