Do Blanket BMI Restrictions Harm Arthroplasty Patients?

By: Peter Pollack

Study data suggest morbid obesity may be an “optimizable chronic illness”

"The morbidly obese patient with severe hip or knee osteoarthritis [OA] poses a treatment challenge,” noted Stephen J. Huffaker, MD, PhD. “With the worsening obesity epidemic, orthopaedic surgeons will be faced with this challenge even more frequently in the coming years.”

Dr. Huffaker presented scientific Paper 136, “Can We Expect Morbidly Obese Patients with Osteoarthritis to Lose Weight in a Weight Loss Program?” on Tuesday.

“Joint replacement in a severely obese patient is a physically challenging and demanding task for the surgeon and also poses increased risk to the patient,” said Dr. Huffaker. “Multiple studies have demonstrated increased operating time, increased complication rates, and decreased functional outcomes in patients with increasing BMI. This has led many surgeons to place BMI restrictions on joint replacement candidates. Because obesity is commonly considered to be reversible, this appears at face value to be a reasonable option. However, we were interested in what this means for the patient. When a morbidly obese patient is told to lose weight, how reasonable is this request? What is the likelihood of success? How much time will this take?”

Many patients fall short
The researchers conducted a retrospective review of 710 patients who participated in a nonsurgical weight-reduction program at a single hospital between 2010 and 2014. All participants were actively enrolled in the program for at least 1 year, were at least 50 years old, had a starting body mass index (BMI) greater than 30 kg/m2, and did not undergo bariatric or joint replacement surgery. Overall, 133 had hip or knee OA and 576 did not. Of those, 44 patients with OA and 172 without OA were morbidly obese (BMI ≥ 40 kg/m2). The researchers determined group differences in BMI of 5 percent to be clinically significant and powered the study accordingly.

Dr. Huffaker and his colleagues found that 17 percent of morbidly obese patients with OA and 18.2 percent of morbidly obese patients without OA lost enough weight to decrease their BMI below the morbidly obese (40 kg/m2) threshold. They noted that 95 percent of patients who achieved such weight loss started with a BMI of less than 44 kg/m2. The mean time to realize the goal was 145 ± 37 days following program enrollment. The amount of time it took patients to lose 5 percent of their body weight was not significantly different across cohorts.

“Only about 1 in 5 morbidly obese patients were able to successfully lower their BMI below 40 kg/m2 within 1 year of enrollment in the weight-loss program,” said Dr. Huffaker. “Not surprisingly, the more obese the patient was, the less likely he or she was to get below the threshold. Based on our data, for 83 percent of morbidly obese patients with OA involved in nonsurgical weight management alone, a 40 kg/m2 cutoff represented an insurmountable barrier for joint replacement surgery. And patients who started with a BMI over 45 kg/m2 had a less than 10 percent chance of losing enough weight to get below the 40 kg/m2 threshold. Most of those who were successful were able to do so within 3 to 6 months. Morbid obesity appears to have only limited reversibility for a great majority of patients.”

Unreasonable expectations
Dr. Huffaker stated that, although BMI cutoffs may represent a simple approach to filtering patients, they can create an unreasonable expectation of weight loss on many patients and can limit access to an important and life-altering procedure.

“Based on our findings, it is reasonable to place morbidly obese patients on a 4- to 6-month trial weight-loss regimen. A small number will be successful,” he said. “Although patients with starting BMI over 45 kg/m2 are less than 10 percent likely to lose weight below 40 kg/m2, 1 in 3 patients may be expected to lose at least 5 percent of their body weight during this time.

“Following this period, we recommend a candid conversation with the patient regarding the significant risks of joint replacement in the morbidly obese, including discussion of more aggressive surgical weight loss options versus an increased risk of perioperative complications given their current weight,” said Dr. Huffaker. “We do not advocate ignoring the effects of obesity on surgical outcomes and risks, but offer these data as a caution against blanket weight restrictions, as this may be a potentially discriminatory practice. We suggest instead that weight be considered an optimizable chronic illness, much as chronic obstructive pulmonary disease, diabetes, hypertension, etc.”   

Dr. Huffaker’s coauthor is Nicholas J. Giori, MD.

Details of the authors’ disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure

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