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Morton's Neuroma.

This often exceptionally painful condition, which usually occurs in the anterior intermetatarsal / metatarsophalangeal area, can be a daily challenge to the patient unfortunate enough to develop it, and no less of a challenge to the practitioner who desires to treat it.

The term 'Mortons Neuroma is usually ascribed to a Dr Thomas G Morton of Philadelphia who published a treatise under the title of "A Peculiar Painful Affection of the Fourth Metatarsophalangeal Articulation" in 1876. In fact, neither Dr T G Morton, nor a later and different Dr T S K Morton (whether a relative is unknown), writing about T G Mortons 1876 treatise in 1895 use the term Mortons neuroma, instead referring to the condition variously as: "Morton's Toe", "Morton's painful affection of the foot", "Neuralgia" or "Metatarsalgia" (Morton TSK 1895).

Whereby the pain is caused by some form of nerve compression or entrapment seems to be accepted by both of the Mortons and a number of other authors discussing the subject in the late 19th Century; although again "Mortons Neuroma" does not figure in their writings, instead such authors use the terms already mentioned as well as "Neuralgia" or "Neuritis" (viz: Erskin 1877, Dana 1885, NYMJ 1892, Roswell 1892 etc). Even more florid descriptions abound such as "Mortons Neuralgia nervi plantaris externi im Metatarsophalangealgelink IV" (Devrient 1895). The mechanism of such nerve compression or entrapment however, is not uniformly agreed upon by such authors, varying from a suggestion that it originates from a 'luxation (displacement of a bone from a joint) of the metatarsals (Devrient 1895) to a 'twisted toe' (Morton 1876) or a descent of the tarsal arch' (Grun 1889).

From the literature already described it appears that Morton (TG) did not seek to lay title to the condition, but merely to describe it and also describe his specific recommendations for its treatment. In fact the condition had already been well described by the British practitioner; Lewis Durlacher (1792 -1864), Surgeon-Chiropodist to the British Royal Households of King George IV, King William IV and Queen Victoria, although, naturally, Durlacher did not call it 'Mortons Neuroma (Durlacher 1845), instead referring to a 'Metatarsalgia'. As an aside, it is perhaps interesting that Durlacher, even in the mid-19th Century, was a strong advocate of regulating the practice of Chiropody; espousing his belief that Chiropody "should become a firmer part of medical practice" and that in particular those with "the requisite surgical information should, after examination, be granted a license to distinguish them from untrained corn-cutters" (Blakemore and Jennet 2001).

The treatments proposed for the condition in the mid--to late 19th Century were as varied as the theories proposed of its cause. As injectable medicines such as our modern corticosteroids and alternatives e.g. prolotherapy (Harvey 2007) were not available, nor of course, were effective oral anti-inflammatory agents

or safe and effective Local Analgesics (the first recorded LA was cocaine used in 1884, which was fraught with the dangers that we now well understand). The treatments frequently included surgery, often quite radical, or electrical treatments', such as faradism or galvanism. Regarding galvanism a 31 year old female teacher reported in 1892; "The last of October the doctor commenced the use of a battery every night,--the interrupted current being used. The sponge was applied under and over the toes five minutes, five on each side of the heel, and five under the knee. The toes twitched a great deal, and I always dreaded when the sponge neared the fourth and fifth toes, for I felt the sting and jerk along the injured side and it made me sick.... "(Morton TSK 1895). The surgical treatments often included removing the affected nerve entirely, splitting or even totally excising one or more metatarsals or entire digits, and although many surgeons of the time report that such procedures were attended with perfect success' (Hoadley 1893), we can perhaps be forgiven for not being entirely convinced from our 21st century perspective. Also, of course, effective transdermal 'in vivo' imaging using x-rays, was only just emerging in its most basic form in the 1890s, and ultrasound, todays imaging agent of choice, would not arrive until well after WW2. This was developed from the British sound wave based ASDIC' submarine detection apparatus first tested in rather basic form in WW1, that later became the more efficient ASDIC (UK) and SONAR (USA) of WW2 (Donald, Macvicar and Brown 1958). The lack of effective diagnostic, and postprocedure imaging, to assess the results of a specific intervention, meant that treatments until the late 1940s remained much as they had been at the start of the 20th Century--and as varied.

