Evaluation of disease chronicity by bone marrow fat fraction using sacroiliac joint magnetic resonance imaging in patients with spondyloarthritis: A retrospective study.

AIM: This study investigated the use of fat fraction (FF) measurements in the sacroiliac (SI) joint to determine radiologic progression in patients with spondyloarthritis (SpA).

METHOD: A total of 138 patients who underwent pelvic magnetic resonance imaging (MRI) between September 2014 and March 2015 were retrospectively evaluated. The FF based upon fat deposition (%) using fat signaling on T1 and T2 weighted images in the sacroiliac joint was quantified using a 6-echo variant of the modified Dixon technique. We defined the normal bone marrow as normal FF, bone marrow edema as active inflammatory FF, and fat metaplasia as post-inflammatory FF.

RESULTS: The mean FF of normal marrow was 52.0% ± 10.4% and 50.5% ± 10.1% in the left and right SI joints, respectively. The mean FF of post-inflammatory fat deposition was 81.9% ± 9.7% and 82.3% ± 9.6% in the left and right SI joints, respectively. The mean FF of active inflammatory fat deposition was 15.8% ± 5.9% and 13.5% ± 6.7% in the left and right SI joints, respectively. In multiple linear regression, post-inflammatory FF was found to be significantly associated with radiologic progression, such as symptom duration, SI joint grade, and modified Stoke Ankylosing Spondylitis Spine Score.

CONCLUSION: Post-inflammatory FF indicates the chronicity of SpA. Evaluating FF using MRI in the SI joint will help to determine radiologic progression.