Cross-cultural adaptation and validation of the Korean version of the facial disability index in patients with facial palsy

Objective To translate and culturally adapt the facial disability index (FDI) into Korean following established guidelines, and to evaluate its reliability and validity in patients with facial palsy. Methods The translation process followed Beaton's cross-cultural adaptation methodology, involving forward translation, back translation, expert committee review, and prefinal testing. This prospective cross-sectional observational validation study included 100 adult patients with facial palsy recruited from a facial palsy center between May and July 2021. Reliability was assessed using Cronbach's α for internal consistency and intraclass correlation coefficient (ICC) for test–retest reliability (3-week interval). Construct validity was examined using Spearman's correlation between the Korean FDI and House–Brackmann (HB) grade, 36-Item Short Form Health Survey (SF-36), and Synkinesis Assessment Questionnaire. Results The Korean FDI demonstrated acceptable internal consistency (total Cronbach's α = 0.783; physical function = 0.810; social/well-being = 0.683). Test–retest reliability showed ICC values of 0.762 for physical function and 0.645 for social/well-being. The physical function subscale correlated moderately with HB grade ( r = –0.461), whereas the social/well-being subscale correlated strongly with SF-36 mental component summary scores ( r = 0.639). These findings were generally consistent with Turkish and Spanish validation studies, although ICC values were slightly lower, possibly due to the longer retest interval and inclusion of patients undergoing treatment. Conclusions The Korean version of the FDI is a reliable and valid patient-reported tool for assessing functional and psychosocial outcomes in patients with facial palsy. Its use may enhance patient-centered treatment planning, monitor treatment responses, and facilitate standardized data collection in clinical research. Future studies should examine its responsiveness in larger and more diverse patient populations and explore its application in clinical trials or real-world studies of integrative treatment strategies. Embedding the Korean FDI within multidisciplinary care frameworks may further strengthen evidence for patient-centered management of facial palsy.