Total Knee replacement- Mako Triathlon robotic assisted cruciate retaining TKR (STRYKER)

The Mako system allows for CT guided, robotic arm assisted arthroplasty. This technique describes a cruciate retaining total knee replacement performed on a patient with osteoarthritis of the knee.

It is important to check imaging and patient history for presence of metalwork or deformity above the knee. In this case there is a screw present which would need removal if intramedullary alignment was to be used.
The valgus deformity is noted too which should not be ignored: it is likely that the lateral femoral condole cuts will be small to reconstitute natural alignment. If the lateral cuts seem to be the same size as the medial cuts in the planning phase, this would suggest something is awry.
These ‘secondary checks’ are a good discipline in robotic surgery to ensure that errors of registration have not occurred.

In this case, the patient also had a history of revision hip arthroplasty above the knee to be replaced. This illustrates the importance of a careful history – attempts to perform intramedullary alignment here would be challenging.
It also illustrates another benefit of robotic arthroplasty, the lack of intramedullary instrumentation.

Whilst the patient is in the anaesthetic room, there is a good opportunity to go through the pre-operative planning for the surgery. The Makoplasty technician will load up a proposed position based on the software matching the patient’s anatomy and combined with any preferences you may have offered to them for your cases.
A common example is setting of the proposed rotation of the femoral component. This can default to being set off the trans-epicondylar axis or the posterior condylar axis.
I start with femoral sizing – this is basically a shape-matching exercise to restore anterior and posterior condylar offsets.
Choose the largest size that doesn’t overhang the bone posterior, medially or laterally and also restores the anterior condylar offset. Don’t forget that you can add or take off extension of the femoral component e.g. if notching is likely to be an issue (triathlon has single radius of curvature so there is minimal other effect of this).
You can access the menus and choose anterior or posterior referencing if you wish which will change how increases or decreases in sizes are applied. Tibial sizing is basically about coverage. I start with a 3 degree slope and then will adjust based on later readings. If there are obvious errors in shape matching, I correct them at this stage.
The most common changes I find are to downsize the femur, downsize the tibia or change the rotation of the femur.
In this case I externally rotated the femoral component one degree more as the knee was a little tighter on the medial side than the 0 degree cut had suggested. This is an ‘educated guess’ and is easily remedied when actual measurements are achieved.
I also have a look at the shape of the proposed distal femoral cut on this view. This can be seen on the middle image on the upper line. It typically forms a butterfly shape – just like on conventional TKRs.

All changes are live and instantaneous – they will show you the resection depths. It is worth having a look at the distal femoral and posterior femoral cuts in particular. A “sense check” is wise here.
In a typical varus knee, one would expect smaller resections medially than laterally for the distal and posterior cuts for example. In a hypoplastic lateral femoral condyle, there will be far smaller cuts on the lateral side.
In this valgus knee case, after moving the proposed position, it estimates we will take 0 off the lateral condyle distally, this makes sense. We also took off a degree of external rotation to better match the shape.
Once you are happy with the sizing and proposed cuts, tell the Makoplasty technician and he or she can now set up the robot with the scrub team.

It can be useful to have a look at the 3D reconstruction views of the knee without implants in cases where there is a deformity.
For example, in this case, it might seem weird that the prediction is for a 7.5mm distal femoral medial cut and 0.0mm off the lateral side. You can see, however, that there is significant lateral femoral hypoplasia so this makes sense.

The Makoplasty technician will help the scrub nurse to apply a sterile, disposable mako draper – this can also be done before the patient has come into theatre. The robotic arm will be on the same side as the surgeon and the camera stand will be on the opposite side of the table to the surgeon.

The robot base and arm must be registered – the Makoplasty technician will do this with the scrub nurse for you as well – it involves following some simple movement steps on the screen to ensure that the robot arm is calibrated. It does take a couple of minutes, particularly for the first few cases. It is worth asking the scrub nurse to be ready nice and early before the patient comes in.

