Pre-operative and Post-Operative Alpha Angles are Significant Independent Predictors of Patient-Reported Outcome Measures at Two Years After Hip Arthroscopy

Objectives: Residual impingement after hip arthroscopy for femoroacetabular impingement (FAI) is a common cause for re-operation; however, the relationship between preoperative and postoperative radiographic parameters and patient-reported outcomes has not been defined.Methods: 749 consecutive patients were reviewed two years after primary hip arthroscopy. Patients undergoing revision surgery were excluded. Pre-operative and post-operative radiographs were analyzed to measure the alpha angle on standardized anteroposterior (AP) pelvis, Dunn-lateral, and false profile (FP) views and anterior and lateral center-edge angles (ACEA, LCEA). Univariate analysis evaluated the association between demographic variables, radiographic measures and hip outcome scores (Hip Outcome Score (HOS)-Activities of Daily Living (ADL), HOS-Sports Specific (SS), and Modified Harris Hip Score (mHHS)). Multivariate modeling was subsequently performed. Significance was defined as p<0.05.Results: 706 patients with mean age of 33.2±12.3 years and mean BMI 25.1± 5kg/m 2 were included for final analysis. The alpha angle on the AP, Dunn-lateral, and FP views and the ACEA and LCEA decreased after surgery (p<0.001 for all). Significant univariate correlations with the postoperative HOS-ADL included age, BMI, pre-operative AP, FP, and Dunn and postoperative FP alpha angles. Postoperative HOS-SS was correlated with age, BMI, medial post-operative joint space width (JSW), pre-operative AP, FP, and Dunn and postoperative FP alpha angles, and pre-operative and post-operative (ACEA). Postoperative mHHS correlated with age, BMI, post-operative lateral JSW, pre-operative AP, FP, and Dunn and postoperative FP and Dunn alpha angles, and post-operative ACEA. Multivariate modeling ( Table 2 ) demonstrated that preoperative and postoperative FP alpha angles were independent predictors of postoperative outcomes.Conclusion: Pre-operative and post-operative alpha angles were negatively correlated with the HOS-ADL, HOS-SS, and mHHS at 2 years after arthroscopic surgery for FAI. Specifically, pre-operative and postoperative FP alpha angles were independent predictors of postoperative outcomes. These results highlight the importance of resecting anterior cam lesions to prevent residual impingement and inferior outcomes.Table 2:Multivariate Regression Results for Association Between Radiographic Measurements and Patient-Reported Outcome ScoresVariable Coefficient P ValueHOS-ADL at 2 YearsPre-op HOS-ADL score 0.29 <0.001Workmen's compensation -8.51 0.045Pre-op AP alpha angle -0.18 0.039Post-op false profile alpha angle -0.42 0.030HOS-SS at 2 YearsPre-op HOS-SS score 0.33 <0.001Workmen's compensation -18.7 0.016Pre-op AP alpha angle -0.43 0.005Pre-op false profile alpha angle -0.30 0.039Modified Harris Hip Score at 2 YearsPre-op MHHS 0.32 <0.001Age -0.21 0.025Workmen's compensation -11.3 0.044Pre-op false profile alpha angle -0.17 0.046Post-op false profile alpha angle -0.52 0.040