This is a Post-Marketing Surveillance of GMK Sphere knee prosthesis.

The clinical performance of the GMK® Sphere, manufactured by Medacta International, will be evaluated by a multicentre, prospective clinical surveillance study.

The Elective Orthopaedic Centre (EOC), in Epsom, Surrey, will be the study coordinating centre. Four further centres will participate in the clinical study, for five total centres. Each participating centre will recruit approximately 100 patients. Patient recruitment will cease when a cohort of 500 GMK® Sphere knee replacements have been implanted.

Inclusion Criteria:

• A disabled or severely disabled joint as a result of arthritis, traumatic arthritis, rheumatoid arthritis, poly-arthritis or avascular necrosis
• Patients must be between the age of 18 and 80 at the time of consent
• Listed for total knee replacement surgery.
• Patients who are willing to give informed written consent

Exclusion Criteria:

• Progressive local or systemic infection
• Muscular loss, neuromuscular disease or vascular deficiency of the affected limb, making the operation unjustifiable
• Severe instability secondary to advance destruction of condylar structures or loss of integrity of the medial or lateral ligament
• Any patient who cannot or will not provide informed consent for participation in the study
• Those whose prospects for a recovery to independent mobility would be compromised by known coexistent, medical problems
• Patient whose BMI exceeds 40
• Any case not described in the inclusion criteria