Characterizing the effects of muscle weakness on margins of stability and joint mechanics during gait in persons with incomplete paraplegia due to spinal cord injury.

Abstract

Individuals with incomplete spinal cord injury (iSCI) exhibit diverse walking capabilities due to partial sensory and/or motor impairment below the injury level. This study examined how neuromuscular weakness patterns influence compensatory gait strategies, dynamic balance (margins of stability, MoS), and joint-level mechanics across iSCI subgroups compared to non-disabled controls. We analyzed gait data from 21 iSCI participants previously classified into four subgroups through dynamic time warping and hierarchical clustering. Temporospatial parameters, anterior-posterior (AP) and mediolateral (ML) MoS, and joint kinetics were analyzed using linear mixed-effects models with walking speed as a covariate to isolate group differences beyond speed. The most functional individuals, with mild plantarflexor weakness, walked comparably to controls but exhibited elevated peak hip flexion moments, suggesting a possible long-term hip joint health concern. The individuals with moderate plantarflexor weakness adopted slower walking speed as their primary compensation, with no residual differences from controls once speed was accounted for. The two most impaired groups of individuals, with combined plantarflexor and hip muscle weakness, additionally compromised frontal-plane balance - adopting wider step widths and higher ML MoS - and showed a redistribution of mechanical demand during stance, with the hips contributing a larger proportion of total positive joint work than the ankles. The individuals with most impairment further showed elevated AP MoS persisting beyond speed reduction, lower peak plantarflexion moment, and a shift of mechanical work toward the knee. These findings indicate that gait adaptations in iSCI depend on the muscle weakness profile rather than severity alone, supporting tailored rehabilitation strategies.