Robotic Surgery. What Robotic Surgery Isn't!

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1 Robotic Surgery Dr Keith Holt Robotic surgery is a term which covers a wide range of possible scenarios. It is a topic much publicised in the media, and often heralded as having great benefits such as: earlier discharge from hospital, faster recovery from surgery, and better long term outcomes. The term 'Robotic Surgery' also leaves the impression that a robot actually does the surgery: and hence why the outcomes might be better. Unfortunately, none of the above is true at this stage of our technological development, and nor is it true within our legal structure (which defines what we are allowed to do and not do). What remains therefore, is an experimental method of aiding the surgeon, which may or may not turn out to be beneficial, and which may indeed turn out to be just an expensive version of currently available techniques. What is Robotic Surgery? The implication of the term 'Robotic Surgery' is that, similar to car manufacturing, a robot is used to perform the surgery, by itself, under the guidance of an in-built program. For this scenario, a surgeon would need to be present to open and close the wound, but all the work would be done by the machine. Whilst this is possible for knee replacement surgery, it is not an option in our country with no such devices being approved to be supervision free. Indeed, even if approved, the exact alignment of the components still needs to be decided upon based on the findings at surgery, referenced to the limb in question, and then programmed in. The reality is that, Robotic Surgery in its current form, is just an aid to making the actual cuts in the bone. The alignment criteria used is still decided upon by the operating surgeon, be that pre-operatively or during surgery, and this is guided by computer navigation as it has been practiced for over a decade. All the robot does is to help the surgeon do the cuts based on that alignment, but still in accordance with his preference. For those surgeons who never moved to computer based alignment techniques (so-called computer navigation), and who still rely on rods and jigs to aid component alignment, this is an advance. For those who have embraced computer alignment, this may prove to be no different in terms of the end result. In other words, the final alignment and positioning of the components is probably going to be the same, it is just a question of whether the robotically aided cuts are significantly more accurate than saw cuts using navigated jigs: and to a degree which will change the end result. In terms of the accuracy we are talking about, the difference in the cuts will be less than a millimeter in most cases and, unfortunately, that difference is thought to be insignificant in terms of the overall result. Alignment techniques Instrumented techniques are the originally designed methods of determining component alignment (and therefore resulting leg alignment) in knee replacement, and consist of passing a rod up the central (medullary) canal in each bone to establish the bony alignment. From that rod a cutting jig can then be used, this being set at a predetermined angle off that rod (for example the femur is usually cut at 94º - 95º from the rod What Robotic Surgery Isn't! Surgical robots merely carry out, and/or limit, movements made by a human surgeon; be that with his hand holding the instrument itself, or at a console elsewhere. They neither make decisions themselves, nor do they operate independently. (hence from the line of the femoral bone) to re-establish a horizontal joint line). With the instrumented alignment technique, the end of the

2 femur is always cut off the intra-medullary rod as described. On the tibial side however, external jigs that use rods outside the knee to line up with the ankle, are sometimes used instead (so-called extra-medullary alignment). There are many advantages to the instrumented alignment methodology, including ease of use and time taken. The problem however, relates to the accuracy and to what are referred to as 'outliers'. A final (post surgical) leg alignment that is within +/- 3º of straight, is said to be within the accepted range, whereas any alignment that ends up more than 3º out could be called an Outlier. That +/- 3º range is acknowledged as acceptable because, within that range, the prostheses show no signs of extra wear or decreased longevity, and the clinical results are the same. Despite this, the aim of computer based navigation systems has been to largely eliminate the Outliers that can be a consequence of instrumented alignment and its inherent limits and, by and large, this has been achieved. This has now led to a situation where a preferred leg alignment can be reliably attained: an achievement which has opened up questions as to what alignment angles are actually best, and does the answer vary with each individual? This is the current debate that all knee replacement surgeons are having, and one that may take many years to answer. We have said that despite what is sometimes a cosmetically poor result, excessive varus (bow legged deformity) or worse still, excessive valgus (knock knee deformity), the clinical results of knees aligned by instruments remain good. Indeed, only recently have any studies been published that even suggest that the outcome of knee replacement is improved by constraining the leg alignment to much tighter limits (that is with less errors). In addition, while computer navigation has enabled the elimination of the so-called 'significant outliers', there remains a question as to whether the expense (usually thought to be about $1000 per case when navigation camera, computer hardware, software with its updates, and operator time are all taken into account) can be justified. For those who have embraced computer navigation, the