EFFECT OF IMPLANT MATERIAL PROPERTIES ON THE PERFORMANCE OF A HIP-JOINT REPLACEMENT

A composite material implant prosthesis for hip replacement has been d eveloped. The design of the Prosthesis substructure was based on inves tigation of the stress and strain fields that Le,ere developed in the human femur at the proximal end when a prosthesis stem had been insert ed into it. The prosthesis stem structure was of unidirectional fibrou s composite material core (graphite fibres in polysulfone matrix), wra pped with four layers of the same material but orientated at different angles. The orthotropic moduli of the outer layer are very close to t he moduli of a human cortical bone in the vertical and circumferential directions. The moduli increased gradually from the outer layer to th e inner core. A three-dimensional finite element model of the prosthes is and the bone has been constructed and loaded with the range of forc es that might appear upon operation. The behaviour of the composite pr osthesis and the femur was then compared with the intact femur and thr ee other types of prosthesis materials, namely stainless steel, titani um, an isoelastic material and a hypothetical one with moduli identica l to the cortical bone. The titanium has modulus of elasticity that is only half of the stainless steel. It was Sound that the composite pro sthesis gave the best performance for most of the categories that were examined.