Tibio-Talo-Calcaneal (TTC-Double )fusion using Zimmer Ankle Fix plus plate

A 46 year old female presents with a history of pain and deformity with limb length discrepancy. She is an insulin dependant diabetic with good control and is a smoker. She was treated for a supramalleolar ankle fracture and subsequent Charcot arthropathic change. She also suffered a medial ulcer from her brace and found that she was unable to weight bear due to the severe recurvatum deformity in addition. She was treated with plaster initially and then with a brace.
Risk factors included previous infection of a medial ulcer with Staph Aureus, moderately heavy smoking habit, diabetes,and a small diameter of tibial canal below the isthmus (8mm)

Anteroposterior view shown.

Lateral view shows the severe recurvatum and at the fracture site as also relative plantaris deformity of the foot. The combination of the severe valgus and recurvatum puts her at high risk of further ulceration and she in effect has an unbraceable foot.
The algorithm of surgical treatment is complex :
The issues of diabetes and smoking will adversely affect healing both of soft tissue and of bone
She had already got significant limb length discrepancy with her fracture and every attempt was to be made to retain length sacrificing minimum amounts of bone during the fusion process.
She had got problems with the opposite side with midfoot OA secondary to previous Charcot arthropathy: therefore post operative mobility will be difficult. She was referred to occupational therapy and Social services with a view to ensuring that both physical aids and accommodation appropriate to her level of mobility was made available BEFORE the operation to ensure that she did not stay in hospital anymore than required.
She had a compromised renal function along with a high HbA1C which had to optimised prior to surgery.
The tibial canal below the isthmus was only 8 mm and this was about 14 to 15 cm from the floor . This would have been too narrow to consider the use of intramedullary nailing as the current implants only offer a minimum diameter of 10 mm which would require reaming to 11.5 cm making it dangerous to use for fear of stress fracture or splitting the tibia.
It was therefore decided to use the Zimmer AnklePlus plate as a suitable device to span both the ankle and subtalar joints.

Patient is positioned to give full access medial lateral and posterolateral. This also allows for access to the heel in this patient for insertion of compression screw.
It is important that the knee is left visible (or easily palpable) to allow correct realignment of the foot ,which is done by ensuring the 2/3 ray lines up with the patella.

The important landmarks for the lateral transfibular approach to include access to the subtalar joint.
It is useful to mark out the tibial crest, tibial tuberosity, the medial and lateral malleoli, base of the 4th and 5th metatarsals, and the mid line of the foot between the 2nd and 3rd metatarsals which will define the extent of the malalignment (when referenced from the tibial crest).

Lateralisation of the axis of the foot due to severe fibular shortening.
The 2/3 rays should sit in the line of the patella.

The incision is made starting on the distal fibula, midway between its anterior and posterior borders about three inches above its tip. The incision is extended to the base of the 4th to allow for relaxation of the skin in a valgus deformity such as this.
It is important to note that the superficial peroneal nerve lies anterior to the incision and the sural nerve posterior to it. Aberrant nerves are often encountered which sometimes need to be sacrificed to gain proper access.. the incision lies over the Extensor Digitorum Brevis muscle at its distal end and can be used to expose the calcaneocuboid joint if a pantalar fusion is planned. It is important to dissect the anterior and posterior flaps as full thickness going subperiosteally to avoid delamination and devitalisation of the skin flaps.

The distal 2 1/2 inches of fibula is carefully dissected to denude it on all sides. This segment of fibula can be useful for bone graft if the bone is healthy

The fibula is then dissected 3 ½ inches proximal to the lateral malleolar tip. A sagittal saw is used taking care to avoid damage to surrounding soft tissues structures. The fibula is then cut at the site of osteotomy at an angle of 45 degrees to the horizontal aiming distally and medially bevelling it in such a fashion that there are no sharp spikes of fibula that present themselves to the skin. This gives an excellent view of the ankle and the subtalar joint.

The process of distal fibulectomy is sometimes quite difficult and needs to be done with due attention to surrounding tissues. In particular the sural nerve posteriorly along with the peroneal tendons need to be protected with a Hohmann retractor or a similar instrument. Anteriorly and especially whilst cutting through the syndesmosis, the inter-osseous vessels need to be protected by direct visualisation as they can bleed considerably and can be difficult to find and cauterize.

