Talo-navicular fusion using Zimmer-Biomet locking plate

A fairly typical pre-operative image of isolated talo-navicular arthritis showing a reduction in the joint space and associated dorsal osteophytic lipping. There is also subtle subchondral sclerosis effecting the talus.
In severe cases the talar dimensions can be effected and bone lost to the extent that fixation into the talus can be challenging. This is not the case here.

Under the sheets the patient positioning cassette is placed so as to contact the pelvis and tilt it. It can be easily raised and lowered during the case without much disruption and I prefer this to the use of sandbags. It has a well padded surface in order to distribute pressure and avoid sores.

Here the ratchet here is seen to hold the pelvis tilted and thus the iliac crest is “delivered” towards the skin minimising soft tissue dissection to get to the iliac crest.

The harvest site is marked and draped with an Ioban adhesive dressing to keep the drapes insitu and keep the field sterile

Here the swelling can be clearly seen (A). This is the lateral aspect of the talo-navicular joint. This needs careful debridement as part of the fusion. In order to get access to this area I select a dorsomedial approach to the TNJ. The skin is marked after prep with my incision planned just lateral to the tibialis anterior tendon and centred on the TNJ. The incision will be approximately 6cms in length. An alternative approach frequently used is the utility medial approach positioned between tibialis anterior and tibialis posterior tendons, but access laterally is difficult with the medial approach.

The incision is made just lateral to the lateral border of the tibialis tendon. Dissection is carried on to the superficial layer of the inferior extensor retinaculum with the tendon of extensor hallucis longus used to keep the dorsal neurovascular bundle safe from inadvertent surgical insult. there are often many small superficial branches of the superficial peroneal nerve around the wound and these can be careful freed up and reflected laterally. Those that cannot be reflected are divided with a scalpel on the basis that small areas of numbness may result but in my opinion this is preferable to causing traction to the nerves and painful parathesia resulting around the wound.

Care is taken to leave a cuff of inferior extensor retinaculum lateral to the tibialis anterior tendon sheath to allow stable closure at the end of the procedure and to avoid bowstringing if the tendon is not well held down. The tendon sheath itself is often expposed as the tendon is enveloped superficially and then deeply by divergent parts of inferior retinaculum but my goal is to keep the tendon within its sheath by resection along the lateral margin rather than directly over the tendon itself.

The tendon is retracted medially and deep dissection to and then, inline with the skin incision, through the deeper fascia of the retinaculum and subsequently the capsule. This allows access to the lateral aspect of the joint to debride the osteophyte there. Once through the capsule I use sharp dissection medially deep to the tibialis anterior tendon, and laterally deep to the extensor hallucis longus and extensor digitorum longus tendons. I stay on the bone during this dissection to prevent any potential injury to the dorsal pedis artery or the deep peroneal nerve which are kept lateral to my incision throughout.

Once the capsule is incised and the deep layer elevated form the bone on either side of the joint is it is safe to position a self retaining retractor deep. I try to keep the sharp tines of the self retaining retractor deep to the skin edges in all foot and ankle procedures as they can cause pressure with prolonged use and thereby hamper wound healing. They should always be used judiciously in my opinion.

Once the capsule has been elevated adequately the whole dorsum of the joint is exposed. Dorsal debridement is done by initially removing loose osteophytes (L) by shape dissection. Here these loose fragments were responsible for much of the swelling seen at the beginning. Once these have been excised the joint is easier to inspect.

I like then to open the joint with non-invasive Hinterman distractor placed over two 2mm single ended K-wires. This allows excellent exposure of all of the joint surfaces. The capsule has to be adequately released or there is a risk that the 2mm wires will simply cut through the bone. The wires are positionned approximately 1cm form the joint margin in the navicular and one in the talar neck. I tend to put one wire in the put the Hinterman over this wire and drive the second wire using the second hole in the Hinterman as a wire guide (A).

Once the Hinterman is well positioned the wires are bent to prevent the device creaping off the bone when under tension and the joint is cranked open with the ratchet holding the joint in this position. Radiographs are not needed to position the Hinterman distractors as this is a clinical feel.

Joint surfaces are now prepared with a mixture of tools, I like to use long nose curved rongeurs especially for any loose areas. For breaking through the remaining chondral surface and into the subchondral bone I use small osteotomes. For areas where the bone is eburnated or the subchondral bone is very dense I use the drill from the rearfoot plating system – this is 2.5mm in diameter. I find drilling with wires generates too much heat and risks necrosis of the bone surface.

Again the navicular is prepared in the same manner – especially when it is very sclerotic. Once the surfaces have been completely prepared the distractor is released to ensure the surfaces are well paired and to ensure that any deformity can be corrected by gaining coverage of the talar head with the navicular. An image intensifier view may be used once the Hinterman distractor is released to check apposition and adequate deformity correction prior to stabilisation, especially when one is relatively new to this procedure.

Small lambottes are used here allowing me to respect the convex curved surface of the talar head and the concave partner surface of the navicular. Its is vital to breach the subchondral bone into cancellous bone on both surfaces. The talar head is often soft and easy to “over-debride” and generate bone defects; whilst the navicular is often sclerotic and eburnated.

The navicular is similarly prepared and this eburnated and dense surface must be cleared. Careful and steady use of small sharp osteotomes is required as well as lots of patience. Rapid destructive debridement will potentially leave large defects and reduce the likelihood of successful union.

Often the surfaces require the use of a drill to create a “pepperpot” appearance and here I use the 2.5mm drill from the Zimmer Biomet locking plate that I am using to stabilise the joint later. No more than 5mm of drill depth is required.

