Cam and pincer femoroacetabular impingement: CT findings of features resembling femoroacetabular impingement in a young population without symptoms.

Abstract

The purpose of this study was to use CT to determine the presence of radiologic parameters associated with cam and pincer femoroacetabular impingement (FAI) in a young population without symptoms. A retrospective review of 50 patients (age range, 20-40 years) with no current or previous hip disorder who underwent CT of the abdomen and pelvis was conducted. Multiplanar images were reformatted with a soft-tissue and bone algorithm and assessed for the presence of parameters associated with FAI; alpha angle greater than 55°, femoral head-neck offset less than 8 mm, angle of acetabular version less than 15°, lateral center edge angle greater than 40°, acetabular index less than 0°, pistol-grip deformity, acetabular crossover, and prominent posterior wall signs. At least one abnormal parameter was present in 66% of joints, and two or more abnormal parameters were present in 29% of joints. In seven patients the findings were bilateral. Parameters of mixed morphologic characteristics (cam and pincer) were found in 22% of joints. In side-by-side comparison, high alpha angles were seen in 36 joints measured in the radial plane compared with only three joints measured in the axial oblique plane. The CT finding of FAI-like features was made with high frequency in a young symptom-free population. Cutoff values for defining morphologic abnormalities associated with FAI may have been set too low in the current literature. Alpha angle measurements in the radial plane may be a more accurate quantitative assessment of asphericity of the femoral head-neck junction than are measurements in the axial oblique plane.