At first glance the word arthritis seems straightforward: it means “joint inflammation.” The reality, however, is far more complex. There are several different types of arthritis, and the two most common—rheumatoid arthritis (RA) and osteoarthritis (OA)—have very different causes, symptoms, and treatments.
Osteoarthritis affects an estimated 27 million adults in the United States. Unlike rheumatoid or psoriatic arthritis, osteoarthritis is not an autoimmune disease but rather a condition characterized by the breakdown of cartilage in a joint, which also involves changes to bone, ligaments, and other parts of the joint.
The deterioration in the cartilage of joints most commonly occurs as people grow older. Normally, cartilage covers the ends of bones, acting as a shock absorber and allowing bones to glide smoothly past each other. As cartilage is lost, bones can begin to rub against each other, causing pain and swelling. Osteoarthritis can affect any joint, but most commonly affects the hands, knees, hips, or spine.6 Factors that increase the risk of osteoarthritis include aging, being overweight, joint injury, and stress on a joint.
Cartilage contains specific components that are maintained by chondrocytes. Over time, chondrocytes also lose the ability to produce cartilage components that support the joint. Cartilage deterioration is associated with roughening of cartilage surfaces and local joint inflammation directed against cartilage debris. In response to this cartilage deterioration, the cartilage thins allowing greater forces to be placed on the underlying bone. The bone responds to these abnormal forces with overgrowth. Joints with osteoarthritis have abnormal contours and are painful. Joints in the spine are prone to develop osteoarthritis.
Intervertebral discs start to lose water when you are in your 20’s. When discs lose water, they lose their ability to act as shock absorbers between the vertebrae. They become thinner. When the space is narrowed, greater pressure is placed on the facet joints in the back of the vertebrae. These joints are made for guiding motion, not for weight-bearing. Cartilage covers joint surfaces and acts as cushions. When increased pressure is placed upon these facet joints, the cartilage wears out causing the bones to rub together, potentially causing pain and stiffness. This change is known as osteoarthritis or OA.
Borenstein DG, Wiesel SW, Boden SD: Low Back and Neck Pain: Comprehensive Diagnosis and Management. 3rd Edition. Philadelphia: W. B. Saunders, 2004.
Lawrence RC, Felson DT, Helmick CG, et al. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States: Part II. Arthritis & Rheumatism. 2008;58(1):26-35. doi: 10.1002/art.23176.