Ankylosing spondylitis is an inflammatory disease that cause pain primarily in the joints of the spine and pelvis (buttock area).
The exact cause of ankylosing spondylitis is currently unknown but a strong hereditary component has been observed. Unlike other causes of back and joint pains, it is not associated with wear and tear or particular jobs or lifestyle choices.
Ankylosing spondylitis tends to progress overtime to other joints and other parts of the body but early intervention can dramatically reduce the impact it has on quality of life.
Braun, J. and J. Sieper (2007). "Ankylosing spondylitis." The Lancet 369(9570): 1379-1390.