As the west continues to get bigger, you can add knee problems to the list of ailments they are likely to face after lugging around extra pounds.

Being extremely overweight leads to more than half of the nation's 850,000 annual operations to repair tears in the cartilage that cushions the knee joint, according to a study from the University of Utah.

The study, published in the May edition of the American Journal of Preventive Medicine, focuses on the correlation between injuries to the meniscus — which acts basically as a washer in the knee — and doesn't address why it's happening.

Although obesity is hardly a new phenomenon, the list of reasons to stay fit seems to be getting longer.

"I'm afraid there's a lot more we're going to find out," said Dr. Kurt Hegmann, who directed the study.

Nearly two out of three Americans are overweight or obese, putting them at risk for a number of related health problems like high blood pressure, diabetes and sleep disorders — even premature death.

"It's a very wide spectrum," said Dr. George Mensah, acting director of the National Center for Chronic Disease Prevention and Health Promotion.

Mensah hadn't seen Hegmann's study, but said the idea made sense. People with a higher body-mass index, a formula used to gauge obesity, put themselves at a greater risk for serious health problems.

Hegmann, director of the University of Utah's Rocky Mountain Center for Occupational Environmental Health, and his team studied 544 patients who had a cartilage tear repaired from 1996 to 2000. The patients were men and women ages 50-79 who had surgery on meniscal tears.

The cartilage can break down over time, but Hegmann thought there was a correlation between meniscal injuries and obesity. Hegmann said there are probably several factors involved in the correlation, but he expected it was more than just putting more pressure on the knees.

One possibility is that obese people have circulation problems that reduce the blood supply to the cartilage.

"We're just barely at the point of recognition of the severity of the problem, and we don't have good treatment and prevention strategy, just as we didn't with respect to smoking in the '50s and '60s," Hegmann said.

The premise that heavier people have more knee problems made perfect sense to Hegmann, but he found no one had made a thorough investigation.

His study found that people whose BMI was even just slightly over the healthy range were three times more likely to have a cartilage tear. The heaviest men were 15 times more likely to tear the cartilage and women in the same category were 25 times more likely.

"There's a rule in science. When you get numbers this big, there's something going on," Hegmann said.

And the study is based only on those patients who needed surgery. Patients who were treated without an operation and those who didn't bother getting their knees checked out could push the number of injuries higher.

Despite the increase in awareness of obesity-related ailments, Mensah said few are taking heed and noted 16 percent of American children (ages 6-19) are overweight.

"The epidemic has no signs at all of slowing," he said.