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Tarsal tunnel decompression (for tarsal tunnel syndrome)

    Overview

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    Tarsal tunnel syndrome classically presents with neurological symptoms effecting the sole of the foot in the distribution of one or both terminal branches of the posterior tibial nerve. Classically the symptoms are worse at night and only the sole of the foot is effected. It may though produce symptoms anytime and sometimes daytime symptoms are the more prevalent. Other than the classical distribution of symptoms the other standout feature is usually the severity of the pain which can be very significant.
    Most commonly it is due to tight fascial layers or peri-neural fibrosis compressing the posterior tibial nerve and its branches though extrinsic compression from ganglions and other space occupying lesions can less commonly cause the condition.
    Nerve conduction testing is diagnostic in two thirds or so of and physical examination is more often equivocal or unrevealing. Often the strongest indication of the diagnosis is the history. Lumbar spine and more general nerve pathology should be excluded but the possibilty of a “double crush” phenomenon should always be borne in mind.
    Surgical treatment if performed with rigorous attention to detail is highly successful in my experience and warranted in symptomatic cases irrespective of their chronicity. Pain is most consistently dealt with by the Tarsal tunnel release and is also the earliest feature expected to improve, though sensory improvement is also to be expected.

    Indications

    INDICATIONS.
    Symptomatic Tarsal tunnel syndrome
    SYMPTOMS & ASSESSMENT.
    Pain is the most common presenting complaint , usually associated with varying degrees of sensory symptoms in the distribution of the plantar nerves (both or either). On occasion no pain is present
    The classical presentation is night time paresthesia , effecting the sole of the foot and severe enough to wake a person from sleep. This is by no means invariable and some patients may have activity related symptoms only.
    Clinical examination is sometimes helpful with a positive Tinnels test along the line of the Posterior Tibial nerve but more often it is simply the delineation of sensory alteration/pain effecting just the one or both plantar nerve distributions which is most diagnostic.
    As with carpal tunnel a strong clinical history may ultimately be all there is to go on.
    These patients will on occasion present late , having passed through the care of non-specialists for whom the diagnosis may not be self evident. Chronicity of symptoms should not be a bar to decompression which is a straightforward procedure whose effects can be rapidly transforming.
    Other causes of neuralgic plantar pain and sensory alteration should always be considered , in particular low back pathology causing root compression and peripheral neuropathy. Be aware also of the “double crush” phenomenon which describes the “nerve” or nerve supply to the limb being compressed concurrently at two levels , the Tarsal tunnel may simply be one of them and more proximal pathology may also need to be treated.
    INVESTIGATIONS.
    MRI:On occasion external compression of the tarsal tunnel is the cause of the problem and if suspected an MRI is a baseline investigation that should be done. The clinical features that would lead one to suspect external compression are either a reduction in the range of movement of the ankle or subtalar joint or a palpable asymmetry in the region of the Tarsal tunnel between the two ankles. During decompression the local anatomy will of course be easily appreciated but on occasion soft tissue or bone tumours can present here and this changes the management obviously.
    Nerve conduction: This should be checked in all cases but a normal result does not preclude the condition. Consider ignoring the results if normal and clinical symptoms strongly suggests the diagnosis.
    Ultrasound: Is mainly indicated to theraputically infiltrate local and/or low dose steroid around the nerve if it is acutely inflammed (which can occur post-operatively) or if the presentation is one of severe ,unremitting pain . An injection around the nerve can be used on occasion to aid diagnosis.
    NON-OPERATIVE OPTIONS.
    There are limited non-operative options for this condition . There is no harm in infiltrating local and steroid around the nerve under ultrasound guidance. Equally if a compressive ganglion is present (which is not common) this could be aspirated for temporary relief.
    If symptoms are mainly nocturnal consider a neutralising splint such as one might choose for plantar fascitis.

    Setup

    Tarsal tunnel decompression is easiest carried out with the patient supine
    The incision used is postero-medial & positioned between the back of the medial malleolus and the Achilles tendon
    One or two side supports should be placed on the operated side , at thigh and trunk level , whilst several sandbags are placed under the opposite buttock , thus turning the operated leg into external rotation
    The further addition of rolled up sterile towels allow an extra element of helpful rotation and access to the back and lateral aspects of the ankle.
    Thigh tourniquet to be used and Flowtron on non-operated calf.
    Prophylactic antibiotics and LMW-Heparin peri-operatively & post-operatively
    Bipolar diathermy

    Operation

    A postero-medial skin incision, midway between the Achilles and posterior aspect of the medial malleolus, is made.

    The exposure needs to extend down into the sole of the foot to the level of the Navicular. Proximally it should go high enough (which currently this incision isn’t) to release as much deep fascia overlying the neurovascular bundle which is palpably tight.

