MRI of the sacroiliac joints in athletes: recognition of non-specific bone marrow oedema by semi-axial added to standard semi-coronal scans.

OBJECTIVE: Assessment of combined semi-axial and semi-coronal SI joint MRI in two cohorts of young athletes to explore frequency and topography of non-specific bone marrow oedema (BMO), its association with four constitutional SI joint features, and potential restriction of false-positive assignments of Assessment of SpondyloArthritis International Society-defined sacroiliitis on standard semi-coronal scans alone. METHODS: Combined semi-axial and semi-coronal SI joint MRI scans of 20 recreational runners before/after running and 22 elite ice-hockey players were evaluated by three blinded readers for BMO and its association with four constitutional SI joint features: vascular partial volume effect, deep iliac ligament insertion, fluid-filled bone cyst and lumbosacral transitional anomaly. Scans of TNF-treated spondyloarthritis patients served to mask readers. We analysed distribution and topography of BMO and SI joint features across eight anatomical SI joint regions (upper/lower ilium/sacrum, subdivided in anterior/posterior slices) descriptively, as concordantly recorded by ⩾2/3 readers on both MRI planes. BMO confirmed on both scans was compared with previous evaluation of semi-coronal MRI alone, which met the Assessment of SpondyloArthritis International Society definition for active sacroiliitis. RESULTS: Perpendicular semi-axial and semi-coronal MRI scans confirmed BMO in the SI joint of every fourth young athlete, preferentially in the anterior upper sacrum. BMO associated with four constitutional SI joint features was observed in 20-36% of athletes, clustering in the posterior lower ilium. The proportion of Assessment of SpondyloArthritis International Society-positive sacroiliitis recorded on the semi-coronal plane alone decreased by 33-56% upon amending semi-axial scans. CONCLUSION: Semi-axial combined with standard semi-coronal scans in MRI protocols for sacroiliitis facilitated recognition of non-specific BMO, which clustered in posterior lower ilium/anterior upper sacrum.

Frequency and Anatomic Distribution of Magnetic Resonance Imaging Features in the Sacroiliac Joints of Young Athletes: Exploring "Background Noise" Toward a Data-Driven Definition of Sacroiliitis in Early Spondyloarthritis.

OBJECTIVE: Low-grade bone marrow edema (BME) has been reported in the sacroiliac (SI) joints of 25% of healthy individuals and patients with nonspecific mechanical back pain, thus challenging the specificity and predictive value of magnetic resonance imaging (MRI) for the discrimination of early spondyloarthritis (SpA). It is unknown whether stress injury in competition sports may trigger BME. This study sought to explore the frequency and anatomic distribution of SI joint MRI lesions in recreational and elite athletes. METHODS: After pretest calibration, semicoronal MRI scans of the SI joints of 20 recreational runners before and after running and 22 elite ice hockey players were assessed for BME and structural lesions. Three readers assessed the MRI scans in a blinded manner, using an SI joint quadrant-based module; scans from tumor necrosis factor inhibitor-treated patients with SpA served for masking. The readers recorded subjects who met the Assessment of SpondyloArthritis international Society (ASAS) definition of active sacroiliitis. For descriptive analysis, the frequency of SI joint quadrants exhibiting BME and structural lesions, as concordantly recorded by ≥2 of 3 readers, and their distribution in 8 anatomic SI joint regions (the upper and lower ilium and sacrum, subdivided in anterior and posterior slices) were determined. RESULTS: The proportions of recreational runners and elite ice hockey players fulfilling the ASAS definition of active sacroiliitis, as recorded concordantly by ≥2 of 3 readers, were 30-35% and 41%, respectively. In recreational runners before and after running, the mean ± SD number of SI joint quadrants showing BME was 3.1 ± 4.2 and 3.1 ± 4.5, respectively, while in elite ice hockey players, it was 3.6 ± 3.0. The posterior lower ilium was the single most affected SI joint region, followed by the anterior upper sacrum. Erosion was virtually absent. CONCLUSION: In recreational and elite athletes, MRI revealed BME in an average of 3-4 SI joint quadrants, meeting the ASAS definition of active sacroiliitis in 30-41% of subjects. The posterior lower ilium was the single most affected SI joint region. These findings in athletes could help refine data-driven thresholds for defining sacroiliitis in early SpA.