First MTP Fusion- Revision of malunion using Synthes MTP fusion plate

The sole of the foot shows a large callosity on the plantar medial aspect of the 1st MTP joint. This is due to an abnormal prominence of the 1st MT head as a consequence of a dorsiflexion malunion.
There is also a hallux valgus deformity with abutment of the hallux on to the 2nd toe. There is clawing of the 3rd and 4th toes in addition with a callosity at the tip of the 3rd toe. There are no obvious transfer lesions over the lesser metatarsals in the sole of the foot.

A sagittal photo shows the dorsiflexion deformity at the 1st MTP joint as well as features of a dorsal prominence and plantar medial callosity.

The anteroposterior radiograph show the recurrent hallux valgus deformity with a fracture of the plate at the 2nd hole proximal to the fusion site.
This was a 1/3rd tubular plate and did not have a locking facility. Note to lateral subluxation of the sesamoids.

The lateral image shows the fracture of the plate well as well as the dorsiflexion deformity of the toe along with clawing of the lesser toes, which demonstrates a common response with the lesser toes.

CT is required in most cases to adequately document the bone stock, extent of bony union and accurately record the extent of deformity.
A sagittal CT section shows the partial union of the dorsal bone at the fusion site.

The foot is prepped past the ankle with alcoholic Povidon-Iodine solution above the ankle. Note the interdigital flossing being performed, which is an essential part of the prep procedure.

The foot is now draped. Note the hallux valgus which is now clearly seen pushing against the 2nd toe. The interphalangeal joint carries a thickening of the skin over its dorsal surface. The clawing deformities of the lesser toes are also obvious.

The skin incision is marked dorsally just medial to the extensor hallucis longus tendon as a surface marker.The incision extends from the proximal end of the plate to just proximal to the interphalangeal joint.
The IP joint is flexed to make the EHL prominent.

As there is a previous scar in this region which was used for the initial exposure, care needed to be taken with adhesions between skin and tendon.
These can sometimes cause the operator to inadvertently cut into the tendon. Careful dissection is required to separate the skin and subcutaneous tissue from the tendon.
Medially lies the dorsal medial cutaneous nerve whilst laterally at the 1st interdigital cleft lie the terminal branches of the deep peroneal nerve.

The skin and subcutaneous tissue is dissected as one flap from the capsule of the 1st MTP joint and the extensor hallucis longus.I prefer sharp dissection with a size 15 blade rather than dissecting scissors.
One must be extremely careful particularly when the skin is thinned out and densely adherent to underlying bone especially medially, that the skin is not buttonholed during raising the flap: a most undesirable complication that can lead to skin necrosis!

The capsule medial to the extensor tendon is identified and the skin and subcutaneous tissue dissected off it.The capsule is then incised, having ensured that the dorsomedial cutaneous nerve is often snarled in scar tissue and must be identified and protected throughout the procedure.
This is best done by dissecting out the nerve proximal to the area of scarring in healthy tissue and following it into the scar releasing it with dissecting scissors. This may involve careful neurolysis and cutting away of dense scar tissue from around the nerve.
An alternative to consider is careful elevation of the skin and fat as a complete flap off the capsule.

An osteotome is used to identify the joint line and the non-union site as well as the plate .An osteotome is used to identify the joint line and the non-union site as well as the plate. This can be difficult on occasion particularly if there is partial union dorsally or there is significant bone overgrowth over the plate. The osteotome is also used to chip away at bone overgrowth which was substantial in this patient,

The osteotome is used to identify the interface between overgrown bone and plate.
Then the osteotome is used to lift of the bone from the plate medially. It is important to exercise caution at this stage for the Dorsomedial cutaneous nerve is at risk of damage medially

This carried along the edge of the plate from proximal to distal.
.

Using the same plane deep to the over grown bone, continue the elevation of bone from proximal to distal till the entire plate is exposed. In cases where there is a heavy overgrowth of bone it is often difficult to identify the non union site particularly if there is dorsal or medial non union. In this situation the dorsal bone is cut away and the proposed non union is stressed by dorsiflexing and plantarflexing it: this will create a small arc of movement with indentation of scar tissue and non union fibrous tissue and this leads one to the non union site.

Laterally, the procedure is repeated until the lateral border and the dorsum of the plate are cleared of all bony tissue.

