First MTP fusion (hallux rigidus)- Dorsal approach with Synthes MTP fusion plate

In this case there are severe signs of arthritis with loss of joint space, sclerosis, osteophytes and cysts. There has been some loss of bone with mild shortening of the metatarsal.
There is reasonable alignment at the MTP joint, though with significant valgus at the IP joint (Hallux interphalangeus) which will make positioning more important.

The joint is approached dorsally, to the medial side of the EHL tendon which is retracted laterally.
Mark the skin from IP joint to MTP joint and same distance along metatarsal. This will give the right amount of exposure to allow the plate placement on the proximal phalanx and metatarsal.
Place the incision just medial to EHL tendon. This will avoid the dorso-medial nerve but bare in mind the dorsal cutaneous nerves that run 5mm either side of EHL, in the subcutaneous tissues.

A skin incision is made in the dorsal midline, running from the mid point of the metatarsal to the level of the IP joint.Incise the skin and subcutaneous layer to expose the EHL tendon and sheath. The sheath is clearly seen and forms part of the extensor hood around the proximal phalanx.
Incise the fascia / extensor hood 5mm medial to EHL – its important to leave a cuff of tissue to repair back to during closure. Continue this along the extent of wound to the IP joint. Note that the fascia thins out quickly over the phalanx.

Blunt dissect the fat with scissors, identify the EHL sheath and Incise the fascia / extensor hood 5mm medial to EHLRetract EHL laterally exposing the capsule and synovium beneath. Continue to divide this longitudinally over the top of the metatarsal and along the proximal phalanx. Reflect this layer medially and laterally along the whole length.
Proximally this lifts easily, and at the joint it is thickened by the capsule and the collateral ligaments. Continue distally over the proximal phalanx – it thins out rapidly and becomes a subperiosteal dissection. The EHB insertion is in the lateral layer here and isnt really seen, simply elevated as part of the dissection. (Note, the EHB will become 100% obsolete with the fusion).

Continue the dissection either side, reflecting the capsule and ligaments off the medial and lateral sides of the joint.
This needs to be done on both the metatarsal side and the phalangeal side of the joint. The ligaments become thicker as they attach inferiorly and its important to stick to the sides of the bones to ensure a clean resection.

Insert Homanns retractors between the metatarsal and the capsule to improve exposure of the plantar tissues, by putting them on traction. Continue dissection inferiorly and stick close to the side of the metatarsal, until a full release of the ligaments is achieved.
Remember the main blood supply to the MT head is on the medial side just underneath the neck of the bone. Its lies amongst adipose and connective tissue. Take care to avoid this area and only to dissect the thick ligamentous structures, which are easily seen under traction and do not go underneath the metatarsal.

Once a good release is achieved, the joint can be plantarflexed and opened up to exposed the arthritic surfaces.
Use a towel clip or bone holding forceps around proximal phalanx – this gives a good grip on the phalanx and makes it easier to plantarflex the joint.

Its important to get complete access to the whole joint, by flexing the phalanx to 90 degrees relative to the metatarsal head.This allows the reamers to fit easily and without causing damage to the surrounding soft tissues, especially the plantar ones.
Further plantar releases are needed to open the joint fully. Using a scalpel, release any remaining collateral ligaments off the inferior edges of the proximal phalanx and continue along the base – stay close to the bone and this will avoid any damage to the FHL.
The sesamoids often stuck down to the joint and can prevent full exposure of the proximal phalanx – they can be easily mobilised with a rounded elevator or pennybacker.

Initially identify the long axis of the metatarsal and insert the 1.6mm guide wire into MT head along this axis.Take care here, often the correct entry point is not the centre of the articular surface, as this is often distorted by abnormal anatomy and arthritic changes.
Once a clear view of the entire MT head is achieved, there is no need to take off any osteophytes yet – these will all come off with the reamers. Although tempting to remove them first, its easy to be too enthusiastic and this step is better left until after reaming.

The spherical reamers come in pairs of “cup and ball” reamers, from 18mm-24mm diameter. Usually the largest ones are the best fit.
They attach with the standard quick release coupling.

The tissues on either side are protected with Langenbeck retractors and the spherical “ball” reamer is placed over guide wire (trial the approach to ensure clear passage of the reamer). The reamers are extremely sharp and its very easy to damage the soft tissues either side, unless care is taken to protect them – The EHL tendon is easily cut without notice!
The proximal phalanx will need plantarflexing fully to get it out out of the way.
Be careful reaming – The initial bone will be hard and the reamer will make slow progress requiring more pressure. As the soft cancellous bone is reached, its very easy to ream / destroy a large volume of the metatarsal head, especially in rheumatoid cases!