    The sharp dissection through the skin is followed by blunt scissors dissection through the fat layer.Further blunt dissection is also usefully done using swabs to push and detach the fat off the deep fascia of the flexor retinaculum.

    The deep fascia, which is a well defined layer, is identified and carefully defined, and through it can be seen the neuro-vascular bundle(to which the scissor tips are pointing).Before proceeding it is worth making a few points about how to handle operating on and around a significant nerve such as the Posterior Tibial nerve.
    The scissors used need to have fine, delicate tips such as a pair of tenotomy scissors and the forceps used are best fine and non toothed .Once the nerve is identified keep it in sight at all times and dissect confluently along its course, rather than jumping along to a guessed next location (on this point be aware of the expected anatomy and its variations rather than embarking on a blind exploration of the nerve). Keep the nerve and branches moist at all times (local anaesthetic works well for this) and if retracting be gentle and use only short periods of traction even with vascular sloops. Diathermy must be bipolar and used sparingly away from the direct vicinity of the nerve . Finally spend time throughout the dissection, from the skin incision onwards, ensuring that any bleeding vessels encountered are cauterised or tied in a safe fashion.

    The deep fascia is opened by carefully dissecting onto a McDonalds that has been inserted through a small nick in the fascia. The McDonalds should be initially swept proximal and distal to clear any adherent parts of the bundle. Immediately deep to the fascia it is the neurovascular bundle and it can be slightly adherent to the overlying fascia. A small, careful cut is used to open the facsia and then fine tenotomy scissors are used to start mobilising the vessels.
    This fascia is of variable thickness, on occasion being very dense and fibrotic. If this is the case then the vessels may not be visible beneath it and so not an immediate guide to where to open the deep fascia. Under such circumstances one should be clear that the point of opening this layer is exactly in the midpoint (measured from posterior edge of tibia to the anterior margin of the Achilles). Anteriorly in this space and in separate sheaths are the postero-medial tendons which do not need to be exposed.

    Once the retinaculum is opened(1) the neurovascular bundle is easily identified, the vessels can be seen(3) sitting anterior and superficial to the posterior tibial nerve(2).
    As the decompression progresses it is most important that care is taken to ensure all bleeding points are cauterised with bipolar diathermy (well away from the nerve and its branches). A low power setting should be used. Larger vascular branches should be tied-off.
    A post-operative haematoma is a complication to avoid as it risks acute re-operation being required.

    A Langenbecks retractor should be placed into the proximal extent of the wound to elevate the skin & fat layer and allow visualisation of the deep fascia more proximally, followed by a scissors release.It is important that the deep fascia(1) is completely decompressed proximally. Careful scissors dissection should be used to continue the deep fascia splitting incision proximally.
    An index finger is a good way to judge when there is no remaining tension in this layer. Only cut under direct vision with the scissors proximally.

    The posterior tibial artery (2) sitting between the veins(1), and anterior and superficial to the posterior tibial nerve(3). Distally the deep fascia(4) is still intact.
    It is worth looking carefully at how the nerves look when first seen. They have a fairly adherent layer of peri-neural fat and are not especially well defined. On occasion this peri-neural layer can also be fibrosed and tight and careful freeing it off the nerve and branches is not only required for identification but also as part of the decompression.

    Further careful dissection is required with fine tenotomy scissors to trace the course and braches of the posterior tibial nerve(2). Posteriorly is running the medial calcaneal branch. Distally thick fascia overlies the Abductor Hallucis muscle belly(3), which marks the distal extent of the dissection.

    Vascular sloops are carefully placed around the vessels to allow gentle retraction(1). Thick adherent fat overlies the nerve and is carefully dissected to identify the nerves terminal branches(the medial and lateral plantar and medial calcaneal branch).The level of bifurcation of the nerve is variable and rather than specifically seeking out the bifurcation I’d suggest being aware that of the fact and the existence of the other branches as one dissects out the nerve.
    The medial calcaneal nerve(2) is most often is a branch from the posterior tibial nerve but in this case it is seen issuing as a branch of the Lateral plantar nerve(3) which can occur in as many as 25% of people.

    A McDonalds being used to gently lift the vessels and identify the onward course(2) of the medial plantar nerve(1), The lateral plantar nerve (3) lies posterior and behind it the medial Calcaneal branch.
    During the dissection the vessels and nerve are liable to dry out easily. This should be avoided by regular application of moisture. My own preference is only to use diluted Marcaine throughout which results often in absolutely minimal post-operative pain.

    Distally the deep fascia(2) overlying the abductor hallucis attachment and muscle belly(1)needs to be released to allow the medial plantar nerve to be freed.Beneath it the nerve is usually well encased in fat and not immediately identifiable. Care should be excercised with a methodical dissection to identify the nerve.

