Reliability and validity of the Turkish version of the Foot Function Index in patients with foot disorders

Background/aim: The Foot Function Index (FFI) is a valid, reliable, and widely used self-reported questionnaire for the foot. The purpose of this study was to provide evidence for the validity and reliability of the Turkish version of the FFI (FFI-TR) among patients with foot disorders such as plantar fasciitis, hallux valgus, pes planus, and hammertoe deformities. Materials and methods: One hundred and fifty-nine patients with foot disorders were enrolled. The psychometric properties of the previously translated and adapted FFI-TR were assessed. The internal consistency and test-retest reliability were evaluated. Construct validity was examined for correlations with the Short Form-36 (SF-36) questionnaire. Results: Cronbach's alpha ranged between 0.821 and 0.938. Reproducibility was satisfactory, with intraclass correlation coefficient values between 0.960 and 0.985. Weak correlations were found between FFI-TR and some SF-36 subscales for validity (|rho| < 0.30). There was a ceiling effect for the activity limitation subscale. There were no floor effects for any items or application times. Good accuracy was determined for all scores. Conclusion: FFI-TR is a reliable and valid scale. This tool can be used in routine practice and clinical research for evaluating foot disorders and foot-related functional impairments.