Ankylosing spondylitis is a type of arthritis in which there is long term inflammation. It can occur in other parts of the body, particularly the spine where over time the bones fuse together and create a rigid spine. It can range from mild to severe and possible result in changes in posture. Early diagnosis may help progression, reduce symptoms or prevent deformity. Ankylosis refers to the bony fusion, which is typically best seen on X-rays.