The idea of injecting anti-inflammatory drugs to the 'Neuroma (whatever its causation and true nature--more on that later) only came on the scene as the 1950s approached. It frequently surprises us in modern medicine as to how recent this intervention using corticosteroids actually is. It is for example only from the 1920s onwards that the 'father' of much of current conventional musculoskeletal and soft tissue wisdom; James Cyriax MD, started to formulate his orthopaedic theories of cause, effect and appropriate intervention (Cyriax 1993). In later years he enthusiastically embraced the use of injected corticosteroids but these were not developed until a Mayo Clinic researcher, Edward Calvin Kendall discovered the antirheumatic properties of cortisone in 1948, building on his own, and other, researches that had been conducted throughout the 1930s . On September 21, 1948, compound E (later renamed cortisone) became the first glucocorticoid to be experimentally administered to a patient with rheumatoid arthritis at a New York hospital (Kendall 1949). Kendall and two other researchers; fellow Mayo researcher Philip S. Hench and Swiss researcher Tadeus Reichstein were jointly awarded a Nobel prize for this discovery in 1950.

Endless recounting of other varied theories and interventions of what we now habitually call Morton's neuroma in Podiatry could continue, but it may now be appropriate to come forward to the current time and review our collective medical understanding of causation, diagnosis and a few currently believed to be appropriate interventions. In passing we can make a nod towards a certain LO Betts, active in the 1940s, regarding whom the researcher may often encounter repeated in Orthopaedic textbooks the statement: "Then in 1940, L.O. Betts confirmed that Mortons neuroma pain was attributed to a swelling of the interdigital nerve...." such tomes being apparently unaware that generations of a veritable plethora of Physicians from Durlacher onwards, had been proposing along these lines, and TSK Morton in his 1895 publication specifically states; ".... (in) instances where the nerves have been excised a condition of swelling and inflammation, neuritis, has been proved...." (Morton TSK 1895)

So, the current situations stands thus:

Terminology

Podiatrists and GP's habitually use the term Mortons Neuroma--and both groups appear to know what we mean when we communicate with each other. Surgeons, Anatomists and Orthopaedists can and sometimes do dispute this term, sometimes preferring what they believe to be a more exact descriptor of "perineural fibrosis", arguing that histological examination of tissue samples from such demonstrate a degeneration of the neural tissue component and a proliferation of the supporting collagenous connective tissue fibres. To be perhaps somewhat pedantic, an '..oma' appended to another word can often be suggestive of a (sometimes malignant) swelling--carcinoma, melanoma etc. The opponents of the term 'Neuroma' claim that it seems to suggest that the neurons are swelling, when in fact they are atrophying--it is the collagenous fibrosis that is proliferating. Perhaps as Chiropodists / Podiatrists we should highlight and celebrate the fact that one of our founding fathers first suggested what this affliction was, and campaign for it to henceforth be known as Durlachers Perineural Fibrosis?

Presentation and diagnosis

Typically a client attends with a report of forefoot pain, usually but not invariably unilateral, most frequently of the space between the 3rd and 4th distal metatarsal / metatarsophalangeal region followed by the region between the 2nd and 3rd (Weinfeld 1996). A patient may describe characteristically and temporally different pain. The first, sharp, burning, intense pain lasts for about 5-10 minutes and can be precipitated by direct compression of the neuroma. This pain then often becomes a dull ache for the next 2-3 hours.

