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Wedge tarsectomy- For correction of isolated cavus deformity

    Overview

    Learn the Wedge tarsectomy: For correction of isolated cavus deformity surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Wedge tarsectomy: For correction of isolated cavus deformity surgical procedure.
    There are various disparate causes of a cavo-varus foot and ankle deformity all of which result in varying degrees of characteristic deformity secondary initially to imbalanced muscular action. The objective of all treatment, operative and non-operative, when dealing with foot and ankle deformity is to place (and hold) a balanced foot squarely beneath the tibia. The surgical management of such cases in particular is often referred to as “A La Carte, alluding to the very specific nature of individual interventions for individual components of the deformity (as opposed to any self-congratulatory dining following a successful surgical intervention) .
    The indication for a Wedge tarsectomy is for correction of a comprehensive midfoot cavus. It is also possible to correct an element of adductus by excising an asymmetric tarsal wedge. If the excised tarsal wedge is truncated in its plantar aspect (in other words a wide based rather than sharp apex is cut) then secondary tightening of the plantar fascia is less likely to occur upon acute closure of the wedge.

    Indications

    There are various disparate causes of a Cavo-varus ( or Equino-cavo-varus) foot deformity all of which result in varying degrees of characteristic deformity secondary to imbalanced muscular action.
    The Cavus foot can be classified according to the level of the pathology causing the problem. Central neurological causes include CVA, Cerebral Palsy, and MS , spinal located causes include polio and spinal cord injury, peripheral nerve lesions for example due to HSMN or Leprosy and anatomically most distally amongst the causes muscle pathologies to be considered such as muscular dystrophy and the sequelae of a compartment syndrome.
    The objective of all treatment is to place (and hold) a balanced foot squarely beneath the Tibia .Whilst a deformity remains flexible this can be done with orthotic management or if required operatively by means of tendon transfers and osteotomies. Once fixed however fusion surgery is likely to be required required though there remains a role for osteotomies to be combined.
    The various elements of the deformity should be identified and both their level and nature must be documented. A careful assessment of the opposing neuromuscular units is always required. How to proceed surgically depends upon the level, extent of deformity and flexibility the balance of power of the agonist/antagonist muscle groups , their absolute strength(judged by the MRC scale) and also the passive correctability of components of the deformity.
    On the MRC grading scale no muscular contraction is graded as 0, contraction but no movement as 1, active movement that cannot overcome gravity 2, active movement that can overcome gravity 3 ,active movement against gravity and resistance 4, normal muscle muscle strength 5. It should be remembered that in transferring a muscle to a different position and function it is expected that its MRC grading will fall by 1 or 2 points on the MRC scale , which makes transferring an MRC 1 or 2 power muscle of dubious value.
    How to deal comprehensively with the Cavo-varus foot is beyond the scope of this section but its surgical management in particular is often referred to as “A La Carte”, alluding to the vary specific nature of individual interventions for individual components of the deformity.
    A contracted Achilles may require lengthening. In the younger patient a global mid/forefoot equinus may respond to a Steindler plantar fascia release. In the adult with a stiffer deformity and comprehensive midfoot cavus this is an indication for a wedge tarsectomy. An alternative is multiple basal metatarsal closing wedge dorsal osteotomies. An isolated plantar flexed 1st ray should also be looked for which may require correction with a first ray dorsiflexion osteotomy. This deformity in isolation can drive/produce a compensatory calcaneal varus in order to allow the foot a degree of stability as a weight-bearing platform. This relationship between the hindfoot and forefoot should be explored with the Coleman block test. By removing the first ray from ground contact this reveals whether the hindfoot deformity is flexible and secondary to the 1st ray position. If it is the heel will correct to neutral and surgery to the 1st ray will deal with the hindfoot deformity. If the hindfoot stays in varus it may need discreet surgical correction, by means of a lateralising calcaneal osteotomy.
    Weakness of dorsiflexion with a relatively powerful Peroneus longus and poor Tibialis anterior may benefit from transferring Peroneus Longus to the Brevis. If on the other hand the Tibilais posterior is overpowering a weak Peroneus Brevis and Tibialis anterior it should be considered for transfer.
    Most patients will present to the Surgeon already with a diagnosis and having been diagnostically worked up. If this is not the case then a complete neurological examination (including recording of power , reflexes and the presence of spasticity in upper and lower limbs) needs to be performed. The opinion of a Neurologist should also be sought.

    Setup

    GA or regional anaesthesia
    Femoral & sciatic blocks for post-operative pain relief
    Laminar flow , peri-operative antibiotics , 2-4 weeks of post operative LMW Heparin
    Thigh tourniquet and Flowtron on contra-lateral calf
    Ankle positioned into neutral using sandbags & side supports
    Large , rolled up sterile towels behind the ankle to improve access for cuts.
    Kit required : Large single sided reciprocating saw blade, large power unit, large round nosed periosteal elevator, Hibs osteotomes.

