Proximal femoral endoprosthesis- Revision of THR to Adler Pantheon for metastatic bone disease progression

Pre-operative AP radiograph of the proximal femur showing a long-stemmed cemented Exeter hybrid total hip replacement with bone loss around the proximal femur and trochanter in keeping with progressive metastatic bone disease. Distal to the tip of the cemented stem the cortices appear to be normal.

Whole body bone scan showing uptake around the right proximal femoral prosthesis indicative of ongoing metastatic bone disease.

T1 weighted axial MRI scan showing a 6 x 5 cm extra osseous soft tissue mass around the femoral prosthesis indicative of progressive metastatic bone disease.

CT scan of the pelvis and proximal femur showing satisfactory appearances of the acetabular component and bone loss around the cemented femoral stem.

Patient positioned laterally and initial skin preparation and drape.Patient is positioned left side down right side up. Pre-operatively the patient has routine hip props, anteriorly and posteriorly. An initial pre-prep of the skin using alcoholic chlorhexidine is performed.

Second skin preparation and incisional drape application.After drying a secondary alcoholic skin preparation further drapes are applied and Ioban incisional drapes are applied to the skin. The likely skin incision has been marked over the trochanter.

Previous skin incision marked centred over greater trochanter.Skin incision is shown marking the previous incision which is centred over the greater trochanter extending down the femur for a routine posterior approach to the hip.
This helps with approximating the skin closure at the end of the operation to minimise tension and optimise wound healing.

Skin incision through subcutaneous fat down to fascia.The skin incision is made through the old scar using a scalpel. This is deepened through the skin and fat down to the deep fascia and fascia lata.

Mark the deep fascia prior to its incision to assist its accurate closure.The fascia has been exposed. Careful haemostasis is performed to minimise blood loss in a vulnerable patient. A marker pen has been used to mark the deep fascia (over the trochanter) prior to incision, so that the fascia lata and gluteus maximus fibres are approximated accurately for function and wound healing.

The deep fascia is incised from distal to proximal using McIndoe’s scissors, taking care as this layer has become adherent to the trochanter or trochanteric bursa.Therefore, start the incision distally over the vastus lateralis (as the silver muscle layer is easily identified), get your assistant to elevate the knee to reduce the tension use your right index finger to sweep under the fascia lata to help to elevate it off the trochanter.

Split the gluteus maximus fibres to expose the trochanter.As the deep fascia is incised proximally the (Gmax) gluteus maximus is encountered; split the muscle fibres in line with the incision of the deep fascia to minimise blood loss and optimise healing of this layer. Occasional bridging vessels are encountered as the muscle is split which need cautery. The (GT) trochanter, external rotators and posterior aspect of gluteus medius comes into view.

A Charnley bow(CB) retractor is placed onto the deep fascial layer, excercising care not to damage the sciatic nerve.This is identified running in the (F) fat plane between the external rotators and the (Gmax) gluteus maximus (posteriorly). Also visualised is the (Gmed) gluteus medius inserting onto the (GT) greater trochanter distal to which lies the silvery fascia of (VL) vastus lateralis.
The (SN) sciatic nerve runs over the (QF) quadratus femoris inserting onto the posterior aspect of the femur as shown and then beneath the gluteus maximus insertion which was previously released and then runs deep to the biceps femoris into the posterior compartment of the thigh. The quadratus femoris is the most inferior of the external rotators that are found at the posterior aspect of the proximal femur which maybe released during a routine posterior approach to the hip.

An artery clip is placed under the (GmaxT) gluteus maximus tendon as it inserts onto the posterior aspect of the proximal femur, underneath the (VL) vastus lateralis, and it is incised.Diathermy is used to incise and divide the gluteus maximus tendon to improve the exposure and access to the proximal femur. Taking care not to damage the first perforating vessel from the profunda femoris artery. The sciatic nerve also runs under the gluteus maximus tendon and this also must be protected, and then runs deep to the biceps femoris into the posterior compartment of the thigh.

The plane between the (P) piriformis tendon and the (Gmed) gluteus medius tendon is identified using blunt dissection and diathermy is used to develop this plane down to the joint capsule.This is the plane traditionally used to facilitate a capsulotomy during the posterior approach to the hip.
As this is a revision procedure, the tissue planes have been disturbed and repaired, indeed green ethibond suture material is visible within the substance of the piriformis tendon.

