Reliability and validity of the Dutch version of the foot and ankle outcome score (FAOS)

BACKGROUND The Foot and Ankle Outcome Score (FAOS) is a patient-reported questionnaire measuring symptoms and functional limitations of the foot and ankle. Aim is to translate and culturally adapt the Dutch version of the FAOS and to investigate internal consistency, validity, repeatability and responsiveness. METHODS According to the Cross Cultural Adaptation of Self-Report Measures guideline, the FAOS was translated into Dutch. Eighty-nine patients who had undergone an ankle arthroscopy, ankle arthrodesis, ankle ligament reconstruction or hallux valgus correction completed the FAOS, FFI, WOMAC and SF-36 questionnaires and were included in the validity study. Sixty-five of them completed the FAOS a second time to determine repeatability. Responsiveness was analysed in an additional 15 patients who were being treated for foot or ankle problems. RESULTS Internal consistency of the FAOS is high (Cronbach's alphas varying between 0.90 and 0.96). Repeatability can be considered good, with ICC's ranging from 0.90 to 0.96. Construct validity can be classified as good with moderate-to-high correlations between the FAOS subscales and subscales of the FFI (0.55 to 0.90), WOMAC (0.57 to 0.92) and SF-36 subscales physical functioning, pain, social functioning and role-physical (0.33 to 0.81). Low standard response means were found for responsiveness (0.0 to 0.4). CONCLUSIONS The results of this study show that the Dutch version of the FAOS is a reliable and valid questionnaire to assess symptoms and functional limitations of the foot and ankle.