This is a randomised control trial to assess the benefits of using patient specific instrumentation in total knee replacement surgery. Patient specific instrumentation is an individualised system for total knee replacement surgery. The system has been marketed and is already in use in some centres. The type of implant used remains the same but the sizing of the components, and alignment of the implant is expected to improve. This study assesses any improvement in implant alignment in using the patient specific instrumentation, any improved intra-operative outcomes and any long term clinical outcome improvements for patients.

This is a randomised control trial to assess the benefits of using patient specific instrumentation in total knee replacement surgery. Patient specific instrumentation is an individualised system for total knee replacement surgery. The system has been marketed and is already in use in some centres. The process is similar to traditional knee replacement surgery but approximately 6 weeks prior to the operation patients will undergo an MRI scan of their knee, hip and ankle. From this data the dimensions and rotation of the knee can be accurately measured, and a custom made jig can be made specific to that patients anatomy. The jig is used intra-operatively to make accurate bone cuts according to this pre-operative plan, the type of implant used remains the same but the sizing of the components, and alignment of the implant is expected to improve. This study assesses any improvement in implant alignment in using the patient specific instrumentation, any improved intra-operative outcomes and any long term clinical outcome improvements for patients.

Inclusion Criteria:

• Males and females aged 18-75 years at time of surgery.
• Those presenting with primary or secondary osteoarthritis and/or rheumatoid arthritis of the knee.
• Those deemed capable of giving informed consent, understanding the aims of the study and expressing willingness to comply with the post-operative review programme.
• Patients who signed the study consent form prior to surgery.

Exclusion Criteria:

• Pregnant women.
• Those whose prospects for a recovery to independent mobility would be compromised by known coexistent, medical problems.
• Those with a known co-existent medical condition where death is anticipated within five years due to the pre-existing medical condition.
• Previous knee surgery including those already treated by with a total knee replacement (i.e. requiring a revision knee replacement).
• Muscle contracture around the knee joint
• Individuals with active or suspected infection or sepsis.
• Patients with contraindication to MRI