The proximal end of the plate is traced excising scar and bone that overlies the plate.

Screw heads are identified and cleaned of debris inside their heads.Screw heads are identified and cleaned of debris inside their heads. This is important to do, as using the screwdriver without properly engaging in the slot of the heads increases the risk of wearing away the facets of the head with the result that a smooth slot is created that makes screw removal difficult.

The longer section of the plate is levered off the bone after all of its boundaries are freed of bone. The broken part of the plate and a screw remain.

The proximal broken part of the plate is now extracted after removal of the remaining screw.

Load and move the pseudo-arthrosis once the metalware is removed to help identify the non union site.Now one can see the entire dorsal surface of the MTP joint. As mentioned earlier it can be difficult to locate the site of non-union particularly if there is bony union or bone overgrowth over the non-union.
Here there appears to be bone bridging the dorsal surface but a faint outline of the joint line(1) can still be seen.

Further debridement reveals a screw that was securing the plate proximally. This was surrounded by the fracture in the plate and is removed.

The screw has now been successfully removed and the dorsal bridge of bone is clearly visible over the non union site (1)

Once the non-union site is identified an oscillating saw is used to divide and freshen the bone at this level as flat cuts.The site of the non-union/ partial union is identified . The primary fusion was performed using flat cuts.
In fusion where a ball and socket fusion was performed using congruent reamers, this is interface can be quite tricky to find unless there is complete non union which is unstable when movement of the non-union site on toggling the toe leads the operator to the fusion site: if in doubt use image intensification.

Care must be taken with the saw at both medial and plantar aspects of the cut. Medially, the oscillations of the saw can damage the dorsomedial cutaneous nerve, whilst in the plantar aspect, it is easy to damage the sesamoid apparatus, the flexor tendon and the medial digital nerve.
One must exercise great caution to use a saw blade that will oscillate within the diameter of the bone surfaces so as to avoid the saw exiting the interface or causing injury to medial skin or the neurovascular bundle particularly medially where it now lies along side the medial cortex of the proximal phalanx.
It is further complicated by dense scar tissue that needs to be debrided to identify the medial edge of the cortex on both bones. It is also important to stop from time to time and ensure that the saw is still within bony boundaries described above.
It is absolutely essential to use irrigation with normal saline particularly if the bone is dense and sclerotic to avoid thermal necrosis. It is also important to frequently inspect the plantar aspect especially if there is any bone bridge formation in the plantar part of the non union so as to ensure that the plantar structures are not divided.
One may use a sharp osteotomy to divide the bone carefully rather than a saw blade and then use fine nibblers to excise the small bony ledges on either side of the joint that will ensue with such division. Once the non union is completely divided, the joint can then be opened for further inspection by plantarflexing the toe.

This is the cut when finished. The hallux valgus deformity persists as seen as the corrective wedge excisions are planned.

The bones are distracted to inspect the gap, following recutting, and to check for any fibrous tissue that may have filled the non-union gapThese are thoroughly debrided using curettes and nibblers. A pair of Rongeurs are especially useful in excision fibrous tissue and bone from the plantar aspect of the non union site especially when it is difficult to completely expose the plantar aspect due to excessive scaring of the periarticular area.
The joint surfaces can often be sclerotic and biologically inert and thus need careful preparation. In these circumstances it is necessary to debride the fibrous tissue, identify the joint and prepare the fusion surfaces to make it biologically active.
I use a combination of multiple drill holes with an irrigated drill or K-wire, a small sharp osteotome to petal the surfaces and curettage of any screw holes that are on the surface. I also occasionally use bone graft harvested from the calcaneal body through a separate small incision and using a bone harvest system to get cancellous bone graft to act as a osteo-inductor as well as an osteo-conductor to fill any voids.

The surfaces need to be inspected for bleeding to ensure viable surfaces for re-fusion.
If there is a history or suspicion of infection then swabs and bone samples must be taken for microbiological testing for culture and sensitivity. It is also important if Avascular necrosis is the pathology for areas of dead bone need to be excised.
Once this has been done, then the first stage of the correction of deformity is planned. The wedge for correction of hallux valgus is best excised from the metatarsal rather than the proximal phalanx for there is more cancellous bone in this region. Excising proximal phalangeal bone may result in the cut being made in cortical bone thereby decreasing healing potential.
If there is no deformity to correct then bone wedges are not required to be excised and the surfaces can be apposed after preparation s described above.

