How fat or thin a person is doesn’t seem to have much bearing on the rate of failure of knee implants, and the time to failure, research suggests.

Obesity is a risk factor for knee arthritis and knee replacement surgery is the definitive surgical treatment for severe knee arthritis. Therefore, a high percentage of subjects treated are overweight.

Dr. Barbara Bordini, of Istituto Ortopedico Rizzoli, Bologna, Italy, and colleagues examined how being overweight or obese affects the outcome of knee replacement surgery. They studied 8892 patients who underwent total knee replacement surgery between 2000 and 2005 and were followed for an average of 3 years.

Based on their body mass index (BMI), 19 percent of the patients were normal weight, 48 percent were overweight, 31 percent were obese, and almost 2 percent were morbidly obese.

Knee implant failure rates were similar among the different weight groups. Among 1840 knee implants in normal-weight patients, there were 36 failures (1.96 percent). Among overweight subjects, there were 87 failures out of 4692 (1.85 percent) implants. There were 59 failures out of 3031 (1.94 percent) implants in obese patients, and 4 failures out of 172 (2.3 percent) implants in morbidly obese patients.

The average time to failure was also not markedly different among the groups. Time to knee implant failure was 1.57, 1.48, 1.60, and 1.77 years, respectively, in the normal-weight, overweight, obese, and morbidly obese patients.

“The link between excessive body weight and health is an important concern for public health policy,” the investigators note. “Based on our evidence, however, it does not appear justified to give low priority to obese subjects for total knee arthroplasty, which would, in virtue of restored ability to move, lead to weight loss, which undoubtedly should be the primary objective.”

SOURCE: BMC Musculoskeletal Disorders, March 2009.