Osteoarthritis is also known as degenerative arthritis. It is the most common form of arthritis, affecting more than 20 million people in the United States. Osteoarthritis becomes more common as we age. Interestingly, it affects more males under the age of 45 and more females over the age of 55. Osteoarthritis commonly affects the hands, feet, spine, and large weight-bearing joints, such as the hips and knees. The majority of cases of osteoarthritis have no known direct cause. Such cases are referred as primary osteoarthritis. In cases where a direct cause has been established, the condition is referred to as secondary osteoarthritis. The causal factor may be obesity, trauma or surgery to the joints, congenital abnormalities, gout, diabetes or hormone disorders.