    Operation

    The medial approach to the midfoot should be in the region of, and dorsal to, the Tibialis anterior insertion (Medial cuneiform/first metatarsal base).
    Approximately a 3-4 cm incision is required. Once Tibialis anterior is identified dissection can be sub-periosteal and should proceed laterally to the cuboid.

    The bone wedge will be taken from the apex of the deformity which is often between the navicular(3) and cuneiforms(2) medially & centrally and through the cuboid laterally (not shown).
    It may on occasion be more appropriate to excise dorsally based wedges from the 5 TMT joints , slightly more distally. This technique may require 3 dorsal incisions.

    The subperiosteal plane is continued across the dorsal midfoot(1) using a combination of sharp dissection and blunt stripping using a large round nosed periosteal elevator(2).

    The end of the periosteal elevator is dissected down onto laterally. This is in the region of the Extensor Digitorum Brevis muscle belly(2) for lateral access to the Cuboid.
    The Sural nerve should be looked for in the fat layer here and avoided .

    Lying directly lateral to the navicular-lateral Cuneiform articulation is the cuboid(2), deep to the Extensor Digitorum muscle. The osteotomy will pass through the cuboid and its proximal extent needs to be better exposed. The anterior process of calcaneum is marked 1.

    A well defined dorsal passage needs to be created by careful sub-periosteal dissection & elevation of the soft tissues to allow safe use of the reciprocating saw.
    Several passes with the round nosed large periosteal elevator(1) are usually required combined with sharp sub-periosteal dissection to produce adequate elevation of the soft tissues.

    The osteotomy is performed using a large single sided reciprocating saw blade(2). The dorsal soft tissues need to be held away from the blade during sawing(1). The blade should be positioned before cutting commences with its tip at the lateral extent of the osteotomy.It is useful to have an assistant visualising the lateral resection as it occurs as well as holding the soft tissues retracted.
    In terms of the amount of bone to be excised this is determined by the degree of the deformity. Generally the dorsal dimensions of the wedge will be somewhere in the region of 1 cm + medially. The dimensions of the lateral part of the excision will need to be less , the lateral longitudinal arch being less inclined than the Medial longitudinal arch. If forefoot adductus is also being corrected this can be added into the corrective wedge.
    Care should be taken not to exceed the plantar aspect of the bone with the reciprocating saw.

    The dorsal wedge being completed(2) carefully with an osteotome. The wedge produced should ideally be truncated(3) and not with a sharp apex . This reduces the chance of potential ongoing problems with plantar fascia tightness after closure of the osteotomy.

    The completed dorsal wedge(1). This one looks very much as though the plantar aspect has not been truncated in which case a plantar fascia release may also be required if it remains obviously tight following closure of the osteotomy.

    Once the wedge is closed the arch profile should be reassessed visually as well as the extent to which the metatarsal heads are now prominent (if at all).

    Fixation is with Wright Charlotte staples. Usually a mixture of inter-axis 15mm, 20mm and 25mm implants is required with appropriate depth

    Care should be taken when drilling the holes for the staples to avoid the immediately neighbouring joints. Multiple staples are required.
    The staples are all first placed before being compressed. This to ensure that enough staples can be placed. Compression is generated with these implants by placing a specific forceps into the central portion of the staple and forcing it open this widening it .This brings the prongs of the staples closer, generating compression.

    The apex of the deformity lies at approximately the navicular-cuneiform articulation. Note how the arch profile has been reduced following the osteotomy.

    Post operative AP Xrays.
    By designing the wedge appropriately, and removing more bone laterally, the adductus deformity has also be corrected.

    Post Operative

    2 weeks in back-slab , dressing changes at 1 & 2 weeks
    Complete cast between weeks 2 to 6 & non-weight bear
    Check X-ray at 6 week stage .
    Patient depending into long post-operative boot and gradual increase in weight-bearing at this stage.For poorer bone quality patients or possible compliance issues continue in a walking cast until 12 weeks.
    Add an “off the shelf” supportive , semi-rigid 3/4 length orthotic to be used once in post-operative boot and until return is made to normal shoe wear.
    May be comfortable enough to make transition into stiff soled walking boot by 12 weeks.
    Remain in this for all weight bearing for a further 6 weeks.

    Recommended Reading

    Tarsometatarsal truncated Wedge arthrodesis for Pes Cavus and Equinovarus deformity of the fore part of the foot.
    J Bone and Joint Surgery.1980.62-A;713-722
    M.H.Jhass.
    A description of the technique and results in 25 cases.

    Reference

    • orthoracle.com

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