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SALT LAKE CITY, April 22-Americans are buckling under their own weight insofar as their knees are concerned.

In an effort to quantify the damage to menisci from bulky bodies, a University of Utah team found in a study of more than 10,000 people that there is a dose-response relationship between body mass index (BMI) and meniscal surgery in middle-aged and older adults.

That goes for both men and women, Kurt T. Hegmann, M.D., M.P.H., and colleagues reported in the May issue of American Journal of Preventive Medicine. Knee meniscal injuries are common with the prevalence of degenerative meniscal changes in reported asymptomatic persons, ranging between 11.1% and 31.5%.

The study found that men with a BMI of 27.5 or higher and women with a BMI of 25 or higher were three times more likely to tear menisci. What's more, men with BMIs over 40 were 15 times more likely and women who had a BMI of 40 were 25 times more likely to suffer a torn meniscus.

A relationship had been previously suspected, but never measured between weight and the disruption of the fibrocartilage pads between the femoral condyles and the tibial plateaus.

In the retrospective case-control study, the researchers looked at 515 patients who underwent meniscal surgery between 1996-2000 at two hospitals in Utah. They were compared with 9,944 Utah residents enrolled in the National Cancer Institute's Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial during that same time period.

Participants age 50 to 79 were grouped into 10 BMI categories ranging from 20 to greater than 40. A BMI over 25 is categorized as overweight; over 30 means clinical obesity.

Age-adjusted odds ratio for an increased chance of needing meniscal surgery with those who had a BMI of 40 or higher were 15.0 (95% confidence interval=3.8-59.0) for men, and 25.1 (95% CI=10.2-60.8) for women.

For both sexes with a BMI between 27.5 and 29.99, men had a three times greater risk for knee surgery (95% CI=1.2-7.4) and women faced a 2.9 increased risk (95% CI=1.5-5.8).

Of the 515 operations, 29 patients or 5.6% underwent two meniscal operations, one on each knee.

Dr. Hegmann said the extra pounds Americans carry accounts for up to 450,000 of the 850,000 operations for meniscus tears each year, at an average of $3,000 per procedure.

"There's a potential savings of $1.3 billion in the costs associated with meniscus tears in overweight and obese people," Dr. Hegmann said.

Menisci tears are a common athletic injury, but now they are being seen more in obese individuals. "As body mass index increases, the strain and torque in the knee joint during rotation likely increases," the researchers wrote. "Whether other mechanisms contribute, such as reduced blood flow to the menisci or low-grade inflammation associated with obesity, is unclear."

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