Aspirate the joint for culture and sensitivity to exclude occult prosthetic joint infection.Prior to deepening the incision into the synovial cavity, a needle and syringe are used to aspirate a fluid for microscopy and culture.
The fluid is transferred using fresh sterile needles into aerobic and anaerobic blood cultures bottles on a back table in theatre by a member of staff wearing personal protective equipment. This is routine practice for all revisions involving endoprostheses to exclude occult prosthetic joint infection.

After incising the joint capsule and elevating gluteus medius anteriorly using the Hohmann’s retractor, the femoral stem and the polyethylene from the total hip replacement can be seen.The Hohmann’s retractor should be placed under the gluteus medium tendon and anterior to the acetabular cup onto the ileum at the 11 o’clock position (assuming that the transverse acetabular ligament is at 6 o’clock).
Stay suture has been placed into the capsule and piriformis tendon for later reattachment using a No. 1 vicryl suture. Distal to this the external rotators are divided off the posterior aspect of the proximal femur.
From proximal to distal the structures released are piriformis, superior gemellus, obturator internus, inferior gemellus, obturator externus, and quadratus femoris with the joint capsule beneath.
Allow the rotators to reflect over the sciatic nerve for protection during the procedure. The (VL) vastus lateralis is shown to the right of the photo arising from the flare of the trochanter.

Using diathermy and some Lane’s soft-tissue holding forceps a plane between the deep fascia of the vastus lateralis and the extraosseous spread of the tumour is developed to preserve viable tissue whilst maintaining a cuff of normal tissue around the metastatic tumour to maximise the excision margins. By preserving a cuff of normal tissue (measuring only a few millimetres) around the malignant tumour, we can minimise the risk of local recurrence.

Having elevated the (VL) vastus lateralis off the tumour the dissection is continued anteriorly and superiorly to divide the (Gmed) gluteus medius and minimus off the proximal femur in a sleeve of continuous tissue to maintain later abductor and walking function.

The resection point is now measured based on the tip of the greater trochanter to locate the level of bone resection as determined from the pre-operative imaging.We decided to bisect the femur 2cm distal to the extent of the tumour on the T1-weighted images on the coronal MRI scan (https://link.springer.com/article/10.1007/s00256-014-1979-2). Conveniently this was just at the terminal extent of the cement mantle.

Osteotomise the femur at the resection point.Bone holding forceps are grasping the proximal femur whilst a 1.92mm oscillating saw blade is used to osteotomise the proximal femur at the resection point determined from the pre-operative planning using the MRI scan.

Elevate the femur to access and divide the adductors.Having divided the bone, the adductor muscles are released off the medial aspect of the proximal femur using cautery to enable elevation of the osteotomised proximal femur away from the body.
Care is taken to identify any perforating vessels and the profunda femoris to avoid bleeding. These are carefully ligated with 2.0 vicryl sutures to minimise bleeding.

The femur is manoeuvred out of the body using the bone holding forceps. Diathermy is used to release the abductor muscles from the proximal femur heading up towards the acetabulum. Once the acetabulum has been reached and the capsule divided the proximal femur is easily explanted.

Here the clinical photograph shows the wound after removal of the proximal femur. Haemostasis is now achieved and any clot removed with copious lavage.

The excised proximal femur on the back table showing the head of the cemented femoral prosthesis in situ.
A reasonable layer of normal tissue covers the tumour which can be seen to have caused swelling of the femur in the mid-portion.
The tissue is wrapped and sent to the histopathology laboratory fresh for analysis including measurement of the resection margins to confirm an en-bloc resection has been completed.

Obtain medullary tissue sample for histology.A spoon is used to take a sample from the medullary cavity at the resection point. This is sent separately in formalin for histopathology to exclude the possibility of tumour at the resection point.

The femoral canal is reamed with sequential straight reamers starting at 8mm increasing by 1mm increments until a “scratch fit” is confirmed by chatter of the endosteum on the reamer.Knowing when to stop having encountered this is a feeling that surgeons develop with practice and experience.
Alternatively, reaming can be done by hand with a T-handle. The reamer is slightly longer than the length of the femoral stem at 120mm.
These reamers are specific to the Adler Pantheon set are a prerequisite to complete the next preparatory steps safely.

