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

Abstract

To investigate the individual and combined contributions of acetabular and femoral morphology to hip range of motion (ROM) in patients with femoroacetabular impingement syndrome (FAIS) by use of computed tomography measurements and hip ROM evaluated on physical examination. A retrospective chart and radiographic analysis of patients presenting with hip pain suggestive of FAIS was performed. The femoral neck-shaft angle, femoral version, magnitude and clock-face location of the alpha angle, midcoronal center-edge angle (CEA), midsagittal CEA, acetabular version, and McKibbin index were measured on computed tomography scans. 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° of flexion. Two hundred hips that met the inclusion and exclusion criteria during the eligibility period were included in the analysis. The mean age was 31.9 ±10.0 years, there were 145 female patients (72%), and the mean body mass index was 25.2 ± 5.0. Multivariate linear regression analysis showed that the midsagittal CEA was the only measurement correlating with flexion (q= .031) whereas the femoral neck-shaft angle and McKibbin index were the only significant variables that correlated with external rotation (q= .031 and q < .001, respectively). Finally, the McKibbin index and maximum alpha angle were the only variables that correlated with internal rotation (q < .001 and q= .034, respectively). Multivariate analysis showed that combined acetabular and femoral version significantly correlated with internal and external rotation whereas 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 pathomorphology and acetabular pathomorphology and that careful evaluation of both should be conducted prior to corrective osteoplasty or osteotomy. Level IV, retrospective case series.