A three-headed beast is out there compounding, accelerating, and perhaps even causing osteoarthritis in the knee joints. Its name: Obesity-a condition that affects up to 30 percent of all Americans. When that percentage is combined with that for those who are simply overweight-short of being obese, but moving in that direction-the number rises to a frightening 60 percent. "Patients who are overweight have a clear risk factor for developing osteoarthritis," says M. Elaine Husni, MD, MPH, a staff member of the Department of Rheumatic and Immunologic Disease at Cleveland Clinic. "Population-based studies have consistently demonstrated a link between being overweight or obese and knee osteoarthritis. Just being 10 pounds overweight increases the force across the knee by three to six times, or 30-60 pounds with each step." Dr. Husni adds that among women of normal height, for every 11 pounds of weight loss, the risk of knee osteoarthritis drops by more than 50 percent.