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Mortons Neuroma Excision

    Overview

    Learn the Mortons Neuroma Excision surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Mortons Neuroma Excision surgical procedure.
    There are a limited number of pathologies which present with pain in the 2/3 or 3/4 inter-metatarsal area, a mortons’ neuroma being one of the commoner ones. Others are mechanical pain from the metatarsal head, MTP joint synovitis or least commonly degenerative change of the MTP joint.
    Pain may be located purely under the effected metatarsal heads or may radiate into the toes and be associated with numbness in the web space or toes. On occasion splaying will effect the position of the toes in the effected web-space. There is a well recognised association between Mortons neuroma and plantar plate tears, leading to cross-over toe deformities. One method of surgically treating this is detailed on OrthOracle at https://www.orthoracle.com/library/crossover-second-toe/
    The first line of management of a Mortons’ neuroma is usually non-constricting and supportive shoe-wear with a low threshold for steroid and local infiltration to reverse the reactive swelling of the digital nerve that comprises a neuroma. The injection may be performed with or without ultrasound guidance, though intercurrent pathologies such as MTP joint synovitis or plantar plate tears are not confirmed without imaging being used. MRI can also be used to diagnose the condition.
    Surgical excision is highly effective, though not invariably successful, for treatment of the intrusive pain associated with the condition but minor degrees of residual associated symptoms are not uncommon post-operatively and realistically the forefoot takes 6 to 8 weeks to resolve after such surgery.



    Indications

    SYMPTOMS AND ASSESSMENT.
    A Mortons’ neuroma normally presents with pain present on weight-bearing that is localised underneath either the 2/3rd Metatarsal heads or the 3/4th heads (these are the narrowest web-spaces).
    Sometimes both web-spaces are symptomatic discreetly or more commonly a patient has difficulty differentiating exactly where the pain is located. Neuromas may also exist in a web space and cause no symptoms at all.
    More often than not pain or tingling radiates down into the effected toes. Sometimes of course it does not.
    The severity of symptoms is variable but it is not uncommon for significant functional restriction to the extent sport can’t be played and only short distances walked.
    On examination the foot usually looks entirely normal. On occasion though there can be subtle swelling in the effected web-space. This is most easily noted when the patient weight-bares. In the effected web-space the toes may splay.
    A rare association , though one worth recognising , is that between the neuroma and MTP (most commonly 2nd MTP) instability. This may be associated with a cross-over toe deformity of the toe plus or minus a plantar plate tear .Full correction of this deformity and the associated symptoms are much more involved than a simple neuroma and patients should be warned appropriately. See technique in the Atlas on cross-over toe deformity.
    Usually pain is reproduced during examination by compression through the effected web-space both medio-laterally and axially. In other words compress 5th and 1st Metatarsals towards each other with one hand whilst compressing the effected web-space with a “pinch” from Thumb and Index finger of the other hand from superior to inferior at the same time. On occasion a “Mulders’ click” will be felt which is a clicking sensation during the above manoeuvre. This is not a frequent finding.
    Other causes of forefoot pain should be considered including mechanical pain from the metatarsal heads and lesser MTP joint synovitis.
    NON-OPERATIVE MANAGEMENT.
    -Advise non-restrictive shoe-wear with supportive and shock absorbing soles such as the UK produced Fit-Flop shoes.
    -Some advise the use of orthotics and though these may transfer weight away from the metatarsal head area they also add volume into the shoe often accentuating compressive forces through the forefoot.
    -Local anesthetic and steroid injection into the effected web-space is most often used and is effective in 65% of patients or so. This may be done without ultrasound guidance by an experienced person. Patients should be warned that an immediate flare in pain is usual and it may take weeks to improve fully or partially (or in 35% not at all). If this route is likely to be definitive then a significant reduction in symptoms with a single injection is expected. There is also a small chance of fat necrosis around the point of injection , effecting the dorsal foot .This is purely a cosmetic issue but one patients should be warned of.
    -Other invasive non-operative procedures such as phenol injections and cryotherapy as less well proven
    INVESTIGATION.
    Though on occasion an MRI will pick up neuromas it is not as sensitive as a well performed ultrasound. Some published evidence does go against this (see results).
    It must be appreciated that even ultrasound is not the absolute determinant of whether a neuroma is present. There is no absolute amount of swelling required for a nerve to become symptomatic or visible as a neuroma. Logic would say that a small foot with very narrow inter-metatarsal spaces will require far less swelling to become symptomatic than a large foot with wide inter-metatarsal spaces where a nerve would need to swell far more. A not uncommon finding is a bursa in the region of the nerve. Whether the nerve by itself is the issue or the nerve plus associated bursa the treatment is exactly the same both in terms of injection or surgery.
    If pre-operative ultrasound scanning fails to show a neuroma but the symptoms and examination strongly are in keeping with a Mortons’ neuroma then excision is still indicated. There is no indication for web space “exploration” in this context. The nerve will likely be normal visually if ultrasound imaging pre-surgery is normal . The absolute determinant of whether a neuroma is present is the histological diagnosis once the nerve has been removed.

