Specific causes for most forms of arthritis are not yet known. The ends of the bones at the joint joint are covered with a material called cartilage, which cushions the bone and allows the joint to move easily without pain. The joint is surrounded by a membrane called the synovium, which contains a lubricating fluid that helps reduce friction and wear in a joint. Ligaments, bands of strong fibrous connective tissue, connect the ends of the bones together to keep the joint stable and to facilitate or limit movement. Tendons, fibrous connective tissue that connect bones to muscle to enable it to move.
Inflammation is an immune-system response that occurs with any type of bodily injury.
In arthritis, inflammation occurs in the damaged area of a joint. Damage may be caused by any number of conditions, including trauma, infection, neurogenic disturbances, degenerative joint disease, metabolic disturbances, or for unknown reasons. Symptoms of inflammation include redness and warmth in the area of the injury, swelling, and pain. It is a chronic disease involving the joints, particularly the weightbearing joints such as the knee, hip, and spine. It occurs in most people as they age, but also may occur in young people as a result of injury or overuse.