Posterior-caudal talar displacement and muscle stiffness during ankle dorsiflexion in chronic ankle instability: A cross-sectional ultrasonographic study.

BACKGROUND: Restricted ankle dorsiflexion range of motion is a common impairment in individuals with chronic ankle instability and may be related to altered talar kinematics. However, the relationship between talar displacement during dorsiflexion and gastrocnemius muscle stiffness remains unclear. This study compared posterior and caudal talar displacement during ankle dorsiflexion, measured using ultrasonography, and medial and lateral gastrocnemius muscle stiffness between individuals with chronic ankle instability and controls. METHODS: This cross-sectional study included 40 male participants (chronic ankle instability group: n = 20 feet; control group: n = 20 feet). Ankle dorsiflexion range of motion was assessed under non-weight-bearing and weight-bearing conditions. Posterior and caudal talar displacement were measured at 0°, 10°, and 20° of ankle dorsiflexion using B-mode ultrasonography. Muscle stiffness of the medial and lateral gastrocnemius was evaluated using a MyotonPRO device. Group (chronic ankle instability vs. control) and dorsiflexion angle served as the between-subject and within-subject factors, respectively, in a two-way repeated-measures analysis of variance. RESULTS: The chronic ankle instability group showed significantly smaller posterior talar displacement during ankle dorsiflexion than the control group, with a significant interaction between group and dorsiflexion angle. Between-group differences in posterior talar displacement increased with greater dorsiflexion. For caudal talar displacement, no significant interaction was observed; however, significant main effects of group and dorsiflexion angle indicated that the chronic ankle instability group exhibited smaller caudal talar displacement than the control group, and caudal talar displacement increased with increasing dorsiflexion angle in both groups. For muscle stiffness of both the medial and lateral gastrocnemius, no significant interaction or main effect of group was observed, whereas a significant main effect of ankle dorsiflexion angle indicated that muscle stiffness increased with increasing dorsiflexion angle. CONCLUSIONS: Individuals with chronic ankle instability exhibited reduced posterior and caudal talar displacement during ankle dorsiflexion compared with controls, whereas no between-group differences were observed in medial and lateral gastrocnemius muscle stiffness. These findings may provide fundamental information for the assessment of dorsiflexion limitation in individuals with chronic ankle instability.