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.

The Effect of Ankle Bracing on Kinematics in Simulated Sprain and Drop Landings: A Double-Blind, Placebo-Controlled Study.

BACKGROUND: The efficacy of external ankle braces to protect against sudden inversion sprain has yet to be determined while taking into account the possible placebo effect of brace application. PURPOSE: To assess the protective effect of an external ankle brace on ankle kinematics during simulated inversion sprain and single-legged drop landings among individuals with a history of unilateral lateral ankle sprain. HYPOTHESIS: The primary hypothesis was that active and placebo external braces would reduce inversion angle during simulated inversion sprain. STUDY DESIGN: Controlled laboratory study. METHODS: Sixteen participants with ankle instability and previous sprain performed single-legged drop landings and sudden inversion tilt perturbations. Kinematics of the affected limb were assessed in 3 conditions (active bracing, passive placebo bracing, and unbraced) across 2 measurement days. Participators and investigators were blinded to the brace type tested. The effect of bracing on kinematics was assessed with repeated measures analysis of variance with statistical parametric mapping, with post hoc tests performed for significant interactions. RESULTS: Only active bracing reduced inversion angles during a sudden ankle inversion when compared with the unbraced condition. This reduction was apparent between 65 and 140 milliseconds after the initial fall. No significant differences in inversion angle were found between the passive placebo brace and unbraced conditions during sudden ankle inversion. Furthermore, no significant differences were found among all tested conditions in the sagittal plane kinematics at the knee and ankle. CONCLUSION: During an inversion sprain, only the actively protecting ankle brace limited inversion angles among participants. These results do not indicate a placebo effect of external bracing for patients with ankle instability and a history of unilateral ankle sprain. Furthermore, sagittal plane knee kinematics appear to remain unaffected by bracing during single-legged landing, owing to the limited effects of bracing on sagittal ankle kinematics. These results highlight the role of brace design on biomechanical function during sports-related and injury-prone movements. CLINICAL RELEVANCE: Athletes prone to reinjury after lateral ankle sprain may benefit from brace designs that allow for full sagittal range of motion but restrict only frontal plane motion.