Weight Loss Before Knee Surgery May Boost Mobility, But Doesn't Lower Complications

A Duke University School of Medicine study suggests that losing weight before knee replacement improves mobility three months of surgery, but it doesn’t appear to affect the risk of infection or other complications. 

Despite common advice for patients to slim down before such surgeries to improve surgery results, the study, published in the February issue of the Journal of Arthroplasty, offers a more nuanced perspective of the impact of preoperative weight loss.  

The study based on 90 total knee arthroplasty patients showed no significant difference in rates of revision surgeries, prosthetic joint infections, emergency department visits, or hospital readmissions between those who lost weight during a medically supervised weight loss program and those who didn’t lose weight. 

Weight loss could be a valuable tool for a faster recovery, but it may not translate to a direct reduction in post-surgical complications.  

“Our findings encourage larger, better controlled investigations that I’m hopeful and optimistic will show patients who lose weight are decreasing their risk of complications,” said Albert J. Rechenmacher, a fourth-year medical student at Duke School of Medicine who led the study co-authored by a weight loss specialist, physical therapist, and orthopedic surgeons. “But that hasn’t been borne out by the data yet.”   

In the meantime, he said, “it’s troubling to see patients who are trying hard to do something that’s difficult in order to improve their health, and not be able to tell them there is outstanding consensus that losing weight will mitigate surgical complications.”   

Pain Perceptions 

Researchers used the PROMIS system to assess patient function and mobility, in which individuals report the difficulty or ease of performing tasks like walking 100 feet or climbing stairs.  

Surprisingly, there was little difference in pain interference scores in the weight loss group, said senior study author Maggie Horn, PhD, MPH, a physical therapist and researcher who is an assistant professor in the Duke Department of Orthopaedics. Pain interference tracks the extent to which pain hinders sleep or daily activities.

After surgery, pain interference scores were 57.8 in the weight loss group and 58.2 among those without weight loss; although all patients had less pain after surgery.  

Authors of the Duke study included obesity researcher William S. Yancy, Jr. MD, professor in the Department of Medicine, and orthopedic surgeons Michael Bolognesi, MD, Sean P. Ryan, MD, and William A. Jiranek, MD.   

Higher levels of obesity are associated with complications from surgery, but it's not clear that preoperative weight loss will necessarily reduce that risk, authors note.

Although small and based on observational findings, the Duke study aligns with a 2014 study that examined preoperative weight loss and knee surgery results:  no significant difference was found in surgical site infection or 90-day hospital readmission among patients who lost weight. 

The current study distinguished itself by focusing on participants actively attempting to lose weight through a supervised program, eliminating ambiguity about whether weight loss was intentional or unintentional due to an undiagnosed health condition.  

Managing Weight Loss Expectations  

Many patients try to lose weight before a total knee replacement, either to ease symptoms of osteoarthritis or optimize surgery results. 

In fact, orthopedic surgeons and insurers often advise those with obesity or are overweight to lose weight to meet a BMI cutoff of 40 or lower before undergoing total knee arthroplasty.  

The retrospective study included mostly women, aged 42 to 82, who engaged in a supervised weight loss program 18 months before knee surgery.   

Half of them experienced weight loss through dietary counseling, exercise, and behavioral modifications, resulting in an average BMI reduction of 10%. At the time of surgery, the participants’ average BMI was 37.7.  

“From the surgeon's perspective we will always want our patients to do everything they can to optimize their overall health,” said Bolognesi, chief of the Division of Reconstructive Surgery at Duke Health. “Preoperative weight loss is something that we have tried to implement for many years. Sometimes we as the surgeon are actually the first person to talk about weight loss with a patient.

“The results from the present study are mixed, like many other studies, but we have to keep studying interventions like this to make sure we are doing the right things for the patients who need these operations,” he said.

The new research comes as knee replacements are on the rise, in part because of the aging population and increases in obesity.

The nearly one million knee replacements done each year is expected to triple to 3.5 million by 2030, according to the American Academy of Orthopedic Surgeons.