Total Knee replacement- MAKO robotic triathlon cruciate substituting knee replacement

Preoperative planning modes within the mako workflow allow the surgeon to check the plan and assess sizes required for the patient.
These should be carefully examined by the surgeon and makoplasty technician together. The plans can be changed at this stage. It does not govern which philosophies or balancing technology you use.
As you interact with it, you might find yourself introducing more kinematic alignment into your knee replacements, particularly in cases with oblique joint lines. Alternatively, the proposed ‘standard’ positions can be accepted and assessed at a later stage.
The interface allows you to learn from the changes you make to balance the knee and you soon come to predict simple changes to prevent obvious issues. One example is using a few extra degrees of femoral component flexion to prevent notching if you want to bring the femoral component a few millimetres posterior. As the triathlon is single radius of curvature this makes no real difference to the balance of the knee.

preoperative radiographs in the anteroposterior and lateral planes should be available and displayed in theatre.
Notes of the functional range of motion in clinic should be checked. Have a good look for big osteophytes, particularly posteriorly, as they will effect the balance of the knee and the robotic program doesn’t really factor this aspect in.

Long leg alignment views are ofter helpful in cases of significant deformity. They allow assessment of deformity and can give an idea of joint line alignment.
You can then decide whether to reconstruct oblique joint lines back to the patient’s normal anatomy or to more conventional angles. You will probably find that the robot makes you more confident to reconstitute native anatomy.

The makoplasty technician will help the scrub nurse to apply a transparent sterile drape to the RIO arm and body of the mako robot. Ideally, this is done when the patient arrives to the anaesthetic room to save time.

Please note that parts of the conventional instrument tray are still required. Trial components, femoral box preparation instruments, tibial keel instruments and a full patella set (if to be resurfaced) are required.
In addition insertion and implantation tools for the definitive prosthesis are used in the total knee replacement workflow.
Please be aware that the Makoplasty technician is not there to subsitute for a thorough working knowledge of the implant technique itself, which is your responsibility as a Surgeon.

After the robot is draped, an optical tracker (A) and a power tool (B) are attached. Care is taken to maintain sterility at this stage.
The Mako has a “draping mode” which should be selected. The robotic arm will be on the same side as the surgeon, i.e. the side of the knee being replaced. Once draped, “standby mode” is selected which ‘parks’ the robotic arm to stop it lowering into an unsterile position. You can park this outside of the immediate perimeter of the operating table so that the initial stages of registration are unimpeded.

The camera stand is located on the opposite side to the robot. It must have an unobstructed line of site to the lower femur and the upper tibia.
The powertool is next “registered” by facing it towards the camera stand which houses the optical recognition (A) and screens (B).
The scrub nurse will perform a series of guided motions to ensure accurate registration. This will be supervised by the Makoplasty technician.
The robot will not allow progress if this is omitted or inaccurately done.
Ideally, aim to do this just before the patient is introduced to the operating theatre.

Cutting is performed with a specially designed saw which allows cuts without a cutting guide and was a key part of the development of the TKR workflow for Stryker.
The first use is on a perpendicular attachment as shown here. The saw contains a small cutout to allow for registration and confirmation of the saw blade position by the robot. Once more, this can be assembled by the scrub nurse just as the patient is coming into theatre.

Analyse the leg for a pre-operative fixed flexion deformity of the knee.
Where a pre-operative fixed flexion deformity exists, it will be measured and confirmed in the robotic workflow. Make sure that you have a reasonable idea of FFD to “sense check” the proposed cuts.
I also tend to aim for a slightly slacker knee in cases of 10 degrees or more FFD as hyperextending is a rare issue In these cases.
Preparation of the skin with antiseptics is performed by the surgeon and assistant. You can prepare the foot but I prefer to completely exclude it from the surgical field.

A skin incision is made running from 10cm above the superior pole of the patella in a straight line to a point just medial and distal to the tibial tuberosity.Use as Skin marker to mark a skin incision running from 10cm above the superior pole of the patella in a straight line to a point just medial and distal to the tibial tuberosity. In obese patients this may need extending. As you put the femoral reference pins for the mako inside the surgical cut, this may be a little more proximal extension than you are used to.
If you go medial to the tibial tuberosity it reduces kneeling tenderness.

