Inter-joint coordination during gait in people with multiple sclerosis: A focus on the effect of disability

Background: Walking difficulties, which are widespread among people with MS (pwMS), represent one of the major factors contributing to physical disability and, as such, may greatly affect an individual's independence and quality of life. In this context, the study of lower limb kinematics may provide an important contribution to unveiling the underlying mechanisms of walking dysfunctions in MS. However, limited information about the inter-joint coordination during gait—the functional relationship between joint pairs during the whole gait cycle—is available. Methods: We retrospectively analyzed the gait patterns of 104 pwMS (56 women, 48 men, mean age 46.3, average Expanded Disability Status Scale score 3.5) and 84 unaffected individuals age-and-sex-matched, who underwent 3D computerized gait analysis carried out using an optical motion capture system. PwMS were also stratified into two groups according to their level of disability. Those with EDSS ≤ 3.5 (n = 62) formed the “low-mild disability” group, while those with EDSS > 3.5 (n = 42) were assigned to the “moderate-severe disability” group. The raw data were processed to calculate the main spatio-temporal parameters and the kinematics in the sagittal plane at the hip, knee, and ankle joints. At each point of the gait cycle, the angular values were employed to build angle-angle diagrams (cyclograms) for the hip-knee and the knee-ankle joint couples. Inter-joint coordination was quantified using geometric features of the cyclograms (i.e., area, perimeter, and dimensionless ratio) and compared between groups. For pwMS only, we also explored possible relationships between cyclograms parameters, disability level, and spatio-temporal parameters of gait. Results: PwMS exhibit a well-known gait pattern characterized by reduced speed, stride length, increased step width, and double support phase duration. Their inter-joint coordination was found altered at both hip-knee and knee-ankle joint couples, as indicated by the significantly reduced cyclogram area and perimeter with respect to unaffected individuals. However, the detailed analysis of the angle-angle diagram trajectories showed some differences associated with the level of disability. In particular, pwMS with mild-low disability exhibit cyclograms partly superposed with those of unaffected individuals in the first half of the stance phase (hip-knee couple) and the second half of the swing phase (knee-ankle couple), while in those with a moderate-severe disability, the differences are substantially extended to the whole gait cycle. Significant moderate to large correlations were also observed between cyclogram area and perimeter, EDSS score, and spatio-temporal parameters of gait. Conclusion: The study of inter-joint coordination during gait in pwMS represents a useful source of information about the way lower limb joints interact, thus potentially expanding the knowledge of the mechanisms underlying walking dysfunctions associated with the disease. From a clinical perspective, the availability of reference data for the co-variation of hip-knee and knee-ankle joint angles during gait can effectively support both the characterization of the progression of the disease and the assessment of the effectiveness of rehabilitative treatments.