The Effect of Shape Optimization and Bimaterial Stem on Increasing the Performance of a Cemented Tibia

The stem design, geometry and material change the mechanical behavior of bone around tibia tray and stem after TKA. In this study a shape optimization of a cemented tibia stem has been carried out to solve the stress shielding at the proximal tibia as well as the stress concentration at the stem tip. It is found that the optimal shape is a short stem with small diameter at the distal stem tip increased gradually to reach a maximum value at the proximal tibia stem. This optimal shape is increased von Mises stress at the lateral and medial cancellous bone by 130% and 140%, respectively compared to initial stem shape. On the other hand the stress concentration in bone at stem tip using the optimal stem shape is reduced by 25% compared to initial shape. However, the optimal stem shape is reduced the stresses in cement at stem tip by 28% laterally and 17% medially compared to the initial stem shape. Finally, a bimaterial stem (titanium with a polymer stem tip) has been applied to the optimal shape to improve the stress concentration reduction at the stem tip. The results are approximately the same compared to the optimal titanium stem