The "Ankle Instability Instrument": Cross-cultural adaptation and validation in French.

BACKGROUND: Functional ankle instability affects 20-40% of individuals who have already suffered from a sprain. Such dysfunctions are difficult to diagnose. Therefore, the information provided by self-administered questionnaires is essential. Thus, the Ankle Instability Instrument (AII) was developed and initially validated in English. Our goal is to create a French version of the instrument, named AII-F, by scrupulously respecting the cultural adaptation phases and to make sure the new instrument has good psychometric properties. METHODS: International recommendations have been rigorously followed for the cultural adaptation and the French-translation phase. Six steps are recommended: I) two initial translations from English to French; II) synthesis of the two versions; III) back-translations from French to English; IV) comparisons between the back-translations and the original questionnaire by the expert committee; V) pretest; and VI) approval of the final French version of the AII. In order to validate this French-translation, 91 subjects suffering from ankle instability matched to 91 healthy subjects were asked to complete the AII-F. The Short Form Health Survey (SF-36) was used as a comparative questionnaire as well as the French Cumberland Ankle Instability Tool (CAIT-F). The psychometric properties of the questionnaire were evaluated by determining the test-retest reliability after a 10-14-day interval, the internal consistency, construct validity, and the floor/ceiling effects. RESULTS: The French-translation did not pose a problem and could be validated by the expert committee. The AII-F showed a very good test-retest reliability for the total score, with an Intra Class Coefficient of 0.983. The internal coherence is high with an alpha coefficient of Cronbach of 0.861. The association of the AII-F with the CAIT-F was high, for the summary of the physical component of the SF-36, meaning a great convergent validity. The other subscales of the SF-36 (mental health) were weakly correlated with the AII-F, reflecting good divergent validity. An optimal cut-off score was obtained to dissociate pathological patients from healthy subjects: when the subject responded to "yes" 5 times or more, he is considered, with a very high degree of confidence, to be pathological. CONCLUSION: The AII-F is reliable and valid for evaluating and measuring functional ankle instability.