Femoral endoprosthesis- MUTARS intercalary EPR (Implantcast) for pathological fracture of spindle cell sarcoma of bone

Pre-operative AP radiograph whole femur showing a pathological mid-diaphysial fracture with permeative changes at the fracture site. ‘Permeative’ changes describe a medullary lesion invading the cortex causing endosteal lucency which is poorly marginated and may also be known as a ‘moth-eaten’ pattern.
Causes include osteomyelitis, Ewing’s sarcoma, lymphoma and eosinophilic granuloma.

Pre-operative coronal T2-weighted MRI of both femora showing displaced pathological mid-femoral fracture with evidence of cortical thinning of the lateral cortex in keeping with a malignancy arising in the bone.
The residual femur proximal and distal to the fracture site is normal, indicating that a diaphysial resection and reconstruction would be a joint sparing surgical option.

CT chest excludes distant pulmonary metastases and is a mandatory investigation to complete distal staging.

Position the patient in the lateral decubitus positionUnder general and spinal anaesthesia the patient is positioned laterally and routine hip props are used to hold the pelvis and sacrum. The effected left leg is isolated with initial drapes. Wasting of the calf musculature indicative of a period of immobility since emergency admission with pathological fracture, investigations, biopsy and MDT diagnosis and surgical planning. In this case the patient was bed-bound on skin traction during this period and is why the staging bone scan was omitted in this case to prevent delay.

Prior to application of incisional Ioban skin drapes the lateral skin incision is marked with the biopsy tract marked centrally for excision with an ellipse of skin. For this procedure a direct lateral approach to the femur is used so the anatomical landmarks are the greater trochanter proximally and the lateral epicondyle distally. The length of incision is guided by the resection but is essentially the length of the entire femur. If needed it by be extended proximally and distally to perform a total hip arthroplasty and total femoral resection and endoprosthetic replacement (via a lateral parapatellar approach).

A longitudinal anterior thigh skin incision is made, with an elliptical biopsy tract excisionMake the skin incision using a scalpel along the marked line excising the (BT) biopsy tract with an ellipse of skin and fat all the way down to the deep fascia.
This will be kept attached to the tumour resection specimen for histological analysis for seeding of sarcoma cells at the time of biopsy.

Deepen the skin incision through the fat and fascia lata, using cutting diathermy onto an instrument placed immediately beneath the fascia. Cutting the fascia onto an instrument, as shown, avoids penetration into tumours and is a preferred technique for precision.
In the photograph, the fascia overlying the (VL) vastus lateralis muscle can be seen with the fibres running longitudinally. The likely level of distal femoral resection is marked with a sterile marker pen.

Identify the tendon of gluteus maximus as it inserts onto the posterior femur. This is identified just distal to the tip of the (GT) greater trochanter and inserts just under the posterior edge of the (VL) vastus lateralis arising from the vastus ridge. Also shown is the (BT) biopsy tract distally.

Release the (GM) gluteus maximus tendon by inserting an artery clip underneath the tendon, to protect the sciatic nerve which runs deep to it, from the diathermy.Releasing the (GM) gluteus maximus tendon will improve exposure and identification of the sciatic nerve for protection throughout the procedure, but also help to mobilise the femur for resection.

After release of the gluteus maximus tendon the posterior aspect of the (VL) vastus lateralis overlying the femur and the (IMS) intermuscular septum and its anatomy can be better appreciated. Also seen here is the (BT) biopsy tract which is attached to the fascia overlying the vastus lateralis at the level of the pathological fracture.

Having identified the posterior edge of the (VL) vastus lateralis, a ring-handled spike is inserted under the muscle to elevate it off the femur.Once the instrument is placed beneath the muscle it is used to lever the edge of the muscle away from the bone allowing diathermy to release the muscle from the bone from proximal to distal.

Using soft tissue holding forceps the posterior edge of the (VL) vastus lateralis is elevated off the femur and a plane is developed through the muscle between the fascia overlying the muscle and the femoral bone and pathological fracture. Inadvertently cutting into the haematoma at the fracture site would contaminate the surgical margins and promote local recurrence of the bone sarcoma, which is sadly associated with significantly worse survival. Therefore, care is taken to preserve as much muscle as possible without contaminating the field.

A flap of vastus lateralis is elevated as the dissection moves from posterior towards the anterior aspect of the femur keeping a surgical margin of muscle tissue on top of the pathological fractureIts purpose is to retain the hematoma and tumour cells.

The dissection of the vastus lateralis muscle is now complete from proximal to distal and from posterior to anterior.

The sciatic nerve is traced into the posterior compartment to the thigh so that it can be protected as dissection moves into the posterior compartment. 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.
From proximal to distal the structures released during the classical posterior approach to the hip are piriformis, superior gemellus, obturator internus, inferior gemellus, obturator externus, and quadratus femoris with the hip joint capsule beneath.