The syndesmotic and lateral ligaments are dissected off the distal fibula. It may be necessary to use an osteotomy especially if the syndesmosis is heavily calcified. The fibular graft is then stored in wet swab soaked in saline to be used when necessary.
The fibula can be split sagitally if an RAF fusion(fibular strut augmentation) is contemplated . This can however be difficult as a lateral plate is being used and therefore the fibula will require excision in this situation.

Both the ankle and subtalar joints are accessible from the lateral side.
Two West’s self retaining retractors are used to gently retract the joint frequently loosening them off to prevent soft tissue damage. the anterior distal tibia is then stripped of the soft tissues especially the capsular attachment to expose the joint almost to the medial gutter. Care needs to be taken whilst doing this especially when using a periosteal elevator as the anterior tibial vessels and the superficial peroneal nerve lie anteriorly. The entire anterior preparation needs to be sub-periosteal in order to avoid this. I often resort to sharp dissection to initiate the step and then use the periosteal elevator when I am certain I have reached the right plane. Anterior osteophytes need to be carefully exposed and then excised as they may give a false impression as to the plane of the flap. The removal of the osteophytes is also essential to ensure that the ankle can be suitably dorsiflexed when the position of fusion is decided.
The approach also gives an excellent view of the posterior aspect of the tibia. Again careful sharp dissection of the posterior tibia followed by very careful dissection with a periosteal elevator will expose the posterior tibia. Once the tendon/muscle belly of the Flexor Hallucis Longus is visualised then dissection should stop as any further dissection will put the posterior tibial neurovascular bundle at risk of damage. A posterior capsular release is also done from this part of the dissection.Any loose bodies or osteophytes can also be removed.

A medial incision is then made directly over the medial malleolus after identifying the joint and the medial gutter from the lateral side. It is useful to pus a blunt artery forceps through the joint from the lateral exposure until it tents the medial skin to locate the exact position of the joint.
The incision is made longitudinally in the middle of the long axis of the medial malleolus so as to ensure equal flaps can be raised to expose the medial malleolus. Posterior dissection is carried out with great care to ensure the tendons of the tibialis posterior and flexor digitorum longus as well as the posterior tibial neurovascular bundle are protected.

Medial wound closure

The incision is then extended and the whole of the medial malleolus, the medial aspect of the distal tibial articular surface and the medial are talus exposed. This step is necessary as the excision of the medial malleolus is necessary to centralise the talus underneath the tibia

Due to the severe nature of the articular deformity , straight cuts are made in this patient to prepare the fusion surface . It is important to note that the medial end of the cuts are not completed through the lateral side for fear of injury to the neurovascular structures on the medial side of the ankle behind the medial malleolus. Image intensifier is used to ensure that both the trajectory of the cut and the amount of bone resected are accurate.
It is useful to place a K-wire perpendicular to the long axis of the tibia from lateral to medial to ensure that the cut made is correcting the deformity and the minimum resection required to correct the deformity is made so as to minimise further limb length loss.

Correction of the deformity is to be assessed in all three planes. if there is residual deformity in equinus, it may be necessary to perform a tendo-achilles release and a posterior capsular release. Care is to be taken to ensure that the posterior tibial neurovascular structures are protected throughout the procedure by not dissection medial to the tendon of FHB

When the cut is started on the tibia, the ankle is screened to confirm that the right trajectory is being followed by the saw both in the coronal and sagittal planes to prevent valgus or varus cuts. It is particularly important in this case that the first cut is the right cut because further corrective cuts will significantly increase the limb length discrepancy. Care needs to be taken to ensure that the whipping motion of the saw does not cut vital structures both anteriorly and posteriorly. In the posterior aspect of the joint care needs to be taken to ensure that undue division of the FHL and the posterior tibial neurovascular bundle does not happen. It is therefore preferable to complete the cuts with an osteotome. I leave the posterior lip intact, break off the remaining tibial cut and then excise the posterior lip with an osteotome.

