Objective: Transcultural adaption of the two most widely used and accepted functional indices in ankylosing spondylitis, the Bath Ankylosing Spondylitis Functional Index (BASFI) and Dougados Functional Index CD-FI). Methods: The instruments were translated and tested for internal consistency (Cronbach's coefficient alpha), test-retest reliability (intraclass correlation coefficient, ICC), construct validity (testing for association with Schober's test, finger floor distance, occiput wall distance, frequency and duration of awakenings at night, and a visual analog scale pain), and responsiveness (standardized response mean, SRM). Results: The study sample consisted of 72 patients of a randomized, controlled clinical trial receiving either Diclofenac or placebo. Visual assessment of distribution patterns revealed a ceiling effect of both instruments. Both questionnaires had a high internal consistency (Cronbach alpha: 0.81 [BASFI], 0.85 [D-FI] and a high test-retest reliability (ICC: 0.92 [BASFI], 0.89 [D-FI]). The limited responsiveness to Diclofenac treatment (SRM: 0.46 [BASFI], 0.33 [D-FI]) may be related to the selected study sample. The BASFI was significantly correlated with all tested validation parameters. The D-FI was only significantly correlated with finger floor distance, occiput wall distance, and duration of awakenings at night. Conclusion: The transculturally adapted version of both functional indices are valid. reliable, and internally consistent. Because of psychometric advantages, the BASFI may be preferred in clinical trial settings.
