At random, the researchers assigned patients to receive either the physical therapy program or placebo. (Placebo is an inactive therapy provided to a comparison group.) The placebo in this study was ultrasound treatment of the knee that was too weak to produce any medical effect. Physical therapy consisted of manipulation of the knee, hip, spine, and ankle by experienced therapists; patients were also taught knee exercises that they did both in the clinic and at home. The physical therapy and the placebo treatments were carried out two times a week for 4 weeks. At the beginning and end of the study, the researchers asked patients to rate their pain and stiffness by using a standard questionnaire. They also measured how far patients could walk in 6 minutes. Patients were then followed up for 1 year to see who needed surgery for their arthritis.