Revision total Knee replacement- Second-stage with distal femoral EPR (Implantcast MUTARS MK) and EPORE collar and tibial cone

‘AP’ radiograph prior to first-stage of an infected and grossly loose hinged revision knee prosthesis with gross metaphyseal femoral bone loss, tibial lysis and impending peri-prosthetic fracture. Amazingly he was able to walk with two elbow crutches.

AP radiograph of a static reinforced distal femoral spacer showing the medullary Küntscher nails which are overlapping at the site of the excised distal femur wrapped in antibiotic loaded cement with skin clips from the previous closure and evidence of a (S) super-cable clip closing the proximal extended tibial osteotomy used for explant at the first-stage. The patient also has a splint on shown on his radiograph.

‘Lateral’ view of the same, also showing stimulan beads inside the joint cavity for further antibiotic delivery after the first stage procedure.

Coronal CT showing deficient metaphyseal bone remaining (L) laterally (nil medially) and that the previous (ETO) extended tibial osteotomy has united.

Sagittal CT highlights that there is a rim of bone (P) posteriorly but nil anteriorly and that the (ETO) extended tubercle osteotomy has united.

Axial CT at the level of the (F) fibula tip showing an uncontained metaphyseal defect in the proximal tibia (AM) anteromedially.

The patient is positioned supine and the limb is isolated using exclusion drapes proximallyA tourniquet is applied around the the proximal thigh (not shown).

After 70% alcoholic chlorhexidine skin preparation and repeated draping, Ioban incisional drapes are applied to the knee and distal thigh, down to the mid-tibiaA bowel bag is placed over the foot for assessment of vascular supply during the operation.

Midline skin incision using the old incisionBegin the skin incision over the marked previous incision on the mid-line of the knee. Some surgeons excise skin incisions, but unless the skin is very poor I wouldn’t excise to avoid undue tension on the wound when healing.

Identify the patella which helps to identify the deep capsular layer using McIndoe’s dissecting scissorsAfter completing the skin incision, develop full thickness skin-flaps which are elevated off the joint capsule medially and laterally to expose sufficient space for the medial para-patellar arthrotomy. I begin this over the patella as this provides guidance as to the depth of the capsular layer and is obviously difficult to inadvertently penetrate with dissecting scissors. Full thickness skin flaps are believed to minimise the risk of wound necrosis and therefore optimise wound healing.

Aspirate the joint cavity for microbiological analysisAfter elevating the full thickness skin-flaps, a needle and syringe are used to aspirate the joint for sampling of the synovial fluid around the antibiotic loaded cement spacer, which is transferred into aerobic and anaerobic culture bottles for microbiological analysis.
These (two) bottles represent one of the five representative microbiological samples that are submitted in all cases at first and second stage. Choosing an odd number of samples is more helpful for the MDT to make decisions, two or more or the same organism is confirmatory of ongoing PJI. Thankfully all cultures were negative after 14 days in this case at second stage.

Identify and mark the medial border of the patella for the arthrotomyUsing the needle of the syringe as a probe, identify where the patella is lying and mark the medial para-patellar arthrotomy using a marker pen, which helps with closure at the end of the procedure.
Often in multiply revised knees identifying the border of the patella and patella tendon can be challenging and using the needle to identify the medial border of the patella is convenient and simple.

Retract the rectus tendon laterally to avoid crossing the tendon with the arthrotomyProximally, using the McIndoe’s dissecting scissors, I identify the (RF) rectus femoris tendon which is retracted laterally so that the proximal extent of the arthrotomy does not divide or cross the rectus tendon, so that the rectus remains in continuity with the superior pole of the patella, to prevent extensor lag.
When the rectus tendon is retracted laterally the arthrotomy incision passes through the medial portion of the quadriceps tendon and then splits in the mid-line the vastus intermedius muscle, which has proximal innervation and vascular supply and will heal satisfactorily when closed.

Medial parapatellar arthrotomyUsing a scalpel, begin the arthrotomy along the marked line of the para-patellar arthrotomy from distal to proximal.

