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. Unfortunately, whilst there is great promise from this technology, none of the above outcomes are proven at this stage. There are however, some early encouraging signs, most notably for isolated Patello-Femoral Replacement and for Hemiarthroplasty (essentially for Medial Compartment Resurfacing) of the knee, suggesting improved short term results with this technology over other methods. For Total Knee Replacement however, the jury is still out, but the optimism remains.
The term 'Robotic Surgery' also leaves the impression that a robot actually does the surgery (an 'active' robot rather than a 'passive' one): and hence why the outcomes might be better. For the moment however, this is not the case either even though there are orthopaedic robots that can, theoretically, be programmed to do that: and more are in development.
Perhaps what the current generation of robots bring to Total Knee Replacement is documentation; an ability to record how each and every prosthesis is implanted. Such documentation of alignment and ligament balance, in association with the knowledge of the kinematics (how the knee works and moves) of each particular prosthesis which is implanted, can then be used to contribute to 'Big Data': and from that data set, it is hoped that we will eventually learn how to implant each of the variously designed prostheses to obtain an optimal outcome for each. And from there, prosthetic design should be able to be improved by being able to test new ideas against that data set, perhaps eventually leading to a knee that functions very like a normal one: something that most believe is likely provide the best outcome in terms of function and satisfaction.
Why use a Robot?
For Partial Knee Replacement (medial compartment or patello-femoral resurfacing), the ability to plan the procedure on screen, and to then carry out that plan, provides a level of precision that is hard to achieve with other methods. This surgery is harder to do than Total Knee Replacement, and has a higher failure rate in all registries including the Australian National Joint
Medial Compartment Resurfacing(Hemi-arthroplasty) using a robot
Although early, the results of robotic insertion of these partial knee replacements can already be seen.
ANJRR 2019
Replacement Registry (ANJRR). Whilst the reasons for the premature failure of these devices are multi-factorial, a percentage is considered to be due to mal-positioning of the implants and to the resulting ligamentous imbalance throughout the range of motion. In keeping with this, we are now starting to see short term benefits emerging from the use robotic technology
The Blue Belt Robot (Smith & Nephew)The burr is held free in the hand. The screen provides colour coded guidance by showing both what bone is to be removed and where the instrument is. The burr retracts whenever the colour coded area is exceeded.
for this sort of surgery. Of course the long term is unknown, but with improved short term outcomes starting to appear in the literature, one can only expect that improved longer term outcomes will follow.
For Total Knee Replacement, where conventional surgery with computer navigation can provide good outcomes, particularly when using the newest navigation systems (as used by the Robots), improvements in outcomes using robotic assistance are less easily achieved and demonstrated. This is because, if the navigation and alignment systems are the same, the operative planning, and the execution of that plan, can be done identically. However, what robotic technology does provide, is not just the latest planning software, but an improved facility to use that software along with some checks and balances which otherwise would not be there.
Such balance is now seen as very important to stability, knee function, and patient satisfaction; whereas overall limb alignment is now seen as somewhat subservient to that rather than of primary concern. That is, we no longer try to make a leg perfectly straight (Mechanical Alignment), as has been the aim since knee replacement was first conceived. Rather, we try and reproduce, at least to some degree and within some limits, the original leg alignment that existed before the arthritis set in (Modified Kinematic Alignment). If this is done, then one should expect that the ligament tension throughout the range of motion should be good, and hence, stability of the knee throughout the range should also be good.
Having said the above however, it should be noted that balancing the ligaments alone does not make the knee work like a normal knee: and that is the case even when modern prosthetic designs are used (i.e. Medial Pivot, Medial Congruent, Bi-Cruciate Stabilised and Bi-Cruciate Retaining knees). Whilst these newer designs do not fully replicate the complexity of function of a normal knee however, they certainly come closer to this than the older designs (CR = Cruciate Retaining, but means PCL but not ACL retaining; and PS = PCL stabilising, but where the native ACL and PCL are both removed and then just the PCL substituted for).
