Oxford Signature vs. Conventional Global Study

Inclusion Criteria: * Intended for use in individuals with osteoarthritis or Avascular necrosis limited to the medial compartment of the knee that is also lacking patellofemoral or lateral compartment disease. * Use of cementless femoral fixation is permitted outside of the United States if it complies with all local, state, and/or national and international regulations. The same technique must be used consistently throughout the course of the study with all cases * Patients 21 and over Exclusion Criteria: * Use of Cementless Fixation in the United States * Infection, sepsis or osteomyelitis * Use in lateral compartment of the knee * Rheumatoid arthritis or other forms of inflammatory joint disease * Revision of failed prosthesis, failed upper tibial osteotomy, or post traumatic arthritis after tibial plateau fracture * Insufficiency of the collateral, anterior, or posterior cruciate ligaments which would preclude stability of the device. * Disease or damage to the lateral compartment of the knee * Uncooperative patient or patient with neurologic disorders who is incapable of following directions * Osteoporosis in the United States / Insufficient bone stock outside the United States * Metabolic disorders which may impair bone formation * Osteomalacia * Distant foci of infections which may spread to implant site * Rapid joint destruction, marked bone loss, or bone resorption apparent on roentgenogram * Vascular insufficiency, muscular atrophy, neuromuscular disease. * Incomplete or deficient soft tissue surrounding the knee. * Charcot's disease * A fixed varus deformity (not passively correctable) of greater than 15 degrees * A flexion deformity greater than 15 degrees. * Non-staged Bilateral patients * Patients who refuse, cannot, or should not receive a CT or MRI. Since patients are randomized into treatment groups, all patients must be able to receive an MRI (should follow local MRI screening protocol). This excludes patients who have metal artifacts in the knee, patients who are too large to fit into the knee coil, patients with pacemakers, patients unable to lie still for the duration of the MRI, and patients who are claustrophobic.