Osteoarthritic changes in the knee are a common cause of pain that restricts the subject's ability to move and may lead to surgical intervention with total knee replacement. Quadriceps muscle strengthening has been shown to improve the dynamic stability of the knee, decreasing pain during locomotion and increasing knee function. However, the gains associated with improved quadriceps strength have been difficult to achieve on a routine clinical basis because the currently available ways to increase muscle strength- through voluntary exercise or surface electrical stimulation- have significant practical problems that limit their use. The aim of this prospective study is to evaluate the safety and effectiveness of neuromuscular stimulation using implantable microstimulators called BIONs to improve the strength, range of motion, and health of the knee in patients with knee osteoarthritis. This investigation is expected to last 12 weeks for each study participant; the trial will be completed over a 3-year period. Patients recruited into the study will have advanced knee osteoarthritis for which total knee replacement surgery is being considered. The proposed study extends a feasibility study carried out in Milan, Italy on five patients with knee osteoarthritis, who were implanted with BIONs.