Ankle function during hopping in subjects with functional instability of the ankle joint.

A common mechanism of inversion injury involves a lateral movement producing a hypersupination of the ankle joint. To date, no study has investigated patterns of muscle activity, three-dimensional (3D) joint kinematics and kinetics simultaneously in a group of subjects with functional instability (FI) compared with a non-injured control group during a lateral hopping test. Twenty-six subjects with the subjective complaint of FI of the ankle joint and 24 non-injured healthy control subjects volunteered to participate in the study. We measured 3D lower limb kinematics, kinetics and surface electromyography (EMG) of the rectus femoris, tibialis anterior, peroneus longus and soleus muscle in all subjects during a lateral hop task for the period 200 ms pre- and post-initial contact (IC). FI subjects were observed to have a less-everted position of the ankle joint during the time period from 45 ms pre-IC to 95 ms post-IC (P<0.05). FI subjects were also found to have an increase in pre- and post-IC rectus femoris, tibialis anterior and solues EMG activity. The results suggest that subjects with FI exhibit changes in ankle joint movement and neuromuscular control that could predispose to further injury.