Osteoarthritis primarily affects cartilage, a smooth tissue that covers the ends of the bone in the joint. Healthy cartilage allows bones to slide across each other and reduce the impact of exercise and pressure. When the cartilage of an osteoarthritis person ruptures and wears, causing the bones under the cartilage to rub against each other, this friction causes pain, swelling, and reduced range of joint activity. After a long time, the joints may be deformed and the edges of the joints may even grow spurs. Small pieces of broken bones and cartilage floating in the joint cavity may cause more pain and damage.