What is AS?

Ankylosing Spondylitis (AS) is an inflammatory arthritis.

It mainly affects the spine but can also affect other joints, tendons and ligaments.

Ankylosing means fusing together. Spondylitis means inflammation of the vertebrae. Both words come from the Greek language. Ankylosing Spondylitis describes the condition where some or all of the joints and bones of the spine fuse together.

Entire fusing of the spine is unusual. Many people will only have partial fusion, often limited to the sacroiliiac joint.

Other areas such as the eyes and bowel can also sometimes be involved with AS.

What happens in AS

  1. Inflammation occurs at the site where ligaments or tendons attach to the bone. This is known as enthesis.
  2. The inflammation is followed by some wearing away of the bone at the site of the attachment. This is known as enthesopathy.
  3. As the inflammation reduces, healing takes place and new bone develops. Movement becomes restricted when bone replaces the elastic tissue of ligaments or tendons.
  4. Repetition of this inflammatory process leads to further bone formation and the individual bones which make up your backbone (vertebrae) can fuse together.

AS is a very variable condition

Some people with AS have virtually no symptoms whereas others suffer more severely.

Ankylosing spondylititis and spondylosis

These two conditions do sound very similar but are actually very different.

While ankylosing spondylitis is a form of inflammatory arthritis, spondylosis is a medical term for the general wear and tear that occurs in the joints and bones of the spine as people get older.

Cervical spondylosis specifically refers to wear and tear occuring in the neck (the cervical spine). You can find really useful information on cervical spondylosis on the NHS Choices website.

Last reviewed: February 2014