What is Computer Assisted Total Knee replacement?

CAS is an acronym for Computer Assisted Surgery. It implies the use of high level computing power in surgery, with the aim of making the surgery safer and more accurate. It is not robotic surgery. In CAS the surgeons are in control throughout and they use the computers as tools, supplementing or replacing traditional instruments. CAS has an established role in neurosurgery where it has been used for several years. It is currently being used in facio-maxillary surgery. Similar computerised localisation techniques have been used to deliver radio-therapy. In neurosurgery and ENT the operated part remains static. When replacing jonts or fixing fractures the limbs have to be moved during the operation. The movement adds a degree of complexity and the surgeon needs to keep track of the relative positions of the bones throughout the procedure. It is the difference between hitting a stationary ball and a moving one.

How is CAS applied in Joint Replacement?

The patient is prepared for surgery in the usual manner. In the majority of cases no special x-rays nor any unusual preparation is required for Knee Replacement. For computer assisted (CA) hip replacement pre-operative CT scans may be needed. The usual anaesthetic is applied and standard incisions are made. The computer navigation process starts with two mounts (pins or screws) being fixed to the bones of the patient. A signal source (usually infra-red) is attached to the mounts. The computer identifies the position of these fixed signal sources and uses them as a reference to other anatomical landmarks. The computer program contains a rough model of the surgical region (knee or hip) that is having the surgery. This model is enhanced by detailed measurements of the anatomy of the patient who is having the surgery. The surgeon identifies important anatomical landmarks, for the computer, by using an infra-red pointer. Once the anatomical map is complete it is possible to ‘navigate’ around the region with the computer keeping track, much as GPS keeps track of the position of a plane, boat or car. A special tool is used, the Position And Plane Indicator (PAPI). It communicates with the computer and signals the position and attitude of any surface that it rests upon. The other equipment that an orthopaedic surgeon uses in conventional joint replacement surgery consists of cutting tools (saws, mills, knives, etc), cutting blocks and alignment devices (rods, clamps etc). PAPI can be attached to any of these so that the computer sees what the other stuff is doing. Put PAPI onto a cutting block and everyone can see what is about to happen. Put it onto the cut bone and it shows the surgeon the angle of the cut and the amount of bone that has been being removed. The result is better information before a bone cut is made and a quality check afterwards. If an error has been made, even one of 2-3 degrees or 2-3 mm it can be corrected! Once all the cuts have been made the prosthesis is positioned. The computer provides information on the overall result and indicates if there are problems with the soft tissues. If these are too tight then they can be released.

What are the potential benefits of CAS?

CAS provides constant guidance throughout the operation. The chance of making a mistake is reduced. This is very valuable to the surgeon in training. It has been shown to be very helpful in situations where the knee is badly deformed and when there has been previous surgery in the area. It is known that mal-alignment of a prosthesis can cause significant problems. A badly mal-aligned prosthesis may cause the joint to be unstable, have a poor range of movement, be painful, wear badly and not last as long. If a CA system improves alignment then the function and longevity of the prosthesis should improve. In a conventional total knee replacement rods are often put into the marrow cavity of the bones. This process causes bleeding and pushes marrow fat into the circulation. These events put a strain on the patient which may have serious adverse effects. Computer Assisted total knee replacement does not broach the marrow cavity to any significant degree. It is therefore safer.

What is the current scientific evidence for CAS Total Knee Replacement?

There is good scientific evidence to support the use of two systems, the BrainLab and the Stryker. Both produce a significantly better alignment outcome than conventional total knee replacements in all the parameters that they control. The evidence for this has been published in the most prestigious Orthopaedic Journal, the Journal of Bone and Joint Surgery. These articles show that with CAS; · the average alignment is better, · there are fewer poorly aligned prostheses and · the severity of mal-alignments that do occur is less. The CAS_WA database gathers information on both CAS and non CAS total knee replacements and on average the CAS total knee replacements give a 40% improvement in alignment. There are fewer badly mal-aligned replacements and an increase in the number of ‘perfectly aligned’ ones. Information from the CAS_WA database suggests that there is one parameter (the rotation of the femoral component) which in part determines how much pain the patient is left with after knee replacement. CAS give better femoral alignment and therefore produces less patellar pain. A listing of important articles on CA total knee replacements is provided in the bibliography section.

Are there any risks?

Using a CA system does not guarantee a perfect result. There are a range of potential complications in knee replacement that Computer Assistance cannot influence. Not everyone having a CA total knee or hip replacement will have a perfect outcome. At present there are no medium or long term outcome studies of CAS and there is no proof that the better alignment of knee replacements will produce significantly better function. The computer assistance systems are complex pieces of equipment which can go wrong. Not all the computer assistance systems on the market are fully evaluated. They have to be used by people who are well trained in their use. There is a learning curve with the systems and results improve with experience. The mounts which are fixed to the bones can cause local problems, including infection, fracture and nerve damage. The incidence of these complications is very low but they can occur.

What orthopaedic operations use CAS?

Total Knee Replacement is the only operation which is widely used with CA. It is being modified now to use a smaller incision (Minimal Incision Surgery, MIS) and surgeons are attempting to use a combination of CA and MIS. The results of such combinations have not yet been evaluated. Computer assisted total hip replacement is in the development stage. It is likely that prototype versions will be available within the next year but evaluation of their safety and outcomes is likely to need another year or more. Computer Assisted anterior cruciate ligament reconstruction has been reported.

Do all knee surgeons use CAS?

No. Currently only a small proportion use CAS in total knee replacements.

Why don’t all knee surgeons use CAS?

Firstly CA systems are not yet widely available and most surgeons do not have access to them. The systems are expensive and either the prosthetic company or the hospital has to bear the cost. In Australia the patient is not charged for the use of CAS. Secondly surgeons need training in CAS and there are still only a few training courses available. Thirdly CA surgery takes, on average, 15 minutes longer than non CAS operations. This extra time results from ‘fine tuning’ of the knee. Some surgeons are reluctant to spend the extra time.

Scientific Publications which are Significant

Aspects of current management; Computer-Assisted Orthopaedic Surgery: Do we need CAOS? J M Sikorski, S Chauhan, Journal of Bone & Joint Surgery, Vol 85-B, 319-323, 2003

Positioning of total knee arthroplasty with and without navigation support: A prospective, randomised study. M Sparmann, B Wolke, H Czupalla, D Banzer, A Zink. Journal of Bone & Joint Surgery, Vol 85-B, 830-835, 2003

Computer-assisted knee arthroplasty versus a conventional jig-based technique: A randomised, prospective trial. S K Chauhan, R G Scott, W Briedahl, R J Beaver. Journal of Bone & Joint Surgery, Vol 86-B, 372-377, 2004

Computer-assisted revision total knee replacement. J M Sikorski, Journal of Bone and Joint Surgery, Vol 86-B, 510-514, 2004