Stryker Omega Dynamic Hip Screw for extra-capsular neck of femur fracture

This plain AP radiograph shows a left pertrochanteric hip fracture. It is seen in this case that the fracture is an 31A2.2. There is varus deformity of the neck and the lesser trochanter is displaced

The lateral view shows the external rotation of the femur on the neck. There is no significant displacement, only a rotational deformity (follow the anterior neck from the femoral head and neck. There is an obvious ‘gap’ where the femur has rotated laterally).

Following transfer to the fracture table a padded post is inserted into the fracture table and the patient is positioned such that the post is in contact with the pubis. Care is taken in males to avoid scrotal trauma.

A significant number of patients have dementia and we have found that the hands can often migrate down to the frature site during surgery. To avoid this we use a sling as shown . To the base of this sling, a cord is attached and tied to the table rail. This inhibits the patient getting their hand down to the lateral side of their thigh.

The velcro straps are tightened. It is important that the foot is firmly in the boot, the heel should touch the metal plate. This is often easier if the foot plate is positioned as in the image (i.e. foot plate in ‘equinus’). It can be moved after the foot is secured with a bandage

Finally, as significant traction with be placed on the lower limb it is important that the foot is secured. We use an additional bandage to sure the foot.

All fracture tables are different but principles remain.
The set up of the fracture table is important. As two DHS operations were taking place in tandem in our trauma theatres, we used the fracture table donated to the hospital when it converted from the workhouse to a hospital in 1906.
It is also important that it is the registrar who has to bend down close to the retaining post. This is a consultant free area.
There are many ways to position the non affected hip. I use a foot plate and flex and abduct the hip (the lithotomy position). It is essential that the foot plate lock on the non-affected side is loose when this manoeuvre is attempted to reduce stresses across the knee. Alternative foot supports are available.

The 3D position of the lower limb can be altered with a series of locks. The locks should be arranged so that the arms of the table are initially taken medially. By doing this they do not get in the way of fluoroscopy. The slide shows the bars when so positioned, leave the hip imaging unobstructed.

Once securely positions the lower limb is internally rotated. The patella should be at a minumun, parellel to the floor. This corrects the external rotation of the femur seen in slide 2

It is next important to ensure that the fluroscopy arm is able to move around the patient to obtain an AP and lateral image of the hip.

This is the initial image of the hip, taken in the AP plane before traction is applied. There is disruption of the distal end of Shenton’s line. Shenton’s line is an imaginary line drawn along the inferior pubic ramus and the inferior border of the femoral neck.

Following traction the reduction is improved. In this image it can be seen that reduction is not 100% perfect. Attempts should be made to improve reduction as much as is possible, in this case they were. Most fractures will reduce with traction, internal rotation and adduction.
Occasionally fractured require an open reduction. In my experience these tend to the fractures with a larger medial component (either attached to the head or separate) As noted above, medial buttressing is required for DHS stability. Blunt dissection is required both anteriorly and posteriorly. Haygrove bone holding forceps are useful to hold reduction. I personally use simple (and cheaper) Charnley wires to hold the reduction.
In this case a 135 degree plate was used. Others (130-150) are available. Another guide pin insertion guide is used for these plates.

One way of assessing whether the longitudinal traction is satisfactory is to assess an imaginary line drawn at right angles to the long axis of the femur at the greater trochanter. This line should intersect the centre of the femoral head.
Correction of reduction with adduction, internal rotation and longitudinal traction should all be used to maximise hip reduction. It is not always perfect and it is experience that will determine when good reduction is good enough. In this instance (in retrospect when formally analysing) another 2-3mm of traction would have improved the reduction

This image shows correction of external rotation of the femur.
The superimposed lines shows the neck.

The non-injured leg is wrapped in a forced air warming blanket and the patients torso is similarly draped. Hypothermia during surgery is associated with increased morbidity and mortality.
There has been some recent evidence that forced air warming increases the risk of surgical site infection. Ongoing multi-centre randomised controlled trials (Reducing Implant Infection in Orthopaedics (RIIiO)) are ongoing addressing this question.

A self adhesive sterile exclusion drape is then applied. The sterile sheet should be centred 5 cm below the tip of the trochanter. Note distal extension may be required and the drape should not be placed to cephalic.
In very large legs it is important not to place the drape too posteriorly.