Having made the incision for the arthrotomy extend it proximally and distally using cautery.

Extend the incision through the vastus intermedius proximally to gain access to the spacer.

Finish the arthrotomy distally ensuring that it comes down onto the tibial bone, elevating full thickness flaps of capsule off the medial proximal tibial metaphysis using the subperiosteal plane around the tibia medially.

Having completed the arthrotomy the antibiotic loaded cement spacer is seen within the joint cavity prior to explantation.

Remove the cement surrounding the reinforcing Küntscher nails using osteotomesUsing osteotomes, the cement surrounding the Küntscher nails is chipped away to reveal the nails beneath.
Use eye protection as the fragments can fly!

Sometimes with longer segmental spacers it is useful to put rolled drapes beneath the posterior distal femur for support when impacting the cement to prevent hyperextension and damage to the posterior neurovascular structures.
Always hit the osteomtome onto metal to avoid puncturing the posterior soft-tissues for the same reason.

Having removed all the cement around the Küntscher nails they are now separated using Kocher’s forceps and ready to be removed from the residual tibia and femur.

Using the end of the Küntscher nails with a joystick, the nail from the femur is removed.

Again, the tibial nail is removed using the tip of the nail as a joystick. The ‘knee’ will now flex to permit access to the tibia and femur.

Perform a radical debridement and synovectomy of the effected joint space.Using (L) Lane’s soft tissue holding forceps and grasping the lining of the joint space cavity with (K) Kocher’s forceps, identify the layer of the lining of the joint space for debridement.

I prefer to use McIndoe’s dissecting forceps to identify the correct plane for dissection, on the side of the joint cavity opposite to where I am standing.

Having identified the correct plane this can be developed rapidly using cautery, removing the layer of tissue that has been exposed to the spacer and to the previous infection, debriding back to healthy bleeding tissue as shown.

Continue the debridement of the medial side of the joint, down into the medial gutter. On the medial side there are no particular structures at risk.
Posteriorly the capsule overlies the neurovascular structures of the popliteal fossa which from medial to lateral are the popliteal artery, vein, tibial nerve and peroneal nerve.

Dissection continues proximally under the vastus medialis.

All of the medial side of the debridement has now been done. The tissues have been debrided right back to the proximal extent of the wound around the residual femoral bone.

The posterior capsule is then debrided in which ever direction is convenient and comfortable, in this case from distal to proximal.
Elevate the layer of debrided tissue out of the wound to maintain soft tissue tension, as one carefully debrides the back of the knee and popliteal fossa.

The residual tissue is collected on the back table after four representative tissue samples have been sent for culture. We routinely send five samples for microbiology, including four tissue and one fluid in both aerobic and anaerobic bottles, totalling five microbiological samples. We know that positive culture at second stage is a negative prognostic fact for recurrent prosthetic joint infection according to Theil et al.
Theil C, et al.
Do Positive Cultures at Second Stage Re-Implantation Increase the Risk for Reinfection in Two-Stage Exchange for Periprosthetic Joint Infection? The Journal of Arthroplasty 2020;35(10):2996-3001.https://doi.org/10.1016/j.arth.2020.05.029).

Begin the debridement of the proximal tibia, debriding the tissues from the bone in the metaphysis using curettes, nibblers and grabbers.Now flexing the knee, we can see the (P) patella and the debrided joint cavity and the outline of the proximal (T) tibial metaphysis which looks deficient as the radiographs and CT suggested. We begin debriding the tissues from the bone in the metaphysis using curettes, nibblers and grabbers.

Further the debridement of the tibial medullary canal using a Cobb to debride the layer of granulation tissue from the metaphysis to reveal bleeding endosteum.
Back-scratchers can be used more distally to cleanse the canal of debris and finally nylon brushes can be used to complete the canal debridement before reaming.

Using curettes, back-scratchers and brushes begin the process of debriding the proximal femoral canal.Grasp the residual distal femur using the (H) Heygroves bone holding forceps to elevate the femur our of the wound.

