Ankylosing spondylitis is a type of arthritis that causes inflammation in the joints and ligaments of the spine. It may also affect peripheral joints like the knees, ankles, and hips. Normally, the joints and ligaments in the spine help us move and bend.

If you have ankylosing spondylitis, the inflammation in the joints and tissues of the spine can cause stiffness. In severe cases, this may cause the vertebrae (bones in the spine) to fuse (grow together). When the vertebrae fuse, it can lead to a rigid and inflexible spine.