Enthesitis: The clue to the pathogenesis of spondyloarthritis?

The term "spondyloarthritis" designates a group of conditions whose shared characteristic is inflammation at the interface between the bone and either the tendons and ligaments or the joint capsule. This interface, known as the enthesis, can be the site of ossification in spondyloarthritis. The advent of high-performance imaging techniques such as magnetic resonance imaging has rekindled interest in the enthesis by providing new insights into the sequence that leads to entheseal ossification. These techniques have established initial inflammation and fatty metaplasia as key events that precede ossification. The pathophysiological mechanisms that trigger the initial inflammation probably involve multiple factors such as mechanical stress and the presence of resident cells responsive to interleukin-23 and capable of releasing proinflammatory cytokines. Research into the triggers of entheseal inflammation and ossification may thus provide the clue to the pathophysiology of spondyloarthritis.