Once the reamer has enough stability both axially and in rotation, it is uncoupled from the power handpiece and left in situ as shown. There is a laser mark on the reamer to line up with the level of osteotomised femur, this step is crucial to complete the next step of the operation.

A “face reamer” is now attached to the power reamer.Face reamers are used to remove excess bone so that the femoral osteotomy is perpendicular to the long axis of the bone, which means that the collar of the prosthesis will seat against the cut surface of the femur perfectly. Traditionally endoprostheses were end-bearing, so this was crucial. In the case of the Adler Pantheon prosthesis, the far reaming maximises contact between the 3D riding collar and host bone to maximise bone ingrowth and ingrowth to prevent aseptic loosening.

The power reamer is cannulated and inserted over the protruding stem of the last reamer left inside the bone so that it cuts perpendicular to the long axis of the bone.

Next an endosteal reamer is attached to the handpower reamer as shown.

The endosteal reamer is also cannulated and reams over the last canal reamer left in the medullary cavity.
This device cuts the endosteum so that it can receive the 3D printed collar which allows ingrowth and ongrowth from the endosteum to prevent aseptic loosening.

Leaving the last femoral reamer in situ, a modular trial is now assembled to replicate the length of the segmental bone loss.
The trial is added to the protruding end of the femoral reamer. As an acetabular cup is already in situ, a trial 32mm head is put on top of the trial neck for assessment.

The assembled modular trial is now reduced into the acetabular component as shown. Routine assessment for anteversion, limb-length and stability as one would for a hip replacement is now performed.
I prefer to shorten patients between 5-10mm with reduced offset to reduce the moment arm for abductor deficient patients such as this. If the limb-length and offset are matched to the pre-operative anatomy it is more difficult to walk, even with a trendelenberg gait, because the abductor muscles have been detached and will never regain previous levels of function.

Assemble the definitive prosthesis.Having selected the sizes of the modular components these are now requested from the storeroom unwrapped and shown here on the back table prior to assembling. Also shown are the instruments required for assembly.

First the 3D printed bridging collar is inserted over the stem.

The stem is now turned upside down and the trunnion of the bridging collar impacted onto the stem using this cannulated tube.

The stem is rested on a metal assembly base plate and the mallet is used to impact the collar onto the trunnion of the stem.

The modular shaft and the additional extension piece are now added to the stem and collar as shown.

The tip of the stem is now rested on the metal base plate on the back table. This is recessed to allow the tip of the stem to sit inside the bowl. The top of the extension piece is struck with the mallet to impact the two tapers as shown.

After adding the trochanteric segment of the implant a screw is now inserted through the hole at the top as shown. No alignment with anteversion is required with this implant because the cemented femoral stem is short enough to accommodate the femoral bow, therefore anteversion is determined by the surgeon and not by the implant.

The screw is tightened with an anti-rotation device placed over the trunnion of the prosthesis whilst tightening the screw as shown. Crucially, the anteversion of the stem can be changed after cementation if required by un-tightening this screw.

Lastly the 28mm cobalt-chromium head and the polyethylene dual mobility liner are prepared using a compress which forces the 28mm head inside the bearing so that it rotates freely. This has to be checked prior to insertion.

The assembled dual mobility head and bearing are shown on the back table. To confirm correct assembly the cobalt chromium head should spin freely within the polyethylene liner.

The femoral canal is now washed with pulsed-lavage and dried with ribbon gauze. Prior to cementation the canal should be cleaned of fat and blood clot to optimise cementation. The anaesthetist is warned of impending femoral cementation, due to the risk of a reaction to the cement monomer.
Bone cement implantation syndrome is more likely in patients aged greater than 60 and/or in the presence of lung metastases (Schwarzkopf E, et al. Journal of Surgical Oncology 2019; https://onlinelibrary.wiley.com/doi/abs/10.1002/jso.25675.)

