Conversion of Dynamic Hip Screw to Avantage Dual Mobility Cup (Zimmer-Biomet) and Proximal Femoral Replacement (METS, Stanmore)

This lady sustained a displaced three part intertrochanteric fracture. There are many classifications for extra-capsular fractures. I would direct the reader to the summary article below to get a good overview. As can be noted there is no medial support as the lesser trochanter has displaced.
Classifications of Intertrochanteric fractures and their Clinical Importance Sonawane. Trauma International. 2015:1;7-11

The fracture has not been fully reduced. There is no medial support, the lesser trochanteric fragment remains displaced. The lag screw is also low in the femoral head.

The lateral view of the hip shows the tip of the lag screw is posterior within the head. The risk of failure of this type of fracture can be predicted using the Tip-Apex distance classification. There have been modifications to this system to allow for radiographic variations.

Intramedullary versus extramedullary fixation for the treatment of intertrochanteric hip fractures. Baumgaertner et al Clin Orthop Relat Res. 1998:348;87–94

As can be seen, this fracture failed to unite.
The proximal femur is fragmented. There are separate lesser and greater trochanteric fragments, the neck and head appear intact but there is a lateral wall “blow-out”. At best, the fracture is now in at least 5 pieces. With a complex fracture there is always the risk of failure prior to union.
A DHS acts in tension, however to achieve this is requires an intact or reduced medial wall. With this complex fracture the medial structures were non-supporting. A combination of this and the increased forces through the hip secondary to increased body habitus has lead to failure.
The lag screw has cut through the head and is impinging on the inside of the acetabulum. This leads to acetabular articular cartilage erosion. The only satisfactory treatment for this is a total hip replacement.

This lateral view shows internal rotation of femur on the femoral neck (the femoral neck is pointing posteriorly). It is apparent that the femoral shaft appears intact.
The only thing worse than a non-union is an infected non-union. This patient should have inflammatory markers for infection (CRP, ESR and a WCC). In an ideal world, if pain is not too severe, the hip should be aspirated. In common with primary hip arthroplasty literature there is a 5% seronegative infection rate, i.e normal inflammatory markers in the presence of infection.
If the patient cannot wait and is immobile with the increased morbidity this brings, I personally take at least 5 samples at the time of surgery and treat empirically with antibiotics until culture results are available. The samples should have extended cultures in enriched broth for at least 7 days, with analysis by microbiologists experienced in orthopaedics. These cultures should not be performed on the “benchside” where contamination is high. In Sheffield our broth culturing is performed in a Class II laminar flow cabinet.

Templating for surgery in my view is exceptionally important. This image shows two potential options. Both however rely on gaining a good fit in the femur. A knowledge of the patient, their expectations and current level of functioning is also required. Cementing a stem into this fracture was a possibility but would not have been ideal. The support around the proximal stem would be poor, increasing the risk of stem fracture. A claw to hold on the abductors would also be required. These are often poorly tolerated in thin patients. The hold of the claw plates in osteoporotic bone is also often tenuous.
It was known that this patient’s pre-morbid state was complex and pre-operative function was limited. However (as can be seen later) the BMI was a considerable challenge. There were to be a lot of forces through this hip.
Radiographs also tend to over-simplify the fracture pattern. Planning for more robust revision implants or a proximal femoral replacement were made.

Utilise the old DHS scar and extend it superiorly and distallyThe approach for a DHS has been fully documented in my OrthOracle technique at https://www.orthoracle.com/library/stryker-omega-dynamic-hip-screw-extra-capsular-neck-femur-fracture/
The incision is along the mid-point of the femur below the greater trochanter (to see the exact measurements of this please review slides 18-23 of the DHS technique).
Where possible please make every effort to gain the old operation notes as some surgeons split vastus lateralis whilst others elevate this. The old approach should be used to avoid devitalising tissues.
In converting this into an approach to allow a total hip replacement the following factors needs consideration.
Firstly the posterior curve of the posterior approach to the hip can be incorporated superiorly. To do this I flex the leg to 60 degrees and incise the skin in a straight line over the tip of the greater trochanter. When the leg is fully extended once more the skin incision is naturally curved posteriorly.
Distal skin extension is in the midpoint of the femur.
It should be noted however that whilst the bony anatomy does not change, a midpoint skin incision with the patient on a traction table (for the DHS) and in the lateral position (for a total hip) may differ. Whilst in the lateral position for the total hip, the old DHS scar may be more anterior than anticipated. Still utilise the DHS scar but be cautious not to drift anteriorly with the extensions of the wound.
Following skin, the fat layer is incised. As landmarks may be obliterated it is important to regularly reassess ones position. It is now relatively easy to drift posteriorly, missing the femur. Keep palpating deeply during the initial exposure and feel for the femur.

