FEM Simulations Of Prosthesis Hip JointImplants

Abstract

The scope of this report is to present the non-linear finite element method (FEM) calculations for two artificial hip joint implants (system composed of a spigot, head and cup). For the implants the influence of the boundary conditions, the variation of the taper angle difference, the coefficient of friction between the spigot and the head and also the material of spigot and head on the stress distribution in the system are determined. For each of the two implants, based on the designs of the producer Metoxit AG, an axisymmetric FE model was generated. Note that the head of the two implants possesses different bore depths. The geometry of the spigot and cup are similar in both models. The calculations were carried out with ABAQUS/Standard. The results of the analyses show that the boundary conditions of the implant and the variation of the taper angle difference have a strong influence on the tensile hoop stress distribution in the head. In addition, it was found that the variation of coefficient of friction determined by measurements and the different materials considered for the spigot and head have a small effect on the stresses. Moreover, the stresses in the head of the system with the deeper head bore do not necessarily have to be higher than those in the head with the shallow head bore, since the resulting stresses depend on the support conditions and the taper angle difference. The dominant influence of the boundary conditions on the stress distribution in the head raises doubts as to the correctness of the ISO 7206-5 standard; while the in vivo circumstances of the implant are not completely simulated by the test specified in this guideline. Transactions on Engineering Sciences vol 24, © 1999 WIT Press, www.witpress.com, ISSN 1743-3533