Causes:

The exact causes of osteoarthritis are not known. Scientists think that osteoarthritis likely develops from a combination of factors, including genetic susceptibility to joint injury.

Aging Cells

The body's ability to repair cartilage deteriorates with increasing age. Although osteoarthritis generally accompanies aging, osteoarthritic cartilage is chemically different from normal cartilage of the same age. As chondrocytes (the cells that make up cartilage) age, they lose their ability to make repairs and produce more cartilage. This process likely plays an important role in the development and progression of osteoarthritis.

Genetic Factors

Osteoarthritis tends to run in families. Genetic factors may be involved in about half of osteoarthritis cases in the hands and hips, and in a somewhat lower percentage of cases in the knee. Several genes that might contribute to an inherited risk are under investigation.

Inflammatory Response

The inflammatory response is an overreaction of the immune system to an injury or other assault in the body, such as an infection. This response causes specific immune factors, called cytokines, to gather in injured areas and cause inflammation and damage to body tissue and cells. The inflammatory response plays an important role in rheumatoid arthritis and other muscle and joint problems associated with autoimmune diseases.

Inflammation probably plays at most a minor role in the formation of osteoarthritis and is more likely to be a result -- not a cause -- of the disease. However, inflammation may play an important role in the progression of osteoarthritis and in its chronic nature. The effects of the inflammatory response in osteoarthritis are likely to be different, and less severe, from those in rheumatoid arthritis.

Joint Injury

Joint damage from injuries or recurrent stress to the joint is the starting point in the osteoarthritis disease process. Osteoarthritis sometimes develops years after a single traumatic injury to or near a joint. Patients with knee injuries may be up to five times more likely to have osteoarthritis in the injured knee than those without injuries, and patients with hip injuries may be more than three times more likely to develop arthritis in the injured hip. Proper treatment of injuries, such as surgical repair of ligament tears in the knee with a strong rehabilitation approach, may help prevent the development of osteoarthritis.

Other Medical Conditions that Can Cause Osteoarthritis

Other causes of osteoarthritis include:

• Bleeding disorders that cause bleeding in the joint, such as hemophilia
• Disorders that block the blood supply near a joint, such as avascular necrosis
• Complications of persistent, inflammatory arthritic conditions, particularly chronic gout, pseudogout, or rheumatoid arthritis
• Conditions that cause iron build-up in the joints, such as hemochromatosis