Once both surfaces are prepared and the deformity can be corrected, attention is turned to stabilising the joint. I use a single 5mm partially threaded cannulated titanium (ACE screw from DePuy) compressive screw which I introduce through a percutaneous stab incision over the navicular tubercle. This screw has a 20mm threaded segment with a good head size to allow compression. I do not usually use a washer as this can leave the screw head prominent on the medial border of the foot.
The entry point is plantarward to the wound and over the navicular tubercle where there is plenty of strong bone. Care must be taken not to introduce the wire and subsequent screw too distal or there is a risk of involving the naviculo-cuneiform joint. Again an image intensifier will assist here.

The joint is again distracted at this stage so that I can see where the guide wire exits (A) at the fusion site which should be as central to the fusion in the transverse plane and plantar on the lateral view. This direct view ensures that the screw is well positioned to get compression and minimises passes of the guide wire under image intensification.

The wire tip is positioned into the talus and then the Hinterman released and removed ensuring that the deformity and or alignment is correct the wire is then driven across the arthrodesis site with the length then checked with image intensification. Interference between the K-wires and the bayonette tipped screw guide wire is avoided by ensuring removal of the 2mm wires before final passage of the screw guide wire.

A lateral image intensifier view is obtained to check guide wire orientation which should of course avoid both the subtalar joint and the ankle joint. The image shows a plantar entry point aiming for the middle of the talus on the lateral view. Note the joint surfaces are congruent, but there is still a patent joint space in contrast to the image after compression (slide 25).

A ‘Canale’ AP image (That is an AP view of the TNJ with the foot 40 degrees plantar flexed at the ankle) is is used to check the wire position which should also be aimed centrally in the bodu of the talus and the tip short of penetrating the lateral ankle joint. The wire can be seen to enter the navicular close to the NCJ.

Once the guide wire attitude and length is acceptable, an extraction measurer is used to gauge screw length using a partially threaded cannulated screw to provide good compression. In this case the suitable screw length is determined to be 60mm in length. It is important to consider that the threads of the screw must not be across the arthrodesis site or the screw will not act in a lag manner and no compression will be achieved. It is for this reason that I like to use a screw such as the DePuy ACE where the thread lengths are variable – in this case a 20mm thread length is correct.

The drill is not laser etched for length and so I use a marker pen to make 10mm marks so that I drill deep enough (60mms) but without the wire coming out on drill removal. Steady drilling is needed and care taken not to heat up the bone as this might result in bone resorption and loss of compression.

An appropriate (60mm x 5mm diameter) cannulated screw is selected and introduced by hand – good compression is essential. I use the ACE DePuy 5mm screw because it has a good head shape to allow compression without the need for a washer. Its threads are 20mm which is well on the far side (talar) of the arthrodesis site and thereby reliably giving good compression. The screw diameter is strong to provide excellent bending resistance too.

A further check Xray is taken to ensure the compression is adequate. Compression can be seen on this image (in contrast to the lateral image on slide 20) and the screw head is situated proximal to the naviculo-cuneiform joint.

Although now quite stable and well compressed I prefer to use a plate also to provide further robust stability. There is biomechanical evidence especially at both the 1st MTPJ and more recently at the talonavicular joint (see ref Jarrel et al ) that a screw and a plate provides the most stable construct. Outcomes with the use of plates are also good (see ref Diezi et al). The plate is used in a locking neutralisation manner.
I use a simple and inexpensive titanium plate made by Zimmer Biomet. It is low profile and well contoured. I use the Universal plate and this comes in one profile but lengths from 16 to 50mm. It has 4 screw holes and generally I use all of these. These screws are not variable angle and so careful plate positioning is needed.
Plate length is selected to have fixation points close to the arthrodesis site but long enough that the screws are not to penetrate the fusion site.
The plate is positioned such that the locking screws do not interfere with the cannulated screw. The guide wire for the cannulated screw can be re-introduced to show the position of this.

The plate is held with a wire and the holes are made with a 2.5mm drill through a tower type threaded drill guide. Locking screws are used in each hole provided that the plate seats well as we do not want the plate to be prominent – if not seated down to the bone, a non locking screw or two may be used but once well positioned I prefer to swap these to locking screws for a stronger construct. In this case non-locking screws were not needed. This construct provides a very strong arthrodesis site.

Careful and controlled drilling to ensure the subtalar joint is not violated. Screw lengths are determined with a traditional type of depth gauge. An image intensifier can be used to double check the depth gauge measurements.

Again check images are taken and a satisfactory degree of stability has been achieved with correct length screws, note no screws are in the subtalar joint (A).

The AP image confirms this and it can be seen that the locking screws do not interfere with the 5mm cannulated lag screw.

The wound is lavaged with saline prior to closure

Care is taken to close off the paratenon of the tibialis anterior tendon to keep the tendon well down and away from the wound and prevent it from adhering to the scar, hence the need for the cuff of the inferior extensor retinaculum as was mentioned in the approach section. This is very important to prevent the tendon bowstringing and potentially causing wound healing problems.

The wound is closed with interrupted monocryl sutures as mattresses stitches. These will have been absorbed by the time the cast is removed avoiding the need for wound maintenance in the post op period.

A well padded plaster backslab in neutral alignment is applied, this serves several functions, namely to keep the wound still and assist healing, keeping the operative site rested assists analgesia and splintage is necessary to encourage union.

Images here are of the arthrodesis at 12 weeks when union is confirmed. The concept of a compression screw and neutralisation bridge plate can be clearly seen on this post operative plain radiograph.

The AP radiograph is a little harder to interpret but union can be seen here.