An Ioban adhesive fixes the drapes in situ and provides some protection against ingress of commensal skin bacteria through the surgical incision. Outer gloves must be exchanged for clean ones after this stage. Take care not to move the skin over the knee as your incisions can be dragged laterally if you do.

Bend the knee up to over 90 degrees to stretch the anterior skin. Use a scalpel to incise through the skin. Afterwards the blade is considered contaminated for any deeper work and is put aside to perform stab incisions for the guide-pins only.

Once full thickness skin & fat flaps are raised reflect the soft tissues both medially and laterally to expose the quadriceps tendon proximally, the patella in the centre of the wound and the patella tendon distally.Use a single plane of dissection until you can see enough of the extensor mechanism. Generally aim for access up to around 1cm beyond the edges of the patella centrally tapering towards the apices in an almond shape.

For the medial parapatellar approach identify the natural rolled edge of the patella tendon medially.This is an important landmark when making your medial para-patella approach. Incise along the border of the medial patella tendon from the patella superiorly to the tibial tubercle distally. Skirt the incision around the patella medially proximally until you reach the quadriceps tendon where a 5mm cuff of tendon should be left medially as you extend up the quadriceps tendon leaving the majority of the tendon lateral to the incision. Once the joint has been entered for the length of the approach, sublux the medial tissues to expose the medial femoral condyle shown. Reflect the medial tissues off the medial tibial plateau proximally, staying subperiosteal.
Stay on the tibial bone and reflect the tissues off the medial proximal tibia starting centrally from your medial para-patella incision working around the medial side of the tibial plateau. In the more fixed varus cases this release needs to be more extensive often passing the “equator” of the plateau. If inflamed, the infrapatellar fat pad is excised.

The tibial array is now attached. Drill the first 3mm pin in 10cm below the distal pole of the incision(A).Stop drilling when you feel the cutting tip penetrate the far cortex. Remove the drill pin holder and check that the pin is well fixed in bone.

Place the tibial array stabilizer over the first pin (A)and press the distal tower against the skin to make a small mark.
Use the skin knife to create a second stab incision at this point and insert a second 3mm pin through the array stabilizer(B). You will find the pins are around 15mm apart. Concentrate on making the pins parallel as it will make the construct easier to assemble. Leave the stabiliser in place.

Attach the tibial array (A) by sliding it down onto the stabilizer, making sure that it points towards the camera stack and away from the surgeon.The array holds 4 discs which are used to calculate the position of the tiba in all 3 axes.
They only work if clean and there is a clear line of site to the optical pickup.
Insert the femoral pins in the same fashion as the tibial pins, usually in the upper extent of the surgical incision. A separate stab incisions can be used in very muscular or obese patients.If using separate incisions, it is best to put the pins in with the knee in at least 90 degrees flexion to stop it pinning the extensor mechanism down.
If pinning in the surgical incision, it is important that the pins don’t get compressed by the apex of the incision and don’t overlay the area where the anterior femoral cut will lie. They don’t have to both be exactly in the middle of the four – I tend to put the most proximal one a bit lateral and the most distal one a bit medial as it allows you to get a bit more distance between the distal pin and the joint line. It helps to keep them out of the way when you come to do the anterior femoral cut.

Insert the femoral pins in the same fashion as the tibial pins, usually in the upper extent of the surgical incision, followed by the femoral stabiliser, then the optical recognition discs.Position the optical recognition discs on the stabilizers to achieve the right position. If they are too low, the drapes or soft tissues impede the line of sight.
If they are too high, particularly if they are above the cylindrical portion of the pins in the drill pin driver attachment area (A), they will toggle or move.
Take time to get the position right, working in conjunction with the makoplasty technician. A minute adjusting them a few degrees now is time well spent and prevents a lot of ‘robot yoga’ later (attempting to get the leg in a position where the arrays are visible, the robot in a position where the saw will cut and the knee at an angle where it is possible to proceed).

This view from the opposite side of the operating table gives an idea of the final alignment required for the optical arrays. As you can see, we try to avoid the arrays facing down to the floor and bias them slightly upwards as it helps pickup on the optics.

