Exeter stem (Stryker) and Gap II restoration acetabular cage (Stryker) for acetabular metastases

The anterior prop holding the patient has been placed on the symphysis pubis. This will allow access to the ilium and iliac crest if one needs to augment the procedure with Harrington rod placement. (Threaded pins placed into acetabulum from iliac crest – in tumour cases only). The aim is to position the pelvis in a perpendicular position to the flat operating table. The uppermost anterior superior iliac spine should be positioned exactly above the lowermost anterior superior Iliac spine (ASIS). Note lower limb has TED stocking and mechanical calf pump.

Anterior Prop placement on symphysis pubis.

The prop is placed posteriorly on the sacrum and lumbar spine, again it is placed in such a manner that the iliac crest is not impeded during the procedure by the prop placement.

Prior to surgery it is prudent to check the patient’s leg lengths in the lateral position as shown above. Make sure to abduct the leg to get a true reflection of the leg length. It is important to check the patient’s leg lengths when they are supine prior to positioning as well to get a more accurate idea of their clinical picture. Compare the clinical leg lengths to the radiographs.

Pre-operative radiograph showing superior acetabular destruction and femoral head migration superiorly secondary to metastatic breast carcinoma. Note sclerotic metastases throughout rest of pelvis.

Pre-operative CT – an axial slice is presented which highlights the superior acetabular bone destruction secondary to the disease process.

The patient is prepped and draped. Prior to this 2% Chlorhexidine prep has been applied to the skin. An Ioban preparatory skin drape (Iodine impregnated) has been applied to the thigh. The incision has been marked on the patient. The incision is centred over the tip of the greater trochanter, distally the incision is straight in line with the vastus lateralis fibres and proximally the incision curves towards the posterior iliosacral joint.

Incision through the skin into the fat. Cut perpendicular to the skin, if the dermis is not cut perpendicular the skin edges are harder to close.

The fascia lata is identified and a fasciotomy is made with the scalpel. The fascia lata is then opened with the use of dissecting scissors both distally and proximally (as shown) in the line of the skin incision. Proximally the fibres of gluteus maximus are split in the direction of its fibres using blunt dissection.

Two self retaining retractors have been applied to the fascia lata. The trochanteric bursa overlying the greater trochanter is seen. In this case the bursa is filled with fluid. As we are using a posterior approach the sciatic nerve is at risk. Do not delve deeply and blindly with the retractors, instruments or your hands!
The sciatic nerve exits the pelvis through the lower part of the sciatic notch. It is particularly at risk during the posterior approach to the hip. Identify the nerve at this point to identify where it is before proceeding, if it looks small it may of divided into its tibial and common peroneal branches before piriformis. The nerve appears below the piriformis muscle and lies over superior gemellus, obturator internus, inferior gemellus and finally the ischial spine.

For the posterior approach to the hip the piriformis tendon is identified as shown. An incision is made in line with the piriformis tendon over its superior border.

In this photograph we have a Langenbach retractor holding the gluteal musculature. Internally rotate the femur to lengthen the tendon and aid identification. The piriformis tendon can be found by palpating the greater trochanter and when you feel a small “nipple” of bone the tendon is adjacent to this. Once the fat is swept/dissected off the tendon it is readily seen. The scissors have now been passed over the piriformis tendon superiorly.

This image shows the position of superior retractor. A blunt Hohmann is placed superior to the piriformis tendon placed in the incision in step 12. To achieve this pass the curved dissecting scissors into the incision you have made with them superior to the piriformis tendon next place the Hohmann retractor over the scissors into the same space, then remove the scissors.

To insert the distal Hohmann retractor use the curved dissecting scissors to enter the space between the joint capsule sueriorly and the quadratus femoris muscle inferiorly. A blunt Hohmann is then placed in the same tract made by the scissors and the scissors are then removed in essence swapping the Hohmann retractor for the scissors.

A 2 Vicryl stay suture is applied to the piriformis tendon using 2 “throws” of the suture into the tendon as close to its insertion on the greater trochanter as possible. Maintain as much length of the tendon as you can.

The priformis tendon is now released from its distal insertion on the greater trochanter, control of the tendon is achieved by tension placed on the stay suture.

Now an arthrotomy is made as an L-shaped limb starting proximally at the edge of the acetabulum heading towards the tip of the greater trochanter, the arthrotomy is then continued distally along the edge femoral neck until the quadratus femoris muscle is reached. Inferiorly and distally there is often a venous vessel which bleeds – this will require diathermy.

