Cannulated Hip screws (Asnis III – Stryker) for fixation of intracapsular neck of femur fracture

This patient presented following a fall. The left hip was symptomatic with pain upon attempted weight bearing. The examination reavealed a ‘suprisingly’ near normal range of movement but there was pain at the extremes. However axial loading was tender.
Two main classification systems for intracapsular fractured neck of femur have widespread attention. Garden and Pauwel’s. Both have pros and cons.
The Garden classification is made from the AP views only. Whilst grade I-II (undisplaced – minimally displaced) may guide you to whether cannulated screws may be possible, the classification does not take account of the lateral radiograph which may show displacement (and hence disruption of the blood supply).
Pauwel’s classification is based on the angle of neck fracture in relation to a horizonal axis. I <30, II – 30-50 and III >50 degrees. Type III are more common in younger patients and are biomechanically more unstable.

Ref: An update on Pauwels classification. Shen et al Journal of Orthopaedic Surgery and Research 2016;11:161

As can be seen on the lateral radiograph, no fracture is apparent.
The lateral view is important as angulation or displacement here indcates that the blood supply to the head may be at risk. I am not going to teach you the blood supply to the femoral head (this is a favourite exam question so look it up) but it comes from 3 main arteries; the medial and lateral circumflex arteries and (in children) the obturator artery via the ligamentum teres. Each supplies an area of the femoral head (which will be tested). Disruption of these vessels leads to osteonecrosis.
Speaking of osteonecrosis, the incidence of osteonecrosis for a displaced neck of femur fracture (Garden III or greater) in the elderly is above 50%
Ref: Management of femoral neck fractures in young adults. Thuan et al IJO 2008:42(1);3-12

An MRI was undertaken. The T2 image is the most useful. This does show bone oedema transversing the neck of the femur.
Our decision was therefore to fix the fracture with cannulated screws.
‘Back in the day’ these fractures, or more accurately the valgus impacted intracapsular neck of femur fractures, were treated non-operatively. However failure in this group ultimately lead to a requirement for ‘complex’ hemiarthroplasty. This procedure is not simple with patients having suffered shortening and contracture, making leg length restoration and stability more difficult.
Currently the majority of minimally / non-displaced fractures are treated with either a short plate DHS or cannulated screws.
Secondary displacement is frequent (up t0 46% in some studies) and may be unpredictable.
Ref : High secondary displacement rate in the conservative treatment of impacted femoral neck fractures in 105 patients. Verheyen et al, Archives of Orthopaedic and Trauma Surgery 2005;125:166–168
Ref: The Management of hip fracture in adults (https://www.nice.org.uk/guidance/cg124

The set up in theatre is as for a DHS, however less traction is used. The thigh is still internally rotated.

The fluoroscopy image still does not reveal a fracture (or iatrogenic displacement!)

The C-arm must have clearance and the hinges on the table should not impede the images. As can be seen on this image, the hinges are all ‘medialised.’ The post holding the foot needs to counter the ‘medialisation’ and the foot post is lateralised. (take a look at your own table to see how this is achieved)

The C-arm must also be clear to swing through for a lateral. It can often catch on the table and must be set up correctly before the patient is prepped.

The lateral view does not show any displacement. For those in which the femur is displaced upon the head the Leadbetter manoeuvre has been reported (there are many others in the literature).
However with displaced fractures, before any reduction procedures are attempted it is very important to review the fracture for areas of comminution (obviously this should be done in the planning meeting but on plain radiographs this is not always apparent). Posterior comminution (and hence loss of a significant butress) is associated with non-union. If posterior comminution is noted pre-operatively or after any reduction procedure, I would strongly recommend reviewing your planned surgery and consider the requirement for a hemiarthoplasty.
The problem is ‘how much’ comminution is acceptable. It is difficult to categorise this but as a guide, if there is mild loss of the posterior butress and perfect reduction cannot be achieved I would convert to a hemi, no matter how much ‘pressure’ comes from the nursing staff or anaesthetic colleagues. Revision of cannulated screws is not necessarily simple and straightforward. It is a lot ‘riskier’ operation in an already frail patient.
Varus angluation and inferior displacement are also associated with poor outcome and non-union. The bottom line is get very good reduction. This may need to be open.

