Relationship Between Functional Ankle Instability and Postural Control

STUDY DESIGN: Controlled laboratory study using a cross-sectional design. OBJECTIVES: To investigate the relationship between postural control and functional ankle instability during a hop-landing task, and to investigate whether postural control is altered in people with functional ankle instability. METHODS AND MEASURES: Sixty volunteers classified by the Cumberland Ankle Instability Tool (CAIT) scores formed the external control group (CAIT score, >= 28; n = 31) and the instability group (CAIT score, <= 27 and history of at least 1 ankle sprain; n = 29). Postural control was measured with the landing test, in which participants stood on 1 lower extremity for 3 seconds on a step, then hopped down onto a force plate and regained postural stability after landing. The main outcome measurements were time to stability (ITS) after landing for ankle inversion and dorsiflexion, and summated electromyographic (EMG) signal amplitude for the tibialis anterior, soleus, and fibularis longus. The secondary outcomes were the proportion of movement in the frontal plane for hip and ankle, the variability of inversion movement prior to hopping, and the variables from ground reaction force. RESULTS: There were no associations (P>.05) between the CAIT scores and the ITS for ankle inversion (r = -0.25), dorsiflexion (r = -0.04), summated EMG (r = -0.13), and proportion of movement in the frontal plane (r = 0.005). Participants in the instability group took longer to regain stability in inversion and displayed greater inversion variability prejump than the control group (P =.05 and .009, respectively). CONCLUSIONS: Ankle inversion control is affected in people with functional ankle instability in tasks of postural control after landing from a hop. J Orthop Sports Phys Ther 2008,38(12):782-789. doi:10.2519/jospt.2008.2766