Having completed the debridement, the tibial and femoral canals are thoroughly washed using pulse lavage

At this point the tourniquet is deflated and haemostasis is achieved, checking that there are no perforations of the femoral and popliteal vessels caused inadvertently by the radical debridement of the posterior joint space.
If there are any concerns then a 5.0 prolene can be used to repair any holes in vessels. Cautery is used to control the bleeding from the debrided tissues, any areas not bleeding usually require further debridement.

Insert and tighten the definitive bolt which secures the distal femur to the shaft and to the cemented stem and collar.

AP radiograph after two months post-operatively, walking with single elbow crutch pain free. Satisfactory reconstruction, early signs of ongrowth to EPORE collar medially.

Lateral view after two months. Again early radiographic signs of ingrowth to the EPORE collar posteriorly noted, but satisfactory appearances of the prosthesis.

Using powered rigid drills, ream out the proximal tibia using the 150mm drill until isthmic fit is achieved.Leave the last and largest diameter drill in situ. The drills range from 11mm to 27mm in uneven numbers; cementless stems are available from 12mm to 28mm, cemented stems range from 11mm to 19mm. For this case we will use uncemented stems, so a stem diameter 1mm greater (an even number) than the last drill is selected for press fit. Stem lengths range from 125mm, 150mm, 200mm to 250mm in both cemented and cementless versions.

Having achieved stability with the canal reamer at the isthmus of the tibial diaphysis, the knee is flexed, and medullary alignment of the proximal tibia resection can begin.

The tibial intra-medullary alignment jig is fixed to the last drill left in the tibial canal. This jig can move up and down and forwards and backwards and rotate. It is aligned using the alignment rod shown outside of the bone with the centre of the ankle joint (I personally mark the EHL at the level of the tibial plafond pre-operatively when the patient moves their toe and take this as the centre of the ankle joint for rotational alignment).
The 0 degree cutting block is pinned using the threaded screw pins on either side to the residual tibia and the level of resections checked using the angel wing supplied on the set. Alternatively there is a 2mm stylus that attaches to the block for gauging resection level.

Having confirmed the level of resection make the “freshen-up” cut using a 1.27 mm oscillating saw.In this case the cut is few millimetres only to achieve a flat metaphysis to rest the tibial tray, and only the lateral and posterior bone is cut due to the severe anteromedial deficiency.
As there is insufficient bone to pin the cutting block, Kocher’s forceps are used to help steady the block when using the oscillating saw.

Leaving the drill in the medullary canal, a tibial sizing (T) tray is placed over the drill and centralised on the reamer using the (OAT) Offset Alignment Tool If the coverage of the tibia is suboptimal, then there are three offset centralisers (2/4/6mm offsets) which can rotate 360 degrees so that you can position the prosthesis in the optimal position for coverage of the residual tibia.
Rotate the offset alignment tool until you are happy and pin the tibial tray in situ before preparing the tibia using a proximal tibial reamer and fin punch (neither were required in this case as there was no bone left to ream nor fin punch). Tibial preparation is now complete and trialling can (normally) begin.

Prepare the tibial metaphysis for a cone.
Viewed from the side it can be seen that the (OAT) offset alignment tool can be rotated to position the tibial tray for optimal coverage.
The three holes at the front of the tibial tray accept a tibial alignment handle which combines with an alignment rod for checking rotational alignment before pinning and preparing the tibia.

Prepare the EPORE tibial cone broaches
Attach the cone impactor to the tibial cone broach prior to impacting into the tibia. There is an updated tibia cone impactor design for the EPORE tibial cones. There are four widths of cone/broach available (sized 2-5, corresponding with the tibial tray sizes of the MUTARS Distal Femoral MK) available in 20mm or 30mm depths with left and right asymmetrical stepped versions for each size and depth also.

Using the tibial cone broaches, impact until stability is achieved in the metaphysis.Check stability by checking resistance to movement antero-posteriorly and medio-laterally using the broach impactor.

