Primary study outcome achieved; investigator decided to conduct the study without sponsor support after 2009.

This post-market clinical follow-up study was designed to compile long-term knee replacement outcomes of the PFC Sigma fixed and PFC Sigma mobile Rotating Platform (RP) knee systems. The first patient had surgery on November 8, 2001 and the final patient had surgery on July 29, 2005. There were 120 knees consented by a single site, which was the planned sample size in the study protocol, with 117 receiving one of the study devices. The study was terminated as the primary outcome was met and the investigator decided to conduct the study without sponsor support after 2009.

Performance and safety will be assessed using the following surgeon and patient based outcome tools:

1. American Knee Society Knee and Function Scores
2. Knee Society Radiological Analysis
3. Oxford Knee Score
4. SF 12 Score
5. Anterior Knee Pain Score

Specific objectives of the evaluation being to assess the following:

1. Improvement in functional recovery
2. Incidence of anterior knee pain
3. Improvement in Quality of life
4. Incidence of tibial loosening
5. Incidence of excessive polyethylene wear

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.