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.