///

Ankle replacement-Star ankle replacement (revision of mensical component)

    Overview

    Learn the Ankle replacement-Star ankle replacement (revision of mensical component) 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-Star ankle replacement (revision of mensical component) surgical procedure.
    The polyethylene bearing of a mobile bearing ankle replacement may fracture, wear or dislocate.
    If this happens, the whole ankle replacement may need to be revised, or just the meniscal bearing – mindful of the fact that some wear may also have occurred to the metal surfaces of talar and tibial components.
    It is important to identify any precipitating factors which may have caused the meniscus to fail (such as ankle instability or component malalignment) and to correct these at the same time as revising the bearing.
    For those undertaking ankle replacement surgery the ability to identify and deal with its potential complications (both in the short and longer term ) should be a consideration.
    The following operation demonstrates my technique for managing the isolated failure of a meniscal component of a STAR ankle replacement , one of the implants with the longest track record.

    Indications

    INDICATIONS:
    The mobile bearing may fail due to wear or fracture(age related), dislocation (secondary to trauma or instability) or a combination of these factors.
    SYMPTOMS & ASSESSMENT:
    The patient may feel progressive pain, swelling or instability of the ankle, or failure may be detected on routine follow up xrays.
    INVESTIGATION:
    The patient must be carefully examined, to check stability and alignment of the joint.
    Plain xrays should be carefully studied, looking to see where the bearing or its components lie, checking the alignment and fixation of the components, and looking for causative factors such as impinging new bone formation, which may have caused maltracking.
    Routine blood tests looking for raised inflammatory markers and infection should be performed.
    Patients should have a spiral CT scan performed, looking for cyst new bone formation, signs of loosening, and looking for cyst formation which may occur secondary to polyethylene wear.
    OPERATIVE ALTERNATIVES:
    The surgeon should always consider whether other procedures need to be performed at the time of bearing exchange.These may include stabilisation procedures, excision of impinging intra-articular scar or osteophytes, or grafting of cysts.
    If there is visble wear of the metal surfaces, or major cyst formation, then revision ankle replacement or conversion to fusion may be needed. Sometimes the decision whether to revise or fuse can only be made at surgery, and the surgeon must be equipped and ready for either of these eventualities.
    NON-OPERATIVE ALTERNATIVES:
    Non-operative treatment should only be undertaken for patients who are too frail for surgery. in such cases a light ankle brace may help stabilise an unstable ankle, and provide some symptomatic relief.
    CONTRAINDICATIONS:
    Replacing the mobile bearing is contra-indicated in patients with infection, and should be postponed if there is adjacent skin infection.
    The presence of loosening, malposition,large cysts,or wear of the metal surfaces may all be contra-indications , and point to the need for ankle joint revision or fusion.

    Setup

    All the equipment needed for a revision ankle replacement (including revision extra thick bearings) should be available.
    If there is a possibility of proceeding to fusion, a suitable nail or plate set and bank bone (or consent to take iliac crest bone) should be ordered.
    An image intensifier is mandatory.
    The patient is positioned prone, a touniquet applied and the leg prepped according to hospital protocols.
    Antibiotics should be withheld until any biopsy samples have been taken.

    Operation

    The central part of the original incision is reopened. the tibialis anterior muscle is identified, and dissection carried down to the joint.
    technical tip: do not drift laterally at this stage, otherwise you can damage the neurovascular bundle which will lie in scar tissue beneath or lateral to extensor hallucis longus.

    A self retaing retracor may be used ( but use one with blunt teeth, be gentle and avoid plantarflexing the foot with it in situ, as this will tighten the skin onto it and may cause skin damage).
    The joint line is identified and a longitudinal arthrotomy made through to expose the ankle joint.

    Dorsiflex the foot to release the tissues.
    Then, using a periosteal elevator, carefully lift the anterior capsule from the tibia and talus.Excise any dense capsule which does not easily elevate.
    It is possible thereby to expose the whols width of the ankle from medial to lateral malleolus.
    If infection is suspected, biopsies can now be taken, and antibiotics administered according to local protocols.

    Any anterior osteophyte is now removed using an osteotome and/or nibblers.
    Here a small antero-medial osteophyte is preventing access.

    In this case the bearing has fractured into two parts. The smaller anterior fragment can be removed easily – however there is a large residual fragment which lies in the back of the ankle,. It is not easy to remove as it cannot easily be grasped by instruments without risking scratching the metal surfaces, and needs to be withdrawn over the apex of the tlar component..

    In this situation, the self retaining retractor is again loosened, and the assistant applies traction to the foot to improve visiblity.
    Then a 2.0 mm ‘small fragment’ drill is mounted onto a power drill, passed via a guide onto the retained posterior segment of the bearing, and a drill hole made into the residual component.

    A suitable tap from the same set is then screwed into the drill hole, until a good grip is achieved.

    Then, by applying traction to the foot, and pulling on the tap/handle the component can be easily and safely removed.
    (In the UK fractured components should be kept and sent to the Medical Devices Agency.)

    The joint surfaces, and surrounds should be thoroughly irrigated, and then inspected- looking for significant damage to metal sufaces,and impinging lesions.
    If the metal surfaces are visibly damaged, they should be replaced of the joint fused.
    If there are impinging bony or soft tissue lesions, these should be excised.
    Posterior osteophytes can be excised via the joint, using an up-cutting spinal cutter.
    Impinging osteophytes in the medial or lateral gutters can be seen directly and excised with nibblers.

    Trial bearings are then inserted to determine the correct thickness. This is rarely smaller (less thickness) than the original bearing. but may be deeper.
    Once a suitable trial bearing is in situ, check that the ankle can still dorsiflex 1odeg with it in situ. If it won’t then you’ve probably inserted too big (deep) a bearing and should try smaller sizes until dorsiflexion can be achieved.

    The definitive bearing is inserted.
    The STAR bearing shown in this case is universal (except that it comes in different thicknesses), but other implants may be sided (left or right) and be narrower at the back. Check before inserting that you have the correct thickness, and that it is properly aligned..

    Once the component is inserted, check the range of movement (must be able to dorsiflex 10deg minimum) and perform xray screeening to check that all is well aligned.
    The wound is then closed in layers – a drain is optional.

    Post Operative

    The foot should be immobilised in a cast or boot to protect the wound for 2 weeks.
    The patient may bear weight through the cast boot during this period.
    Anticoagulation is administered throughout the period of immobilisation if local protocols dictate.
    Provided the wound has healed at 2 weeks, the sutures can be removed and the patient mobilised with a light ankle brace for security.
    the cast /boot is retained until the wound is dry and healed.
    On removal of the cast/boot the patient should be taught active and passive dorsiflexion exercises.
    Annual review with radiographs is mandatory after bearing replacement, in case irregularity of the metal surface (caused during the period that the bearing has been deficient) causes early repeat failure.

    Recommended Reading

    It is not possible to define the incidence of bearing failure, as many studies and some long-standing registries do not record failure of the bearing, nor count replacement of the bearing as a revision.
    It is similarly not possible to define the longevity of the bearing replacement procedures , although increasingly registries – including the UK National joint registry- are recording survival of ankles after bearing replacement.
    Surgeons and patients should be aware that the bearing may suffer early failure, and patients having this procedure should be carefully followed up with regular xray checks for life.

    Reference

    • orthoracle.com

    Tags:

    You might be interested in

    Dark mode powered by Night Eye