benefit remains that of increased accuracy, and hence a better cosmetic result. What it brings is reliability, with a much lower chance of being outside the limits of acceptability. Whether or not this ultimately relates to better function or not remains to be seen, but most users of this technique believe that it does, and that this will eventually be shown. Tracking devices attached to tibia and femur. These have reflective balls on them which are picked up by a camera. This allows accurate positioning of the bones and, after mapping, accurate identification of the joint landmarks. Locating the centre of the femoral head during computer navigation Computer navigation is a technique that has variable penetration across the globe. Australia has the biggest percentage uptake of this technique of any country, and this is probably in keeping with the generally high standard of Orthopaedic training in this country. Although not difficult to learn, the technique is often criticised for adding time to an operation for little proven benefit. With practice however, that extra time comes down to about 5 minutes in a 1 hour case: that is, an insignificant amount of extra time which most feel can be justified by the increased accuracy and reliability of the procedure. Computer navigation involves the use of reflective arrays which are tracked by a camera (like cricket and tennis balls are now tracked so that their position and path can be assessed after delivery). In this process, each of the bones around the knee (the femur and the tibia) have 2 pins placed into them onto which the arrays are fixed. By moving the femur (thigh) around, the camera can track the array attached to that bone, and hence it can track the position of that bone in space. Computer Screen showing alignment during computer navigation

3 Because the hip is a ball and socket joint, the femur rotates about the centre of that joint. By moving the femur around in space, the computer can work out where that centre of rotation is, and hence it knows where the centre of the hip is. This can be done to an accuracy of a few millimetres in most cases (see diagram of screen shot above). Using a pointer with an attached tracking array, the knee can then be mapped out and the ankle located. The computer will then adapt that information to conform to one of the standard models (specific for every different make of knee) in its reference memory, which then leads it to be able to demonstrate knee alignment in real time and in all 3 dimensions. By using the information that the computer generates, and by using cutting blocks with tracking arrays attached to them, the level of the cut to be made in each bone can be determined. Similarly, the angle of that cut in both other planes, can also be determined. Using this information helps to get a well fitting prosthesis and a well aligned leg (straight, not bowed or knock-kneed). These systems are accurate to much better than the 3º overall that was previously accepted, and this small an error has never been shown to be significant in terms of outcome. Kinematic Alignment is a more recent idea in which the final alignment of the knee after replacement is designed to be the same as it was before any arthritis set in. That is, if you were bow legged (varus) as a teenager, then you will be made bow legged at the time of replacement; and similarly, if you were knock-kneed (valgus) as a teenager, you will be made knock-kneed again. The reason for this is so that the ligaments on each side of the knee are brought back out to there normal tension rather than having a tight ligament on one side or the other that may need releasing. The upside of this is that it is thought that natural alignment (as your knee was originally made) should provide a more natural feel and hence a better result in terms of pain and function. One way of performing a knee replacement with kinematic alignment, is by using the computer designed cutting blocks outlined below. This is because the centres of rotation of each side of the knee can be worked out from the bone structure, independent of the degree of arthritis (wear) present. The problem with this is that there are many people born with legs that are very varus or valgus, and cosmetically these may be unacceptable. Similarly, the prosthesis is not designed to be used in other than near straight alignment, and hence implantation at odd angles can lead to other problems, particularly patella mal-tracking and pain. For this reason, the companies that have previously offered this technique, have recently stopped marketing this technology: and hence it is now unavailable in its original form. Despite the above problems that have occurred whilst trying to make the knee work as it used to, the idea still remains attractive. With computer navigation as described above, not only can the knee alignment be made such that the leg is straight, it can also be set at any other angle desired. Unlike instrumented alignment, the individual component alignment can be changed, and the overall leg alignment can be adjusted. Hence, if ligaments on one side of the knee or other are tight, then instead of just releasing these to allow the leg alignment to be adjusted such that the leg becomes straight, the leg can be left slightly varus or valgus so that those ligaments are not over tensioned: and given that it is possible to reliably achieve a range final alignments, the alignment can still usually be left within the range of acceptability. Only in the situation where an acceptable alignment cannot be achieved, would tight ligaments then have to be released to allow a correction to be made. The sort of adjustment described above is how Dr Holt performs all knee replacement surgery: that is, making adjustments during the final stages of the procedure depending on the overall balance and alignment. It