Translation and validation of the German version of the foot and ankle outcome score

Abstract

Outcome assessment is critical in evaluating the efficacy of orthopaedic procedures. The Foot and Ankle Outcome Score (FAOS) is a 42-item questionnaire divided into five subscales, which has been validated in several languages. Germany has no validated outcome score for general foot and ankle pathology. The aim of this study was to develop a German version of the FAOS and to investigate its psychometric properties. Forward and backward translation was executed according to official guidelines. The final version of the FAOS was investigated in 150 patients with various foot and ankle disorders. All patients completed the FAOS, Short Form-36, numeric rating scales for pain and disability, and the Hannover questionnaire. The FAOS was re-administered after 1 week. Test-retest reliability, internal consistency, minimal detectable change, construct validity, and floor and ceiling effects were analyzed. Test-retest reliability and internal consistency of each subscale were excellent (intraclass correlation coefficient, 0.88-0.95; Cronbach's α, 0.94-0.98). The minimal detectable changes of each subscale were 17.1-20.8 at the individual level and 2.0-2.4 at group level. There were moderate to strong correlations between FAOS subscales and physical outcomes and low to moderate correlations between FAOS subscales and mental outcomes. Floor and ceiling effects were not present. The German version of the FAOS is a reliable and valid instrument for use in foot and ankle patients.