Prevalence and determinants of sacroiliac joint bone marrow oedema in the general population in Germany: a population-based cross-sectional study

BACKGROUND: MRI-detected bone marrow oedema in sacroiliac joints is central to diagnosing axial spondyloarthritis, influencing treatment decisions including anti-inflammatory therapy initiation. However, the prevalence of bone marrow oedema in the general population remains unknown, restricting interpretation of MRI findings and potentially leading to overdiagnosis when imaging findings are considered without clinical context. We aimed to establish the prevalence and determinants of sacroiliac bone marrow oedema in the general adult population.

METHODS: In this national, population-based, cross-sectional study, we analysed adults aged 20-69 years from the German National Cohort who underwent whole-body MRI between May 1, 2014, and Dec 31, 2016. Three masked experts independently assessed randomly selected participants for sacroiliac bone marrow oedema. The remaining participants were evaluated using a validated deep-learning algorithm that automatically segments and quantifies bone marrow oedema volume from fat-suppressed proton density sequences. We examined associations between the presence of bone marrow oedema (primary outcome) and demographic, lifestyle, and reproductive factors using multivariable logistic regression with sex-stratified analyses to identify differential patterns. There was no patient or public involvement in this study.

FINDINGS: Of 11 163 participants (median age 53·0 years [IQR 45·0-61·0], 5432 [48·7%] women and 5731 [51·3%] men), sacroiliac bone marrow oedema was detected in 288 (28·9% [95% CI 26·2-31·9]) of 998 participants analysed by expert readers and 3131 (30·8% [29·9-31·7]) of 10 165 participants analysed by the deep-learning algorithm, approximately 50 times higher than the 0·6% prevalence of self-reported axial spondyloarthritis diagnosis. Bone marrow oedema prevalence was higher in women (33·9% [95% CI 32·6-35·3]) than in men (27·8% [26·6-29·1]; adjusted odds ratio [OR] 1·33 [95% CI 1·23-1·45]). In women, pregnancy history was associated with bone marrow oedema compared with nulliparous women (OR 1·43 [95% CI 1·21-1·71]). In men, age (OR 1·28 per decade [95% CI 1·21-1·35]) and intensive recreational physical activity (1·24 [1·08-1·42]) showed independent associations, whereas age effects were minimal in women (1·16 per decade [1·11-1·23]). Of modifiable risk factors, BMI of 25 kg/m(2) and above showed the highest OR (1·62 [1·47-1·79]). Physically demanding occupational work was associated with bone marrow oedema overall (OR 1·25 [95% CI 1·14-1·36]).

INTERPRETATION: Sacroiliac bone marrow oedema affects nearly one-third of adults, showing associations with pregnancy, overweight, and occupational physical stress rather than inflammatory disease. This prevalence exceeds self-reported axial spondyloarthritis by 50 times, providing essential population reference data for contextualising MRI findings. These findings show that bone marrow oedema, the key imaging marker for sacroiliitis in Assessment of Spondyloarthritis International Society criteria, commonly occurs from non-inflammatory causes. These population-based data can inform diagnostic interpretation and support development of more specific imaging thresholds to reduce misdiagnosis and inappropriate treatments.