The Influence of Vestibular-Ocular Reflex Training on Static and Dynamic Postural Stability in Subjects with Chronic Ankle Instability
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Context: The vestibular-ocular reflex (VOR) is a low latency, reflexive eye movement that allows the eyes to compensate for head rotation in order to stabilize gaze during the movement. The VOR is important during physical activity because it is initiated each time the head starts to move, and causes the eyes to move in the opposite direction of the head so that the intended image can be centered on the fovea of the eye.
Objectives: To compare the ability of traditional and VOR-enhanced rehabilitation protocols to improve postural stability, dynamic visual acuity and gaze stabilization among chronic ankle instability (CAI) patients.
Design: Randomized controlled trial.
Setting: Research laboratory setting.
Participants: 16 physically-active women and men (age, 22.2+1.5 yrs; hgt, 171.1+7.0 cm; mass, 73.5+18.3 kg) with unilateral CAI, defined as a history of at least two ankle sprains on the same ankle and self-reported feelings of giving way. Participants were free of any neurological or vestibular impairments.
Interventions: Subjects were randomly assigned to 1 of 2 treatments: Traditional rehabilitation group (N = 8) (TRADITIONAL) utilized a CAI ankle rehabilitation protocol modified from McKeon et al. (2009), or a VOR rehabilitation group (N = 8) utilized a modified McKeon CAI protocol with the addition of side-to-side head movements incorporated into all exercises. Each patient participated in 3 rehabilitation sessions/week for 4 weeks. The 2 experimental groups were tested on 2 occasions: a pretest (Week 0) and posttest (Week 4); we used a Group (2) x Time (2) mixed factorial ANOVA (p=0.05).
Main Outcome Measures: Motor control tests (MCT) obtained with the NeuroCom EquiTest™; overall stability indices obtained bilaterally from standard (OSI) and modified (mOSI) Athlete Single Leg Stability Tests with a Biodex BalanceMaster™; dynamic visual acuity (DVA) and gaze stabilization test (GST) using the NeuroCom inVision™.
Results: Vertical GST scores were significantly better in the VOR group 150.5+19.3 deg/sec compared to the TRADITIONAL group, 122.8+21.7 deg/sec (F (1, 14) = 11.02, p=0.005). Significant positive group differences were also observed for the VOR group on the horizontal DVA test (p=0.038). Six of the 9 outcome measures evaluating postural stability, gaze stabilization and dynamic visual acuity significantly improved from pretest to posttest (p=0.001). Of particular interest were the OSI and more challenging mOSI dynamic postural stability tests that improved for both right and left limbs over the 4-week intervention: OSI pretest (8.4+3.4) to posttest (3.1+1.8), p=0.001; mOSI pretest (11.7+2.4) to posttest (5.5+1.8), p=0.001).
Conclusions: As hypothesized, subjects in the VOR group demonstrated significantly better scores on the vertical GST and horizontal DVA tests. Both the TRADITIONAL and VOR rehabilitative protocols produced significant positive changes from pretest to posttest, suggesting that both are effective in improving postural stability, gaze stabilization and dynamic visual acuity in CAI patients.