17-Italian Foot Function Index with numerical rating scale: Development, reliability, and validity of a modified version of the original Foot Function Index

•The painful foot and ankle conditions limit the activities of daily living and are the leading cause of immobility and disability.•FFI is one of the most frequently used self-reported questionnaires that is used across national and international clinical and research communities.•The adapted 17 Italian Foot Function index is a reliable and valid outcome measure that showed more specific and sensitive properties than a generic questionnaire such as the LEFS.

BackgroundClinical research quantifies symptoms and signs of pain.ObjectiveTo develop a brief outcome measure to assess foot and ankle conditions, the psychometric properties of a modified version of the original Foot Function Index (FFI) were examined.MethodsEighty-six subjects with musculoskeletal foot and ankle disorders were enrolled. The internal consistency and test–retest reliability were evaluated by using Cronbach's α and intraclass correlation coefficient (ICC). Criterion validity was tested by Pearson's correlation coefficient between 17 items of the Italian FFI (17-IFFI) and the Lower Extremity Functional Scale (LEFS). The responsiveness was calculated using the receiver operating characteristic curve (ROC).ResultsCronbach's Alpha was 0.95 (95% CI: 0.92, 0.99). The intra-interviewer and inter-interviewer ICC values were, respectively, 0.92 (95% CI: 0.88–10 0.96) and 0.90 (95% CI: 0.89–0.94). Correlations between the 17-IFFI scores and the LEFS scores were −0.564 and −0.456 at the initial and at the end of the treatment, respectively. The ROC analysis revealed an area under the curve of 0.732 (95% CI: 0.61–0.82) for the 17-IFFI and 0.633 (95% CI: 0.52–0.71) for the LEFS score.ConclusionsThe 17-IFFI is a reliable and valid scale and we recommend its application to evaluate the effectiveness of a treatment in patients with musculoskeletal foot and ankle disorders.