This view from the end of the table gives an idea of the final alignment required for the optical arrays.
They are pretty much parallel to the long axis of the bones.

Once the position of the optical recognition discs appears satisfactory, move the leg through flexion and extension to ensure that the array can visualise the tibial and femoral arrays throughout the surgical range to be used.You will see the arrays displayed a s a large blue and large grey dot on the screen. The arrays can now be tightened down onto the pins with the square driver in the mako set. Your assistant will need to stand proximally, out of the way of the arrays.

Registration can now begin and is guided by the Mako.
Begin with patient landmarks. These allow the robot to register the limb anatomy. First you will circumduct the hip to allow the computer to capture the hip centre.
Next, take the green optical Probe and follow the instructions on screen to complete the patient landmarks phase.
This captures the medial and lateral malleolus to calculate the centre of the ankle.

Insert a bone registration metal marker 3 or 4 cm above the medial femoral condyle and a marker medial to and above the tibial tuberosity.Insert a bone registration metal marker 3 or 4 cm above the medial femoral condyle and away from the intended bone cuts.
This is pushed in on a hexagonal inserter.
A similar reference point is inserted in the tibia in the same fashion. Insert this medial to and above the tibial tuberosity.
Next use the green optical probe to confirm these points for the robot which completes the checkpoint registration phase. These are used as position checks before cutting and should be stable and near the joint but out of the field of bone cuts.

The principles of gap balancing are the same as always. Start with simple a few simple rules:
‘symmetrical problem = adjust the tibia, ‘assymetrical problem = adjust the femur’, ‘too tight = take more’, ‘too loose = take less’.
Make a single change at a time and assess again for at least your first ten cases until you get used to the subtleties. Don’t forget that you can still revisit tissue releases and also that osteophyte removal can have significant effects on balance.

The Screen will continually guide you to which cut you are doing and where the safe boundaries are set. These need to be very close to the edges of the bone to protect soft tissues like the MCL, patella tendon etc. If you keep getting yellow boundaries, you can ask the Makoplasty technician to move the boundaries outwards a little. If you do, take extra care to protect the soft tissues.

You can see on the screen here that the areas you are likely to cut off are marked in grey – stay a few cms proximal to this on the femur and distal on the tibia.

The final registration phase is bone registration. This uses the blue optical probe which has a sharper point to allow the surgeon to push through cartilage or soft tissues and register the underlying bone.
You need to collect 40 points on the femur, following the onscreen map once more. The points are distributed around the surfaces of the distal femur.
Use the blue probe to capture the point marked as a large blue sphere and progress through all 40 spheres as directed. Where there is preserved cartilage, push through gently until you feel bone. Where it is already worn down to bone, just rest the tip on the surface.

Once completed, you will see a screen showing the mapped points and some more large spheres.
The small points will then light up green, yellow or red indicating complete accuracy, near accuracy and inaccuracy of position.
You need most to be green or yellow to proceed. The large dots act as a second check – they will light up blue and you will use the blue probe to ‘pop the bubbles’ of these spheres.
This checks the surface of the bone in the selected position. It is a key step and takes a little while to get used to but is not overly time consuming after a few cases.

The blue bubbles are highlighted and the probe shows up as an arrow. If the point is within 1mm of the anticipated position of the bone surface, the robot will register the point as captured.
The screen will provide three references to help with this process. The main picture (A) is the main guide and will help you to aim the probe to the right place.
The dot will go white if you year win the right place. The small picture (B) gives you a magnified capture of how close the probe is to the anticipated bone surface. The visualiser (C)shows a numerical distance. If this is less than 1mm, it turns green and you can capture with the foot pedal or the technician can do it for you. As you get more experienced, it is quicker and easier to do it yourself with the foot pedal.

Repeat the same process for tibial registration, again following the map of blue spheres over the tibial surface

Use the blue probe to check that the surface map is accurate once more. You do need to be quite accurate to ‘pop the bubbles’. You can see on this picture that the probe is not close enough to the bubble even though it is on bone and very nearby. This will not capture and the probe will have to be slid a few millimetres proximally.

Before final planning and cutting begins, the femoral and tibial checkpoints are probed agian to ensure that there has been no movement of the optical markers.
You might need to try a few angles to get it to register. This automatically captures if within 1mm.

