27 Too lax: mechanical ankle instability impairs joint control in the ankle sprains mechanism

Abstract

Background Lateral ankle sprains can result in the development of chronic ankle instability (CAI). It remains an open question how mechanical ankle instability (MAI), i.e., an excessive inversion/anterior laxity, affects joint control directly in ankle sprain mechanisms. Objective The purpose of the present study was to evaluate if individuals with MAI have impaired ankle joint control in a close-to-injury sprain mechanism compared to individuals with functional instability (FAI) but without MAI and compared to healthy controls. Design Cross-sectional study. Setting Laboratory setting. Participants Nineteen participants with MAI+FAI (indicated by a manual stress test of an orthopaedist and by a CAIT score ≤24) were compared to 9 subjects with FAI (CAIT-score ≤24 but no signs of mechanical instability) and 18 healthy controls (no signs of mechanical instability and CAIT score ≥28). Interventions Using a tilt-platform an ankle sprain mechanism was imitated during standing, walking and hopping trials. Main outcome measurements Dynamic ankle joint control was assessed by the means of three-dimensional motion analysis and electromyography of the peroneus longus and tibialis anterior muscles. Results Persons with MAI+FAI had a significantly increased ankle inversion angle (+5°) and inversion velocity (+50°/s) compared to those with solely FAI and controls in the walking and hopping conditions. Moreover, MAI+FAI had a significantly increased pre-activation of the m. peroneus longus compared to solely FAI (+40%) in the hopping condition. No differences between groups were found regarding plantar flexion and internal rotation as well as muscle activities during the standing task (i.e. after release of the tilt-platform). Conclusions The present study demonstrates that MAI is able to impair frontal plane joint control in a close-to-injury situation. This probably makes these individuals more prone to sprain their ankle and suggests that additional mechanical support like braces or even surgery may be a viable option for those with MAI. In addition, the study highlights that dynamic experimental test conditions are needed to further unravel the mystery of CAI.