Ankle replacement-Wright Infinity ankle replacement

The limb is positioned so that the patella the anterior tibial crest and the axis of the foot can be easily assessed for alignment. it is essential that this long axis of the leg is well aligned and not rotated or inclined in the sagittal plane. The common error made is either an internal rotation malalignment that is overlooked because the surgeon has forgotten the sand bag underneath the patients buttock/ it is best to mark out the outline of the malleoli, the extensor hallucis and tibialis anterior tendons, the joint line, and the superficial peroneal nerve if found.

The skin incision centred on the intertendinous gap between the the tibialis anterior and the extensor hallucis longus is used most commonly. This allows for safe and predictable dissection of the joint line. The incision will encounter the neurovascular bundle which can be seen identified and protected throughout the procedure by retraction. It is also the reason that retractors need to be periodically released so as to avoid injury to the neurovascular bundle. Superficial nerves may be encountered in the fat layer which are either the deep peroneal nerve (laterally) or the saphenous nerve (medially).

The skin incision is deepened without laminating the skin from the deeper layers so as to avoid visualisation of the entire anterior aspect of ankle joint. Osteophytes and other bony prominences SHOULD NOT be excised for fear of losing the vital landmarks for seating the Prophesy cutting guides. Careful excision of all soft tissues including all periosteum from the bone on both the distal tibial and the talus is vital to the success of seating the cutting guide templates to hit the soft spot. The use of a wet swab to periodically moisten the soft tissues is essential to keep them from being devitalised by dehydration. As mentioned before the self retainers if used need to be removed/ relaxed every few minutes to avoid pressure necrosis of the skin and soft tissues

It is useful to practice the use of the tibial cutting jig by positioning the models on the model of the distal tibia which is available with the cutting guide template kit. This further helps with attainment of the optimal position of the cutting jig template.two trimmed 2.4 mm Steinman pin fragments are place on holes either side of the mid-line of the template to act as radiographic markers in holes that are pre-drilled during manufacture.

The cutting jig template is then positioned accurately over the bony landmarks on the distal tibia. This step is extremely important and it is worth spending some time to ensure that the right position has been achieved with no compromise in the feel of the sweet spot. If the template toggles or does not feel like a perfect fit, it is essential to remove the template and re-excise any areas of soft tissue or periosteum and then trying again with the template. once the position of the template is deemed to be accurate a 2.4 pin is drilled through one of the side holes for temporary fixation and trimmed . a further 2.4 mm pin is inserted into the hole in the midline of the template to act as a radiographic marker between the 2 small wires. this will be used to confirm that the cutting jigs are in the correct position and are in the middle of the tibia on AP screening

Once the screening images confirm that the long pin i in the middle of the tibia and is lying equidistant between the 2 smaller pins , then a further 3 pins are inserted into the remaining 3 holes to confirm the final position of the template
The ankle is then screened to get the final position of the template confirmed.

The template is then removed leaving the wires in situ

The Prophecy conversion instrument is then inserted into the superior 2 pins
The coronal sizing guide is then threaded over the inferior 2 pins and guided into position to interdigitate with the conversion instrument into position

connect the two components with hex driver and firmly tighten the coupling screw until the two components are secure

Now screen the ankle in AP and Lat projections. It is essential to get the bulls eye sign where the central AP pin is in the middle of a circular radiological marker. This determines that the true AP of the cutting block has been achieved
Then assess size with lateral and medial gutter positions in perspective using the sizing block. If need be after such assessment change sizes as in this particular patient where i needed to upsize one up

It is essential to get the bulls eye sign where the central AP pin is in the middle of a circular radiological marker. This determines that the true AP of the cutting block has been achieved

Use corner post drill to establish the gutter dimensions and create a stress free intersection of vertical(gutter) and horizontal tibial cuts.

Complete drilling on both sides. It is essential to hold the ankle dorsiflexed so as to avoid any injury to the talar dome at this stage.

