Measuring Postural Stability After Perturbation In Recreational Athletes With And Without Chronic Ankle Instability

Abstract

Chronic ankle instability (CAI), the recurrent spraining, “giving way,” and sensation of instability at the ankle joint, is a common occurrence after a sports-related ankle sprain. The specific factors that contribute to CAI have yet to be established, but deficits in proprioception and muscle activity certainly play a role. PURPOSE To test for proprioception-related and muscle onset latency deficits in a group of recreational athletes with CAI using a standardized perturbation via tibial nerve stimulation. METHODS A group with CAI (n=10) was compared to a group of matched controls (n=10) with no history of ankle injury. Subjects were matched by gender, height, mass, and limb dominance. Subjects stood on a forceplate with tibial nerve stimulating electrodes placed bilaterally. Proprioception was indirectly measured using static and semi-dynamic balance tasks. Three trials of quiet standing for 15 seconds with no stimulation were performed, followed by seven perturbation trials, each 15 seconds long with a variable foreperiod. A 1 ms stimulation of maximum intensity activated every motor axon in the tibial nerve, causing both calves to contract maximally. Subjects were instructed to regain balance as quickly as possible. Electromyography measured onset of peroneal muscle activity in the test leg. Tibial acceleration was measured in the anteriorposterior direction. Center of pressure sway length, velocity, and area were calculated. Independent samples t-tests compared the groups' age, mass, and height. The maximum and minimum values for all dependent variables were discarded, and remaining values were averaged across trials. One-way ANCOVAs, covarying for maximum tibial acceleration, compared groups. RESULTS The groups were equivalent in age, mass, and height (p >.05). The CAI group self-reported significantly lower ankle stability on a questionnaire regarding ankle function (56.1 ± 9.7 vs. 94.9 ± 6.3; p <.05). No differences were found between CAI and controls for quiet standing sway length, velocity, or area (p >.05). No significant differences were observed between CAI and controls, respectively, for perturbation trials (sway length 447.06 ± 56.41 vs. 449.79 ± 43.40 mm; velocity 29.79 ± 3.77 vs. 29.98 ± 2.89 mm/s; or area 1513.97 ± 733.83 vs. 1220.75 ± 349.24 mm2; p >.05). The CAI group had a 26% larger sway area compared to controls. No significant differences were found between the CAI and control groups in muscle onset latency. CONCLUSION Perturbation via tibial nerve stimulation is not challenging enough to detect proprioceptive deficits in individuals with CAI. Funded by the UNC Injury Prevention Research Center Student Small Grant.