Knee replacements: good for gaining function, bad for gaining weight

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Knee replacements can be a boon, making it possible for people be more mobile. But there may be a catch, as a new study has discovered: with a knee replacement can come weight gain.

It seems counterintuitive, since being more mobile might motivate one to be more active. But that’s not what researchers from the University of Delaware found when they studied two groups of people over the course of two years.

One group consisted of 106 men and women who had had a total knee replacement; the other, 31 people who had no knee pain and no surgery, who acted as a control group. Both groups had their body mass index tracked and were given functional evaluations that included testing the strength of their quadriceps (thigh) muscles. The surgery group went through a six-week comprehensive physical therapy program.

Over the two years the surgery group showed a substantial average weight gain--66% of people in that group gained an average of 14 pounds compared with the control group, which showed virtually no change in body mass. Those in the surgery group who had the weakest quadriceps muscles also gained more weight.

The researchers noted that despite gaining weight, those in the surgery group felt they increased their functional abilities. In the paper, the researchers wrote, ‘This reinforces the idea that high body weight should be treated as a separate condition that will not resolve with an increase in functional ability.’ The authors also make the case that while osteoarthritis is not life-threatening, gaining weight does carry risk factors such as cardiovascular disease.

The study appears in the online edition of the journal Osteoarthritis and Cartilage.

-- Jeannine Stein