This photograph highlights that the medial side of the proximal tibia is deficient, but we have bone laterally and posteriorly to achieve a stable cone. There are various classifications for categorising tibial bone loss, I prefer the AORI classification (Engh GA, Ammeen DJ. Bone loss with revision total knee arthroplasty: defect classification and alternatives for reconstruction. Instructional Course Lectures. 1999 ;48:167-175), as is simple and logical. This would be a T3 using Engh’s classification as there is an uncontained defect requiring a cone and long-stem fixation: http://eknygos.lsmuni.lt/springer/238/116-132.pdf.
Tibial porous cones are typically indicated in AORI 2B and 3 defect and all papers (that i can find) show good clinical and radiological outcomes with low rate of complications.

Prepare the trial tibial prosthesis by connecting the trial tibial tray to the trial offset adaptorUse the hex screwdriver on the set to loosely tighten the bolt connecting the two components (accessed from above, not visible).

Ensure the correct rotation of the offset adaptor using the tibial offset alignment block e.g. 4mm offset at 5 o’clock, which should correlate with the offset rotation predetermined when the offset alignment tool during tibial preparation.
Tighten the bolt connecting the two components to maintain this position.

Attach a trial stem that matches the length and diameter of the last drill used when reaming the tibial diaphysis to the offset adaptor and trial the tibial prosthesisHand screw and tighten before inserting the assembled trial tibial prosthesis through the trial tibial cone broach that has been left in the tibia.

The trial tibia almost sits flush on the cone broach but has a half cm gap which is sometimes due to the flanges of the trial prosthesis fouling on the cone internally.
The tibial trial is assessed for a rotation and to plan the optimal rotation of the prosthesis relative to the tibia and ankle joint, and mark the bone or soft-tissues with a marker pen or cautery to recreate this rotation when inserting the definitive tibial prosthesis.

Prepare and then insert the definitive EPORE tibial coneIf required there are ‘U’ shaped cutouts that can be removed from the tibial cone to prevent the flanges of the tibial tray from fouling the cone, which is usually the reason for the trial tibia not sitting onto of the cone. This allows 25 degrees of rotational variation, something to be borne in mind when impacting the trial and definitive cone.

Carefully insert the definitive tibial cone into the tibial metaphysis by hand and then impact to the desired level using the same tibial cone impactor.

I prefer to use the trial tibial prosthesis to finish the cone impaction to confirm that the correct rotation of the definitive tibial prosthesis can be achieved without fouling on the cone. The impactors for the trial tibial allow you to twist the tibial tray when impacting to control rotation which is a useful feature often lacking on other systems.

Use sequential rasps which are impacted into the femur until stability is achieved axially and rotationally, to prepare the distal femur.Using Heygroves bone holding forceps to elevate the residual proximal femur out of the wound. The rasps are slightly curved and have 3 marks showing the correct rotation in the sagittal plane. They come in 12 to 20mm diameters; for a cemented stem, as in this case, the definitive stem will be 2mm smaller the the diameter of the last rasp. The definitive cement less stems match the diameter of the last rasp. Once the last rasp is stable mark the anterior aspect of the femoral bone with cautery or an osteotome so that the definitive stem matches the rotation of the rasp (to match the antecurvation/bowing of the femur and the rasp/stem).

Once the rasping of the femur has been performed next there is a “face reamer” to freshen up the end of the residual femur.This helps to maximise the contact between the EPORE collar of the femoral prosthesis and the host bone.

There is next a small reamer that burrs out the endosteum of the femoral medullary cavity by a few mms to improve contact between the collar and the host bone.

Connect the trial stem to the trial EPORE collar and impact into the residual femurThe diameter of femoral stem trial matches the diameter of the last rasp used. The collars range from 24 to 36mm in diameter for the round collars and there are 24/27mm 7 36/39mm oval collar options.
These trial components are attached to an impactor/extractor with a clover leaf device that screws into the end of the collar and stem as shown.

The trial stem is then impacted into the residual femur, matching the rotation of the trial to the rasp by observing the mark on the anterior femoral cortex.

The debrided joint cavity with a trial tibial prosthesis and definitive cone in-situ and the trial femoral stem and collar ready for a trial femoral endoprosthesis.

