Total hip joint replacement

Abstract

In the replacement of the hip joint, full access to the hip joint is obtained by separating the trochanter, a large protruberance on the upper portion of the upper leg bone, or femur, from the remainder of the femur, and the subsequent dislocation of the hip joint. Following dislocation, a minimum amount of bone is removed from the femoral ball and sufficient bone is removed from the socket to accommodate the minimum thickness surface replacement elements. A thin hollow inert metal ball or shell member having an outer diameter close to that of the original hip joint is then cemented onto the upper end of the femur, and an ultra high molecular weight polyethylene cup is cemented into the hip bone socket, with acrylic bone cement. To achieve maximum strength with minimum thickness, both the metal and plastic surface elements, although spherical at their mating surfaces, are thicker at their maximum load bearing points toward the top, and are of lesser thickness elsewhere. The two joint surface elements which are both generally hemispherical, have inner and outer surfaces which are both eccentric and asymmetric, with the thicker portion of the plastic liner being about 45.degree. off the central hemispherical axis, and the thicker portion of the metal shell being its upper portion.