An artery clip is placed superficial to the sciatic nerve but deep to the short head of biceps femoris and diathermy is used to divide the biceps femoris as it arises from the posterior lateral aspect of the femur.The short head of the biceps femoris is innervated by the common peroneal nerve. In contrast the long head is innervated by the tibial division of the sciatic nerve. This is a crucial anatomical point in orthopaedics: the short head of biceps is the only peroneal-innervated muscle above the fibula neck and is useful for EMG studies to identify whether a peroneal nerve injury has occurred proximal or distal to the fibula neck.

Having released the biceps off the back of the femur the (SN) sciatic nerve can be seen coursing into the posterior compartment and it is clearly visible at the base of the wound.

At this stage, as much of the dissection has been done as possible before osteotomies are required to help enhance the access to the medial soft tissues and vessels.

At the level of the proximal femoral resection and osteotomy the vastus lateralis muscle is incised down to the bone using diathermy.Once bone is reached, a periosteal elevator is used to expose the bone for the osteotomy.

Two hohmann’s retractors are placed at the level of the osteotomy around the proximal femur to protect the sciatic nerve and the profunda femoris vessels medially.The resection level is checked by measuring from the tip of the greater trochanter.

Measure and identify the proximal femoral resection level.Having measured and confirmed the correct level of the proximal femoral resection an oscillating saw with a 1.27mm blade is selected and used to osteotomise the proximal femur perpendicular to the long axes of the bone. The resection level is decided pre-operatively on the T1-weighted MRI coronal images measuring from any reliably identifiable anatomical landmark: in this case we measured 128mm from the tip of the greater trochanter (https://link.springer.com/article/10.1007/s00256-014-1979-2). We typically allow a margin of error of around 15mm, thus resect 15mm proximal and distal to the tumour.

Measure and identify the distal femoral resection level.Measure and identify the level of the distal femoral resection from the end of the femur using the metal ruler, again after careful measurements on the pre-operative T1-MRI.

Using a 1.27mm oscillating saw blade, and two Hohmann’s retractors to protect the femoral vessels medially, osteotomise the distal femur.The Hohmann’s are protecting the tibial and peroneal divisions of the sciatic nerve posteriorly and the femoral artery & vein medially.

The osteotomy is displaced to allow dissection of the adductor longus inserting medially.

The deep fascia the (VI) vastus intermedius is divided using cautery to mobilise the proximal femur and permit dissection on the medial side of the femur.

By elevating the intercalary segment the adductor insertion on the medial side of the femur can be divided.Care is required at this stage: the adductor canal will be encountered as dissection moves proximally. Each release of the adductors increases the mobility of the specimen for resection.

Identify the femoral vessels as they traverse the adductor canalIdentify the femoral vessels as they traverse the adductor canal on the postero-medial aspect of the femur. They are seen here with the Coleys forceps resting gently on them.
The adductor canal (Hunter’s canal/subsartorial canal) is an anatomical tunnel located in the proximal to mid thigh. It is approximately 15cm long, running from the apex of the femoral triangle to the adductor hiatus – a gap between the adductor and hamstring attachments of the adductor magnus muscle.
The adductor canal is bordered by sartorius (anteromedially), vastus medialis (laterally) and adductors longus and magnus (posteriorly). The contents include the femoral artery and vein (posterior to the artery), nerve to vastus medialis and the saphenous nerve.

Divide the remaining adductor longus inserting onto the medial femur Divide the residual adductor longus inserting onto the medial aspect of the femur, here being released over the surgeon’s finger.

As the adductor longus is released the profunda femoris vessels will be encountered and need to be ligated.The profunda femoral artery originates from the posterolateral side of the femoral artery in the femoral triangle immediately giving off the medial and lateral circumflex arterial branches. It then runs between pectineus and adductor longus and then between adductor longus and adductor brevis to supply the three perforating arteries to the posterior compartment of the thigh. The terminal part of profunda femoris pierces adductor magnus as the fourth perforating artery to get to the back of the thigh, often encountered at the linea aspera in the distal thigh.

The tumour specimen and pathological mid-femoral fracture are removed from the wound.

On the back table the specimen can be seen to have a good surgical soft tissue margin around the anterior aspect of the thigh.

Again, on the medial aspect of the specimen a good surgical margin is evident.

Haemostasis of the wound cavity is perfomed following tumor excision.The wound cavity is now inspected for bleeding vessels and careful haemostasis is achieved. The femoral vessels are seen in the base of the wound between the residual osteotomised femur.

Sample the medulla at the proximal resection margin Using a spoon or a currette, a sample of the medullary canal tissue at the proximal resection margin is sampled for histological analysis. This is to confirm that the resection is clear and no tumour cells have been left behind.

Sample the medulla at the distal resection marginThe same procedure is repeated at the distal femoral resection margin.

Ream the proximal femurUsing sequential flexible reamers the femoral canal is reamed proximally until the flexible reamers begin to ‘chatter’ on the endosteum, indicating that the proximal femoral canal has been sufficiently opened to permit rasps to be inserted. These reamers start at 8mm and increase in 1mm increments to 16mm maximally.

Ream the distal femurAgain, the distal femur is reamed with sequentially larger flexible reamers until cortical ‘chatter’ is encountered.

