RehabMove 2018: CAN LOW-COST MOTION CAPTURE SYSTEMS BE USED TO MEASURE ACCURATELY JOINT REACTION IN POWERED-EXOSKELETON USERS?

The purpose of this study was to investigate if a low-cost marker-less motion capture system, coupled with low-cost force sensors, could be used to accurately assess joint reactions during assisted gait. The case of powered-exoskeleton users who lost their locomotion due to Spinal Cord Injury (SCI) is of interest because (i) shoulder joint reactions are difficult to assess by therapists with visual inspection, but are critical factors to avoid secondary health issues, (ii) exoskeletons induce unexpected visual occlusions and shape deformation with respect to standard motion capture protocols, (iii) SCI subjects wearing powered exoskeletons still need to use crutches, but for balance only, with load patterns scarcely studied in the literature. One expert user of a Rewalk© P5 model was asked to test a pair of instrumented crutches with force sensing capabilities, inside a gait lab monitored by a reference motion capture system and a low-cost system composed of time-of-flight cameras. Two set of inverse dynamic analyses were performed to assess joint reactions: one using kinematic data from the reference MoCap and one using kinematic data assessed with the low-cost setup. The root mean square (RMS) error for shoulder joint reactions assessed starting from the low-cost measurement ranged from 0.4% (longitudinal) to 1.1% (vertical) of the body weight.