The cement nozzle and the canal pressuriser for the femoral stem are shown assembled on the back table. A size specific canal pressuriser is supplied with each cemented stem. The canal pressuriser replicates the displacement of the definitive stem such that the correct amount of cement is filled into the canal to avoid the cement interfering with the endosteal collar.

Fully insert the pressuriser into the femoral canal ready for cementing through the channel.

Retrograde cementation is followed by definitive prosthesis insertion.The nozzle of the cement gun is placed through the pressuriser to permit retrograde cementation. As the canal fills up with cement it reaches the cement tool it will lift away from the cut surface of the bone and no further cement needs to be placed into the canal. This is to leave space for the displacement of the femoral stem when it is inserted into the endosteum, to avoid excessive cement creeping between the endosteal collar and the bone which would prevent any osseous ingrowth or ongrowth to the endosteal surface of the collar.

Insert definitive prosthesis into femoral canal.The assembled prosthesis is now inserted smoothly into the femoral canal. The bone holding forceps hold the distal femur. Care is taken to insert it in the correct anteversion as determined from the trialling stage.

Reduce the hip joint during cementation. Using a trial femoral head the prosthesis is reduced into the hip joint. It is important to hold the prosthesis still to prevent movement during cement curing which could lead to early loosening; by reducing the joint the implant is held still during the next eight minutes as the cement hardens. One tip is to be alert to the prosthesis rotating externally in the cement mantle during this stage if you do not maintain the anteversion. This can be corrected if necessary after the cement cures.

Changing anteversion.
If you do need to change the rotation of the prosthesis after cementing, simply un-tighten the screw in the trochanter and insert a longer trunnion uncoupling screw (which pushes the trunnion of the trochanter and shaft apart), rotate to the corrected position and re-tighten the screw down the trochanter.

The acetabular liner is exchanged for a dual mobility liner.Prior to cementation of the endoprosthesis the polyethylene liner for the acetabular component is removed and a dual mobility liner is clicked into place. There are grooves on the liner which line up with grooves in the acetabular prosthesis to ensure this component sits flush into the socket. The liner is impacted with three blows to ensure it is seated correctly.

Impact the dual mobility femoral head and liner onto the trunnion of the prosthesis.The head pusher is used to strike the definitive femoral head and liner onto the trunnion of the femoral neck.
Dual mobility liners have been shown to reduce the risk of dislocation with total femoral endoprostheses compared to small metal heads (22-28mm) and polyethylene bearings in our institution .
It is now our routine practice to use dual mobility liners where possible in our hip reconstructions when the acetabulum needs resurfacing. The implant can also be used with uni- or bipolar hemiarthroplasty heads.
(https://online.boneandjoint.org.uk/doi/abs/10.1302/0301-620X.101B5.BJJ-2018-1106.R1)

Reduce the femoral head into the acetabular shell.The endoprosthesis is reduced into the acetabular dual-mobility component. I use a bone hook and longitudinal limb traction to achieve this safely. Care is taken to check that the correct anteversion has been achieved to avoid instability by re-trialling for stability in flexion, extension, internal and external rotation (as you would for any hip replacement).

Apply anti-infective coating.Whilst the cement is curing two mixes of Defensive antibacterial coating (DAC) hydrogel are applied to the surface of the prosthesis to reduce the chance of prosthetic joint infection.
This hydrogel is mixed with powdered antibiotics of the surgeons choice and applied to the surface of the implant to prevent the formation of biofilm which can lead to prosthetic joint infection
(https://online.boneandjoint.org.uk/doi/full/10.1302/2058-5241.4.180095).

A 55mm Implantcast polyester soft tissue reattachment (Trevira) tube is placed over the endoprosthesis like a sock. Fixation of the residual surrounding soft tissue on the implant represent a challenge for the surgeon and the use of a polyethylene terephthalate (PET) tube over it, also known as Trevira, is currently a common choice for reattachment with good clinical outcomes reported by Gosherger et al. (https://journals.lww.com/clinorthop/Fulltext/2001/12000/Soft_Tissue_Reconstruction_of_Megaprostheses_Using.30.aspx). Cellular adhesion has been confirmed in-vivo by D’Adamio et al (https://www.researchgate.net/profile/Stefano_DAdamio2/publication/321366019_Soft_tissue_adhesion_patterns_over_Trevira_tube_on_modular_endoprosthesis_for_malignant_bone_tumours_An_in_vitro_study/links/5ac784be4585151e80a3a512/Soft-tissue-adhesion-patterns-over-Trevira-tube-on-modular-endoprosthesis-for-malignant-bone-tumours-An-in-vitro-study.pdf). As a result of the soft-tissue adhesion we can attempt to restore the functionality of the muscles earlier detached from the excised proximal femur, particularly the abductor and quadriceps muscles.
Also shown is a drain which has been tunnelled out through the fascia and subcutaneous tissues distal to the wound along the thigh.

