BMI Not Sufficient to Deny Total Joint Surgery: New Study

If Mr. Smith is a few pounds too heavy for total knee arthroplasty (TKA), are we denying surgery to someone who may in fact have a comparatively complication-free experience?

This is the zeitgeist of new work from the University of Iowa titled, “What is the Impact of Body Mass Index Cutoffs on Total Knee Arthroplasty Complications?” The study appears in the December 21, 2021 edition of The Journal of Arthroplasty.

“The national obesity epidemic and increasing demand for total knee arthroplasty led to interest in this topic,” co-author David DeMik, M.D., Pharm.D. told OTW. “In addition to being a growing national problem, many patients who are deemed too ‘high risk’ for joint replacement are prescribed weight loss.”

“Unfortunately, many are unable to achieve this, then undergo a surgery at a higher body mass index (BMI) and with potentially worse arthritis. A similar study from Stanford by Dr. Nicholas Giori found similar results in veteran patients and our goal was to see if the findings were similar in a more generalizable patient sample.”

The researchers looked at individuals who had elective, primary TKA from 2015 to 2018 (from the American College of Surgeons National Surgical Quality Improvement Program database; Common Procedural Terminology code 27447). They used BMI cutoffs of 30, 35, 40, 45, and 50 kg/m² to model the incidence of complications if TKA would have been permitted or denied based on the BMI.

“A total of 314,719 patients underwent TKA, and 46,386 (14.7%) had a BMI ≥40 kg/m²,” wrote the authors. “With a BMI cutoff of 40 kg/m², 268,333 (85.3%) patients would have undergone TKA. A total of 282,552 (94.8%) would experience complication-free surgery, and 17.3% of all complications would be prevented.”

“TKA would proceed for 309,479 (98.3%) patients at a BMI cutoff of 50 kg/m². A total of 293,108 (94.7%) would not experience a complication, and 2.8% of complications would be prevented. A BMI cutoff of 35 kg/m² would prevent 36.6% of all complications while allowing 94.8% of complication-free surgeries to proceed.”

“The majority of obese patients can undergo elective total knee arthroplasty without experiencing an early complication,” commented Dr. DeMik to OTW. “Any BMI cutoff for knee replacement will deny some patients a procedure that would have occurred without any complication. Raising the BMI cutoff allowed more patients to undergo complication-free surgery while preventing a relatively smaller number of complications. Conversely, lower BMI cutoffs did seem to considerably restrict access to surgery.”

“This study provides additional information about how to navigate risks of total knee arthroplasty in the obese and morbidly obese. While many patients with BMI exceeding the traditional cutoff of 40 kg/m² can undergo surgery without an early complication, it is important to remember complications still do occur and the follow-up period for this study is relatively short (30-days). The decision to undergo joint replacement is best done with shared decision making between patients and surgeons, taking into account all patient factors rather than just a BMI number.”