Joint stiffness of the ankle during walking after successful mobile-bearing total ankle replacement.

INTRODUCTION It has been shown that walking kinematics remain near to normal after mobile bearing total ankle replacement (TAR). However, no information is available on mechanical joint loading. The purpose of this study was to determine whether mechanical load and 'quasi-stiffness' of the ankle joint after TAR differs from the normal load and stiffness of a healthy ankle joint during walking. METHODS Ten TAR patients and 10 age-matched healthy control subjects (CO) participated in this study. Participants walked barefooted on an indoor track at self-selected walking speed. 3D ankle kinematics and ground reaction force were measured and used for the calculation of 3D net joint moments, joint quasi-stiffness coefficients and internal net joint ankle work. RESULTS Between patients and control subjects no differences were observed in peak moments and stiffness coefficient at the ankle. Internal work at the ankle during the step differed however, significantly (-0.078 (0.088) J kg(-1) versus 0.005 (0.048) J kg(-1) for TAR versus CO, p=0.02), although it could be argued that this difference was due to a minor difference in walking speed between both groups (1.02 (0.07) versus 1.09 (0.07) for TAR versus CO, p=0.02). CONCLUSION Despite the small difference in internal work at the ankle, there was no significant difference in mechanical loading of the ankle after TAR compared to normal.