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. As you can see in this picture, we set the knee up with a little abduction. We set the side support up with the nut done up gently. This allows us to move the hip into abduction a little when we come to registering the hip centre. We can then reposition the side support through the drapes.

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.
Undermine the fat, outside of the fascia, up to the edge of the patella. It doesn’t need much as this will make an anatomical dead space and can compromise vascularity of the skin flaps. You should end up with an almond shape of fascia visible over the extensor mechanism – the centre will be a couple of centimetres wider than the patella, tapering to each end of the incision.

In this case, I have used a medial parapatellar 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 as 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 next phase is attachment of the optical arrays to the bones. This is done with 4mm screws to which a bracket is attached. The optical array is then attached to the bracket.
The drill screws are powered in with an adaptor on the mako set. Begin with a stab incision 10cm or so below the tibial tuberosity and on the medial side of the tibial crest.
Drill straight through until you feel the drill in engage in the posterior cortex and then stop. A short ‘tower’ from the set is used to place the second drill pin – this can go either above or below the first, depending on the length of the leg.

This ensures the pins are parallel and the mounting bracket will fit on.

The bracket is mounted onto the pins. The bracket must be on the cylindrical section of the pins (it clamps on here and needs to be rock solid) and the attachment for the optical array should be distal and facing medially to allow the optical array to be visible to the mako camera stand.

Next, tighten the clamp on to the drill pins with a square screwdriver provided in the set.

The black optical array (the tibial array) with the discs on is now mounted to the clamp. It can be angled and tilted on the clamp to align it to be perpendicular with the mako camera stand.

The femoral array is positioned in the same way. This can usually be done right at the top of femoral incision. The femoral array is silver in colour.

Go back over all of the clamps with the square screwdriver to make sure that they are all tight. Any movement of the arrays from now on will altar the measurements and is very difficult to adjust for subsequently.
This is an idea of the appropriate spacing and angulation to aim for. Ask your Makoplasty technician to check that they are happy with it. Then look on the screen and you will see the trackers marked as two large dots.
Move the knee in a full range of flexion and extension to check that the dots stay on the screen i.e. the trackers will be visible throughout.

The next phase is registration of the landmarks.
This follows a protocol on the screen and begins with capture of the hip centre of rotation.
This is done by rotating, flexing, abducting, extending and addicting the hip. It only takes five seconds and is done automatically.
If you left the lateral support a bit loose in the set up phase, you can now advance and tighten this to position the hip in a more neutral position and stabilise the knee.

The next phase is registration of the ankle centre which is done with an optical probe. The green probe is blunt ended and is used for this. Again, you just follow the instructions on the screen. It asks for the probe to be positioned on the prominence of the medial and the lateral tibial plateaus in turn.
This is done outside of the drapes just by palpation.

In order to check that they’re have not been errors, such as accidental movement of the trackers, bone registration ‘checkpoints’ are inserted into the femur and the tibia.
These need to be easily accessible and out of the way of bone cuts. The femoral checkpoint has a dish which is perpendicular to the screw. It is inserted on the medial femoral condyle with the dish pointing downwards. Make sure that it is well away from the upcoming bone cuts – this can be seen on this illustration.

The tibial ‘checkpoint’ is the one where the reference cup is parallel with the screw. It should be inserted medial to and just above the tibial tuberosity.
As seen here the green (blunt) probe is then used to register these checkpoints.

The mako takes you through the order on the screen: register – remove the probe and reinsert it in each ‘checkpoint’. Then Register again. If the probe tip is within 1mm of the first registration, it will allow you to proceed. It can take a bit of fiddling to get this and it can be sensitive to the angle. If it is over 1mm, do both registrations again. Don’t try and fiddle it – it is far easier to get right at this point.

Now the blue handled probe with the sharp point is selected to move to the next phase of bone registration.
The sharp point allows for penetration through remaining articular cartilage or overlying soft tissues.

