America feels its weight: Knee replacements on the rise

WASHINGTON — America’s obesity epidemic is doing a number on our collective knees.

Total knee replacements more than tripled between 1993 and 2009, and researchers reporting in the June issue of the Journal of Bone and Joint Surgery say most of the increase was in younger patients with a body mass index over 25.

They crunched all kinds of data and found that knee replacement surgeries far outpaced hip replacements, which doubled during the same time period.

“The new statistics on knee replacements are consistent with the trend we have been seeing,” says Dr. Robert Bunning, with Medstar National Rehabilitation Hospital.

Studies have long showed a link between excess weight and osteoarthritis in the knees. Bunning says the hips are a bit more stable, have better muscular support and are in the middle of the body, which helps.

The knees feel that weight more, and since younger people on the whole are now gaining weight faster than the over-65 set, they are fueling the increased demand for new knees.

Bunning also notes that some of these younger patients may have sustained injuries as kids playing playing sports such as soccer or volleyball that left their knees more vulnerable. He says the knees of people who suffer minor injuries in their youth may lose their balance a little bit and wear out faster.

Add on the pressure of supporting extra weight, and the result can be big-time trouble. Bunning says to imagine a normal-weighted car on unbalanced tires, which wear out a bit quicker than normal tires. Now, take the analogy a step further. “Imagine loading up that car and [having] unbalanced tires and then driving it,” says Bunning. “You will see that the tires wear out very rapidly.”

Obviously, a good way to help prevent knee trouble is to maintain a healthy weight. But it’s equally important to strengthen the muscles that support the knees — especially the quadriceps in the front of the upper leg.

Bunning says studies in 90-year-old patients have shown that resistance training can make a big difference and lessen knee pain. And he says his number-one prescription for his patients is to stay strong or, as he puts it, “lean and mean.”

He also points to a disturbing trend: Total knee replacements usually last about 15 to 20 years, occasionally 25. When most of the people opting for the surgery were over 65, that wasn’t much of an issue. But Bunning says in the not-too-distant future, replacing the replacements will become more and more common. It’s predicted that by 2020, the number of people getting their second knee replacement will surpass those getting their first.

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