The number of knee replacement surgeries in people younger than 60 jumped 130-fold between 1980 and 2006, according to a Finnish study published online in Arthritis & Rheumatism in January. The greatest increase was among people ages 50 to 59 and occurred during the last 10 years of the study. It’s a trend that is raising concern among some experts.

“The finding was higher than we suspected. We noticed a certain increase in our own practice, but the overall increase was still surprisingly high,” says the study’s lead author, Jarkko Leskinen, MD, an orthopaedic surgeon at Helsinki University Central Hospital in Finland. “That led us to [wonder if it’s a] wise direction. We don't know how well knee replacements function in younger patients – or what is the longevity of these implants in younger people. More studies [like] this are needed.”

Dr. Leskinen and his team analyzed data on almost 75,000 partial and total knee replacements, or TKRs, performed in Finland for “primary osteoarthritis” between 1980 and 2006. They found that over the course of the study, the number of TKRs increased from 0.5 to 65 per 100,000 Finns ages 30 to 59. The number of partial knee replacement surgeries grew from 0.2 to 10 per 100,000 in the same age group.

While the incidence of TKR increased for both men and women younger than 60, it remained consistently higher throughout the study period for women; by the end of the study, TKRs were more than twice as common in women as in men.
 

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.”