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.
Digits like the fingers are the first to be affected by such a disease. Arthritis in the fingers can also put pressure on the joints, constricting nerves and vessels which can lead to the fingers feeling numb. Some diseases will cause the digits to feel numb as they begin to affect the body.