Medacta GMK Sphere® vs. Medacta GMK PS Post-Market Outcomes Study

Inclusion Criteria: * Patients willing to sign the Informed Consent. * Patients able to comply with follow-up requirements including postoperative weight bearing restrictions and self-evaluations. * Male and non-pregnant female patients ages 21 - 80 years of age at the time of surgery. * Patients requiring a primary total knee replacement. * Patients with a diagnosis of osteoarthritis (OA), traumatic arthritis (TA), or avascular necrosis (AVN). * Patients with intact collateral ligaments. Exclusion Criteria: * Patients with inflammatory arthritis. * Patients that are morbidly obese, body mass index (BMI) \> 40. * Patients with a history of total or unicompartmental reconstruction of the affected joint. * Patients with neuromuscular or neurosensory deficiency, which would limit the ability to assess the performance of the device. * Patients with a systemic or metabolic disorder leading to progressive bone deterioration. * Patients that are immunologically compromised, or receiving chronic steroids (\>30 days), excluding inhalers. * Patients bone stock is compromised by disease or infection, which cannot provide adequate support and/or fixation to the prosthesis. * Patients with knee fusion to the affected joint. * Patients with an active or suspected latent infection in or about the knee joint. * Patients whose surgery will utilize computer-assisted surgical navigation (CAOS) techniques. * Patients whose surgery will utilize minimally invasive surgical techniques. * Patients that are prisoners.