Incise the fascia lata over the midpoint of the femur to exposure the lateral hip structures. This fracture fixation is almost 2 months old. The fracture collapse in conjunction with the high BMI makes identifying structures difficult.
As a tip, find vastus lateralis (A). You can always work superiorly from it’s posterior border, even when most other structures are stuck down or encased in scar tissue.

Working proximally initially the fracture is exposed (A). It is known from the radiographs that the fracture is comminuted. However with reference to the AP hip radiograph the fracture shown would appear to be the lateral wall blow-out fragment and therefore the DHS plate is distal to this.

Expose the DHS plate by elevating vastus lateralisThe initial DHS was performed by elevating the posterior border of vastus lateralis and using not a lateralis splitting approach. Therefore to decrease devascularisation risk, the posterior border was again elevated (A). Again the anatomical appearance is distorted.

Expose the proximal DHS plate and forward elevate the fracture with vastus lateralis attached.It was apparent that proximally, the vastus was attached to a free fragment of femur. This was moved anteriorly en-mass. At this stage I am still not entirely sure how to reconstruct this fracture. Therefore elevating vastus off the lateral femoral bone would completely devascularise the bony fragment. This was therefore avoided.
The DHS plate is just about visible in the bottom of the wound (A)
The tip of the trochanter is approximately marked (B) with the hip abductor anterosuperiorly (C).

Using diathermy and the Hohman’s retractors the lateral structures (vastus lateralis and bone fragments) are again retracted anteriorly. Further bone fragments are becoming apparent (A).
Vastus lateralis is seen (B) with the trochanteric fragments (C)

Expose the remaining DHS plate by by working distally, elevating vastus lateralisFurther work is required to release vastus lateralis now distally. Keep to the posterior border, release and elevate anteriorly. Use a Bristow’s or Cobb retractor
The superior perforating vessels from the profunda are at risk here. They are usually visible if exposure is measured and controlled. The perforators a run with corresponding venous structures.
The profunda femoris (deep femoral artery) supplies the muscles of the thigh. It arises from the lateral side of the femoral artery in the femoral triangle (the borders of femoral triangle are – Superior – Inguinal ligament, Medially – Adductor longus, Laterally – Sartorius). Profunda passes deep to adductor longus, the femoral artery passes anteriorly.
Generally when elevating vastus anteriorly it is safe around the lateral aspect, the terminal ends of the perforators are usually visible but stay close to bone. Posteriorly however the perforators of the thigh present a rather more tricky problem as they pass through the lateral intermuscular septum (and they tend to be larger here too as they have not terminally divided).
There are three classical perforators from the profunda. Dissection around the posterior aspect around the linea aspera should be meticulous. Search for the perforators before cutting them. I use ligaclips to occlude before cutting. Others use ties. Diathermy doesn’t work.
If a perforator is cut inadvertently I release the linea aspera proximally and distally to the bleeder. This releases the lateral intermuscular septum allowing access to the posterior compartment, it is then simpler (but not easy) to control the bleed. Caution is required around the medial side of linea aspera as the profunda artery and vein are close by on the adductors.
The most proximal branches of the profunda are the medial and lateral femoral circumflex arteries. The medial circumflex passes between iliopsoas and pectineus and lies on adductor magnus. It passes between quadratus femoris and adductor magnus and divides into ascending and descending branches. The ascending branch lies on the anterior border of quadratus and is at risk during the posterior approach to the hip.
Regarding the three perforators, the first passes between pectineus and adductor brevis and pierces the adductor magnus posteriorly very close to the linea aspera.
The second pierces adductor brevis and magnus. It is located around mid thigh.
The third arises distal to adductor brevis and pierces adductor magnus. As a rule of thumb it is located one hands breadth above the flare of the metaphysis.

