Osteoarthritis, also known as degenerative joint disease, is the most common arthritic disease. In addition to man, nearly all vertebrates suffer from osteoarthritis, including porpoises and whales, which discounts the theory that the disease is caused by walking upright. Osteoarthritis occurs in the joints of the body when cartilage is damaged or lost and bones begin to undergo abnormal changes.
Joints are designed to provide flexibility, support, stability and protection. These functions, essential for normal or painless movement, are primary functions of cartilage and synovium, the slippery tissues that coat the ends of the bones and the membranes that surround the entire joint. The synovium is filled with lubricating fluid or synovial fluid, which supplies nutrients and oxygen to cartilage. The cartilage itself is composed of water and collagen, which forms a mesh that gives support and flexibility to the joint. This combination of the collagen meshwork and the high water content creates a resilient and slippery pad in the joint, which resists compression between bones during muscle movement.
When the cartilage in a joint deteriorates, osteoarthritis develops. In the early stages of the disease the surface of the cartilage becomes swollen and there is a loss of other tissue parts. Fissures and pits appear in the cartilage and as the disease progresses and more tissue is lost, the cartilage loses elasticity and becomes increasingly prone to damage due to repetitive use and injury. Eventually, large amounts of cartilage are destroyed, leaving portions of the bone or joint unprotected.
Unlike some other types of arthritis, such as rheumatoid arthritis, osteoarthritis concentrates in one or more joints where deterioration occurs. Osteoarthritis affects joints differently depending on their location in the body. While osteoarthritis is commonly found in the joints of the fingers, feet, knees, hips and spine, it is rarely found in joints of the wrist, elbows, shoulders, and jaw.