Abstract
Associated with the presence of HLA-B27 antigen, this inflammatory disorder of unknown etiology predominantly affects young adult men. Most patients present with low back pain and stiffness. Radiographs may show erosions, sclerosis and ankylosis in the pelvis and in the discovertebral, apophyseal, costovertebral and atlantoaxial joints. Hips and shoulders are the peripheral joints most commonly affected. Although most of the axial and appendicular skeleton may be involved, bilateral and symmetric sacroiliac involvement is the hallmark of ankylosing spondylitis.