Objective: To assess the reliability and validity of Foot Function Index Thai version [FFI-TH].

Materials and Methods: The cross-sectional descriptive study was conducted in patients with painful foot/ankle problems at Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Foot Function Index [FFI] is a self-administered patient-reported outcomes [PRO] measure for evaluating foot/ankle problems. It comprises three domains including pain, disability, and activity limitation. It was translated into Thai language using internationally recognized translation standards. Internal consistency reliability coefficients and coefficient of stability were calculated to test for reliability. The average test-retest interval was 3.90 days. Construct validity was evaluated by the Pain Visual Analogue Score [VAS-pain], the Visual Analogue Scale Foot and Ankle Thai version [VASFA-TH], and the Medical Outcomes Study [MOS] 36-item short form Thai version [SF36-TH].

Results: Ninety-seven patients were enrolled. Most participants were female (80.47%), with an average age of 45.74 years and an education level of at least bachelor’s degree (81.40%). The most common diagnoses were plantar fasciitis, ankle sprain, and hallux valgus. Median time to onset of problem was 5.5 months. Three domains revealed Cronbach’s alpha coefficient values, as follows, pain subscale (0.94), disability subscale (0.96), and activity limitation subscale (0.72). Intraclass correlation coefficient as 0.92 indicated high stability. Construct validity demonstrated significant correlation between the total and subscale of FFI-TH scores when compared to VAS-pain and SF36-TH for bodily pain, as determined by moderate correlation from Pearson’s correlation coefficients that ranged from 0.5 to 0.7. Average time to complete the FFI-TH was 4.67 minutes. A higher level of impairment will correspond with and result in a higher FFI score.

Conclusion: FFI-TH demonstrated good reliability and validity with appropriate completing time. FFI-TH is suitable to be one of the Thai PRO measures that provide clinical benefit for patients with painful foot/ankle problems.

Keywords: FFI-TH, Foot Function Index, Patient-reported outcome questionnaire, Foot pain, Ankle pain, Validity, Reliability