Race and ethnicity, along with gender, are important factors in determining both short-term and lifetime risk of developing symptomatic knee osteoarthritis, according to new research findings presented this week at the American College of Rheumatology Annual Meeting in Washington, D.C.

Knee osteoarthritis is caused by cartilage breakdown in the knee joint. Factors that increase the risk of knee osteoarthritis include obesity, age, prior injury to the knee, extreme stress to the joints, and family history. In 2005, 27 million Americans suffered from osteoarthritis, and one in two people will have symptomatic knee arthritis by age 85.

Researchers at Brigham and Women's Hospital in Boston used a validated computer simulation model (the Osteoarthritis Policy model) with data from published studies to project short-term and lifetime risk of diagnosed symptomatic knee osteoarthritis based on gender, as well as race and ethnicity.

"We know that osteoarthritis of the knee is a very prevalent and disabling condition. We also know that the only definitive, curative treatment for knee OA right now is total knee replacement surgery," says Elena Losina, PhD, co-director of Orthopedic and Arthritis Center for Outcomes Research at Brigham and Women's Hospital in Boston, and lead investigator in the study. Dr. Losina and her colleagues sought data to show what segments of the population were most at risk of developing knee OA and most likely to need total knee replacement over their lifespan.

The study's results showed that in people free of knee OA at age 40, the lifetime risk of developing knee OA ranged from 10 percent in white men to 17 percent in African-American women. While the risk for developing symptomatic knee OA increases with age, the disease can develop in relatively young individuals: 11.3 percent of African-American, 10.5 percent of Hispanic and 10 percent of white women free of the disease at age 40 will develop it by age 65.

"It is often perceived that osteoarthritis is a disease of older age. So if you're 40, you are not worried about it. Our analyses indicated that three of 100 African American women are likely to be diagnosed with symptomatic knee osteoarthritis by age 50 and five of 100 by age 65," Dr. Losina says. "We need people to start thinking about prevention earlier. We don't want to send prevention messages at 50 or 60. We need to promote awareness of osteoarthritis risk much earlier so that prevention can work."

"Higher rates of obesity among African-American and Hispanic women may contribute to the higher rates of knee OA risk seen in the study," says Jeffrey N. Katz, MD, professor of medicine and Orthopedic Surgery at Harvard Medical School, a senior author of the study.

"We know that obesity is a risk factor for developing knee osteoarthritis. Reducing obesity is likely to reduce the risk of knee osteoarthritis and the need for total knee replacement," Dr. Losina says. Prevention messages about increasing physical activity and managing weight may be more effective if they are targeted to each unique population group, Dr. Losina added.

Funding for this study was provided in part by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health.