Ankylosing Spondylitis
Definition
Ankylosing spondylitis is a form of arthritis predominantly affecting the spine and pelvic joints. Unlike osteoarthritis, ankylosing spondylitis or AS is not caused by wear and tear on the joint surfaces (cartilage). Instead, it is a result of immune cells in the blood attacking the areas where ligaments insert into bone.
In the spine, immune cells attack the edges of the vertebral bones, causing irritation and inflammation. The ligaments surrounding the spinal discs consequently stiffen, and bones stimulated by the inflammation grow thin bridges or osteophytes. These two processes cause the spine to gradually stiffen, eventually fusing into place.
Although AS initially begins in the lower back, it can also effect the neck and upper spine. This can result in a frozen neck, a forced hunch (or kyphosis) and eventually difficulty breathing. AS also commonly affects joints in the pelvis (sacro-iliac joints), hip, shoulder and feet, and occasionally affects other areas in the body including the eyes, bowel and lungs.
AS tends to progressively worsen over time, but early intervention can dramatically reduce the impact AS has on quality of life. In severe cases, the gradual fusion of the spine results in deformity that impacts on activities and breathing. In these cases, surgery may be required to straighten the spine.