How does a patient’s weight impact total knee replacement surgery? That was the focus of two studies presented recently at the 2013 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS). While one study, out of Singapore, found that surgical outcomes were not so different between obese and normal-weight patients, a second study, out of the United States, found that the costs were.

Obese patients have long been told to lose weight before undergoing joint replacement surgery in the hopes of reducing complications, achieving faster recoveries and producing better outcomes. But researchers from Singapore didn’t find that to be the case.

The researcher followed 77 obese patients and 224 normal/overweight patients for two years, starting right before surgery. Obese was defined as having a body mass index (BMI) greater than 30. They found that obesity alone did not significantly raise the risk of surgical complications and  – after taking into account age, gender and other health conditions – obese patients overall had outcomes as good as those of normal-weight patients.

“Despite some studies highlighting the increased propensity for wound complications, deep infections and thromboembolism among the obese, these possible complications did not translate to poor clinical outcome in [our study’s] obese group in the short term follow-up of two years,” explains lead study authors Chin Tat Lim, MD, from the University Orthopaedic Hand and Reconstructive Microsurgery Cluster at the National University Health System in Singapore.

Dr. Lim says that because his team’s results don’t indicate that weight has a large effect on the outcome of a knee replacement, perhaps it’s not necessary for doctors to insist that patients lose weight before getting a total joint replacement. “Physicians should not withhold knee replacement therapy from obese patients. Obese patients do seem to benefit in similar ways from knee replacement surgery compared to non-obese patients,” Dr. Lim says.

But others are not convinced. Andrew Urquhart, MD, an associate professor of orthopaedic surgery at the University of Michigan Health System in Ann Arbor, is concerned that Dr. Lim’s study results are based on a relatively small number of participants. More importantly, he says, the researchers didn’t stratify obese patients. He says there can be complications following joint replacement surgery in those with a BMI greater than 35 – and the risks go up even more when BMI tops 40.

“If they chose a BMI cutoff of 35 or 40 I think they would have had a much different outcome,” Dr. Urquhart says. “I think they lumped in so many good performing, slightly obese patients with a BMI just above 30 with the morbidly obese – it skewed their data.”