People with Multiple Sclerosis (pwMS) often experience walking impairments such as foot drop which can lead to trip and falls. Foot drop can be either transient and is often induced by exercise (fatigability) in pwMS whose walking ability is not affected and can become more fixed with disease progression. The overall aim of this PhD was to explore foot drop, its presence in pwMS with different disability levels and the psychometric properties of outcomes used to evaluate walking impairments. The first study in this thesis was a systematic review into the level of evidence for the psychometric properties of walking measures that have been used to evaluate the effect of assistive technology such as FES for foot drop in MS. Moderate to strong psychometric evidence was found for the Multiple Sclerosis Walking Scale, Timed 25 Foot Walk, 6 minute and 10 meter walk tests. There were no psychometric studies for three-dimensional (3D) gait kinematics in pwMS even though it was one of the most frequently used outcome measures. The second study assessed the test-retest reliability of 3D ankle kinematics and spatiotemporal parameters in pwMS, with low Expanded Disability Status Scale (EDSS < 3.5) and in those with moderate to high EDSS (EDSS: 4-6). Reliability was excellent for ankle kinematics and spatiotemporal parameters in both groups, with lower minimal detectable change (MDC95%) values in the low EDSS group compared to the higher EDSS group. The third study investigated transient exercise induced foot drop in highly physically active pwMS (EDSS < 3.5) and health controls using 3D kinematics. It was found that 6 out of 15 pwMS and none of the healthy controls presented this phenomenon. The fourth study examined the direct orthotic effect of FES during dual-tasking (i.e. walking combined with a cognitive task) and after inducing fatigability. Low to moderate effect sizes indicated that the direct orthotic effect was higher under dual-task and fatiguing conditions but this needs to be confirmed in appropriately powered studies.
In conclusion, the studies in this thesis have contributed to the psychometric evidence of gait kinematics in pwMS, have objectively documented the presence of transient foot drop in highly physically active pwMS and orthotic effect of FES under a variety of conditions simulating the perceived benefits in ‘real life’ reported by FES users.
Key words: multiple sclerosis, foot drop, fatigability, FES, psychometric properties, 3D gait kinematic