In the majority of confirmed cases, women ages 45-50 are affected, although men are also affected to a lesser degree (Thompson, Wood and Rendall 2001, Singh and Chiodo 2005). It is not usual to have more than one active focus of pain but certainly not impossible (Thompson, Deland 1993). To this end an extract from a recent diagnostic ultrasound ordered by the author at one of his hospital clinics is given in the appendix, to additionally demonstrate this from personal experience, and also illustrate the terminology such reports use. On the subject of terminology used by the professional Radiographers /Sonographers performing the procedures and providing a report thereon, it is not unusual for the terms; 'low reflectivity' and 'hypoechoic region (or lesion, or area)' to be used interchangeably by them to describe an area that can be consistent with the presence of a Mortons Neuroma' (or Intermetatarsal Perineural Fibrosis if such a term is preferred by them). Such areas of 'space' on the diagnostic U/S scanner, when combined with your own necessary physical examination and diagnostic palpation, are strongly indicative of Mortons Neuroma (or Durlachers Perineural Fibrosis if you prefer). When reading the foregoing mentioned diagnostic U/S report in the appendix, it can be noted that the Consultant Radiologist has kindly provided valuable additional information enabling the attending clinician to consider, and in this case reject, possible differential diagnoses of osteoarthritis, tenosynovitis, capsular fibrosis and plantar plate tears.

Preliminary to ordering the diagnostic U/S, the attending clinician is advised to use their palpation skills (which the author suggests are worth assiduously cultivating, even more so in an age when attending general medical practitioners frequently have no time to lay hands upon flesh). Before any physical examination takes place the podiatric (or indeed any other type of) clinician, should naturally obtain the clients permission to physically touch them, identify the area they wish to touch, and explain what they propose to do. Then it is essential to obtain a comprehensive history of the complaint, whether it has occurred before, any other medical problems and vitally, if you at some stage propose to utilise any kind of medication or perform injections or surgery, take a full report of any allergies and any medicine used by the client, prescribed or over-the-counter. It is advised that your medicines review should include so-called complementary medicines such as glucosamine sulphate, St Johns wort etc., which can have, for example, implications for increased bleeding, bruising, or in the case of St John's wort--skew the effect of other medicines such as Warfarin (Barnes, Anderson and Phillipson 2001). On the subject of complementary / herbal medicines interactions, several authoritative reference sources exist that can be consulted, one example used by the author is Stockleys Drug Interactions Pocket Companion (see: www.pharmpress.com for details). For general pharmaceutical drug interactions the appropriate appendix of the current edition of the British National Formulary (BNF) is regarded as the 'Gold Standard' of information, and if clinicians make judgements based on the BNF they can have confidence that such decisions will be accepted by the majority of professional opinion in the UK (see: www.bnf.org).

It is suggested that an example of a physical examination should include looking for 'Mulders Click'--when one palpates the web spaces with your fingers superiorly and inferiorly, then with the other hand you laterally and medially compress the metatarsal heads together. A positive suggestion of Mortons Neuroma is when you or the patient feel, or occasionally hear, a click. The click is almost invariably accompanied by the patient reporting a lancinating pain. What the actual cause of the click' is forms a subject of much debate although the most frequent suggestion is; 'subluxation of the neuroma between the metatarsal heads' (Mulder 1951). In many confirmed cases the sufferer is unable to stand on their toes without severe pain so some clinicians ask them to do this as part of their evaluation of symptomology. The clinician is advised to consider differential diagnoses such as capsulitis by pressing under the metatarsal heads which would not usually elicit pain in a Neuroma, similarly, pain on the dorsal aspect of the metatarsals may be suggestive of a stress fracture, not usually a Neuroma. Additionally, especially in adolescent females, Freiberg's infraction which usually occurs with dorsal pain over the 2nd metatarsal head should be considered as a differential diagnosis, as of course should be tumours and similar. Another useful diagnostic tool can be to inject inferiorly from the dorsum a small volume of swift acting local anaesthetic to the area already suggested by palpation, using, for example, 1ml of plain 1% lidocaine or a similar agent such as mepivacaine 3% plain (Thomas et al 2009). A rapid (albeit very temporary) relief of the pain when subsequently palpating the area that originally hurt, is suggestive of having found the fibromatous mass and also that either its surgical excision or its percutaneous infiltration with a suitable corticosteroid may improve matters.

Treatments

This brief discussion of the perhaps surprisingly wide subject of Morton's Neuroma cannot do more than briefly mention many of the interventions that are frequently performed on diagnosed, or suspected, cases.

