Mobility Characteristics of Total Ankle Replacements

Follow-up studies of the first generation of total ankle replacements indicate failure rates between 52% and 95% at 10 years, mainly attributable to prosthetic loosening linked to compromised subtalar joint motion and excessive intrinsic constraint. Contemporary designs claim to withstand forces across the ankle and minimize loosening by allowing functional motion without excessive constraint. A dynamic testing system was used to measure the anteroposterior, medial-lateral, and internal-external rotational constraints for 4 contemporary total ankle designs under normal gait loads. The force-displacement curves were analyzed for component sliding and tibiotalar surface geometry-generated shear forces. Two designs, with essential soft-tissue load sharing and no mechanical stops on the talar tray, offered the greatest degree of mobility. The others presented substantial differences in mobility due to tibiotalar interface geometry and the locking mechanism of the polyethylene insert.