Osteoarthritis is the most common form of arthritis, It occurs when the protective cartilage that cushions the ends of the bones wears down over time. A type of arthritis that occurs when flexible tissue at the ends of bones wears down. Although osteoarthritis can damage any joint, the disorder most commonly affects joints in your hands, knees, hips and spine. A joint is where two bones come together. The ends of these bones are covered with protective tissue called cartilage. With Osteoarthritis, this cartilage breaks down, causing the bones within the joint to rub together. This can cause pain, stiffness, and other symptoms. It occurs most often in older people, although it can occur in adults of any age. OA is also called degenerative joint disease, degenerative arthritis, and wear-and-tear arthritis.