Increasing Foot Toe-out Angle Reduces Inversion Ankle Sprain Risk During Drop-landing Among People With CAI

PURPOSE: People with chronic ankle instability (CAI) are susceptible to ankle inversion sprains during landing, and a moderate increase in foot abduction during landing may have the effect of reducing the risk of sprains. The purpose of this study is to investigate the effects of increased foot toe-out angle on inversion ankle sprain risks during drop landing among people with CAI, represented by the peak ankle inversion angle, peak inversion angular velocity, and the peak inversion time, and explore the relationships of toe-out angle and the representative variables. Methods: Thirty participants with CAI (23 males; 21.5±1.4 years; 177.0±7.4 cm; 73.1±8.2 kg) were recruited. They dropped down from a 30 cm high platform and landed on a trap door apparatus bilaterally, one of the two platforms would tile with 24° inversion and 15° plantarflexion, and the position of the two platforms could be interchanged so the affected limb could be landed on the trap door platform. They landed in two conditions, namely, natural landing (NL) and toe-out landing (TL) conditions, the latter has a higher foot toe-out angle of about 120 - 150% of that in the former condition. The kinematic data were captured using a twelve-camera motion capture system. Paired-sample t-tests and Pearson correlation analysis were used to analyze data. Results: Compared to NL condition, participants showed a decreased peak ankle inversion angle (NL: 7.53±1.07°, TL: 5.56±0.98°, p<.001, Cohen’s d=1.993), a slower peak inversion angular velocity (NL: 23.64±2.31°/s, TL: 18.94±2.69°/s, p=.053, Cohen’s d=0.751), and an earlier peak inversion time (NL: 110.78±8.99 ms, TL: 84.43±11.63 ms, p=.001, Cohen’s d =1.346) in the TL condition. The foot toe-out angle during drop landing was negatively correlated with the peak ankle inversion angle (p=.005, r=-.374), peak inversion angular velocity (p=.006, r=-.356), and the peak inversion time (p=.001, r=-.451). Conclusion: Increasing the toe-out angle during drop landing could reduce the peak ankle inversion angle and advance the peak inversion time, thereby reducing the risk of inversion ankle sprains among people with CAI.