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Ankle replacement-Wright Prophecy

    Overview

    Learn the Ankle replacement-Wright Prophecy surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Ankle replacement-Wright Prophecy surgical procedure.
    Customised Patient Specific Instrumented ankle replacements are the latest advance in this emerging field.
    The first ankle replacement was implanted in 1970 by Lord & Marotte. It was effectively an upside down hip stem and naturally the results were poor. Since that time there have been several generations of implants. Initially the implants were constrained and cemented, later followed by unconstrained using a mobile bearing meniscal implant and the most modern of implants are now two component fixed bearing.
    Ankle replacement technology is an emerging but rapidly growing field. Approximately 900 ankle replacements are performed in the UK each year, in comparison to perhaps 2000 ankle fusions (NJR and HES Data).
    The basic premise for ankle replacement technology is based on a lack of understanding how the joint actually works. Initial concepts that the joint is a monoaxial hinge are of course incorrect. Aside from just plantarflexion and dorsiflexion, the joint rotates, inverts and everts and translates forwards and backwards. Indeed even sagital plane motion is not just in one plane as the arc of motion of the talus on the lateral side is greater than the medial side hence creating a rotatory motion within the mortise by the frustrum shaped talus.
    Modern thinking and newer generations of implants have removed the need for cement, using porous coatings or HA coatings for osseointegration, ultra high moleccular weight polyethylene (UHMWPE) as an articulating surface, and better instrumentation. Most implants use cobalt chromium allow although some implants are made also of titanium. The most recent innovation was the use of patient specific instrumentation (PSI) which enables CT scan data of the patient to produce patient specific jigs from nylon that can be used to plan the surgery in advance avoiding the need to determine variables such as alignment, size and rotation on table.
    The INFINITY™ Total Ankle System is produced by an American company Wright Medical. Several surgeons were brought on to provide a clinical perspective and the resulting replacement has benefitted from the collaboration between themselves and Wrights’ design engineers.
    The Infinity ankle consists of a highly polished metal talar dome, a titanium alloy tibial tray, and an UHMWPE bearing surface.
    The key features they claim to have introduced are:
    Low-Profile tibial implant design
    Resurfacing talar component
    Fluoroscopic Visualization
    Talar Component Interchangeability with other revision implants
    Optimized to use PSI preoperative navigation.
    The tibial tray design is low profile and has 3 pegs which are angled backwards so that it can be inserted and impacted from the front. It requires the same standard resection depth for all implant sizes. It comes with a standard and long option to allow for optimal AP coverage.
    The spacer or meniscus is made of UHMWPE which is fixed into the tibial component. This seems counter intuitive to the European mobile bearing implants where the meniscus is not fixed but instead is mobile between the joint surfaces. However, there are several reasons they have gone for the fixed bearing solution. Firstly, the FDA (the US regulatory body) does not recognise mobile bearing implants but does recognise fixed bearing implants. Second, the evidence to demonstrate a difference in performance between mobile and fixed bearing implants in knees isn’t there and indeed a small non randomised study by surgeons involved in the Salto Implant (Tournier) failed to show any advantages of mobile bearing over fixed bearing menisci.
    Obviously, many of the elements of the Infinity’s design had been used before by other implants on the market and the real innovation in my mind was the ability to use PROPHECY PSI to plan and perform the surgery.

