New Weight-Loss Target for Total Knee Arthroplasty

Michael Vlessides

March 13, 2019

Benjamin Keeney, PhD, presenting data showing that patients who lose at least 20 pounds before surgery have significantly better outcomes.

LAS VEGAS — For morbidly obese patients, a loss of at least 20 pounds before total knee arthroplasty might be the key to improving postoperative outcomes, a new study shows.

Patients who achieved this benchmark enjoyed shorter hospital stays than those who did not, and were less likely to be discharged to a nursing facility.

These are both "key drivers for cost, burden to the patient, and burden to the healthcare system," said researcher Benjamin Keeney, PhD, from the Geisel School of Medicine at Dartmouth College in Lebanon, New Hampshire.

Many surgeons routinely ask their morbidly obese patients to lose weight before total knee arthroplasty, but the optimal weight-loss target has remained elusive, Keeney said here at American Academy of Orthopaedic Surgeons 2019 Annual Meeting.

"There's been a debate in orthopedics over the past several years about what we do with morbidly obese patients," said Keeney, who also serves as director of healthcare research and analytics at Berkley Medical Management Solutions in Overland Park, Kansas.

"More surgeons and hospitals are refusing to operate on these individuals if their BMI is over 40 kg/m²," he told Medscape Medical News. "We wanted to get away from a single number and instead quantify the effect of weight loss for patients in an easy-to-understand fashion."

To that end, Keeney and his colleagues reviewed data from their institution from 2011 to 2016. They identified 203 people who met the criteria for morbid obesity at least 90 days before total knee arthroplasty and had a BMI measurement documented immediately before the procedure.

Of this group, 41% patients lost at least 5 pounds before surgery, 29% lost at least 10 pounds, and 14% lost at least 20 pounds. Although 27 patients (13%) no longer met the criteria for morbid obesity at the time of surgery, 23 of these still met the criteria for severe obesity (BMI, 35–40 kg/m²).

For the morbidly obese patients, the risk for discharge to a specialty nursing facility was significantly lower if they lost at least 20 pounds before surgery than if they did not (odds ratio [OR], 0.28; 95% confidence interval [CI], 0.09 - 0.94; P = .039).

And hospital stays were significantly shorter for those who lost at least 20 pounds than for those who did not (–0.87 days; 95% CI, –1.39 to –0.36; P = .001). In addition, hospital stays of at least 4 days were about 75% less common with a weight loss of at least 20 pounds (OR, 0.24; 95% CI, 0.07 - 0.88; P = .31).

A loss of 5 or 10 pounds was not associated with a difference in any outcome. And there were no differences among any of the groups with respect to operative time or pain score.

"The interesting thing is that among people who lost at least 20 pounds, their mean BMI actually never fell below 40; they were still considered morbidly obese at surgery," Keeney reported. "Furthermore, they gained a lot of the weight back after surgery, and yet they still did better."

Even if the weight loss is temporary, we see better outcomes.

"So even if the weight loss is temporary, we see better outcomes," he said. "Obviously this is a first study and we've got to replicate these findings in bigger groups, but they're promising nonetheless."

This study is particularly timely. "We all have many patients with a BMI over 40," said Charles DeCook, MD, from Arthritis and Total Joint Specialists in Atlanta.

"We often tell those patients to lose weight and come back when they're done," he explained. "But given the findings of this paper, do we really need them to come back when their BMI hits 40, or is it good enough if they just lose 20 or 30 pounds?"

Nevertheless, DeCook said he is somewhat skeptical of the findings: "The results seem to suggest that weight loss changes disposition and length of stay, which I don't necessarily buy."

"I find it hard to believe that someone losing 20 pounds is really going to determine if they go to a skilled nursing facility or if they go home, and when they go home," he told Medscape Medical News.

Despite this, he said, "I think the researchers are to be commended for their efforts. Their study certainly helps us ask more questions about what our goals should be with these individuals."

I find it hard to believe that someone losing 20 pounds is really going to determine if they go to a skilled nursing facility or if they go home, and when they go home.

Keeney said he believes the study has the potential to make a significant impact, particularly with respect to patient burden and cost reduction.

"Previous research has examined whether being discharged to a nursing home is helpful, with conflicting results," he explained. "If we can get patients away from that, it can only benefit them — and society.

"In the end, we want to make sure that such valuable space is reserved for people who truly need it," he added.

This study received no external funding. Keeney and DeCook have disclosed no relevant financial relationships.

American Academy of Orthopaedic Surgeons (AAOS) 2019 Annual Meeting: Abstract P0090. Presented March 12, 2019.

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