Comparing X-3 To N2vac Polyethylene With the Triathlon Total Knee System

Inclusion Criteria: * The subject requires a primary cemented total knee replacement. * The subject has a diagnosis of osteoarthritis (OA), traumatic arthritis (TA), or avascular necrosis (AVN). * The subject has intact collateral ligaments. * The subject has signed the ethic committee approved, study specific Informed Patient Consent Form. * The subject is willing and able to comply with post-operative scheduled clinical and radiographic evaluations and rehabilitation. Exclusion Criteria: * The subject has inflammatory arthritis. * The subject is morbidly obese, BMI \> 40. * The subject has a history of total or unicompartmental reconstruction of the affected joint. * The subject has had a high tibial osteotomy or femoral osteotomy. * The subject has a neuromuscular or neurosensory deficiency, that would limit the ability to assess the performance of the device. * The subject has a systemic or metabolic disorder leading to progressive bone deterioration. * The subject is immunologically suppressed, or receiving chronic steroids (\>30 days duration). * The subject's bone stock is compromised by disease or infection and cannot provide adequate support and/or fixation to the prosthesis. * The subject has had a knee fusion at the affected joint. * The subject has an active or suspected latent infection in or about the knee joint. * The subject is a prisoner.