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 kappa 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.