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Posterior ankle decompression- Open technique

    Overview

    Learn the Posterior ankle decompression- Open technique surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Posterior ankle decompression- Open technique surgical procedure.
    Posterior ankle impingement presents with postero-medial or occasionally postero-lateral ankle pain whilst the foot is in positions of full plantar-flexion (such as kicking a ball , dancing en-pointe or descending an incline). There are often no symptoms referable to the joint outside these activities.
    It is a condition which not only occurs as a result of repetitive athletic activity but can complicate an ankle inversion injury which usually has a component of forced plantar-flexion as well as inversion.
    Irrespective of whether the MRI findings demonstrate bony impingement it is worth commencing interventional treatment with an ultrasound guided injection into the soft tissue envelope posteriorly. This will target the Flexor Hallucis Longus tendon sheath behind the ankle as well as the posterior ankle joint capsule and joint.
    The operation described here is an open one though the arthroscopic technique is also well established and described by Nick Cullen from Stanmore in another of OrthOracles techniques.

    Indications

    INDICATIONS.
    Primary: Posterior ankle impingement that has failed to settle with activity modifications and ultrasound guided injections.
    Revision: A different (and if necessary more extensive ) view of the postero-medial structures is achievable with the open technique compared in particular to the arthroscopic technique.
    SYMPTOMS & EXAMINATION.
    Mostly patients present with postero-medial ankle pain which is experienced just in full (or fullish) plantar-flexion of the ankle . Kicking a ball , jumping , the en-pointe position in dance , landing forcibly with plantar -flexion (such as during a cricket bowling action) and walking down an incline are all activities which may produce symptoms. Pain can also be exclusively postero-lateral on occasion.
    There are broadly speaking 2 groups of patients who suffer with the problem. Professional Athletes engaged in relevant activities ,Football , dance ,cricket being the obvious ones . They will often have no history of discreet injury , the issue being a chronic ,repetitive “at-risk” activity. The other more numerous group are patients who have suffered an ankle sprain that has failed to settle. It should be remembered that the mechanism of injury is not necessarily simply weight bearing and inversion with an ankle sprain but also an additional plantar-flexion moment , which is when the injury occurs.
    If posterior impingement occurs as part of a sprain then anterior ankle joint symptoms may also exist and require treatment also.
    In the patient with a severe sprain as the precipitant of symptoms post-traumatic pathologies are also looked for ( lateral joint instability, anterior joint tenderness , peroneal tendon subluxation , peroneal synovitis , bony tenderness) .
    Patients will predominantly have tenderness to the postero-medial ankle and this is well localised to the posterior Talus. The Tibialis posterior is an easily identified structure in this region and as well as being specifically examined can be used to guide the examiner. The Flexor Hallucis Longus should also be specifically examined and resisted activity tested to try and elicit pain. This can be done with the ankle in plantar-flexion. The pain and tenderness may sometimes be postero-lateral. If this is truly postero-lateral ankle(as opposed to the peroneal tendons) and if on MRI a significant predominantly lateral bony pathology exists then a postero-lateral approach to the ankle may be considered. This will allow poorer access to the FHL and little visualisation of the neurovascular bundle and would be a rare occurrence.
    In all patients a “posterior impingement ” test should be performed. Most commonly This entails placing the patient supine , supporting the calf on a pillow to allow free posterior ankle movement and forcibly plantar-flexing the ankle (after warning the patient about what is to come). A positive test equates to posterior pain , on occasion severe , that reproduces the pain in question. Anterior ankle pain is not uncommon but simply indicates anterior ankle pathology. The classical version of the test includes infiltrating local anaesthetic into the posteromedial area and then repeating the test with the expectation of no pain after local has been infiltrated. I would suggest an ultrasound is used to guide this aspect if one feels the need to though I never have.
    Plantar and postero-medial sensation should be examined in all patients in particular if there have been previous attempts at corrective surgery.
    INVESTIGATION.
    Mri :An Mri scan will be required in all patients whole fail to settle conservatively. Its purpose is to identify the size and location of any posterior bony prominence (either Os Trigonum or Steida process) as well as to confirm that bony oedema exists which will indicate that the bone is at least part of the problem.
    Inter-current FHL synovitis , retro-calcaneal bursitis and potentially ankle pathology (in particular if the condition has resulted from an ankle plantar-flexion and inversion injury) can be diagnosed.
    The location and size of the bony pathology is best appreciated in particular on the axial scan slices and it is key to read and understand these . On occasion a significant proportion of the width of the posterior Talus may be effected and need to be excised .
    Ultrasound: This is perhaps more sensitive for identifying ankle synovial , posterior ankle capsule and FHL or peroneal paratenon inflammation. The ultrasound is used in most cases as a safe way of placing a theraputic injection around relevant inflammed soft-tissue structures. It has no role is settling bone oedema effecting an Os trigonum of course but just because this is visible on MRI does not absolutely mean it is this and not the soft tissue component that is the source of symptoms (both may of course be).
    Ideally imaging should support the diagnosis .On occasions all imaging will be negative in the presence of a clear diagnosis of posterior impingement . The decision for operation is made upon clinical grounds.
    NON-OPERATIVE MANAGEMENT.
    Activity modification:This has normally occurred out of necessity by the time patients present.
    Ankle bracing: For certain sports an appropriately designed brace can help by limiting full plantar-flexion enough without inhibiting function. An example would be the use of a fully laced up Swede-O-lok ankle brace in a cricket bowler , which limits the end range of plantar-flexion as well as stabilising the joint .
    Ultrasound guided injection: As described above. This is an entirely legitimate first line of treatment in most cases. See results section and the paper by Bollen for more detail.
    ALTERNATE OPERATIVE MANAGEMENT.
    Arthroscopic posterior ankle decompression : Smaller external scars are created and a smaller operative field is created internally .This could logically be expected to result in less post-operative scar tissue to the back of the ankle and a more rapid return to activity with less potential to limit full plantar-flexion . Some published results support the former though the time advantage is relatively small and not seen in all.

