Biomechanical design of a composite femoral prosthesis to investigate the effects of stiffness, coating length, and interference press fit

Abstract

Traditionally, high stiffness hip prostheses are associated with aseptic loosening. Hence, the effects of stiffness, coating length, and interference press fit on load sharing and micro-movements are investigated for a better understanding from a mechanical perspective. A simplified 3D model of the femur and prostheses composed of cobalt chrome (CoCr), titanium (Ti), and glass/polypropylene (Twintex [0]2nT) composite are constructed. Three interference fits corresponding to 5, 25, and 50 µm are used with half, three-quarter, and full lengths of coating that are used to assemble the prostheses with bones to investigate micro-movements at the bone-prosthesis interfaces, interfacial failure, and stress transfer to the bone. The reaction forces of body weight and muscular forces in the femur are used to simulate the FE model. The results indicate that the CoCr and Ti prostheses exhibit low micro-movements at the proximal end and high micro-movements at the distal end and vice versa for the Twintex [0]2nT composite prosthesis. Uniformity of stress transfer to the bone along the prosthesis efficiently increases with increases in the coating lengths and interference press fits for all the cases. A fully coated length of Twintex [0]2nT composite prosthesis with a 50-µm interference press fit provides the most efficient load sharing and stress transfer to the bone and micro-movements at the bone–prosthesis interface.