Figures from the Agency for Healthcare Research and Quality show that more than 600,000 knee replacements are performed each year in the US. This surgery has become increasingly more common over the past 15 years, with studies showing a 162% annual volume increase in Medicare-covered knee replacement surgeries during 1991-2010.
Experts are divided on the reasons for this growth, with some maintaining it demonstrates that the procedure is effective, while others argue the surgery is being overused. One concern of the critics who believe total knee arthroplasties (TKA) are being overused is that the procedure "is highly reliant on subjective criteria."
For the new study, researchers from Virginia Commonwealth University in Richmond examined the criteria that is used to determine appropriateness for TKA.
The authors point out that the investigated criteria have not been studied in the US and have been developed in other countries.
"To my knowledge, ours is the first US study to compare validated appropriateness criteria with actual cases of knee replacement surgery," says lead author Dr. Daniel Riddle from the Department of Physical Therapy at Virginia Commonwealth University.
Dr. Riddle examined a modified version of an appropriateness classification system developed in Spain and the Western Ontario and McMaster Universities Arthritis Index (WOMAC) Pain and Physical Function scale.
In the study, Riddle and colleagues note that the Spanish criteria are considered by many experts in the field to be "among the most powerful tools for improving quality of care and controlling costs."
Analysis finds that 44% of TKA surgeries are 'appropriate' and 34% are 'inappropriate'
The classification systems were used to assess participants enrolled in the Osteoarthritis Initiative - a 5-year study of 4,796 people partly funded by the National Institutes of Health.
One concern of critics who believe total knee arthroplasties are being overused is that the procedure "is highly reliant on subjective criteria."
Looking at a sub-set of 175 people who underwent TKA surgery, Dr. Riddle's analysis found that 44% of surgeries were classified as "appropriate," 22% were "inconclusive," and 34% were "inappropriate."
The mean age of knee replacement patients in the study was 67 years old, and 60% of them were female.
"Our finding that one third of knee replacements were inappropriate was higher than expected and linked to variation in knee pain [osteoarthritis] severity and functional loss," says Dr. Riddle. "These data highlight the need to develop patient selection criteria in the US."
"I agree with Riddle and colleagues," writes Dr. Jeffery Katz - from the Orthopedic and Arthritis Center for Outcomes Research at Brigham and Women's Hospital in Boston, MA - in a linked editorial.
"We should be concerned about offering total knee replacements to subjects who endorse 'none' or 'mild' on all items of the WOMAC pain and function scales."
The new study also highlights that there are many variables involved in the decision to undergo TKA surgery. Severity of symptoms and the psychological readiness of the patient are two important factors, but in addition to the variables examined in the study, there are a wide range of variables specific to the patient that a surgeon will consider when making the decision for or against TKA surgery.