Check the depth of bone resection frequently, stopping only when there is a uniform cancellous “ball” . Once the optimum resection has been achieved, there will often be excess bone dorsally, medially and plantarly which needs removal with a bone nibbler.
If there are still areas of sclerotic bone or cysts, these are best perforated several times by being “peppered” with the 1.6mm guide wire.

After reaming there should be a consistent cancellous surface. Often there are one or two cysts, which need clearing of soft tissue but can be ignored otherwise.
In cases of severe valgus, where the tissues are tight, resect more metatarsal head to provide slack in the soft tissues to allow correction.

Remove the guide wire from the MT head. Plantarflex the toe to expose the joint fully and re-insert the guide wire in the phalangeal side of the joint, centrally in the articular surface.A similar procedure is performed to ream the proximal phalanx (PP)

Change to the phalangeal reamer (“cup reamer”) in the matching size, whilst protecting the tissues with retractors and ensure clear passage.
Ream to cancellous bone – the bone on this side is often more sclerotic and wont look as cancellous. Its important to maintain as much width as possible – take care not to over ream as the proximal phalanx tapers quickly!
In severe arthritis, the subchondral sclerosis may be too thick and it may not be possible to get to cancellous bone. If after 1-2 mm of reaming no cancellous bone is apparent, stop reaming and “pepper” the joint with the guide wire or the 2.0 drill.

Spherical cancellous surfaces should look like this. Note the bone on the phalanx is not as cancellous.
Remove any excess bone / spurs on the periphery but be mindful not to take too much away, which will effect the congruency of the joint and the stability of the fusion construct.
The joint can now be placed in the correct position for fixation.

Positioning the toe is done by temporarily fixing the joint with a wire and then reassessing the position by eye and with a flat plate to mimic the ground surfaceIn order to get the alignment of the fusion correct, it needs careful positioning and multiple checks.
The first step is to pass the guide wire into the phalanx, but only half way so that the joint is still mobile. Place the wire at an angle that will transfix across the joint and into the metatarsal, once advanced.
It can take several readjustments before the position is right.

The valgus/varus position is assessed by eye from above. Ideally between 10-15′ of valgus – Its important not to be too straight or in varus as the forefoot won’t fit into shoes.
The ideal dorsiflexion / elevation is achieved using a sterile flat surface. I use the metal top to one of the trays. The ideal position is with the pulp of the toe, the forefoot metatarsal head pad and the heel pad all in line. A little extra dorsiflexion can be added which will allow a small high-heel to be worn.
Once satisfied, advance the wire across the joint and into the metatarsal to secure the position.

Check dorsiflexion / elevation using a metal tray top.
Its should contact the heel pad, forefoot pad and toe pulp with equal pressure.
If too dorsiflexed this cause problems with the tip of the toe rubbing in shoes and metatarsalgia under the lesser metatarsal heads as the first ray is defunctioned.
If too plantar-flexed this causes real problems walking, with pain at the tip of the toe and difficulties in the 3rd rocker phase of gait.

In the right position, there should be enough extension at the IP joint to allow some dorsiflexion, ideally to allow a 3cm heel.

Dorsal locking plates :
These are either in titanium or steel and come in Rt or Lt sides, with 0′ degree, 5′ or 10′ degree bends.
The plates come in small, medium and long sizes – I tend to use the longest one that doesnt impinge on the distal IP joint – usually medium on women and large on men.
The locking holes (1) are variable angle and using the variable angle guide, screws can be inserted in different trajectories.
The plates are normally used with locking screws but can be used with non-locking screws too. There is also a DCP compression hole (2) but I have never used it.
There is a compression slot (3) in the plate and a static hole (4) for use with the compression clamp and wires.

Position the plate over the first ray. There is a black line on the plate, to mark the joint line but in practice this is often better placed 1-2mm distal to the joint line.The plates come in titanium or steel (there is no difference clinically between the two types).

The plate should rest well on the bone surfaces without rocking or lifting on any high spots. Check the length and position by dorsiflexing the IP joint – its important to make sure the plate doesn’t intrude on this joint.

Bending pliers.
Rarely, the angle or contours of the plate do not fit the fusion construct. If so, further adjustment of the plate can be made with the bending pliers.
More commonly, I use the “cam and post” section of the pliers to adjust the dorsiflexion angle.
The wings of the plate can also be adjusted using the jaws of the pliers, using the special areas to grip the locking holes.