The reattachment tube is brought down to the junction between the prosthesis and the host bone and no. 1 ethibond sutures are used to attach the trevira tube to the soft tissues of the residual distal femur. I prefer to suture it to the linear aspera and to the deep fascia of the vastus lateralis as it inserts onto the femur to prevent it rolling up.

Ethibond is then used to reattach the cut margin of the vastus lateralis onto the trevira reattachment tube with bites approximately 2cms apart.

Soft-tissues are reattached to the Trevira tube.The soft tissues are reattached to the trevira tube from distal to proximal as shown. The suture throws are locked at each bite. This ensures appropriate soft-tissue coverage of the prosthesis and hopefully maximises function of the muscles released off the excised femur.

In the middle of the photograph the (Gmax) gluteus maximus tendon has been reattached to the trevira tube and to the posterior aspect of the (VL) vastus lateralis using the ethibond suture. This helps with stability as well as soft tissue coverage of the endoprosthesis to reduce the risk of infection.

Gluteus medius reattachment.
The origin of the (VL) vastus lateralis and the (Gmed) gluteus medius tendon and (P) piriformis tendons are attached to the reattachment tube in the trochanteric region of the endoprosthesis using modified Mason Allen sutures so that the suture material does not cut through the soft tissues as they are brought down tight onto the reattachment tube. This is done purposefully to attempt to attach these anatomical stretches onto the prosthesis to restore some abductor function and restore some quadriceps function.

After completion of the reattachment of the (P) piriformis tendon and the (Gmed) gluteus medius and the (VL) vastus lateralis and (Gmax) gluteus maximus tendon the endoprosthesis has almost been covered with soft-tissue, except for were the bare area of the native trochanter has been excised. The reattachment tube is only exposed in that area. Optimising soft-tissue coverage of the prosthesis is desirable to reduce the risk of infection, dislocation and to maximise function particularly abductor function.

Using a No. 0 looped PDS monofilament suture, the deep fascia lata is closed from distal to proximal as one would do routinely for a revision hip replacement.I prefer to lock the sutures with each bite.

As the looped PDS reaches the gluteus maximus tendon reattachment a “mass closure” technique is used to further aid soft-tissue coverage of the prosthesis.
This involves taking a bite on the anterior side of the fascia lata and before taking a bite through the posterior side, the deeper tissues, namely the reattachment tube and the vastus lateralis are included with the bite of the needle. This is done to bring the fascia lata down onto the prosthesis to cover the bare area over the trochanter of the prosthesis, to aid soft tissue coverage, to minimise the risk of infection. This also has the additional benefit of allowing the gluteus maximus and the tensor fascia lata muscles to function as a check rein in an abductor deficient patient, thus maximising function and reducing the risk of a trendelenberg gait.

After completion of closure of the deep fascia lata the endoprosthesis and the trevira tube are now completely covered. The rest of the subcutaneous tissues is now closed with interrupted 2.0 vicryl sutures.

After the interrupted 2.0 vicryl sutures only the skin remains left to close.

Skin closure.A subcuticular 2.0 vicryl suture is used to close the skin prior to skin clips.

Apply vacuum dressing.As this is a high risk wound a prophylactic incisional vacuum dressing is applied to the wound using duoderm around the wound edges to manage the seal and roll cotton. The vacuum is attached to the suction machine using an aperture that is cut into the adhesive dressing in the centre of the wound.

Post-operative x-ray showing satisfactory reconstruction of the segmental bone loss of the proximal femur following incision of the recurrent tumour.

Shows satisfactory cementation of the distal femoral stem and endosteal fit of the additive manufactured 3D titanium collar.