The enthesopathy of ankylosing spondylitis.

The enthesopathic lesion of ankylosing spondylitis consists of a nonspecific, nongranulomatous inflammatory lesion which leads to destruction of the attachment of ligament to bone. Resulting erosion leads to reactive bone formation which may form a new enthesis and around the outer fibres of the annulus may lead to syndesmophyte formation. What determines the distribution of the enthesopathy and ankylosis is not known.