Prevalence of Imaging Features on CT Thought to Be Associated With Femoroacetabular Impingement: A Retrospective Analysis of 473 Asymptomatic Adult Hip Joints

The objective of our study was to investigate the prevalence of imaging features on CT thought to be associated with femoroacetabular impingement (FAI) and the associations among them. Of 430 consecutive adult patients (age range, 18-40 years) who underwent hip CT at our institution for hip symptoms or trauma surveillance, the asymptomatic hips were selected for the study, which resulted in the inclusion of 473 hip joints in the study group. Images were obtained using an MDCT scanner and were reformatted using a bone algorithm. The CT images were retrospectively evaluated by two radiologists for features indicative of FAI such as the alpha angle, femoral head-neck offset, acetabular version angle, and center-edge angle. The intraclass correlation coefficient was used to evaluate intra- and interobserver variabilities. Associations among these parameters were evaluated by calculating the odds ratio between each of the parameters separately. Of the 473 asymptomatic hip joints we studied, 190 (40%) joints showed at least one of the following features on CT: alpha angle greater than 55°, head-neck offset less than 8 mm, acetabular version angle less than 15°, or center-edge angle greater than 40°. At least one feature was found in the hips of male patients (43.2%), which is more frequently than in the hips of female patients (35.4%). There was a high degree of coexistence (odds ratio > 2) among these CT findings. Imaging features on CT that are known to be associated with FAI are common in asymptomatic adult hip joints, especially in men, with a high degree of coexistence among the findings.