The system can be used in a pure measured resection or as a gap balancing technique. It is also possible to measure both and allow for correction to a ‘compromise position’ between the two. This is my preferred method and seems the most commonly used.
The knee is ‘stressed’ to establish the appropriate ligament tensions. This certainly works best in a knee which will correct to neutral varus/valgus alignment and is easiest with knees with wear predominantly on one side.
The stressing in extension is pretty easy to do with just a correction force at the knee and the ankle to push the knee towards the neutral position. I find it pretty hard to correct in flexion and prefer to use the spoons that Stryker supply.
Typically you will need to put a spoon in the worn side and the thickness of the spoon will push the joint apart and tension the ligaments. Sometimes you will need a spoon in each side as it is not uncommon for valgus knees in particular to be looser in flexion.

Bring the saw to 2cms from the bone. Ensure that soft tissues are out of the way and protected. Squeeze the trigger again and advance to the bone. This should be done without any real pressure.
If you press too hard, the saw catches on the bone and the bone moves – this will cut out the saw. By advancing gently and with minimal pressure, the saw will remain in the cutting plane and begin to perform the resection.
The saw will cut out if it hits the haptic boundaries, if the knee is incorrectly positioned or there is gross movement. As the saw progresses, the screen shows the resection. If it is resected to the right depth, it shows up as white. If there is more bone to cut, it shows up as green. If you have over-resected it shows red.

The screen now shows a series of clusters of points to be collected.
The blue points are the ones to collect next and they are all done with the blue probe. Try to follow as close as you can to the pattern on the screen.
Ensure that the point is directly on bone.
When in the correct place you can press the foot pedal. It is possible to do it with the Makoplasty technician capturing each point but the pedal is easier. There are 40 points per bone i.e. 80 in total.

Once a cluster is completed, you just move on to the next cluster and collect again. Take your time to start with – you will soon get quicker naturally. Once all of the clusters have been captured, move on to the next screen and repeat the process for the tibia.

Once completed, the mako moves onto a further check phase to ensure the surface map is accurately registered against the CT uploaded image. This shows all of the points gathered as green, yellow or red dots to denote perfect, near or off registration compared with the CT scan.
If most are green it will accept and move on to a confirmation stage, as seen on this illustration. Six large blue spheres are projected on key areas of the bone. The blue probe is used again to ‘pop the bubbles’. This involves the probe being placed on the bone surface where the blue bubble is situated.
When close enough the bubble goes white and you can press the pedal. If it is within 1mm of the predicted position, the bubble will be accepted and turn white permanently. You can then move on to pop them all in turn. There are six for the femur then six for the tibia.

If the point is over 1mm away, the bubble will turn red and you will need to try again. You can see here that there is a distance to bone displayed on the screen.
You can use this to guide you as to whether it is close enough. On this one, the distance is now 0.3mmm so you can press the pedal and the bubble will now turn white.

Take an osteotome and remove the osteophytes. Check on the X-ray and the knee to ensure that they are removed back to the natural rim of the femur and the tibia.
When you do robotic knees you can see how important a step this is. It makes a big difference to ligament tension. You cannot remove posterior osteophytes at this stage but it is wise to look for them as they will effect gap balancing in the next phase.

The next phase is the joint balancing phase and this corresponds with the mako moving onto the joint balancing pages of the programme.
It begins with capturing range of the knee and the degree of varus/valgus deformity. Begin with the knee in full extension and capture any fixed flexion deformity or recurvatum.

The screen will illustrate the findings for you. For example, this screen would suggest an 18 degrees fixed flexion deformity which the mako will take into account for you. It also shows that the gaps are 12mm on the medial and the lateral side. The implants in total with a 9mm insert are 18mm – i.e. if you did this it predicts that the medial and lateral sides will be 6mm tight.
This was taken from another case to illustrate – this case had minimal fixed flexion deformity.

