Ankylosing spondylitis (AS) is a progressive inflammatory rheumatoid arthritis that affects the small joints in the spine and pelvis (sacroiliac joints), eventually causing them to fuse, making the spine become stiff, inflexible, and hunched over. As the disease progresses, it can also affect the ribs, eyes (acute iritis), and cause fractured spinal vertebrae.
There are two subtypes of ankylosing spondylitis: 1) non-radiographic ankylosing spondylitis (nr-axSpA), which means that the joint damage cannot be seen on X-ray, and 2) ankylosing spondylitis (AS), when the joint damage can be seen on X-ray.
Ankylosing spondylitis affects more men than women, and usually begins in adolescence or early adulthood.