With the ankle in a plantigrade position, the talus is then cut parallel to the tibial cut . Again if there are any concerns about malpositioning of the saw it is useful to screen the ankle to assess the position of the cut before completing it. It is also important to avoid cuts that would result in an equinus or calcaneus position of the ankle. The use of straight cuts will mean that changes in the angle following the first cuts, will result in further bone requiring to be excised. This is highly undesirable in deformity correction and all steps need to be taken to ensure that the first cut is the only cut:’ the first and only bite at the cherry approach!’
It is also useful especially in situations such as this to put the talus against the tibia in the desired position and stabilise with a k wire or two before the talar cut is made. With the talus thus positioned a talar cut can be initiated and then completed after the k wire is removed. This will ensure again that the first cut is the right cut. Like the tibia, great care needs to be taken to ensure that the talar cut is carefully completed. I will break off the talar cut 2/3rds of the way posteriorly and medially then excise the remaining whilst using a laminar spreader to distract the joint allowing me good visualisation

The subtalar joint is accessed after cutting away the capsule . A Hintermann K-wire distractor can be used if access is tight or the joint is poorly visible. In this case access was easy and visualisation of the joint did not require any distraction. The redundant cartilage, osteophytes and exuberant synovial and fatty tissue in the sinus tarsi are all excised to ensure that the talocalcaneal joint is well reduced and the os calcis is in the right plane relevant to the tibial long axis. The posterior face of subtalar joint is then denuded of cartilage and osteophytes, drilled and petalled to break into the subchondral bone until good bleeding is observed. I do not routinely perpare the middle and anterior facets but these can be accessed and prepared if desired.

From the medial side through the incision the cuts are carefully inspected after ensuing that all soft tissue is resected from the medial malleolus. The medial malleolus and the adjacent tibial articular cut is then excised with the reminder of the tibial surface cut being extracted from the lateral side. Similarly the talar surface is inspected and any uncut edges are completed and excised.

The joints are temporarily stabilised using 2 K wires and screened to check for position and apposition. It is vital to get the position of fusion perfect. The optimal position is plantigrade in the sagittal plane with physiological valgus and external rotation which can be assessed preoperatively on the opposite side if it is normal. An angle of 5 deg of valgus and 5-10 deg of external rotation is desirable. The rotation and valgus angle can be made relevant to the tibial tubercle and the sagittal axis of the patella: hence the importance of prepping above the knee in these procedures.It is important to assess this position with the knee flexed and the subtalar and midfoot joints stabilised with the hand to avoid keying in gastrocnemius tightness, midfoot dorsiflexion etc. The foot can also be placed on a plantigrade right angle template if available and screened in simulated weight bearing.

It is my practice to let the tourniquet down to check for circulation and ensure no damage to the posterior tibial artery has occurred in view of the saw traversing the width of the distal tibia. It also ensures that the artery is not trapped in the fusion on the medial side. The use of lateral to medial k wires to temporarily stabilise the joint also increases the risk of injury to the medial neurovascular structures.

Implants are now inspected and carefully assessed for the side and size as the implants are side specific. The AnkleFix Plus comes in two sizes, standard and large and must not be confused with the AnkleFix plate. The latter are used to fix an ankle fusion only and lack the calcaneal extension required to effect a tibiotalocalcaneal fusion

The set contains the plates and screws along with instrumentation including the compression device. 4 mm locking and standard screws are available with locking screws useful in the soft bone of the os calcis for good fixation. 2.7 and 3.5 mm drills are used with the 3.5 drill used in the harder bone of the tibia particularly in hard subchondral bone

It is necessary to use the threaded drill guides for the locking screws to ensure that the drill holes are made such that the screws lock into the threaded holes in the plate. As many of the screws are divergent, using a regular drill guide or eyeballing the trajectory will result in either an inability to lock the screw fully leaving a proud head or damaging the threads in the hole. The standard drill guide is used for the non locking screws.

The distraction device is very useful in achieving compression prior to fixation with screws across the ankle joint. As it is used from lateral side it is important to ensure that it does not pull the fusion construct into valgus which is one of the reasons why it was not used in this case. this is particularly the case when the fibula and the medial malleolus are excised which leaves the construct unstable; hence the need for stabilisation with temporary K-wires.