    Setup

    Posterior ankle 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 to be used.

    Operation

    The approach for a posterior ankle decompression is through a skin incision situated midway between the posterior border of the medial malleolus and the posterior border of the tendo-Achilles.
    It is useful to identify the posterior talus/posterior aspect of the ankle joint by plantar & dorsiflexing the ankle to detect movement and centre the incision over this point. The incision can be relatively small in length compared to that required for a Tarsal tunnel decompression which has the same approach.
    A postero-lateral approach is also described but will not allow such direct and straightforward avoidance of the neurovascular structures nor clear display of the FHL tendon.

    After blunt dissection through the fat the deep fascia is seen. The vessels sit superficial to the nerve, can be seen through the fascia, and lie safely beneath it.
    Whilst dissecting through the fascial layer orientate yourself to the plane that runs from the posterior lip of the Tibia to the anterior edge of the Achilles. The plane of dissection should be strictly at right angles to this. If this is not adhered to it is easy to enter the deep fascial layer obliquely and potentially not come onto the bundle directly.

    The deep fascia is opened by sharp dissecting initially onto a McDonalds’ retractor in a limited fashion.
    Fine tenotomy scissors and the McDonalds are also used to ensure the neurovascular bundle is not adherent to the under surface of the fascia. The fascia is then carefully opened with the tenotomy scissors. In performing this fascial release the objectives are both to allow adequate exposure of the back of the Talus but also to ensure that no tight bands are left to constrict the bundle either proximally or distally. These releases of the deep fascia at either end of the wound must be performed under direct vision .

    Once the neuro-vascular bundle is exposed it can be seen that the posterior tibial nerve lies posterior and deep to the vessels. The relative size of vessels and nerve does vary but the nerve is always deep to the vessels.
    Though the nerve and its branches does not need to be formally dissected out as for a Tarsal tunnel decompression it is important to be aware of the location of the branches also. The posterior Tibial nerve may have already bifurcated by this point and the medial & lateral plantar nerves may be diverging beneath the overlying vessels. Do not therefore guess where the distal portion of the nerve runs based on its proximal line.

    To access the posterior ankle the neurovascular bundle (1) needs to be retracted and this is easiest usually done in a posterior direction. Small vessels passing anteriorly may need to be ligated or carefully diathermised. Bipolar diathermy should be used. Careful blunt (scissor) dissection is used to probe and identify channels to pass fine vascular sloops (2)around the vessels to allow safe retraction. It may be necessary only to mobilise the vessels and not the nerves (as seen here). This is a decision to make during surgery.
    On occasion the location and mobility of the vessels may be such that they are better mobilised in an anterior direction.
    Once the neuro-vascular bundle is mobilised the Flexor Hallucis Longus tendon(3) can be seen .This is the guide to the back of the Talus. Moving the ankle joint also assists this at this juncture.

