Obesity is defined as a BMI -- or body mass index -- of more than 30. According to the Rothman Institute, more than a third of Americans are obese as of 2010, which is a 110 increase over the preceding 25 years. Obesity is strongly associated with arthritis, which is the most common condition that necessitates knee replacement surgery. Although obese patients have more complications with their knee replacement surgery than non-obese individuals, the vast majority of these procedures are successful.

Knee Replacement Features

Knee replacements are usually performed when a patient's knees have been so severely damaged by arthritis or injury that everyday activities -- such as climbing stairs or walking several blocks -- become impossible. According to The American Academy of Orthopaedic Surgeons, the first knee replacement was performed in 1968; now, about 581,000 knee replacements are performed yearly in the United States 1. In a total knee replacement, an orthopaedic surgeon removes the damaged cartilage and bone of the knee, then positions new metal and plastic joint surfaces to restore knee alignment and function 1. The AAOS adds that more than 90 percent of individuals who undergo a total knee replacement experience a dramatic reduction of pain, as well as significant improvement in the ability to perform normal activities.

Considerations of Knee Surgery for Obese People

According to the Rothman Institute, obesity is responsible for 200,000 joint replacements a year in the U.S. Knee replacement surgery is more difficult with obese patients, who have a higher risk of infection, blood clots and wound complications. The Rothman Institute states that because the surgery is more difficult to perform, malpositioning and joint instability problems are more common. An orthopaedic surgeon may advise weight loss before knee surgery; with morbidly obese patients, bariatric surgery is sometimes performed before the knee operation is undertaken.

Expert Recommendations

According to HCPlive, experts at the 2007 annual meeting of the American Academy of Orthopaedic Surgeons reported that although extremely obese patients had a greater rate of minor wound complications and need for revisions in surgery, the problems were relatively infrequent overall 1. Five percent of the obese patients needed revision surgery for alignment problems -- compared with none in the non-obese group -- but 85 percent of the obese patients reported satisfaction with the operation, compared to 95 percent of the non-obese individuals. In addition, the extremely obese who had undergone knee replacements made substantial improvements in Knee Society scores, which assess functional outcome, pain, range of motion, and the ability to walk and ascend and descend stairs. The overall conclusion was that obese people derive important benefits from knee replacement surgery and should not be denied it on the basis of their weight.

Research

There is some research supporting the belief that total knee replacements offer satisfactory results in obese patients. In a study conducted by N. Hamoui and colleagues and published in the January 2006 issue of "Obesity Surgery," the results of total knee arthroplasties in 21 obese patients were compared to results of knee arthroplasties in 41 non-obese patients 2. Researchers used clinical and functional parameters, radiographic results, and the need for reoperation to assess the success of the operations. Eleven years later, there were no statistical differences, leading researchers to conclude that moderate obesity does not affect the outcome of total knee replacements.