Time-to-boundary analysis of postural control following acute lateral ankle sprain

Acute lateral ankle sprain (ALAS) impairs unipedal balance both with the injured and uninjured limb, suggesting that balance during bipedal stance may also be compromised. However, a previous study failed to find such impairment because of poorly sensitive balance outcomes. Time-to-boundary (TTB) analysis may be sensitive enough for detecting latent deficits in bipedal balance following ALAS.

We aimed to examine postural stability during bipedal stance in patients with ALAS using TTB outcomes, and to determine bilateral deficits in unipedal balance.

Twenty-seven patients with ALAS and 26 persons without a history of ALAS participated. ALAS was operationally defined as a traumatic injury to the lateral ligaments of the ankle joint occurring within 24-72 h. Both limbs of the control group were side-matched to those of the patients as either injured or uninjured limbs. All participants performed 3 trials of bipedal stance with eyes open and closed. Next, they completed 3 trials of unipedal stance on both the injured and uninjured limbs in both visual conditions. Order of limb and visual condition for each limb was randomly selected. Means and standard deviations of TTB minima in the anteroposterior and mediolateral directions were computed to assess balance, with lower values indicating poorer balance.

Independent t-tests revealed significant group differences for almost all measures (p=<0.001 to 0.021), indicating that the ALAS group presented poorer bipedal balance. For unipedal balance, there were no significant group-by-limb interactions for all measures (p > 0.05), indicating no side-to-side differences in the ALAS group. However, group main effects were found for all measures (p=<0.001 to 0.048), showing poorer unipedal balance in the ALAS group.

TTB analysis revealed impaired balance during both unipedal and bipedal stance conditions following ALAS. These results support the emerging hypothesis that centrally mediated changes in postural control may occur following ALAS.