If you have knee osteoarthritis and could stand to lose weight, a new study, which was presented at the 2008 American College of Rheumatology Annual Scientific Meeting in San Francisco, gives you more reason to start a weight-loss program sooner rather than later: It could reduce your risk of needing total knee replacement down the line.

The study about osteoarthritis (OA), weight issues and knee health – funded in part by the Arthritis Foundation – found that people who are obese are more likely to develop advanced, end-stage disease requiring total joint replacement than those who are of a healthy weight.

Using a computer model of knee OA progression based on published national data, scientists from Brigham and Women’s Hospital, New England Baptist Hospital in Boston and University of North Carolina in Chapel Hill projected the occurrence and progression of knee osteoarthritis among several groups of people. They found that 70 percent of obese adults with mild knee OA at age 60, who survive 20 years, will develop advanced, end-stage disease by age 80. In contrast, just 43 percent of non-obese adults with mild knee OA will have end-stage disease after 20 years.

Other research has shown that weight is a factor not only in the progression of osteoarthritis, but also in its development. The reason is that for every pound you gain, your knees gain three to four pounds of added stress. Over time, the stress of excess body weight can cause the cartilage that cushions the knee to break down – in other words, osteoarthritis. Obesity clearly exacerbates the disease.

In a previous analysis done as part of the Framingham Knee Osteoarthritis Study, a population-based study that evaluated knee OA by X-ray over a 10-year period, researchers found that women with a body mass index (BMI) of 25 or greater significantly increased their risk of knee OA with relatively modest weight gains. However, losing just 11 pounds reduced their risk of developing knee OA by approximately half.

Experts say that in addition to preserving joint cartilage and preventing advance of OA, losing weight is likely to reduce pain level as well.