Size the segmental femoral defect and prepare and trial an appropriately sized distal femoral prosthesis and extension shaft which are connected to the femoral stem & collar.We then judge the length of reconstruction to confirm that the limb length has been approximately reconstructed, although in these scenarios often the leg ends up slightly shorter due to the nature of multiple operations of this type.

Having confirmed the right length of femoral shaft has been selected, screw together the distal femoral shaft and trial femoral stem. The central screw fixes rotation of the prosthesis, but can be infinitely adjusted as required for optimal patella tracking.

The trial hinge coupling is inserted into the femoral notch with the knee in flexion and the coupling is rotated 90 degrees clockwise to lock it into the femurWhen assembled correctly the hinge ‘peg’ sits pointing towards the tibial tray.

Using this ‘setting’ instrument as a joystick for the hinge coupling assembly, push the hinge through the trial polyethylene tibial bearing and into the trial tibia and then check for rotation, limb-length and alignment of the trial distal femoral endoprosthesis.
If you wish, the hinge coupling can be secured by inserting the locking screw through the hole at the front of the tibial tray.

Having confirmed that the correct length of reconstruction has been achieved, we request the definitive implants from the implant room, explant the trials (though not the definitive cone) and thoroughly wash the joint space and medullary canals using pulsed lavage. as we are cementing the femoral stem, the femoral canal will need drying with ribbon gauze also.

Tibial implant assembly
Assemble (S) the uncemented hydroxyapatite coated tibial stem, (OA) offset adaptor and (T) tibial prosthesis using the (I) tibial tray impactor and the tibial (OAB) offset alignment block on the back table.

Begin by connecting the definitive tibial tray to the 4 mm offset adaptor as shown.
The tibial (OAB) offset alignment block is placed over the face of the underside of the tibial tray and the offset adaptor is aligned to the correct number on the clock face as shown e.g. at 2 o’clock as in this photograph.

Once the correct rotation for the offset adaptor has been achieved, the definitive uncemented stem is impacted on top of the offset adaptor as shown.

Remove the screw-in peg which locks the hinge assembly mechanism using the hex screwdriver and retain this screw for later when assembling the hinge at the end of the procedure.

Insert the uncemented tibial prosthesis into the tibia leaving the tibial tray sat out of the cone by a few centimetres.Confirm that the prosthesis is correctly rotated and aligned with the ankle (using the ankle or the previous marker pen/cautery mark on the proximal tibia).

Insert some Palacos G high viscosity cement under the tibial tray to bond the tibial tray to the cone and to prevent any metal debris from the tibial tray resting on the cone.We do not want the cement to go inside the tibia but merely to lie between the tibial tray and the cone.

Impact the definitive tibia down to the level of the reconstructed meta-epiphysis formed by the cone and rim of residual posterolateral bone stock.

Having impacted the tibial tray to the desired depth and rotation allow the cement to cure. We can see that the tibial tray is just resting on the residual bone laterally and posteriorly.

On the back table assemble all the components that will be required for the femoral assembly including the (DF) distal femoral endoprosthesis, the (S) cemented femoral stem, the (E) Epore collar, the (FS) silver coated femoral shaft and the (B) bolt that bolts all four parts together. Also shown is the (P) polyethylene tibial insert to articulate with the tibia. The tibial inserts do not come in different thicknesses which is common with limb-salvage systems.

Start with the femoral stem which has a mark on it to show you the anterior line of the bowed femoral stem.

Place the EPORE collar over the end of the femoral stem as shown (rotation of the collar is not important here).

Using the same clover leaf impactors that we used before for trialling, these are screwed onto the end of the femoral stem as shown.

A longer impactor can be attached into the clover leaf if required for impaction.

Femoral medullary canal cementationHaving washed and dried the femoral canal, high viscosity Palacos G cement is inserted into the canal in a retrograde fashion (having pre-warned the anaesthetist about imminent pressurisation of cement in the femoral canal due to the risk of bone cement implantation syndrome).

