Limited Reliability of Radiographic Assessment of Sacroiliac Joints in Patients with Suspected Early Spondyloarthritis.

Objective: To determine the reproducibility of evaluation of sacroiliac joint (SIJ) radiographs among readers with varying levels of experience, and to identify potential drivers of disagreement in classification among 5 predefined radiographic lesion types.

Methods: The study sample consisted of 104 consecutive patients aged 18-40 with low back pain ≥ 3 months of duration who met the Assessment of SpondyloArthritis international Society (ASAS) definition for a positive SIJ magnetic resonance image, or were HLA-B27-positive and had ≥ 1 spondyloarthritis (SpA)-related clinical/laboratory feature according to the ASAS classification criteria for axial SpA. Seven blinded readers (2 musculoskeletal radiologists, 5 rheumatologists) classified pelvic radiographs according to the modified New York criteria (mNY) and recorded presence/absence of 5 lesion types in both SIJ: erosion, sclerosis, ankylosis, joint space widening, and joint space narrowing. Reproducibility of mNY classification among 21 reader pairs was assessed and potential drivers of disagreement were identified among 5 lesion types. A generalized linear mixed logistic regression model served to analyze to what extent discordance in lesion type was associated with discrepant mNY classification.

Results: Mean κ values (percent concordance) were 0.39 (84.1%) for mNY classification over 21 reader pairs, 0.46 (79.8%) between 2 musculoskeletal radiologists, and 0.55 (86.5%) and 0.36 (77.9%) between the most experienced rheumatologist and the 2 radiologists. Erosion showed the lowest agreement (25%) among patients with discordant classification and gave the highest OR of 13.5 for disagreement.

Conclusion: Reproducibility of radiographic SIJ classification in an SpA inception cohort was only fair to at best moderate among 7 readers with varying levels of experience, questioning the applicability of mNY in early SpA.