It is characterized by the 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. Most commonly affecting middle-aged and older people, OA can range from very mild to very severe. It affects hands and weight-bearing joints such as knees, hips, feet and the back. Although age is a risk factor, research has shown that OA is not an inevitable part of aging. Obesity may lead to osteoarthritis of the knees.