Evolving concepts of new bone formation in axial spondyloarthritis: Insights from animal models and human studies.

New bone formation potentially leading to ankylosis of the sacroiliac joints and the spine is the main type of structural damage to the skeleton that characterizes axial spondyloarthritis. New data from animal models, imaging, and patient cohort studies support the view that sustained suppression of inflammation by therapeutic interventions can slow down the ankylosing process, at least in a large proportion of the patients. Although specific growth factor molecular signaling pathways are the key to drive the progenitor cell differentiation process that leads to ankylosis, inflammation plays an important role, most likely in combination with biomechanical and environmental factors, in both the onset and progression of the disease. Therefore, early and effective treatment strategies and smoking cessation are important in daily patient management, in particular in those individuals at risk to develop progressive ankylosis. It should be further explored whether different treatment strategies will have distinct effects on ankylosis.