Bone formation versus bone resorption in ankylosing spondylitis.

Ankylosing spondylitis (AS) and other forms of seronegative spondylarthritis (SpA) are characterized by two major processes in joints-the first is chronic inflammation and the second is progressive ankylosis. Both features go hand-in-hand and determine the clinical picture of disease, which is joint pain, progressive stiffness and, in case ofperipheral joint involvement also joint swelling. The interplay between inflammation and ankylosis is best illustrated in AS, where chronic inflammation of the spine leads to progressive stiffness, reduced spinal mobility and kyphosis. AS may thus be considered as a synthesis of inflammatory disease and bone disease.