Ankle Joint Stiffness and Fibula Position among Individuals with Ankle Instability, Copers, and Controls

Abstract

Ankle instability (AI) develops in 40-75% of people after acute ankle trauma, and mechanical adaptations such as altered joint stiffness and a mal-positioned fibula have been suggested as a cause. However, 25-60% of people who sprain their ankle can maintain high level activities and are thought to have a coping mechanism (copers) which would limit common mechanical adaptations from occurring and allow copers to function as if they were not injured. Studying differences in mechanical adaptations between copers and AI patients may provide insight into the mechanisms of AI. PURPOSE: To determine if ankle joint stiffness and fibula position differ between healthy, coper, and AI groups. METHODS: 72 subjects (21.4±2.4 yrs), 24 per group were assessed for the magnitude of their mechanical adaptations during a single test session. Ankle joint stiffness was determined by the slope of the curve generated by an instrumented arthrometer during an anterior drawer test. Fibula position was calculated by measuring the distance between the anterior margin of the fibula and the anterior margin of the tibia from a lateral radiographic image. Separate two-way ANOVAs were used to determine group (healthy, coper, AI) and limb (side to side) differences. RESULTS: A significant group main effect [F(2,138)=3.16, p=.045] revealed that copers (14.98±2.7N/mm) and AI (14.95±2.0N/mm) subjects had significantly greater ankle joint stiffness than healthy controls (14.00±2.64N/mm). However, no group or limb main effect or group x limb interaction was seen for fibula position. A frequency analysis revealed that more copers (n=8, 33%) and non-copers (n=7, 29%) had a mal-positioned (anteriorly positioned) fibula on the involved limb greater than the standard deviation of the control group (3.3mm) when compared to the healthy reference group (n=2, 8%). CONCLUSION: Ankle joint stiffness is increased in subjects who have had at least one lateral ankle sprain but fibula position does not differ across groups based on AI status. In addition, some but not all subjects who had at least one lateral ankle sprain will develop an anterior positioned fibula. The results suggest that structural adaptations are not part of the coping mechanism that prevents the development of AI. Supported by a College of Healthy and Human Performance, University of Florida Grant