Ankylosing spondylitis is a type of joint that occurs primarily affecting the spine. This disease is characterized by pain and stiffness in the joints along the spine. The knee and shoulder joints can also be affected.
With ankylosing spondylitis, inflammation of the spinal joints usually results in the vertebrae and spinal joints fused together. As some of these vertebrae grow together, the spine becomes more rigid and inflexible.
Fusion or fusion occurs as a reaction to inflammation of the ligaments or tendons at the site of bone attachment. Inflammation causes bone to erode at the site of attachment, and then as the inflammation subsides, the body's natural healing process causes new bone growth to fall out of place.
Because this new bone is stiff, as opposed to the elastic qualities of tissues or ligaments, the normal range of motion of the spine is reduced.
Ankylosing spondylitis is most often diagnosed in young men between the ages of 15 and 30, although it can affect anyone. Almost everyone with ankylosing spondylitis carries a specific gene called HLA-B27.