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Extreme Obesity No Obstacle to Knee Replacement Surgery

From the American Academy of Orthopedic Surgeons
Substantial Benefits Justify Intervention, Experts Claim

SAN DIEGO—Physicians should not discourage patients who are extremely obese from undergoing total knee arthroplasty because of concerns about increased risk of complications or failure thought to be associated with excessive weight, experts reported at the American Academy of Orthopedic Surgeons annual meeting.

Robert J. Krushell, MD, associate director of the Baystate Medical Center Hip and Knee Replacement Program in Springfield, Mass, and colleagues compared the results of total knee arthroplasty in 39 extremely (or morbidly) obese patients (body mass index [BMI] >40 kg/m2) and 39 nonobese patients (BMI <30 kg/m2). The 2 groups were matched for age, gender, and date of their procedure.

Although extremely obese patients had a greater rate of minor wound complications, suboptimal alignment, and need for late revision, problems in this group were relatively infrequent overall. In addition, a substantial improvement in Knee Society scores and a high rate of patient satisfaction were evident in the severely obese cohort. (The Knee Society scoring system is a widely accepted functional outcome measure for total knee arthroplasty that assesses such parameters as pain, range of motion, and ability to walk on level surfaces and ascend and descend stairs.)

“The rapidly growing incidence of extreme obesity, coupled with the fact that obesity is known to be associated with an increased risk of osteoarthritis, means that doctors are experiencing a surge in the number of morbidly obese patients who require knee replacement surgery,” Dr Krushell pointed out.  

“Unfortunately, there has been relatively little information about the short- and long-term outcome of total knee arthroplasty in this population,” he said. “For example, the question arises as to whether morbidly obese patients have more perioperative complications, as well as a higher long-term failure rate, due to the increased load on their arthroplasty or, alternatively, if a possibly lower physical activity level is sufficient to decrease the risk of mechanical failure.”  

Overall, 8 knees in the severely obese group had minor complications that resolved with conservative treatment and without sequelae. There were no wound problems in the control group.

There was also a tendency for the total knee arthroplasty in the severely obese group to be suboptimally aligned, with the knee left in “somewhat excess varus.” And indeed, in this group, 5% of the patients needed revision surgery compared with none of the control patients.

Nevertheless, although the severely obese patients had overall lower knee function scores pre as well as postoperatively, the important conclusion from this study is that both groups had marked improvements in their Knee Society scores at the latest follow-up at a mean of 90 months.

Scores improved from 61 points preoperatively to 136 points in the severely obese group and from 72 to 158 points, respectively, in the control group. In addition, 85% of severely obese patients and 95% of controls reported being satisfied with their revised knees.

Dr Krushell said that these results demonstrate that severely obese patients can derive important benefits from total knee arthroplasty, even if the benefits are not as great as for patients who are not severely obese.

He added that ongoing follow-up will be needed to assess even longer- term success and failure rates for total knee arthroplasty in extremely obese persons.

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