Knee Osteoarthritis is a common problem with people over the age of 50 and is often debilitating because of the challenges it poses to normal walking function. Research has shown that exercise can lessen the effect of the osteoarthritis in the knee if done diligently. BION®s implanted in the thigh can produce contractions of the quadriceps muscles without much movement of the knee joint, an advantage if moving the knee is painful. In this study, teh subjects will be divided into three groups. Two groups of experimental subjects will receive stimulation using BIONs. The first group will have a stimulation paradigm like that used in a previous feasibility study that preceded the proposed trial, using low-frequency (1-5 PPS) "twitch" stimulation. The second group will have a stimulation paradigm in which tetanic-frequency stimulation (25-50 PPS) is used to produce fused muscle contractions. A third group of experimental subjects will have a standardized program of voluntary exercise.. In Groups 1 and 2, the femoral nerve will be stimulated electrically according to the assigned protocol during the 12 week experimental period after implantation of the devices. Individuals assigned to Group 3, receiving conventional exercise therapy for 12 weeks, will be allowed to receive BIONs at the end of the trial, providing they request BION therapy and they have been at least minimally compliant with the exercises. All participants will be eligible to continue treatment following the initial 12 weeks if medically appropriate and resources permit.