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Ankle fracture- Medial malleolar fixation with ASNIS screws

    Overview

    Learn the Ankle fracture: Medial malleolar fixation with ASNIS screws surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Ankle fracture: Medial malleolar fixation with ASNIS screws surgical procedure.
    Most fractures of the medial malleolus occur as a component part of an injury pattern involving either the lateral malleolus and/or the posterior malleolus to varying degrees. However, a fracture of the medial malleolus can appear to occur in isolation. It is important to make sure that the energy imparted to the medial malleolus to create a fracture has not travelled through the distal tibia-fibular syndesmosis, the interosseous membrane and exited more proximally in the fibula as in the classic Maisonneuve injury. If this has been excluded, then the relatively uncommon injury of an isolated medial malleolar fracture can occur.
    Using the Lauge-Hansen classification, these isolated medial malleolar fractures can occur with the foot either in supination or pronation with either a external rotational moment applied across the ankle or with the foot adducted or abducted. The pronation-abduction injury pattern is probably the most common mechanism for generating an isolated fracture. Herscovici described a 4-part fracture classification specifically for the medial malleolus which can offer guidance on how best to fix the varying fracture patterns. The relatively uncommon Type D injuries occur with supination and adduction creating a shearing force to the medial malleolus and leaving a more vertically oriented fracture line. In my opinion, these are unstable fractures that need internal fixation with an anti-glide buttress plate. Alternatively, multiple partially threaded screws can stabilise these fractures as long as they are placed perpendicular to the reduced fracture line. However, most isolated medial malleolar fractures exhibit a transverse fracture line either at the level of the tibio-talar joint line or immediately distal to it. Therefore, the common methods of fracture fixation are to apply compression either with two part-threaded cancellous screws or application of a tension band wiring technique. In this example, the former technique is employed using two Stryker partially threaded 4mm ASNIS screws.


    Indications

    Indications
    The literature does not clearly indicate a clear reason for fixing a displaced isolated medial malleolar fracture. Clearly, if the injury forms part of a greater fracture pattern or is part of a Maisonneuve-type fracture where the ankle is unstable, then fixation is warranted. The most common quoted reason for fixing isolated medial malleolar fractures is that there is a high incidence of painful non-union if left unfixed. In reality, the literature doesn’t support this argument even though, as surgeons, when we open these fractures to fix them, we frequently find that the local periosteum interposes between the fracture fragments and would seem a logical barrier to union.
    Symptoms & Examination
    As with most fractures, the patient presents with pain and swelling that localises to the medial malleolus. In the event of a more complex Maisonneuve-type injury, the pain and swelling is likely to be less specific to the medial ankle and more diffuse. The patient may complain of knee pain or pain in the lateral aspect of the calf.
    Examination should include a thorough assessment of the knee for tenderness, palpation for tenderness along the whole shaft of the fibula as well as around the ankle. Assessment of the function of the common peroneal nerve is mandatory especially in the presence of proximal fibula tenderness.
    Investigation
    Orthogonal plain radiographic views of the ankle are mandated. If in any doubt, then further imaging of the knee and the whole of the fibula is a sensible and safe management strategy.
    Operative alternatives
    A reasonable alternative to compressing the medial malleolar fracture with two part-threaded cancellous screws is to consider tension band wiring. This technique is especially useful in more comminuted bone but has the disadvantage of leaving prominent hardware that may require a second surgical procedure for removal.
    Contraindications
    The soft tissue envelope is thin overlying the medial malleolus. Tenuous soft tissues with infection may dissuade any surgical intervention, although this is extremely unlikely in isolated medial malleolar fractures.
    Non-operative intervention
    The literature supports the use of cast immobilisation as an alternative to operative treatment with low rates of non-union.

    Setup

    The patient is positioned supine on the operating table and may require a sandbag under either buttock so that the foot points vertically towards the ceiling. Fluoroscopy should be available with an image intensifier and a trained radiographer.
    Appropriate antibiotics are administered and a thigh tourniquet and exclusion drape are applied.
    The limb is prepared with Chlorhexidine from toes to tourniquet.

    Operation

    Plain radiographic assessment includes the ipsilateral knee
    A 42 year old male presented with a painful left ankle having fallen off his bicycle at a low velocity. He complained solely of pain around the medial malleolus and denied and knee symptoms. Examination of the knee and the whole of the fibula was unremarkable. A plain radiograph of his ankle revealed a medial malleolar fracture and this warranted plain radiographic imaging of his ipsilateral knee.

    This A-P radiograph demonstrates the transverse fracture line through the medial malleolus at the level of the tibio-talar joint. The lateral view did not reveal any injury to the posterior malleolus.

    Note the significant zone of bruising demarcated around the medial ankle.

    There are no clear clinical signs of injury to the lateral ankle or calf adding evidence to the radiographic findings that this injury is an isolated medial malleolar fracture.

    Determine the surface anatomy by drawing the anterior, inferior and posterior boundries of the medial malleolus. The longitudinal skin incision should bisect the AP distance of the malleolus.The boundaries of the medial malleolus are determined and marked on the skin with dots. The skin incision is planned to lie midway between the anterior and posterior borders of the medial malleolus.

    Having incised the skin, the saphenous vein is identified and preserved.Anteriorly, the saphenous vein, and its accompanying nerve are intimately related to the anterior part of the medial malleolus and care should be taken to preserve these structures from iatrogenic injury.

