Dynamics of postural control in individuals with ankle instability: Effect of visual input and orthotic use

The present study investigated the effect of visual deprivation and the use of an ankle orthosis on the dynamics of center of pressure (COP) trajectories during unilateral stance in individuals with ankle instability (AI). Sixteen individuals with AI and nine healthy individuals performed four trials of 30s unilateral stance on a force platform with 1) eyes open wearing no orthosis, 2) eyes closed wearing no orthosis, 3) eyes open wearing orthosis, and 4) eyes closed wearing orthosis. The anterior-posterior and mediolateral COP trajectory were extracted. Regularity was quantified by sample entropy, dimensionality was quantified by correlation dimension and level of time dependency was quantified by entropic half-life. The AI individuals had lower sample entropy and longer entropic half-life in their COP trajectories. The effect of visual deprivation did not differ between groups. Wearing an ankle orthosis increased the sample entropy in the anterior-posterior direction and decreased the correlation dimension in the mediolateral direction for the AI group only. Individuals with AI have higher COP trajectory regularity and higher level of time dependency compared to healthy individuals. Additionally, individuals with AI do not alter the dynamics of their postural control during unilateral stance with visual deprivation compared to healthy individuals. This suggests that alterations in visual or somatosensory information differently affect the executed postural movement pattern. Finally, wearing an orthosis significantly alters the COP dynamics of individuals with AI.