Each year, Americans make nearly 20 million visits to their doctors for knee problems. In fact, its the most common reason for visiting an orthopaedist. According to the American Academy of Orthopaedic Surgeons, more than 500,000 knee replacements are performed annually in the United States. An arthritic knee can cause tremendous pain and limitations in day-to-day living. But knee pain and replacement surgery are not inevitable. There are steps you can take-from lifestyle modifications to exercise to less-invasive forms of surgery-to protect your knees. All this attention to the knee comes as no surprise to George Balis, MD, an orthopaedic surgeon at Cleveland Clinic. "There are multiple factors predisposing the knee to arthritis, including genetics, obesity, and the peculiar biomechanics of the knee," he says.