    Indications

    INDICATIONS:
    There is only one indication for an ankle replacement and that is end stage osteoarthritis of the ankle and failure of non operative measures.
    There are of course several causes of end stage ankle OA. The commonest is post traumatic arthritis following a fracture or severe ligamentous disruption. The latency between injury and arthritis can be 25 years or longer. Other causes include rheumatoid arthritis, seronegative arthropathy, haemachromatosis, and haemophilia). Less common is primary osteoarthritis (unlike the knee and hip where this is the commonest cause).
    There are several patient characteristics that would lend support for an ankle replacement over the alternative ankle fusion.
    Age – patients over 60
    Adjacent joint arthritis – patients with stiffness of other joints for example pantalar arthritis, might receive an advantage of having a replacement on top of perhaps a triple fusion to avoid the impact of having a completely stiff construct.
    CONTRAINDICATIONS:
    Vascular insufficiency
    Neurological disease (with severe muscle weakness or Charcot joints)
    Poorly controlled diabetes
    Poor soft tissue coverage
    Avascular necrosis (more than 30% of the talus)
    History of or active sepsis
    Deformity – traditional dogma (and the literature) suggests that varus or valgus defromity of greater than 15 degrees should not be replaced. That said this not entirely true because most deformity can be managed and corrected intraoperatively. For example a varus ankle may have lateral ligamentous insufficiency but following ligament reconstruction is stable. A severe planovalgus foot might require a triple fusion prior to consideration of an ankle replacement. If you are looking to develop your experience in ankle replacement you should not be replacing patients with deformity at the outset as these cases are complex.
    SYMPTOMS & ASSESSMENT:
    Pain, stiffness and impact on quality of life are the main symptoms. As with any arthritic condition you want to find out about walking distance, climbing up and down stairs, managing with slopes and uneven surfaces, ability to work, drive and participate in recreational activity and sports. Ankle arthritis typically causes pain on activity, but patients often describe a start up type of pain and some patients have a history of instability but latterly stiffness, which is classical of an unstable ankle that has developed stabilising osteophytes. Most patients are very concerned by swelling and indeed swelling is a symptom that we as doctors interpret disproportionately to patients, namely we arent worrried but they are very concerned by their swollen ankle.
    When assessing the patient stand them up and look at their total lower limb alignment in both the coronal and sagital planes. Look for high arches (peekaboo sign); or flat feet. Look at the heel for varus or valgus malalignment. If there is a cavovarus deformity carry out a Coleman Block test to look for a hindfoot driven varus due to a plantar flexed first ray. Assess the gait as well as the motion at the ankle joint and all adjacent joints. Assess stability at the tibiotalar joint and also the subtalar joints. Carry out a careful and full neurovascular assessment.
    INVESTIGATION: Standing anteroposterior and lateral radographs should be performed. I routinely also carry out a long leg alignment film to assess the mechanical and anatomic axes. If pathology of the midfoot or Chopart joints is suspected then also carry out a DP and lateral of the foot.
    MRI Scans are useful to document the absence or presence of adjacent joint arthritis as well as to assess the soft tissue envelope eg Achilles, peroneals and tibialis anterior and posterior tendons which can also be a problem in ankle arthritis.
    For the PROPHECY ankle a CT scan is performed. There is a full protocol available from the company but essentially this involves a scan which includes the knee to assess the mechanical axis of the tibia. This may or may not be reflective of the mechanical axis of the limb, which is why I also obtain a long leg alignment films (as often these two axes can differ in the case of genu valgum or genu varum). The information is uploaded onto a US server and so appropriate data permissions need to be obtained from the patient and from the hospital.
    The PROPHECY system produces 3D printed models of the tibia and talar surfaces as well as a report which allows the surgeon to determine the parameters of the surgery and plan ahead. The 3D printed models are sterilised and made on the set during the surgery. The CT scan should ideally be within 3 months of the surgery date to avoid any interim changes in the ankle to be replaced.
    OPERATIVE ALTERNATIVES:
    The obvious alternative is an arthrodoesis. Arthroscopy has a role in early osteoarthritis. Distraction Arthroplasty (arthodiastasis) is an option but the evidence is controversial. Bony osteotomies around the ankle for correction of alignment have a role in certain indications.
    NON-OPERATIVE ALTERNATIVES:
    Non operative methods (weight loss, activity modification, ankle braces, and pain killers) must always be tried first.

