Prolonged reaction time in patients with chronic lateral instability of the ankle.

Impaired proprioception has been suggested as one cause of chronic lateral instability of the ankle. We subjected 15 ankles in 13 patients with symptoms of chronic lateral instability to sudden angular displacement. The reaction times in the peroneus longus and the tibialis anterior muscles were recorded and compared with those from 15 control ankles. Significantly longer ipsilateral reaction time was recorded in the patients (65 ms) compared with the controls (49 ms). We concluded that delayed proprioceptive response to sudden angular displacement of the ankle may predispose an individual to or be a cause of chronic lateral instability of the ankle.