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.
This can happen when you are outside in extreme temperatures without gloves, or when you hold onto something cold, such an iced beverage. However, fingers that turn white and go numb may also be a result of a condition called Raynaud's Syndrome. Another phenomenon that can cause whiteness and numbness is Vibration-Induced White Finger (VWF). It's similar to Raynaud's, but VWF is caused by using vibrating hand tools, like jackhammers.