    Setup

    The preoperative WHO check should confirm the availability of the kit and implants and their sterility. The nature of the operation and the side of surgery should be crosschecked with surgeon patient and theatre staff.
    Imaging must be available and displayed in theatre for referencing during the procedure.
    Antibiotics are administered at induction and a popliteal and saphenous nerve block are performed under USS control.
    The operation is typically performed with the patient supine in the centre of laminar flow theatre under a general anaesthetic. I have the II machine coming in from the contralateral side to the operative side. The screen is on the ipsilateral side close to the patient’s head. A thigh tourniquet is applied and set at 280mmHg. A sandbag is invariably placed under the ipsilateral buttock.
    Routine draping is performed above the knee (like a knee replacement). Diathermy and suction should be available. I use an Esmarch just prior to knife incision to maximise the time of surgery and minimise the tourniquet time.
    Specific to the PROPHECY system the following steps are important:
    Have the report from the manufacturers on display confirming the implant sizes and any items that you need to know about preoperatively such as depth to cut with the saw, presence of deformity, bone cysts etc. You may need additional equipment such as bone graft/substitute; bone anchors (eg for ligament reconstruction); and screws or plating systems (in case of the need to fix a malleolar osteotomy)
    Confirm the jigs number and corroborate this as being for the correct patient.

    Operation – 1

    My set up of the operating theatre has the bed located so that the operated foot is in the centre of the laminar flow. I have the image intensifier coming in from the opposite side and the screen at the top of the patient on the operated side. This way, by standing at the foot of the operating table I can have full sight of the screen and easy control of the image intensifier.

    I place the leg on a covered foam elevator (termed the baby) so that the heel is not supported and can drop below the level of the tibia. The skin incision is midline between the medial malleolus and the fibula. I tend to mark the skin with transverse lines to aid closure at the end. I mark the joint line and usually go 8 cm above this and 6cm below this (14-15cm incision).

    The skin incision is deepened to the deep fascia where you will see the superficial peroneal nerve crossing the distal end of the wound. This should be identified and I typically use a blue vascular loop at the lower end of the wound to protect the nerve carefully. I do not keep the clip (as it often gets pulled on by accident), but instead I merely tuck the two ends of the vascular loop under the lateral side of the leg.

    I then identify tibialis anterior and its covering sheath. I make a small incision and insert a McDonald retractor underneath to protect the tendon and then divide the extensor retinaculum with a blade just like performing a carpal tunnel release.

    The tibialis anterior tendon is then retracted medially and dissection continues through the bed of the tendon onto bone. Frequently small vessels are encountered and should be coagulated using diathermy.

    Dissection onto bone then allows dissection medially and laterally to expose the gutters. The neurovascular bundle (which includes the deep peroneal nerve) sits under the extensor hallucis longus (EHL) and extensor digitorum brevis (EDB) both of which are retracted laterally to protect them with any retractors placed deep to the reflected capsule. I never use self retainers (for fear of skin necrosis) but do use angled ring handled spikes and Langenbeck retractors.

    Ensure the area of the anterior tibia where the patient specific guides will surface match is completely free of soft tissue. I use diathermy to do this, others use a periosteal elevator but its important to avoid removing any osteophytes or bony structures that have been referenced off.

    I then bring the Prophecy guides to the table, these are 3D printed models of the distal tibia and talus and allow you to see the fit of the patient specific instruments which are designed to perfectly fit in only one position. Two trimmed 2.4mm Kwires are inserted vertically on either side of the midline into prefabricated holes for later use with the II.

    The cutting jig template is then positioned onto the tibia as per the model. A central 2.4mm K-wire sits between the parallel vertical cut K-wires which sit either side of it, and so the user will see three parallel K-wires to confirm it is an appropriate AP view.

    Once the screening images confirm that the long pin is centred exactly between the two smaller pins we are confident that this is a true AP image. In this image two pins have been inserted bicortically through the predrilled holes in the template.

    The PSI jig is removed and replaced with the appropriate sized tibial cutting block.

    The Prophecy conversion instrument is then inserted into the superior 2 pins and the coronal sizing guide is then threaded over the inferior 2 pins and guided down to bone.

    The two components are connected and tightened with the hex driver.

    An image is then taken which needs to be a true AP. In this image you will see the central circle is not round reflecting rotation in the sagittal plane and also the two corner holes are not round indicating angulation in the axial plane. Adjustments are made.
    To correct for parallax the coronal adjustment guide contains a “pin-in-circle” feature.