A second stay suture is now applied to the joint capsule along its free edge after the arthrotomy has been performed.
Using the two stay sutures that are now in place reflect the tissues posteriorly to protect the sciatic nerve throughout the rest of the operation.

The femoral head has been dislocated. The head is marked with annotation F, the dislocation manoeuvre is to internally rotate the hip as it is adducted over the lower limb. Note – if this is a protrusio case it may be prudent to cut the femoral neck insitu prior to dislocation. If there are excessive osteophytes posteriorly sometimes it is necessary to remove the osteophyte rim from the posterior acetabulum wall with an osteotome first. Both these manoeuvres are there to prevent fracture of the femur or posterior acetabular wall during the dislocation manoeuvre. In this case the protrusion was minor and had present for only a short period of time – the femoral head was easy to dislocate.

Remove the remnants of the piriformis tendon in the piriformis fossa on the greater trochanter. This aids femoral neck visualisation.

Cut the anterior capsule fibres, under quadratus femoris. This release aids femoral head exposure by allowing increased rotation of the femur.

The femoral neck is now exposed clearly.

Sleep test with the leg adducted over the contralateral limb hold the foot and internally rotate the foot, at this point, allow the leg to flop in to this position and the hip should be stable.

An osteotomy is made with the sagittal saw at the level of the neck cut as per pre-operative templating. Measure up from the lesser trochanter to your planned resection level.

Sometimes a superior osteotomy into the femoral head neck junction is required to complete the previously cut femoral neck osteotomy and remove the femoral head as shown above. This osteotomy is made only when the first osteotomy does not completely separate the femoral head from the neck and is only a few mm in depth – use an osteotome 1.5 to 2cm in width.

The excised femoral head is noted above and the forceps point to the defect in the femoral head secondary to the femoral head wearing on the outer edge of the acetabulum as expected as per radiographic findings pre-operatively.

A Judd pin has been inserted in to the ischium. To insert this Judd pin place the tip of the pin inside the acetabulum gradually walk it back until you go over the acetabulum margin posteriorly in the space before the short external rotators are and then aiming for the ischium hammer the pin insitu this acts as a retractor.

As the cage is going to be utilised in this construct increased access is needed to the ilium. Use an osteotome or Cobb elevator to elevate the gluteal musculature up the side of the ischium to allow placement of the two proximal screw rows attached to the gap cage cup.

A superior Judd pin has also been placed. Use the tip of the pin to go superior to the acetabulum under the gluteal musculature aiming to retract the gluteal muscles with the pin once it has been hammered into the ilium. A sharp Hohhman retractor is now placed anteriorly on the acetabular margin to mobilise the femur anteriorly and out of the way of the acetabulum.

The labrum and soft tissues are excised around the acetabulum margin to expose the acetabulum 360o. Sometimes you might need to release the reflected head of rectus femoris to allow the femur to mobilise forward to gain better exposure of the acetabulum. The reflected head is extra-articular on the superior and anterior margin of the acetabulum – release the fibres by sharp dissection onto the bone.
The transverse acetabular ligament is identified. This is a valuable landmark for cup positioning (Archibold et al’s paper (J Bone Joint Surg Br. 2006 Jul;88(7):883-6.). Aligning your acetabular component with the transverse acetabular ligament seems to be the optimal cup position for specifically reducing dislocation rates (0.6%).
IN THIS CASE WE IDENTIFY THE TRANVERSE ACETABULAR LIGAMENT BUT LATER WE HAVE TO EXCISE IT TO FACILITATE INFERIOR CUP CRIMPING HOOK POSITIONING.
(Please note the camera angle has now changed and our photographer is looking face on to the acetabulum from the patient’s anterior side).

Acetabular preparation now starts after the foveal ligament remnants have been excised. In the base of the acetabulum the first reamer is used to remove the sclerotic bone and remnants of cartilage in the foveal fossa. Subsequent reamers are used to widen the acetabulum until good cancellous bleeding bone is seen circumfurentially in the remaining acetabular bone.
Caution should be excercised during this procedure when there are lytic deposits in the acetabulum. The bone will be incredibly soft and weakened and therefore acetabular reaming should proceed in a judicious fashion to prevent catastrophic bone loss and penetration through the acetabulum.
In this case the metastatic destruction is superior to the acetabulum and therefore the intra-articular socket was well preserved.

