MRI of the axial skeleton in spondyloarthritis: the many faces of new bone formation

Abstract

Spondyloarthritis has two hallmark features: active inflammation and structural lesions with new bone formation. MRI is well suited to assess active inflammation, but there is increasing interest in the role of structural lesions at MRI. Recent MRI studies have examined the established features of new bone formation and demonstrated some novel features which show diagnostic value and might even have potential as possible markers of disease progression. Although MRI is not the first imaging modality that comes into mind for assessment of bony changes, these features of new bone formation can be detected on MRI—if one knows how to recognize them. This review illustrates the MRI features of new bone formation and addresses possible pitfalls.

Baseline Severity of Sacroiliitis and Extensive Fat Metaplasia Predicts the Progression of Backfill at the Sacroiliac Joint in Patients With Axial Spondyloarthritis

“…A multivariate analysis of new bone formation in ankylosing spondylitis (AS) showed that fat metaplasia and backfill were significantly correlated with ankylosis ( 14 ). Typically, backfill indicates the initiation of new bone formation ( 1 ). However, no study has explored the correlation between fat metaplasia and backfill.…”

“…Axial spondyloarthritis (axSpA) is a chronic inflammatory rheumatic disease affecting the spine and the sacroiliac (SI) joints. The prominent feature of axSpA in the new bone formation is ankylosis in the SI joints and bridging syndesmophytes in the spine ( 1 ). This feature is associated with irreversible spinal immobility and functional limitation.…”

“…Magnetic resonance imaging (MRI) is superior to radiography because it can demonstrate active inflammation and structural damages, even in patients in early axSpA with normal radiography findings. Fat metaplasia in an erosion cavity, also known as backfill, is a feature that can be detected on an MRI and is associated with new bone formation in the SI joints ( 1 , 2 ). It has been defined as the presence of high signal intensity on T1-weighted images (T1WI) within the SI joint space and is hypothesized to represent reparative tissue refilling the eroded subchondral bone ( 2 ).…”

Manubriosternal Joint Involvement as a Presenting Feature of Axial Spondyloarthritis

“…MRI can detect early changes in spondyloarthritis, revealing subtle erosions, bone edema, and signs of inflammation. Another hallmark feature of AxSpA that has been well documented is structural lesions with new bone formation [13]. This can be assessed on MRI, and early signs of bone formation can help lead to the diagnosis of AxSpa.…”

“…formation can form not only in the sacroiliac joints but also in the manubriosternal joint potentially impacting chest wall movement. Findings of bone formation can also be helpful in monitoring disease progression [13]. Early evaluation and diagnosis of spondyloarthritis can lead to earlier initiation of treatment with both pharmacologic and nonpharmacologic interventions.…”