Lateral ankle ligament anesthesia significantly alters single limb postural control.

Lateral ankle anesthesia has been used as a model to explore effects of ligament deafferentation related to ankle sprain on single limb postural control with conflicting results. Time-to-boundary (TTB) is a postural control measurement technique found to be sensitive in detecting subtle deficits in postural control in those with chronic ankle instability. The objective of this study was to determine the effects of lateral ankle ligament anesthesia on TTB measures of single limb postural control in healthy adults. Twenty-two healthy adults with no history of lower extremity injury within the past 6 months or balance disorders participated in the study. All subjects received a lidocaine injection to the lateral ankle structures on one of two testing days. On both testing days, subjects performed 3 eyes open and 3 eyes closed, 10-s trials of barefoot single limb stance on a forceplate. The dependent variables were the mean of TTB minima(s) and standard deviation of TTB minima(s) in mediolateral (ML) and anteroposterior (AP) directions. Separate condition (anesthesia, control) by vision (eyes open, eyes closed) ANOVAs with repeated measures were used for each TTB variable to determine the effects of anesthesia on postural control. Alpha level was set a priori at p≤0.05. The anesthesia day TTBAP magnitude (p=0.008) and variability (p=0.044) measures were significantly lower than the control day, regardless of vision. Anesthesia of the lateral ankle ligamentous structures significantly reduced the magnitude and variability of TTBAP measures. These findings are similar to deficits found in those with chronic ankle instability.