Posturography and Muscle Synergies in Patients with Chronic Ankle Instability

This thesis aims to evaluate whether motor control deficits in individuals with Chronic Ankle Instability (CAI) can be characterized by analysing muscle synergies extracted from surface electromyography, using traditional posturography as the gold-standard methodology for comparison. Furthermore, it explores the added value of integrating these two assessment approaches for a more comprehensive understanding of the CAI condition. Twenty patients with CAI and twenty healthy control subjects were evaluated during a single limb stance task under two experimental conditions: Eyes Open (EO) and Eyes Closed (EC). From each trial, two sets of parameters were extracted: one related to the center of pressure and one to the muscle synergies shared between the two groups. For each group of subjects, a separate analysis was performed on posturography and muscle synergies, and finally, the correlation between the two sets of parameters was analysed. The analysis of posturographic parameters revealed greater instability in CAI patients than in controls in the EO condition. However, the analysis of the Romberg Ratio (RR) of posturographic parameters suggested differences in the reliance on visual feedback between the groups. Control subjects exhibited a significantly greater relative deterioration in postural control in the EC condition, indicating a strong reliance on vision. The CAI group, in contrast, demonstrated a less pronounced worsening, suggesting a potential reliance on alternative compensatory strategies rather than visual feedback, plausibly due to their mechanical and proprioceptive alterations. Muscle synergy analysis was crucial in elucidating the adaptive strategy of CAI subjects in the EC condition. Compared to controls, CAI subjects coped with the higher complexity of the motor task by adopting a simplified motor control strategy, characterized by a greater number of co-activations of the analysed muscles, particularly in the EC condition. Specifically, this strategy involved: greater activation (both in terms of intensity and duration) of synergies associated with ankle control; a more persistent motor control (as inferred from the Hurst exponent); and increased recruitment of muscles associated with different control strategies for the knee and hip joints. The correlational study highlighted the presence of a different level of motor control organisation between the two populations. The control subjects displayed numerous and strong correlations between posturographic and muscle synergy parameters, indicating a more complex and repeatable motor control strategy. Conversely, in CAI patients, most of these correlations were absent. Their motor control patterns were less structured, exhibiting greater inter-subject and, in some cases, intra-subject variability, which indicates a less organised and less repeatable strategy. These findings suggest that the apparent reduced reliance on vision observed in CAI subjects is not the result of an efficient control strategy, but rather the consequence of a compensatory muscular co-contraction adopted to cope with the mechanical and proprioceptive deficits caused by the injury. It can therefore be inferred that posturography and muscle synergies provide complementary information, enabling a deeper understanding of the CAI condition. This integrated approach could lead to a more accurate diagnosis and, consequently, to the development of more effective rehabilitation and therapeutic pathways.