Acetabulum now reamed to remove all remaining host cartilage. The cage sizes start at 48mm and go up in 4mm sizing. 48,mm to 72mm cages are available. Typically I over-ream by 1mm to allow ease of cage placement if line to line reaming proves for difficult cup placement. In this case we reamed to 53mm. Any lytic areas should be curetted at this point, any sclerotic bone areas should have drill holes made in to them. Where lytic areas exist they can be filled with bone cement in the metastatic disease cases or bone graft if the cage is being used for an aseptic revision.

The cage sizes start at 48mm and go up in 4mm sizing. 48,mm to 72mm cages are available. The inner diameter of the cage is 3mm smaller than than the outer diameter except for size 60 and 68mm cages which are 4mm smaller. The cages are sided left and right. Notice the two bone plates proximally which facilitate the insertion of 5 and 6 screws depending on the limb chosen and the inferior crimp. The cage is orientated as you would look at it intraoperatively.

After trialling the cage into the acetabulum and identifying how to make it fit the best. Use the benders to bend the two bone plates proximally to conform to the patient’s ilium anatomy once the cup is seated in to the socket. Aiming to place the more posterior limb straight up the ilium, do not place it posteriorly as this wall alter the anteversion (increase) of the cup.

Bend the inferior crimp so that it can be seated inferiorly to the acetabulum.

Final acetabulum component shape post-initial bending.

Mount the acetabular cage component on to the cup introducing rod. There is a threaded screw hole in the centre of the cage for attachment. Using the cup introducer allows better placement of the cup and finer adjustments once inside the patient.

Initial cage placement into acetabulum.
Remove the transverse acetabular ligament and soft tissues inferiorly so that the inferior margin of the acetabulum is seen. Between the superior pubic ramus anteriorly and the ischium posteriorly, the inferior edge of the acetabulum will curve away medially. The hook is to rest on this bone, in dissecting this area be warned the acetabular branch of the obturator artery can bleed. Sacrifice this vessel with cautery when seen.
Start with the crimp of the cage introduced inferiorly to the acetabulum. Seat the cup from inferior to superior by levering it down in to the socket with the proximal screw rows aligning on ischium.
If the cup doesn’t seat correctly re bend the cage bone plates until the cup seats perfectly. Sometimes to get the cage to seat neatly into the scoket a small piece of bone from the superior acetabular margin has to be removed with an osteotome.

Final cup placement, note the bone plates aligning along the ilial bone. If the cup does not seat fully consider re-bending the screw rows +/- flange area, please note caution constant changes to the bone plates will weaken the construct it is titanium based and multiple bendings would risk fracture of the bone plates and therefore this should be avoided.

With the cup held in position using the cup introducer start by introducing screws in the proximal screw rows sequentially. I favour a non-flexible drill. Drill through both cortices of the ilium to get good purchase.
Caution should be noted in these tumour cases due to underlying tumourous bone that may be very soft. There are obviously important structures intra-pelvic which we do not want to damage with the drill bit, namely pelvic veins. If a patient has had previous radiotherapy these structures may be stuck to the inner table of the ilium and therefore very cautious drilling is recommended. As each drill hole is drilled, measure and the insert the appropriate screw before moving on to the next screw. Note that the closer you are to the acetabulum the longer the screw depth should be, more proximally the screw depths are very small often 10 or 15mm.
If a lytic area in the superior acetabulum/ilial area has been filled with cement prior to cage application screws can be applied into the hardened cement.

Screwdriver used to place screw. Note assistant holding the cup in position annotated A. The screws are 6.5mm cancellous bone screws (Restoration GAP bone screws).
Where screws are in metastatic bone these should not be placed. Use good remaining host bone only.
Once all screws are placed through the proximal limbs on the gap cage cup the construct is now ready to receive its cemented component.
Any dome screws should now also be passed. These screws are important as they “pull” the cage into the acetabulum and lend it extra support.

A cemented polyethylene cup needs to be cemented into the central portion of the cage. In this case we are using a Stryker contemporary polyethylene liner. The inner diameter of the 52mm cup will accept a 48mm outer diameter polyethylene liner and have a satisfactory cement mantle. Our unit favours the contemporary cup as we routinely use this cemented Stryker cup.
Remove the backing baubles on the temporary cup (not all cemented cups have this design). These are easily removed with the use of a bone nibbler as shown in the figure.
Omnifit series II cups were originally used in the construct. A compatibility chart exists for use with the restoration GAP II cages.

