Osteoarthritis is the most common type of arthritis, most often occurring in older people. The condition mostly affects cartilage, the tissue that covers the ends of bones where they meet to form a joint. In healthy individuals, cartilage lets bones glide over one another and absorbs some of the shock from physical movement. In patients with osteoarthritis, the surface layer of cartilage breaks down and wears away. Because of this, the bones begin to rub against one another instead of against the cartilage, causing pain, swelling, and loss of motion of the joint. Over time, the joint may lose its normal shape. It's possible for small deposits of bone (called osteophytes or bone spurs) to grow on the edges of the joint. Additionally, bits of bone or cartilage can break off and float inside the joint space. This can cause more pain and damage.
People with osteoarthritis tend to have joint pain and some movement limitations. Unlike some other forms of arthritis, such as rheumatoid arthritis, osteoarthritis affects only joint function and does not affect other areas of the body, such as skin tissue, the lungs, eyes, or blood vessels.