Perform the same measurements again in 90 degrees looking at mid flexion values

Again, the screen mirrors the angles around the knee. It needs to be between 85 and 95 degrees to read – when in the range you will see the limb flexion number turn green. There is quite a range of differences you will start to appreciate as the knee goes from extension to flexion. A reasonable number of knees go from varus towards a neutral position as flexion increases and some don’t change much at all.
This is all valuable information to obtain to maintain balanced ligaments through the range of motion.

The process is repeated with the knee in maximum flexion to capture the end pre-operative range of motion and the deformity in maximal flexion.
Don’t worry too much about the picture – it has a glitch where it can look like you have subluxed the knee as seen here, which is artefact.

We can see the effects on the screen live as we make these adjustments. This picture is a live and unstressed picutre for the knee.
In this case, the knee opened a few mm into valgus in extension with gentle pressure – this took the ‘true’ lateral reading in extension up to 19mm. It was also 1mm loose medially in flexion and extension. (see next picture for corrected positions)

We can see in this picture the gaps for this knee when it is opened up into the correct tension for the ligaments. This gives a balanced reading of 19mm in extension and 18mm in flexion.
The combined implant thickness on a standard poly bearing is 17.5mm – so we are aiming for symmetrical 18mm gaps. To get 18 all around on this case, we need to distalise the distal femoral cut by 1mm – this is done by the technician just moving the implant down 1mm on the screen.

In more complex cases, the balance will require adjustment of the tibial component, AP adjustment of the femoral component or rotational correction of the femoral component.
The principles are the same as with conventional techniques. Make sure that you are trying to recreate appropriate tension within an accpetable limb deformity – most would agree at least within 3 degrees varus to 3 degrees valgus and some accpet more.Once achieved, move on to the bone cutting phase.

The reigstration points are checked agian at this point to ensure accuracy of position and that no markers have moved. There is a divot in the saw blade which must also be registered at this point.

Position the knee in around 90 degrees and ask the mako technician to bring the rio cutting arm into place. There is a pedal to raise and lower the machine. The correct position will have the machine perpendicular to the operating table and about in line with the hip.It will need to be quite close to the table in order to reach the knee.
Check that the arm will be able to reach the knee and that it will come across a few cms medially. This helps when you are trying to cut the lateral tibial plateaus without damaging the patella tendon.

Begin with a perpendicular saw blade and the distal femoral cut. Once in position and ready to begin, the mako technician will free the arm and you will be able to move it.
Move to the rough alignment where you would begin distal femoral resection, around 10cm away from the bone. Squeeze the trigger and the saw will align to the correct plane.This is the mako in ‘alignment mode’.
Gently guide the saw in this alignment towards the bone. When you get about 4cm away from the bone, the saw power is activated and it goes into ‘cutting mode’.
As well as feeling and seeing this, it is visible on the screen as the cutting boundary outline and picture of the power tool will go from yellow to green. This indicates that the saw is active.

The robot needs to be able to see the arrays on the femur and on the rio so make sure that there is nothing in the way on the other side of the table.
I find this easier with the assistant on the operating side of the table and reaching over the arm (if you have a tall assistant) or under the arm (if you do not).

If you hit the boundaries, or the leg moves, sometimes it will reactivate by waiting a few seconds. If it doesn’t, bring the blade back to 15cm or so away from the bone and squeeze the trigger again. This will realign the saw blade and you can come back to bone and squeeze the trigger again to re-start cutting.
If you are struggling with the boundaries, the mako technician can expand them out a little bit. NB the boundaries only apply to the saw tip, not the whole blade.
The distal femoral cut and the posterior femoral chamfer cut are done in sequence with this blade. The remaining cuts are done with the straight rather than perpendicular blade. The mako technician will hep your scrub nurse to change this over.

Once the straight blade has been applied, the divot registration is repeated on the new position of the blade.

The anterior femur and anterior chamfer cuts are completed in exactly the same way.