The wedge is then carefully cut to correct the valgus, once again with great care to the medial structures.Here only about 2 mm of medial wedge excision was required and this was carefully completed. If more than one dimension requires to be corrected as in this case with a valgus and dorsiflexion deformity, then further planning is required to get the wedge as close to perfect as possible. It is also possible to excise a medially based wedge and then selectively remove of a plantar-based wedge very carefully to get the desired correction.
If in doubt then a small thickness can be sequentially removed rather than excising too much and having to make other cuts to rectify the deformity created by excising too much as will be seen in the next few slides.

The plantar aspect of the cut is finished with an osteotome for safety reasons mentioned above. This move excised a small plantar based wedge in addition to the medial based wedge to correct the dorsiflexion deformity.

The wedge is carefully toggled free using the osteotome nibblers and forceps. This is bone that can be used as graft to fill defects prior to application of the plate and therefore must be stored in a wet swab to prevent drying of the bone.

The medial and plantar based wedge is seen here from from the site of osteotomy and after removing any soft tissues to be stored in a wet swab as bone graft. Occasionally this is extremely useful if too much of a wedge is excised when a reverse correction can be made, using part or all of this wedge in the osteotomy thereby avoiding taking more wedges to rectify the over correction that has been made!

The plantar aspect is inspected and cleared of any bony shelves or spikes.

A pair of Rongeurs are used to excise bone fragments and soft tissue from the interface.

Scarring or soft tissue in the plantar aspect must be excised to allow good apposition of the bony surfaces. The presence of soft tissue or scar tissue in the interface is a deterrent to fusion. Using a small laminar spreader can help inspect the plantar aspect.

The bones are now apposed in the corrected axial alignment, with no residual valgus.
Some idea of the sagittal plane correction should be estimated at this point also, though its definitive assessment comes following temporary stabilisation of the arthrodesis with K wires.

The surfaces are carefully matched to get the widest surface area contact, and minor recuts as needed made.It may require chamfering of the edges, rasping of any irregular ridges and filling in of any bony defects to achieve a sound surface area contact through the maximum cross-sectional area of the fusion interface.
A 2 mm K wire is now inserted across the fusion site and driven far enough to just exit the distal fusion surface of the proximal phalanx.
It is important to get the entry point slightly plantar and driving the pin slightly dorsally. Ideally the exit point into the fusion surface needs to be as close to the centre of the surface of the proximal phalanx.
Medially, a ‘cut and spread’ technique is employed to avoid injury to the neurovascular bundle. Roughly about the middle third of the proximal phalanx and perhaps just distal to the mid point of the length of the proximal phalanx would be a reasonable entry point to get the desired trajectory of the wire. One should avoid going too close to the distal end as it would be difficult to get the right angle .

The wire is allowed to broach the proximal phalangeal surface by a couple of millimetres. This allows one to visually confirm the position of the wire in the bone to be as central as possible and also the protruding sharp end of the wire can be used to broached the cut surface of the metatarsal and driven through.
If a large wedge is excised to correct deformity, then the fusion position is difficult to maintain in a stable fashion due to laxity of the soft tissues as a result of shortening.
Note that as straight cuts were employed to make the fusion site active biologically with bleeding bone , the previously mentioned drilling and petalling was not required here.

Once the desired position is confirmed then a temporary K-wire is driven across the fusion site.Once the desired position is confirmed then the K-wire is driven across the fusion site. The position is inspected for residual deformity and adjusted as required once the wire is in place and holding the fusion stable to allow such inspection.

A second K- Wire can be driven roughly parallel and proximal to the first to obtain rotational stability, if adequate stability is not achieved with one wire.

