Cross-cultural adaptation and validation of the Foot Function Index for use in German-speaking patients with foot complaints.
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.


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.


CONCLUSIONS
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.
Naal
Florian D
FD
Department of Orthopaedic Surgery, Foot and Ankle Center, Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland. florian.naal@gmail.com
Impellizzeri
Franco M
FM
Huber
Martin
M
Rippstein
Pascal F
PF
D003431:Cross-Cultural Comparison; D005260:Female; D005528:Foot; D005534:Foot Diseases / Q000145:classification*; D005858:Germany; D006801:Humans; D007802:Language; D015141:Los Angeles; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000145:classification*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D014177:Translations