can also be done by using the computer navigation system to assess ligament tension at the commencement of the procedure and then relying on that data to aid in determining the location and angles of the cutting blocks. This method is a bit more fiddly to do, and is not always perfectly accurate because of bone spurs associated with the arthritis that inhibit the ligaments reaching their full length, but of course the final position can still be adjusted at the end. The importance of the navigation systems being able to determine ligament length and tension is that this is the method used to provide information to the robotic systems, which then guide the surgeon to make the cuts based (entirely) on that information. In order to do this, the computer makes up a 3D picture of the limb with the components shown in situ. The positioning of those components is then adjusted by the surgeon, based on the personal preference of the surgeon, but taking into account the ligament tension that might result; both at all degrees of knee flexion during the procedure, and at the end of the procedure. Whether this is any better than the method of adjustment used when this is done in real time with computer navigation remains to be seen: and bear in mind that it is the same computer navigation system used in both instances. The only difference is that, in one system the adjustment is done on screen before the final cuts, and in the other, it is done during the procedure. Computer designed cutting blocks: Sometimes referred to as PSI (patient specific instrumentation), this alignment technology also involves the computer but, in this system, the computer is used pre-operatively and not intra-operatively (see picture below). In this system, an MRI scan of the knee (or CT in some systems) is taken, usually along with long leg alignment x-rays. This does not produce either pictures or a report, but instead, digital information is acquired which is Slot for saw cut A computer designed cutting block based on CT scanning of the knee

4 Computer Design for Cutting Blocks Femur (above) and Tibia (below) sent to the manufacturer of the prosthesis. Engineers then put this information together to develop a 3D image of the knee and leg on a computer. A virtual knee replacement is then performed on screen. Prosthetic size and placement is determined, including the level of the cuts, the angle of the cuts and so forth. Once this has been done, these pictures, including 3D models which can be viewed from any angle, are forwarded to the surgeon for approval or adjustment. Cutting blocks are then made which fit on the ends of the bones (specific for every individual patient), enabling cuts to be made (see pictures below). The purported benefits of computer generated cutting blocks are many but, when the first 200 of these were reviewed by Dr Holt, it became clear that this method did not always get it right. Also, there was no way of checking the alignment in the theatre at the time of surgery: hence, if it is incorrect, that may not be known until after surgery. Currently therefore, Dr Holt's preferred method is to use the in-theatre computer navigation system, which, in his hands, seems to produce the most consistent alignment results. It is also important to note that PSI refers to the 'instruments' that are used for the surgery (that is: the cutting jigs) and not to the prosthesis. There is often a misconception that by using this technique, a prosthesis will be specifically made for a patient. This is not the case however. The prostheses used are the same off the shelf range as is used with all of the other alignment techniques. What can be helpful however, is a guide to component sizing which this technique seems to get right most of the time. On the other hand, sizing is rarely a problem, either with the available measuring instruments or with computer navigation systems. Computer derived cutting blocks require a scan that, Final Computer Model (Prostheses in situ) theoretically at least (because it is not diagnostic), is not covered by Medicare. However, Medicare do actually seem to cover them, at least for now. It then requires computer design time, with supervision by an engineer, to get the cutting blocks designed and ready for surgeon approval. It is thought that this can be done for about $1500, which is a bit dearer than the cost of standard computer navigation. However the prosthetic companies like this technology because it means that they know what prosthetic sizes are going to be required ahead of time. This means that they do not have to have a full range of prostheses available for every case (usually providing the size chosen, plus one size bigger and one smaller) which, in turn, limits infrastructure storage. Similarly, the Hospital likes this system, because they only have to sterilise and provide instruments for the specific size range that is likely, and not a full range of sizes. In addition, they have to provide less storage space for sizes that are not being used regularly; so, some of the cost of providing these blocks can be offset by these benefits. Whilst overall this would seem to be reasonable, it is to be noted that the cost savings are to the hospital and to the equipment companies, whilst the extra costs are to Medicare and the Private Health system: and because these are different purses, this does not balance out and lead to decreased Medicare and health insurance premiums. To date, other than making the surgery easier, the results have not shown any patient benefit, and the overall alignment has not been shown to be as good as 'in theatre' computer navigation. Whilst still in use for the above reason, this methodology is less popular than it was, perhaps because of the loss of final control over alignment, and the loss of the ability to adjust that at the end of the procedure if needs be.

