Nearly one out of every three knee replacements is considered “inappropriate,” according to new research reports. The latest reports suggest that a third of all knee replacements in the U.S. were deemed inappropriate based on findings when using a patient classification system created and validated in Spain.

The study was published in Arthritis & Rheumatology, a journal of the American College of Rheumatology. The new research indicates the need for agreement among medical professionals in the U.S. on patient selection criteria for individuals in need of a knee replacement surgery.

According to the Agency for Healthcare Research and Quality reports, an estimated 600,000 knee replacements or more are performed every year in the U.S. Over the past 15 years, there has been a significant growth in the use of total knee arthroplasty. In addition, studies indicate a yearly volume increase of 162 percent in knee replacement surgeries covered by Medicare between 1991 and 2010. While some experts think the growth is lined to using an effective procedure, others believe that the surgery is overused.

Dr. Daniel Riddle, study leader, from the Department of Physical Therapy at Virginia Commonwealth University in Richmond, said in a statement, “To my knowledge, ours is the first U.S. study to compare validated appropriateness criteria with actual cases of knee replacement surgery.”

According to the Mayo Clinic, knee replacement surgery can assist in relieving pain and restoring function in severely diseased knee joints.