The drape is then passed over a bar and stuck down. This needs assistance. Note lack of watch and lanyards.

An aid to centralising the incision is relatively simple.
Firstly, a guide pin is placed anteriorly on top of the hip joint and a fluoroscopy image is taken.

The pin should approximate along the neck of the femur.

The pin is then ‘rolled’ around the thigh until it is vertical. It can be marked with a skin marker or simple pressure leaves a temporary indentation.

The anterior and posterior borders of the femur are then palpated. The incision should be approximately 2 cm above the guide pin mark and approximately 5 cm below it in the the mid point of the femur.

Skin and fat incision follows and haemostasis is achieved.

The facia lata is incised.
The next step includes exposure of the lateral border of the proximal femur.
There are two methods of obtaining this. The first is to split vastus lateralis and a combination of diathermy and blunt dissection exposes the bone. This was the method used in this situation.
The second option involves inserting a Trethowan (Ring handled spike) at the posterior border of vastus, advancing the lever medially and anteriorly over the anterior femur. The spike is elevated and dissection occurs at the interval between the posterior border of vastus and the IM septum. Post-operatively the muscle reamains intact however dissection is more prone to encountering the perforators which, if inadvertently cut before quarterisation, may retract into the posterior compartment of the thigh and be difficult to locate. These can bleed profusely. Therefore careful dissection is essential and perforators much be quarterised before division.

The guide pin guide is placed firmly on the lateral border of the femur. In the AP plane, care must be taken to ensure the insertion is in the midpoint of the femur. It is also important to ensure that the guide is placed ‘flush’ on the femur. A common mistake is to have the most cephalic part of the guide either ‘off’ the femur or have soft tissue trapped underneath it. This will effectively initially result in elevation of the neck shaft angle. Once the fixed angle plate is then attached to the lag screw, the hip will be forced into varus. This has the effect of increasing the lever arm of the hip, increasing the joint reaction force. These forces, if high enough, will clinically manifest as either malunion or more catastrophically non union and implant failure.

This is a simple image of the guide pin and guide. Of note, the guide has 5 holes. If positioning of the initial pin is incorrect (too superior, inferior, proximal or distal) BUT correctly angled a second pin can be placed to optimise the guide pin insertion. The secondary holes are spaced at 5mm.

The guide pin is advanced under fluoroscopic guidance

Once across the fracture the image intensifier arm is swung around to assess the lateral positioning

As can be seen here, the entry point of the pin is correct but the pin has been aimed too anteriorly.

The pin must be withdrawn fully before correction is attempted.

Failure to withdraw fully can result in the guide pin following it’s initial trajectory.

Finally, correct placement is obtained.

The optimal position of the pin and ultimately lag screw has been widely studied. The seminal paper by Baumgaertner et al described the ‘tip apex distance (TAD).’ This is the sum of the tip of the screw to the apex of the head on the AP and lateral films.
This study reviewed 198 pertrochanteric fractures. Those that failed by cut-out had a mean TAD of 38mm. None of those with a TAD <25mm failed.
The Value of the Tip-Apex Distance in predicting Failure of Fixation of Peritrochanteric Fractures of the Hip. Baugaertner et al 1995 JBJS (Am)

Back in the AP plane the pin is advanced.

Unfortunately the guide pin here has been inserted too far. This has resulted in penetration of the joint. This increases risk of chondrolysis. As will be seen in the following slides, the guide pin tends to follow this tract during subsequent instrumentation.

The guidewire is withdrawn. It is important to read the operation technique for each companies kit. For the Stryker kit it is stated that the wire should rest in the subchonrdal bone in the ‘centre’ of the hip.

The depth gauge is then slid over the guide wire and advanced until it touches the bone on the lateral border of the femur. It is important to ensure the guide rests on bone before reading.
Again the reading and length of lag screw required differs between companies.
For the Stryker kit is recommended that for reaming, the triple reamer is set 10mm less than the depth guage reading
Each company will recommend a method for estimating the length of lag screw required. It does differ if compression is required and Stryker state that the estimate of compression required is estimated from fluoroscopy images (in practice this is not simple).
Therefore in a worked example. If the depth gauge measurement was 120mm. Reaming should be to 110mm. If no compression was required, the screw length should be 110, if 5mm of compression was required the screw should be 105mm.
Whilst reduction is very important, significant compression is rarely required.
Firstly all attempts at reduction should decrease the amount of displacement at the fracture site.
The second and most important reason is the mechanism in which the lag screw and plate function. The screw is designed to slide (hence sliding or dynamic screw). However (as is seen in slide 63) this slide is controlled. The screw cannot rotate, or move in the varus / valgus or anterior / posterior plane but dynamises along it long axis. Therefore with weight bearing, the effect of body weight in combination of controlled dynamism results in fraction impaction.

