Osteoarthritis, or degenerative joint disease, is one of the oldest and most common types of arthritis. It is characterized by a breakdown of the joint's cartilage. Cartilage is the part of the joint that cushions the ends of bones. Cartilage breakdown causes bones to rub against each other, causing pain and loss of movement. Osteoarthritis can range from very mild to very severe, and most commonly affects middle-aged and older people. It affects hands and weight-bearing joints such as knees, hips, feet and the back.