**1. Introduction**

Ankle sprains are among the most common of sports injuries, and lateral ankle sprains comprise more than 80% of these [1]. Even though most of them heal well with conservative treatment, a 56–74% recurrence rate has been reported [2]. Up to 30% of patients with lateral ankle sprains end up having chronic ankle instability (CAI) [3]. The predictors of patients with single or repeated ankle sprains who may develop CAI include a grade II–III sprain [4], postural instability [5], lower limb muscle weakness or imbalance [6], and decreased ankle dorsiflexion [7].

#### **1.1 Pathophysiology**

The pathophysiology of CAI includes anatomical and/or functional deficiencies. Anatomical factors consist of pathological laxity of ankle ligaments and problematic bony structures such as hindfoot varus [8, 9]. Functional factors include neuromuscular and proprioception impairments [6, 10].

The traditional spectrum of CAI is divided to mechanical instability, which means a structurally unstable ankle and functional instability, which means a perceptionally unstable ankle. Mechanical instability of the ankle can be demonstrated manually or subjectively. Functional instability is much more difficult to evaluate; a comprehensive questionnaire is usually needed for better communication and understanding [11].
