Plantarflexor Weakness Negatively Impacts Walking in Persons With Multiple Sclerosis More Than Plantarflexor Spasticity

Abstract Objectives To determine whether plantarflexor (PF) spasticity or ankle strength best predicts variance in walking capacity or self-perceived limitations in walking in persons with multiple sclerosis (MS) and whether persons with MS with PF spasticity are weaker and have greater walking dysfunction than do persons with MS without PF spasticity. Design Cross-sectional study. Setting University research laboratory. Participants Forty-two adults with MS (mean age, 42.9±10.1y; Expanded Disability Status Scale score, median=3.0, range=0–6) and 14 adults without disability (mean age, 41.9±10.1y). Intervention Not applicable. Main Outcome Measures PF spasticity and dorsiflexion and PF maximum voluntary isometric torque were assessed using the modified Ashworth Scale and a computerized dynamometer, respectively. The Timed 25-Foot Walk Test was the primary outcome measure of walking capacity. Secondary measures included the 6-Minute Walk Test and the 12-item Multiple Sclerosis Walking Scale. Results PF strength was the most consistent predictor of variance in walking capacity (Timed 25-Foot Walk Test: R2 change=.23–.29, P ≤.001; 6-Minute Walk Test: R2 change=.12–.29, P ≤.012), and self-perceived limitations of walking (12-item Multiple Sclerosis Walking Scale: R2 change=.04–.14, P .05) between persons with MS with PF spasticity and persons with MS without PF spasticity for any of the outcome measures. Conclusions Our study suggests a unique contribution of PF weakness to walking dysfunction in persons with MS, and highlights the importance of evaluating PF strength in this clinical population.