Functionally graded materials reduce the stress shielding in the tibia bone for total ankle replacement

Metals, ceramics, and polymers are commonly used as orthopedic implant materials. Conventionally, Cobalt Chromium (CoCr) alloys, Titanium (Ti) alloys, Alumina (Al₂O₃) ceramic, Hydroxyapatite (HA), and Polyetheretherketone (PEEK) are used. Bone resorption owing to stress shielding is one of the reasons for the failure of total ankle replacement (TAR). The stiffness mismatch between the tibia bone and the implant is responsible for stress shielding. It is hypothesized that stress shielding can be reduced by tailoring the implant material similar to the tibia bone by using functionally graded materials (FGMs). The aim of the study is to understand the effect of FGMs on the stress shielding of the tibia bone for TAR. Finite element (FE) models were prepared for, the natural bone, and the implanted bone with the tibial component made from CoCr alloy, Ti alloy, Al₂O₃ ceramic, FGM of Al₂O₃ ceramic at the bottom and PEEK at the top, and FGM of Ti at the bottom and HA at the top. Material properties for FGMs were assigned using Ansys APDL code. The results indicated that the highest stress shielding was present in the Al₂O₃ ceramic model. Whereas, the least stress shielding was in the Ti + HA FGM model. This implies that the stress shielding and subsequently the bone resorption can be reduced by using the FGMs. Thus, FGMs are advantageous when compared to conventional implant materials in order to reduce stress shielding.