Abstract
Introduction: The factors causing chronic instability, a common sequela of ankle inversion sprains are unclear, despite wide investigation. However, few studies have examined potential factors during the injuring movement. We therefore measured the ability of dancers to control ankle movement during quiet stance and after a perturbation into inversion in a group with chronic instability (N=16) and healthy controls (N=26).
Methods: Control of ankle movement was determined by the magnitude of lateral oscillation at the ankle, measured by a 3SPACE Fastrak. The oscillation was measured during single leg stance (baseline oscillation) for two foot positions, flat and demi-pointe. In both positions, the time taken to return to the baseline oscillation after an inversion perturbation (perturbation time) of 15° for the flat foot and 7.5° for the demi-pointe position was also determined.
Results: The baseline oscillation was significantly smaller (P< 0.005) on the demi-pointe for the sprained group (2.5 ± 0.5 mm) than for controls (4.0 ± 2.3 mm). In addition, the perturbation time for the flat foot was significantly longer (P< 0.05) for the sprained group (2.2 ± 0.4 sec) than for controls (1.8 ± 0.5 sec). However, there was a higher (P< 0.05) failure rate among the sprained group for both the perturbation test with the foot flat and for baseline oscillation on the demi-pointe than among the controls.
Conclusions: Our findings demonstrate altered sensorimotor control in chronically unstable ankles. Those sprainers who successfully completed the tasks “braced” the ankle, allowing a small range of oscillation. The increased perturbation time in the sprained group may reflect a deficit in either detection of inversion movements, peroneal muscle response, or both.
Correspondence should be addressed to Mr Carlos Wigderowitz, Honorary Secretary BORS, University Dept of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School, Dundee DD1 9SY.
