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First MTP Fusion (using Stryker Anchorage MTP arthrodesis plate )for Hallux Varus

    Overview

    Learn the First MTP Fusion (using Stryker Anchorage MTP arthrodesis plate )for Hallux Varus surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the First MTP Fusion (using Stryker Anchorage MTP arthrodesis plate )for Hallux Varus surgical procedure.
    Hallux varus is a deformity of the big toe caused by a variety of reasons, the commonest of which is iatrogenic following hallux valgus surgery
    The condition is characterized by a coronal plane deformity where the hallux is deviated medially and the intermetatarsal angle between the first and second metatarsals is decreased to below the normal angle of 9-11 deg. In longstanding cases there might be medial dislocation of the medial sesamoid and an inability to toe off as a result of an unstable metatarsophalangeal joint. Foot wear is a significant problem in these patients as the forefoot becomes wide. It is often associated with worsening osteoarthritis as the incongruence of the joint surfaces increase.
    Arthrodesis of the 1st metatarsophalangeal joint is reserved for those cases of hallux varus where there is severe symptomatic arthritis causing pain

    Indications

    INDICATIONS:
    Hallux Varus associated with osteoarthritis
    Severe deformity with irreducible dislocation of medial sesamoid
    Failed reconstruction for hallux varus.
    SYMPTOMS & ASSESSMENT: Patients mainly complain of difficulty with footwear and a sense of instability as the hallux subluxes at the MTP joint into varus. Pain is often felt over the medial sesamoidal area and is often increased with worsening deformity. Once there is sufficiently severe defunctioning of the weight bearing function of the hallux, patients start to suffer transfer pain with the emergence of plantar callosities on the sole of the foot over the lesser metatarsal heads. There is also a significant cosmetic component to the condition as the foot is severely widened and in its severe stages is grotesquely deformed. Painful range of movement indicates pathology at the MTP joint and is usually osteoarthritic in nature.
    An elaborate history should be taken which include a history of familial varus deformity, details of previous operations, trauma, diabetes and hypermobility all of which can cause hallux varus. Smoking and systemic diseases such as diabetes are known to adversely affect the outcome of this operation. Careful and meticulous examination of the whole lower limb should be undertaken. The neurovascular status of the patient must be assessed as a priority and the position of the hindfoot is of crucial importance. Any equinus deformity should be assessed as this may be corrected at the time of the operation . Gait and footwear characteristics are important and a photograph of the deformity taken whilst weight bearing before the operation is very useful to have a record of the deformity for the patient. The range of movement of, and pain in the TMT and IP joint must be recorded Pain in these joints may worsen after fusion of the MTP joint. Painful range of movement and reducibility of the deformity is also important to assess.
    INVESTIGATION: Weight bearing dorsoplantar, lateral views and non-weightbearing medial oblique radiographs are essential. Occasionally other investigations such as an MRI or SPECT are useful in defining the presence of osteoarthritis and avascular necrosis in the MTP joint.
    OPERATIVE ALTERNATIVES: If the deformity is fully correctable and the arthritis is mild or moderate, it may be possible to avoid a fusion of the joint by techniques to increase the intermetatarsal angle such as a reverse Scarf and reverse Akin osteotomy . It is also possible to use procedures such as Extensor Hallucis Brevis tenodesis to correct the deformity in the absence of severe fixed deformity or arthritis..
    NON-OPERATIVE ALTERNATIVES: Modification of foot wear, the use of strapping to reduce the deformity, offloading orthoses to deal with transfer metatarsalgia are some of the conservative measures that can be used.
    CONTRAINDICATIONS: Active infection or established irreversible peripheral vascular disease, non compliant patients and the very elderly patients would have a suboptimal outcome from this operation. Smokers should be warned of the potential complications of wound breakdown and nonunion which are significantly increased in smokers.

