P.F.C. Sigma Fixed Versus P.F.C. RP Mobile Bearing Total Knee Systems

Inclusion Criteria: 1. Administrative - The patient or their authorised representative is able to understand the evaluation, is able to give voluntary written informed consent and will comply with the post operative follow up regime. 2. Age - There are no restrictions relating to age of the patient. The patient's age must be considered suitable by the clinical investigator for a bi-compartmental or tri-compartmental knee arthroplasty using either of the two systems available in the evaluation. 3. Sex - Male or female (providing that they are not pregnant) may be recruited to the evaluation. 4. Diagnosis - patients that require a tri-compartmental knee arthroplasty for primary surgical management of idiopathic osteoarthritis. 5. Suitability - Patients who in the opinion of the Clinical Investigator are considered to be suitable for treatment with a fixed or mobile bearing tibial knee system and are suitable for patella resurfacing. Exclusion Criteria: 1. Patients with rheumatoid arthritis. 2. Patients requiring revision total knee arthroplasty surgery. 3. Patients with any tibial deformity requiring tibial component augmentation. 4. Patients that in the opinion of the clinical investigators require a constrained prosthesis. 5. Patients with a known history of poor compliance to medical treatment. 6. Patients who are known drug or alcohol abusers. 7. Patients with a pathology which in the opinion of the clinical investigator will adversely affect healing. 8. Patients who are currently participating in another clinical evaluation. 9. Patients with other disorders which in the opinion of the Clinical Investigator will / could impair rehabilitation. 10. Contra-indications for use of the device, as detailed in the package insert.