A description from the NHS website:
Ankylosing spondylitis (AS) is a type of chronic (long-term) arthritis that affects parts of the spine, including bones, muscles and ligaments.
Arthritis is a common condition that causes pain and inflammation of the joints and tissues around them.
The symptoms of ankylosing spondylitis can vary, but most people experience back pain and stiffness. The condition can be severe, with around one in 10 people at risk of long-term disability.