    Setup

    Day case.
    GA or regional anaesthetic used
    Ankle tourniquet required.
    Inter-metatarsal nerve block for pain relief
    Pre-operative antibiotics
    Aim for subcuticular wound closure.

    Operation

    A dorsal incision is made, in the marked inter-metatarsal space, from the metatarsal neck to the commencement of the web space.
    The location of the metatarsal heads(and necks) is best identified by fully plantar-flexing the relevant toes at the MTP joints.
    Immediately pre-operatively the foot should be examined and the effected web space marked. This should correlate with the Ultrasound report. It is not unusual to have neuromas in both 2/3 as well as 3/4 web-spaces.
    Most often only one space is symptomatic.
    However if both are symptomatic then one space will be more symptomatic than the other. My advice is that this is established by examination pre-operatively. This should have the neuroma excised and the less symptomatic space an injection of steroid and local intra-operatively. The risk with operating on two web spaces next to each other at the same time is that if the digital vessels are damaged in both then there is the potential to devascularise the toe with web-space incisions either side.
    If injection into the less symptomatic space does not provide long term relief then a subsequent operation may be required , but after a collateral circulation has established itself, perhaps 4-6 months or so later.
    A plantar incision can be used but are slow to heal and more painful than dorsal approaches. The anatomy can be easily visualised with a dorsal incision and there is no reason not to use this for all cases.
    Try to avoid going too distally the wound into the web-space as healing can be more of an issue here.

    Once the skin has been incised use tenotomy scissors to dissect through the fat layer deeply, avoiding small digital nerve branches where possible.At this stage it is useful to use a small self-retaining retractor placed carefully under the skin edges to place the deeper tissues under some tension to aid visualisation.

    Once through the fat layer the fascia overlying the interosseous muscle is encountered proximally in the wound. The distal interosseous muscle should be separated easily off the metatarsals with scissors dissection to reveal the transverse metatarsal ligament beneath it.The area of main interest is the immediate junction between the interosseous muscle and the web space where the nerve will be encountered.
    The self-retainer (or small laminar spreader) makes this deeper dissection easier.
    On occasion when a large neuroma is present this may become visible immediately in the distal extent of the wound at this stage. Do not be tempted to simply excise what can be seen.
    To lessen the chances of symptomatic recurrence (if the cut end of the nerve should later hypertrophy) the nerve should be sectioned as proximally as possible and well away from the metatarsal heads. This means dissection needs to proceed proximal to the transverse metatarsal ligament.

    The transverse metatarsal ligament is identified in the proximal aspect of the wound and a McDonalds retractor slipped beneath its leading edge(1) to confirm the structure.Again the small self-retainer is very useful and can be placed deeply onto the metatarsals to distract them , placing the ligament under tension and making its identification easier.
    This will sometimes not stay put and an alternative is to place a very small laminar spreader directly between the metatarsal necks to tension to ligament. This will usually require an assistant to hold it.
    On occasion the nerve can be seen at this stage as it exits from beneath the ligament. Still avoid the natural surgical urge to remove the neuroma yet.

    The transverse ligament is partially divided with a knife cutting directly onto the McDonalds.Once it has been sectioned scissors are required to dissect beneath it, first longitudinally in the line of the nerve to allow its identification. Transverse dissection will then will help open a space through the ligament and aid visualisation.

    The common digital nerve(2) is identified proximally, under the transverse metatarsal ligament(1), and then separated (if possible) from the accompanying vessels.This can be very difficult as they are small and not infrequently very adherent to the nerve and easily damaged during dissection.
    As long as the neighbouring web spaces are not being operated on at the same time there is no real risk in ignoring these digital vessels.

    The common digital nerve is sectioned proximally which is done by pulling the nerve to deliver normal nerve, that lies proximal to the neuroma, into the operative field.It is the cut as far proximally as possible , allowing the stump to retract back well away from the weight-bearing area of the forefoot. The nerve is then sectioned from proximal to distal including all plantar branches encountered.
    Irrespective of the appearance of the nerve it should be excised. This is a decision that is made pre-operatively not intra-operatively. There is no role for simply inspecting the nerve. The degree of swelling of the nerve will vary significantly and on occasion the diagnosis is simply a histological one with no visible swelling at the time of operation.