Once the canal is full, remind the anaesthetist of impending pressurisation of the femoral canal with cement. According to Rassir et al. bone cement implantation syndrome is more common in arthroplasty than perhaps we appreciate, although severe reactions are rare (Rassir R et al. What are the Frequency, Related Mortality, and Factors Associated with Bone Cement Implantation Syndrome in Arthroplasty Surgery? CORR 202o doi:10.1097/CORR.0000000000001541).
Age, ASA class III or IV and renal dysfunction are risk factors for developing severe reactions including hypotension and cardiopulmonary collapse, and it is associated with greater 30 day mortality following surgery.
Lavage of the medullary canal prior to cementation, femoral venting and inserting the stem slowly and smoothly are recommended.

Insert the cemented femoral stem into the femoral canal smoothly and carefully ensuring that the rotation is correct. I use the mark on the anterior femoral cortex to align with the anterior notch on the femoral stem and bowing of the stem.

Impact the cemented stem all the way down so that the Epore collar is sat flush against the edge of the cut residual femur as shown.

Allow the cement to cure before inserting the rest of the implants.

Insert the distal femoral endoprosthesis and carefully connect the silver coated femoral shaft and the distal femoral prosthesis onto the collar.The use of silver coatings in limb-salvage surgery has proven to reduce the risk of PJI in high risk patients following sarcoma resection (Parry, MC, et al. Silver-coated (Agluna®) tumour prostheses can be a protective factor against infection in high risk failure patients. European Journal of Surgical Oncology 2019; 45(4):704-710
https://doi.org/10.1016/j.ejso.2018.12.009).

After placing the tibial polyethylene insert onto of the tibial tray, rest the distal femoral prosthesis ontop with the knee flexed at 90 degrees to confirm rotation.This helps to treble check the correct rotation of the distal femoral EPR using the tibia as a reference for rotation in 90 degrees of knee flexion.

Tighten the bolt of the femoral prosthesis. Using the (CT) counter torque wrench on the endoprosthesis, a (W) torque wrench is used to tighten the bolt inside the prosthesis until it gives firm resistance.

There is an end cap that is screwed over the bolt to stop any joint fluid getting into the mechanism that secures the modular prosthesis components.

The gold (HA) hinge assembly is inserted into the distal femoral prosthesis upside down on a silver introducer (I).The two click together with two little prongs, insert this into the gold portion of the distal femoral prosthesis notch as shown.

Once inserted, the silver portion is rotated 180 degrees clockwise until the hinge assembly clicks into place, leaving the peg pointing towards the tibia.

The hinge assembly is dropped through the polyethylene into the tibial prosthesis. Then align the hole through the peg inside the tibia using this pointed instrument (called a positioner on the surgical technique) to prepare for the bolt that holds it in place.

In extension carefully, insert the screw using the hex screwdriver to lock the hinge assembly together connecting the tibia to the femur.

Insert the tibial end capThere is next a tibial end cap that goes over the bolt to stop any joint fluid getting into the mechanism.

The definitive prosthesis has now been implanted as shown. We can see the collar with the uncemented tibial prosthesis, the distal femur, the silver coated shaft and the Epore collar.

Viewed from the front, the patellar is reduced over the front of the prosthesis and this photograph highlights the medial proximal tibial bone loss, which has been restored using the tibial cone.

Closure of the arthrotomy using 1.0 vicryl, begin by closing the subperiosteal sleeve around the proximal tibia and the medial parapatellar arthrotomy.

Having closed the arthrotomy around the patellar, the proximal wound is then closed, and a (D) drain inserted exiting laterally as shown in the photograph.

The wound is closed in layers with interrupted vicryl to close the full thickness soft tissue flaps over the arthrotomy and vastii. A subcuticular 1.0 vicryl is then used.

Skin clips are inserted to close the skin.

Apply vacuum dressing. An incisional vacuum dressing has been fixed to the wound. This is a high risk wound because of the numerous operations and co-morbid status of the patient. Prophylactic incisional vacuum dressings are used to aid wound healing. This is set at 100 mmHg and is kept in place for a week but does not prevent rehabilitation commencing. Also shown are the dressings around the drain.