Ankylosis in ankylosing spondylitis: current concepts.

Ankylosing spondylitis (AS) is the most common form of spondyloarthritis and is characterized by both inflammation and new bone formation. Despite many years of arduous efforts, we still do not clearly understand the pathogenesis of AS. The mechanisms behind new bone formation have been especially challenging to decipher due to the difficulty in obtaining tissue from spinal joints. The link between inflammation and bone formation looks obvious, but how inflammation drives spinal fusion is not evident. There are now two genes linked to prostaglandins (PG) that could be involved in AS pathogenesis. The first one is PTGER4 that codes for the EP4 receptor for PGE2 and the other one is PTGS1 that codes for prostaglandin-endoperoxide syntase 1 or cyclogenase 1. The bone morphogenic protein and Wnt signaling pathways could be important in signaling increased bone formation in AS. The disease-modifying potential of anti-inflammatories and tumor necrosis factor alpha inhibitors is discussed.