Osteoarthritis is a disease where the cartilage of the joints wears away, and the bones start to rub together.
The knee is the biggest joint in the body, and it carries a lot of weight.
Harvard Medical School state that the knees support the equivalent of one-and-a-half times a person's body weight. For a 150-pound woman, that works out to 225 pounds of force per step.
As people get older, the task of carrying this weight can wear down the cartilage that covers the ends of the bones in a joint.
