Mechanisms of Sensorimotor Impairment in Multiple Sclerosis

Sensorimotor impairments in people with multiple sclerosis (MS) might alter coordination and balance strategy during functional movements. People with MS often have symptoms such as weakness and discoordination in the lower limbs, resulting in poor walking and balance function. This decrease in function can result in falls, decreased community activity, unemployment, and reduced quality of life. As MS is a progressive disease resulting in a range of dysfunction, the amount of lower limb impairment can cause changes to walking and balance strategies to maintain functional performance. The overall objective of this dissertation was to quantify the impairment at the hip and ankle, and characterize the effects of impairment on walking and balance in MS. To quantify the lower limb impairment, a custom-built robot was used to impose movement to the legs about the hip and ankle joint separately. Joint torque and work done were used as quantitative measures of strength during isometric contraction and coordination during subject assisted leg movements in MS and healthy control subjects. To characterize the effect of impairment on functional movements, motion analysis was used to record kinematic and kinetic parameters during overground walking and during a challenging arm tracking task in standing. Hip and ankle sagittal moments were used to quantify the contribution of each joint to functional movement. The findings from these studies suggest that there is a greater sensorimotor impairment at the ankle than the hip in MS, resulting in a reduced reliance on the ankle during walking and an increased hip versus ankle strategy during upper body movements. This was observed by increased negative work at the ankle during assisted bilateral leg movements, reduced ankle moments during stance in gait, and increased hip versus ankle contribution during arm tracking movements in standing. These results indicate that differential impairment between the hip and ankle can drive changes to walking and balance strategy to maintain functional performance, highlighting the importance of joint specific rehabilitation methods in improving function in MS