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Dorsi-flexing osteotomy of first metatarsal

    Overview

    Learn the Dorsi-flexing osteotomy of first metatarsal surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Dorsi-flexing osteotomy of first metatarsal surgical procedure.
    Dorsiflexion osteotomy of the first ray may be performed in isolation to relieve excess pressure through an overlong or overloaded first ray, to relieve pressure through an overloaded and painful sesamoid bone , or to correct a plantar flexed first ray in a cavus foot.
    In cavus foot, the plantar flexed first ray strikes first on loading the forefoot, and causes the foot to roll into varus.
    Correction of the first ray in cavus is occassionally performed in isolation, but more commonly is performed in association with other procedures such as lateral displacement calcaneal osteotomy, midfoot correction or triple fusion – with or without corrective tendon transfers.
    The operation is simplified by the use of a staple to hold the osteotomy, which allows the osteotomy to be performed within 1 cm of the proximal end of the metatarsal, and with correct technique will provide enough stability for the patient to bear weight and mobilise early. The decision as to how much to dorsiflex the first ray is clinical and cannot be calculated accurately pre-operatively . It is judged clinically during the operation.
    Because of this, orthotics shoud always be trialled prior to surgery, and the patients should be aware that orthotics are also often needed to get good results after surgery. The osteotomy will adjust the major deformity, but orthotics are usuall needed to achieve fine adjustment and optimal function.

    Indications

    Dorsiflexion osteotomy is indicated when orthotic management has failed in the following conditions:
    1.An excessively plantarflexed (and often long) first metatarsal , causing pain and callosity under the first metatarsal joint.
    2. To correct an excessively plantarflexed first ray in cavus foot – usually as part of a combination of corrective procedures.
    3. More rarely it can be performed to weight relieve a painful sesamoid region – when presenting with pain and plantar callosity.
    Preparation depends on the condition underlying the deformity, but every patient should have a thorough examination of the foot and ankle, including observing gait, and noting the flexibility of the joints and the pattern of callosity on the sole of the foot.
    In any case of cavus with plantarflexion of the first ray potentially driving inversion, a Coleman block test should be performed to show that the plantarflexion is driving the deformity, and to check that dorsiflexion of the ray is likely to correct this. The Coleman block test is performed by standing the patient with a block of wood supporting the heel and lateral forefoot, but with the first ray unsupported. If plantarflion of the ray is driving the deformity, varus of the heel will be corrected in this position.
    Xrays of the foot should be always be performed , to check that adjacent joints are free of arthritis, and if these are not diagnostic, CT or MRI scan may be helpful..
    Footprint studies / and or pressure studies are helpful to study the outcome of the operation.
    Patients should receive pre-operative antibiotics according to local protocol, and assessed using local protocols for thromboprophylaxis.
    Alternatives to surgery: patients must have a trial of orthotic offloading/correction with a corrective and accomodating insole.
    Alternative operations: for patients whose first ray overload relates mainly to an overlong first ray , other procedures such as a modified Scarf osteotomy (modified to allow shortening) or any technique of shortening, sliding osteotomy may be used.
    When there is arthritis of either the first metatarsophalangeal joint, or the metatarso-tarsal joint, corrective fusion at the affected joint should be considered.

    Setup

    The following special equipment is required:
    A small oscillating saw.
    A small compression staple set (thermal or mechanical varieties are available).
    The operation may be performed under regional or general anaesthesia, usually using an ankle tourniquet
    The patient needs to be positioned to allow easy access to the medial aspect of the forefoot, so should be supine without a sandbag under the hip – to allow the leg to fall into external rotation.
    If other procedures are indicated for complex cavus correction, the correction should start proximally, and work distally. In this instance the foot may have to be internally rotated (for example for a calcaneal osteotomy or triple fusion), and a sandbag should then be used to internally rotate the foot, removing it prior to the metatarsal surgery.

    Operation

    This slide shows a typical case where dorsiflexion osteotomy is useful. It can be seen on the medial side that the first ray is plantar flexed severely – contributing to both caves and planters.

    The lateral view shows that the fifth metatarsal (and the other lesser metatarsals) are essentially normally aligned (so that the cavus is centred on the first ray – with the apex of the arch prominent dorsally on the medial side, and the first metatarsi-phalangeal region shown to be prominent in a plantar direction.

    The proximal end of the metatarsal is identifed – using an image intensifier, and the level of the metatarso-cuneiform joint marked.

    A longitudinal incision is made distal to this mark , medially along the line of the metatarsal, and centred on the metatarsal.
    The incision should be about 3 cm long – to allow the osteotomy to be performed through the metatarsal about 1cm distal to the metatarso-cuneiform joint.

    A 2.5 mm drill (A) is inserted, about 5mm distal to the tarso metatarsal joint (the position of which has been marked , but may be checked directly with a needle if there is any uncertainty).
    The drill should be placed in the upper (dorsal) half of the metatarsal.
    The drill is driven in perpendicular to the bone, through both cortices, and is left in situ.
    The self retaining retractor in this illustration is retained for clarity of vision, but in practice small ring handled retractors should now inserted around the proximal shaft of the metatarsal.
    Then, using a small oscillating saw, a transverse osteotomy is made through both medial and lateral cortices of the metatarsal. It should include the top cortex, but should stop 2-3 mm short of the lower cortex – which should if possible be left intact at this stage.

