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Ankylosing spondylitis

Ankylosing spondylitis (AS) is a form of arthritis. It mainly affects the lower back, although it can affect other parts of the body.

AS is caused by inflammation. Over time, this leads to the growth of new bony deposits in place of existing cartilage that form a bone bridge between two bone surfaces, such as the joints around the hip (pelvis) and spine (sacroiliac joint) causing pain, stiffness and reduced mobility.

The main symptom is back pain, usually mild at first but becoming worse over a period of months rather than days or weeks. You may also notice pain in your buttocks and thighs. Pain tends to be worse after resting for example, when you wake up in the morning, and is better when you get going. In the early stages, AS causes considerable pain, but this often settles down.

Most people with back pain do not have AS. It is quite unusual about 1 in 1000 people develop the disease.

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