Chronic Ankle Instability and Corticomotor Excitability of the Fibularis Longus Muscle

Context: Neuromuscular deficits are common in people with chronic ankle instability (CAI). Corticomotor pathways are very influential in the production of voluntary muscle function, yet these pathways have not been evaluated in people with CAI. Objective: To determine if corticomotor excitability of the fibularis longus (FL) differs between individuals with unilateral CAI and matched control participants without CAI. Design: Case-control study. Setting: Laboratory. Patients or Other Participants: Ten people with CAI (4 men, 6 women; age = 21.2 +/- 1.23 years, height = 175.13 +/- 9.7 cm, mass = 77.1 +/- 13.58 kg) and 10 people without CAI (4 men, 6 women; age = 21.2 +/- 2.3 years; height = 172.34 +/- 8.86 cm, mass = 73.4 +/- 7.15 kg) volunteered for this study. Main Outcome Measure(s): Transcranial magnetic stimulation was performed over the motor cortex on neurons corresponding with the FL. All testing was performed with the participant in a seated position with a slightly flexed knee joint and the ankle secured in 10 degrees of plantar flexion. The resting motor threshold (RMT), which was expressed as a percentage of 2 T, was considered the lowest amount of magnetic energy that would induce an FL motor evoked potential equal to or greater than 20 mu V, as measured with surface electromyography, on 7 consecutive stimuli. In addition, the Functional Ankle Disability Index (FADI) and FADI Sport were used to assess self-reported function. Results: Higher RMTs were found in the injured and uninjured FL of the CAI group (60.8% +/- 8.4% and 59.1% +/- 8.99%, respectively) than the healthy group (52.8% +/- 8.56% and 52% +/- 7.0%, respectively; F-1,F-18 = 4.92, P = .04). No leg x group interactions (F-1,F-18 = 0.1, P = .76) or between-legs differences (F-1,F-18 = 0.74, P = .40) were found. A moderate negative correlation was found between RMT and FADI (r = -0.4, P = .04) and FADI Sport (r = -0.44, P = .03), suggesting that higher RMT is related to lower self-reported function. Conclusions: Higher bilateral RMTs may indicate deficits in FL corticomotor excitability in people with CAI. In addition, a moderate correlation between RMT and FADI suggests that cortical excitability deficits may be influential in altering function.