A Medial Pivot Design (Medacta)Looking from the lateral side it can be seen how this
prosthesis pivots on the medial side and is free to rotate about that pivot point because it has reduced, or sometimes even no, constraint on the lateral side. This is much nearer to the design of a normal knee,
and this motion is very important for patella function. If the LCL is too loose however, then instability may
occur.
Medial sided ball & socket
Flat lateral side ‘Unconstrained’
Free to slide butLCL too loose here
GMK Sphere
Computer Navigation at work Note infrared beams are generated and reflected off
the balls and back to the camera. This then sends information to the computer to determine both the
position and the alignment of the bones.
With such advanced navigation and planning systems, what we can aim for is, not only the ability to accurately reproduce a limb alignment that has been planned for, but also a knee with balanced ligament tension throughout the range of motion - that is: not too loose and not too tight.
A CR (Standard) Knee in FlexionThis shows no real rotation in flexion, hence working
like a hinge (but with some sliding on the tibia). This is not how the normal knee works, but it is how traditional TKR design is. This design still represents the majority of TKRs implanted in the world today.Compare this to the Medial Pivot design on the left which includes some rotation on one component on
the other during knee flexion. This is much more how a normal knee works.
Navigation and Robotically Assisted Surgery
In order to achieve alignments other than 'mechanical' (traditional straight leg alignment with a joint line at 90º to that), computer navigation in one form or another is required. These systems not only look at overall leg alignment, but they can also determine ligament tension throughout the range of motion. With such knowledge, the knee replacement can be planned before any bone cuts are made. Of course, this sort of alignment was originally designed to make the creation of mechanical alignment more accurate, but it has been
Robotically Assisted SurgeryNote that this is based on computer navigation. The
near arm contains an infra red light source and a camera. The silver balls which the light reflects off can be seen attached to the leg. On the other side of the table is the actual robotic arm that will bring in
the cutting blocks, and position them in line with the on screen plan. Cuts can then be made.
Camera
Robot
arm
Planning Screen
Zimmer
shown that just achieving this artificial alignment ever more accurately with a traditional prosthesis, has not significantly improved outcomes.
Computer Navigation vs. Non-Navigated This graph shows that in the under 65 year olds, the most active group, the chances of needing revision
seems to be lowered if a computer navigation system is used. Robotic systems should at least follow this
curve or hopefully even do better.
The initial planning is done on-screen after the knee has been mapped out and the ligament tension recorded. The prostheses are then digitally added, the position and angle of each bone resection is then adjusted so as to both balance the collateral ligaments, and to control the overall leg alignment and the joint angle.
Once the above has been done, the cuts can be made as planned, and the prosthesis inserted. The alignment and balance can then be re-checked and altered as necessary, making sure that the knee can go through a full range of motion including full extension (getting the knee fully straight, which is something that is often lost with progressive arthritis).
Final Alignment screens on RosaThe top screen shows the leg straight (extension) view, the bottom shows the 90º flexion view, with
the prostheses in situ. Their positions are fine tuned by adjusting the amount of bone to be removed on each side and the angle of the joint line, whilst still controlling the overall leg alignment. This is done
within the knee envelope such that ligament balance is also achieved. The cutting blocks are then brought
in by the robot, and the bones are cut.
Extension View
90º Flexion View
Using standard navigation tools alone, but current generation ones, the cutting blocks can be affixed to each bone in turn under the control of the navigation system. If a Robot is used, it will either manoeuvre the cutting blocs into place for fixation to the bones, or it will hold a saw in place directly. In neither case does the robot actually do the surgery. The surgery is robotically assisted, not done by the robot. Hence these are referred to as 'Passive' Robots rather than 'Active' ones, noting that they do not really fit the established definition of a robot.
What we still don't know about Knee Replacement
Within the context of trying to achieve acceptable ligament balance (not too loose and not too tight), other considerations need to be accounted for.
