About one-third of knee replacement surgeries in the U.S. were classified as “inappropriate,” which is higher than expected, Virginia researchers assert in a new study.

The data supports the need for “consensus development of criteria for patient selection” among U.S. practitioners who treat candidates for knee replacement surgery, the researchers said.

Daniel L. Riddle, Ph.D., and his colleagues from the Virginia Commonwealth University in Richmond, VA, conducted the study using data from 205 people who had undergone total knee arthroplasty surgeries. Each individual was enrolled in the Osteoarthritis Initiative, a prospective 5-year study sponsored by the National Health Institute.

The researchers then used an appropriateness classification system to classify each surgery as “appropriate,” “inconclusive,” or “inappropriate.” They also used pain, physical function, knee motion, laxity, age and radiographic measurements. The average age of a person in the data set was 67 years, and 60% were women.

Results showed that about 44% of the surgeries were appropriate, about 22% were inconclusive and about 34% were inappropriate. Based on previous evidence and research, the hypothesized prevalence rate for inappropriate classifications was 20%.

The Agency for Healthcare Research and Quality reports more than 600,000 knee replacements are performed in the U.S. each year. By 2030, the AHRQ estimates an 85% increase in knee replacement surgeries.

Results appeared June 30 in Arthritis and Rheumatology