Cementless Bony lngrowth Total Hip Prosthesis (Anatomical Contact Porous Coated Total Hip Prosthesis) Design using Computed Axial Tomography and Computer Aid Design

ABSTRACT

The purpose of this study is to design an Anatomical Contact Porous Coated Total Hip Prosthesis(ACP) which can transmit stress to the bone more physiologically and which can also eliminate the shortcomings of the currently available total hip prosthesis as much as possible. In the designing process, we have utilized computed axial tomography(CAT) and computer aid design (CAD). To obtain the shape of the femoral canal nondestructively, computed axial tomography data was obtained from fourteen male and fourteen female cadaver femurs and from twenty male and twenty female patients. To create the medullary canal in the computer, the actual dimension of each CAT-scan image was traced and digitized. For each femur a close-fit prototype of the stem was made with polyester and this was inserted into the corresponding femur in usual surgical manner. To test the accuracy of the fit of the prototype in the canal, an image of the cross-section of the canal with the polyester stem was obtained by CAT-scan in the same way that the original CAT-scan of the canal of the femur was done. We then had our computer display fit ratio between the prototype and the canal. We made sure all of the prototypes fit in the canal anatomically, especially around the defined regions (proximal medial and distal lateral regions). Further improvement was made on the fit of the stem in the canal by optimized computer programming. From studies on the shape and the size of the femoral canals of the sixty-eight femurs, eight sizes of ACP femoral stems were designed for each side. Also, on the basis of the anthropometric measurement of the acetabuli in twenty-eight cadaver hips and in the hips of forty patients with femoral neck fracture, different sizes of ACP hemispheric acetabular components were designed, ranging from 40 and 70 millimeters with 2 millimeter increments.