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.
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