Substitute the coronal sizing block with the tibial cutting block. This should fit in the top two pin holes.An optional divergent pin is then inserted medial or lateral for extra stability of the cutting block. It is necessary to trim the superior pins flush to the cutting block except for divergent pin so that the saw is not obstructed during the process of resection.

first the horizontal cut is made. It is important to ensure that the saw is sitting straight in the slot for it on the cutting block . it is also important not to bend the saw during cutting as it caused the saw to vibrate violently and can indeed cut wrong when doing so. it is also important to ensure that the saw is not deflected by sclerotic bone

the gutter cuts are then made. the medial cut should not be completed with the saw to avoid injury to the posterior tibial neurovascular bundle

Now take the conversion instrument and the cutting block off but leave distal tibial pins in situ.
With 1cm fine and sharp osteotome angled at 60 degrees to axial plane divide resected distal tibial fragment into anterior and posterior portions.Remove anterior portion and leave posterior for after as there is significant merit in doing this process with more space and better visibity due to vulnerable structures in the posteriomedial aspect of the joint. this step is best done after the talar horizontal cut excision

The anterior fragment is usually taken out as one fragment

The posterior fragment is left in situ for later. it can be cut up into sections as shown prior to excision

Now the talus model and the talar cutting guide template asre used to practice the sweet spot for its placement . Similar to the steps in the tibia identify the sweet spot and if in any doubt search for and excise any soft tissue that remains

The plunger inserter is taken off and a final check is made of the poly insert and whether it is sat flush within the tibial tray

Position the cutting guide template by plantarflexing the ankle to get the guide into perfect position.
Next the template is fixed with a 2.4 Steinman pin in either of the 2 upper holes.

Now drill 2 further pins into the anterior holes as shown.
Following this the Talar cutting template can be removed.

Then the ankle is now screened to confirm both anterior pins are parallel and also overlap each other perfectly so that image has only 2 pins seen superior and inferior. The distance between the lower pins and the articular surface of the talus indicates thickness of cut.
This parameter should be cross checked with the engineers report

The template is now exchanged for talar resection block
Gutter pins are placed in holes in the corners of the cutting guide to mark the lateral and medial gutters and protect them so as to avoid cutting through malleoli
The talar horizontal cut is now completed taking care to complete the posteromedial part of the cut by hand with osteotome to avoid injury to the neurovascular bundle.

Remove resection block and talar wires

Insertion of laminar spreader to aid taking out the remaining portions of anterior tibial cut.
This is now much easier as the posterior recess of the ankle can be opened up. the sections are taken out with the pituitary rongeurs or similar graspers. This process can sometimes be quite as they are densely connected to the capsule at their level. It is essential to completely clean out the posterior aspect of the joint to avoid heterotopic calcification that can sometimes be seen here if fragments are left. A periosteal hook is available to excise the periosteum off the bone segments but i do not find this useful and would prefer to grasp the fragment and rotate it to avulse the fragment. If the posterior part of tibial resection is not segmented then a corkscrew is also available to try and remove the posterior half en-bloc. Again I do not find this useful as often the bone breaks on application of traction or torsion

A corner chisel is now used to divide the posterolateral and posteromedial tibial cut cortices and these are carefully picked out. The chisel should be carefully dislodged often using a hammer after cutting through the cortices and not levered out of position as it will cause huge stresses on the malleoli leading to fractures

Wash out to remove loose fragments leaving the posterior recess clean and free of bony debris

Now the tibia is ready to receive the tibial tray insert which can now be threaded over the distal tibial pins. It will usually fit snugly into the resected tibial surface. Occasionally theremight be incomplete resection of the gutter or the posterior corner cuts which might prevent sitting of the tray. These need to be redone or filed down . An osteotome can also be used to gently chisel away prominences

The ankle is then screened to ensure that
a) The tray is siting flush on the resected surface
b) The tray is of adequate length and extends beyond the posterior cortex of the tibia by a millimetre
c) The tray is perpendicular to the long axis of the tibia in the sagittal plane

The tibial implant needs 3 peg holes which are now created through the tibial tray insert. First an angled broach is introduced into the central hole and gently tapped into position until the laser line on the broach enters tibia. This is then left in situ. a lateral broach is now used to make the remaining two peg holes by a similar process whilst the central broach stabilizes the tray.

