EP1.84 Evaluating the Definition of Borderline Hip Dysplasia: A Propensity-Score Matched Analysis Based on 18–20° Versus 20–25° Thresholds for the Lateral Center-Edge Angle in Patients Undergoing Hip Arthroscopy

Abstract

Abstract Background The lateral center edge angle (LCEA) is a commonly used radiographic measure of acetabular coverage in the preoperative evaluation of patients undergoing hip arthroscopy. However, the definition of borderline hip dysplasia (BHD) based on lateral center edge angles remains variable, with commonly reported thresholds ranging from 18°-25° or 20°-25°. Methods Patients who underwent hip arthroscopy with a LCEA of 18.0°–19.9° or 20.0°–25.0° between March 2012-December 2018 were propensity-score matched. Radiographic measures of acetabular coverage and 5-year patient-reported outcomes (PROs), including the Hip Outcome Score–Activities of Daily Living (HOS-ADL), Hip Outcome Score–Sports Subscale (HOS-SS), modified Harris Hip Score (mHHS), International Hip Outcome Tool–12 (iHOT-12), visual analog scale (VAS) for pain, and VAS satisfaction, were compared between cohorts. Clinically significant outcome achievement and reoperation-free survival were also analyzed. Results After matching, 63 hips were included in each group. The 18.0°-19.9° group had a higher preoperative Tönnis angle (P = .049), lower anterior center edge angle (P = .01), and higher Sharp’s angle (P = .024). Both groups experienced significant improvement on average in all PROs (P < .001). No statistically significant differences in mean PROs were observed at minimum 5-year follow-up (P ≥ .24). Furthermore, rates of minimal clinically important difference and patient acceptable symptom state achievement were comparable between the groups (P ≥ .37 & P ≥ .27). Time-dependent reoperation-free survival was comparable between groups (P = .30). Conclusions Among patients with borderline hip dysplasia, lateral center-edge angles of 18.0°–19.9° were associated with more severe acetabular undercoverage compared with those with lateral center-edge angles of 20°–25°. However, no clinically meaningful differences in patient-reported outcomes or reoperation-free survival were observed at 5-year follow-up, suggesting that grouping patients using either 18°–25° or 20°–25° thresholds is appropriate for clinical outcomes research and that LCEA should be interpreted in the context of other morphologic parameters.