Revision total Knee Replacement- Legion Rotating Hinge Knee ( Smith and Nephew)

Lateral radiograph shows a well fixed Nex Gen TKR

Skyline Radiograph shows reasonable congruence in the PFJ, but with slight lateral tilt and tracking

The CT scan shows reasonable rotational alignment, but with slight internal rotation form ideal. Whilst this is not a reason to revise, it is useful information for planning the revision.
In general mal-rotation over 5 degrees of each component relative to defined anatomic axes in the axial plane is usually associated with another problem, such laxity, mal-tracking or stiffness. Thus it is important to appreciate the mal-rotation in order to solve the presenting prblem.
In addition whilst each component can be mal-rotated, there is often a more signifiant problem if there is an overall construct mal-alignment between femoral and tibial components. For example if the femoral component is internally rotated (relative to the Trans Epicondylar Axis) and the tibial component is externally rotated relative to the tibial posterior consular axis then there is a likely to be a significant rotational mismatch between the femur and the tibia which may present as extensor mal-tracking, pain or laxity. A combined construct mal-rotation of over 5 degrees is likely to be significant.

Carefully set-up with the heels over the end of the bed and the leg carefully relieved from pressure with gel pads. Side support and foot roll and a contra-lateral foot pump. Here I have used a forced air warmer, but extreme caution should be used in the application of this. I apply this myself during set-up with the sticky tape adherent to the patient’s skin and then covered with a blanket to prevent any sticky drapes touching the hot air blanket and then making holes allowing air escape and turbulence in the laminar flow zone.
The bed must be positioned ‘high’ in the theatre with the head on the edge of the laminar zone so that a screen can be raised outside the laminar zone on the anaesthetic side.

Careful positioning of the operating table allows all the trays to be within the laminar flow. Remember the worst place for your trays is in the turbulent area on the boundary of the laminar flow zone!
Overhead operative lights have been used for this case for photography but I would not normally use these. Caution as to the position of the lights, allowing a clear down-draught from the laminar flow above the knee should be achieved before starting the case. Ideally the lights (even ‘sterile handles’) should not be touched during the case.

The planned incision (usually the most recent) is then excised and the surgeon’s chosen approach made to the knee. This should be the standard approach used by the surgeon, for most this will be medial parapatella, but for some surgeons a medial subvastus will be the preferred approach for primary TKR.
I have used the subvastus in revision TKR for over 10 years now without regret. However it is important to know how to extend your chosen approach to relieve tension to reduce the risk of extensor rupture and to provide better access.

The next stage will be the start of sampling with a fluid sample through the capsule not through skin, but in order to keep clarity of writing, I will deal with all sampling now. We follow the Oxford sampling advice (Atkins BL, Athanasou N, Deeks JJ, Crook DW, Simpson H, Peto TE, McLardy-Smith P, Berendt AR. J Clin Microbiol. 1998 Oct;36(10):2932-9.) and perform sampling under the polyethylene, deep and superficial samples from tibia and femur, plus or minus the patella depending on patella management at the primary and the cause for revision; a well fixed patella component should not be removed unless a diagnosis of infection is very likely or known.
The fluid should be tested in the Operating Room/Theatre for the presence of white blood cells on leukocyte esterase strips (‘urinalysis dip sticks’), with 2+ or 3+ being consistent with a very high chance of infection. Alpha Defensin testing of synovial fluid is another useful test to diagnose infection.
In addition a good section of synovium should be sent for histology.

The surgeon’s chosen approach should be performed. As explained above I use the medial subvastus approach, maintaining the Vastus Medialis with the patella and subluxing the patella into the lateral gutter as the knee is flexed.
A formal synovectomy from all around the knee should be performed. This really helps with access, and is vital for the management of infection; unfortunately some diagnoses of infection are only made after the revision specimens are returned, so it is important to perform a thorough debridment in all cases. This synovectomy will recreate the medial and lateral gutters and supra-patella pouch.
Implant interfaces should be carefully exposed such that the correct interface can then be addressed during extraction.

Usually the first step of the extraction phase is removal of polyethylene. Knowledge of the implant being removed is essential as this may require fixation clips to be removed first or particular ‘tricks’ as to the angle of insertion of the operators favourite removal tool. Remember some implants are non-modular monobloc constructions of moulded polyethylene on a metal baseplate giving the impression of modularity on the X-Ray but behaving as an all polyethylene construction on the tibia; these need to be removed in one from the tibial bone-implant interface. Another important ‘must remember’ point is to check that the poly already inserted does not have a stabilising post or locking mechanism down into the tibial metal baseplate.
My favourite extraction tool is the Bristow as it has a sufficiently sharp tip to enter the polyethylene, yet is robust enough to lever on the metal tibial baseplate to lever up the polyethylene.
In this image the Bristow is being inserted between the poly and the tibial baseplate.

