A shortened 10‑item Spine Functional Index: clinimetric properties indicate a reliable, responsive and practical measure.

Abstract

Background: To assess the 10-item Spine Functional Index (SFI-10) clinimetric properties in a general musculoskeletal disorder (MSD) spine population. Ascertain the psychometric characteristics' consistency with the developmental study findings for structural and criterion validity, internal consistency, and floor/ceiling effect; establish the longitudinal characteristics for test-retest reliability, responsiveness, construct validity, and error scores; and clarify practical characteristics of readability, missing responses, and time/errors for completion/scoring related to administrative burden. Methods: A longitudinal study of deidentified spine MSD patients (n = 1317, 53.4% female, age = 18-91yrs, av = 49.5 ± 16.4yrs; neck = 36.5%, mid-back = 8.4%, low back = 56.0%, multi-site = 0.3%) who completed the SFI-10, the Patient Specific Functional Scale (PSFS), and Numerical Rating Scales for Global-function (G-NRS) and Pain (P-NRS). Structural validity used factor analysis, exploratory (EFA) and confirmatory (CFA), plus Rasch analysis. Criterion validity used Spearman's correlation coefficient (r) between the SFI-10 and criteria (PSFS, G-NRS and P-PRS) scores, and construct validity (n = 91, known-groups independent t-test). Internal consistency used Cronbach's alpha (α) and floor/ceiling effects were determined. Subgroups determined reliability (n = 104, intraclass correlation coefficient, ICC2.1); error (n = 171) through the standard error of measurement (SEM) and minimum detectable change (MDC90). Responsiveness (n = 171) was calculated using effect-size (ES), standard response mean (SRM), and area under the curve (AUC). Conclusions: The SFI-10 demonstrates sound measurement properties in a general physiotherapy outpatient MSD spine population for both psychometric and practical characteristics. Further investigation in culturally diverse settings that include both inpatients and community settings with whole-spine and regional-spine criteria is required.