    Once three round holes are noted, this is a true AP of the cutting block and the markers illustrate the amount of tibia or talus to be resected.

    You then use the corner drill to drill two vertical holes in the corner of the cutting block and allow the cutting saw to cut into the holes which is a stress free way of removing the section of bone.

    You then substitute the coronal sizing block with the tibial cutting block. The technique then allows for either a coupled talar cut or a independent Prophecy guided talar cut. I am using a coupled technique.

    As such I place two further pins into the talus being careful to ensure that the foot is plantigrade.

    A lateral image is then checked to ensure the cuts are as per planned.

    The image intensifier is brought in and the knee internally rotated to try and obtain a true AP of the ankle.

    Four pins are then inserted bicortically into the tibia through the predrilled holes in the jig.

    The pins are then trimmed short. The technique describes cutting them flush but I tend to leave them about 12mm proud so that they can be removed afterwards using the wire driver.

    I then saw the tibial cut. I always measure the medial depth on the prophecy plans and mark this depth on the saw so that I am conscious when to stop as the neurovascular bundle is sitting behind the tibia. I cut both proximally and the distal saw slot which is for the talar cut.

    I then replace the saw with an oscillating Christmas tree shaped blade to complete the medial and lateral walls again marking the depth and being particularly careful on the medial side to avoid any issues with the tibial nerve.

    I then use a corner cutting osteotome to finish the corners and disposable osteotomes to remove the posterior capsule.

    Operation – 2

    The Infinity set has on it a threaded pin for insertion to the distal tibial resection.

    The threaded pin is then connected to the green handle to allow traction.

    The resection fragment is always removed as one fragment in my practice, although standard practice is to fragment with an osteotome and remove it piecemeal. In my experience careful traction and coaxing allows it to be removed but you need to be conscious of the neurovascular bundle medially incase it is adherant to the posterior capsule which is the main reason removal is difficult.

    A blunt laminar spreader is inserted to enable sight at the back and any os triginum or loose fragments are then removed using a pituitary rongeur.

    This leaves a nice square resection margin to trial into.

    I then place the appropriately sized tibial tray trial over the two remaining tibial pins and into the resected joint space. This is the size recommended on the Prophecy guide or as measured on the II.
    The laminar spreaders should be inserted between the trial and the talus to ensure the trial is seated flush to the distal tibia. I normally at this point check this on a lateral II.

    I then place the appropriately sized talar dome trial into the joint space and use a poly insert trial holding tool and a 6mm poly trial.

    The ankle is then screened to ensure that
    a) The tibial tray is siting flush on the resected surface
    b) The tray is of adequate length – in this case it is a long tray
    c) The talar component is flush to the talus and appropriately positioned.

    Using the Posterior Tibial Peg Broach (marked 1) I prepare a hole in the resected tibia by hitting the broach through the posterior opening of the trial. There are three holes and this is in the posterior hole. I leave this in place and then use the second broach (2) and prepare the two anterior holes.

    The talar cutting guide is then inserted again and using lateral screening I confirm that it is sitting flush and in the correct position front to back. Motion of the joint is carried out with the trial meniscus in situ to ensure it has the best fit and motion is optimised. The anterior and posterior chamfer cuts are noted to ensure they are in the correct trajectory. The foot has to be rotated to ensure that an inverted “V” is visible and a true lateral is noted. Two pins are inserted into the talar cutting guide so that the trial can be removed (by sliding over the pins).

    The pins are left in situ to slide over the talar resection guide base flush onto the talus.

    The talar resection guide base is now inserted into place.

    This is secured flush onto the talus using two screws laterally and a pin centrally.
    To achieve this threaded screw pins are inserted into the posterolateral holes initially by a driver and finished by a T handle pin driver to avoid threading the wires.

    Once secure I remove one of the anterior pins and place it into the central hole, which in my set has been modified to point backwards and avoid any iatrogenic damage to the talonavicular joint which sits just beneath. This pin is then cut flush and the second pin is removed. The cutting block is now being stabilised by 1 central pin and two lateral screws.

