A Study on Development of the Total Hip Prosthesis Design Fitted for Japanese Patients (2nd Report, Shape Accuracy Estimation of the Femur CAD Model and Improvement in the Canal Fill Ratio of Prosthesis)

In order to devolop the total hip prosthesis design fitted for Japanese osteoar throsis (OA) femurs, the authors analyzed their canal shapes geometrically. The canal shapes of Japanese OA femurs were classified into three types, and prosthetic stem designs corresponded to each femur type were proposed in our previous paper. 3-dimensional CAD models of the proximal femurs based on computed topographic (CT) images were used in the classification and the design. Shape accuracy estimation of the CAD models is required to establish the classification. In this paper, femur CAD models were constructed from not only the CT Images but real images of sliced femur specimen, and proximal canal shapes of the models were compared each other in same coordinate. Shape differences of the models were estimated quantitatively, and accuracy of the model based on CT images was entablished. Furthermore, a prosthetic stem design was improved to increase fill rate of the stem to femoral canal. Finite-element analysis of proximal femur with the improved prosthesis was carried out. Stress distribution of bone around the stem was compared between case of the improved and previous design. Effect of increasing the canal fill ratio on the stress distribution was discussed.