The Bipolar Hip: How Acetabular and Femoral Pathomorphology Affect Hip Motion in Femoral Acetabular Impingement Syndrome.

Abstract Purpose To investigate the individual and combined contributions of acetabular and femoral morphology on hip range of motion (ROM) in patients with femoroacetabular impingement syndrome (FAIS) using computed tomography (CT) measurements and hip ROM evaluated on physical examination. Methods A retrospective chart and radiographic analysis of patients presenting with hip pain suggestive of FAIS was performed. Femoral neck-shaft angle, femoral version, magnitude and clock-face location of the alpha angle, mid-coronal center edge angle (CEA), mid-sagittal CEA, acetabular version and McKibbin index were measured on CT scan. Univariate and multivariate linear regression analyses determined which measurements correlated with hip ROM including: hip flexion as well as hip internal and external rotation with the hip in 90 degrees of flexion. Results Two hundred hips were included in the analysis that met inclusion and exclusion criteria during the time period of eligibility. The mean age was 31.9 ±10.0 years, 145 (72%) patients were female, and mean body mass index (BMI) was 25.2 ± 5.0 kg/m2. Multivariate linear regression analysis demonstrated mid-sagittal CEA was the only measurement correlating with flexion (q=0.031), while femoral neck-shaft angle and McKibbin index were the only significant variables that correlated with external rotation (q=0.031 and q Conclusion Multivariate analysis demonstrated that combined acetabular and femoral version significantly correlated with internal and external rotation while femoral version in isolation did not. Increased cam morphology remained a significant contributor to reduced internal rotation but did not affect hip flexion. These data suggest that hip ROM is affected by both femoral and acetabular pathomorphology, and careful evaluation of both should be conducted prior to corrective osteoplasty or osteotomy.