Commentary: Functional Ankle Instability Revisited.

Chronic ankle instability is a clinical problem frequently seen in athletes. Various complicated mechanical and neuromuscular factors seem to be involved in chronic ankle instability. The purpose of this special communication is to revisit the concept of functional ankle instability and to discuss its clinical relevance. The 2 hypothesized causes of chronic ankle instability have been labelled mechanical instability and functional instability. Mechanical instability (MI) is defined as ankle movement beyond the physiologic limit of the ankle’s range of motion. The term ‘‘laxity’’ is often used synonymously with MI. Functional instability (FI) is defined as the subjective feeling of ankle instability or recurrent, symptomatic ankle sprains (or both) due to proprioceptive and neuromuscular deficits.