Improved Stress Shielding on a Cementless Tibia Tray using Functionally Graded Material

Abstract Aseptic loosening of the tibial component is a primary concern of total knee replacement (TKR), which may be caused by stress shielding in cancellous bone of tibia and may require subsequent revision surgery. There is no doubt that materials and design are important issues within general product development and even more in biomedical products. In this study, a 2D axisymmetric finite element model of the tibia and tibial prosthesis is designed to find the optimal functionally graded material (FGM) constituents as well as the optimal gradation direction. The results showed that the optimal design of a tibia tray material is represented by grading it vertically from hydroxyapatite at the end of stem tibia to collagen at the upper layers of the tibia plate. This new design is found to reduce stress shielding in cancellous epiphyseal and diaphyseal bone by 78 % and 68 %, respectively, compared to cementless titanium tibia tray. However, the interface shear stress in cancellous diapyseal bone is reduced by 24 % using FGM tibia tray, which will reduce the pain at the end of stem after the surgery. It is concluded that the new tibial design will increase the life of the knee prosthesis.