Analysis of stress shielding reduction in bone fracture fixation implant using functionally graded materials

Abstract

Bone density reduction occurs when implants are used to arrest fracture propagation. Bones are stress shielded by the implants when enough loads are not placed on the bones. Stress-shielding occurs when stiffness mismatch between the bone and the fracture fixation implant is significant. The aim of this study was to perform an analysis of stress-shielding reduction using functionally graded material (FGM) implants when Young’s modulus vary along the length of the implant. In this study, the finite element method (FEM) was used for the simulation of functionally graded implant mounted on a bone. The effect of FGMs on the reduction of stress-shielding imposed on a bone was studied parametrically by conducting simulations of various two-dimensional (2D) and three-dimensional (3D) computational models. First, a low-fidelity 2D model was created where it was observed that the FGMs were capable of reducing the stress-shielding substantially. Then, high-fidelity models such as single-sided with and without screws as well as double-sided FGM implants with different shapes for consideration of partial cracks were simulated. Several simulations were carried out to investigate the minimum required number of layers in an FGM to avoid stress concentration at the FGM layer interfaces. Furthermore, various material gradations in an FGM were tested to present the FGM gradation index that can reduce the stress shielding. Lastly, it was established convincingly through the finite element simulations that FGMs were able to reduce the stress-shielding on a bone with a crack.