    Setup

    The preoperative WHO meeting should confirm the availability of implants and their sterility. The nature of the operation and the side of surgery should be crosschecked with surgeon patient and theatre staff.
    Radiographs should be appropriately displayed in theatre for referencing during the procedure.
    The operation can be done under general anaesthesia in conjunction with an ankle block or under regional anaesthesia such as a spinal anaesthetic or a popliteal block.
    In the absence of any other additional procedures such as a gastrocnemius release, the patient is positioned supine on the table with a sandbag under the ipsilateral buttock so as to position the foot orthogonally, with the axis of the foot perpendicular to the coronal plane. Diathermy is needed to cauterise veins that will be encountered during the procedure.
    Antibiotics are administered at induction or after regional anaesthesia. A thigh tourniquet is used with GA and a high above ankle tourniquet for regional block anaesthesia. A thromboembolic deterrent sock and Flowtron calf pump are used on the contralateral limb for thromboprophylaxis during surgery.
    The following pieces of equipment are essential for this procedure.
    Laminar spreader
    Self retainer
    Congruent MTP reamers
    Image Intensifyer
    Fixation plate and screws
    Cannulated Compression screw to be available if needed

    Operation

    The preoperative photograph shows the medial angulation of the hallux with some lesser toe deformities. Radiographs confirm arthritic change at the MTP joint. There are no transfer lesions in the sole of the foot.

    A mid medial approach is used to approach the MTP joint. This lies midway between the dorsal and plantar surfaces of the 1st ray and is a safe internervous approach to the MTP joint. Dorsal to it runs the dorso-medial cutaneous nerve and plantar to it is the medial digital nerve to the medial side of the hallux. Other incisions that can be used are the dorso-medial approach which puts the dorso-medial cutaneous nerve at risk and the dorsal approach which risks scarring the extensor tendons.

    The incision should be safe enough to raise a full thickness flap by subperiosteal dissection: however due to anatomical variations in the course of the dorso-medial cutaneous nerve, it is essential to locate the dorso-medial cutaneous nerve and protect it throughout the procedure.

    The nerve is especially vulnerable when the incision is made over a scar as the nerve may be trapped in scarring from a previous operation as is often the case with hallux varus.

    The dorsal flap is dissected as far as the lateral aspect of the MTP joint so as to allow acess to the lateral soft tissues.
    On the plantar aspect one must avoid dividing the capital nutrient artery to the metatarsal head which enters the neck of the metatarsal on the plantar aspect

    The medial structures are almost always very tight in Hallux Varus due to the nature of the deformity. As the two metatarsal heads are closer together due to the reduction in intermetatarsal angle, paradoxically the lateral aspect is also tight!
    Beginning with the medial capsule the medial collateral ligament, the suspensory ligament of the medial sesamoid and the insertion of the Abductor Hallucis into the proximal phalanx are carefully dissected off the bone making sure to avoid damage to the medial digital nerve. It is then possible to dislocate the joint plantarward.

    It should now also be possible to fully correct the varus deformity. It may be necessary to release the lateral collateral ligament, the lateral capsule and if accessible the intermetatarsal ligament to mobilise the first metatarsal and correct the 1-2 intermetatarsal angle.

    Any dorsal osteophytes and a prominent medial eminence are pared down with nibblers from both the metatarsal and proximal phalanx.
    A 1.6 mmK-wire is now drilled into the metatarsal shaft from the centre of the head and angled slightly plantarward at an angle of approximately 5-7 degree to the plane of the floor with the foot flat. This would be the optimal position of the fused hallux and the convexity of the metatarsal can be sculpted by the congruent reamer accordingly. It is not absolutely essential as the desired dorsiflexion can be dialled into the fusion because of the congruous nature of the fusion surfaces.

    The metatarsal head is then sized with the reamer and an appropriate sized cannulated conical reamer is used to ream the head. It is very important to protect the skin and soft tissues on the lateral side which are vulnerable to damage from the reamer. The use of bone levers will minimize this damage. It is also extremely important to proceed carefully with the reamers for fear of reaming too much of the head. Irrigation is required for hard sclerotic bone during reaming to minimize the damage from thermal necrosis. Enough bone needs to be reamed off to expose subchondral bone. It may be necessary to stop reaming when a congruous subchondral surface is created even if there are areas where the head is deficient and still has some cartilage covering it. These areas can be debrided of cartilage and drilled to expose subchondral bone . A reduction in length of the metatarsal can give rise to subsequent problems of transfer metatarsalgia.

