Total ankle replacement: Rationale and history of the designs and recent advances

The treatment by arthrodesis of severe erosions of the ankle articular surfaces caused by various forms of arthritis is not completely successful. Unfortunately, ankle arthroplasty is not showing more satisfactory results. The poor clinical outcome of total ankle replacement have been attributed to the incomplete knowledge of the mechanisms which guide mobility and stability at this joint. This has resulted in a long series of tentative attempts with inhomogeneous clinical results. Rationale and requirements for ankle prosthesis design is first provided in this paper. A comprehensive list of the known designs, either published or patented, is reported. The technical developments from the congruent and incongruent 2-component to the current 3-component designs are reported. These designs are also discussed in term of the relevant clinical results. It is pointed out the definite failure of the early congruent 2-component designs. This historical outline ends up with a brief summary of recent findings on ankle biomechanics which have elucidated the physiological pattern of sliding plus rolling motion and the resistance to external forces in terms of mutual action of the ligaments and the articular surfaces. These findings have resulted also in a possible novel design for total ankle replacement. To restore physiological function at the ankle joint, for the first time the shapes of the prosthetic surfaces have been designed to be compatible with the original pattern of slackening/tightening of the ligaments. Current 3-component designs using a flat tibial component and physiological talar shapes cannot be compatible with physiological ligament function.