Sensory Reweighting System Differences on Vestibular Feedback With Increased Task Constraints in Individuals With and Without Chronic Ankle Instability

Context: Chronic ankle instability (CAI) is associated with a less flexible and adaptable sensorimotor system. Thus, individuals with CAI may present an inadequate sensory reweighting system, inhibiting their ability to place more emphasis (upweight) on reliable sensory feedback to control posture. However, how individuals with CAI reweight sensory feedback to maintain postural control in bilateral and unilateral stances has not been established. Objectives: To examine (1) group differences in how the sensory reweighting system changes to control posture in a simple double-limb stance and a more complex single-limb stance (uninjured limb and injured limb) under increased environmental constraints manipulating somatosensory and visual information for individuals with and without CAI and (2) the effect of environmental and task constraints on postural control. Design: Case-control study. Setting: Laboratory. Patients or Other Participants: A total of 21 individuals with CAI (age = 26.4 +/- 5.7 years, height = 171.2 +/- 9.8 cm, mass = 76.6 +/- 15.17 kg) and 21 individuals without CAI (control group; age = 25.8 +/- 5.7 years, height = 169.5 +/- 9.5 cm, mass = 72.4 +/- 15.0 kg) participated. Main Outcome Measure(s): We examined the equilibrium scores based on the first 10 seconds of trials in which participants completed 6 environmental conditions of the Sensory Organization Test during 3 tasks (double-limb and single-limb [uninjured and injured] stances). Sensory reweighting ratios for sensory systems (somatosensory, vision, and vestibular) were computed from paired equilibrium scores based on the first 10 seconds of the trials. Results: We observed 3-factor interactions between groups, sensory systems, and tasks (F 4,160 = 3.754, P = .006) and for group, task, and environment (F 10,400 = 2.455, P = .007). The CAI group did not downweight vestibular feedback compared with the control group while maintaining posture on the injured limb (P = .03). The CAI group demonstrated better postural stability than the control group while standing with absent vision (ie, eyes closed), fixed surroundings, and a moving platform on the injured limb (P = .03). Conclusions: The CAI group relied on vestibular feedback while maintaining better postural stability than the control group in injured-limb stance. Group differences in postural control depended on both environmental (absent vision and moving platform) and task (injured limb) constraints.