Mechanism of New Bone Formation in Axial Spondyloarthritis

The purpose of this review is to discuss new evidence explaining the progress from bony inflammation over repair tissue to new bone formation in axial spondyloartrhitis and its correlations in imaging and histology of the bone. Data from imaging, histology and treatment interventions indicates that the disease starts with inflammation, followed by replacement of subchondral bone marrow by repair tissue which presence is crucial for the stimulation of new bone formation. The magnetic resonance imaging (MRI) sequences of STIR and T1 are currently the most commonly used imaging techniques to follow this process; explanations are offered for the limited sensitivity to detect these bony changes on MRI in their different phases. Early and effective anti-inflammatory treatment is crucial for the prevention of long-term ankylosis. Whether there are currently also treatment options targeting new bone formation in these patients directly is less clear.