Here both broaches are seen in situ

Leave the tibial trial in situ after careful extraction of the broaches. These may have to be tapped out gently so as to not widen the holes by twisting too much.Now the talar dome trial of appropriate size can be introduced with the appropriate sized poly insert using a special introducer handle which is fitted on to the poly in a special recess on its anterior surface. This will require some distraction and plantarflexion usually.

The completed assembly confirms easy but firm insertion of the poly insert and a comfortable seating of the talar dome trial

Now the ankle is screened in the lateral view to confirm Ap length and talar cover adequacy as also the anterior and posterior chamfer cut trajectory. This is carefully assessed by adjusting the image intensifier so that the dome trial shows an inverted ‘v’ both anterior and posteriorly. This will confirm a true lateral view of the trial and also will show the correct trajectory of the chamfer cuts. It may be necessary to move the dome trial anterior or posterior to adjust for the best cover but usually is well positioned automatically. This is however a useful stage to adjust position if required. This is also the stage where an estimate of the range of movement can be made especially in dorsifexion to decide if a tendoachilles release may be required of the ankle is in equinus and cannot dorsiflex. This is usually done in a percutaneous manner by the use of the 3 cut technique.

Once the above parameters have been examined and confirmed to be satisfactory then two wires into talar dome trial to mark the site for the talar resection guides

Now the talar resection guide can be introduced by threading over the pins through 2 anterior holes in trial

Lateral temporary fixation screws are then introduced through oblique holes which are placed quite posteriorly on the trial.An assistant holds the cutting block securely in place when this is done. One needs to plantarflex maximally to make it easy for the introduction of these screws as they often catch on the tibia. Occasionally one or the other might miss the talus entering the gutter instead. It may then be necessary to use only one of these screws. Initial insertion can be done on power then finish with ‘T’ handle to avoid stripping the thread.
Now the posterior talar chamfer cut can be performed between the two anterior pins. i would ask my assistant to stabilise the cutting guide at this stage as the vibration from the saw could still dislodge the screws and pins!Take care to ensure that the saw does not slide off the talar dome especially in sclerotic bone.

Then take one pin out and reinsert it into the central anterior hole on the cutting block. This is done to facilitate the seating of anterior talar pilot guide.Now cut the central pin short and remove the other pin. The cutting block is now being stabilised by 1 central pin and two lateral screws

insert the anterior talar pilot guide which cuts a the first of the chamfers on the anterior face of the talar implant foot print using the correct sized talar reamer. This is scalloped and the reamer enters each scallop in turn from lateral to medial . It is essential to turn the power off the reamers during entry and exit . This will ensure that the reamer does not dislodge the cutting block by catching the sides of the scallop when being introduced or removed

Sequential enter each scallop and ream until the collar of the reamer engages with the talar pilot guide.

The scalloped anterior talar pilot guide is now inverted so that it now functions as a reaming guide to deepen the anterior part of the talar resection to create the second of the the anterior talar chamfer to seat the anterior edge of the implant

A smooth guide is now saddled in place of the scalloped one and repeat the process as above by inverting the smooth guide.The reamer now moves from side to side in the slot of the smooth guide and takes out the prominences between scallops. It may be necessary to use a nibbler to take out any remaining prominences after cutting guides have been removed. These are particularly anteriorly and usually are in the anterior part of the anterior chamfer as ridges that are outside of the cutting guides’ area

The Chamfers now appear smooth and the pins and the cutting block can be taken out

The tibial, talar and spacer trials are inserted. The tibia is inserted first then the talus and finally the spacer is introduced carefully with its introducer handle. This is quite tricky as the handle can slip off its slot if not careful. One should not force the spacer trial with significant force as it may distract the joint unnaturally and the malleoli can be avulsed. At this stage it is useful again to check range of movement and medial lateral stability as well as rotational stability. I would screen the assembly at this stage again merely to ensure that the final assembly before the talar pegs are drilled is satisfactory.

