The Influence Of Ankle Instability On The Kinetics Of Gait Termination

Abstract

Chronic ankle instability (CAI) is a common occurrence after an ankle sprain. Yet, some people (copers) maintain dynamic activities without recurrent injury. Alterations in both feed-forward and feedback control exist in CAI patients but little is known about alterations in copers. Understanding differences between copers and CAI patients may help elucidate the mechanism of CAI. PURPOSE: To examine control differences among controls, CAI, and copers during gait termination (GT). METHODS: Twenty controls (20.85 ± 1.6yr), 20 with CAI (20.5 ± 1.0yrs) and 20 copers (21.9 ± 2.9yrs) participated. Copers and CAI patients had a previous moderate ankle sprain but copers resumed all pre-injury activity without limitation or recurrent injury while CAI patients had recurrent sprains. Each subject was tested bilaterally (each limb as the lead and brake limb) during ten planned and ten unplanned GT trials. An auditory signal cued subjects to stop during randomly selected trials (unplanned GT) and catch trials ensured that anticipation of the auditory signal did not occur. Ground reaction forces, collected at 1200Hz, from two adjacent force plates were used to calculate the maximum propulsion (lead limb) and braking forces (brake limb). A 3×2×3 mixed model (group [control, CAI, coper], limb [involved/uninvolved], and task [planned GT, unplanned GT, catch]) MANOVA examined differences among force variables. RESULTS: Both control and coper subjects produced significantly less propulsive force than the CAI group (CAI: 11.2 N> healthy and 9.9N > copers). Subsequently, braking forces were higher for CAI patients than controls (45.5N greater) or copers (26.8N greater). CONCLUSION: CAI patients did not reduce their propulsive forces during GT trials (planned and unplanned) to the same extent as controls or copers and relied on greater braking forces to stop forward momentum. This indicates an altered motor program and slower neuromuscular response in CAI patients during GT. Further, both feed-forward and feedback neuromuscular control alterations appear to exist in CAI subjects. Copers, however, produce similar movement patterns as controls suggesting a return to normal neuromuscular control or successful compensation pattern which may represent a potential coping mechanism. Supported by SEATA Grant 2007-1