Purpose: The aim of this study was to develop a Dutch language version of the Foot and Ankle Outcome Score (FAOS-DLV) and evaluate its measurement properties according to the definitions of the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN).
Methods: After a standard forward-backward translation procedure, the Dutch version of the FAOS was evaluated for reliability and validity in 110 patients with various hind foot and ankle complaints. Reliability was evaluated by calculation of intraclass correlation coefficients (ICC), Cronbach's alpha for internal consistency, and the smallest detectable change (SDC). Construct validity of the FAOS was assessed by calculation of Spearman's correlation coefficients with similar and dissimilar domains of the SF-36 health survey, American Orthopedic Foot and Ankle Society Ankle and Hindfoot Scale, and visual analogue scales for pain and disability. Dimensionality was tested with confirmatory factor analysis.
Results: Reliability of the FAOS-DLV was good. The ICC of the subscales ranged from 0.83 to 0.88. The minimal value of Cronbach's alpha was 0.76. The SDC at individual level ranged from 18 to 21 and at group level between 2.1 and 2.5. Construct validity was supported by confirmation of 85 % of the hypothesized correlations. Unidimensionality of the FAOS-DLV domains was moderate.
Conclusion: The Dutch version of the FAOS seems to have acceptable measurement properties. The questionnaire can be used for functional assessment of patients with varying hindfoot and ankle symptoms. It is, however, more suitable for clinical evaluation at group level than for monitoring a specific patient.
Level of evidence: Diagnostic study, Level I.