MRI findings for unilateral sternoclavicular arthritis: differentiation between infectious arthritis and spondyloarthritis.

To analyze and identify magnetic resonance imaging (MRI) and clinical findings for the differentiation between infectious arthritis and spondyloarthritis in patients with unilateral sternoclavicular arthritis. We retrospectively collected and evaluated the magnetic resonance (MR) images of 21 patients diagnosed with unilateral sternoclavicular arthritis, including 12 with infection and nine with spondyloarthritis, between 2004 and 2017. Capsular distension, extracapsular fluid collection, periarticular muscle edema, the prevalence and distribution of bone marrow edema, and the prevalence and size of bone erosions were assessed on the MR images. Clinical data were also reviewed. Capsular distension was more prominent in patients with infectious arthritis than those with spondyloarthritis (p = 0.002); extracapsular fluid collection and periarticular muscle edema were also more common in infectious arthritis than spondyloarthritis (p < 0.001, respectively); moreover, bone erosions were larger in infectious arthritis than spondyloarthritis (p = 0.023). Other findings significantly associated with infectious arthritis included advanced age (p = 0.007), an elevated C-reactive protein (CRP) level (p = 0.001), and erythrocyte sedimentation rate (ESR) (p < 0.001). The prevalence and distribution of bone marrow edema and the prevalence of bone erosions on MRI, the white blood cell count, and sex showed no significant differences between the two groups. Capsular distension, extracapsular fluid collection, periarticular muscle edema, and the size of bone erosions on MRI, as well as the age, CRP level, and ESR of patients, could be helpful for differentiating infectious arthritis from spondyloarthritis involving the sternoclavicular joint.