This study aimed to investigate the anatomical location and distribution of MRI lesions in the sacroiliac joints(SIJs) in patients with axial spondyloarthritis(axSpA), women with and without post‐partum pain (childbirth within 4‐16 months), patients with disc herniation, cleaning staff, runners, and healthy persons.

In a prospective cross‐sectional study of 204 participants, MRI of the entire cartilaginous compartment of the SIJ was scored blindly by two independent, experienced readers, according to the SPARCC SIJ Inflammation Structural (SSS) lesion definitions, in each SIJ quadrant/half in each of 9 slices. The lesions’ location (unilateral/bilateral, upper/lower, sacral/iliac, anterior/central/posterior slices) were analyzed based on concordant reads. Bone marrow edema (BME) occurred in all quadrants in nearly all participant groups, but rarely bilaterally, except in axSpA and women with post‐partum pain. Fat lesions (FAT) were mainly found in axSpA, occurred in all quadrants but mostly bilaterally in sacral quadrants. Erosion was rare, except in axSpA, where it was mainly iliac and often bilateral.

In conclusion, the location and distribution of common SIJ lesions in axSpA and non‐axSpA were reported, and group specific patterns were revealed. This study indicates that FAT’s presence, especially when widespread, and erosion, mainly when located centrally or posteriorly, are diagnostically essential and should be investigated further.

Ref: https://onlinelibrary.wiley.com/doi/10.1002/acr.24473

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