Finite element modelling of the neck-stem interface of a modular hip implant for micro-motion study

A three dimensional, non-linear finite element modelling was used to analyse component stresses and relative micromotion at the modular junction interface of a Ti-alloy modular hip implant, using ANSYS finite element software. The model was developed to simulate a modular implant system which consisted of a neck, part of the stem, and the interface between the two. Various FE analyses were performed to study the effect of various factors on the extent of relative micromotion at the mating taper interfaces. Failure of surfaces due to fretting, fretting corrosion and fretting fatigue in modular implants results from the presence of the excessive relative micromotion at the modular interfaces, and stress fluctuations in the components. By controlling these factors the performance of modular interfaces can be improved. The finite element study has shown that a proper control of an angular tolerance between the male and female components of the modular implant is important in reducing the chances of fretting failure. The best is the one with a bigger taper angle on the neck. Other beneficial factors are high friction coefficient at the interface, high assembly load applied to the implant before the application of functional physiological load and high neck stiffness.