Anterior and Lateral Femoroacetabular Excursion Angles Are Helpful for Assessing Femoroacetabular Impingement Syndrome: A Cross-Sectional Cohort Study

Abstract

This study aimed to develop a radiographic measurement to evaluate the femoroacetabular space using 3-dimenstional hip models in asymptomatic hips, and to evaluate the reliability and validity of the femoroacetabular excursion angle (FAEA) in symptomatic patients. From January/2020 to December/2020, we recruited healthy hips to establish 3-dimensional models. Through the simulation of fourteen activities of daily living (ADLs), anterior and lateral impingement-free FAEAs were measured. Another cross-sectional cohort was formed from consecutive symptomatic subjects with impingement signs during the same period. In the validation cohort, anterior and lateral FAEAs were assessed on modified Dunn's and anteroposterior views of the hip, respectively. We evaluated the reliability and clinical implications of the FAEAs. In the discovery cohort (n=33), hips with collisions tended to have smaller computed tomography-based FAEAs than collision-free hips, although alpha and lateral center-edge (CE) angles were comparable. Additionally, hips with a lower quartile of FAEAs had a significantly higher number of ADLs with collisions. In the validation cohort (n=411), the FAEA measurement was highly reliable (kappa statistics >0.95 for both inter- and intra-observer reliabilities). The femoroacetabular impingement syndrome (FAIS) group (n=165) showed significantly smaller anterior and lateral FAEAs than the non-FAIS group (all P<0.001, Cramer V=0.420). The optimal cut-off values for anterior and lateral FAEAs were 32.6° and 48.9°, respectively. In univariate regression, anterior (odds ratio (OR)=0.91 [95% confidence interval (CI), 0.89-0.94]) and lateral (OR=0.91 [95% CI, 0.89-0.93]) FAEAs were significantly associated with FAIS. Moreover, in multivariate regression adjusted for alpha and lateral CE angles, anterior FAEA remained a significant predictor (OR=0.96 [95% CI, 0.93-0.99]), and small FAEA was an independent risk factor for FAIS (OR=1.99 [95% CI, 1.06-3.71] for any small FAEA; OR=2.88 [95% CI, 1.32-6.31] for both small FAEAs). The FAEA is a valid measurement for FAIS with high reliability.