Variability of motion in individuals with mechanical or functional ankle instability during a stop jump maneuver.

BACKGROUND: Movement variability may influence episodes of instability following lateral ankle sprain.
METHODS: Sixty-three recreational athletes with a history of moderate-severe ankle sprain were recruited. Mechanically and functionally unstable ankle groups had 2 episodes of instability in the last year. Mechanically unstable had clinically lax lateral ankle ligaments; functionally unstable and copers did not. Copers had a history of sprain but no residual instability. Lower extremity 3-dimensional kinematics and ground reaction forces were measured during a 2-legged stop jump. Average ensemble curves of eight trials normalized to 100% of stance phase were created. The coefficient of variation and average standard deviation of the ensemble curves of each variable were identified. A log(e) (ln) transformation was performed on the data. One-way ANOVAs with Tukey post hoc testing were utilized with alpha=0.05.
FINDINGS: The functionally unstable group demonstrated greater mean (standard deviation) ln coefficient of variation ankle inversion/eversion 3.56 (1.19) than the mechanically unstable 2.77 (0.95) and copers 2.74 (1.05) (P=0.05 and P=0.04; eta(p)(2)=0.12), and greater ln standard deviation ankle inversion/eversion 1.07 (0.78) than copers 0.61 (0.31) (eta(p)(2)=0.13). The mechanically unstable group demonstrated greater ln coefficient of variation anterior-posterior ground reaction force 3.69 (0.27) than functionally unstable 3.43 (0.25) (P=0.02; eta(p)(2)=0.13).
INTERPRETATION: Functionally unstable individuals demonstrated greater ankle frontal plane movement variability during a stop jump, which may increase risk of instability. Mechanically unstable participants demonstrated greater anterior-posterior ground reaction force variability, which may indicate difficulty mitigating landing forces with lax ligaments. Movement variability may influence episodes of ankle instability.