Cross-cultural adaptation and validation of the Thai version of the functional index for hand osteoarthritis (FIHOA)

Background The Functional Index for Hand Osteoarthritis (FIHOA) is a simple tool to assess functional impairment for hand OA patients. The purpose of this study was to translate the FIHOA into the Thai language, and validate it in Thai hand OA patients. Methods The FIHOA was translated into Thai (T-FIHOA) according to the principles of cross-cultural adaptation and administered to 102 hand OA patients recruited between September 2020 and July 2021 together with the modified Health Assessment Questionnaire (mHAQ), Disabilities of the Arm, Shoulder and Hand (DASH), and visual analogue scale (VAS) for hand pain. Spearman's correlation coefficient and intraclass correlation coefficient (ICC) were used to check the test-retest reliability of each item and the total scores in the translated questionnaire. The internal consistency reliability was evaluated using Cronbach's alpha. The external construct validity was assessed using correlations between the T-FIHOA, mHAQ, DASH and hand pain VAS. Results The T-FIHOA had a unidimensional structure. The ICC was > 0.9 and the Cronbach's alpha of 0.92 indicated excellent reliability and internal consistency, respectively. The external validity tests indicated moderate correlation with the hand pain VAS (r = 0.37, P < 0.01) and moderate to strong correlations with the mHAQ (r = 0.63, P < 0.01), and DASH score (r = 0.52, P < 0.01). The T-FIHOA had the highest effect size (ES) and standardized response mean (SRM) (- 0.37 and - 0.58 respectively) among all questionnaires except for the VAS when assessing changes between baseline and week 4. Conclusions The T-FIHOA is a good and reliable assessment tool freely available for practitioners/researchers to evaluate functional impairment in Thai hand OA patients.