    Deep dissection proceeds to bone taking care not to cut the deltoid ligament and the tendon of tibialis posterior.The skin is incised and further deeper sharp dissection is in line with the skin incision. The deltoid ligament should not be detached and care should be taken not to injure the tendon of tibialis posterior lying posterior or the saphenous vein lying anteriorly to the malleolus.

    The periosteum is removed from the fracture.The periosteum is removed from the fracture site with forceps or a pick, together with the fracture haematoma.

    The periosteum is reflected away from the edge of the fracture lines.The periosteum is then reflected away from the edges of the fracture so that the fracture can be accurately reduced. If the periosteum is not removed from the fracture site, then reduction is impeded and interposed material may lead to non-union. A good way of helping ascertain the accuracy of reduction is to open the joint anteriorly to fully appreciate the contour of the anterior aspect of the medial malleolus.

    Distract the fracture and remove the fracture haematoma. The fracture can then be distracted to inspect the medial aspect of the dome of the talus which may reveal a chondral injury in the presence of a shearing injury to the malleolus. Quite often the view of the joint is improved by washing away haematoma.

    Inspect the medial talar dome and make sure tendon of tibialis posterior does not block reduction.This photograph is taken from the opposite side of the operating table to demonstrate that lying posteriorly to the medial malleolus, the tendon of tibialis posterior is always clearly identifiable. This tendon can interpose fracture fragments in some cases.

    Reduce the fracture.Quite reasonably, some surgeons use a pointed reduction forceps to aid reduction. Personally, I trust my thumb as the most accurate reduction tool by thus avoiding crushing of the bone fragments! The fracture is then held with two guide wires inserted to cross the fracture line to temporarily hold the reduction.

    Apply two guide wires across the fracture site and check wire position fluoroscopically.The two wires are inserted to provide stability against rotation of the fracture fragment with drilling or screw placement. In the A-P plane, they are passed medio-laterally from the tip of the malleolus. The wires are best passed well beyond the fracture line so that overdrilling does not inadvertently remove the wires. The positioning of these wires are checked with fluoroscopy.

    The placement of the two wires should be in the anterior 2/3 of the medial malleolus because posteriorly placed wires may inadvertently injure the tibialis posterior tendon. It is important to make sure that the wires are parallel in two planes of fluoroscopic imaging so that even compression can then be applied with the two screws.

    Make stab incisions longitudinally in the deltoid around the wires before over-drilling.The thick fibres of the deltoid ligament are clearly visible [A]. In soft bone, compression with screw fixation is supplemented by the use of washers. In order to seat the washers well against the tip of the medial malleolus, the fibres of the deltoid can be divided with a blade passed along the guide wires [as demonstrated in the image]. In this case, the bone quality was sufficiently robust to obviate the need for supplementary washers.

    Apply each partially-threaded screw one at a time.The cannulated drill is passed over the guide wire and drilled to a suitable depth for the first screw – usually 35-40mm is sufficient length. The first of the 4mm diameter screws is then inserted fully before drilling the second screw so that the reduction is not lost with the instrumentation of the small medial malleolar fragment. Once this has been achieved, the process is repeated for the second screw.

    Check the screw position on the image intensifier.Two views are then taken with the fluoroscope to confirm the positioning of the screws.

    Reassess the syndesmosis for stability.I think it is always worthwhile meticulously checking for a syndesmotic injury as the consequences of missing one are a proven link with the onset of arthritis. An external rotation force and an abduction force can be applied to the ankle with the fluoroscope performing live screening of the stability of the syndesmosis. Anterior to posterior gliding of the fibula or hook testing cannot be performed as tests for syndesmotic stability as there is no lateral wound.

    This fluoroscopic image is taken at the point of maximal external rotation force across the fixation.

    Skin closure and temporary plaster of Paris application.Closure is with 2/0 Vicryl to the deep tissues and 3/0 Monocryl to the skin. A Jelonet dressing is applied followed by dressing gauze, orthopaedic wool, Plaster of Paris slabs and secured with Velband.

    Post Operative

    The patient is placed in a below the knee back slab for the first two weeks after surgery.
    At two weeks, the wounds are inspected and re-dressed and a complete, lightweight below-the-knee cast is applied for a further four weeks.
    Weight bearing is not permitted for the first six weeks after surgery to lessen the risk of non-union.
    In my practice, rivaroxaban is prescribed for this duration to prevent thrombo-embolic events.
    At six weeks, the patient can commence weight bearing in normal shoes and may require physiotherapy input to improve ankle range of motion.

    Recommended Reading

    Conservative treatment of isolated fractures of the medial malleolus. Herscovici D, Scaduto JM, Infante A. J Bone Joint Surg 2007B; 89(1); 89-93.
    This oft-quoted paper reviews almost 60 isolated medial malleolar fractures treated in a cast and found that there was >95% union rate with reasonable patient satisfaction. The authors recommend fixing medial malleolar fractures as part of more unstable fracture patterns or in resolving painful non-union.
    Marginal plafond impaction in association with supination-adduction ankle fractures: a report of eight cases. McConnell T, Tornetta P. J Orthop Trauma 2001; 15(6): 447-9.
    This small subgroup of isolated medial malleolar fractures were often associated with some local marginal impaction and were all fixed. The authors experience forms the basis of my opinion that these fractures are the unstable, shear-type fractures, mentioned in the “Overview” section, that require anti-glide fixation.

    Reference

    • orthoracle.com

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