The knee joint is especially vulnerable to injury in both healthy-weight active people and those who are overweight. But until today's Mayo Clinic presentation, no one had published results of what happens to knee implants under the stress of extreme extra weight known as superobesity. Superobesity is defined as having a Body Mass Index (BMI) that is greater than 50. Normal-weight BMI ranges from 19 to 25.
Replacing a knee joint is a common surgical procedure called total knee arthroplasty. What is less common is having a large enough group of superobese patients to comprise a statistically powerful sample to determine how implants fare in this population.
As a center of orthopedic excellence, Mayo Clinic surgeons treated 105 of these surgically and medically challenging patients between 1996 and 2006. The patients had a mean BMI of 53.6, and average age at the time of surgery was 61 years. Their outcomes were followed an average of three years after surgery.
- Overall, 40.6 percent had surgical complications and 14.3 percent had medical complications — including two deaths after the surgery.
- Surgical complications included 20 knees that had prolonged wound drainage —increasing the chance of deep infection of the implant.
- Nineteen cases needed additional operations to trim slowly healing wound edges, treat deep infection or repair failed implants.
"As with hip replacement in the superobese patient, total knee arthroplasty also is associated with a markedly higher complication rate compared to patients of normal weights," says Mayo Clinic orthopedic surgeon David Lewallen, M.D., senior author on the study. "The real concern here is that clinicians and patients need to be aware of that fact when they are making treatment decisions. In general, this group of patients is in desperate circumstances — and we really want to help them. To do that, we are trying to get the data out there that will guide management of the superobese patient. A big part of that has to be helping them lose weight prior to knee arthroplasty whenever possible."
Mayo Clinic orthopedic surgeons presented this research at the annual meeting of the American Academy of Orthopedic Surgeons (AAOS) in Las Vegas, Feb. 25-March 1.
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