Abstract
In this biomechanical analysis, alumina ceramics was employed for the part coming in contact with the bone and the combination of HDP with alumina ceramics for the sliding part. For prevention of sinking and loosening, the femoral component was designed to be loaded on the cancellous bone at the distal end and the anterior and posterior cortical bone of the femur, the tibial plate was designed to be loaded on the plateau, and the posterior slanting surface of the tibial stem was designed to be loaded on the posterior cortical bone. In order to prevent the stem from rotating, small brims were provided on both sides of the stem. Since 1980, 120 knee joints have been replaced and clinical results have been excellent in all cases. Analyses on the stability of the tibial component inserted into the bone were made by means of three-dimensional FEM. The MSC/NASTRAN program was used. The numbers of solid elements, nodal points and degree of freedom were 1188, 1469 and 4100, respectively. Certain tibial bone conditions were assumed; namely, that the cancellous bone was relatively healthy (with Young's modulous of 100kg/mm^2) and remarkably atrophic (with Young's modulous of 10kg/mm^2), and that the subchondral bone was removed completely or partially. Four kinds of loading conditions on the plateaus were assumed; namely, (1) vertical loading on the medial and lateral sides, (2) on one side, (3) loading obliquely at an angle of 45°on one side, and (4) parallel loading to the plateau surface on one side. When the bone is healthy, a large amount of load is transmitted to the plateau. However, when the bone is atrophic, it is transmitted to the posterior slanting cortical bone from the stem. The posterior slanting surface of the stem plays a greater role as a supporting area. Even when the load is applied to the plateau on one side, the compressive load is kept between the plate and the bone on the opposite side. Under the severest condition, that is, when the load is given obliquely on one side, the stem as well as the brims prevent the component from moving anteriorly, rotating laterally, or tumbling. It is concluded that even under the severest condition, our designed tibial component remains quite stable on the tibia.
