U Research Shows Obesity Has No Bearing on Need for Knee and Hip Replacements

U Research Shows Obesity Has No Bearing on Need for Knee and Hip Replacements

Nov 24, 2003 5:00 PM

Obesity is a risk factor for osteoarthritis (OA) that may lead to hip- or knee-joint replacement surgery, but it does not affect how quickly the new joints wear out, according to a recent study by University of Utah School of Medicine researchers.

Osteoarthritis, a degenerative joint disease, is one of the most common types of arthritis. It affects about 5 percent of Americans, usually middle-aged and older people.

"We expected all along that overweight people are more likely to develop osteoarthritis and are at risk for joint replacement surgeries," said Kurt Hegmann, M.D., M.P.H., research associate professor of family and preventive medicine and the study's principal investigator. "But it surprised us that there was no direct relationship between obesity and the need for revision surgeries." Research results appear in the November issue of American Journal of Preventive Medicine.

Hegmann, director of the Rocky Mountain Center for Occupational and Environmental Health at the U medical school's Department of Family and Preventive Medicine, said the effect of obesity on OA is a serious concern in this country because of rising obesity rates. According to 1999 national statistics, 61 percent of the American adult population is either overweight or obese. Overweight is defined as having a body mass index (BMI) of 25-30, and obesity, as having a BMI of more than 30.

The study involved a case group of 840 hip- and 911 knee-joint replacement surgery patients at LDS Hospital in Salt Lake City, ages 55-74, from 1992-2000. It also included a control group of 5,578 healthy Utah residents enrolled in the National Cancer Institute's Prostate, Lung, Colorectal, and Ovarian Cancer screening trial from 1996-2000, which is a study that is under way at the University of Utah.

Participants from the case group were categorized according to age, gender, and BMI. Participants from the control group were categorized according to age and self-reported height and weight. BMI was calculated for each control.

Computer analyses showed a strong relationship between increasing BMI and the likelihood of hip and knee replacement surgery, but it did not show any link at all between increasing BMI and revision of hip- and knee-joint replacements. "Either obesity does not play a role in wearing out the surgical joints faster than in non-obese patients, or perhaps activity levels of non-obese patients confounded this relationship," according to the study.

In addition to Hegmann, the other investigators in the study are: Aaron M. Wendelboe, M.S.P.H., Jeremy J. Biggs, M.S.P.H., Chad M. Cox, M.P.H., Aaron J. Portmann, Jacob H. Gildea, M.P.H., Lisa H. Gren, M.S.P.H., Joseph L. Lyon, M.D., M.P.H., all from U medical school's public health program.

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