比嘉 昌

The present paper introduces an optimum design of the hip prosthesis and a method for shape optimization which minimizes the stress concentration within the cement mantle. A gradient projection method of numerical optimization and a p-version three-dimensional FEM of stress analysis were employed. A generic three-dimensional FEM model of the proximal femur containing a cemented fomoral stem of a total hip arthroplasty was developed. The three types of analysis was then performed in this study. First, stastic stress analysis measuring the stress in the bone cement was performed. The generic model was then valified parametrically by changing the each parameters individually that compose the stem geometry measureing the stress occuring within the cement mantle concurrently. As it is called design sensitivity analysis was performed. Finally, optimal stem shape was desigend using shape optimization. The design objective was to minimize the largest maximum principal stress in the cement. The results of shape optimization showed considerable reduction in stress concentration within the cement mantle compared to the starting design that were used. Moreover, the optimal stem shape obtained in this study showed unique geometry differ from the standard trend that has been believed to be better. The results of this study has shown to be attractive for evaluating stem design and develop the optimal new stem shape.

New surface structure with regular patterning for the frictional surfaces of the artificial joints was designed to improve the wear problems. The lubrication properties for the cup ( ultrahigh molecular weight polyethylene, UHMWPE) vs. ball ( Co-Cr alloy) were studied to evaluate the wear and surface roughness. The surface structure is the dents pattern which has diameter of 0.5mm, pitch of 1.2mm. In this study, such surface patterns were applied to artificial hip joints, and the effects of regular patterning on the frictional surface were investigated by using a joint simulator. The amount of wear of the cup that was in contact with the patterned head was only half that of the cup that was in contact with the non-patterned head, and the surface roughness of the cup with a non-patterned head was three-times greater than that of the cup with a patterned head. These results demonstrates that the lubrication properties can be improved by patterning of the frictional surface of the artificial joint. Consequently, the life of the artificial joint can be extended by the patterning on the frictional surfaces.