Stress distributions in the acetabular region--I. Before and after total joint replacement.

Two-dimensional finite element analyses of the acetabular region before and after hip replacement were conducted. The distribution of pressure at the acetabular surface for the single limb stance phase of gait was transformed to nodal loads to stimulate in vivo loading conditions. A nonhomogeneous distribution of bone elastic properties was incorporated in the models. The results demonstrated that the principal stresses in the normal acetabulum were aligned with the principal orientations of the trabeculae. Total joint replacement increased the von Mises' equivalent stresses in the cancellous bone immediately superior to the acetabular cup, and increased stresses in the medial wall of the ilium. Biaxial, tension-compression stresses were created in the layer of bone cement and introduced in the medial wall of the ilium. Tensile stresses in the bone cement were greatest at the superior roof and at the inferior margin of the cup. Tensile stresses in the cup were more pronounced at the margins, particularly near the inferior lip. The cup tended to close in such a manner as to grip the head of the femoral component as it was pressed between the medial and lateral walls of the ilium.