The tibia is then resected. Take care of the patella tendon it is my practice to retract it further with a small spiked retractor.
It generally takes a number of passes to complete the cut. I begin with cutting right through the medial side, then pass through the central plateau, then take several passes to do the lateral side – initially one centrally, then one to the posterior aspect and finally one to finish the anterior tibial laterally.

Use Kochers or similar to pull the resected tibial plateau forward and begin to release the soft tissues which hold it in place. Start medially and take particular care around the insertion of the PCL.
You will see that there is a horseshoe of bone preserved anteriorly to it.This is a feature of the mako as it helps to prevent iatrogenic PCL injury. Continue laterally to release the tibial plateau.

The cut portion of tibial plateau can be turned over and used as a sizer with the tibial trials as seen here.

The femoral trial of a size calculated by the mako is mounted to its inserter and introduced to the femur.
Line it up with a slight bias towards the lateral side if there is room for manoeuvre medially to laterally.
Aim for it to go on in a few degrees of extension – i.e. keep the handle up high – femoral components tend to err towards flexion and this counteracts that tendency.

The correctly sized tibial trial with its trial bearing is then inserted into the joint.
At this point, I recommend a standard trialling to check how it feels before even looking at the computer screen. Think about how easily the tibial trial and bearing can be be inserted – is it a real struggle or is it really loose?.
If it is balanced well it should involve a firm push but not a battle to get it in. Bring the knee into extension and see if it feels balanced – there should be minimal movement on varus and valgus stressing.
Bring the knee to 90 degrees.
If the tibial tray is lifting off anteriorly, it may be too tight. If you can pull it out with just a finger and thumb pulling on the introducer handle, it may be loose.
There is nothing wrong with swapping the ‘standard’ 9mm insert for an 11mm and seeing if it feels too tight – if it does it just helps to confirm the sizing for you. Reduce the patella to feel the tension again as it may be a little less tight. Then assess patella tracking by moving the knee through a range and observing for any tilting or tightness, generally towards the lateral side.
Make sure you have the insert that feels best in place and then turn back to the screen.
Use the screen to confirm the range of motion – in most cases, aiming for 0 degrees – dead straight – through to over 130 degrees of flexion. This may be reduced in morbid obesity, pre-existing patella baha or cases where previous surgery has been performed.
Some surgeons will advocate acceptance of a few degrees of hyperextension in very mobile patients – I would not recommend going over 2 degrees of hyperextension. You can also confirm the overall varus/valgus alignment of the knee and measure if there is any laxity.

Once satisfied wth stability and range of motion, the rotational position of the tibial insert should be noted. Generally the centre point of the anterior tray lines up with a point just medial to the midline of the patella tendon. This can be marked with a diathermy mark if wished.
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.

Use two HEADED pins to firmly pin the tray down flat against the bone. Double check the position and that it is flush.Once satisfied, remove the handle and clip in the chimney guide for the fin punch.

The fin punch can then be inserted into the chimney guide, keeping the fin punch handle pointing upwards.

The fin punch is tapped down with a mallet until it hits its stopper. It is removed by pulling the fin punch handle up and anteriorly. The handle is then used as a lever to bring the punch back out of the bone.

The headed pins and tibial tray trial can now be removed. There are special pliers to remoce the pins but I find using a pair of bone nibblers a lot easier.

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.

THe handle has a ratchet mechanism to firmly grip the drill guid eonto the patella. Once satisfied with the position and security, drill the three peg holes with the patella drill.

At this stage, I remove the to bone reference points so that they are not forgotten. This is easiest to do with bone nibblers but can be done with their inserter if preferred.

Insert a posterior retractor and gently bring the tibia forward (This is a CR knee and I do not want to rip the PCL).
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. You can also check that there are not large meniscal remnants at the back of the knee which would be resected at this stage if encountered.

It is the surgeon’s resonsibility to check all of the implants before opening. They should be opened onto a clean surface, using clean gloves.

