Joint Replacement Weight Loss Requirements Challenged

Laird Harrison

July 31, 2017

Obese patients with osteoarthritis do not need to lose weight before knee or hip replacement to benefit from the surgery, a large study has found. They can benefit as much or more from the surgery as patients with normal weight, researchers say.

Wenjun Li, PhD, and colleagues from the University of Massachusetts Medical School, Worcester, published their findings in the July 19 issue of the Journal of Bone & Joint Surgery.

"Our data shows it's not necessary to ask patients to lose weight prior to surgery," Dr Li said in a news release. "It's challenging for a patient who is severely overweight and suffering in pain to exercise — often they just can't do it."

But the researchers acknowledge complications from joint replacement surgery are more likely in obese patients. Therefore, it is premature to change guidelines such as those of the American Academy of Orthopaedic Surgeons, Robert Quinn, MD, an academy spokesman, told Medscape Medical News. "We should absolutely not be telling people you don't have to lose weight," he said.

The researchers analyzed data from the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) cohort, which represents a cross-section of US patients who underwent hip and knee replacements.

They identified 2964 patients who underwent primary unilateral total knee replacement and 2040 who underwent primary unilateral total hip replacement for osteoarthritis between May 2011 and March 2013.

At baseline, the patients' scores on the Physical Component Summary, the Hip Disability and Osteoarthritis Outcome Score (HOOS), and the Knee Injury and Osteoarthritis Outcome Score, on average, were lower the more obese they were.

Six months after surgery, the average scores of all the weight groups improved on these scales. The scores of the heaviest patients remained worse than those of the normal and underweight patients, but they improved at least as much relative to baseline.

The change in Physical Component Summary scores did not differ significantly by body mass index (P = 0.37), and the HOOS and Knee Injury and Osteoarthritis Outcome Score scores improved more in some of the higher-weight groups than in the normal or underweight group.

For example, the baseline HOOS score (where 0 is worst and 100 is best) for morbidly obese hip replacement patients was 38.2 compared with 51.0 for the normal to underweight patients. But 6 months after hip surgery, the HOOS score was 88.4 for the morbidly obese patients and 91.8 for the normal to underweight patients.

The relative improvements of these groups remained similar after adjustment for baseline score, sex, age, race, education, household income, living alone, type of insurance, medical comorbidities, low back pain, number of other painful joints, and hospital surgical volume.

The findings generally correspond to those of similar studies in other cohorts, Dr Li and colleagues report.

This study did not include data on complications. The authors acknowledge that they and other researchers have previously found more complications, such as hospital readmission, among morbidly obese patients undergoing joint replacement surgery than among normal weight patients. And they write that they plan to publish a risk–benefit analysis in the future.

The authors also acknowledge the cohort in this study was not ethnically diverse: 92.7% of the knee patients and 94.1% of the hip patients were white.

Those undergoing hip replacement were 65.2 years old on average, and 42.2% had some other medical condition in addition to their osteoarthritis. Twenty-six percent were under or of normal weight (≤24.99 kg/m2), 37% were overweight (25.00 - 29.99 kg/m2), 22% were obese (30.00 - 34.99 kg/m2),10% were severely obese (35.00 - 39.99 kg/m2), and 4% were morbidly obese (≥40.00 kg/m2).

The knee replacement patients were 67 years of age, on average, and 48.7% had some other medical condition. Twenty-nine percent were obese, 15% were severely obese, and 9% were morbidly obese.

The number of total joint replacements and the prevalence of obesity in the United States have both increased during recent years. At the same time, government and private healthcare plans both are beginning to base payments on outcomes such as complications, pain, and function.

Until now, however, all the studies on obesity and hip and knee replacements Dr Li and colleagues could find were performed in other countries with patients who were older and less obese than the average patient undergoing these procedures in the United States, and these studies used data from single institutions.

Obese Patients Should Understand Potential for Complications

Surgeons should discuss the increased risk for complications with their obese patients, Dr Li said in the news release. "Patients who can lose weight should, but we acknowledge many people can't, or it will take a long time during which their joints will worsen. If they can get the surgery earlier, once function is restored they can better address obesity."

Dr Quinn said the risk for complications and the difficulty of the surgery should not be underemphasized in discussions with obese patients. "That's why I would disagree with the press release," he said. "We don't want to tell them you no longer have to lose weight. If you can you should."

However, he agreed that obese patients who cannot lose weight may still benefit from joint replacement, and he said this study adds to that understanding. "We believed until recently that the benefit part of the equation wasn't there; there is now evidence to say it is," he said.

The FORCE-TJR cohort was funded by the Agency for Healthcare Research and Quality. Three authors report receiving grant funding from Biomet outside the submitted work. Two authors report receiving grant funding from Zimmer outside the submitted work. The remaining authors and Dr Quinn have disclosed no relevant financial relationships.

J Bone Joint Surg. 2017;99:1183-1189. Abstract

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