Development of Custom-made Design Method of Artificial Hip Joint Stem

In the hip replacing arthroplasty, to make the stem shape of an artificial hip joint fit to the morphology of proximal femoral canal is generally effective to the fixation in an initial stage. Furthermore, it contributes to reduce a stress shielding at the proximal femur. Therefore, this paper proposed the design method of the custom-made stem corresponding to each patient in order to improve the fill ratio of the stem to the proximal femoral canal. This modeling is mainly achieved by means of a Boolean operation (logical AND operation) of the cross sectional contours of the proximal femoral canal along the circular insert axis, which is decided by the bow of the femoral canal morphology with 3D X-ray CT images and a CAD system. As a result, the fill ratio of the stem to the proximal canal by the proposed method was higher than that by a method with the simple straight type as an insert axis. Also, the fill ratio and the spatial distributions of it in the femoral canals with this proposed method were so similar between the different femoral morphology. The result is important for a design of the custom-made model corresponding to variable femoral morphologies.