After removal of the polyethylene a sample is taken from the ‘hidden’ surface of the tibial component with Oxford sampling technique (5 blade handles and 5 forceps to yield 5 samples) to minimise cross-contamination of samples.

The bone-component interfaces are then cleared with sharp dissection.
There are various ways to remove an implant – narrow saw blades, plaster saw, osteotomes or Gigli saw. My preferred method is the double impaction technique where a shock-wave is created by simultaneous osteotome strikes from different directions at the implant-cement interface – most commonly medial and lateral at the same time; the best practical advice on this is to insert the osteotome on the medial (assistant’s) side and ask the assistant to strike this osteotome with a regular timing. The surgeon the inserts and osteotome (1) from the lateral side and simply strikes ‘on the beat’ with the assistant’s rhythm!
In uncemented implants the double impaction technique is less rewarding and I personally use a combination of saw and osteotomes.
After the component has debonded it can be removed easily by hand, but in cases where more force is required, extraction sets may be used, for example the Smith and Nephew Renovation set which has a very good slap clasping device which attached to a slap hammer.

The femoral component has been removed and attention turned to the tibia where an osteotome is inserted under the tibial component, above the cement mantle. The alternative technique of fine saw on the cement interface is demonstrated below.

Note the swabs protecting the soft tissues. As the saw generates cement debris this is simply collected on the swabs which are exchanged as the tibial component is removed.

After removal of the tibial component it is important to take out any cement plug within the tibial canal. This can easily be reached with standard osteotomes and then simply pulled out with a clamp such as a Kocher.

Once the components have been removed. Specimens are taken (superficial and deep tibia and femur) then pulsed lavage should be performed. I prefer to use aqueous chlorhexidine for the pulsed lavage irrigation solution. This can be seen as the frothy fluid in the centre of the tibia. Remember that if cell salvage is being used the chlorhexidine must not be scavenged; instead a separate suction should be used and then the joint washed with normal saline before resuming cell salvage.
The extraction, sampling and cleaning is complete and we are now ready for reconstruction.

The tibia canal is reamed with sequential reamers from the Legion set. I prefer to perform this by hand rather than on power, although the reamers can attach to a power driver.
The reamers go up in 1mm increments from 9 to 16 and then 2mm increments from 16 to 24.
There are various stem lengths: 90, 120, 160 and 220mm. In order to unify the system (using the same stems for the tibia and femur) there is a key measurement difference between the tibial and femoral preparation. The tibial preparation assumes that an offset will be used and the measurement of the construct length comes for the cut bone surface.
This is in contrast to the femoral preparation which assumes that there is no offset used and the measurement of stem length is from the joint line – ie the most distal part of the femoral component.
For most medium sized patients the most common stem length is 120mm, with width being determined by achieving some chatter with the cortex. On the femoral side 160mm is the most common length.

The tibial cutting block is then applied either directly to the reamer or to a trial stem with and additional stem extension.
There is a 1mm stylus allowing a minimal “freshen up” cut. The cutting block is a zero slope block so there is no need to pin this in situ and the block can be secured with screwdriver tightening alone, although pin holes exist should the surgeon prefer (as in the next image). The advantage of avoiding pinning means the block can be rotated around the reamer or stem extender allowing easier access for the proximal saw cut of the tibia.
Pins can be used to secure the tibial block. The pin holes can be pre-drilled depending on surgeon preference.
Appropriate care should be taken with the saw during proximal tibial cut, particularly with the Patella Tendon, Medial Collateral Ligament and of course caution and protection posteriorly for the neurovascular bundle

The proximal tibia is sized and an estimate made of the difference between the centre of the cut-out in the sizing template and the stem extender. This is the difference between the centre of the metaphysics and the centre of the diaphysis. This difference gives rise to the concept of ‘offset’. There is considerable anatomic variation in metaphysical – diaphyseal offset with the mean offset being 4mm, but a selection of offset couplers is available on the Legion system of 2, 4 and 6mm.
A 4mm offset was most appropriate in this case to match the black tibial sizing template with the stem extender on the trial stem in the diaphysis of the tibia. The offset coupler is rotated until the best fit coverage and rotation of the tibial component is achieved.
We usually record this as a 4mm offset at 3 o’clock, describing the number on the tibial sizing template that the 4mm offset coupler’s arrow points.
The tibial baseplate template is then pinned in position. There are four holes available in the template, but beware situations when there is a defect medially or laterally as the template will not sit down on the bone over such a defect; the medial or lateral augments are cut in at a later date. Consequently the pins should be inserted into good bone stock first.

