Arthritis is a general term that means inflammation of the joints. Osteoarthritis, commonly known as wear and tear arthritis, is the most common type of arthritis. It is associated with a breakdown of cartilage in joints and can occur in almost any joint in the body. It commonly occurs in the weight-bearing joints of the hips, knees, and spine. It also affects the fingers, thumb, neck, and large toe.
Osteoarthritis -- also called OA -- usually does not affect other joints unless previous injury , excessive stress or an underlying disorder of cartilage is involved.
Cartilage is a firm, rubbery material that covers the ends of bones in normal joints. Its main function is to reduce friction in the joints and serve as a "shock absorber." The shock-absorbing quality of normal cartilage comes from its ability to change shape when compressed (flattened or pressed together).