    Using the small saw a second osteotomy is performed at an angle to the first cut, allowing a closing osteotomy.- again preserving the inferior cortex if possible.
    The position of the second cut, and the size of the wedge, is estimated during surgery to allow the degree of angular elevation required.
    In cases of plantar flexed first ray, the wedge should be big enough to allow the first metatarsal to be about parallel to the lesser metatarsals when viewed from the side. As a rule of thumb, make the proximal cut square to the metatarsal, and the distal one at about 20deg (a secondary cut and excision can be made later if this is not enough – but you can’t put bone back if you take too much to begin with).
    When performing this procedure to unload the sesamaoids, the wedge should correct any relative plantar flexion, but any additional correction (and hence elevation) should be small – to avoid excess transfer load to the lesser metatarsals.

    The wedge is then excised.

    Next, using a 5-7 mm osteotome, the osteotomy is completed with one short sharp hit.
    This produces a crack down into the inferior cortex, so that the lower edge of the osteotomy can act as a stable hinge.
    If the inferior cortex is destabilised by completing the osteotomy with the saw, or by excessive use of the osteotome, the osteotomy can still proceed – as a soft tissue hinge will still exist. However in this case care has to be taken to prevent displacements other than the desired angular correction (e.g. linear, dorsal or plantar displacement). So a stable hinge makes the operation easier and more reliable and is worth trying to achieve.

    A test reduction is performed , pressing beneath the MTP joint, and watching the osteotomy close.
    If it doesn’t close, check that all the wedge has been removed. Then if it still doesn’t close, take the osteotome or saw to increase the inferior crack a bit, until it does close.
    Then check that the 20deg wedge has produced enough dorsiflexion to allow the first metatarsal to fold up to be parallel with the lesser metatarsals when seen from the side. If the metatarsal does not fold up enough, then repeat the distal osteotomy cutting a small additional wedge, to increase the dorsiflexion that can be achieved. If necessary this can be repeated until full reduction can be achieved.

    In this operation we used the Orthosolutions memory staple to stabilise the osteotomy.
    A 12 mm interaxis staple is ideal to obtain compression.
    To get maximal compression, set the interaxis setting on the jig to 13mm (one millimetre above the staple width to increase in vivo compression).
    Then apply one arm of the jig over the 2.5mm drill which is already in place above the osteotomy.
    Rotate the jig, so that the second hole lies below the osteotomy.
    Compress the osteotomy manually, to close it – then using a second 2.5mm drill, drill into the metatarsal, just above (dorsal to) the midline, and through both cortices.
    Remove the drill after drilling the hole.
    NOTE : IT IS CRITICAL TO COMPRESS THE OSTEOTOMY WHILST DRILLING THE SECOND HOLE.

    Then remove the jig and the remaining drill, exposing the osteotomy and drill holes.
    Measure the depth of each drill hole, and chose an interaxis 12mm staple of appropriate size (they come with arms of equal or different lengths to fit different sized bones).

    The introduction jig can be set up for a variety of different sized staples. Assemble the jig with the 10/12mm jaws, and screw the jaws into place.
    Apply the staple to the introducer, positioning it – as shown – in the jaws of the spreader.
    Place a thumb on the staple to keep it in positin on and then apply pressure to the handles. Press the arms of the handles together until the arms of the staple are parallel to each other (they will spring together to give compression after they’ve been introduced), then lock the introducer in this position, using the threaded adjuster and nut which passes through the handle.

    Support the foot firmly and insert the staple as far as the jig allows. You may need to tap the handle of the introducer lightly with a small hammer in some cases – but major force is never needed.
    Once the staple is in, remove the jig and complete insertion using a punch – lightly hammering it in until it lies on the surface of the bone.
    The wound is then closed in layers, and a cast or boot applied.

    Post Operative

    If the osteotomy has been performed with a stable inferior bridge and stable fixation, the osteotomy is stable to compression and the patient can be mobilised early in a cast or rigid boot using crutches.
    Weight bearing is permitted within the bounds of comfort (subject to the limitations of any other procedure performed at the same time).
    If there is doubt, then it is wiser to non-weight bear for 6 weeks to allow union.
    At eight weeks, a check X-ray is taken before mobilising out of the cast (into a supportive shoe) providing position is maintained and union confirmed.
    Whatever the indication, most patients will require orthotic care (at minimum insoles) after this surgery.
    The first orthotic insole fitting is usually best delayed until 16 weeks from surgery, to allow the majority of swelling to settle.

    Recommended Reading

    There are no published results for isolated dorsiflexion osteotomy.
    Ward et al.(Long- Term Results of Reconstruction for Treatment of a Flexible Cavovarus Foot in Charcot-Marie-Tooth Disease , J Bone Joint Surg Am (2008) Dec 1:90(12) 2631-2642), reviewed 25 patients who had dorsiflexion osteotomies performed as part of a correction for CMT. All osteotomies united, and correction of cavus was achieved.
    They noted high levels of satisfaction, but worse results in smokers than non-smokers. Most patients required orthotic aftercare.,

    Leeuwesteijn AE, de Visser E, Louwerens JW in (Flexible cavovarus feet in Charcot-Marie-Tooth disease treated with first ray proximal dorsiflexion osteotomy combined with soft tissue surgery: a short-term to mid-term outcome study.Foot Ankle Surg. 2010 Sep;16(3):142-7.) reviewed 35 patients having CMT correction with dorsiflexion osteotomy,
    No major complications were seen. Pressure callosities diminished in 81%. Seventy percent of the patients could walk barefoot after the operation and 77% of the patients had less pain after surgery. Foot function was considered better after surgery by 84%. Ninety percent were satisfied with the correction of the deformity.

    Reference

    • orthoracle.com

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