Validation of a Russian-language version of the Foot Functional Index (FFI) questionnaire
The Foot Functional Index (FFI) questionnaire most completely reflects the functional status of patients with joint diseases of the feet. Objective: to study the psychometric properties of a Russian-language version of the FFI questionnaire. Patients and methods. The reliability, sensitivity, and validity of the Russian-language version of the FFI questionnaire were assessed in 55 patients with rheumatoid arthritis (RA). The investigators checked the reliability by assessing the internal consistency (calculating Cronbach 's alpha) and reproducibility by a test-retest analysis. The criterion validity was evaluated by correlation analysis using HAQ, RAPID3, and pain visual analogue scale (VAS) scores. The sensitivity of FFI was studied by comparing its dynamics with RAPID3 changes during treatment. Results. Evaluating the internal consistency yielded a high Cronbach 's alpha (0.78). The test-retest analysis demonstrated a significant correlation (0.83) between the results of primary and secondary testing. Assessing the criterion validity showed a high or near-high relationship to the scores of RAPID3 (0.78), HAQ (0.69), and pain VAS (0.76). The group of patients who were observed to have a decrease in disease activity according to RAPID3 from a high (16.2+4.1) to moderate (10.5+5.2) degree displayed a more marked reduction in FFI (AFFI = 20.5+2.3) than the group that did not exhibit significant changes in disease activity (AFFI = 6.9+3.4). Conclusion. FFI is a reliable, valid, and sensitive tool to evaluate the functional status of patients with foot diseases in RA.