Uniglide™ Mobile Bearing Unicondylar Knee System vs the Uniglide™ Fixed Bearing Unicondylar Knee System

Inclusion Criteria: * skeletally mature * need to obtain pain relief and improved function * moderate or severe pain with either walking or at rest on the Hospital for Special Surgery Score * preoperative medial tibiofemoral joint space narrowing on x-rays (Kellgren Lawrence grade 3 or 4) * preoperative Hospital for Special Surgery Knee Evaluation total score of \< 69 * preoperative arc of motion of \> 90o in the affected knee * diagnosed with osteoarthritis in the medial compartment of the knee and non-surgical treatment options have failed to provide relief for symptoms * able to understand this clinical trial, co-operate with study procedures, and are willing to return to the clinic, and/or hospital for all the required post-operative follow-ups * able to give and have given voluntary, written informed patient consent to participate in this clinical investigation and have provided Authorization for Release of Personal Health Information (HIPAA) for the purpose of this clinical study * willing to be randomized with either of the devices used in the clinical trial as determined by the randomization schedule Exclusion Criteria: * neurological disorders which may interfere or adversely affect gait or weight bearing (e.g., muscular dystrophy, multiple sclerosis) * a nutritional problem (protein, calorie, or vitamin/mineral deficiency) that may impair wound healing mechanisms * a diagnosed systemic disease that would affect their welfare or the overall outcome of study (i.e. Paget's disease, renal osteodystrophy) * immunologically suppressed * on chronic corticosteroid or non-steroidal anti-inflammatory therapy * with Charcot's disease * with metabolic disorders (e.g. osteomalacia), which may impair bone formation * with distant foci of infections, which may spread to the implant site * have presence of vascular insufficiency, muscular atrophy and neuromuscular disease * have diagnosed osteoporosis as evidenced on a DEXA scan (within the last 12 months) * ave diagnosed rheumatoid arthritis or other forms of inflammatory joint disease * have diagnosed avascular necrosis * with malunion, arthrodesis or severe dysplasia in the affected limb * with rapid joint destruction, marked bone loss or bone resorption in the affected knee apparent on x-ray * have incomplete or deficient soft tissue surrounding the affected knee * have infection, sepsis or osteomyelitis in the affected knee * have had revision of previously failed prosthesis, failed upper tibial osteotomy or post traumatic arthritis after tibial plateau fracture in the affected knee * with a fixed varus deformity (not passively correctable) of greater than 15 degrees and a flexion deformity greater than 15 degrees in the affected knee * with insufficient collateral, anterior or posterior cruciate ligaments in the affected knee, which would preclude stability of the device * with disease or damage to the lateral compartment of the affected knee (Outerbridge classification II, III, or IV) * with a Body Mass Index \> 36 * with a sensitivity to device material * Females who are pregnant * prisoners,known drug or alcohol abuser, smoker, or have a psychological disorder * Based upon intra-operative assessment, cartilage and bone erosions involving more than the anterior and middle parts of the medial compartment. The posterior part of the medial compartment and the lateral compartment having cartilage of less than normal thickness. (as assessed using the Outerbridge Classification system).