5 Alignment for Robotic Surgery is essentially the same as for standard 'in theatre' computer navigation, The same pins and arrays are used, the same computer system is used, and hence the overall accuracy should be the same. All the parameters that can be looked at for use with a robot are obtainable and available for surgery with in-theatre computer navigation. These include not only overall alignment assessment as discussed above, but ligament tightness, or laxity, at various positions of the knee. The latter, in turn, defines what is known as the 'envelope' of mobility of that knee. Such information can then be used to create an alignment plan for that knee: and that alignment plan can take into account both overall leg alignment and individual component positioning to achieve that alignment. So what does the Robot do? There is no difference between the technique of in theatre navigation and navigation for robotic surgery; and the possibilities for alignment and tension adjustment are the same. What differs is that the former technique uses saws through cutting blocks that have been positioned using the navigation system, and the latter uses a burr with the robot restricting the passage of the burr outside the programmed area to be resected. That area however, is determined by the very same navigation system. The burr is like a dentists burr in that it is attached to the main planning computer by an arm or a cord. Essentially, there are two types of systems available: 1) Haptic Robots These are connected by an arm which the computer controls to stop the burr going outside the required area. The robot, via that arm, essentially provides limits as to how far the burr can be pushed. This means that the burr can be used without having to worry about where it goes; it will not allow bone to be removed where it shouldn't. The information for this is provided by the navigation system, essentially the same as for in-theatre navigation. It is called 'haptic' because of the feed back it gives the burr, presenting a barrier to the burr if taken off the prescribed area. The limits of the surgical field can be felt. 2)Non-Haptic Robots These are connected by a cord for power and control but, instead of an arm providing limits to what can be burred, the burr is withdrawn into a sheath if the edges of the surgical field are exceeded. This information is provided by a navigation array attached to the burr and linked to the general navigation set up. Like the haptic computer, the process can be watched on screen to make sure that the burr is working within the area required. That is, to plan. It is not haptic however, so it does not provide feedback (such as artificial resistance) to burring outside the planned area. If anything, the latter system, the 'non-haptic' robot, is the easier to use. It also has the most flexibility in terms of access to difficult to get at areas. From a planning and outcome point of view however, the two systems are pretty much the same. Both are expensive at $1.5M to $2.0M each. Both require the additional expense of the 'in-theatre' navigation system to function, over and above the amortised cost of the robotic hardware and software; so these systems add considerably to the expense of each procedure: and in turn to the expense of health insurance. The Mako Robot Note that the tool is held by the machine arm which prevents movement outside the planned area. (Haptic) The Blue Belt hand-piece This has navigation sensors attached to it. It is not attached to a rigid arm. Instead, the burr retracts when it goes outside the planned area. (Non-Haptic) What can we expect to gain with Robotic Surgery? Currently - not much. It is the same operation, done with the same navigation systems. It is just the method of bone removal that is different - burr versus saw. The question is as to whether the (theoretical) ability to place prostheses in better positions or alignment (and we are now talking fractions of a milli-metre on top of an alignment plan for which no-one knows the best solution for any given individual) will lead to better results. For total knee replacement, and probably for hemi-arthroplasty, (half knee replacement), the likelihood of improvement over current systems would seem to be small. However, for operations like isolated patello-femoral replacement, there is some hope that better positioning will improve the results which are currently far from consistently excellent. Where are robots useful? Robots have found their place is several fields of surgery. Where they are most helpful is where they can increase available light and increase vision, and in some areas use robotic arms to be able to do things that are normally out of reach. In cardiac surgery, there are centres where all the coronary bypass surgery is done without opening the chest. By using cameras, small light sources, and arms that hold needles and forceps, the vessels can be harvested and joined to

6 the coronary arteries in exactly the same way as in open surgery, but without opening the chest. The advantages here are clear: shorter hospital stay, less pain, and perhaps better vision for the surgery. In addition, these machines, which just transmit the surgeons movements on control instruments to the instruments on the end of their arms, can take out any shake or vibration, hence perhaps aiding the surgery for some. These machines have also shown promise in operations like radical prostatectomy (see the picture of a Da Vinci robot below) where a lot of the work is done in deep cavities, or behind structures that normally obscure vision. Here, it is not so much the ability to use the instruments better that is the advantage, but the ability to use better lighting and cameras to enable visualisation. Having said that, the evidence that it is better than open surgery is still being sought, but if it can decrease the risk of complications, it will ultimately be deemed worthwhile. The Blue Belt Robot This is a Non-Haptic device which means that it has no rigid attached arms. This allows freedom of motion of the cutting instrument which, potentially, makes it more versatile that a Haptic Robot. The Da Vinci Robot Performing Urological Surgery Here the instruments, attached to the various arms, are placed by the attending surgeon. One or more of the arms has a camera attached to it which then allows the surgeon to operate within the abdominal cavity from a remote console. This technology has no Orthopaedic applications as yet. The Blue Belt Robot The burr is held free in the hand, the screen provides colour coded guidance by showing both what to cut and where the instrument is, and the burr retracts whenever the colour coded area is exceeded. Getting back to knee surgery, it is clear that the things that make robots useful elsewhere are things that are not really applicable to the knee. Accordingly, it is thought that it will be some time before a genuine place for this sort of surgery in the knee is found: and one that improves results and is economically viable, may be some time away. In the meantime, the available robots will continue to be used on an experimental basis until they either find their place in Orthopaedics by evolving to become more useful, or by virtue of cost, are left in mothballs. For further information: On this or other related topics keith.holt@perthortho.com.au URL: <