    The lateral plantar nerve (4) also passes also deep to the abductor hallucis muscle and is also traced distally by blunt dissection.With the deep fascia opened(1) the overlying vessels still require mobilisation using vascular sloops(2) to ensure that both the medial (3) and lateral(4) plantar nerves are free.

    The medial calcaneal branch(es) is the third terminal branch to be identified and should be freed. This sits behind the lateral plantar nerve(2) and on occasion(as here) is present as multiple branches(3,4) rather than a single structure. It is much more common as a single structure.
    The medial plantar nerve (1) is seen going beneath the fascia of Abductor Hallucis(5).

    The medial plantar nerve is traced distally to the level of the Navicular where it sits in a fibro-osseous tunnel, and ensured its free to this level.

    After the release is completed the medial plantar nerve (2) should be seen traversing deep into the foot , the lateral plantar nerve (1,3)running deep to the abductor and the medial calcaneal branches , (6) ,(5) , (4) lying most posterior of all.Before closure any bleeding points that have been missed should be carefully diathermised. If tricky areas consider applying a haemostatic product such as surgicel . Avoid placing this directly on any nerve tissue.
    The fat layer is closed with interrupted sutures , the fascia is left un-sutured ,and the skin is closed with a sub-cuticular closure. Consider using a drain but placed carefully away from the nerve. Avoid using sutures that require removal. Soft tissue healing times are prolonged in this area and swelling will place early and persistent tension on the wound .

    Post Operative

    The first two weeks are spent in a lightweight cast , limited weight bearing. If this is not done the ankle may tend towards equinus and then work needs to be done by the patient getting the position back to neutral. By two weeks this is not an issue and cast can be removed.
    The first symptoms to improve , often within days of the operation , are those of any neuralgic pain experienced pre-operatively. Sensory alteration takes longer to improve and may resolve less completely.
    After two weeks into long post-operative boot and commence weight bearing
    Of greatest importance is that from 2 weeks , once out of cast , active and passive ankle range of movement exercises are started and pushed aggressively.This should be under physiotherapy supervision . There is a risk that the posterior ankle will stiffen and result in restricted ankle range unless this is done.
    Of great importance through-out the post-operative period is that the wound is looked after . Wound infection and small areas of breakdown occur easily in a freshly healed wound that is allowed to rub on socks/shoe-wear.
    Any exudate from the wound which is allowed prolonged contact with the wound will further exacerbate any skin breakdown . Dressing changes may therefore need to be frequent if such a complication ensues.
    Once out of cast I advise another month of daytime dressings when in shoes and also nocturnal dressings whilst any of the wound remains unhealed
    Showering & bathing is from when out of cast
    Beware if symptoms initially settle though recur rapidly . Haematoma formation , deep infection or acute neuritis of the nerve can both produce this. Ultrasound aspiration/injection is indicated .Re-operation may be required for a large haematoma or deep infection so best to avoid these.
    Scar hypersensitivity can occur anytime during the initial 3 post-operative months and if it does should be treated aggressively as soon as it manifests by a course of scar desensitisation .

    Recommended Reading

    Tarsal Tunnel Syndrome:Diagnosis, Surgical technique and functional outcome.
    Foot & Ankle International :19, 2, 65-72 .1998
    D Ballie & A Kelikian.
    36 feet were reviewed at approximately 3 tears post-op. 81% had abnormal pre-operative nerve conduction tests. 72% satisfied with the results of operation .
    13% complication rate reported (one haematoma and other minor wound infective complications) . 8 scars noted to be hypersensitive & 5 hypertrophic.
    Tarsal tunnel syndrome. Causes and results of operative treatment.
    J Bone Joint Surg Br.1991 Jan ;73(1):125-8
    Takakura Y et al
    5o feet operated on with the condition. Unusually most of the cases unusually were due to extrinsic compression , 18 ganglia ,15 Talo-calcaneal coalitions , 5 post trauma , 3 tumors and no cause in 9 cases.
    Tarsal tunnel syndrome and additional nerve lesions in the same limb.
    Foot & Ankle 1993 14(2):71-7
    Sammarco G, Chalk D, Feibel J.
    13 patients with Tarsal tunnel syndrome diagnosed by nerve conduction with also at least one additional proximal nerve lesion reported. 7 cases warranted surgical decompression and 6 of those improved significantly.
    Short term operative outcome of tarsal tunnel syndrome for benign space occupying lesions
    Foot Ankle Intl 2009. 30(8):741-5.
    20 patients followed up after decompression . 13 had space occupying lesions removed as well as a formal decompression. Of these 7 were satisfied 3 were not and 3 rated the result only as fair.

    Reference

    • orthoracle.com

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