Osteoarthritis. This is the most common type of arthritis. It is a chronic disease of the joints, especially the weight-bearing joints of the knee, hip, and spine. It destroys the coating on the ends of bones (cartilage) and narrows the joint space. It can also cause bone overgrowth, bone spurs, and reduced function. It occurs in most people as they age. It may also occur in young people because of an injury or overuse.

Rheumatoid arthritis. This is an inflammatory disease of the joint linings. The inflammation may affect all of the joints. It can also affect organs such as the heart or lungs.