Effect of ankle flexion angle on axial alignment of total ankle replacement.

Abstract

The Salto Talaris Anatomic® (Tornier) total ankle replacement (TAR) has found widespread use in the United States and features rotationally mobile trial components that auto-align the final components, which themselves are rotationally fixed and highly congruent. Based on recent work on prosthetic and native ankle kinematics, we investigated the influence of the ankle flexion angle at the time of final component preparation on the axial alignment of the Salto Talaris TAR. Following a power analysis based on a clinically meaningful difference of five degrees, eight fresh-frozen cadaveric thigh-to-foot specimens underwent installation of trial components using the Salto Talaris TAR system. Specimens were cycled from maximal dorsiflexion (DF) to plantarflexion (PF), as called for in the surgical technique guide, and drilling for the final component was carried out in both five degrees of DF and 15 degrees of PF using separate drill holes. These were compared with a reference drill hole previously placed along the axis of distal tibial cutting guide. Data were analyzed to determine whether components prepared in DF differed from those prepared in PF with respect to median (and variance) rotation. We found no significant difference in median axial alignment (p = 0.139) or in variances between the two groups (p=0.937). The ankle flexion angle at the time of final component preparation did not significantly alter the axial alignment of the Salto Talaris TAR. Therefore, the rotational alignment of the tibial component is determined by the tibial bone cuts and will not auto-align to the rotation of the talar component.