A novel evaluation system for arthrokinematic ankle motion using a rotary encoder

Ankle joint control is considered important for walking. The relationship between the kinematic indices and neurophysiological indices that reflect neuromuscular control of the lower extremity by upper motor centres must be evaluated to capture the essence of ankle joint control and construct rehabilitation. Herein, we developed the articulation motion assessments system (AMAS) to measure both these indices synchronously. The aim of this study was to validate the validity and reliability of the AMAS’ ankle kinematics analysis. This study included 14 heathy adults. AMAS, a reflective marker and inertial sensor was attached to their right foot, and they performed different ankle joint tasks, such as dorsiflexion, plantarflexion, inversion, and eversion with subjective maximum and mild angular movements. Each task was performed randomly under two conditions; comfortable and slow speeds. Two-dimensional motion analysis and the AMAS had moderate-to-high correlation. The mean root mean square error (RMSE) was significantly lower than those of inertial sensor. The repeatability of the AMAS was better than 0.76 for intraclass correlation coefficients (3,1) and (3,k). However, the Bland-Altman analysis showed fixed errors. Errors should be considered when comparing measurement methods. Synchronised kinematic and neurophysiological measurements should elucidate ankle joint control mechanisms and improve rehabilitation.