The surgical plan is now available and shows information specific to the case.
Begin by looking at the basic information (A) which shows the type of implants sizes of implants and the size of bearing to be used. Check these are sensible – they almost always are.
Next look at the shape of the bone and the shape of the implants (B) to see if they roughly match up. Sometimes it tries to go a bit large on the femoral side but it is often right.
Finally, look at the 4 images on the left to assess resection measurements, alignment and coverage.The default position is for the robot to try to produce flexion and extension gaps of 18mm on the medial and lateral sides of the joint i.e. measured resection to reproduce the anatomy when the implants are inserted.
Check the resections for overhang and underhang and adjust the implants in six degrees of freedom to achive the desired balance. Note, if there is severe deformity or very large posterior osteophytes this can be difficult.

The next phase is ligament balancing to ensure that the knee will be stable throughout its range.
The technician will help you to capture medial and lateral gap measurements at 0 degrees 90 degrees and full flexion to asses ligament tension. These are captured with the knee in neutral, stressed varus and stressed valgus positions. The easiest way is to apply the forces manually. On your first few cases, it is well worth adjusting the parameters one at a time to gauge their effect on the predicted outcome. E.g. externally rotating the femoral component will increase the medial flexion gap and decrease the lateral flexion gap. There are a few other ‘tricks’ not available to a conventional cutting block technique. For example, if you are worried about notching… you don’t want to anteriorise the femoral component and increased the flexion gap if it is well balanced. The system allows you to add flexion onto the femoral component instead – this will stop notching without affecting the flexion gap.
Typically we aim for 18mm in the medial and lateral compartments in flexion and extension – i.e. the thickness of the implants to be inserted. In a fixed flexion/tight knee I often aim for 19mm balanced extension. In a valgus and hyperextension knee, conversely, I aim for 17mm.
This case was tight in extension and normally balanced in flexion. I wanted it to be a little looser in the extension gap and to correct the flexion gap to match the inserted material. It is simply a matter of adjusting the bone cuts to make the figures match – 19mm for both extension gaps and 18mm for both flexion gaps in this case.

There is a lot of information available to the surgeon which you may not be used to having. Expect to spend ten minutes on this phase in your first few cases.
Ask the technician to show you pictures with and without implants so you can see the shape of the bone cuts as well. In most cases, they will look like familiar shapes to you.

The makoplasty technician will now reposition the Rio cutting arm so that bone resection can begin. This is the main bulky piece of the robotic mako equipment with the robotic arm on the top. It is a multi-jointed arm which allows for passive movement and constrained active movement within boundaries. In the case of a total knee replacement, the end attachment is a saw blade.
You will proceed to use this with the robot guiding the saw into the correct plane of the cut to be made – this is an active robotic movement. From then, the robot will lock the saw into this plane and attemts to move the sawblade out of this plane will cut power to the blade. The outer bondaries of the cut are automatically detected and boundaries drawn by the mamo system. If you attempt to cut outside of these boundaries, power is cut to the saw blade.
The perpendicular attachment (A) will be in place so that the saw blade will point 90 degrees downwards, towards the knee. Ensure with the technician that the femoral, tibial and Rio arrays are all visible and that the saw will reach the knee properly when the knee is in around 110 degrees of flexion. You may need to move the knee towards or away from the robot as well. If so, the screen will guide you.

The saw is registered with the optical probe and the checkpoint is checked once more.
Make sure that the knee is in a stable position. It can help to ask the assistant to steady the femur with one hand. Beginning with the distal femoral cut, sequential cuts are performed. The screen guides through the order of the cuts. These can be altered for the surgeon preference if desired – it is unnecessary to do so.

The makoplasty technician will free the arm and it should be guided into an approximate position for distal cutting with the saw around 3cm away from the bone.
The screen will display the bone to be removed in green and boundaries within which the saw will be active. The haptics will engage and the saw will align with the planned cut. The saw boundaries will then change from yellow to green lines. Take care not to move the knee too much.
If it moves or the haptics do not engage, move the saw further away and try again until the saw power becomes active. The screen will have green boundaries when active and revert to yellow boundaries if it detects an issue and has to shut off the power.