    The Flexor Hallucis Longus (FHL) tendon (1) is identified easily once the vessels are retracted within its sheath. Here its sheath has been opened already to reveal the tendon and a fair amount of synovial inflammation(2) is evident. This needs to be removed and the tendon then inspected for any tears or degenerative change (though both are rare in these patients).
    The FHL should be traced down into its fibro-osseous tunnel and inspected and treated here also.

    A full inspection of the length of the FHL tendon(1) within the operative field should be undertaken. There is still synovial inflammation to remove. On occasion there may be a low lying muscle belly of FHL which can make exposure more troublesome . Some muscle tissue can be removed but it is key that any bleeding points are diathermised using the bi-polar probe
    It is important to handle the vessels carefully through-out the operation. The tension seen applied here with vascular sloops is only momentary.
    It is also important to keep both nerve and vessels adequately moist whilst exposed. I favour a diluted solution of local anaesthetic washed over these structures throughout the operation which usually ensures a prolonged and effective post-operative block results.

    With the FHL exposed it can be retracted (here done with the McDonalds’) to reveal the posterior aspect of the ankle joint (1). It is also a safe structure to retract against , thus allowing indirect retraction of the neurovascular bundle also.
    The ankle joint location can be usefully confirmed by plantar and dorsi-flexing the ankle whilst palpating and looking for the point of movement. It will not be immediately visible due to the presence of the posterior capsule. This capsule will need to be reflected/resected to allow definition of tibia and talus. There is not infrequently also capsular thickening & posterior ankle joint synovitis contributing to the symptoms of impingement . I usually excise the posterior ankle capsule at this point with a careful sub-periosteal dissection. Bleeding points will be encountered and should be carefully coagulated as encountered. This is especially true in the deep postero-lateral depths of the exposure on the back of the Tibia where bleeding can be difficult to access and pinpoint unless dissection is meticulous.

    With the ankle joint opened and posterior capsule excised the lower tibia(1) and posterior talus(2) are identified. The FHL remains retracted(3).
    Though the posterior Talus will be identifiable at the ankle its most posterior aspect (and any Trigonal type process) will be covered by the capsule of the posterior Subtalar joint. It helps to confirm that a prominence is the Os Trigonum by loading it directly with the blunt end of a McDonalds and looking for movement at its articulation with the posterior Talus. It will also usually be necessary to sharp dissect around the posterior aspect of the Talus in this area, sectioning capsular attachments and opening the subtalar joint also assists in identification of the posterior process.
    Another step which helps identification of the Os Trigonum is fully plantar-flexing the ankle to identify any bony “pinch points”.

    The FHL tendon(1) freed from its investing sheath , inspected and retracted anteriorly in this case. This tendon is healthy. The posterior aspects of tibia(2) and talus(3) are exposed. A very small Os Trigonum is identified(4) and can now be excised.The vessels and nerve continue to be retracted(5).

    The posterior ankle joint exposed and back of the talus visible (1) in another case. Note that here the neuro-vascular bundle has been easier to retract superiorly.
    The Os Trigonum will not necessarily define itself. Placing the ankle into full plantar-flexion at this point will help to define the area of interest on the posterior Talus . This can then be explored by probing directly any posteriorly prominent bone. The smallest amount of movement can sometimes define the interface that needs to be taken down.

    Care should be taken not to damage the posterior aspect of the Subtalar joint in excising the bone. It is important also to reference the axial MRI or CT at this point to ensure that adequate lateral bone in particular has been removed with the process.

    With the Os Trigonum excised (1) the most posterior aspect of the Subtalar joint(2) can be seen beneath its previous position . In removing the process its capsular attachments to the posterior facet of the Subtalar joint will need to be sharp dissected free. The foot should now be fully plantar-flexed to ensure adequate clearance has been achieved at the posterior ankle joint.

    A plain X-Ray showing a small Os Trigonum with clear fibrous interface between the talus and the Os Trigonum.
    The T1 weighted MRI image on the right demonstrates that oedema can be present also effecting the associated posterior aspect of the Talus.
    It is important to get familiar with looking at the Axial MRI (or CT) which reveals whether the bony prominence is postero-medial or more postero-laterally placed. The entire posterior span of the Talus should be accessible (if an open technique is used) through a postero-medial approach but it is useful to have an idea of where to look for the prominence.

