Thin and Plain Supplementary Motor Area in Chronic Ankle Instability: A Volume and Surface-based Morphometric Study.

ABSTRACT

CONTEXT The supplementary motor area (SMA) is involved in the functional deficits of chronic ankle instability (CAI), but the structural basis of its abnormalities remains unclear. OBJECTIVE: To determine the differences in volume and surface-based morphological features of SMA between patients with CAI and healthy controls, and their relationship with the clinical features of CAI. DESIGN: Cross-sectional study. SETTING: Sports medicine laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 32 CAI patients (10 females; age 32.46 ± 7.51 years) and 31 healthy controls (12 females; age 29.70 ± 8.07 years) participated in this study. MAIN OUTCOME MEASURE(S) Participants perform T1 structural magnetic resonance imaging and calculate volume and surface-based morphological features of SMA subregions. These included anterior and posterior subdivisions of Brodmann's area 6 m (6 ma/6 mp), and supplementary and cingulate eye fields. Between-group comparisons and correlation analysis with clinical features of CAI were performed. RESULTS: Moderately thinner 6 mp (Cohen's d = -0.61) and moderately plainer 6 ma (Cohen's d = -0.70) were observed in patients compared with controls. Before and after regressing out the covariates, the thinner 6 mp was correlated with the lower foot and ankle ability measure scores of daily activities (r-before=0.400, r-after = 0.449). CONCLUSIONS: Patients with CAI had a thinner posterior subdivision (motor-output site) and a plainer anterior subdivision (motor-planning site) of SMA than that of controls. The thin motor-output site of the SMA is associated with ankle dysfunction in patients. These morphologic evidence of maladaptive neuroplasticity in SMA might promote more targeted rehabilitation of CAI.