Movement Control And Cortical Activation In Functional Ankle Instability

Abstract

Background: Functional ankle instability (FI) is a common development following first-time lateral ankle sprain, resulting in functional limitations. Local tissue damage has not been a satisfactory explanation. Evidence exists of changes in motor control within the central nervous system in individuals with FI. Further investigation of the nature of these changes is warranted. Methods: Twenty subjects with FI and twenty healthy control subjects allowed comparisons between ankles within groups and between groups. Two primary methods of investigation were used. A kinematic analysis using electromagnetic motion capture was used during a step down task to assess repeatability and variation in patterns of ankle dorsiflexion/plantarflexion and inversion/eversion motion and speed and phase timing characteristics. A normalized coefficient of multiple correlations was used for motion cycle comparisons, and means and variance were compared for discreet time variables. Motor control was measured with an accuracy index from an ankle tracking task. A sub-group of 8 right-involved FI subjects and 10 control subjects underwent functional magnetic resonance imaging to detect cortical activation in sensorimotor areas while performing the tracking task. Results: With the step down task no between-group differences in the repeatability of ankle motions were found, although both groups showed greater variability in inversion/eversion than dorsiflexion/plantarflexion. Increased ankle instantaneous angular speed when contacting the step was found in the FI subjects, with trends to reversing instantaneous linear velocity and more rapid weight acceptance also noted. No differences in tracking accuracy were identified; however, differential patterns of lateralization of cortical activation were found within groups between ankles during the task, with greater contralateral hemisphere activity in the primary motor area and more symmetrical activity in the primary sensory cortex (S1) and supplementary motor areas in FI subjects tracking with the involved ankle than was observed in control subjects tracking with the right ankle. Between-group comparisons found areas of greater activation in left S1, premotor cortex, and anterior cingulate gyrus compared to control subjects. Conclusions: The results of this study support that processing differences exist at the cortical level between FI and healthy control subjects. Motor performance differences are also present.