    The posterior talar process doesn’t have to have a pseud-arthrosis with the talus to produce an issue.
    A significant posterior prominence can exist which is in bony continuity with the talus in which case it is called a Steida process, as shown above. This may understandably cause exactly the same issues as an os trigonum.

    The T2 weighted image demonstrates a fair degree of bony oedema associated with the Steida process, supporting the diagnosis of posterior impingement. A lack of oedema may indicate that the issue is more one effecting the soft tissues as opposed to an incorrect diagnosis.
    It is usually worth trying a guided injection into the posterior ankle soft tissues and around the FHL tendon & sheath but with a large process like this the chance of long term resolution of symptoms with injection is going to be limited.

    Post Operative

    The first two weeks are spent in a lightweight cast , limited weight bearing
    After two weeks into long post-operative boot and commence weight bearing using crutches.
    Usually by the end of 3 weeks post op it is comfortable to weight-bear just in the boot without the need for crutches.
    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 great risk that the posterior ankle capsule will stiffen and result in restricted ankle range unless a very active and early mobilisation program is persued. These patients are often athletes or dancers and early and appropriate frequent rehabilitation can make the difference between return to optimal rather than sub-optimal sporting performance.
    Static bike is allowed from as soon as the wound permits and cross-training from as soon as adequate balance and proprioceptive capacity has returned
    Light jog on treadmill and sport specific protocols thereafter.
    Of huge importance also 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 excacerbate 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

    Recommended Reading

    Posterior Ankle impingement in professional soccer players:effectiveness of sonographically guided therapy.
    American Journal of Roentgenology.2006.187:53-58
    P.Robinson , S.R.Bollen.
    A retrospective review of 10 professional soccer footballers at a median of 26 months post initial intervention (this being an ultrasound guided posterior ankle injection).
    MRI performed in all patients and findings were a thickened poster-lateral capsule and synovitis in all patients ,Tibial plafond oedema in 5 , os trigonum oedema in 1 , lateral Talar process oedema in 3 patients and FHL sheath effusion in 7 patients.
    Return to sport by 3 weeks in all cases
    2 recurrences of symptoms , both in players with Os Trigonums (& posterolateral synovitis) both of whom had repeat injections. One required surgical excision subsequently.
    Subacute posteromedial impingement of the ankle in athletes: MR imaging evaluation and ultrasound-guided therapy.
    Skeletal Radiol (2006) 35:88-94
    C Messiou, P Robinson, PJ O’Connor, A Grainger
    9 Elite athletes with postero-medial impingement imaged by MRI and then injected postero-medially under ultrasound guidance. Imaging was also reviewed from 6 athletes with postero-lateral impingement.
    All postero-medial Athletes had both postero-medial synovitis and capsular thickening ( postero-lateral and posterior synovitis was also present in most however). In addition 8 had postero-medial tendon sheath effusions and 2 Os trigonums. Injection was just into the postero-medial capsule (and also dry needling undertaken).
    Return to sport 3 weeks. 18 month follow up. 1 patient with a large medial Talar process required its resection.
    Outcome of posterior Ankle arthroscopy for hindfoot impingement.
    Arthroscopy 2008. 24(2):196-202
    Willits K et al
    16 cases reviewed a mean of 32 months post operation.
    11 had an Os Trigonum removed , 5 a posterior Talar process ,FHL tenolysis in 5 and posterior ankle arthrotomy in 1.
    14 returned to pre-injury sport at a mean of 5.8 months and back to work by 1 month.
    Os Trigonum excision in dancers via an open postero-medial approach.
    Foot & Ankle International Aug 22 ,2016.
    Heyer AH, Rose DJ.
    38 Dancers (8 professional & 30 students)with 40 operated ankles . Open technique and all underwent Os Trigonum excision and open FHL tenolysis. Average return to dance 7.9 weeks and pain-free 17.7 weeks. 35 returned to previous level of dance and 38 felt the operation to have been successful. 4 minor wound complications.
    Return to training and playing after posterior ankle arthroscopy for posterior impingement in elite professional soccer.
    Am J Sports Med 2010.38(1):120-4.
    Calder JD, Sexton SA, Pearce CJ.
    27 elite players followed up after operative arthroscopic treatment. 13 Os Trigonums removed , 9 avulsed posterior bony fragments , 5 “soft tissue” resections with FHL release. A mean of 34 days to return to training and 41 to playing. No major complications.

    Reference

    • orthoracle.com

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