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.
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.
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.
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 early stages of osteoarthritis and is more likely to be a result -- not a cause -- of the disease. However, inflammation may contribute to 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, than those in rheumatoid arthritis.
Joint damage from injuries or recurrent stress to the joint is often 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.
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
- Anatomical abnormalities, such as mismatched surfaces on the joints, can become damaged over time. Legs of unequal length or skewed feet can cause jerky movement and may cause osteoarthritis.
Review Date: 06/16/2010
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.