The main area of the screen now shows a live figure of the distal femur and the saw. There will be green areas on the distal femur, indicating the area of bone to be resected. This will be distal femoral resection for the first cut. There will also be lines marking the boundaries of the cutting zone. This is the area where the saw will be active. It will display the flexion angle of the knee. If it is an appropriate angle for the saw to cut, the angle figure will be in green. If the saw icon in the top left corner is green, the saw is active. If the boundaries are green, the saw blade is active too and you can begin cutting.

You will mainly look at the screen for this part – ask your assistant to watch the knee and warn if any soft tissues appear to be in danger. Once the haptics are engaged, advance the saw to a few millimetres off bone and squeeze the trigger.
If you are within the safe cutting zone outlines, the saw will activate and you can perform the distal femoral cut of each condyle. The saw teeth must remain within the outline or power will cut. If this happens, back off to 3cms back from bone and re-engage the haptics.
As with conventional power tools, it is not necessary to press hard, just gently advance the saw within the haptic controlled path provided by the robotic arm. Begin the saw when a millimetre or two off the bone so that it doesn’t judder the knee when it first starts as this will cut off the saw. Once completed, back the arm off 10cm or so and tell the technician that you have completed the first cuts.

The screen will now move to the next cuts which are again performed with the saw in the perpendicular position. It is helpful to have a retractor in place to displace the patella tendon laterally.
Perform the posterior femoral chamfer cut in the same manner. This is the final cut with the perpendicular saw blade.

The scrub nurse will now swap to the parallel saw blade so the blade is now parallel with the cutting tool. This is used for the rest of the cutting workflow.
Follow the order on the screen to do the rest of the 4 in 1 cuts for the femur. It is common to be right up against the haptic boundaries when doing the posterior cuts.
If there is a large osteophyte, you may want to complete this with an osteotome instead.

It can be helpful to ask your assistant to retract the tissues laterally with a Mikhail or similar spike. The assistant will need to be standing on the same side of the table as you for this so as not to block any of the optical arrays. The assistant should watch the knee and warn of any likely soft tissues in the way.

As you move on to the tibial cuts, you can use retractors to protect the soft tissues again. I use a double-pronged retractor at the back of the knee.
Whilst performing bone cuts, the surgeon should mostly follow progress on the screen, with glances down to the knee to ensure that the assistant is protecting the soft tissues. The boundaries protect most tissues well but the patella tendon has the potential to be cut.
Uncut areas or areas where there is at least 0.5mm more to cut, show up as green. Perfectly cut areas are white. If there is an overcut of 0.5mm or more, it shows up red.

It is only the saw teeth that need to be within the cutting zone, not the whole blade. If you cannot reach a portion of bone, you may have to expand the cutting perimeter in the affected area.The alternative is to try a different angle which is typically needed in the posterolateral area of the tibia.

The final result should be clean cuts in the same fashion that one would expect from conventional techniques. If you are not sure whether to go for cruciate retention or substitution, you can place CR trials and assess stability at this stage.

In this case a posterior stabilised implant was decided pre-operatively.
The posterior stabilisation box for the femur is performed with conventional instruments.
Position the cutting guide centrally in most cases. If it is a large femur and the patella is laterally maltracking, you can bias the box slightly to the lateral side. The guide can then be pinned in position.

A specific chisel is provided by Stryker to cut the floor of the box.
Use a narrow blade oscillating saw to cut the walls and complete the resection.

Insert trial femoral, tibial and meniscal bearing components as per the plan.
Firmly tap the components into place and visually check that they are down on the cut bone surfaces. In particular check that the femoral component is not flexed.

With trials in place, check the feel of the knee for range of motion, stability and balance. This can be confirmed on the robot to ensure full extension and assess flexion range.
Reduce the patella and assess patella tracking.

The mako workflow does not currently include tibial keel preparation. This is done conventionally.
Take the tibial tray trial and align it with the rotation you would like. I tend to line up the posterolateral corner of the tibial tray with the posterolateral corner of the tibial cut then swing it round until it shape matches the anteromedial tibia.
This is then double checked by looking at the position of the centre of the tray against the patella tendon. The other method is to mark the centre of the tray with a diathermy on the bone during the trial period and align it with that.
Use two HEADED pins to firmly pin the tray down flat against the bone, as shown here.

