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Patient Specific Technology

Patient Specific Technology

Technological advances are striving to improve upon the results that we are current able to achieve. Whilst total hip replacements have been widely successful over time, knee replacements still require fine tuning in order to reach the same levels of patient satisfaction. Current worldwide literature suggests that the success rate (As judged by patients who rate their total knee replacement as good or excellent) of a total knee replacement is approximately 80%, whilst those of total hip replacements are around 95%. There are multiple methods of inserting a knee replacement. 3 main ways exist.

  • Conventional: Using alignment guides and rods during surgery to judge the alignment of the cuts required to fit the prosthesis on.
  • Navigation: Using a computer to judge where the cuts are being made prior to insertion of the prosthesis
  • Patient specific instrumentation: Using a pre-operative scan to create specific moulds used as cutting guides during surgery.

Given that surgeons are striving to improve upon the 80%, various methods are used in the effort to improve on alignment. Patient Matched Technology or Patient Specific Instrumentation uses technology to try to improve the accuracy and reproducibility of surgery, especially when it comes to arthroplasty (replacement).

The alignment of a knee replacement is crucial to the success of the knee. Mechanically, the bone of the knee is cut to reproduce what the normal knee should be like, with attention to the angles and rotation of the cuts. This makes the knee more “anatomic”, and can lead to the best kind of a knee – a forgotten knee. A forgotten knee is one that feels so normal, that a patient will forget that they have had a knee replacement in normal day to day life. In most cases a total knee replacement will still have differences to a normal knee. In 100% of cases, the skin to the side of the scar is always numb due to cutting small superficial nerves during a standard skin cut. In addition, it is usually discouraged to kneel after a total knee replacement.

Over the last 15 years, total knee replacements can either be performed in a conventional way, or using navigation. Convention total knee replacements use alignment rods and jigs that allow accurate cuts during surgery to recreate the alignment. Navigation uses a computer that determines if the bone cuts are correct, and references in real time. The third and newest kind of methodology is Patient Specific Instrumentation. This requires a patient to have pre-operative investigations done in a specific way to enable the images to be used to recreate the exact anatomy of the knee in a 3D environment. The 3D image is then used to create specialised cutting blocks which are then used to make the accurate bone cuts. The benefit of this technique is that it may reduce the amount of damage to surrounding structures, as no pins are inserted into the bone as in navigation, and no rods are inserted into the medullar (shaft) of the bone as in conventional techniques. Current evidence is evolving, with large debates on the best type of knee replacement technique to be used. In all cases, this is highly dependent on the experience and training of a surgeon. Dr Chien-Wen Liew sees theoretical and real benefits of using Patient Specific Instrumentation.

Dr Chien-Wen Liew performs almost all total knee replacements using patient specific technology using the philosophy of reduced damage to bone and soft tissue when performing any surgery. This technique not require any rods to enter the femoral or tibial shaft, and does not require additional pins to be inserted around the knee. Dr Liew believes that this technique allows an element of “Pre-Navigation”. This means that the bone cuts can be assessed, changed and planned prior to surgery rather than making those decisions during surgery. This requires a computer to view what the new knee replacement will look like in the patient’s bone. This can reduce the time taken to perform surgery, which in turn reduces the amount of time the wound is open. Dr Liew performs total knee replacements using patient specific instrumentation in Adelaide, South Australia.

Not all patients are suitable for patient specific instrumentation. However in some complex cases, it can be easier to use patient specific instruments than rods in the femur and tibia, like when there are implants in the femur or tibia already.

The results of a well performed total knee replacement performed by any means is the same. Various methods are aimed at improving the longer term outcome. There is considerable debate as to the better method for performing a total knee replacement, and no consensus has been reached in the literature of what the best method is. It is important to note that the best total knee replacement technique is likely to be the one that a surgeon is most familiar with.

To get the best idea of whether you are suitable for patient specific technology in improving your outcome, please discuss this technology with your General Practitioner or obtain a referral to see Dr Chien-Wen Liew.

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