Knees — Your knees shouldn't wear out

Philip J. Goscienski, M.D.

January 2013

Why is knee replacement surgery one of the commonest procedures in any modern medical center? Every year more than a half-million worn out or damaged knee joints are replaced at enormous cost and with a risk of infection or other complications. Most recipients of a new knee joint can expect it to last 20 years or more but increasing lifespan will lead to eventual need for replacement in a growing number of patients.

The most common reason for knee replacement is osteoarthritis, which has several contributory factors, some of which are avoidable. Aging is the most common one and some forms of osteoarthritis are familial. Repetitive injury to the knee joint, as occurs in competitive skiers, is a common cause of arthritis but the "wear and tear" theory is not the whole story.

In the past half-century obesity has become a serious medical problem and it is a growing factor in a host of diseases. One of these is osteoarthritis but the extra weight pounding against the knee joint is not the only reason. If repeated trauma were the major cause the wrist joint and fingers would not be affected, but they are. Inflammation plays a major role in osteoarthritis. Fat cells produce chemicals that promote inflammation and degrade the cartilage of the knee joint.

Those who are overweight are twice as likely to develop osteoarthritis of the knee and for the obese the chances are nearly 3 times higher than persons whose weight is normal. Some studies show a staggering 18-fold risk for obese women. Obese diabetics face an even greater hazard because persistent elevation of blood sugar causes damage to joint cartilage

Lack of physical activity leads directly to obesity and to wasting of muscle. When the muscles of the leg become weak because of lack of exercise they no longer are able to apply a braking action with every step. Not only does that increase the impact of joint surfaces against each other, it makes the joint less stable and more prone to injury.

Moderate physical activity that strengthens leg muscles and prevents weight gain is a key factor to avoid osteoarthritis. Ordinary exercise does not contribute to the problem. However, intense, sports-related activity does increase risk, partly because of a higher likelihood of injury. Persons with established arthritis of the knee respond differently to exercise and should consult with a physical therapist.

Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at