A computer simulation study of normal and abnormal hip joint contact pressure.

The contact pressure on 112 normal hip joints and 66 acetabular dysplastic hip joints was analysed using a three-dimensional rigid body spring model. Geometric models were made from conventional anteroposterior radiographs, with the assumption that the acetabular surface was spherical. In normal hips, the distribution of contact pressure was almost even over the joint surface, and the maximum contact pressure was relatively low. However, in a dysplastic hip joint, the pressure was concentrated on the anterolateral edge of the acetabulum and increased enormously not only with the reduction in lateral coverage but also with the reduction in the anterior coverage of the acetabulum. This result indicates that a three-dimensional analysis is indispensable for estimating the mechanical effect on acetabular cartilage.