Proximal femoral varus osteotomy using angled Blade plate fixation

Surgery can be performed in supine or lateral position. Lateral position allows easier access to the proximal femur and retraction of tissues. A back rest/prop and anterior sand bag are ideal. The patient does not need to be held ‘rigid’ by the props.

The operative limb is prepped and draped free to allow movement. Prep as far as the iliac crest. Mark out the greater trochanter.

The skin incision is in the mid lateral plane extending from the tip of the trochanter for a distance of approximately 10cm. Sharp dissection down to the tensor fascia lata which is then split.

Any bursal tissue needs to be divided to allow good visualisation of the greater trochanter and vastus lateralis. The posterior border of vastus lateralis and the insertion of gluteus maximus should be easily visible.

One of the advantages of the lateral position is that the leg can be held internally rotated by the assistant. This improves visualisation of the vastus lateralis.

The femur is approached by reflecting vastus lateralis forwards. It is detached in an ‘L’ fashion with one limb at its insertion/origin from the ridge on the greater trochanter. This is at the level of the apophysis. The distal limb is along the posterior border of vastus leaving a small cuff of tissue for repair.

As the vastus is elevated it is important to identify and coagulate perforating vessels that run close to the bone. These are best identified by blunt dissection when one is close to the origin of vast us posteriorly to the bone. If they are inadvertently cut before being coagulated they have a tendency to retract into the posterior compartment and can then be difficult to access. The first perforator is roughly at the level of the lesser trochanter.

Once the vastus has been elevated the peritosteum will be visible over the lateral aspect of the femur. In children this is often a thick layer. A longitudinal incision is made in the periosteum with a size 15 blade. A periosteal elevator is easily inserted and it should be possible to elevate the periosteum circumferentially around the femur as an intact sheet.

Homann retractors or Lane’s levers are placed anteriorly and posteriorly around the femur underneath the periosteum. Aim to place them just above the lesser trochanter.

The image intensifier ‘C’ arm is next introduced. This is best done in a horizontal position. After draping it is guided in from the foot of the bed. In this position one naturally obtains an AP view when the patient is in a lateral position.

By flexing and abducting the hip a ‘frog’ lateral view is easy to obtain.

Various implants are available for stabilising proximal femoral osteotomies. Modern locking plates are easy to use because they have cannulated screws. Historically blade plates were the most popular implant and still have a role. An amount of finesse is required to insert the seating chisel but the plates are strong and stable (and relatively cheap).
The first step is to insert a guide wire.

The guide wire (typically 2mm) is inserted bearing in mind that there needs to be sufficient room for the seating chisel underneath.
In most instances the aim is for 20-25 degrees of varus. The neck-shaft angle should not be reduced to below 110 degrees. Therefore more correction will be possible in a hip where there is relative valgus and less if varus. Ultimately enough correction is needed to allow containment. This will usually have been determined by performing an arthrogram prior to the osteotomy procedure.
If a 90 degree implant is used the guide wire should be inserted at 70 degrees to the lateral shaft of the femur.
Generally, the guide wire will be inserted approximately at the level of the apophysis.

Place the hip in frog lateral position to obtain lateral projection. The guide wire should be approximately in the centre of the femoral neck.

A track has to be created in the femoral neck for the blade plate. This is achieved using a seating chisel.
The standard seating chisel is not cannulated although cannulated versions do now exist. It is imperative that the seating chisel is inserted accurately since once a track is created it is very difficult to alter later on.
There are various profiles depending on the size of the patient. For adults a ‘U’ profile chisel and plate should be used. For children and adolescents the ‘T’ profile is more appropriate (as shown).

The seating chisel is inserted just below the guide wire. Care must be taken to judge flexion and extension since once the outer cortex has been breached it is very difficult to alter angle of insertion in this plane. Varus/valgus and direction in the lateral plane can be altered to an extent so repeated imaging should be performed as the seating chisel is advanced.

In young patients the seating chisel can easily become stuck in the bone. Intermittently backing it out slightly with the slap hammer is a good idea.

Confirm positioning in the lateral view.

Prior to performing the osteotomy 2 guide wires can be inserted parallel to each other. One is percutaneous in the femoral shaft and the other in the proximal fragment (greater trochanter). This allows rotation to be judged. Generally no rotation is required and the aim is for pure varisation.

Insert homan retractors in front of and behind the proximal femur at the level of the osteotomy. The retractors should be inside the periosteum. and usually just above the lesser trochanter.

Do not make the osteotomy too close to the seating chisel. If this occurs there is risk that the blade will cut out of the bone. Make the osteotomy parallel to the blade of the seating chisel approximately 1-1.5cm below the blade and aim just above the lesser trochanter. Do not complete the osteotomy and aim to leave a few mm of bone and periosteum intact medially.

The size of plate will depend on the size of the bone. The length of the blade can either be read off the seating chisel or by measuring the guide wire. The blade should not cross the physis.
90 degree blade plates have an offset. This varies between 8mm and 15mm. This causes some medialisation of the shaft which is often desirable in neuromuscular patients. In Perthes disease an increased offset results in slight shortening of the femoral length. Use the minimal offset if possible.

Try to avoid levering the osteotomy open with the seating chisel as this will cause it to become loose and make accurate insertion of the implant difficult. The osteotomy can be opened using a laminar spreader but be careful not to crack the bone in the proximal fragment.

As the seating chisel is removed slide the blade plate along the track created. This should occur easily. If there is resistance check with II to ensure that a false track is not being created. The plate should lie along the shaft of the femur. Original blade plates do not have locking screws so one will not be able to adjust position.
If the osteomy is not correct it is possible to bend the implant to more/less than 90 degrees using spinal rod benders. This is not ideal however.

Screws are inserted into the plate (3.5mm or 4.5mm depending on size of implant). Check with II to ensure satisfactory position of implant.

The wound should be closed in layers. The Vastus may be difficult to close over the metalwork but can usually be approximated with interrupted 1 vicryl or similar. TFL is usually easy to close with the hip abducted. I use sub-cuticular monocryl to skin.

Patients are quite understandably in discomfort for several days following surgery. One of the consequences of this is that they will be reluctant to move the hip. This is not ideal given that one of the main aims of treating Perthes is to maintain movement, particularly abduction. Application of a removable broomstick cast with the hips slightly abducted and in neutral or slight internal rotation helps to maintain coverage.

An AP pelvis radiograph should be performed prior to discharge to ensure that the osteotomy has not displaced and to ensure that the femoral head is well contained.