Postural control quantification in minimally and moderately impaired persons with multiple sclerosis: The reliability of a posturographic test and its relationships with functional ability

Background: Postural control has been associated with the functional impairment in persons with multiple sclerosis (pwMS). However, there is a need for reliable methods to assess postural control in early stages of the disease, when subtle changes can be difficult to detect. The aims of this study were to assess the absolute and relative reliability of a standing and a sitting posturographic protocol in minimally (Expanded Disability Status Scale <= 2) and moderately (2.5 <= Expanded Disability Status Scale <= 4) impaired pwMS, and to analyze relationships among postural control and functional mobility and gait performance. Methods: To assess postural control in an upright stance, 14 minimally and 16 moderately impaired pwMS performed six 70 s trials in tandem stance, 3 with their weaker leg behind (TSWL) and 3 with their stronger leg behind (TSSL). Additionally, participants completed five 70 s trials using an unstable sitting protocol (US) to assess trunk stability. The mean radial errors of TSWL, TSSL, and US trials were calculated as postural control indexes. Furthermore, participants performed the Timed Up and Go test (TUG) and the Timed 25-foot Walk test (T25FW) to measure their functional mobility and gait speed, respectively. Reliability was evaluated using the intraclass correlation coefficient (ICC3,1) and the standard error of measurement (SEM). Analyses of variances were carried out to assess between-group differences. Hedges' g index (d(g)) was used to estimate the effect size of differences. Pearson correlation analyses (r) were performed to examine the relationships among the postural control and the functional tests. Results: Posturographic tests showed a high reliability in both minimally (0.87 <= ICC <= 0.92; 9.32% <= SEM <= 11.76%) and moderately (0.80 <= ICC <= 0.92; 10.33% <= SEM <= 15.33%) impaired pwMS. Similarly, T25FW and TUG displayed a high consistency in minimally (0.89 <= ICC <= 0.94; 3.43% <= SEM <= 5.17%) and moderately (0.85 <= ICC <= 0.93; 5.57% <= SEM <= 6.56%) impaired individuals. Minimally impaired pwMS showed a better performance on the TUG, T25FW, and TSWL than moderately impaired individuals (p < 0.05; d(g) <= 0.8). The TSWL, TSSL, and US variables correlated with TUG scores (0.419 <= r <= 0.604; p < 0.05), but TSWL also correlated with T25FW scores (r = 0.53; p < 0.01). Furthermore, US scores correlated with both tandem stance parameters (TSWL: r = 0.54, p < 0.01; TSSL: r = 0.43, p < 0.05). Conclusion: Tandem and sitting posturographic tests provide reliable measures of postural control in pwMS, even in individuals with a homogeneous disease profile. Gait speed, functional mobility, and weaker leg status seem decisive in assessing the degree of physical activity limitation in pwMS. Finally, although trunk stability does not seem to be so affected by the course of the disease, it remains relevant for postural control and functional capacity.