The Foot Function Index: a measure of foot pain and disability.

A Foot Function Index (FFI) was developed to measure the impact of foot pathology on function in terms of pain, disability and activity restriction. The FFI is a self-administered index consisting of 23 items divided into 3 sub-scales. Both total and sub-scale scores are produced. The FFI was examined for test-retest reliability, internal consistency, and construct and criterion validity. A total of 87 patients with rheumatoid arthritis were used in the study. Test-retest reliability of the FFI total and sub-scale scores ranged from 0.87 to 0.69. Internal consistency ranged from 0.96 to 0.73. With the exception of two items, factor analysis supported the construct validity of the total index and the sub-scales. Strong correlation between the FFI total and sub-scale scores and clinical measures of foot pathology supported the criterion validity of the index. The FFI should prove useful for both clinical and research purposes.