The stem extender and offset coupler have been removed and the central hole in the templates been filled with the centralising collet for the tibial reamer to allow the tibial boss to offset in the same position as the template.
Remember one of the differences between the CCK and RHK systems is the longer tibial boss which accommodates the hinge locking mechanism within the tibial component; this needs to be remembered to prevent an under-reaming of the tibia, risking fracture during implantation.

The tibial counterbore reamer demonstrating the positive stopper set on ‘femur’, despite preparing to ream the tibia.
The counterbore reamer is used twice. One reaming is over the stem extender or original hand reamer to widen a sufficient margin to accommodate the offset coupler. The 2nd counterbore reamer use is to accommodate the tibial boss as in this photo. Remember for the RHK the reaming depth is deeper than for the CCK.

The tibial counterbore reamer is then inserted, down to the positive stopper set on ‘femur’, rather than ‘tibia’, despite reaming the tibia. This is explained in the slide below.

A size 3 left Legion trial baseplate. This conforms to the basic the CCK design, which is very similar, but there are some differences as described below. The idea is that a Legion RHK may be performed as a stand alone hinge or can be added as needed during a Legion CCK revision if there is intra-operative concern over the integrity of the medial collateral or medial condyle itself supporting the MCL.

Size 3 left tibial CCK baseplate (1, at the top of the picture) being compared to the size 3 Legion RHK (2, on the bottom). A MacDonald retractor has been placed across the base of the Legion CCK to the RHK to demonstrate the increased amount of the tibial boss. It is for this reason that the tibial counterbore needs to be performed to the ‘femoral’ marking on the counterbore for the Legion RHK. This is one of the differences between the systems which needs to be remembered to prevent an under-reaming of the tibia, which would risk fracture during implantation.

The tibial trial is then prepared with the appropriate sized tibial baseplate, offset and stem. Note that the stem and the offset attach via a spring-loaded bayonet-type fixation. This is important as the trial may be very slightly longer than the length of the prepared bone by the spring loading distance. The next slide shows how to address this.
If the tibial baseplate ‘sits up’ on the cut tibial bone, the stem needs to be inserted slightly deeper to accommodate the spring-loading of the trial. This may be achieved by a gentle tap of the Legion Set Hex Screw-Driver located in the grub screw situated in the offset coupler, accessed through the centre of the tibial trial plate
By attaching drop rods (ideally 2) then the alignment of the tibial component can be checked in the sagittal, coronal and axial planes, before this is confirmed by preparing the tibial keel or any augments that may be needed. Should an augment be needed then this is cut using a block attached to the quick connect handle attached to the front of the trial. This was not needed in this case.

Attention is then turned to the femur and in a similar manner to the tibial preparation, the intra-medullary canal is reamed until good interference fit is felt. As in the tibia I prefer to use hand reaming. Care should be made when introducing the reamers, by comparing the diaphyseal alignment and position relative to the metaphysis on the long-leg radiograph displayed in theatre.

If the last reamer used is smaller than 18mm then it is necessary to ream twice with the counterbore as described for the tibia. This can be performed over the final reamer or the stem trial with stem extender.

The distal femoral cutting block is attached to the reamer or a trial stem and stem extender as an alternative.
I prefer to work out joint line position using the Romero method of multiplying the trans-eipcondylar width by 0.4. This gives the distance form the medial epicondylar prominence to the joint line. By subtracting the 10mm (the thickness of the femoral component) this gives the distance where the distal femur should be cut – of course if there is bone loss then this will need building up, but this is a useful tip to help determine a good joint line position.
The trans-epicondylar width is measured simply by a ruler.
Be sure to check that the 6 degrees valgus central bushing is inserted with the ‘lateral’ marking on the lateral side!

Here the angel wing is placed through the 15mm cutting slot on the distal femoral cutting guide. A very useful trick is to use the Romero joint line calculation mentioned earlier and to work out the distance from the medial epicondylar prominence to the joint line and the back of the femoral component…..this allows an estimate of appropriate augment use before the cuts are made. With the angel wing through the 15mm slot, the angel wing tip can be placed at the medial epicondyle. This would equate to the distal cut being 15mm from the medial epicondyle and thus the joint line 25mm form the medial epicondyle.
However if the trans-epicondylar width is 80mm in a large patient then the distance from the joint line to the medial epicondyle will be 0.4 x 80mm = 32mm. As the implant is 10mm then the distal most bone should be 22mm from the medial epicondyle; thus the block should be distalised by another 7mm (32-25mm). Conversely, in a small patient with a width of 62mm the the joint line should be (0.4 x 62mm) 24.8mm from the medial epicondyle and so the ’15mm angel wing slot trick’ will place the distal cutting block slot at the correct position to create a 25mm distance from Medial epicondyle to joint line.
Remember though that this technique is far from perfect as it is highly dependent from where on the epicondyle the measurement is taken.

