iAssist vs. Conventional Instrumentation in Total Knee Arthroplasty

Inclusion Criteria: * Patient is male or female * Patient needs a primary total knee replacement using the NexGen LPS Flex or Persona knee implant * Patient is diagnosed with non-inflammatory degenerative joint disease (e.g., osteoarthritis, post-traumatic arthritis, avascular necrosis, etc.) * Patient is over 18 years old * Patient is able to: * Understand what participation in the study entails and willing to consent (patient or his/her legal guardian) to participate in the study by signing and dating an IRB/EC (ethics committee) approved inform consent form, and * Follow surgeon/staff instructions, and * Return for all follow-up evaluations, and * Able and willing to undergo a preoperative full-leg, standing radiographs and/or CT-scan * Patient meets an acceptable preoperative medical clearance and is free of or treated for cardiac, pulmonary, hematological or other conditions that would pose excessive operative risk. * Patient has a presence of varus or valgus deformity of 15 degrees or less. Exclusion Criteria: * Patient is currently enrolled in an investigational new drug or device study. * Patient has an active infection (including septic knee, distant infection, or osteomyelitis). * Patient has severe hip arthrosis. * Patient has neurological disorders (including, but not limited to Parkinson's disease). * Patient has had a prior ipsilateral unicompartmental knee arthroplasty, TKA, knee fusion or patellectomy. * Patient has hip or knee ankylosis. * Patient has inflammatory joint disease. * Patient has rheumatoid knee arthritis. * Patient has indications of intra- and/or extra-articular deformations that would eliminate or tend to eliminate adequate implant support or prevent the use of an appropriately sized implant, such as polio, history of tibial plateau fracture, etc. * Patient has any metal within 150 mm of the joint line for the operative-side knee. * Patient has knee deformities greater than 15 degrees of fixed varus, valgus, or flexion contracture on initial physical examination. * Female who is pregnant or lactating. * Patient currently involved in any personal injury litigation, medical-legal or worker's compensation claims. * Patient has arterial disease or stents that would exclude the use of a tourniquet. * Patient has insufficient quality or quantity of bone to support the implant due to prior knee surgery (or surgeries), cancer, metabolic bone disease, osteoporosis/osteopenia (diagnosed or treated with medication), active/old/remote infection, etc. * Patient has a mental condition that may interfere with his/her ability to give an informed consent or interfere with his/her ability or willingness to fulfill the requirements of the study. * Patient has a condition that would place excessive demands on the implant (e.g., Charcot's joints, muscle deficiencies, multiple joint disabilities, skeletal immaturity, etc.). * Patient has collateral ligament insufficiency. * Patient has an immunosuppressive disorder (e.g., AIDS, etc.) that would require cytotoxic drugs, corticosteroids, large dose of irradiation, or antilymphocytic serum. * Patient has an existing condition that would, in the opinion of the investigator, compromise participation or follow-up in this study.