Remove the handle and insert the chimney device to guide the fin cutter. Then insert the fin cutter through the chimney and impact it down.

Lift up the cutter handle and push it downwards and forwards to relesae it from the bone

The mako workflow does not currently include patella resurfacing: conventional instruments are used.
Use callipers to assess the maximal patella depth.
Apply and secure the patella cutting guide around the patella, aiming to resect 9-10mm, usually the preserved patella will be 12-15mm. Any less gives an increase in fracture risk and any more can be associated with ‘overstuffing’ the guide from the side to ensure that it appears appropriately sited to give an even cut. It is usual to resect the amount to be replaced i.e. the thickness of the patella button. This is 9mm (for 33mm button), 10mm (for 36mm or 39mm button) or 11mm (for 42mm or 44mm button).

Size the patella button to give maximal coverage without any overhang. If the button is slightly smaller than the bone, it is best to slightly medialise the button position and remove any excess lateral patella with an osteotome. This will allow the extensor mechanism to track slightly more laterally. In most cases of error, the patella tilts or glides laterally and allowing the button to be more medial reduces the risk.

Drill the three peg holes with the patella drill.

Local anaesthetic is best inserted at this stage. I use dilute marcaine and adrenaline dosed as per the patient’s weight In most patients, this is 100mls saline, 30mls 0.5% marcaine and 1mls of 1 in 1000 adrenaline. Injection posteriorly is very useful – Use a spinal needle to inject through the capsule (you will feel a slight pop as it pierces capsule) where it can bathe the popliteal plexus with anaesthetic.

Pulsatile lavage and then dry all joint surfaces to remove bone debris, fat and blood from the surfaces.You should be able to see the open structure of cancellous bone throughout the bone cut zones.

This arthroplasty was performed for post infection arthritis in an immune compromised patient. Antibiotic hydrogel was used as a supplemental infection prevention tool. The antibiotic used was guided by microbiology input with the antibiogram from previous infection used a guide.

The hydrogel coat is applied directly to bone and soft tissue surfaces. Leave it to dry in for 2 minutes before cementing.

Antibiotic impregnated medium viscocity cement is used in our institution. Apply a thin layer of cement to the exposed bone surface initially.

Apply a matching layer of cement to the back of the implant and insert it to match the prepared keel cuts in the tibia. This is then punched down into place using the flat tibial insertion punch.
Clear excess cement from around the edges of the component.
Take particular care in the posterolateral area where cement is easily missed.

Apply a thin layer of cement to the femur anteriorly and distally. Do not apply any to the posterior condyles or it will be forced into the back of the knee

Insert the femoral component onto the femoral inserter and apply a thin layer of cement all over the back of the component. Offer it up to the femur such that the component box aligns with the femoral cut out. Impact the femoral component into place.
Keep your hands up high to stop the implant dropping into a flexed position (this is for more common than extending the component).

Clear cement from the bone to implant interface and check that the implant is fully seated. If not, a femoral impactor can be used to fully seat the component.
Carefully remove all excess cement with a McDonald dissector and fine tooth forceps – any loose bodies will accelerate wear so this is important to do carefully.

Click the appropriate thickness of posterior stabilised insert into the tibial tray. If your unsure of the size, it is fine to retrial at this point with a trial insert. You can still use the Mako to recapture the data once more.

Apply cement to the patella button and cut patella surface before compressing together with the patellar clamp. Hold the knee in a few degrees of flexion and compress until the cement is set, typically at around 10 minutes after mixing.
Remove the patella clamp, reduce the extensor mechanism and check for range and stability once more. Thoroughly lavage again and check for loose cement.

Close the medial parapatellar arthrotomy with continuous or intermittent dissolving sutures e.g. vicryl.

It is best to perform the majority of the closure in flexion to ensure that the soft tissues are not overtensioned. IF you feel that they are tense and the patella is laterally tilted, you can do a limited lateral release at this stage.

Close the fat with intermittent dissolving sutures

Close the skin with subcuticular stitches, clips or glue as preferred.

The lateral view allows assessment of AP sizing.

The AP view demonstrates medial to lateral sizing and overall knee alignment