Dynamic force distribution during level walking under the feet of patients with chronic ankle instability.

OBJECTIVES To examine changes in the pattern of force transfer between the foot and the floor associated with chronically sprained ankles by measuring the peak forces and their timing under several regions of the feet during level walking. METHODS Twelve young male subjects (mean (SD) age 21 (2) years) with recurrent ankle sprains were studied. Seven of them had unilateral and bilateral chronic instability and laxity, and five had bilateral instability. Twelve healthy men (without orthopaedic or medical disease) served as a control group. Subjects walked at their own pace along a 7 m walkway, which included a Mini-EMED pressure distribution measuring system. The variables measured were relative peak force (fraction of body weight) and relative timing (fraction of stance time). These variables were measured under six regions of interest in each foot print: heel, midfoot, medial, central, and lateral forefoot, and toes. RESULTS (a) A significant delay to the time of peak force under the central and lateral forefoot and toes in subjects with chronic ankle instability. (b) A significant decrease in the relative forces under the heel and toes and an increase in the relative forces under the midfoot and lateral forefoot in subjects with chronic ankle instability. (c) In the patients with unilateral instability, there were no significant differences in any of the variables between the injured and non-injured foot. CONCLUSIONS In patients with chronic ankle instability, there is a slowing down of weight transfer from heel strike to toe off, a reduced impact at the beginning and end of the stance phase, and a lateral shift of body weight.