Prediction of taper performance using quasi static FE models: The influence of loading, taper clearance and trunnion length.

The head-neck taper junction has been widely reported to corrode leading to adverse tissue reactions. Taper corrosion is a poorly understood phenomenon but has been associated with oxide layer damage and ingress of corrosive physiological fluids. Micromotion may damage the oxide layer; although little is understood about the prevailing stresses which cause this. The ingress of fluid around the joint space into the taper will depend on the taper contact position and the separation of the interfaces during loading. The current work reports on the effect of taper clearances and trunnion length on the taper surface stresses and the taper gap opening. These were determined for CoCr/Ti taper interfaces using FE under loading conditions including walking and stair climb as well as hip simulator load profiles. Shorter trunnions and stair climb loading were shown to generate the greatest taper gaps (82 mu m) and also the largest surface stresses (1200 MPa) on the head taper. The largest taper gaps were associated with smaller taper contact areas. Clearances within +/- 0.1 degrees had no effect on the taper gaps generated, as the tapers engaged over comparable lengths; the taper gap opening was dependent upon the taper engagement length rather than location (proximal or distal) of contact. The walking profile or variants applied by hip simulators, was insufficient to differentiate between taper designs and evaluate differences in the magnitudes of taper gaps. The use of more demanding activity such as stair climb during in vitro evaluations could provide better predictions of taper performance in vivo. (c) 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 138-148, 2019.