4.5 million people in the U.S. have knee replacements

More than 4.5 million people in the U.S. are walking around with knee replacements, a study finds, and replacement surgeries have more than doubled in the last 10 years.

The study, presented this week at the American Academy of Orthopaedic Surgeons annual meeting in San Francisco, provided a glimpse into not only how prevalent knee replacements have become, but who’s having them and why.

Researchers analyzed data from the U.S. Census, the National Health Interview Survey, the Multicenter Osteoarthritis Study and the Osteoarthritis Initiative. They found the biggest increase in knee replacements happening among younger people. Osteoarthritis is the major cause.

Among people age 50 and older, 4.7% have had a knee replacement, with a higher percentage reported among women (5.3%) than men (4.1%). Of those ages 70 to 79, 7.1% of men and 8.2% of women have had the surgery, and among those age 80 and older, about 10% have at least one replaced knee.

Total knee replacements have become so widespread they’re more common than national rates for rheumatoid arthritis and congestive heart failure.

That could translate, the authors said, into more revisions of the replacements as well as more complications.