Cam and post section of bending pliers – much like pipe benders. I find these easier to use than the jaws of pliers.
The central cam can be rotated to produce a greater or lesser arc of “bend” and give a more predictable site and degree of adjustment.

The wings for the locking screws holes curve lower than the plate. Sometimes, these can lift the plate off the bone if there are any high points underneath. You will need to shape the bone and remove any high points with a 3mm osteotome so that the plate is no longer lifted.

Compression wires and clamp.
The jaws of the clamp are shaped to fit only around the ball on the the threaded wire.
There is a ratchet mechanism on the clamp which holds maximal compression.
Using this Synthes compression technique, I have avoided using a lag screw now for many years, with extremely high fusion rates.

The VA set has a nice way of compressing the fusion surfaces.
This uses a ratchetted clamp and compression wires. These are threaded ball wires, that come in a range of lengths from 15mm to 50mm – I use the 20-25mm wires for this joint. They are long enough to secure both cortices, without damaging the plantar tissues.

Secure the plate in place with the compression wires. The wires should go through the proximal side of the slotted hole i.e. furthest from the fusion site and the other through the static hole.
As they are threaded, they pull the plate firmly onto the bones and hold it well. (Be careful here as this manoeuvre can subtly change the dorsiflexion / plantarflexion position.)
This is a good time to check the plate position with xray and also check the toe position clinically.
The wires should be long enough to engage both cortices, otherwise the compression force will be lost.

Use the compression clamp to compress the fusion surfaces.Place the clamp around the ball wires and compress – the ratchet on the clamp needs engaging to hold the squeeze across the joint. Compress and squeeze until the fusion site is apposed and the wires start to cross over.
The slotted hole allows up to 2mm of compression. Take care in soft bone as the compression wires slip easily – use a longer wire to ensure engaging the plantar cortex.

Drill guides.
There are fixed (2) or variable angle (1) drill guides – this allows for a wide variety of screw placements to achieve good fixation.
The guides have specially shaped lugs at the end which require correct orientation to engage the screw holes properly.

Fix the plate in place using locking screws using the 2mm drill with the straight or variable angle drill guides.Once again, check the position, as the compression can increase dorsiflexion.
Drill, measure and insert locking screws, using the torque release fitting on the screw driver – this will stop you over-tightening the screws.
I put these in on power with the torque limiter / screw driver attached to power unit.

Check the depths carefully, especially with the screw over the metatarsal head, its easy to drill into the sesamoids and measure too deep.
If the metatarsal head screws are too long they will penetrate the sesamoid articulation or the sesamoid bones – check this carefully on a good lateral xray.
If the proximal phalanx screws are too long the patient will feel them plantarly.
The locking screws are easiest to insert in the proximal and distal holes. Place two screws in each end.

Once the initial screws are secure, the compression clamp and wires need removing to access the other holes. Undo the clamp first, otherwise the compression wires will snap.There is further compression possible, if needed, using the DCP hole.
I have never had to use this – if the bone quality is very poor, then I use and additional lag screw across the joint.

Lock in place 3 screws proximally and 3 distally.
In revision cases, there is often residual deeper metalwork in place and the variable angle guide is very useful to get around any obstacles.

With screw entry, it’s easy to pick up the EHL sheath and other soft tissues – your assistant needs to retract the soft tissues

Once all screws are entered, perform a final check of the plate and ensure nothing has been trapped underneath e.g. the EHL tendon.
Also check over the bunion area for any loose fragments or sharp edges. Take any prominences off with a chisel.
Confirm the position with AP & Lateral xrays.

AP xray to check for final position of the fusion, toe and plate.
This is performed by bending the knee and placing the foot flat on the operating table, with the image intensifier underneath the table.
Check for any gapping in the fusion site and also that the alignment is good – this one is too straight at the MTP joint to accommodate the interphalangeus / valgus at the IP joint.

Lateral xray to check for screw lengths extending into plantar joint and sesamoids. Its important to rotate the foot fully for a true lateral image and true view of the screw lengths.
This is performed by rolling the leg into external rotation with the Image intensifier underneath the table or off to the side.
This image is not quite rotated fully enough as the 5th MT should be visible.

The closure is done in layers – the first layer is the capsule over the plate, which lies under the EHL and provides a gliding layer. It is closed with 1 Vicryl. Proximally this closes easily but it thins out over the P1 and often can’t be closed there.
The EHL fascia is closed next, using the 5mm cuff of tissue so that the tendon is not transfixed.
Subcutaneous tissue and skin is closed with vicryl rapide, in layers.

The wounds are dressed and covered with gauze, wool and crepe bandages.