Remove the DHS plate screws and remove the plate, followed by the lag screw.It is straightforward to remove the screws. The femoral bone distally and under the plate was intact. The DHS plate was removed by sliding the barrel off the lag screw

Following removal of the plate, remove the DHS lag screw. The DHS lag screw insertion handle was used for this.

As can be seen orientation of anatomical structures is not easy, Vastus remains a landmark (A). Superiorly we know that it’s origin is from the greater trochanter, intertrochanteric line, and linea aspera.
However even with your orientation goggles on it remains very difficult to work out what is left in the base of this wound. This is not simply projectional, What was going on was initially inapparent to me too. There are multiple bone fragments (B). In these instances it is easy to ‘panic’ a bit and start cutting to find normal anatomy. Resist.
There was sufficient (although fractured) lateral bone including the greater trochanter, this was left intact. Mechanically the vastus lateralis and hip abductors are attached to trochanteric bone and act as a sleeve. This continuity improves function after this type of revision.
However, as predicted from the templating, this proximal femur was unreconstructable. A proximal femoral replacement was required.

Isolate the proximal femur then cut the femur with an oscillating saw. The oscillating saw was used to cut the femur. Note that two Hohmann’s retractors are placed under the femur to protect the soft tissues.
Although the hip was still reduced I could estimate the level of the cut required. For the Stanmore Proximal femoral replacement, the shortest resection for the integral body is 82mm (from the centre of the femoral head or tip of trochanter). I made sure I cut the femur less than this as I needed to formalise the femoral cut once the head and body were removed and out of the way.

Complete the medial aspect of the proximal femoral osteotomy with a bone chiselThe bone chisel was used to complete the medial femoral cut as this is more controlled and safer than a saw.

Remove the soft tissue attachments around the proximal femurFinally the proximal femur was delivered. All soft tissue attachments were released from the bone.
Remember that the lateral trochanteric bone was preserved, therefore the structures removed were;
Posteriorly – superiorly to inferiorly, piriformis and the external rotators (gemelli & obturator externus) gluteus maximus, psoas and iliacus.
Anteriorly isolation of the proximal femur entailed removal of gluteus medius & minimus and vastus medialis.
The hip ligaments (iliofemoral, ischiofemoral and pubofemoral) and the capsule are all detached.
In a native hip the muscle insertions are discernible but many of these structures in the revision setting often not seen as individual entities. However it is safe providing you don’t ‘drift.’ As many bosses have said, ‘Get to bone and stay there!’
There are both vascular and neurological structures at risk.
The proximal branches of the profunda artery have been described in slide 13.
The sciatic nerve is also at risk. Its course has been described in nearly all posterior approach presentations, however, the sciatic nerve exits the pelvis inferiorly to piriformis in 90% of cases. The remainder have a high division of the nerve with the common fibular branch passing through or superior to piriformis. (Lewis et al)
The nerve descends on the posterior borders of superior gemellus, obturator internus, inferior gemellus and quadratus femoris. It passes deep to the long head of biceps femoris
It is apparent that the proximal femur, neck and head were in a poor state.
Anatomical variations of the sciatic nerve, in relation to the piriformis
muscle, Lewis et at. Translational Research in Anatomy 2016:5;15-19

The Avantage Trial Cup tray.
The next step is to use the trial cups to confirm reaming. This equipment is on this tray.
The tray consists of;
A. Trial cups
B. Insert (onlay) trial 22mm
C. Insert trial 28mm

The Avantage Cup Trial Handle.
In order to construct the trial cup device the handle is required (A) on this tray. This tray also contains
B. Long Screwdriver (use with uncemented)
C. Insert Extractor (used to remove head/ inlay from femoral trunion in-situ)
D. Impaction Handle
E. Angulation Guide Rod
F. Insert Press (body)
G. Cup Positioner (used in uncemented)
H. Head / Liner Pusher Tip
I. Final Orientation / Impaction Tip
J. Insert Press (base plate)

Expose the acetabulumThe acetabulum was exposed. This is actually straight forward as the proximal femur has been removed.
All the anterior and posterior structures for a Hardinge or Posterior approach have already been released.

