Wear of total ankle replacements : an explant analysis

Abstract

Total ankle replacement (TAR) has increased in popularity in recent years; however, outcomes remain unsatisfactory, with revision rates at 10 years over twice that of hip and knee replacements. Currently, failure mechanisms of TARs are not well understood, and explant analysis studies are limited. This study aimed to characterise the wear-related damage modes and surface changes of explanted TARs in order to investigate the failure mechanisms of contemporary TARs. The influence of design features including bearing constraint on the identified damage was also analysed. Twenty-eight explanted TARs which had been explanted for any reason were included. The cohort comprised 9 different designs of TAR, 3 of which were fixed bearing and 6 of which were mobile bearing. Explant analysis techniques including visual (microscopic and macroscopic) analysis, material characterisation, and surface profilometry were performed to identify damage modes present. Additionally, volumetric wear of the polyethylene component was quantified. All surfaces (articulating and non-articulating) of the TAR components were analysed. A range of wear modes – including intended wear at the bearing as well as unintended wear of non-bearing surfaces and due to third body particles – were observed to have occurred in vivo. Damage to the articulating surfaces of the metallic components in the form of pitting, indicative of material loss, and talar sliding plane scratching, indicative of the presence of hard third body particles, was commonly seen in this cohort of explanted TARs. Evidence of porous coating loss was also frequently identified. Together, this suggests that particulate coating debris may contribute to TAR damage by acting as third body particles. Quantification of the volumetric wear loss at the polyethylene bearing surface revealed relatively low amounts of wear. Based on the findings from the present study, it is proposed that metal debris release may be an underrecognised failure mechanism of contemporary TARs.