Ankle arthrodesis (fusion)- Trans-fibular approach

The approach shown is a trans-fibular one. The skin incision should be in the mid-line of the fibula. For an ankle fusion it extends a generous hands breadth above the ankle and inferiorly runs down past the fibula tip to the proximal end of the sinus tarsi.

An initial limited fine-scissors dissection through the fat layer(2), just in the line of the skin incision, is undertaken to avoid cutaneous nerves. These are the superficial peroneal nerve anteriorly and the sural nerve posteriorly.
This initial scissors fat dissection is followed by a knife dissection down to identify the fibula(1) in the same line with a knife.

An extensive fibula sub-periosteal dissection is required for ankle fusion. Posteriorly the peroneal tendons should be seen and avoided. Anteriorly the lateral edge of the tibia should be identified sub-periosteally by direct dissection across from the Fibula. Inferiorly the fibula tip should be identified, though doesn’t need to be much dissected beneath.

The soft tissues are protected with Trethowans retractors(1) prior to excision of the Fibula.
A large single sided reciprocating saw blade is used to obliquely cut the fibula at approximately a hands breadth above the ankle to allow access to the ankle joint.
Care needs to be taken not to notch the Tibia or cut the peroneal tendons by too aggressive sawmanship at this stage.

Once the fibula is divided proximally it needs to be removed, or reflected, to give access to the ankle. It has numerous strong soft tissue restraints all of which will need to be sharp dissected off it to allow its mobilisation.

The fibula soft tissue attachments which will need to be divided are the interosseous membrane, anterior and posterior Tibio-fibula ligaments, Anterior talo-fibular ligament and the calcaneo-fibular ligament.
As long as all the soft tissue attachments to the fibula are sectioned as close to the fibula as possible then these structures do not need to be individually identified.
Here an osteotome is being used to place soft tissues under tension during division. A large bone holding forceps is helpful for this too to allow traction upon the fibula.
An alternative method of dealing with the fibula through this approach(not shown) is to leave as much of its posterior soft tissue directly attached as possible. The anterior tissues are sectioned as shown to allow it to be swung posteriorly during the joint preparation. At the end of the ankle fusion it is then fixed back onto the tibia and lateral talus as a vascularised graft. Prior to this the medial cortical bone of the Fibula is removed with a saw as is the lateral talar cortical bone.
Following this the fibula is fixed with several long small fragment screws to the lateral aspect of the talus and tibia.

A large bone holding forceps (know as “Lions’ tooth” forceps) is needed for manouvering the fibula(1) as its’ soft tissues are progressively divided.
Care should be taken to avoid dividing the peroneal(2) tendons posteriorly.
Once the lateral talus(4), tibial incisura(3) and antero-lateral tibia (5) are identified preparation for ankle fusion can progress.

The anterolateral edge of the tibia is addressed with sharp sub-periosteal dissection. The aim is to produce a good continuous soft tissue sleeve from antero-lateral joint to the medial aspect of the joint. This sharp dissection to expose the distal tibia need only proceed a few cm before it can be completed using a large “round-nosed” periosteal elevator.

To further expose the tibia the round-nosed periosteal elevator is used to strip across to the medial malleolus. Distally some sharp dissection of the soft tissues off the lateral talus is also required , usually down to the level of the Talar neck.

The next step in every case is an exposure of the medial joint line and medial Malleolus(2). A longitudinal skin incision is used , skirting the medial aspect of Tibialis anterior. The medial Malleolus (2) should be exposed by sub-periosteal dissection and its width noted.
An initial vertical cut should be made with a fine power saw a few mm medial to the junction of the Malleolus and Tibial plafond. More width may need to be taken if the Malleolus has become hypertrophied. The vertical extent of this cut is used to mark the depth of tibial plafond that will be removed (3). This picture shows the transverse cut used to remove the distal Tibial articular surface (4) has already been made. This actually occurs in the next step of the operation.
The objective is to remove enough distal tibial articular surface but not to fracture the medial Malleolus. The Malleolus provides stability during fixation and a sound “buttress” for fixation. If the Malleolus fractures it is not the end of the world. The whole construct will be less stable during fixation and there will be less of an anatomical guide as to how to place the ankle so care should be taken when both positioning and when fixing.
With a very severe fixed varus deformity of the ankle it may on occasion be necessary to excise the Malleolus to get a complete correction of the deformity.
The tip of the long reciprocating blade is aimed from its point of lateral joint insertion to the top of the vertical medial Malleolar bone cut. An assistant is needed with direct visualisation of this medial point to ensure during cutting that the cut bone marker is not over or under shot.

A lateral X-ray of a different type of open fusion where the fibula is decorticated and applied as a vascularised strut graft across the ankle (known in the UK as an RAF fusion).
It is worthy of inclusion as it demonstrates established subtalar and talo-navicular arthritis that has presented circa twenty years following an ankle fusion. Only orthotic management was required.

The postero-lateral edge of the tibia (2) should be defined by careful sharp sub-periosteal and blunt elevator (1) dissection as here. The clear definition of the posterior extent of the Tibia assists in the safe completion of the posterior aspect of the tibial articular surface bone cut.

