About Ankylosing Spondylitis. Ankylosing spondylitis is a form of progressive arthritis due to chronic inflammation of the joints in the spine. Its name comes from the Greek words  ankylos,  meaning stiffening of a joint, and  spondylo,  meaning vertebra.nkylosing Spondylitis. A form of arthritis that affects the spine, the sacroiliac joints, and sometimes the hips and shoulders. In severe cases, the joints of the spine fuse and the spine becomes rigid. PubMed Health Glossary. (Source: NIH-National Institute of Arthritis and Musculoskeletal and Skin Diseases).
The most common cause of numbness in the part of the hand that you describe (the ring finger) would be carpal tunnel syndrome, which is a condition in which the median nerve, which runs down the center of the wrist, becomes pinched or inflamed.
One possible cause of numbness in the finger tips is lack of blood flow. This can be caused by something called Raynaud's phenomenon. Raynaud's phenomenon is a symptom that is seen in some disease such as lupus where blood flow doesn't reach the tips of the fingers, especially in cold weather. Another common cause of numbness in the finger tips is uncontrolled diabetes. High blood sugars caused by diabetes damage nerves in the finger tips and toes. If you also have nerve problems in your feet, then this could be an explanation. I suggest that you schedule an appointment with your primary care physician.