The on-going concern for Total Knee Replacement is not just one of recreating the pre-arthritic knee alignment and balance, but rather one of knowing exactly how to align and balance a particular design of replacement. There are many different types of Total Knee Replacement and each different design needs a different alignment and balance, particularly in the flexed (bent) knee. Despite how long this operation has been around, the optimal ligament tensions, prosthetic position and so forth, are not really known. Despite this, there are some good theoretical concepts hypothesising on this, and the data obtained from the
robotic systems will hopefully give us the information we need to confirm or adjust those ideas. It should also give us more information about the preferred prostheses, particularly when the registries start to collect outcome data and not just record component revision and reasons for failure. Unfortunately, this sort of information is still some years away.
Things to consider to improve satisfaction:
1. Design / type of prosthesis
2. What alignment is chosen for implantation
3. How tight the ligaments are made
4. What range of motion is achieved at the time of, and following, the surgery
5. What pain management and post operative protocol is used
6. What rehabilitation protocol is used
7. What patient related factors exist
The influence of contemporary knee design on high flexion 2: a kinematic comparison with the normal knee. Morra, Rosca, Greenwald and Greenwald, 2009
In this, the second of 4 articles on these matters co-authored by four authorities on knee replacement, and presenting computer analyses of various available knee designs, the following statement was made.(Seth Greenwald quoting G. Engh - 2009)
“A knee arthroplasty, that closely resembles the feel and function of a healthy un-operated knee, is increasingly identified, by both patients and clinicians, as an objective of knee replacement surgery.”
With the passage of time, and with evolving prosthetic design and implantation techniques, this prophetic statement, increasingly, is being regarded as likely to be correct.
Making Knee Replacement Better
Choosing a RobotChoosing a robotic system is important because currently, each system is approved only to implant the brand of knee that the company selling the robot manufactures. It is important to know that while these systems could be programmed to put in any brand of knee, they are sold on the basis that they will not be so programmed (the profits come from the prostheses and not the robots - even though the latter are very expensive). It is therefore important to know which robotic system a given surgeon uses in order to look at the outcomes of the particular knee design related to that system. Such outcomes can be found in various registries, but the most comprehensive, and best kept one, is the AOA-NJRR (Australian Orthopaedic Association - National Joint Replacement Registry). It is very important to separate out claims of a better robotic system from claims of a better prosthesis because a ‘this years’ robot will not compensate for an older style prosthetic design with poorer satisfaction and/or premature failure.
Understand that a low revision rate is not the same as a high satisfaction rate. A given prosthesis may not have excellent satisfaction rates (traditionally about 80% good to excellent only) but, unless it is bad enough to come to revision, it will not show up in the registry as a poor outcome. This is because the registries were never set up to determine satisfaction: their measurement of failure is revision. They do not collect PROMs (Patient Reported Outcome Measures), meaning that they do not have any record of how well a given knee replacement performs, how suited it is to various activities such as stair climbing or kneeling, how much knee flexion or extension is possible, or even how sore it is at various time points after surgery. Only recently have registries started looking at PROMs, so any meaningful results are some years away.
Unless a replacement is bad enough to come to revision, the registry presumes that it is doing okay.
Revision is defined as being where one or more components are changed. Hence, a subsequent arthroscopy, patella re-alignment, synovectomy, or similar, will not be detected. Clearly therefore, there are many problems that decrease satisfaction rates but which are not captured by registries.
Dr Holt's Preferred Designs
• The Zimmer Persona Knee, in it's Medial Congruent form. It has slightly less lateral sided freedom than some of the other Medial Pivot Designs, and therefore undergoes less rotation; but comes with Rosa (the Zimmer robot). It has been developed from the Zimmer Nexgen knee which has very good longevity as seen in the Australian National Joint Replacement Registry.
• The Medacta GMK Sphere. This is a Medial Pivot design with a fully unconstrained lateral compartment to allow maximal tibial rotation. It has very high satisfaction rates. As yet it does not come with a robot, but it does have a high end computer navigation system which is soon to be upgraded further.
• The Smith & Nephew Journey 11 Knee is a Bi-Cruciate Stabilising design, it has the best kinematics of any knee on the market, and hopefully will be available in late 2020.
