Bone marrow oedema in sacroiliac joints of young athletes shows most frequently in the posterior inferior ilium

Background Low grade bone marrow oedema (BMO) was reported in the sacroiliac joints (SIJ) of up to 25% of healthy individuals and mechanical back pain patients, challenging the imaging discrimination from early spondyloarthritis (SpA) [1]. Potential explanations range from mechanical stress lesions to vascular signals and anatomical SIJ variants. Objectives To determine BMO frequency and anatomical distribution in 8 SIJ regions in hobby and professional athletes. Methods The sample consisted of 2 cohorts of 20 healthy hobby runners (HR) before and after running and 22 professional ice hockey players (IP) from the Danish premier league: HR/IP 40%/100% men; mean age (SD) 27.2 (5.4)/25.9 (4.6) years; mean BMI (SD) 22.6 (1.5)/25.7 (1.6) kg/m2. Semicoronal MRI scans of the SIJ with T1SE and STIR sequences were obtained in HR before and 24 hours after a running competition over 6.2 kilometers (mean duration 35.4 minutes, mean speed 10.4 km/h), and in IP during the competitive season. The scans were assessed for BMO independently by 3 blinded readers (AGJ, AZ, UW) according to the quadrant based MORPHO module (www.carearthritis.com). Paired images of HR were read blinded to timepoint. 7 MRI scans (2 paired images) of SpA patients under TNF treatment served to mask readers. A pre-test reader calibration used MRI scans from 11 patients with active sacroiliitis and 9 healthy volunteers. Reader agreement was assessed by ICC (3, 1). Descriptive analysis comprised mean frequency of SIJ quadrants with BMO and distribution of BMO quadrants in 8 anatomical SIJ regions: upper/lower ilium and sacrum, subdivided in anterior and posterior slices, as concordantly recorded by the majority (≥2/3) of readers. Results Agreement among 3 readers for SIJ BMO was excellent in calibration (ICC 0.93) and moderate in athletes (ICC 0.59) due to low frequency of BMO. The mean number (SD) of SIJ quadrants showing BMO was 3.1 (4.2)/3.1 (4.5) in HR before/after running, and 3.6 (3.0) in IP. The posterior inferior ilium was the single most affected region, followed by the upper anterior sacrum, consistently across 2 cohorts of athletes. Conclusions In hobby and professional athletes, BMO showed on average in 3–4 SIJ quadrants. The posterior lower ilium was the SIJ region most frequently affected by BMO. These findings in healthy controls may help refine thresholds for a positive SIJ MRI in early SpA. References Weber U et al. Curr Rheumatol Rep 2016;18:58. Disclosure of Interest None declared