Modulating the margin of stability and inter-limb symmetry: A before-after trial on the acute effects of a novel hybrid passive spring damper ankle-foot orthosis in hemiparetic multiple sclerosis with drop-foot

Abstract

People with multiple sclerosis (PwMS) are at increased fall risk due to dynamic instability. This clinical trial assessed the immediate effect of a novel hybrid passive spring-damper ankle–foot orthosis (HPSD-AFO) on dynamic stability in hemiparetic PwMS. The primary aim was to evaluate changes in the margin of stability (MoS)—an instantaneous measure of stability derived from the extrapolated center of mass (XcoM)—comparing outcomes between the affected and unaffected sides. This within-subject before-after trial evaluated gait in twelve mildly hemiparetic PwMS (three males, nine females; mean age 35.2 years) under both shod and novel HPSD-AFO conditions. Full-body kinetics and targeted kinematics were recorded along a 10-meter walkway. The analysis focused on spatial–temporal parameters (step width, stride time, step length) and dynamic stability metrics, including anteroposterior (AP MoS) and mediolateral (ML MoS) for the whole gait cycle and key phases. Gait with the HPSD-AFO resulted in significantly reduced step width and stride time. The orthosis also significantly modulated dynamic stability: the AP MoS decreased bilaterally, while ML MoS demonstrated a limb-specific response, decreasing on the non-affected side but increasing on the affected side. Consequently, the symmetry of both spatial–temporal parameters and MoS metrics improved substantially with HPSD-AFO use. The use of the novel HPSD-AFO immediately improved gait by reducing step width and stride time. It differentially modulated stability, decreasing AP MoS bilaterally while increasing ML MoS on the affected limb. This pattern led to a significant improvement in inter-limb symmetry across both spatiotemporal and dynamic stability metrics.