Differences in Topographical Location of Sacroiliac Joint MRI Lesions in Patients With Early Axial Spondyloarthritis and Mechanical Back Pain

Rosa Marie Kiil; Clara E. Mistegaard; Anne Gitte Loft; Anna Zejden; Oliver Hendricks; Anne Grethe Jurik


Arthritis Res Ther. 2022;24(75) 

In This Article


Sacroiliitis is a hallmark in axial spondyloarthritis (axSpA) where the active and often reversible magnetic resonance imaging (MRI) finding, subchondral bone marrow edema (BME) around the sacroiliac joints (SIJ), is interpreted as active sacroiliitis. The majority of axSpA patients have BME on SIJ MRI,[1,2] which plays a major role in the widely used 2009 Assessment of SpondyloArthritis International Society (ASAS) classification criteria for axSpA.[3,4] Unfortunately, BME is not exclusively seen in axSpA; previous studies have demonstrated that up to 25% of patients with low back pain, and even healthy individuals, have non-specific BME on SIJ MRI[5–8] with even higher prevalence rates in pregnant and post-partum women with or without low back or SIJ pain.[1,2,6,9–11]

Despite the apparent low specificity of BME, comparative studies regarding the volume and topographic distribution of BME and other MRI lesions in axSpA patients versus various groups of individuals with and without back pain are sparse. The comparative approach of these diagnostic entities may contribute to the differentiation of this clinically highly relevant and difficult challenge. It has been reported that the location of BME in healthy subjects, patients with mechanical back pain (MBP) and postpartum females is most frequent in the lower ilium and anterior upper sacrum with minimal accompanying structural changes like erosions and fatty lesions.[6,12] However, another study did not find any differences in the distribution.[2] The distribution of BME in axSpA patients has been reported being located more widespread in both the ilium and the sacrum as well as being more voluminous and accompanied by structural changes.[6,8,12,13]

The BME occurring in non-SpA individuals may be due to degenerative changes,[14,15] mechanical load[7] and atypical SIJ morphologies including lumbosacral transitional anomaly,[16,17,18,19] which however also can influence the MRI findings in axSpA patients.

Traditional, one-plane SIJ MRI assessment is used in both the diagnostic[4] and monitoring phase[20] of axSpA, which can limit the precise location of lesions and distinction between the cartilaginous and ligamentous joint compartments.

The aim of this study was to analyse the differences in SIJ MRI changes in early axSpA patients compared with changes in patients with MBP by exploring the differences in volume and distribution pattern of MRI SIJ findings by using a detailed two-plane quantitative scoring system. Furthermore, to analyse whether certain SIJ MRI changes were independently associated with the following conditions: axSpA, anatomical variations, disc degeneration, parity, age, gender and BMI.