    A good section of the common digital nerve(1) both proximal and distal to its bifurcation(2) is removed. Haemostasis is secured and closure with Vicryl.The specimen should always be sent for histological analysis labelled with the queried diagnosis.
    Haemostasis is carefully secured with bipolar diathermy. A post-operative haematoma will easily result in wound dehiscence or breakdown.
    The transverse ligament should be repaired with 2.0 Vicryl and then its not a bad idea to place a 2.0 Vicryl between the metatarsal necks , anchoring through the periosteum. Additionally in those patients with pre-operative splaying effecting the web space inspect the visible joint capsule and repair directly if evidence of a capsular or plantar plate tear. There is a recognised association between Mortons neuroma and a cross-over toe deformity(see separate operative technique in the Atlas).
    The same stitch is used for fat closure and a subcuticular 3.0 Vicryl stitch for skin.
    The soft tissues of the forefoot are slow to heal and a fair bit of swelling is normal so using a slowly absorbable skin closure has significant merit. If removable sutures are being used however these could be left in situ for 3 weeks .Early suture removal risks the wound dehiscence.
    Once the wound is closed an inter-metatarsal block can be infiltrated. Early infiltration of local anaesthetic into the operative field prior to any dissection will make identification of the relevant structures far more challenging.
    A dry dressing and bandage compressive to the web space are applied.
    It is also important not to encourage exposure of the wound in shoes for an appropriate period of time. If the wound is exudating at all or given the post-op swelling rubs in shoes at all then developing cellulitis is likely . This risk is particularly acute for the first 4 weeks post-op.
    Shoes with a conforming insole & stiff rocker profile such as wedges or Fit-flops are especially useful.

    Post Operative

    Compressive forefoot bandage for 5 days and basic post-operative shoe required.
    May return to normal shoe-wear after this once the bandaging is removed. A well fitting Fit-Flop shoe is especially helpful.
    Once in appropriate shoes and entirely pain free patients may be safe to drive. Usually this equates to a week or two post-operatively.
    Keep wounds dry & dressed for 2-3 weeks . If at any stage in the post-operative course the wound starts to leak serous fluid then the dressings will need frequent changes (potentially several times a day) to minimise the chance of secondary wound breakdown.
    At the 2 to 3 week stage the patient may generally wash the foot but should keep the incision dressed with an adhesive and breathable dressing for a further 2 weeks. The protracted use of non-breathable (waterproof) dressings often results in wound breakdown in this area due to excess moisture in contact with the skin. Avoid scar rubbing in shoe wear for further few weeks after. Cellulitis is very common if the wounds rub, even many weeks post-operatively, and patients should be warned to avoid this situation, and represent immediately if it occurs.
    No mobilisation regime is generally required post operatively for the MTP joints which are not operated upon.
    Patients should expect an early loss of any acute neuroma pain (within a week or two) but a degree of forefoot swelling and discomfort from the region of the operation will persist for 6 to 8 weeks. This equates to some pain from the forefoot in the region of the pre-operative symptoms.
    I advise to avoid any impact sports for 4-6 weeks depending on how the foot feels. Bike riding may be fine from 2 weeks and cross-training from 4 weeks.
    Counsel patients on the post-operative protocol well in advance of surgery, in particular wound care.

    Recommended Reading

    Treatment of recurrence of symptoms after excision of an interdigital neuroma.
    J Bone Joint Surg 2004;86-B:48-53
    E.D.Stamatis , M.S.Myerson.
    Operative treatment of inter-digital neuroma. A long term follow-up study.
    J Bone Joint Surg. 2001.83-A.1321-1328
    M.J.Coughlin , T.Pinsonneault.
    71 feet (with 74 neuromas treated by excision) followed up (retrospectively) at a mean of 5.8 years. 85% of patients were satisfied with the outcome & 65% were pain free. Subjective numbness ( only a specific complaint in 4 of the feet) was present in 36 feet.
    The role of MRI and Ultrasound imaging in Mortons’ neuroma and the effect of size of lesion on symptoms.
    J Bone Joint Surg.2003.85-B.999-1005.
    R.J.Sharp, C.M.Wade, M.S.Hennessy, T.S.Saxby.
    29 cases treated by operative removal of neuroma and assessed pre-operatively clinically, by ultrasound & by MRI .
    The highest predictive test was clinical examination. Ultrasound poor for small lesions otherwise little difference between MRI & Ultrasound.

    Reference

    • orthoracle.com

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