The effects of ankle bracing on motion of the knee and the hip joint during trunk rotation tasks

Background. The use of prophylactic ankle braces is common during athletic activities since the ankle is one of the most commonly injured joints. Past studies have focused on the effects of ankle braces on ankle movement restriction, preventing injuries, proprioception, balance and athletic performance. However, the influence of ankle restriction on other joints has not been studied. The constraint of ankle movement may lead to an increased loading on the knee joint, which could be a potential risk of knee injuries during athletic activities. The primary goal of the current study was to determine quantitatively the effect of an ankle brace on the knee axial rotation during two different trunk turning tasks. Methods. Ten healthy subjects performed trunk turning movements while standing on one leg: turning sideways to catch a ball and turning sideways to touch a target with the shoulder. The tasks were performed with and without an ankle brace worn on the supporting leg. The trunk axial rotation in reference to the floor and three dimensional joint angular motions of the ankle, knee and hip were determined. Findings. The use of an ankle brace resulted in reduced trunk axial rotation during the ball catching tasks, and increased knee axial rotation during the target touching tasks. Interpretation. The results of this study showed that the effect of the ankle brace on the knee axial rotation depended on the context of the tasks performed. Under situations that required forceful trunk turning movement while standing on a single leg, the ankle braces may cause an increase in the knee axial rotation indicating higher risk of knee injury.