29 patients (58 knees), undergoing simultaneous bilateral total knee arthroplasty for osteoarthritis, were randomized to receive a high-flex cruciate retaining implant (CR) in one knee and a high-flex posterior cruciate substituting implant (PS) in the other. The goal of this study was to evaluate superiority between these two designs in terms of clinical, functional and patient satisfaction outcomes at a minimum of three years. The PS implant demonstrated significantly greater ROM, patient satisfaction, and a reduction in the incidence of posterior knee pain.