Persons with Multiple Sclerosis Increase Their Dynamic Margin of Stability during Gait

Background: Persons with multiple sclerosis have high fall risk due to altered static and dynamic balance. Previous gait studies in persons with MS have investigated the motion of the legs or trunk independently. To measure dynamic balance during walking, margin of stability (MoS) examines how the center of mass (trunk) moves relative to the base of support (foot falls). It is unknown if MoS is different between persons with MS and healthy controls, and between persons with MS with different levels of mobility impairment.

Objectives: This study investigates how MoS is affected in persons with MS, as well as the relationship between MoS and the Expanded Disability Severity Score (EDSS), fall history, and the activity-specific balance confidence questionnaire.

Methods: Twenty persons with MS without clinical gait impairment, 20 persons with MS with clinical gait impairment, and 20 age-matched healthy controls, walked over ground at their preferred pace, while marker kinematics captured the motion of the pelvis and feet. MoS was evaluated in the anterior/posterior (AP) and medial/lateral (ML) direction at heel strike and midstance. An increased MoS means that the center of mass is further inside the base of support, and a decreased MoS means that the center of mass is closer to the limits of the base of support.

Results: In the AP direction, the MS group with clinical gait impairment had a higher MoS than the healthy control group (p<0.001) and the MS group without clinical gait impairment (p<0.001) at heel strike and midstance. In the ML direction, the MS group with clinical gait impairment had a higher MoS than the healthy control group (p<0.001) at heel strike only. AP MoS correlated with EDSS (p=0.008) and number of falls (p=0.001), and ML MoS correlated with number of falls (p=0.027).

Conclusions: Compared to healthy controls, persons with MS walk with slower, shorter, and wider steps, which results in an increased MoS in both the AP and ML direction. Increased MoS may be advantageous as it allows for more response time to perturbations, such as a trip, however this may be a poor adaptive gait strategy since falls still occur. Increased MoS may decrease the necessity of finely controlled step placements, leading to rigid and unadaptable gait, and contribute to fall risk in persons with MS.