Ream the acetabulum sequentially, the inclination of the reaming should be 45 degrees and the anteversion should be around 15 degrees, using the transverse acetabular ligament (TAL) as a landmark for anteversion.The aceabululm was then reamed using sequential reamers.

It is not always possible to demonstrate clearly with intra-operative images that the inclination of the reaming should be 45 degrees and the anteversion should be around 15 degrees.
I use the transverse acetabular ligament (TAL) as a landmark for anteversion. The TAL is a ligament which crosses the acetabular notch (crosses from point A to point B). The reamer should be parallel to the ligament.
I accept many scientific papers quote different degrees and there is a massive push for CT guided reaming or using a robot. I personally wonder about this ‘pressure.’ To my knowledge I do not have a massive dislocation, impingement or pain problem after THA. Do I need a robot to correct a problem I don’t think I have.
At our most recent Annual Registrars’ Day presentations Javad Parvizi, the guest speaker, gave some sage advice. ‘Stay once step behind the fad.’

Use the trial cup to confirm initial reaming has been to an appropriate level.Once reaming is completed, loose debris is removed and the size of the acetabulum is confirmed.
The trial cup (range 44 to 66mm) is simply snapped onto the end of the trial cup positioner.
The notch seen (A) corresponds to the laser etching on the definative implant.

The acetabular trial in use.The principles guiding this are is explained in the following slides.

These next two slides show the use of the sizing guides.
Firstly I use the cup trial size I have last reamed to. The guide is used to ensure that the bone has been reamed out evenly, to the correct size and depth. In the uncemented cup variant, this would be the only measuring step. The reaming diameter is the same as the trial cup diameter which is the same as the definitive implant diameter (i.e. line to line reaming).

Use the cup trial to ensure both that that the bone has been reamed out evenly, to the correct size and depth and also a good cement mantle around the implant is possible.The op-tech will state that the Avantage cup can be used with a 1mm cement mantle. This in my opinion is a little small and the risk of bottoming out and loosing cement pressure is high. I prefer a 3mm margin. Using a trial that is 6mm smaller than the last reaming aids me to gauge whether the mantle will be satisfactory. In the image you can see a gap around the cup. I have placed the cup against ‘bone’ inferiorly. This would be an incorrect position when cementing the definitive cup.

There is a laser etching in the midpart of the raised superior acetabular wall. This should be placed at the 12 o’clock position in the reamed acetabulum.

The components of the cup impactor.
The impactor device is made of three components, the impactor tip (A), the impaction handle (B) and the expansion rod (C).

The expansion rod is inserted through the impactor tip and screwed home into the impaction handle to construct the acetabular impactor device. The side expansions of the expansion rods (A) then slide into the slots of the impactor tip (B).

Tighten the impactor tip into the definitive acetabular implantThe handle is tightened (see next slide) which grips the implant. As the cup is not uniform (raised superior wall) the base of the impactor tip should be parallel with the elevated lip of the implant (A)
For an uncemented cup the impactor tip should correspond to the size of the implant. However with cemented cups the impactor tip should be 2mm below the size of the cup. This makes extraction more simple. There is greater friction when the sizes of the cup and tip match and therefore the cup can be pulled out of the cement.

Clockwise tightening of the hand draws the expansion rod through the black impactor tip. Tightening the impaction handle expands the inserter. The impactor tip expands gaining traction on the implant.

Set the laser etching to an impaction tip slot.
As can be seen on this slide the slot in the impaction tip does not correspond with the laser etching (A). I would advise when first implanting these cups that these two align as it is easier to orientate the cup when impacting.

Dry the acetabulum, insert cement and pressuriseThere are a couple of tips when cementing the avantage cup.
Firstly do not overfill the acetabulum with cement. Whilst only anecdotal I have found filling the acetabulum completely makes insertion of the implant more difficult. A lot of cement comes out!
Secondly go 15-20 seconds earlier with insertion. I am not sure if it the material or the design of the groves on the back of the cup but inserting the cup at a similar time used in poly cups is difficult. I go in around 3 minutes and 45 seconds (depending on environmental temperature etc).

