Spondylitis involves inflammation of one or more vertebrae. Ankylosing spondylitis is a chronic inflammatory disease that affects the joints between the vertebrae of the spine, and the joints between the spine and the pelvis. It eventually causes the affected vertebrae become stiff or grow together.

The cause of ankylosing spondylitisis unknown, but genetic factors seem to play a role. The disease starts with intermittent hip and/or lower-back pain that is worse at night, in the morning, or after inactivity. Back pain begins in the sacroiliac joint (between the pelvis and the spine) and may progress to include the lumbosacral spine and the thoracic spine (chest portion of the spine).

 Sitting for long periods of time can aggravate the condition and cause severe discomfort in the lower back and legs. Ankylosing spondylitis most commonly develops in individuals between the ages of 20 and 40 but some cases have been reported in children as young as age 10. There is no known cure for ankylosing spondylitis but treatments include anti inflammatory medicine as well as physical therapy and joint treatment. The disease affects more males than females. Risk factors include a family history of ankylosing spondylitis and male gender. About 0.21% of Americans over age 15 are affected.