Development of alumina ceramic bipolar hip prosthesis and clinical application.

The concept of the bipolar type prosthesis is that the articular motion is observed primarily between the HDP bearing insert and the inner head, thereby avoiding the greater frictional shear force between the prosthetic head and acetabulum found with the traditional one piece endoprosthesis. A newly developed ceramic bipolar hip prosthesis utilizes an outer head composed of bio-inert fine alumina ceramic rather than a metal head. The mechanical strength of this prototype bipolar hip prosthesis was tested with static load and impact force, and the dynamic fatigue strength was also tested with repeated loads. Results were judged to show that the device has strength adequate for clinical use. The hip prostheses has been clinically applied in replacement of the femoral head of a neck fracture, femoral head necrosis and osteoarthritic hip. Finally, using a mathematical model, the so-called self-centering effect due to center offset between outer and inner heads is discussed.