Here the angel wing is placed through the 15mm cutting slot on the distal femoral cutting guide.

The block is pinned (drilled and pinned ideally) and then the distal resection is made, sometimes allowing for a distal femoral augment and cutting through the relevant slot (5,10 or 15mm). In this case a 15mm lateral block augment is being prepared which will correct for the valgus of the original component, as well as the bone loss from the primary being removed. A 5mm medial augment cuts was made after the 15mm laterally.

Next the extension space gap is checked. Here the 9mm black gap measurer has an additional 5mm augment medially on the femur (yellow) and 15mm laterally on the femur (green) with an additional 2mm on the tibial side (purple) which would be reconstructed with the 11mm polyethylene, the smallest for the RHK. In this case the gap was larger because of 10mm tibial bone loss after extraction and cuts, and this was replaced with a 21mm polyethylene.
Full extension is achieved with the 21mm spacer block and there was good lateral collateral stability but still medial laxity as expected. The block allows for drop rods to measure alignment too.

With the femoral trial stem inserted on a stem extender, an appropriate size femoral sizer is then used to assess how much offset is required anteroposterior and how much augment will be needed posteriorly (5 or 10mm are available).
In general posterior offset is the normal finding and we describe a pure 4mm posterior offset as “4mm at 6 o’clock”, but if there was a need to offset medially as well then a 6mm offset could be taken but positioned at “7.30” to allow some of the 6mm to offset posteriorly and some of the offset to correct the femoral metaphyseal-diaphyseal mismatch in the medial lateral direction. If the stem lines up with the 0mm then no offset is required on the femur. However this is very unusual and most cases require a 4 or 6mm offset in the posterior direction somewhere between 4 and 8 0’clock.
With the femoral block in position, an angel wing is used to check there is sufficient bone posteriorly. This is an open cutting block, with two slots at 5 and 10mm posteriorly. The purple 15mm distal lateral augment is visible and it is important to remember these augments on the cutting block to prevent elevating the joint line inadvertently during this step.

After checking with the angel wing in last slide, the offset is fine tuned to 5 o’clock, moving the block slightly lateral and anterior from the 6 o’clock position, to achieve best bony contact and a flush anterior cut with the anterior cortex.
The block is pinned in place and the cuts made.
Note that 10mm posterior cuts are required for the Legion RHK to accommodate the hinge mechanism in the femoral component. This is one of the steps which may need adding in during a conversion from a CCK to an RHK.

The stem extender and offset are removed and a bushing placed in the cutting block. The large femoral counter bore is then used similar to on the tibia, reaming 18mm out for the femoral boss and offset.

The femoral component is introduced into the femur and with the surgeon controlling the component rotation to match up with the cuts, an assistant surgeon impacts the implant trial down to the cut femoral surfaces.

With the femoral trial in position, the box cutting guide is inserted.
The femoral box is then prepared by reaming in the anterior and posterior position that the guide will allow by sliding anterograde-posteriorly.
The final preparation of the box is with a specific Legion RHK box chisel in both the anterior and posterior position of the box guide. The box cutting guide is then moved posteriorly and the chisel repeated. Remember the central notch removal is wider on the RHK than on the CCK.

To link the femoral and tibial components, an orange (left) or black (for right knees) articular insert is placed onto the tibial component and then a linkage device placed centrally within the orange insert. This is secured with a 4.75mm Hex screw driver.
A split pin is then inserted, to mimic the axle, in the posterior part of the femoral component usually from medially to avoid the extensor mechanism.
At this stage a patella resurfacing or revision would be performed, but in this case the patella button was well fixed with an appropriate width-thickness ratio and consequently no patella revision was performed.

A trial range of movement showed flexion of 130 degrees to full extension with good patella tracking.

The tibial component boxes are checked and the tibial modular components opened.
It is sensible to open these and assemble the tibial component before opening the femoral components to eliminate a potential source of error in combining the modular components incorrectly, eg tibial offset with the femoral component.

Then the femoral components are checked, opened and assembled.

The articular insert and locking mechanism are checked, but not opened at this stage.