An implant is chosen and temporarily held with K-wires to assess the position and the fit. I usually screen the construct to ensure that the implant is well positioned spanning the 2 joints adequately. It is also necessary to position the implant to ensure that it does not cause an impediment to the gliding excursion of the peroneal tendons. It is for this reason that the screws need to be seated and locked in completely so that prominent screw heads don’t cause attrition of the tendons overlying them.

As a routine a posterior to anterior screw (the so called ‘home run screw) from the tibia to the talus is used to stabilise the ankle and compress it. In this case however, I have used a 8mm cannulated screw from the tuberosity of the Oscalcis through the subtalar and ankle joints and into the tibia to achieve compression of both joints. A further screw from medial tibia to the the Oscalcis was also used to augment compression across both joints. Additional compression can be gained through the plate if required by the use of a compression device that fits on to the plate to achieve compression. It was not used in this case.

A snug fit with as little distance between plate and bone is highly desirable to gain maximum mechanical advantage. This is particularly important in varus deformities of the ankle when the oscalcis needs to be snugly held by the plate to avoid cutting out of the screws. In order that the fit is satisfactory, the lateral bed of the plate needs to be created by sculpting the lateral wall of the oscalcis including excising the peroneal tubercle taking care to avoid injury to the peroneal tendons. Lateral talar and anterolateral lip prominences of the tibia need osteophytes, as also the incisura fibularis on the lateral tibial wall need to smoothened with a saw and nibblers to ensure a snug bed for the plate. It may be necessary to contour the lateral wall of the talus so that the talar part of the plate fits as close to the talus as possible. It is however the case that on occasion the plate may stand off a little from the talar body but the locked screws ensure that the construct is stable.

The implant should be of the right size to comfortably be seated to span both joints. It must also allow for insertion of screws into the body of the talus.

Using a black collared drill sleeve and the appropriate drill, the Os Calcis holes are drilled first using the 2.7 mm drill and the threaded drill guide. The distal end of the implant is secured on to the oscalcis with 3 locking screws. As these are divergent, only 1 screw can be put in at a time. It is important to temporarily stabilise the plate proximally with a wire both at its distal and proximal ends to ensure it does not move posteriorly on the tibia.

Sequential screws can then be driven into the tibia . I prefer to stabilise the plate proximal and distal and finally put the screws into the talus. This ensures that the plate is seated perpendicular to the fusion surfaces and does not slip anterior or posterior. The position should also be checked using the Image Intensifier.

The 3.5 drill can be used in the tibial end of the plate if the bone is hard. Again dedicated threaded drill sleeves will ensure accurate positioning of drill holes for the locking 4 mm screws to be inserted and locked on to the plate.

The lateral view is obtained to confirm the correct positioning of the implant particularly on the tibia as there is a tendency to position it either too posteriorly or anteriorly on the tibia,. This may affect the position of fusion if not careful.
The view also show the correct positioning of the foot relevant to the tibia avoiding either a dorsiflexed or plantarflexed position. The gap seen on this view is actually filled with bone graft .
The plate in this case is somewhat lower than it should be position with the result the talar part of the plate is sitting partially on the Os calcis. This was as a result of poor purchase on the os calcis in the original intended position and hence had to be moved more distally to get good purchase with the screws.

The construct is checked for any voids and gaps as also the final position to ensure the optimal position. Any voids must be filled with morselised bone graft harvested from the excised malleoli. The construct is also checked for rigid stabilisation by gently stressing the consturct and ensuring there is no abnormal movement. Now the tourniquet is let down to confirm satisfactory perfusion of the limb and to gain haemostasis

I routinely aspirate bone marrow from the proximal tibia to inject into the fusion sites . . In this case synthetic BMP was also used as there were significant risk factors( diabetes, smoking)

The periosteal layer is closed over the plate and then subcutaneous interrupted sutures are used to loosely appose the skin

Prior to skin closure bone marrow with or without synthetic BMP is injected around and into the fusion sites. The skin is then closed with interrupted mattress sutures(Vicryl Rapide). 30 mls of 0.5% Chirocaine is injected into all wounds for post operative pain relief