Purpose To study validity and reliability of a Japanese version of the Cumberland Ankle Instability Tool and to determine the optimal cutoff score. Methods In this study, the questionnaire was cross-culturally adapted into Japanese. The psychometric properties tested in the Japanese version of the CAIT were measured for criteria validity, internal consistency and test-retest reliability in 111 collegiate soccer athletes. We also established the questionnaire cutoff score for discriminating between individuals with and without CAI. Results There was a significant correlation between the Japanese version of the CAIT and the Karlsson score (r = 0.604, p < 0.001). The questionnaire had a high internal consistency (Cronbach's α = 0.833) and reliability [intraclass correlation coefficient (ICC) = 0.826, 95% confidence interval (CI): 0.732-0.888]. The optimal cutoff score was ≤25, which was consistent with previous reports. Conclusions The Japanese version of the CAIT has been shown to be a valid and reliable questionnaire for determining the presence of CAI. We expect that researchers and clinicians will use the Japanese version of the CAIT in Japan. Implications for Rehabilitation Chronic Ankle Instability (CAI), which not only increases recurrence rate of ankle sprain but also decreases athletic performance, is a residual symptom after ankle sprain. Cumberland Ankle Instability Tool, which has the reliability and validity to assess CAI, will be critically useful in assessment procedure for CAI. It is preferable for clinicians and researchers to use the native language version of the CAIT.
Keywords: CAIT; Japanese version; cross-cultural adaptation; reliability and validity.