A new study finds that men undergoing total knee replacement (TKR) are more likely to develop certain complications, including wound infection, and have higher revision rates at five years than women do. But researchers stress the surgery is still very safe and effective.

“The risk for complications is low for TKR in both men and women,” says study co-author Jasvinder Singh, MD, a practicing rheumatologist and associate professor of medicine at the University of Alabama at Birmingham School of Medicine. “We found that in risk-adjusted analyses, the relative risk rates were higher in men compared to women. I would not interpret this as TKR being riskier in men. Rather, that certain – but not all – complications may be slightly higher in men than women.”

Nearly 700,000 TKR surgeries are performed in the United States each year, according to the Centers for Disease Control and Prevention in Atlanta – and most are done without a major problem. In fact, the rate of serious complications is less than 2 percent, according to the American Academy of Orthopaedic Surgeons.

The study, which was published in Arthritis Care & Research online, examined data from about 18,000 knee replacement surgeries performed in Pennsylvania during a one-year period. The authors used data from the Pennsylvania Health Care Cost Containment Council, which includes demographic information on all patients discharged from 170 hospitals (excluding Veterans Affairs hospitals, which serve a population different from the general public). The average age for both men and women in the study was 69.

The authors found that men had a 48 percent higher risk of mortality from any cause after one year, as well as a 31 percent higher risk of wound infection. Men were also 25 percent more likely to be readmitted to the hospital within 30 days, and the five-year revision rate – that is, surgery to repair or replace the prosthetic within the first five years – was 20 percent higher in men than in women. There were, however, no significant differences between men and women in the rate of specific complications within 30 days of surgery, such as heart attack, blood clots or prosthetic failure.

The authors suggest men may have a higher five-year revision rate because of differences in knee biomechanics and a higher level of physical activity. And the increased risk of mortality, they write, “likely reflects the gender-specific cardiovascular disease mortality advantage for women.”  

“In practical terms, this means men may need to be watched more closely in the follow-up period,” says Dr. Singh.

“This is a pathfinder paper,” says R. John Wright, MD, attending orthopaedic surgeon at Brigham and Women’s Hospital in Boston. It says, “Here’s what we found. Now you guys find out why.” As such, Dr. Wright says, the study leaves many unanswered questions.

“It’s possible more men are involved in heavy work or heavy exercise,” Dr. Wright says. “But the researchers were not in a position to look at BMIs, so we don’t know if it’s a BMI effect.” BMI refers to body mass index – a number calculated from a person's weight and height that is used to determine if a person is of “normal” weight or not.

The authors acknowledge the database used for the analysis had limitations. It did not, for example, have information about BMI, pre-operative pain or the severity of the arthritis, as seen on an X-ray – all of which can affect outcomes. Additionally, it contained information only on patients older than 65. Dr. Singh says they also did not have information on whether men might have been less compliant after their surgeries than women (for example, by not doing physical therapy).

“This study serves as a reminder that there is much to learn about improving outcomes after TKR in patients,” says Dr. Singh, who adds that the rate of TKRs is expected to soar through 2030. “Closer monitoring might help, but this strategy may need to be tested. … A more reasonable approach might be to investigate the underlying reasons for this disparity, and the development of strategies to address those to improve outcomes.”