Posterior femoroacetabular impact in patients with suspected anterior femoroacetabular impingement evaluated with a 3-dimensional dynamic study

Background: Recently, posterior femoroacetabular impact (PFAI) is considered as a cause of hip pain. The purpose of this study was to estimate the frequency of PFAI in patients with suspected symptomatic Anterior femoroacetabular impingement (AFAI) through 3D dynamic study. Methods: We performed a retrospective observational study of patients with suspected of symptomatic AFAI evaluated by computed tomography (CT) from February 2015 to December 2017. PFAI was identified through a 3-dimensional (3D) dynamic study with Clinical Graphics software (Move Forward™, Zimmer Biomet, Inc. Miami, USA). Acetabular anteversion, femoral anteversion, neck-shaft angle, lateral central-edge (LCE) angle, alpha angle and range-of-motion were collected. Results: The study included 181 hips in 131 patients with a median age of 48 (Interquartile range-IQR: 38–59) years; 61.1% (80) were women. PFAI was found in 18.8% (34/181) of hips [95% confidence interval: 13.8%–25.1%]. Among hips with PFAI, 15 had AFAI. External rotation (PFAI: 40; IQR:40–45, AFAI: 45; IQR: 40–60) and neck-shaft angel were lower in the PFAI group (PFAI: 128.4 ± 4.3, AFAI: 133.7 ± 5.4). Conclusion: The impact between the acetabulum and femoral neck on the posterior-superior zone is a frequent finding in patients with symptomatic AFAI through a 3D dynamic study.