Studying gene activity in tissue removed from injured knees, researchers at Washington University School of Medicine in St. Louis have found that genes related to obesity and aging may contribute to the development of osteoarthritis.

Osteoarthritis is the most common knee disorder. The problem involves the breakdown of cartilage, causing pain, swelling and stiffness that make it difficult, over time, to move the joint or put weight on it.

The frayed, white substance is a torn meniscus being removed during surgery. Each year in the United States, at least half a million people have surgery for meniscus tears. All of them are at increased risk for developing arthritis in the knee later in life.

The new study involved 68 people who had surgery to repair or remove a torn meniscus, the cartilage in the knee that acts as a cushion between the shinbone and the thighbone. The findings are available online in the International Journal of Obesity.

"Having a tear in the meniscus is associated with an increased risk of developing osteoarthritis later in life," says principal investigator Robert H. Brophy, MD. "Some studies have suggested that more than 50 percent of people with a meniscus tear will go on to develop arthritis 10 to 20 years later, but we don't precisely understand how one leads to the other."

For the study, Brophy, a sports medicine specialist and associate professor of orthopaedic surgery, and M. Farrooq Rai, PhD, postdoctoral research scholar in orthopaedic surgery, analyzed the activity of 28 genes related to obesity, aging and the secretion of inflammatory substances in meniscus tissue to learn how genes related to age and body mass might influence the development of arthritis.

"We know there's a mechanical relationship," he says. "People who are obese have increased pressure and force on the knee joint. And older people have more wear and tear on the joints. But we wanted to see whether something else is going on that may accelerate the risk for osteoarthritis."

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