Center of pressure adaptations to tuning of plantarflexion range of motion and stiffness in multi-function articulated ankle-foot orthosis during walking in individuals post-stroke.

Abstract

Articulated ankle-foot orthoses (AFOs) with multi-function joints allow adjustment of plantarflexion range of motion (ROM) and stiffness. In individuals with chronic stroke, impaired ankle function can disrupt forward progression during gait and alter center of pressure (COP) trajectories that reflect the ankle rocker mechanism. Adjustment of articulated AFO settings is a primary strategy to mechanically restore this function. This study investigated how COP trajectories respond to systematic alterations in plantarflexion ROM and stiffness of an articulated AFO during treadmill walking in ten individuals with chronic stroke. The plantarflexion ROM of the Triple Action joint was adjusted to 0°, 5°, and 10° under two stiffness conditions: low (0.44 Nm/deg) and high (1.13 Nm/deg). Gait assessments were conducted across six plantarflexion configurations using a Zebris FDM-T instrumented treadmill. A two-way repeated measures ANOVA was used to evaluate the independent and combined effects of ROM and stiffness on COP, plantar loading, and spatiotemporal parameters in both affected and unaffected limbs, along with symmetry indices. In the affected limb, plantarflexion ROM demonstrated significant main effects on gait line length (p = 0.027) and the anteroposterior COP position at initial contact (p = 0.038). In the unaffected limb, plantarflexion ROM significantly influenced the mediolateral COP position at initial contact (p = 0.023). In contrast, plantarflexion stiffness showed minimal effects on gait parameters. These findings suggest that initial foot placement during walking is primarily influenced by plantarflexion ROM, as it determines the AFO's plantarflexion preload resistance. Incorporating COP-based metrics into AFO tuning procedures may support clinical decision-making and enhance post-stroke gait rehabilitation.