Ankle sprain occurs by a sudden and extreme inversion and plantarflexion at the ankle joint to cause ligamentous
injuries. A portion of
ankle sprain patients experience recurrent
ankle sprains and develop chronic ankle instability (CAI). The present CAI animal models are single events with severe ligamentous injury using surgical transection of ligaments or manually overextending the ankle. Purpose: To simulate the mechanical and recurrent
sprain injuries in CAI patients, we established a new ankle instability model with multiple
ankle injuries using a self-designed machine to
sprain the ankle with a controlled inversion angle and speed. Methods: Male C57BL/6J mice were used and respectively subjected to a
sham operation, calcaneofibular ligament (CFL) transection, and mechanical
ankle sprains. Three mechanical
sprains were performed on the 13th and 185th day after the initial mechanical
ankle sprain. Results: The first mechanical
sprain and CFL transection induced
ankle injury as indicated by an average of a 62% decrease in ankle pressure pain threshold and a 114% increase in the ankle thickness compared with the contralateral untreated ankle. The second and third mechanical
sprains induced recurrent
ankle injuries. The foot slips during beam tests were increased after mechanical
ankle sprains but not after CFL transection, indicating the induction of motor balance deficits. Multiple mechanical
ankle sprains induced significant gait changes in longer duration of stance (an average of 194% increase), swing (134%), and step cycle (147%) compared with CFL transection or
sham operation, and slower walking speed (78% reduction) and shorter step distance (91%) after the third
sprain. Conclusion: These results elucidate that multiple mechanical
sprains, which induce recurrent
ankle injuries, balance deficits, and gait changes, are a good model for investigating the mechanisms of CAI induced by recurrent
sprain injuries.