Previous studies have found that knee and other joint replacement surgeries in recent decades have risen in the United States, as well. Of the more than 600,000 TKRs done in the U.S. in 2009, according to an editorial accompanying the study, the greatest increase was among patients ages 45 to 64. “The findings from Finland are consistent with observation in US, where the number of TKRs doubled in the last decade and the number of knee replacement in younger persons tripled,” says editorial co-author Elena Losina, PhD, an associate professor of orthopaedic surgery at Harvard Medical School, and co-director of Orthopedics and Arthritis Center for Outcomes Research at Brigham and Women’s Hospital.

One explanation for this significant increase “could be that baby boomers may opt for elective operations at an earlier stage with milder symptoms than did earlier generations. And good results after total knee replacements in older patients may have lowered the threshold for performing them on younger patients,” Dr. Leskinen says.

Although an increase in obesity and heavy exercise, both of which can lead to osteoarthritis, or OA, may contribute to the increase, he says they are not the whole story. “In Finland the incidence of OA itself is not increasing at the same rate as the incidence of knee replacement surgery. In fact, the incidence of OA is decreasing,” he says. “So the rise in replacement surgery is not solely due to factors known to increase the incidence of OA.”

Knee replacement surgeries have a high success rate; according to earlier U.S. studies, less than 1 percent have to be revised due to failure and they have an 85 percent rate of symptom relief. But most of those figures come from patients in their 60s and 70s, says Losina. “Younger people undergoing total knee replacement may be more active and at higher risk of revision.”   

Dr. Leskinen agrees. “We don’t know yet if it will be a problem for the younger age group,” he says. “Younger people are usually physically more demanding, and their life expectancy is higher, so they might be at greater risk for revision surgery.”