    The posterior chamfer is now cut using the oscillating saw, being careful medially to avoid any of the neurovascular strutures or the flexor tendons.

    The anterior surface of the talus is now prepared using an anterior talar pilot guide. There are two, one scalloped and one smooth and these are placed in one direction and then rotated in the other to burr out a flat surface on the front of the talus allowing the anterior part of the implant to sit flush.



    The medial and lateral edges are invariably missed and need to be nibbled flush to avoid the implant catching on these edges.

    The tibial trial is reinserted. The talar trial and the 6mm meniscal insert are now inserted together using their respective inserting guides (gold and silver).

    Range of motion and stability are now checked. I also tend to carry out a lateral II screen to ensure the implants are flushly seated.

    In this case plantar flexion is optimal but dorsiflexion is limited to neutral and the Achilles tendon feels tight.

    In that situation I perform a Hoke Achilles lengthening percutaneously.

    My assistant elevates the limb and I carry out three incisions, 2 medial and one lateral in between. The knife is inserted in a longitudinal manner and then turned away from the midline and with a swift motion of the wrist about 20% of the tendon is divided (but up to 40% can be divided). The lowest cut closest to the insertion is medial as the tendon fibres rotate here explaining why a varus thrust is created in tight tendons. I suture the skin at the same time to avoid forgetting afterwards. I would say that an Achilles lengthening is required about 1 in 5 cases.

    As you can see the range of dorsiflexion is significantly increased.

    At this point I plantar flex the foot and drill the two talar pegs ensuring the talar component does not move when going between holes.

    I then remove all of the implants and based on my preoperative Prophecy scans decide if I am to try and plug any large contained cysts. I use a curette initially and then inject a calcium sulphate paste into the defects. If the defect is uncontained I tend to you autograft taken from the resected tibial piece and impact this into the defect where accessible.

    Operation – 3

    After copious saline irrigation we are now ready to implant.
    I carefully remove any loose fragements of bone and soft tissue that could impinge. I apply a laminar spreader and inspect the gutters especially posteriorly for osteophytes that are likely to impinge and at this point I deal with them, sometimes using a Midas Rex to remove any bony osteophytes. I am copious with washout.

    Gloves are changed routinely and the implants are requested and checked. The tibial component is placed onto the insertion tool.

    The tibial component is the inserted from the front using the longitudinal impactor. A check screening from the lateral side is carried out to ensure it is fully seated posteriorly.

    The talar component is then inserted being careful to ensure the two anterior pegs coincide with the drilled holes. There is an introducer but I find it catches on the soft tissues and invariably hinders more than it helps.

    The talar component is impacted initially from the dorsal surface followed by anterior impaction, with your assistants fist providing counter pressure on the heel.

    The trial 6mm insert is trialled and range of motion is once again checked as well as stability both in the coronal plane but also rotational stability.

    A further washout is performed to ensure no further debris remains and then the final meniscus is inserted using thumb pressure to get the meniscus over the talar bump. I then dorsiflex the ankle and impact the front of the meniscus using a flat handled impactor to seat the meniscus onto the tibial component. In soft bone I would use the companies impacting device, but I only use this in soft bone where I dont think the bone will hold the impaction, as otherwise not only is it cumbersome but also the application, in my opinion applies torsional forces on the implants which is equally not good for the seating of the implants.
    Once you are happy with the seating of the implants a final washout takes place. A final range of motion and stability test prior to closure.

    Closure is in layers using 0 vicryl to the capsule.

    And 0 vicryl to the tibialis anterior retinaculum. This is important to close otherwise bowstringing of the tendons can occur.

    I use 2-0 subcuticular vicryl and 3-0 nylon interrupted to the skin. I apply a melolin non adherant dressing, wool and POP backslab being careful to avoid any finger marks or leave any pressure points.

    This is the preoperative ankle AP radiograph.

    This is the preoperative lateral radiograph.

    The Prophecy system creates a 3 Dimensional representation of the patients anatomy based on the CT scan. This allows the surgeon to determine if they are going to use the anatomical or mechanical axis, set rotation and sizing of the implant and plan preoperatively the entire procedure.