The Implantcast MUTARS trays on the back table showing the equipment required for the broaching of the femoral canals including the (R) femoral rasps, (SH) slap hammer and (W) wrenches to tighten the internal screws.

The modular trials on the Implantcast MUTARS trays required for the reconstruction including the (EB) extension bodies, (IS) internal screws, (TS) trial stems and (TCP) trial connecting parts.

The proximal femur is prepared using the rasps which have a hexagonal shape with a slight curve mimicking the sagittal femoral bow. Once the rasp is screwed onto the handle, it is inserted into the proximal femur and can be used as trial once stable in the bone. They increase in 1mm increments from 12 to 18mm diameters and are struck with the mallet carefully into the femur.

Rasps are then sequentially inserted into the residual distal femur until stability is achieved.

After the final rasp has been inserted proximally it is important to observe the positions of the channels cut into the endosteum by the hexagonally shaped rasps.The final rasp is inserted proximally achieving stability in rotation and resists axial forces. The slap-hammer can be screwed onto the final rasp as shown for more control. The Hey Groves bone holding forceps are used by an assistant to control the residual femur and to counter the blows of the hammer.

The trial modular intercalary endoprosthesis is now assembled. With the medullary stems inside the femur proximally and distally two connecting parts and an extension shaft are used to build a trial prosthesis.

Assemble the modular trial, align the intercalary connecting parts and trial the prosthesis.The intercalary connecting parts are aligned and snapped together to a reduced position. This might require some axial traction if limb length is correct; if no traction is required then the implant is almost certainly too short.

The trial modular intercalary prosthesis inside the wound showing satisfactory reconstruction of the segmental bone defect. The limb is now assessed for rotational alignment and length in the same way that you would do for a hip replacement. If the leg is too short then the extension shaft can be changed for a longer one until the correct limb-length is achieved. The extension shafts increase in 20mm increments.
The components are requested for definitive implantation.

Before definitive implants are inserted the femoral vessels are checked to ensure they are patent and haemostasis has been achieved.If concern regarding vascular flow is raised, doppler ultrasound and clinical examination distally to ensure vascularity is preserved distally is essential before implantation.

A haemostatic sheet of surgicel is placed over the femoral vessels for their protection during the final stages of reconstruction.

The definitive uncemented femoral stem is inserted into the proximal femur.The uncemented stems are slightly shorter than the cemented stems and so this was selected proximally to avoid the stem breaching out of the femur into the piriformis fossa.
This is gently tapped into the residual femur using the mallet until a good hold and stable fixation is achieved rotationally and axially. The assistant holds the Hey Groves forceps to resist the mallet blows. The the definitive stem should be inserted such that the hexagonal channels cut into the endosteum are matched by the implant. The stem and collar has a hydroxyapatite coating which sits on the cut-end of the bone to encourage bone on-growth.

The definitive uncemented stem has been seated correctly and the collar is engaging the osteotomised femur which is crucial for loading the residual proximal femur and collar on-growth from the periosteum.

After washing and drying, the distal femur is filled with high-viscosity cement which is inserted in a retrograde fashion.

The definitive cemented distal femoral stem is then inserted slowly to avoid a cement reaction into the residual femur.The stem diameter is 2mm less than the final rasp diameter to allow for an adequate cement mantle. Consequently the hexagonal channels cut by the final rasp do not control rotation which the surgeon must control during cementation.

One half of the connecting parts is attached to a cemented stem without modularity. Therefore one of the two stems has to be cemented, either proximally or distally. In this case distally was selected as pre-operative imaging highlighted that greater residual bone would be available distally rather than proximally and only the shortest uncemented stem would be possible proximally.

Attach the modular shaftThe modular proximal connecting part and the extension shaft are now added to the femoral stem and these components are held with an internal screw, seen being inserted.

The screw is tightened using a swing wrench and an anti-torque wrench as shown, which is not torque limited.

Reduce the intercalary prostheses and fix it with the two locking screws.The intercalary connecting modules are snapped together into the reduced position.
This requires some axial traction if the limb-length is correct by the surgical assistant whilst the surgeon reduces the components.

Two locking screws are placed through the holes in the intercalary adaptors to hold them reduced.

A DAC anti-biofilm coating is added to the prosthesis once all the screws have been tightened to minimise the risk of prosthetic infection(https://cordis.europa.eu/project/rcn/101783/reporting/en).

Suture the vastus lateralis to the intermuscular septum The vastus lateralis is sutured to the intermuscular septum to cover the prosthesis with soft-tissue to prevent infection.

A layered closure is performed, including the fascia lata, the deep dermis layer and then the subcutaneous closure of the skin.

Apply dressingsAdhesive dressings are applied.

Post-operative AP radiograph, at three months showing satisfactory reconstruction of the segmental defect with some periosteal reaction proximally and distally indicating healing of the cut periosteum.

Lateral post-operative radiograph at three months post-operatively again showing the periosteal reaction distally and satisfactory reconstruction of the segmental defect.