The Structural Index Score and its relation to foot function, disability and physical performance tests in rheumatoid arthritis (RA) — A cross-sectional study

Abstract

ObjectivesTo evaluate the Structural Index Score (SIS) – a clinical foot deformity assessment index developed for RA, and to compare its results with foot function, disability and physical performance tests. MethodsIn this cross-sectional study, 104 patients with foot pain were evaluated according to SIS score, subscales (Forefoot SIS and Rearfoot SIS) and items. Results were compared with the Foot Function Index (FFI), the Health Assessment Questionnaire Disability Index (using lower limbs items: LL-HAQ), and physical performance tests: Berg Balance Scale (BBS), the Timed Up and Go test (TUG) and the 5-Time Sit down-to-Stand up Test (SST5). ResultsThere was a weak correlation of SIS score with FFI and LL-HAQ. Rearfoot SIS was correlated with FFI, LL-HAQ and worse performance in BBS, TUG and SST5. Regarding Rearfoot SIS items, the ankle ROM was correlated to all studied outcomes, the calcaneus varus/valgus was correlated with FFI (total, pain and disability subscales) and the planus/cavus deformity with FFI-pain, HAQ-DI and LL-HAQ. Forefoot SIS did not correlate with any outcome measures. In relation to Forefoot SIS items, hallux valgus was associated with foot function (FFI-total, pain and disability subscales), the MTPs joints subluxation was correlated with FFI-disability subscale, and the 5th MTP exostosis was associated with FFI-pain. ConclusionSIS score was correlated to impaired foot function (FFI) and disability (LL-HAQ). Rearfoot SIS was correlated to worse performance on FFI, LL-HAQ, BBS, TUG and SST5. SIS score index can be a useful tool to evaluate the rheumatoid foot deformities, but a better graduation of foot deformities should add sensitivity to this method.