A rigid and flat structure is placed against the sole of the foot to assess the sagittal positioning of the fusion.Now a tray lid from the instrumentation box or a similar rigid and flat structure is placed against the sole of the foot to assess the sagittal positioning of the fusion.
One of the components of the multidirectional deformity in this patient was a dorsiflexion deformity which needs to be corrected. In the ideal setting, the toe needs to be placed in about 10 degrees of valgus and 10 degrees of dorsiflexion relevant to the floor(not the metatarsal axis due to its natural plantar declination) as well as neutral rotation so that the coronal plane of the plantar surface of the toe is parallel to the ground.
This latter position means that the pulp of the toe is approximately 3-4 mm from the plate when at rest, and can easily sit flat on the plate when minimally plantar flexed.
This is the ideal position to prevent the interphalangeal joint from having to acutely plantarflex in order to reach the floor and it can achieve this with only 5 to 10 degrees of flexion.
The coronal position of the toe can be assessed by viewing from above to key in the necessary 7-`10 degrees of physiological valgus if needed and also to assess the quality of correction of the preoperative hallux valgus deformity

The plate is held so that as much of the weightbearing surface of the foot from heel to metatarsals is in contact with the plate to ensure a plantigrade position of the foot. this will then allow you to accurately assess the position of the toe in the sagittal plane.

It is clearly seen that there is still a dorsiflexion deformity with the interphalangeal joint having to acutely flex for the pulp of the toe to reach the floor.
This is a suboptimal position to fuse the toe as it would inevitably lead to problems with the interphalangeal joint, especially its dorsum which will become prominent and symptomatic as the joint flexes acutely to aid in positioning the pulp of the toe flat on the walking surface.

The K wires are backed out and the dorsiflexion deformity corrected with a plantar based wedge excised from dorsally. This can be tricky as the cut has to be aimed plantar and distal if removed from the proximal phalanx, and plantar and proximal if from the metatarsal.
It is best to remove tiny wedges until the desired plantarflexion of the fusion is achieved and over enthusiastic excision of a plantar based wedge will result in a plantar flexion deformity which is equally disabling!

The wires are now driven back into position in order to stabilise the fusion construct for inspection of deformity.

A proximal to distal wire can also be used now to secure the corrected position of the fusion.
The wire is positioned so that it goes from slightly dorsal proximally, starting from just proximal to the medial flare of the metatarsal head to exit into the metatarsal surface just lateral to the midpoint.
A second wire can be inserted at the junction of proximal and middle thirds of the proximal phalanx, on its plantar medial aspect at this level. In the event of using cannulated screw fixation to hold the fusion, a guide wire can be used in pace of K-wires. The use of screws would necessarily require the screw heads to be as low profile as possible if using headed screws and therefore must be appropriately countersunk.

In a well fitting fusion interface, a single oblique wire such as this is enough to provide stability to the construct until the fixation is applied

The toe is now inspected again and the valgus deformity is well corrected. Note that the toe is shortened slightly due to the removal of the wedges. This can be no more than a few millimetres for fear of transfer lesions . This is another important reason why the hallux must be accurately positioned so that one can ensure that the 1st MTP joint can be re-functioned to bear weight.

The plate is now selected and carefully checked for side and length. The Synthes MTP fusion plate has the following features:
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. It’s probably mechanically advantageous to use the longest one that doesn’t impinge on the distal IP joint and this is usually a medium size on women and a large size on men in a primary fusion.
In a revision fusion careful selection of plate length is important as the proximal phalanx may be quite short due to resection for correction of deformity. A contingency option should be available if the Synthes dorsal plate is not suitable
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) which usually is not used as the compression slot is more reliable and easier to use..
There is a compression slot (3) in the plate and a static hole (4) for use with the compression clamp and wires.

The instrument tray contains :
Compression clamp
Balled compression wires to secure plate and compress fusion site. The compression wires are threaded at various lengths in their tips. It is important to choose the length of thread that will penetrate the plantar cortex of the bone so that concentric compression of the fusion site can be achieved otherwise only the dorsal part of the fusion may be compressed, resulting in dorsiflexion of the fusion construct

The plate is now carefully positioned, centring it equidistant over the fusion line.The plate is now carefully positioned centring it equidistant over the fusion line. The compression slot is proximal (1), and the static hole is distant. The compression slot allows for a compression of 3 mm or so by allowing the plate to move proximally when fixed to the proximal phalanx through the round wire hole using the compression clamp.
It is noted here that the plate is not sitting flush on the bone over the fusion site and is lifting off distally.

A saw is used to sculpt the dorsal surface till it is flat.
This may require the dorsal cortex to be thinned out substantially and sometimes even recessed to allow the plate to sit flat.
This is a situation where the use of a locking plate has significant advantages over a non locking plate, as it does not rely on dorsal cortical purchase for stability.