The depth gauge is standard.

The triple (or combination) reamer consists of 3 parts, a reamer drill and a two part barrel reamer.
This reamer produces a ‘channel’ with three different diameters. (hence a triple reamer)
The diameter of the reamer drill is the same as the shaft of the lag screw.
The diameter of the barrel reamer is the samle as the barrel of the DHS plate.
The flare of the barrel reamer (A) accommodates the junction of the barrel and lateral thigh plate.
Construction of the triple reamer is simple but the mechanism needs to known.
There are two sizes of barrel reamer, a short and standard. Short barrels (and corresponding short barrel plate (25mm)) are used when a lag screw of 80mm or less is used. If a longer longer barrel (38mm) is used in these instances, the threads of the lag screw may impact against the barrel during dynamisation and impaction may not be achieved.
Another indication is a very lateral fracture. The barrel should not pass across the fracture site.

The 2 parts of the barrel are simply screwed together.

The drill is passed into the barrel reamer. It will only engage if the flat slide of the reamer is aligned to the flat side of the drill (A and B)

The barrel can then slide to the required reaming depth. (here indicated at 120mm, A). The barrel reamer is however free to move.

The barrel reamer is locked to the drill by turning the locking the stop sleeve (A) counter clockwise. The visible or proud section of the stop sleeve (seen in the previous slide) is hidden (locked) as the stop sleeve moves proximally, away from the barrel reamer (B)

Once the reaming depth is known and set, the triple reamer is advanced over the guide pin. It is essential to follow the ‘line’ of the pin, changing the angle of the reamer can result in fretting or more significantly, the pin may be driven into the pelvis.

The triple reamer is advanced (on full power)

Fluroscopic review of reaming is required to ensure that the pin is not advanced into the pelvis.

This image shows the ‘flare’ of the barrel reamer engaging bone from the lateral femoral cortex. This is required to allow the junction of the the barrel and the plate to sit ‘flush’ to the bone.
Again the guide pin has advanced into the joint. This required frequent resets, pulling the pin back.

If the guide pin is withdrawn along with the triple reamer the re-insertion device can be used to re-insert the guide pin.
This device can also be used to place parallel wires within the femoral neck to act as derotation (anti-rotation) wires, preventing rotation of the head during reaming or tightening of the lag screw.

To re-insert the wire, place the guide into the reamed lateral femur and then insert the wire.

It doesn’t always work. Fluoroscopic confirmation is important.
As a quick note, to remove stuck guide pins from the triple reamer, grip the tip of the pin with a Kockher and power the reamer, pulling the pin out of the reamer.

The lag screw instrument assembly consists of an inner and outer lag screw adaptor (A,B), the lag screw (C), a lag screw inserter (D) and a lag screw inserter sleeve (E). The T-handle (not shown) attaches to the lag screw inserter.

The inner lag screw adapter is placed inside the outer adapter. It will advance approximately halfway and needs to be screwed through threads inside the outer adapter. Once past these it slides out. The ‘teeth’ of the outer adapter sleeve are slotted into the slot of the lag screw and the inner lag screw is tightened.

The T handle is attached to to the lag screw inserter which is passed through the lag screw inserter sleeve and over the lag screw adapter. The adapter and inserter are slotted and you will feel the lag screw ‘sit home.’

Most likely you will be passed the finished article by your scrub nurse, however you should know how to construct it.

For dense bone, a tap should be used. I would recommend an anti-rotation wire is inserted initially. The tap should be advanced to the reamer depth setting.

Occasionally the guide pin will advance even if the initial positioning was correct, the subchondral bone may be osteoporotic. Therefore fluoroscopic imaging is required to view progress. (the guide pin here again is advancing!).