The cup is now mounted on to the cup introducer. Trial the cup in the cage to make sure it fits and you can get appropriate anteversion on the component and cup abduction. Cut the rim of the cup as required to fit into the cage.
The anterversion of the cup should be about 15 to 20 degrees – this is typically the orientation of the transverse acetabular ligament (TAL). Also aiming for an inclination angle of approximately 45o this is guided by the handle which should be parallel to the floor of the operating room. Check that the flange of the cup seats inside the cage and allows enough manoeuvrability to allow correct cup placement.

The cage is lavaged to clean the interface for cement application. All loose bone, fat and blood is removed.

The acetabulum has been lavaged with pulsatile chlorhexidine and is now being dried with a dry swab in the acetabulum and sucker in the base of the socket.

Once the high viscosity cement has been vacumn mixed (in this case Palacos) the cement at approximately 2 minutes 15 seconds is then placed into the cage. Clean any blood off the cement at this stage with a dry swab.

Cement is then pressurised into and through the cage. The cement is pressurised using the rubberised pressuriser for until approximately 3 minutes and 15 seconds after the cement mixing started.
Note if a large lytic defect exists in the acetabulum this should be cemented prior to cage application. The cage should be applied whilst this cement is curing allowing the cement to extrude through the cages holes as you place the screws in the proximal two bone plates. Any excess cement is to be removed at this point. Once the cement has cured use a 3.2mm drill bit to drill into the cement that is visible through any of the cage holes in the acetabulum this allows for better cement interdigitation when the polyethylene cup is eventually cemented into the cage.

The image shows the acetabular component mounted and being compressed into the acetabular cement. Place the leading edge of the cup inferiorly into the cement mantle, once it is seated into the cage, close the cup into the cement mantle – do this by using the pusher instrument to close the cup. Whilst this is occuring ensure correct alignment with by “steering” the introducer to the correct position. Once the cup is closed removed the introducing handle.

Excess cement is removed around the margins and the cup is pressurised in position using the femoral head on the ball adapted stick as seen in the picture. Note the femoral head diameter in this case is 32mm.

Final acetabular construction. The polyethylene is now cemented in to the cage and the bone plates are seen with screws proximally.

A box chisel is then utilised to start the femoral canal preparation. Aiming from the starting point E and dialling in the version of the stem you wish in the canal proximally. Use the box chisel to remove the metaphyseal bone remaining proximally.
Note the photographer is now on the posterior aspect of the patient as the view shown in the initial approach to the hip joint.

Second stage of canal preparation is to use the pencil reamer. You will know you are in the correct place as the pencil reamer will easily follow a correct path of least resistance in most typical canals.
The previous entry point with the box osteotome ensures you will be correct in the lateral position and pencil reamer will pass easily. If the pencil reamer does not pass easily, you may have started in a poor position, the patient may have a tight femoral canal or there maybe an overhanging trochanter.
Final canal preparation before broaching use a Charnley curette in the femoral to remove loose cancellous bone both in the lateral aspect of the canal and the medial aspect of the canal. Remove all loose cancellous bone.

Utilising the femoral broaches of the Exeter stem system. Use serial broaching to prepare the femoral canal. The femoral canal is serially broached starting with an Exeter 37.5 stem 0. Final stem size in this case was an Exeter 44 No 1. Smaller patients can start with the 35.5 broach.
Ensure the serial broaches used are placed in the correct version for the patients femoral canal.

Final position of Exeter stem broach in femoral canal.

A 32mm plus 0 head trial head has been applied to the Exeter stem.

First test your patient’s leg lengths. There is no point continuing if the leg lengths are grossly long or short at this point one must readdress your femoral stem if this is the case. As the leg lengths are equal here we proceeded to test the hip for stability. Next test for abductor subluxation (Shuck test). With the leg in neutral and slightly abducted leg test for femoral head distraction from the socket. If there is no distraction then the offset and or leg length may be too much, if there is more than 0.5cm of distraction then the offset and or leg length may not be adequate. Test again with different head sizes, and consider repositioning the stem to obtain optimum stability and leg lengths.

