Functional Ankle instability (FAI) is defined as the subjective feeling of Ankle instability or recurrent, symptomatic Ankle sprains due to proprioceptive and neuromuscular deficits (1). Ankle sprains have the highest incidence rate, with 32% to 47% of these people having history with symptoms including sensations of giving way, subsequent sprains, and instability (2, 3). After initial injury, a high proportion of patients experienced residual symptoms, such as pain, subjective instability, and repetitive Ankle sprain (4, 5). . . .

Introduction: The Cumberland Ankle instability Tool (CAIT) is a valid instrument for determining the presence and severity of functional Ankle instability. This questionnaire was recently cross-culturally adapted into Persian; however, the reliability of the Persian version has not been examined in athletes. CAIT has also been used with various independently-selected cut-off scores to determine instability. Objective: The present study was conducted to evaluate the psychometric properties of the Persian version of CAIT and to determine its optimal cut-off score in athletic populations. Method: One-hundred and sixteen athletes (volleyball, basketball and track and field players) over 18 years old both with and without Ankle instability completed the Persian version of the CAIT. The internal consistency, test-retest reliability and discriminative ability of the tool were assessed. A receiver operating characteristic (ROC) curve was drawn to confirm the cut-off point of the Persian version of CAIT using the Youden index. Results: The average CAIT score was 25. 14± 4. 98 for the right and 25. 76± 4. 94 for the left Ankle. The Persian version of CAIT had a good internal consistency (Cronbach's α of 0. 78 for the right Ankle and 0. 79 for the left Ankle) and substantial reliability (ICC2, 1 = 0. 88; 95% CI: 0. 86 – 0. 90) in athletes. No ceiling or floor effects were observed. The optimal cut-off score for discriminating between athletes with and without FAI was 24. Conclusion: The Persian version of CAIT was shown to be a reliable tool for assessing functional Ankle instability among Iranian athletes.