Compression across the fracture is achieved on final tightening of the lag screw. For a 135 degree standard plate the lag screw inserter assembly as advanced until the 135 degree ring indicator (A) reaches the ‘0’ mark on the inserter. (confirm that the inserter is firmly engaged in the lateral cortex of the bone). If 5mm of compression is required the ring mark is advanced to the 5mm setting. This can be screened on fluoroscopy.
In practice I have never downsized a lag screw if 5mm of compression was needed and I have sized my lag screw based on ‘no compression.’

The screw is advanced until it is in subchondral bone. Position again is checked on the AP and lateral views. Remember the tip apex distance is important.

A potential disaster is shown on the AP. The fracture has moved. The bone was not particularly sclerotic, but perhaps the the fracture pattern was more basi-cervical than initially appreciated, however, whatever the reason this position is unacceptable. The fracture is not reduced and the biomechanics are not restored. This fracture, if left, will continue to migrage.

Displacement is more likely in left sided hip fractures. This is due to the direction of tightening and the anatomy of the hip ligaments.
For a RIGHT hip, clockwise movements tighten the ileofemoral, pubofemoral and ischiofemoral ligaments which resist displacement. The opposite is true of a left sided hip replacement.

To correct the displacement the lag screw was turned 1/2 of one rotation anticlockwise. This did improve the reduction. However this does not always work, so if in doubt, add an anti-rotation pin.
In practice therefore, anti-rotation pins should be used for basicervial / comminuted fractures, sclerotic bone and where a tap is going to be used. They also may be of use when there has been posterior ‘sag’ of the femur on the neck. The femur is pushed from below and held to the neck / head with pins.
As mentioned earlier additional pins can be inserted with the guide, however in practise I freehand an anti-rotation pin 1.5cm above my guide pin and aim to skirt the superior femoral neck. The anti-rotation pin should be parallel to the guide pin and far enough away so as to not get in the way of the barrel reamer or lag screw.

The handle of the lag screw assembly for the Stryker Lag screw should be left horiontal to the floor. This allows engagement of the plate (see next slide)

This is a demonstration screw and plate. Looking down the barrel of the plate it can be seen that the internal shape of the barrel is not circular. It has 2 flat sides. The lag screw has 2 similar flat sides. For the plate to slide over the screw the 2 flat sides must be aligned. When the insertion handle is horizontal to the floor, the flat sides of the screw are in a also horizontal to the floor.

The plate is slid over the wire and lag screw adapter and engages the lag screw. In cases where the patient is obese or where the skin cut is not large enough the plate can be inserted 180 degrees to those shown above. the plate is then advanced until it engages the plate (i.e moved close the femur) and the re-spun 180 degrees. (clockwise for right hips, anti-clockwise for left hips).

Soft tissue must be cleared from under the plate. Trapped vastus will necrose, increasing infection risk.

The plate is gently ‘knocked home’ using the impactor.

The impactor comes in two parts and is simply screwed together. It is cannulated and fits over the lag screw adapter. The plastic end is bevelled at 45 degrees (the angle formed between the lag screw adapter and the plate).

The plate is finally positioned along the femur. For short DHS plates it is usually obvious that the plate is sitting on bone for its whole length. However with longer plates this is sometimes difficult, be sure to check the distal end.
If there plate is not ‘too’ long, the wound can be extended and the plate palpated. For long plates and minimally invasive plate osteosynthesis (MIPO, ie screws filled with distal stab incisions) the plate should be visualised on fluoroscopy.
If the plate is proud, either anteriorly or posteriorly, it will irritate surrounding structures and obviously will not contribute to stability if screws in the distal hole do not pass through the femur.

Confirm the plate is flush to the bone with an AP fluoroscopy image.

On the Synthes system the screws are 4.5mm and are self tapping. A 3.2m drill is used.
For very osteoporotic bone, locking screw adaptors and 5mm unidirectional locking screws are available.

Once drilled, use the depth gauge to measure the length of screw required. I would focus on the angles created with the depth gauge. These should be recreated when inserting the screw. If the angle of screw insertion is incorrect, the screw may not engage the medial cortical drill hole correctly. This can lead to blow outs. If this occurs with the most distal screw, torsional strength of the femur can be significantly compromised.

