A synergy-based approach to track foot bones motion using different gait analysis protocols

This study shows a novel synergy-based Multibody Kinematics Optimization (MKO) approach for the reconstruction of foot-ankle complex motion from skin marker measures. The complex is considered as a 4 DOF system in which the motion of each bone is the linear combination of 4 synergies, determined in in-vitro experiments investigation through weight-bearing CT. The motion of all complex bones is obtained by computing the synergies’ linear combination coefficients that minimize the residual error on marker positions. To test the approach, the variation of the medio-lateral arch angle (MLA) during gait is computed using different gait analysis (GA) protocols, featuring different number of foot markers, from 2 to 10. The results show the approach estimates the MLA using 3 markers only, with an accuracy similar to that of more complicate GA protocols. Moreover, indentation and separation of foot bones are avoided.