Reliability and reproducibility of computed tomography-based facet joint measurements in patients with AO spine type A2, A3 and A4 thoracolumbar fractures: protocol for the REFACT study

Background: Computed tomography (CT) is widely used to assess facet joint (FJ) degeneration. However, previous studies have reported inconsistent interobserver agreement for the Pathria classification, while the reproducibility of quantitative FJ measurements remains insufficiently investigated. The REFACT study aims to evaluate the interobserver and intraobserver reliability of CT-based FJ assessment in patients with AO spine type A2, A3, and A4 thoracolumbar fractures. Methods: REFACT is a single center, multiobserver reliability study using retrospectively collected, anonymized CT datasets. Six independent raters (three neurosurgeons and three radiologists) will assess at least 142 evaluable FJs using a standardized protocol. Assessments will include Pathria grading, mean FJ-space width, and FJ angle measurements. Each rater will perform two assessment rounds with randomized case order and a one-month washout interval. Interobserver and intraobserver reliability will be evaluated using intraclass correlation coefficients (ICC) for continuous measurements and Fleiss’ kappa or weighted kappa coefficients for ordinal grading, with 95% confidence intervals. Exploratory analyses will assess agreement by specialty, vertebral level, and side. Patient-level clustered bootstrap analyses will account for within-patient correlation. Conclusions: The REFACT study will establish the reproducibility of CT-based FJ grading and morphometric measurements, identify potential limitations of the standardized assessment protocol, and provide a methodological basis for subsequent longitudinal studies of FJ degeneration following thoracolumbar fractures. Trial Registration: ClinicalTrials.gov, NCT07670039.