The role of the assembly force in the tribocorrosion behaviour of hip implant head-neck junctions: An adaptive finite element approach

Abstract

The cyclic loading, in the corrosive medium of the human body, results in tribocorrosion, at the interface of the head neck taper junction of hip implants. The resulting metal ions and wear debris can have adverse effects on the local tissues. The force applied by surgeons to assemble the head-neck junction is proven to play a major role in the mechanics of the taper junction which in turn can influence the tribocorrosion damage. Recently, finite element method has been used to predict the material loss at the head-neck interface. However, in most previous finite element studies, the contribution of electrochemical corrosion has been ignored. Therefore, a detailed study to investigate the influence of the assembly force on the tribocorrosive behaviour of the head-neck junction, taking into account both the mechanical and chemical material removal, is of paramount interest. In this study, a finite-element-based algorithm was used to investigate the effect of assembly force on the tribocorrosion damage at the junction interface over 4 million cycles of simulated level gait. The patterns of the material removal in the modelling results were compared with the damage patterns observed in a group of retrieved modular hip implants. The results of this study showed that chemical wear, after four million cycles, for different cases, was in the range of 25%-32% of the total material loss. A minimum assembly force (4 kN for the studied cases) is needed to maintain the interlock in the junction. Increasing the assembly force above this value does not further reduce the material loss. The computational model was able to predict the damage pattern at the retrieved head-neck interface.