Effects of Exoskeletons on Error Between Marker and Markerless Motion Capture in Children With Crouch Gait: A Pilot Study

Abstract

This study evaluated if a lower-extremity exoskeleton affects error between marker-based ($M^{+}$) and markerless ($\mathbf{M}^{\boldsymbol{-}}$) motion capture in children with crouch gait. Two participants (P1: female, P2: male, ages 6 and 11 years old, cerebral palsy and spina bifida, both with assistive devices) walked with (Exo) and without (NoExo) an exoskeleton spanning the knee and ankle. Mean absolute difference (MAD) between $\mathrm{M}^{+}$ and $\mathrm{M}^{-}$ of gait cycle normalized hip, knee, and ankle angles were analyzed. Key outcomes of an ongoing clinical trial including measures of sagittal knee angle and gait speed were also compared. $\mathrm{M}^{-}$ correlated with $\mathrm{M}^{+}$ kinematics, but MAD ranged 1.57-17.0 deg. Except for sagittal (of P1) and frontal (of P2) hip angles, the Exo increased MAD (range 0.74-8.7 deg). $\mathrm{M}^{-}$ underestimated knee flexion at initial ground contact, peak knee extension in stance, and peak knee extension in swing. No significant difference in MAD (Exo vs NoExo) was observed except for total joint excursion which had distinct trends for P 1 and P 2. For peak knee extension, a primary endpoint of crouch gait severity, the Exo increased MAD beyond minimum clinically meaningful differences (5 deg). Gait speed was consistent, with MAD $<0.03 ~\mathrm{m} / \mathrm{s}$ for all observations (NoExo vs Exo $\mathbf{p = 0. 2 2}$). While $\mathbf{M}^{-}$ has potential to ease gait assessment, early results warrant caution for use with wearable devices, highlighting the need for kinematic estimation algorithms to accommodate diverse end users in clinical and research settings.