Purpose: The purpose of this study was a cross-cultural adaptation of the Spine Functional Index to produce a Polish version (SFI-PL). Further, the psychometric properties were evaluated with standardized criteria patient reported outcome measures (PROMs) in a symptomatic Polish spine population.
Methods: Linguistic adaptation complied with the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines to produce the SFI-PL. Subjects with spine conditions, all areas and multi-area, were recruited from a Polish Specialist Hospital (n = 225, age = 45.7 ± 16.0 years, range 18-87, female = 60%, symptoms duration = 13.93 ± 27.56 weeks, range 5-84). Baseline internal consistency, reliability and validity were examined and included the SFI-PL, Oswestry Disability Index (ODI), Neck Disability Index (NDI), EuroQol 5 Dimensions, 5-level version (EQ-5D-5L) and an 11-point pain Numerical Rating Scale (NRS) with retest at 3-7 days (= 5 days). Practicality for readability was considered within the face and content validity and completion and scoring time calculated.
Results: Statistical analysis showed excellent internal consistency (α = 0.90) and high test-retest reliability (ICC = 0.98). The error score was determined with the SEM = 3.14 (MDC 90% CI = 7.33%). The construct validity analysis demonstrated strong correlations between the SFI-PL, the NDI (r = 0.73) and the ODI (r = 0.82); moderate with the EQ index value (0.70) and EQ-VAS (r = 0.56). Time to complete (229 s) and score (27 s) were determined.
Conclusions: The SFI-PL is a psychometrically sound PROM for Polish-speaking patients with spine conditions. The results support previous findings from the original-English and six other language versions for internal consistency, reliability, measurement error and validity. These slides can be retrieved under Electronic Supplementary Material.
Keywords: Cross-cultural adaptation; Internal consistency; Reliability; Spine Functional Index; Validity.