The entheses: histology, pathology, and pathophysiology.

The entheses are the sites of attachment of ligaments, tendons, and joint capsules to bone. Their ubiquitous distribution throughout the body explains the considerable clinical and radiological polymorphism of entheseal diseases. In addition to aging and mechanical factors, many disorders related to a vast array of pathophysiological mechanisms can produce entheseal disease. The spondyloarthropathies provide the most striking examples of entheseal involvement in inflammatory joint disease. Over the last few decades, major advances have shed light on the biochemical composition of the entheses, their histological features, their mechanical role, and their evaluation by ultrasonography and magnetic resonance imaging. These new insights have generated valuable hypotheses about the pathogenesis of spondyloarthropathies.