A large single edged reciprocating saw blade is used to remove the distal tibial articular surface .
Before deciding on how much Tibia to remove any anterior osteophytes should be removed as these will just confuse the assessment.
The amount to be removed is variable and often a balance needs to be struck. If on every occasion the bone is cut back so that only healthy sub-chondral bone remains there will be cases where significant tibial length is lost. A more immediate problem than the limb shortening this produces will be that this will cause the flared inferior & medial Talus to impinge on the medial malleolus and not compress against the Tibia if too much shortening occurs.
A good example of when not to cut back to the most proximal extent of poor bone is shown in the imaging section at the end. Such deep cystic areas of arthritis can simply be curetted out , drilled into and packed with graft. The bone cut of course needs to be properly aligned.
The plane of this cut needs to be at 90 degrees to the long axis of the tibia which is judged visually by reference to the anterior Tibial crest. The tip of the blade is slid all the way across to the vertical cut in the medial Malleolus

A CT scan showing the shape of the posterior aspect of the tibia (3), the Fibula(1) and anterior tibia (2). This should be studied. There is less depth of bone postero-medially than postero-laterally .
Therefore if resecting the distal tibial articular surface using lateral access (as in this technique) the tip of the saw blade needs to be angled anteriorly after the postero-medial cortex has been cut to avoid penetrating the postero-medial soft tissues which is a bad idea. The most posterior aspect of the cut can also be completed using a large Hibs osteotome in a controlled fashion.

To ensure adequate visualisation for the distal tibial cut a large bone lever (2) is used to elevate the anterior soft tissue envelope. The cut needs to be at 90 degrees to the long axis of the tibia in both sagittal and coronal planes. With bony deformity this will result in the removal of a “wedge” shape of articular surface
The objective of the cuts is to place the ankle fusion in a functional position. Simply put (which is all that is required) in the vast majority of cases the foot should be squarely beneath the Tibia in the coronal plane and at right-angles to the Tibia in the sagittal plane. Good luck with adding in the 5-10 degrees of valgus mentioned in most publications!.
Varus, valgus and equinus need to be corrected. As mentioned in the Indications section there needs to be a pre-op identification of what level these deformities may lie at.
The amount of bone resected with appropriately angled bone cuts in an open ankle fusion allows easy correction of most ankle deformity.

Care needs to be taken with the posterior extent of the distal tibial cut. The large periosteal elevator (1) can be placed behind the posterior border of the tibia as a guide and care should be taken not to over shoot the posterior cortex. Care should also be taken re the angulation of the tip of the saw blade given that there is less postero-medial tibial depth. Angle the blade anteriorly and withdraw the blade laterally once the medial deep cut has been completed or is almost completed.

The distal tibia is removed sometimes in a single piece as here. A sharp Hibs osteotome can be useful to run through the saw cuts before attempting mobilisation.
Posterior soft tissue attachments will still be present and these will need to be sharp dissected off as the articular surface is delivered out under traction using a Kochers’ forceps during the ankle fusion.

The talar dome(2) is placed opposed to the cut tibia(1) so that the foot sits at ninty degrees to the long axis of the tibia in the saggital plane .In the frontal plane the centre of the patella is aligned with the 2/3 metatarsals .This should allow an appropriate position for the talar cut.
The cut is made with a broad oscillating blade , though the large reciprocating blade can be utilised with practice for this.

Once the Tibial cut is correct the talus is simply cut
parallel to the Tibia(1). This is best done with a long and relatively thin oscillating blade. After resection of the Talar dome one should ensure that there are no irregularities on the dorsal Talar surface which will compromise the bone to bone contact of Tibia and Talus.

In cases of arthritis (osteo or inflammatory) where there is extensive cystic change effecting the articular surfaces resecting to the base of the deepest defect can result in the removal of too much bone. The effects of this can be unnecessary shortening of the limb and more immediate problems with achieving good bone to bone contact .It may well be more appropriate to simply extensively drill into the deeper cysts and fill with bone graft .

After parallel tibial and talar resection the talus should easily be translatable proximally to make good contact with the tibia prior to fixation.
In non deformed ankles this is generally the case. In significant varus deformities(as with this case) the hypertrophied medial malleolus will often impinge upon the medial Talar body and provide a bony block to reduction.

To allow reduction several cms of medial malleolar tip will need to be removed. Alternatively(or sometimes additionally) the medial flare of the Talar body can impinge upon the tip of the medial Malleolus and this may need to be similarly removed. Either procedure is best done under direct vision using a Lambotts osteotome or oscillating saw with very small arc. The posterior cortex of the Malleolus overlies the Tibialis posterior tendon and is best divided only with an osteotome.

A Lambotts osteotome being used to lever off the medial malleolar tip(1) prior to ankle fixation.

The appearance of the medial Malleolus (2) after removal of the Malleolar tip (3). If this still does not allow congruent reduction of the ankle fusion then some of the medial wall of the talus (1) may need to be removed. Time must be spent achieving a stable and as near complete contact between the cut bone surfaces as possible.
In terms of fixation use big screws and as many as you can . This stage needs Image Intensification.
Before commencing fixing make sure that the joint is appropriately aligned (as described previously) and almost as importantly the bone to bone contact is excellent with the ankle appropriately positioned. 2 large diameter (2.4 mm +) wires should be placed initially away from the planned position of the definitive screws.
A good starting point for fixation is two short thread partially threaded large (6-5-8mm diameter) fragment cancellous screws. A cannulated screw system should be chosen otherwise getting the orientation of drill holes wrong results in large & unfilled holes being left in the bone. Place all guide wires for intended screws before commencing drilling. The initial 2 screws can be placed from the subcutaneous face of the tibia (avoiding both the thick anterior crest as well as being too posterior). A “spread” of their compressive effect should be aimed for by diverging the screws on both A-P and Lateral projections. The lateral Tibia can also be used for a third screw.
It is key that bone compression and stability is achieved. Use screws of as large a diameter as the bone will tolerate and with a good thread pitch (for example the Orthosolutions 8.0mm cannulated screws ). If with 2 screws the fix is not adequate keep increasing screw number (though it’s difficult to find room often for more than 3). Washers under the screw head may help the bone purchase (if they have been countersunk or are sinking into soft cortical bone). Rarely it may be necessary to have a screw with a longer thread which crosses the fusion site (thus negating its compressive effect) to improve stability .