Morphological Variations of the Femural Head and Acetabulum: Femoro-Acetabular Impingement and Dysplasia as Possible Initiators of Cartilage Degeneration

Morphological deviations of the acetabulum and femoral head may lead to hip dysplasia or femoro-acetabular impingement. Hip dysplasia and femoro-acetabular impingement (FAI), a pathological contact of the femoral neck with the acetabular rim during motion, have been proposed as potential factors in the development of hip osteoarthritis. The effects of these two kinds of disorders on the mechanical environment of the hip joint are analyzed and compared. One of the morphological measures of the acetabulum is the angle of Wiberg (CE angle), which defines dysplastic, normal or over-covered joints. The morphological measure defined for femoral head deviations in orthopedic literature is the alpha (α) angle [1]. A three-dimensional finite element model of the hip joint has been developed. Changing the CE angle, and alpha angle, normal and pathological joint geometries have been simulated with idealized CAD-generated models, and the results of finite element analyses have been compared for different load and motion cases. Internal contact pressures and cartilage stresses were calculated for each case. The results provide an understanding of normal and pathological joint function, as well as a scientific basis for the corrective operations which are already being utilized. Also, this study verifies femoro-acetabular impingement as one of the potential initiators of cartilage degeneration in the hip.