Femoro - Acetabular Impingement is Caused by Several Different Bony Abnormalities

Introduction: Osteochondroplasty of the anterior head-neck junction is often performed to treat femoro-acetabular impingement (FAI) on the assumption that the underlying deformity is inadequate anterior offset of the femoral head. However, other morphologic abnormalities, including reduced anteversion, posterior slip, and widening of the neck can all cause loss of joint motion. In this study we examine whether the impinging femur is a mixture of each of these abnormalities, or whether each abnormality is distinct, suggesting that individualized treatments may be needed for successful outcomes. Materials and Methods: Sixty-six cadaveric femora (30 male and 36 female, average age: 76 years) were obtained from a large osteologic database. Thirteen femora were morphologically normal and 53 were abnormal with the following distribution of primary deformities: Cam-type FAI (Ganz) (n=15), Posterior slip (n=22) and Retroversion (n=16). Computer models were generated by reconstructing high-resolution CT scans of each femur. Each 3D model was segmented into bodies corresponding to the head, the neck, and the diaphysis. Axes and coordinate sytems were derived for each anatomic body. Multiple morphologic measurements were taken to describe the shape of each anatomic body and its relationship to the rest of the femur. Additional parameters included the α angle, the β angle, the anterior offset ratio (OSR), the anterior head-neck ratio, the posterior ‘slip’ of the femoral head, the neck shaft angle and the femoral neck anteversion.