The tibial component is assembled from its three sections – baseplate, offset and stem. Remember to check the real implant with the trial before impacting the stems and locking with grub screws.

The Legion RHK tibial implant comes with a locking screw inserted posteriorly. This is to prevent cement ingress into the locking mechanism during implantation.

The tibial stem and offset are impacted onto the baseplate. The packing around the implant is excellent cover for the implant stem during impaction.

A similar approach is taken to assembling the femoral component – remember to to check the trial before impacting the stems on the definitive implant and then locking home with grub screws.

This picture shows the definitive implants immediately prior to implantation.

Palacos regular cement with Gentamicin is used.
A hybrid cementation technique is my standard, but in this case due to poor bone stock I opted for total stem cementation. I use Palacos regular cement with Gentamicin for standard cases and in general I prefer 2 mixes for the tibia and then an additional 2 for the femur (mixed as the first Palacos gun is handed to me) to ensure plenty cement is available and this buys a little longer working time. This is gunned into the cut tibial surface, but with care not to cement the stem. The back surface of the tibial component and offset are coated with cement, prior to implantation.
The tibial component is impacted and then excess cement is removed.

Remember that this 3.5mm screw will be removed and exchanged during locking of the articular insert later on. Notice the oblique orientation of this locking screw.

A similar technique is then used for femoral implantation, with a fresh mix of cement (mixed as I take the ‘tibial’ cement) gunned onto the distal femur and the implant.
Cementation on the femoral implant and offset region – effectively zones 1 (cut surface of the femur or tibia in a primary TKR) and 2 (metaphysis) is my standard practice, but in elderly patients with poor bone stock I use fully cemented stems as in this case.
Zonal fixation in revision total knee arthroplasty. Morgan-Jones R, Oussedik SI, Graichen H, Haddad FS.
Bone Joint J. 2015 Feb;97-B(2):147-9. doi: 10.1302/0301-620X.97B2.34144. PMID: 25628273

Notice the 10mm thicker posterior condyles of the Legion RHK to accommodate the axle.

Carefully directed and measured impaction of the femoral component during insertion.

The trial polyethylene is inserted and the leg extended to compress the cement interfaces.
At this stage the patella would be implanted as in a primary TKR (if either a revision or primary patella resurfacing was required).
The extensor mechanism has been replaced.
Once the cement has cured range of movement is checked before opening the final polyethylene.

The 3.5mm tibial locking screw is removed once the cement has cured.

A 21mmm articulating insert is placed onto the tibial component and then the new oblique posterior screw inserted with the 3.5 mm screwdriver, thus locking the articulating insert onto the tibial component.

The correct sized sleeve is shown prior to introducing the femoral link into the tibia, the sleeve then locking the construct.

The sleeve has been placed into the tibial articulating insert, without engaging the femoral link for demonstration purposes. Note the anterior chamfer on the sleeve which helps with correctly orienting the sleeve through the linkage device later on. There is a location tab on the sleeve which aids correct positioning.

The 4.75mm screw driver is then used to start the bolt centrally down the sleeve securing the femoral link within the tibial component. This is completed by torque-limiter as below.

The femoral link has now been inserted into the tibia and the sleeve docked down the centre with a hand tightening of the 4.5mm screw. Here the tibial baseplate is being held and the torque-limited device is locking home the hinge mechanism to the correct torque.

Copious aqueous chlorhexidine lavage and then standard closure should be performed.
The medial subvastus approach is repaired – I favour a heavy barbed suture such as 2 Quille or 1 Stratafix, starting at the apex in the centre of the incision (superomedially to the patella) and suturing both proximally and distally.
After the capsular layer is closed, I use interrupted 0-Vicryl in the deep dermal layer, with the knee in flexion.

Interrupted sutures have been placed so I then use running 2-0 deep dermal and a 2-0 or 3-0 barbed subcuticular suture such as Quille or Stratafix, again starting centrally and running distally and proximally. Again I like to suture the knee in flexion.

Skin glue and obliquely placed suture strips – ideally original Steristrips are then used.

A clear occlusive padded dressing such as LeukoMed, Tegaderm Pad, Opsite Postop, Hydrofilm plus etc. is applied in flexion.

Wool and Crepe bandaging.

AP postoperative radiograph – Femur
Fully cemented components with satisfactory alignment (as best as can be appreciated on the short films) and no fractures.

AP postoperative radiograph tibia
Fully cemented components with satisfactory alignment (as best as can be appreciated on the short films) and no fractures.

Lateral postoperative radiograph – femur
Notice the femoral component is flush with the anterior cortex of the femur and the patella sits overlying the femoral component.

Lateral postoperative radiograph tibia