    The process is repeated with the proximal phalanx using the corresponding cannulated cup reamer. The wire needs to be inserted slightly dorsal to the mid point on the articular surface as the plantar cortex of the proximal phalanx slopes dorsally at its distal half.
    Both surfaces are then drilled at multiple points with a wire to increase the subchondral bone exposure and bleeding points.

    The two bones are then fitted into each other in a ball and socket arrangement owing to the congruous nature of the surfaces and then stabilised with a temporary K-wire passed from proximal medial to distal dorsal. The position is checked with screening under the image intensifier, and also by confirming that the pulp of the distal part of the hallux comfortable reaches the floor with the floor placed on a flat surface. This is the optimal position of fusion.

    The angular nature of the deformity generates significant tensions across the fusion site and therefore with severe deformity it would be preferable to use a MTP fusion plate with the facility for compression across the fusion surface. The plate that has been used in this operation is the Anchorage CP MTP Compression Arthrodoesis Plate (Stryker) which combines the unique features of titanium, a low profile and variable locking holes with a compression screw facility through the plate (Plate Buttress) obviating the need for a separate screw to augment fusion rigidity.

    A template of the actual plate is now used to position the plate accurately. A transverse laser mark on the centre of the template is positioned accurately over the fusion line, This positions the plate in such a fashion that there are 3 holes proximal and 2 distal to the fusion site. A wire are used to mark the site of the compression screw through the plate.

    The template is then removed and a cannulated hemispherical reamer is then used over the wire that marked the site of the compression screw through the plate. This acts as a countersink to seat a corresponding prominence on the plate’s under-surface through the distal wall of which the compression screw is inserted subsequently.
    key to Annotations:
    wire in compression screw hole
    laser line marking fusion site
    wire in oblong hole

    The definitive plate is now seated carefully with the plantar prominence fitting perfectly into the cup reamed previously. The plate is stabilised by a wire through an oblong hole distal to the fusion line in its distal end. This wire will also show the compression achieved across the fusion site by moving proximally when the compression screw is inserted

    The proximal screws are now inserted to secure the plate firmly on to the metatarsal using the locking facility.

    Now the oblique compression screw hole is drilled from proximal dorsal on the metatarsal part of the plate to the distal plantar aspect of the proximal phalanx. It is measured and appropriate screw inserted until it engages the proximal phalanx securely. Before compression however, the K-wire temporarily fixing the fusion is removed to allow proximal migration of the proximal phalanx during compression. As the compression progresses one can see the proximal migration of the phalanx as the wire in the oblong hole moves proximally.

    Once compression is completed, the distal screws are now inserted into the plate and locked to hold the compressed fusion securely.
    The fusion is tested for rigidity by gently toggling the proximal phalanx. It is further tested for position on a flat surface as before.

    After checking the position of fusion and the hardware with screening the foot the tourniquet is let down, any bleeding ponts are cauterised with diathermy. The wound is cleaned with Betadine Aqueous solution and closed with No 1 Vicryl to the capsule interrupted and subcuticular Vicryl Rapide to skin. Local anaesthesia (Chirocaine 10 mls of 0.5%) is infiltrated into the wound edges and also used to effect a 5 nerve ankle block if not under regional anaesthesia. Inadine and gauze is then placed over the wound and wool and crepe bandaging is used to cover the wound firmly.

    Post Operative

    The patient is usually discharged on the same day with appropriate analgesia. It is advised that the leg is elevated as much as possible in the initial two weeks to allow the wound to heal without being compromised by swelling. Thromboprophylaxis is not necessary. patient is asked to avoid usage of anti-inflammatory medication if possible because of its inhibitory effects on bone healing.
    The patient is advised to walk using a heel bearing shoe for 4-6 weeks to protect the fusion. The patient is also referred to physiotherapy for intrinsic muscle work and general range motion exercises for the ankle and subtalar joint
    The patient is reviewed at 1 week for a wound ccheck when all bandaging is removed and a dry dressing applied to the wound.
    At 6 weeks the patient is reviewed and weight bearing dorso-plantar, lateral and medial oblique radiographs are performed to confirmed satisfactory union
    The patient is then discharged to physiotherapy for gait instruction.

    Recommended Reading

    Reference

    • orthoracle.com

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