Ankylosing Spondylitis (AS) is a form of arthritis that primarly affects the spine. It will often involve the sacroiliac (SI) joint and other joints other than the spine may become involved. In advanced cases it may contribute to the formation of bone in the spine which may fuse the spine together restricting movement. Functionally an autoimmune disorder, Chinese Medicine diagnosis is critical as it may arise from a range of patterns. Kidney yin deficiency would be common, but other spleen disorders may also be involved.