A screw tightening 45 degree angulation guide can be attached to the impaction handle. This will give an orientation to the ground. To get 45 degrees of inclination the guide should be parallel to the floor (assuming that the pelvis is correctly positioned). I tend to close my cups slightly to 40 degrees as I think this improves stability.

The definitive acetabular component mounted on the impactor is implanted, clearing away excess cement whilst maintaining pressureThe excess cement is cleared away in the standard fashion using a McDonalds. Care should be taken not to have any cement at the edges of the implant. Unlike thick poly cups cement can ‘overflow’ the thin metal cup into the implant.

Remove the impaction handle and then maintain pressurisation with the final impactorThis is something of an artform.
Care should be taken not to move the cup around inside the cement mantle. This is definitely a step that requires focus. With the non-impacting hand, grip the base of the impactor tip. Carefully unscrew the impactor handle (anticlockwise). This allows the tip to contract. A gentle tap on the impactor handle then slides the expansion bolt to the outer rim of the impactor tip (i.e it comes to lie near a position shown in slide 31). The tip is maximally contracted. It can then be removed.
One disadvantage of cementing the smallest cup (44mm) is that there is no 42mm impaction tip. My advice here is not to place the tip fully into the implant before tightening it up.

The final impactor is screwed onto the impaction handle and used to pressurise the cup.It should be placed at the pole of the implant so as not to tip it.
Compared to a standard poly cup, I find the metal shell is prone to movement before cement curing. Be careful and do not move it in the mantel.

Attention is turned to the femur.
This slide shows the femur ‘end on’

Resected bone is used to estimate the initial length of the femoral implantThe resected bone is kept. It can be ‘reconstructed’ on table to get an idea of the amount of bone removed. This can guide the initial size of the trial implant (see next slide)

In this instance it is apparent that even with the head/neck and proximal bone resection, the implant is going to be small. This is the shortest proximal femur trial.

The main focus of this presentation is the dual mobility cup. The use of the Stanmore proximal femur has been covered by others and myself in the following OrthOracle presentations:
Endoprosthetic proximal femoral replacement (Stanmore METS system , Stryker) with trochanteric reattachment for pathological femoral fracture .
Single stage revision of peri-prosthetic hip fracture with Stanmore femoral endo-prosthesis (Stryker) and Trident constrained acetabulum (Stryker),utilising the Zimmer-Biomet Explant and Stimulan bone substitute(Biocomposites).
However, briefly, the slide shows the smallest implant. The femoral resection required to accommodate this is 82mm from the tip of the trochanter (centre of the femoral head) to the base of the collar.

Insert the trial Stanmore proximal femoral stem to estimate approximate length of femoral construct required.The trial was inserted into the unprepared prepared femur following simple lavage.

As can be seen from the image, the trial did not sit down flush with the bone. The stem was impinging in the femoral canal.

The femoral canal is widened using a hand tapered rasp following the initial trial.A comparison of the rasp with the stem of the femoral trial indicated that there would be a sufficient cement mantle upon insertion of the definitive stem. A 2mm mantle is required.

Once the femoral trial is seated well, after reaming, attach the modular trochanter. The trial is modular allowing different offset and sized bodies. These can be used to avoid impingement and to correct leg length and tissue tension.

This image shows the two Avantage trial bipolar head inserts. The blue is the trial femoral head and the green is the trial onlay / insert.
(quick reference – green trial inserts are for 22mm femoral heads and blue are for 28mm)

The Bipolar trial is assembled onto the femoral neck, the head onto the trunion followed by the onlay. As will be seen, the definitive implants are assembled ex-vivo.

The hip is reduced, its stability tested and any adjustments made.The hip is then reduced.
In this instance this was not possible as the hip was too tight and the femoral cut too short.
You can gain an estimate of how much femur to resect by pulling the femur into the reduction position and seeing how far the centre of the trials are away from the centre of the cemented cup. This distance is the amount that needs to be resected.

The femur was further shortened. I start the initial cut with the trial stem still in situ. This gives a guide. The cut should be parrallel to the base of the trial collar.

