In all of your body’s joints, a smooth layer of cartilage covers the ends of each bone in the joint. This cartilage cushions the ends of bones, absorbing shock and preventing the bones from rubbing against each other. Over time and with repeated use, this cartilage can deteriorate, resulting in OA. The smooth surface of the cartilage becomes rough, causing irritation and inflammation. If the cartilage wears away entirely in spots, the bones will rub against each other and incur damage. Over time, the pressure on the bone stimulates it to grow resulting in raised processes called bone spurs that can limit mobility and cause a lot of pain.

What causes the cartilage to deteriorate? Researchers suspect it is a combination of factors including excess weight that puts stress on joints, joint overuse, joint injury or stress, family history, and the aging process. While aging does not cause OA, it is definitely a factor in developing the disease. As we age, the large molecules that help give cartilage the ability to absorb shock are made in smaller amounts and in less-effective forms. This makes cartilage break down more easily and probably contributes to most cases of OA in older people. It is estimated that 70-80% of the population shows evidence of OA by age 70 (although only about half of them will have symptoms of OA).

OA can occur in younger people as well. In these cases, the cause can be a joint injury or severe joint stress such as might occur from playing competitive sports. Another possible cause is a genetic or developmental abnormality in the structure of the joint which can cause excess wear. Finally, inherited abnormalities in cartilage structure can also cause joint cartilage to degenerate at a young age.