    This image shows that in this situation the anatomical axis (red line) is the same as the mechanical axis (blue line) and a size 2 implant has been selected.

    Check Images are saved, AP and lateral – in this case you can see the calcium sulphate injected up the tibia filling a large central defect.

    The defect was visible on the preoperative planning images and hence could be anticipated prior to the procedure.

    Post Operative

    My post op plan is as follows:
    Elevate and neurovascular obs – I use a foam elevation pillow from LEDA Orthopaedics which the patients love more than a braun frame as it keeps the knee bent and the tibia parallel with the floor but elevated to heart level.
    Thromboprophylaxis – as per your hospital’s protocol. NICE recommends thrombprophylaxis and at our institution that is Tinzaparin 4500 IU od sc until fully mobile.
    Initial non weight bearing until the wound is healed.
    Once the wound is healed, my weight bearing status depends on adjunct procedures. In this case where an Achilles release was performed I will keep them in plaster for 6 weeks, weight bearing from week 2 to week 6 and then into a walker boot for a further 6 weeks taking it out for physio and when sleeping.
    I would see them on the ward round the following morning to ensure the block has worn off and analgesia is optimised.
    Analgesia is given as required. Ideally, I like to stop codeine or opiate based medication as quickly as possible to aid bowel motility and psychological recovery.
    Physiotherapy should be started preoperatively with a core stability, and a gluteal programme which they can do in bed and throughout their recovery. This then allows a nice transition to work needed on the ankle and foot and gait retraining, which is secondary in my opinion to proximal chain kinetics.
    Xrays are taken usually once between 6 weeks and 6 months postoperatively to ensure no change from the preoperative images and otherwise biannually thereafter to look for signs of loosening, heterotopic bone or cyst formation/progression.

    Recommended Reading

    In our first 3 years experience we have performed about 150 Prophecy cases with short term positive results. We intend to publish as appropriate.
    A systematic review and meta-analysis of modern total ankle replacements (TARs) by Zaidi et al (BJJ 2013) included 58 papers (7942 TARs) showing an overall survivorship of 89% at ten years with an annual failure rate of between 1.2%-1.9% depending on whether the results are reported by the designers or joint registers. The mean American Orthopaedic Foot and Ankle Society score changed from 40 pre-operatively to 80 at a mean follow-up of 8.2 years. Radiolucencies were identified in up to 23% of TARs after a mean of 4.4 years. The mean total range of movement improved from 23° to 34° and confirmed that TAR has a positive impact on patients’ lives, with benefits lasting ten years, as judged by improvement in pain and function, as well as improved gait and increased range of movement. What is clear however, is that the quality of evidence is weak and fraught with biases.
    Further papers by Zaidi reported quality metrics for ankle replacement. In a study in which the UK NJR was linked to the Hospital Episode Statistics (HES) database (BMJ Open 2016) it was shown that the 90-day mortality following TAR was 0.13% and 1-year mortality was 0.72% ; no deaths were as a result of PE. The incidence of PE within 90 days following primary TAR was 0.51% and that patients with an Royal College of Surgeons Charlson score greater than zero (this means co-morbidity) were at 13 times greater risk of PE.
    A second paper by Zaidi on the same cohort (BMJ 2013) looked at quality metrics for ankle replacement and showed that TAR has a 30-day readmission rate of 2.2%, which is similar to that of knee replacement but lower than that of total hip replacement. It was also shown that 6.6% of patients undergoing primary TAR require a re-operation within 12 months of the index procedure, and that early revision rates are significantly higher in low-volume centres.
    There is an NIHR HTA funded RCT comparing ankle replacement against ankle fusion (ISRCTN60672307) called TARVA is underway and 17 centres in the UK are participating. The study will recruit 310 patients over the age of 50 and randomise them between treatments. All patients have a preoperative MRI and are stratified by the presence or absence of adjacent joint arthritis, so that equal numbers of patients with adjacent joint arthritis will be within each group. The study is likely to report in 2020 with ten year data 8 years later.

    Reference

    • orthoracle.com

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