A ball-ended compression wire is then inserted into the proximal end of the compression slot and secured in place.
It is important to note that the wire must be advanced until the ball engages with the plate and no more rotations should be performed after this point. Otherwise the threads will be stripped off the bone and the strength of purchase of the threaded wire will be lost, making the compression device redundant.

A second compression wire is then inserted into the static hole at the part of the plate distal to the fusion site.Both wires MUST cross the plantar cortex to ensure concentric compression across the fusion site.
Ball tipped wires with different thread lengths inferior to the ball are available.
Note how the first compression wire sits flush with the plate and in the proximal end of the compression slot (1) prior to compression.

The compression clamp that fits around the two wires is now applied and the fusion site is compressed.The compression clamp that fits around the two wires is now applied and the fusion site is compressed. As the clamp is ratcheted, it can be locked at the position of maximum compression.

A close up shows the positioning of the wires through the plate.

The cupped ends of the clamp engage around the ball part of the wires in a secure fashion.

The ratchetted mechanism is used to lock the clamp at the moment of maximum compression.This can be visualised as well as measured by observing the movement of the wire in the compression slot(1). Note how the plate has travelled proximally taking the proximal phalanx with it compression the fusion site. This can be confirmed noting the position of the proximal compression wire position distally in the compression slot.(1)
Over compression is prevented by the distal end of the compression slot, which will stop any further compression.
It is prudent to see the position of the fusion for a final time and image intensification can be used to confirm the position of the fusion as well as the plate.
One should also do the tray lid test again to ensure that the dorsiflexion deformity is fully corrected, following the application of compression.

A drill hole is made using the coned variable angle guide at the proximal part of the plate for the first locking screw, after definitive compression has been appliedThis allows a 30 degree cone of variable angle locking. This is very useful in a revision setting as either broken metalwork, cortical deficiency etc may make fixed angle locking a difficult process, because the presence good or indeed any bone for fixation can’t be taken fore granted.

The appropriate length of locking screw is confirmed and inserted.The appropriate length of locking screw is confirmed and inserted. Note that the compression is maintained well, as evidenced by the position of the ball of the compression wire in the compression slot(proximally).

A second screw is similarly inserted into the proximal part of the plate.

A third screw is inserted into the distal part of the plate angling slightly proximally.

With locked distal fixation of the plate, it is securely fixed across the fusion and therefore the compression wires can be removed as well as the stabilising wire.

The remaining screws are now inserted using a minimum of two locking screws either side of the fusion.As mentioned before, the 30 degrees of flexibility in directing the locking screws are of great use when avoiding broken metalwork or bone voids.

Finally the proximal hole is drilled and measured.

This compression hole can also be used to achieve more compression, although if the compression wire has traversed distally through the compression slot and hasn’t reached the distal end of the slot, it usually means that maximum compression has now been achieved. Instead this hole is now used to insert a locking (non-compressive)screw as the facility exists in this hole to accept a locking screw also.

The plate test is performed for the final time to ensure correct position and correction of the dorsiflexion deformity.The plate test is performed for the final time to ensure correct position and correction of the dorsiflexion deformity and final screening of the fusion is performed using image intensifier and images saved.

If there are any voids in the fusion site the excised wedges can be morselised and used as bone graft to fill these sites. The wound is irrigated with saline.

The capsular layer is now closed with interrupted absorbable sutures.
Care must be taken to ensure that the sutures don’t go through the Extensor hallucis longus tendon for fear of tethering it down to bone. This can cause pain and discomfort postoperatively.

A few sutures may be used for the subcutaneous layer although this is not always necessary.

I use interrupted Vicryl Rapide sutures to close the skin.

Intra-operative fluoroscopic anteroposterior image shows good correction of the Hallux Valgus deformity. It also shows a small gap in the fusion site which must be filled with bone graft to avoid a further non union

Oblique fluoroscopic picture shows excellent correction of the dorsiflexion deformity.
It is especially important that screws are not prominent in the plantar weight bearing aspect of the first ray.

The lateral view also shows the corrected dorsiflexion deformity and a well apposed fusion site

Well padded dressings are used over the wound using absorbent gauze in between the 1st and second toes in addition to act as a spacer. The absorbent dressings are also passed through the first interdigital space to absorb any blood or exudate here and prevent maceration of the skin in this region.

Finally Wool and crepe are used to firmly compress the foot.
The tourniquet is let down to ensure that the perfusion to the toes are satisfactory.