The Stryker op-tech states that the most proximal screw is inserted first. I do not do this..
I start with the most distal screw. Firstly if you are ‘on bone’ distally, the rest of the plate will be on bone.
Additionally, the forces required to seat the plate are reduced as the lever arm is longer.
This is an example of a type I lever. The load is the lag screw and femoral head / neck, the fulcrum is the pivot in the lateral femur where the barrel meets the plate and the effort (force) is the action of screwing home the plate with the screw. The load and fulcrum remain constant. Shortening the lever arm requires greater force to screw home the plate. In osteoporotic bone this force may be greater than the pull out strength of the bone. The threads of the screw are then stripped. A ‘spinning’ screw will not add to stability.
A basic review of levers and some basic orthopaedic biomechanics are reviewed in the following website; http://www0.sun.ac.za/ortho/webct-ortho/physics/biomechanics.html

I personally do not then drill all of the remaining screw holes as there is a risk of fracture doing this. Studies have shown that circular defects act as stress risers. It may be that a single defect representing less than 10% of the diameter of the femur has no effect but multiple holes may do. A 20% defect has been shown to cause a 34% decrease in torsional strength. Remember as part of the set-up, the lower limb is already stressed secondary to the internal rotation through of the ankle.
If a ‘blow-out’ occurs in the distal most hole the extent of the defect needs to be assessed. If it is minor and close to the original drill hole, a cancellous screw could be used. If however the defect is large I would change the plate to a longer one. The length of the plate needs to be sufficient so that the most distal screw is ‘two coritcal diameters’ below the blow out. (i.e measure the width of the femur at the site of the defect and the distal screw needs to be 2X this measurement).
Torsional strength reduction due to cortical defects in bone. Ederton et al JOR 1990

The remaining screws are inserted, one-by-one.
There maybe some evidence that divergence of screws decreases ‘pull out’ failure however in clinical practice, with modern DHS screws I have not encountered this problem (if the DHS is used for the correct fracture pattern).
Additionally when I started training, the most distal screw in the plate tended to be a unicortical screw. This was thought to decrease the stress-riser. I have not seen this used in ‘modern’ times.

Once all the screws have been inserted, they are all sequentially tightened again. To indicate that they are fully tightened, the SpR must release ‘the registrar grunt’ indicating to all around that the screws are as tight as humanly possible.

After insertion, lavage and confirmation of haemostasis is performed. Lavage is a very important part of this operation. We do not use pulsed lavage as standard with DHS surgery. Saline will suffice, however a quick ‘swill’ with a 50ml syringe is not enough. I commonly use at least 500ml minimum. The mortality rate of an infected DHS in this elderly population is extremely high.
The fascia is closed. ‘Bites’ need to be large enough to get an adequate grip. The underlying vastus should not be caught in the suture. One simple method to avoid this is shown in the slide.

This depth of suture is too large. This leads to over-tightening of the fascia and can lead to chronic lateral thigh pain.

I still perfom a 2 layer fat closure. Complications from haematoma are high and closure of the dead space is important.
We use subcuticular monocryl to close wounds (there is less for the ‘pickers’ to go at). We also use glue.
In patients deamed to be high risk of wound complications (Diabetic , on immunosuppression, morbid obesity) we would contemplate a PICO type dressing applied in theatre.
These are not designed to remove and retain excess fluid (as in a suture line VAC) but instead, in the setting of a closed wound, increase the blood flow to the surgical site.
Whilst there have been some studies analysing their effectiveness, to my knowledge there is no study investigating complications following wound closure in fractured neck of femur.
I have never used a drain for a DHS.

For ‘standard patients, the final dressing is an Aquacell which provides a good seal and is very absorbent

A final top-tip to avoid the wrath of the trauma sister is to cut off the waste bag on the DHS drape and dispose of this before removing the remaining drape from the patient. The ‘drastically’ reduces spillages and subsequent negative personal outcomes.

This is the final postition of the fracture after DHS insertion.
The neck is reduced in an acceptable position. As part of the fracture pattern, the lesser trochanter remains mobile and has migrated. This should be taken into account when objectively viewing the post-op films.
The plate is flush to the bone, the Tip-Apex distance in this film was <25mm

An AP film of the plate is also taken. Here it confirms that ALL the screws have passed through bone. The most proximal screw initially looks ‘short’ however as can be seen there is no drill hole medial to the tip of the screw. Therefore the screw is not short but has been angled. The distal screw is not overly long.

A lateral view of the head is also taken to confirm screw position.
The most stable position of the screw is ‘centre-centre’ on the AP and lateral views.

Finally for completion a lateral of the plate can be taken. In practice I rarely do this as it is seen clinically during surgery.