Cross-cultural adaptation and validation of the Foot Function Index for use in German-speaking patients with foot complaints
Related Experiment Video
Updated: Jun 26, 2026
Evaluating the Function of the Foot Core System in the Elderly
Published on: March 11, 2022
Florian D Naal1, Franco M Impellizzeri, Martin Huber
1Department of Orthopaedic Surgery, Foot and Ankle Center, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland. florian.naal@gmail.com
Background:
The purpose of this study was to cross-culturally adapt the Foot Function Index (FFI) for use in German-speaking patients with foot complaints.
Materials And Methods:
The FFI was adapted for the German language according to the recommended forward/backward translation protocol. The following metric properties were assessed in 53 consecutive patients (mean age, 57.2 years; 39 women) undergoing foot surgery at our department: feasibility, reliability (intraclass correlation coefficient ICC), internal consistency (Cronbach's alpha, CA), and construct validity (correlation with the Short Form (SF-36), a VAS assessing pain, a VAS assessing function, and the University of California at Los Angeles (UCLA) activity scale.
Results:
The German FFI (FFI-D) comprised 18 items separated into a pain and a disability subscale. Completion of the FFI-D was feasible. The reliability and the internal consistency were both excellent with an ICC of 0.98 and a CA of 0.97 for the total score. We found moderate to high correlations between the FFI-D and the physical related SF-36 domains (r = -0.43 to -0.80), the VAS pain (r = 0.81), the VAS function (r = 0.77), and the UCLA (r = -0.52). Correlation coefficients between the FFI-D and the mental health related SF-36 domains were significantly lower (r = -0.08 to -0.32; p < 0.01), indicating divergent validity.
Conclusion:
The German version of the FFI is a reliable and valid questionnaire for the self-assessment of pain and disability in German-speaking patients with foot complaints.