As can be seen the collar sits better on the femur now the cut has been redone. A trial reduction this time was sucessful.
My principles for achieving offset, leg length and stability have been described on slide 48 of the Link MP revision operative technique on OrthOracle.
Revision Total Hip replacement: Direct exchange Link MP revision stem for periprosthetic fracture

The Stanmore femoral system is comprised of two parts, the trochanter and the collar/ stem, which require impaction to assemble before implantation.There is no shaft. The collar diameter can vary in diameter (27-36mm in diameter) and can be 15 or 30mm deep to add increased flexibility.

The trochanters are not universal and there are left and right versions. Both have 10 degrees of anteversion.
In this instance as the greater trochanteric bone fragments had not been excised, I used an hydroxyapatite (HA) coated implant. In theory this allows bony on-growth.

The implant is ready for impaction. I was not planning on using the trochanter attachment plate which attaches into the two lateral screw holes (A). Instead I tie the troachanter to the HA surface using fibrewire through the trochanter holes (B)

Gauge the depth to which the cement restrictor must be inserted using the trial.When estimating the depth of the cement trial I squash the restrictor to mimick its position in-vivo. Measure against the inferior aspect of the collar.

Impact the cement restrictor to the required depth.This is performed in the standard fashion. A note however, with a proximal femoral replacement, many of the stem tips lie at the level of the femoral isthmus. Over-zealous impaction can push the cement restrictor past the isthmus into the flare of the diaphysis. The ability of the restrictor to then prevent cement migration down the stem is reduced as is corresponding cement pressures.

Wash and dry the femoral canal and then insert the cement.Remember to warn the anaesthetist prior to cementation. As the canal is relatively narrow, and the cement gun tip relatively wide, cement pressures can be high.

Insert the femoral implant, ensuring there is no impingement of the neck on soft tissues, and ensure approximately 20 degrees of anteversion of the neck.. Ensure that the patients leg is vertical in the legbag.

Build the press to allow impaction of the femoral head into the polyethylene insertThe base plate (A) is slid onto the forks (B).
Note the elevated rim on the base plate (C)

The adjusting knob (A) is tightened over the elevated rim, forming a stable unit.
The black lug (B) will take the femoral head

Place the femoral head on the black lug of the press.

Place the insert over the femoral head and tighten the press screw until the impactor engages the polyethylene.It is important to ensure that the flat surface of the insert stays parallel to the floor. If it twists the femoral head will not be inserted into the polyethylene.
The op tech states that a ‘pop’ should be heard as the femoral head is driven into the insert. In practice this is often two ‘pops,’ the second is most likely just a feeling transmitted through the handle. This indicates that the femoral head is truly in the insert.

Before implantation check that the femoral head is freely moving within the insert.

Impact the bipolar head on the trunion using the head reducer and then reduce the hip in standard fashion.

Once reduced confirm the range of movement, stability, offset and abductor tension. This should not differ from the trials but it is important to confirm.

Reduce and suture the trochanteric fragments back onto the implant using a heavy gauge Fibrewire suture.To hold the trochanter fragment I use fibrewire suture and this needs to be be pulled through the trochanter. I use a straight monocryl needle which is inserted blunt end first through the holes on the trochanter. A loop of monocryl is made and fibre wire is passed through the loop.

The fibrewire is fed through the trochanteric holes by pulling the needle and moncryl back out through the trochanteric holes (A). This pulls a the fibrewire completely through the trochanteric implant (B)

Clip the Fibrewire then repeat the process.

Pass the needle of the fibrewire deep and anterior to the trochanteric fragment.
The passing of a needle through bone (if required) is made much easier if diathermy is placed on the needle.

Firmly tie the fibrewire to complete reduction.
Reduction can be aided by pulling the trochanter fragment with forceps. The trochanter overlies the HA coating.

Close the posterior structures (capsule, and external rotator muscle mass). It was impossible to identify individual muscles, however palpation of the sciatic nerve at all times protected this.
Closure was finished with a fascial, fat and subcuticular suture and finally glue.

Post op radiographs show that the implant is seated well on the femoral cortex. The hip is reduced and the trochanteric fragments remain attached to the implant.

The lateral view shows the asymetrical Avantage cup. The overhang design is apparent anteriorly on the lateral. This is normal.