As the nation's collective waistline continues to expand, so does the average body mass index of patients undergoing total knee arthroplasty. But, as the authors of a new study suggest, the multiple comorbidities associated with obesity can negatively affect the results of — or even preclude — knee-replacement surgery.
The study, published recently in the Journal of the American Academy of Orthopaedic Surgeons, analyzes the risks, benefits and potential complications of total knee arthroplasty in patients considered obese, meaning anyone with a BMI higher than 30 kg/m2. The compounding effects of excessive weight on the human body may be fueling the demand for knee replacement surgery — often at a younger age than patients of a normal weight — and orthopedic surgeons can adopt a number of pre-, intra- and post-operative methods to optimize outcomes, says J. Ryan Martin, MD, the study's lead author.
"If we do decide to embark on a total knee replacement, maybe we choose not to operate on a patient with a BMI over 40," says Dr. Martin, an orthopedic surgeon with OrthoCarolina in Charlotte, N.C. "For someone with a BMI of 42 or 43, you're talking about 20 to 30 pounds, which is manageable. But if somebody has a BMI of 50 or 60, you could be talking about substantial weight loss, and you may not be able to get down to 40. That can be a difficult talk to have."
Dr. Martin says losing weight in advance of the surgery will not only reduce the risk of surgical complications, but also improve a patient's quality of life after the surgery.
"One of common things people think is: Once I get my knee replaced, I'll be more active and lose all that weight, but we need to rethink that concept. Most people either stay the same after the surgery or actually gain weight."
Other pre-operative considerations include helping patients manage chronic conditions, such as high blood pressure and diabetes. Also, optimizing nutrition is essential because many obese patients are also malnourished, a condition that increases the risk of infection and slows wound healing.
Intra-operative concerns include inadequate exposure and poor implant alignment, both of which are the result of excessive soft tissue, while post-operative risks include tibial component loosening, cardiovascular events and respiratory or wound complications. Also, obese patients are at high risk for revision surgery because of the decreased longevity of implants and an elevated risk of infection.
Dr. Martin says earlier interventions might help obese patients become better candidates for surgery.
"The first time you see a patient with knee pain, maybe you put a bug in their ear: 'You may need a knee replacement eventually, so let's do everything we can to lower your BMI now,'" he says. "Maybe we'll do an anti-inflammatory to manage the pain till the weight is lost, because the complication rate for the surgery goes through the roof when you have a BMI over 40."