Study: 1/3 of knee replacements are questionable

Whether to replace aging knees can be a tough decision. More than 650,000 Americans underwent total knee replacement surgery last year, but a new paper from researchers at Virginia Commonwealth University suggests that a third of those were not “appropriate,” based on standard medical criteria.

The study authors analyzed 175 cases, looking at imaging tests to find the degree of arthritis, as well as each patient’s age and reported pain level. Only 44% of the operations were rated “appropriate.” Thirty-four percent were “inappropriate,” while 22% were inconclusive.

But appropriateness is in the eye of the beholder, says Dr. Jeffery Katz, an orthopedic surgeon at Brigham and Women’s Hospital in Boston. When the current criteria were developed in the late 1990s, knee replacement “was considered a treatment of last resort,” Katz writes in an editorial published alongside the study in the Journal of Arthritis and Rheumatism. Today, many are being done in relatively healthy people in their 50s and 60s.

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What’s more, some doctors say, safety and effectiveness have improved significantly since the criteria were first developed.

“Knee replacement is very effective,” says Dr. Joshua Jacobs, an orthopedic surgeon at Rush University Medical Center and a former president of the American Academy of Orthopaedic Surgeons. “The increasing demand is a marker of how well it improves function and relieves pain.”

Whether knee replacement should be used to preserve function and not just restore it “is worthy of debate,” says Dr. Daniel Riddle, the paper’s lead author and a professor in the Department of Physical Therapy and Orthopedic Surgery at VCU. “Some patients play nine holes of golf and they want to play 18, and knee replacement can help with that.”

He says the real question is whether it’s worth the cost – which typically runs between $20,000 and $40,000 – and the potential risks.

A knee replacement is major surgery; potential dangers include infection, deep vein thrombosis and pulmonary embolism. There’s even a non-negligible chance of death, although it’s less than 0.5%, according to the paper.

With younger patients, other factors come into play. Those who undergo the operation early are more likely to achieve a high level of function than patients who wait for their knees to deteriorate. New knees can also help support a higher level of activity and the health benefits that go with it. One analysis cited by Jacobs says there’s a typical lifetime benefit of $10,000 to $30,000 due to lower absenteeism, better overall health and other factors.

On the other hand, anyone getting a knee replacement in their 50s or 60s has a good chance of experiencing a re-run: approximately 10% wear out within 15 years and need to be replaced again, says Riddle.

For more, check out the American Academy of Orthopaedic Surgeons' guide for patients.

 Caleb Hellerman - CNN Medical Supervising Producer