Ankle arthritis affects 1% of the population and can be a painful debilitating problem. One motion preserving treatment option is total ankle replacement (TAR). These devices are currently under researched and have poor clinical outcomes. Despite significant variation amongst device designs no pre-clinical test standards exist to allow comparison of tribological function.
Furthermore, malalignment of TARs is a potential result of surgical technique or failure to correct existing natural varus/valgus deformity. TAR malalignment can result in instability, deformity and is associated with increased wear and higher failure rates. Good alignment is considered instrumental for long term success.
The aim of this research was to develop clinically relevant wear test methodologies for both natural gait and adverse conditions.
First a parameterised test was undertaken to understand the critical parameters for the Zentih (Corin Group) TAR. A knee simulator was used to vary the combination of rotation and displacement and the change in wear rate was assessed gravimetrically.
The effects of malalignment were investigated biomechanically in terms of component lift-off, changing contact area and stress. Adverse conditions were defined based on these results and edge loading observed in retrieved TARs. One coronal malalignment condition and a 3mm translational offset were tested in the wear simulator previously developed.
Rotation proved to significantly increase the TAR wear rate while displacement had no significant effect. Implementing coronal malalignment alone resulted in a significant decrease in the wear rate, due to the reduced contact area while edge loading had no significant effect. This outcome may not translate to reduced wear in a complex biological environment, however simulation methods produced clinically comparable surface form.
This PhD highlighted the critical parameters for TAR wear simulation, however, TAR failure is bigger than wear alone. Further factors must be considered to develop a truly adverse pre-clinical test protocol
