Knee-replacement surgery was once the domain of senior citizens — but no more. In fact, recent figures for the United Kingdom, United States and Finland show more and more of the surgeries are being done on arthritic Baby Boomers in their 50s — and on people even younger.

Experts in the U.K. think the nation’s growing obesity problem is partly to blame, since extra weight puts an unnecessary burden on our knees.

Professor Alan Silman, medical director of Arthritis Research U.K., said, “More knee replacements are being performed because the population is getting older and more obese – two of the main causes of knee osteoarthritis — but also because they are increasingly being carried out on younger people, under the age of 50.”

The durability of the replacement knee joints has only been assessed in patients who get them when they’re at least 60 years old, and most estimates say the joints last for about 15 years in those older and less physically active recipients.

Because of that, some doctors are concerned the new knees won’t last very long in those opting for them so much sooner, which could mean they’d have to be replaced at least once later on.

Dr. Jarkko Leskinen, an orthopedic surgeon at the Helsinki University Central Hospital in Finland, looked at the cumulative incidence of knee replacements in the country over the past three decades and found a rapid rise in the surgery for patients in their 30s, 40s and 50s.

“It is worrying because we do not know the longevity of the replacements in younger patients. We may face problems in the near future because of this,” he said, but added, “Joint replacement design and surgical technique are improving all the time.”

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