This study is to average Forgotten Knee Score (FJS) of those patients receiving the Medacta GMK Sphere® knee at the two and five year time points. 70 subjects, enrolled at the data coordinating center in Medacta GMK Sphere® vs Posterior Stabilized study (WIRB Pro Num: 20141994) and randomized to the Sphere arm, will have their data utilized for this 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 that have had a high tibial osteotomy or femoral osteotomy.
• 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).
• 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 that are prisoners.