Testing for an anterior dislocation in the leg extended position and fully externally rotated leg the implant construct should not dislocate. If there is any dislocation in this manoeuvre it is imperative that you address your component positioning as a hip performed through the posterior approach that dislocates anteriorly at this point is a highly unstable construct and will dislocate.

Test the hip for stability again anteriorly with the hip adducted.

With the hip flexed at 90o gradually internally rotate the hip until it dislocates. In the mobile hip prior to surgery one must get a significantly higher arc of internal rotation to be acceptable aiming for between 70 and 90o.

The Exeter stem has now been opened and is mounted on its introducing handle. Note the plastic protector on its trunnion and distal centraliser. Two centralisers exist and come in the stems packet, one has 3 flutes (as shown) and one is unfluted – this should be used in narrow femoral canals.
The Exeter stems are 150mm long and have offsets of 37.5mm, 44mm, 50mm and 56mm. In each offset range their are differing sizes ranging from 0 through to 4 for the 37.5mm stem, 0 to 6 for the 44mm stem, 1 to 5 for the 50mm stem and 1-2 for the 56mm offset stem. (Smaller stem sizes are available 30,33 and 35.5mm). It is a modular stem with differing head size options available.

We are now happy with the hip in terms of its stability and leg length and therefore we can finish the femoral preparation. A Hardinge cement restrictor is now inserted down the femoral canal to 16cm. Exeter canal restrictors exist. I prefer the one sized Hardinge cement restrictor. You may trim the Hardinge restrictor, however I only ever consider this in the tightest of femoral canals.

Further canal preparation, the canal is lavaged with a pulsatile long nozzeled jet as shown. This removes loose bone, debris, blood and fat from the cancellous bone.

A suction catheter is the inserted down the femoral canal. The femoral canal is then packed with a rolled swab. This occurs while the cement is being mixed by the scrub team.

The femoral canal is then packed with a rolled swab. This occurs while the cement is being mixed by the scrub team.

Cementation of the femoral canal – the cement is applied in a distal to proximal direction after 2minutes and 15 seconds from the start of mixing. Place your nozzle of your cement gun down the femoral canal withdraw to approximately 1cm prior to instilling cement this allows blood pooling distally to be sucked up. Instil the cement and ride it almost like a surf wave allowing the canal to fill from distal to proximal, whilst leaving the suction catheter in situ.

The canal is now filled with cement.

Cut the tube of your cement gun off and follow with pressurisation of the cement in the femoral canal. Pressurise the canal with one movement of the gun handle and then remove the venting tube whilst pressuring. Allow pressurisation up to 3 minutes and 15 seconds.

Cement after pressurisation filling the femoral canal.

The Exeter stem is inserted in to the cement at 3 minutes 15 seconds starting at posterolateral corner with the tip of the implant. This will allow you to have the stem in correct AP and lateral alignment.

Final position stem after cement has cured. The protective plastic is still attached to the trunnion – this needs to be removed prior to femoral head trialling/placement.
Note the needle in the background instilling 120mls of 0.1% Bupivacaine and Adrenalin in to the subcutaneous structures (dosage is weight dependent and in this case the patient was able to take 120mls).

Using 2 drill holes through the lateral aspect of the greater trochanter make two passages for the superior and inferior limbs of the stay sutures attached to the short external rotators and piriformis tendon.

Using a suture passer the stay sutures are returned through the greater trochanter via the two drill holes.

Once the cement has cured retest the the hip replacement construct with trial heads. Once stability and equal leg lengths has been confirmed the definitive ceramic head is applied to a cleaned trunnion with one heavy hammer blow. A 32 + 0mm ceramic head was accepted.

posterior repair, the stay sutures are shown pulled through the two greater trochanteric drill holes.

The short external stay sutures have been tied over the greater trochanter as seen by the knot above and the posterior repair is now sound.

The fascia lata is closed with a continuous loop PDS suture.

The fat layer is now closed with continuous 0 vicyl.

The skin is now closed using a 2/0 quill subcuticular suture running in the dermal layer and then returning back in the skin layer.

The skin is now closed.

Dressing applied to wound after tissue glue and steri-strips have been applied to the wound.

Post-operative AP radiograph. Look for stem and cup position and overall biomechanical reconstruction of the hip joint (leg length, offset). Ensure no dislocation or fractures.

Lateral postoperative radiograph.