Magnetic Resonance Imaging Topography of Bone Marrow Edema in the Sacroiliac Joint of Postpartum Women

Objective A traditional monoplanar semicoronal and a biplanar magnetic resonance imaging (MRI) assessment method were used to compare the topographical distribution of postpartum strain‐related bone marrow edema (BME) at the sacroiliac joint (SIJ). Methods The presence and topographical location of SIJ BME were assessed independently by three readers in 71 women 12 months postpartum. A traditional monoplanar semicoronal and a biplanar BME evaluation by 8 (upper and lower) and 12 joint (upper, middle, and lower) regions, respectively, was performed with >4 weeks between the two assessments. Descriptive results were reported as mean ± SD and ranges, and interreader agreement by intraclass correlation coefficient (ICC). Results By semicoronal assessment, 38 (53.5%) women had BME with a mean ± SD SPARCC score of 2.3 ± 4.0 (range 0–22; ICC 0.93, 95% confidence interval [CI] 0.92–0.94). Forty‐one (57.8%) had BME by biplanar assessment with a mean ± SD sum score of 2.9 ± 5.8 (range 0–32.7; ICC 0.89, 95% CI 0.88–0.91). By semicoronal assessment, the highest frequency and mean SPARCC scores were in the anterior upper regions of ilium (24%, mean 0.6) and sacrum (21%, mean 0.3) followed by the posterior upper sacral (20%, mean 0.4) and posterior lower iliac (20%, mean 0.3) regions. By biplanar assessment, the anterior middle joint regions had highest BME frequency and sum scores, sacral side (32%, mean 1.9) and iliac side (27%, mean 2.0), respectively; frequencies and sum scores were generally higher in the anterior compared to the posterior joint regions. Conclusion The 12‐region biplanar assessment revealed a predominantly anterior middle location of postpartum SIJ BME whereas the 8‐region monoplanar approach did not demarcate distinct strain‐prone SIJ regions. Complementing traditional monoplanar semicoronal SIJ MRI evaluation by a semiaxial assessment may facilitate discrimination of strain‐related conditions from early axial spondyloarthritis.