Abstract
Through the clinical experience of performing head bipolar hip prosthesis, we came to believe that it might be possible to improve this prothesis by changing the head from a metalic one to an alumina ceramic one. We accordingly developed a new bipolar hip prosthesis with an alumina ceramic outer head which is much more bioinert than a metallic one. This prototype model was tested with static load, impact force and repeated load, and having passed these tests well, we judged that it had enough strength for practical clinical use.
Therefore we used this model clinically in femoral neck fracture, aseptic femoral head necrosis and osteoarthritis. No problems in clinical and X-ray findings have been shown in these cases to date, and all patients have rated the results as satisfactorily. The center was made offset in this model, in expectation of the so-called self-centering effect. This effect is discussed biomechanically using a mathematical model from the point of view of the differences of the head size and the frictional coefficient between metal and alumina ceramics.