The talar trial is then stabilised with 2.4 steinman in central anterior hole.

Through holes in talar trial 2 peg holes are now drilled with the appropriate drills
Then remove all trials. Carefully remove all loose fragements of bone and any capsule or other soft tissue traversing the joint .Look for any prominences or rough and irregular area and pare them down.I thoroughly clean and brus the cuts with pulsed lavage with saline and then irrigate with betadine. Dry the area and insert gauze to keep it dry whilst you change gloves and drape to fresh clean ones.

Before implanting, ensure that the size is what was chosen to avoid the error of wrong size implant being inserted
Using no touch technique as far as possible, handle tibial implant carefully with tibial tray inpaction insert and handle.

Implant initially by press fit ensuring the pegs are lined up against the holes.This may require a gentle tap to key the implant as posteriorly as necessary but one needs to be extremely careful not to lengthen the peg holes thereby irreversibly posteriorising the implant

Using special offset tibial tray impactor, carefully impact posteriorly first using notch on the tibial implant tray to ensure that the prosthesis is well seated down on the tibia then move to the anterior notch to repeat the impaction carefully. Do this in turn returning to posterior notch to ensure uniform pressure applied throughout tray. Do not hammer excessively especially in cancellous bone which is soft

The ankle is now screened and on the lateral view it is confirmed that the tibial implant is well seated posteriorly

The poly insert is now carefully positioned on to the guide rail using the special piston spacer introducer in readiness for introduction

Carefully align talar implant pegs and push the talar implant into peg holes . Avoid twisting or toggling the implant during this process to prevent distorting the peg holes. Although there is an introducer available I prefer using my hand to push the implant in with the articulating surface of the implant being protected with gauze. I find this more stable.

A protecting wedge can now be introduced into the joint space before the talar implant is impacted using the yellow tipped talar dome impactor. The ankle is plantarflexed for this procedure. The impaction starts from posterior to ant. This sequential positioning of the impactor ensures uniform pressure to press fit the talar implant.
A screening of the ankle is done to check the position especially of the talar implant

Two attachment screws now inserted into corresponding holes on the anterior face of the tibial tray and tightened.
The poly insert which is now on rails on the poly inserter is readied for use by locking it into place

Insert the plunger over the attachment screws through holes on the plunger until flush onto the anterior surface of the tibial tray. Two attachment nuts are then screwed on over the attachment screws and tightened with box spanners to lock poly inserter in place.

Plunge down with sustained pressure like a syringe as the poly is squeezed on to railings . Once you meet resistance turn handle clockwise to further push home the poly insert on to railings on the tibial tray. This is to be done until the poly can move no further .

Final images are taken to document implant alignment & the state of the malleoli.

The wound is then washed with copious amounts of betadine and saline and any loose fragments of bone removed. Haemostasis is checked and the retinaculum is closed with 2-0 vicryl interrupted carefully without over tightening it or picking up the underlying tendons. The deep fascia is closed interrupted with 2-0 vicryl

Interrupted 3 -0 Vicryl Rapide is used for closure of skin
30 ml of 0.5% chirocaine is used for extensive infiltration of wound and intra-articular injection

The tourniquet is then released to confirm good circulation. wounds are dressed with Inadine and Mepilex dressing
wool and crepe are quickly used to create a tamponade with the limb elevated. A below knee back slab and ‘u’ slab are used to hold the foot in plantigrade position. The patient is recovered with the limb elevated and an ice pack over the anterior aspect of the ankle