Patient Specific Technology uses pre-operative 3D imaging to create custom cutting instruments tailored to each individual patient's knee anatomy — allowing surgeons to plan surgery before the operation even begins.
Why Better Technology Matters
Technological advances are striving to improve upon current results. Whilst total hip replacements have been widely successful over time, knee replacements still require fine-tuning to reach the same levels of patient satisfaction. Current worldwide literature suggests the success rate of a total knee replacement is approximately 80% (patients rating their result as good or excellent), compared to approximately 95% for total hip replacements.
The Three Methods of Knee Replacement
There are three main ways to perform a total knee replacement:
- Conventional: Using alignment guides and rods during surgery to judge the alignment of cuts
- Navigation: Using a computer to judge where cuts are being made prior to insertion of the prosthesis
- Patient Specific Instrumentation: Using a pre-operative scan to create specific custom moulds used as cutting guides during surgery
Various methods aim to improve alignment and push outcomes beyond the current 80% benchmark.
How Patient Specific Instrumentation Works
Patient Specific Instrumentation requires a pre-operative investigation — typically a 3D CT scan — to recreate the exact anatomy of the knee in a 3D environment. The 3D image is used to create specialised cutting blocks which are then used to make accurate bone cuts during surgery.
The benefit is that it may reduce damage to surrounding structures: no pins are inserted into the bone as in navigation, and no rods are inserted into the medullar shaft as in conventional techniques.
Pre-Navigation — Planning Before the Operating Theatre
Dr Liew performs almost all total knee replacements using patient specific technology. He believes this technique allows an element of “Pre-Navigation” — the bone cuts can be assessed, changed, and planned prior to surgery rather than making those decisions during the procedure.
This requires a computer to visualise what the new knee replacement will look like in the patient's bone before any incision is made. This can reduce operative time, which in turn reduces the time the wound is open and potentially reduces infection risk.
Who is Suitable?
Not all patients are suitable for patient specific instrumentation, but it can actually be easier to use patient specific instruments in some complex cases — for example, when there are existing implants in the femur or tibia.
The results of a well-performed total knee replacement are the same regardless of method. Various methods are aimed at improving longer-term outcomes. There is considerable debate in the literature about the best method, and no consensus has been reached. The best technique is likely the one the surgeon is most familiar with.
To discuss whether you are suitable for patient specific technology, speak with your GP for a referral to see Dr Liew.
Patient Information Summary
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