Robot-assisted partial knee replacements


Partial knee replacements have generally had a poor record in orthopaedic joint replacement practice. It is not that they are a bad idea at all. In fact the original ideas of joint replacement surgery in the knee all centred around the idea of partial joint replacements- concept being that there would be no need to deal with the other aspects of the knee like ligaments and menisci that are not affected. Unfortunately these ideas did not find a match in technology and the previous models all turned out to be failures. They were either too difficult to put in accurately or the designs resulted in a loss of too much bone. As they were used the results in joint registries around the world showed them to be dismal.

Meanwhile, to assist in the placement of total joint replacements accurately, the technology of navigation was being developed. Here the various dimensions of the patient were fed into the computer and it would indicate what is the most ideal way to put in an endoprosthesis to be mechanically stable. This was ultimately confined to the mechanical constraints of the joint replacement device and not the patient. It also did not help that these systems were not based on actual images of the patient but rather theoretical norms. One of my articles points out the folly of using Western norms in the the Eastern body type, for example. Very recently it has been shown that navigation-assisted surgery does not improve the long term results of knee replacement surgery.

The MAKOplasty System and why it's different

In the MAKOplasty system, all these factors have been considered in partial knee replacement and so in a sense it's like everything and nothing that has come before. It uses a robot to assist in placing a partial knee replacement in an accurate manner based on navigation data. Apart from the robot, does it not sound like the "same old stuff"?

Well, firstly the navigation used in MAKO is not the "usual" navigation that is used by most surgeons which is "imageless". In MAKO one needs to undergo a CT scan of the knee. This information is fed into the computer so that measurements on the computer are more accurate and customised to the patient. During the surgery the surgeon then registers the anatomy of the patient with that of the images making the surgery very much more accurate. This level of accuracy is then ensured by the robot which ensures that the surgeon is not able to make cuts outside what is determined to be accurate by the surgeon. In addition to this the robot maps where the cartilage with the help of the surgeon (cartilage is not mapped by a CT scan) so that the implant fits flush with the joint surface.

Figure 1. In the pre-operative planning stage, CT scan data is used to recreate an accurate model of the patient in the computer program. This allows the optimal positioning of the tibial (a) and femoral (b) component in virtual space. The tibia is that matched onto the real patient by a series of dots (c) and with that we are able to determine how it would function in real life.

The implant itself is a partial joint replacement and because the robot ensures accurate tracking of the device, it can be done through a smaller incision making post-operative pain much lesser. It is also an inlay implant- the robot houses a burr as opposed to a saw which removes mostly cartilage and not so much bone. The resultant defect is then simply filled in with the device.

Figure 2. This video of an actual case in progress shows the fine cuts that are done in the MAKO system using the RIO robot. Towards the end, the actual procedure is highlighted and shows the minimal precise movement required to achieve these highly accurate cuts. These cuts are more like a sculptors tool rather than the more crude saws and chisels that are used in traditional knee replacement surgery.

Potential for the future

The new technology offered by the MAKO system has resulted in a 10-fold improvement in partial joint replacements over 2 years. This has prompted a number of surgeons to now seriously consider this technology as a viable service for their patients. We are proud to announce that our surgeons at Limb Salvage and Revision Arthroplasty Pte Ltd are now credentialed in the procedure having been trained in the United States by the pioneering surgeons of MAKO. It is our opinion that this technology is best suited to the patient with minimal arthritis in a single compartment of the knee and is also usable in patients with ligamentous loss where the procedure can be combined with ligament reconstruction. We believe that it represents a more cost-effective option to stem-cell therapy in the older patient.

Figure 3. The system allows a very accurate matching of the fit in the knee. The bars in the top right corner (a) show the play in the knee in millimeters. In (b) the femoral component is accurately placed and matches the pre-operative simulation in figure 1 above. This is possible because the system actually matches not only bone through the CT image but also cartilage (yellow areas in C). It is co accurate that if bone is removed less than a millimeter in would stop burring and show up in red.

Figure 4. We are proud to be able to bring this service to our patients having been trained by the original team of surgeons in MAKO in the United States and credentialed to perform the procedure in Singapore.

Figure 5. The essential steps in performing a MAKOplasty knee replacement are pre-planning, registration of bone, ligament tension and cartilage, confirmation and milling of bone. It transforms the way we think about knee replacements in being more patient and less implant-centred.

Figure 6. Ever thought of what's in store in a knee replacement procedure? We present here a comparison of a knee replacement with (left panel) and without (right panel) a tourniquet. We do resort to the latter in the difficult cases of patients with significant vascular risk. On the top panel are the salient steps in MAKOplasty surgery. You will see how there is reduced blood loss and less bone removed in the MAKOplasty procedure.

Figure 7. Afraid of blood? Well we produced this video so you can understand the MAKOplasty procedure better without having to see the blood and cuts!

Table. This is a summary of the essential differences between MAKOplasty using the RIO robot and other forms of robotic and non-robotic surgery.