Measuring Functional Ankle Instability

Abstract

1148 Functional ankle instability (FAI) is a common chronic condition in which an individual's ankle “gives way” and rolls with activity but is not due to joint laxity. PURPOSE: To compare passive joint position sense (JPS), time to stabilization (TTS), and electromyography (EMG) of ankle musculature in recreational athletes with and without FAI. METHODS: 20 recreational athletes aged 18–25 years were placed into functionally stable (n = 10) or unstable ankle groups (n = 10). We measured unilateral range of motion and passive angle reproduction in plantarflexion, dorsiflexion, inversion, and eversion. Unilateral TTS and mean EMG amplitude of the tibialis anterior, peroneals, lateral gastrocnemius, and soleus muscles for a single leg jump-landing were measured. TTS is the point in time after impact when vertical, anterior-posterior, and medial-lateral jump landing ground reaction forces (GRF) resemble static stance. Unstable ankle subjects landed on the unstable ankle and stable subjects landed on the ankle matched for limb dominance. EMG was measured from 200ms prior to 1000 ms after ground contact. Bivariate Pearson correlations were performed for exploratory analysis. RESULTS: Independent samples t-tests showed no significant group differences in range of motion, JPS error scores in any direction, or TTS measures in the medial-lateral plane. No significant group differences were revealed on peak vertical GRF normalized to body mass. The unstable ankle group had significantly longer anterior-posterior TTS (P < .05). Eight repeated-measures t-tests were used to compare the EMG of the four muscles before and after landing in the two groups. The stable ankle group had significantly higher mean soleus EMG amplitude after landing (P< .05). No other significant differences were found for mean EMG amplitudes before or after landing. Pearson bivariate correlations demonstrated significant positive relationships between plantarflexion-dorsiflexion (r = 0.45;P < .05) and plantarflexion-eversion JPS error scores (r = 0.54;P < .05). Negative relationships were found between post-landing EMG mean amplitudes and JPS error scores (r = −0.45;P< .05) CONCLUSIONS: Subjects with FAI demonstrated deficits in landing stability and soleus muscle activity during landing that may represent chronic adaptive changes following injury. The unstable ankle group may undergo decreased closed kinetic chain ankle dorsiflexion upon landing, resulting in decreased eccentric loading of the soleus.