Whilst on the topic of getting good reduction the most commonly quoted manoeuvre is the Leadbetter which is as follows:
The hip is flexed to 90 degrees and adducted, relaxing the muscles around the hip and disimpacting the fracture. Traction is applied and the hip is then internally rotated (relaxing the anterior capsular ligaments). With traction and internal rotation maintained, the hip is extended and adducted. – I am not sure Leadbetter was familiar with the habitus of the majority of my elderly patients.
In practical terms longitudinal traction with lateral traction (from a bed sheet) followed by internal rotation generally results results in good reduction and often little more is required.
I fully accept publications stating that anatomical reduction is paramount however I would be willing to accept valgus impaction providing (and this is important) that there is no displacement on the lateral views and the posterior column is not fragmented.
In summary there are various described closed techniques for reduction though I am not sure of the validity of many. As a junior trainee, I would ask your seniors which works for them. There is also no substitute for practical exposure to difficult reduction techniques.
For young patients it may be necessary to perform an open reduction, in the (very rare instance) I have had to achieve this I have used a Watson-Jones approach between TFL and Gluteus Medius down to the anterior capsule. A ‘T’ incision of the capsule allows visualisation of the fracture. A Smith-Peterson anterior approach can alternatively be used. I would only consider open reduction in the young trauma patient. In elderly patients, a hemiarthroplasty should be considered in the presence of a displaced and difficult to reduce fracture.
Also timing of surgery is often discussed with these injuries. A displaced intracapsular fracture in young patients should ideally be fixed the same day. However for those patients presenting in the late evening, first on the trauma list with staff who are familiar with orthopaedics (not the night general on call team who don’t know where anything is) suffices.
Anyway, back to the surgery…the patient is prepped and the exclusion drape is applied (as per DHS presentation).

Ensure that the C-arm can get into position without tearing off drapes.

This operation relies on a series of 3 lines drawn on the patient prior to the surgical incision.
The first ‘landmark’ to find is the lesser trochanter. Entry of screws below this line increases the risk of periprosthetic fracture.

The fluoroscopy image is taken with the pin (guidewire) for the screws perpendicular to the long axis of the femur.

It can be seen here that ‘slack’ in the drape is important, the C-arm can peal off the drape if it is too tight.

Once the position of the wire is confirmed radiologically, a skin maker traces the position of the pin.

The pin is then moved to ‘aim’ up the inferior border of the neck. Note the proposed entry point still remains above the lesser trochanter.

This line is then traced out. The final line is the ‘mid femoral line’ of the femur which is felt with palpation.

A scalpel is used to make a stab incision where the mid-femoral line and ‘neck’ line intersect.

Blunt dissection to the bone is followed by inserting the pin guide.

This is confirmed radiologicaly. Note the guide should be on bone.

I find it easier to manually feed the pin through the pin trochar. It can be moved superiorly and posteriorly to confirm it is in the centre of the femur in the AP axis.

The pin is mounted and advanced under fluoroscopy guidance.

It should ‘skirt’ the inferior border of the neck.

A 3D appreciation of the anterversion of the neck is important. If on the lateral the neck is anteverted then ‘drop’ your hand.

Check progress with the C-arm.

Once in situ the initial pin acts a marker for the remaining 2 pins.

On the kit, the parallel pin guide device needs assembling. It simply screws together.

Slide the pin over the static, fixed arm of the guide. The mobile 2nd guide can be moved, increasing or decreasing the distance between the two arms.

An imprint into the skin is made with the guide, it can be on or slightly anterior to the mid-femoral line.

Again a stab incision is made with blunt dissection to bone.

The guide is advanced. An idea of the position of the pin trajectory can be made using fluoroscopy.

The second pin is advanced.
The ‘best’ bone is located at the periphery of the femoral neck and the pins should be targeted here. There is a pin guide with the set that has pre-determined pin holes, however in my opinion these are too close together and do not target the stronger bone. 3 screws in the middle of the femoral neck are not stable.
It is my opinion that 3 screws are required however there are endless papers regarding the number of screws and their configuration.

A lateral view is essential.

The final stab incision made midway between the first two incisions, below the ‘femoral line.’

Final blunt dissection is made to the bone.

Again the parallel pin guide is used.

The wire is advanced

A final lateral image is taken.

Each screw is measured, for the Stryker, ASNIS screws this is a direct measurement (ensure the measure is on bone).

There are two types of screws available (I use 6.5mm diameter screws). Both have the same diameter and pitch, however the length of the threaded portion differs. The screws are available in either 2o or 40mm. Choose the longest thread length which still ensures that the threads are entirely in the femoral head. No threads should cross the fracture site. There has been some study into whether a fully threaded posterior screw would prevent fracture collapse. To my knowledge this has not been proven.

Although the operative technique states that the lateral femoral cortex does not need over drilling in my opinion I think it does. The lateral femoral cortex drilled using the supplied 4.9mm cannulated drill.

The screws are then advanced. If compression is required (rarely) the screws should be 5-10mm less than the measure.
Younger patients do not need washers but they may be useful in more osteoporotic bone. As a rule you will unlikely to get all screws to have a washer often the washer impinges against a screw head. If the patient’s bone is so osteoporotic that no hold is possible the fixation will fail. Convert to a hemiarthroplasty. For those somewhere in between it is essential to monitor closely post operatively for signs of collapse.
Current guidelines would suggest that in young patients follow-up to observe for osteonecrosis is for 3 years.

The screws should be tightened with the appropriate registrar grunt indicating ‘super good’ hold.

Confirmation that all screw heads are abutting the lateral femoral cortex is essential.

Once confirmed the pins can be removed.

This lateral view shows all screw heads down on bone.
The wounds are simply closed with monocryl and glue.