The study is a prospective, randomized comparison of total knee arthroplasty with the Medacta GMK Sphere® knee compared to the Medacta GMK PS knee, with comparison to data from previous trials of similar study design.

There is no consensus within the Arthroplasty community as to whether a traditional post and cam-style PS total knee device is superior to a medial-pivot, more congruent device. However, the majority of surgeons seem to prefer the former, though there is a minority that uses the latter device with great success.

To date, there have been few prospective trials directly comparing these devices, and none with the latest generation of TKA implants. Almost all such studies have been retrospective, and/or non-randomized, and/or utilizing older generation devices.

The primary objective of this study is to compare the average Forgotten Knee Score (FJS) of those patients receiving the Medacta GMK Sphere knee with the average FJS of those receiving the Medacta GMK PS knee at the two and five year time points. It is expected that those subjects implanted with the Medacta GMK Sphere knee will show significantly better Forgotten Joint Scores at two and five year follow-up when compared with those receiving the Medacta GMK PS knee. The FJS was not collected in the prior comparison studies, and so cannot be evaluated across the knee systems.

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.