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. If the anaesthetis has done an I-pack and adductor canal/femoral block, this stage can be omitted.

Antibiotic impregnated medium viscocity cement is used in our institution (Palacos). 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.

Carefully extend the knee and push the distal femur forward from the popliteal fossa. This will bring the femur forward again from its dislocated position. Apply a thin layer of cement to the femur where the component is to go. Don’t do the posterior condylar cuts – cement here is just pushed backwards when the component is implanted.

The femoral component is better implanted on an introducer. The Stryker introducer is on a teal coloured handle with prongs which sit in corresponding dents on the side of the femoral component. Once mounted, the femoral component should be coated with a 2mm layer of cement.

Keep the implant aligned with the cuts and offer it up onto the bone. Use a mallet to impact onto the boner with firm blows, maintaining the alignment of the introducer handle with the femur. If anything, err to wards raising your hand higher – the component is more likely to try to drift into a flexed position.

Once properly seated, cement is cleared from all interfaces. Remove the introducer handle. There is a secondary impactor, if needed, which does not attach to the implant but can be used to deliver more blows to complete seating of the implant.
Again, if it is used, it should bias towards an extended position of the implant to prevent flexed positioning. Check the final position and remove any excess cement.

Straighten out the knee, slowly and carefully. This will pressurise the distal end of the femoral component against the tibial insert.
Apply a few mom of cement to the cut patella surface and the back of the patella button.

Align the pegs on the patella component with their holes on the patella and gently press the component into place. This is best done with fingers and thumbs, as shown.

Pressurisation is achieved with an instrument – the annular side fits over the patella button and the spiked side bites into the prepatellar fascia. A ratchet on the end of the handle will allow compression to be maintained.

Once pressurised and held for a minute, the clamp can be removed and excess cement removed with a Macdonald’s dissector.

After ten minutes, as long as the excess cement is set, you can move the knee. If a drain is to be used, it is inserted now.
This patient had a history of bleeding issues with her previous joint. A re-infusion drain was used for her. If a drain is used, it should exit superiority and laterally so it is easier for nursing. The intro-articular portion of the drain tube can be encouraged into the lateral gutter.

Dissolving sutures are used for closure of the deep layer. I use No. 1 vicryl.
Beginning in the angle of the approach above the patella allows for ‘shape matching’ of the extensor mechanism to the medial flap in the sigmoidal sweep of tissue from the medial. Border of the patella up into the suprapatellar portion. This reduces the risk of vertical mis-match of the soft tissues.
I use a few anchors of interrupted sutures in this area and oversew the whole length with a continuous No. 1 vicryl to oppose the deep layer.

Performing this step in 90 degrees of flexion reduces the chance of over tightening the repair. It is an opportunity to assess the tightness of the repair and to check that the patella is tracking well. If it is tracking laterally, a lateral release is possible at this stage.

The subcutaneous fat is closed with vicryl and the immediate subcutaneous layer closed over that with undies vicryl. Skin closure is with skin clips or subcuticular monofilament – here we use monocryl and add steri strips.

Don’t forget the distal wounds from the tibial tracker – these just require skin closure (monocryl and steri-strips or skin clips).

Post-operative, sterile and adhesive dressings are applied to the wounds. This should be done with the knee flexed so they are not too tight.
This should then be covered with a wrap of wool and crepe from mid tibia to md thigh level. The tourniquet can now be released.
Check for return of capillary fill to the foot. A member of the surgical team must help to remove drapes, remove the tourniquet and check that the thigh is not damaged below it.

An AP view shows the medial to lateral sizing and allows checks that the implants are sited onto the cuts correctly and that there are no fractures.

A lateral view demonstrates the AP sizing/anterior and posterior offset recreation, patella restoration and slope of the tibia and the flexion of the femoral component.
This X-ray is the morning after the surgery – the patella is floating off the femur – this is normal at this stage due to swelling.