Influence of Tibial Component Position on Altered Kinematics Following Total Ankle Arthroplasty During Simulated Gait

Abstract

Category: Ankle Arthritis Introduction/Purpose: Correct positioning of total ankle arthroplasty (TAA) implants has been associated with superior clinical outcomes. Furthermore, biomechanical studies have demonstrated that poor alignment of the components may lead to early component wear, compromising the longevity of the prosthesis. Malpositioning of TAA implants affects ligament engagement patterns and joint contact mechanics, possibly leading to altered joint kinematics. However, the correlation between implant position and ankle joint motion is still unclear. The objective of this study was to assess the effect of tibial component position on ankle kinematics following TAA during simulated gait. Methods: Eight mid-tibia cadaveric specimens were utilized in this IRB approved study. The stance phase of gait was simulated both pre- and post-TAA in each specimen using a six-degree of freedom robotic platform. Ground reaction forces and tibial kinematic from in vivo data were replicated while physiologic tendon force profiles were applied to each extrinsic ankle tendons by linear actuators instrumented. Ankle kinematics was measured from reflective markers attached to bones via surgical pins. TAAs were completed using a common fixed-bearing total ankle system following the manufacturer recommended protocol (Salto Talaris, Integra LifeSciences). Using reconstructed CT data, 3D tibial component position relative to a standard ankle joint reference was characterized (Figure 1A). The effect of tibial component position on absolute differences in ankle kinematics (pre – post TAA) was assessed using linear regression with a level of significance set to p = 0.05. Results: Differences in ankle joint kinematics were only identified in the transverse plane, where internal talar rotation was significantly increased following TAA compared to the native condition (Figure 1B). The medial position of TAA tibial components was found to be positively associated with increased internal talar rotation (Figure 1C; β = 1.861 degrees/mm, R2 = 0.72, p = 0.008). No other measurements of tibial component position (anterior-posterior/inferior-superior position, sagittal/frontal/transverse plane angle) were found to be significantly associated with altered ankle kinematics following TAA (All β 0.05). Conclusion: This study suggests that medial positioning of the tibial implant affects ankle kinematics. During operative procedures the tibial component is usually positioned in order to preserve bone stock of the medial and lateral malleolus. However, little attention is given to the position of the implant in relation to the center of the tibial axis. This finding could have clinical implications for techniques implemented during surgical procedures and for the development of new instrumentation systems.