Abstract
In order to minimize complications during THR, we applied two-dimensional photoelastic method and soft x-rays and we carried out both dynamic and structural studies, and obtained the following results.
1) The point where stress is concentrated in the acetabulum is always the same even if there is a change in the abductor, adductors or neck-shaft angle. This means that there is little change in the loading position of the trunk of the body onto the acetabulum and it is thought that the friction area of the socket will be limited.
2) If the abductor muscle of the hip joint is activated, the stress of the hip joint increases and this stress is directed toward the area below the sacroiliac joint.
3) The structure of the trabecular bone in the acetabulum matches well the principal stress line graphs formed from a union of the functional and non-functional groups of the abductor muscles. The results we obtained support the trajectorical theory which is concerned with the principal stress on the trabecular bone.
4) The main loading area of the acetabulum is at the frontal plane from the cotyloid cavity to the outer edge and is thought to be a sagittal plane extending from 1/3 of the frontal edge to the 1/3 of the posterior edge (middle-third), but the subchondral bone area is quite dense. At the frontal plane the main factor strongly affecting the structure of the trabecular bone is the pressure more than the abduction movement within the hip joint and in the sagittal plane the bending and stretching of the hip joint is more important than the pressure.
5) The coxa vara of the prosthesis with a strong curvature of the stem often induces fatigue fracture. Therefore, it is better introduce the prosthesis in coxa valga. Then, it is necessary to study on the form of the stem with cement.
