The Spine Functional Index

Cross-cultural adaptation and validation of the Polish version of the Spine Functional Index:

Abstract

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.

Graphic abstract

These slides can be retrieved under Electronic Supplementary Material.