Background: Functional ankle instability (FAI) is the tendency of the foot to 'give way'. Identification of Functional Ankle Instability questionnaire (IdFAI) is a newly developed questionnaire to detect whether individuals meet the minimum criteria necessary for inclusion in an FAI population. However, the reliability of the questionnaire was studied only in a restricted age group.
Aim: The purpose of this investigation was to examine the reliability of IdFAI across different age groups in adults.
Materials and methods: One hundred and twenty participants in the age group of 20-60 years consisting of 30 individuals in each age group were asked to complete the IdFAI on two occasions. Test-retest reliability was evaluated by intraclass correlation coefficient (ICC2,1).
Results: The study revealed that IdFAI has excellent test-retest reliability when studied across different age groups. The ICC2,1 in the age groups 20-30 years, 30-40 years, 40-50 years and 50-60 years was 0.978, 0.975, 0.961 and 0.922, respectively with Cronbach's alpha >0.9 in all the age groups.
Conclusion: The IdFAI can accurately predict if an individual meets the minimum criterion for FAI across different age groups in adults. Thus, the questionnaire can be applied over different age groups in clinical and research set-ups.
Keywords: Functional ankle instability; IdFAI; Reliability.