Biomechanical Considerations for Total Ankle Arthroplasty

The complex anatomical configuration with high congruency of the ankle joint and the complex dynamic nature of the ankle axis of rotation have essential implications in total ankle prostheses. The closer the total ankle arthroplasty design is to the bony anatomy of the normal ankle, and the more compact the components within the prosthetic system are, the closer the kinematics are replicated for normal joints. The conflict is that most current ankle prostheses have been designed using morphometrics of only healthy ankles, thus not considering the morphologic differences of the osteoarthritic ankle. Restoration of correct soft-tissue tension is essential, particularly with the use of unconstrained ankle prostheses, and this can only be achieved with anatomically shaped devices. Minimal bone resection should be performed to preserve the stronger superficial subchondral bone. To avoid “off-center” forces on a prosthesis and possible collapse of the weak lateral tibia, proper prosthesis alignment and adequate ligament balancing of the ankle must be achieved. Particularly, valgus malalignment must be avoided. Theoretically, the ideal ankle prosthesis should be small (necessitating minimal bone resection), as anatomic as possible (to mimic the physiological joint motion and guarantee proper ligament balancing), and consist of three components (to allow for unconstrained motion).