In cases where small hypoechoic lesions are identified by diagnostic U/S, then relief may be obtained, sometimes at least in the short term, by appropriate padding and support as well as possible modification of footwear to a size and design that does not medially and laterally compress the anterior transverse arch of the forefoot. Sundry biomechanical issues such as hyperpronation or forefoot valgus or varus, which may contribute to the condition can be addressed by suitable orthoses with, if necessary, appropriate posting.

If such ultra-conservative management as the foregoing does not give the desired result, then subject to a patients preferences more technological interventions may be a possibility subject to availability and resources (financial and otherwise). Extracorporeal Shockwave Therapy (ESWT) has been evaluated for such a purpose and a 2009 study concluded that "Extracorporeal shockwave therapy is a possible alternative to surgical excision for Mortons Neuroma" (Fridman, Cain and Weil 2009). The study was a randomised placebo-controlled double-blind trial, albeit with a relatively small sample size of 25 initially, of whom 2 were lost to subsequent follow-up. Interestingly, if details of the above trial are studied then one notes that the authors concluded that the reported cures' involved the ESWT being of sufficient magnitude and focus as to partially destroy the nerves in the perineural fibrosis. This would then place the effect of such a therapy on the same level as other treatments which set out to ablate the aberrant tissue such as cryotherapy, or injection of sclerosing agents (scar tissue forming agents) such as phenol, polidocanol or sodium tetradecyl sulphate (STS)--which are examples of agents that are used in the chemical sclerosing of varicose veins.

On the subject of injections, the agent of choice, certainly in primary care remains corticosteroids. For those UK Podiatrists licensed to use local anaesthetics under the statutory exemption to the 1968 medicines act (as amended by various orders) granted by an 'LA certificate', purchase and administration of the injectable corticosteroid methylprednisolone acetate, available in such parenteral preparations as 'Depo Med' is also permitted within the terms of the LA licence, although it is advised that suitable training should be undertaken in the use of what is a potentially formidable type of medicine. To the authors knowledge, the theory and practice of steroid injections does not currently form part of the curriculum of the standard UK degree in podiatry or podiatric medicine, but it may be that there are exceptions to this of which he is unaware. If not, then for safety appropriate postgraduate training is recommended. The injectable sclerosants adverted to in the previous paragraph, such as STS are prescription-only-medicines and the practitioner using them should have either independent prescribing rights themselves (as well as having an LA certificate to permit injection of therapeutics), or be administering them, after suitable training, in accordance with a patient-specific direction by an appropriately qualified prescriber. Alternative injection therapies seeking to atrophy the neuroma exist, including the glucose and lidocaine described in the authors 2007 Podiatry Review--or Chiropody Review as ourjournal still was then--article: Prolotherapy for Podiatrists. (Chiropody Review Vol. 64 No. 5 September/October 2007). Some authorities suggest that alcohol can be injected to promote atrophy of the neuroma, although supporting research is not in much evidence for this.

Before moving on to the subject of surgical treatments it may be worthy of mention that whilst some studies suggest that ultrasound guidance of whatever injection is utilised is valuable, other studies directly contradict this, two such diametrically opposed examples are: Sofka et al (2007) who concluded that it was of value, versus Schiffer etc al (2013) who concluded it was not. As a matter of personal clinical choice, the author does not routinely perform his neuroma injections under ultrasound guidance except in cases where this is specifically required by certain health insurers, as part of their reimbursement conditions.

In cases, where conservative or parenteral therapies do not give relief then surgery is often considered. Many types of procedure have been quoted since the late 19th century but some current examples are: interdigital nerve excision with intermetatarsal ligament division--with or without submuscular transposition, isolated intermetatarsal ligament division or isolated interdigital nerve excision (Thompson et al 2001, Thompson et al 2004, and Singh et al 2005). The actual perineural fibroma, usually fusiform in shape, is reported to often adhere to the intermetatarsal ligament. On visual exposure it presents as a pale glistening mass and when examined histologically usually exhibits fibroblast and Schwann cell proliferation, represented by extensive juxta- and intraneural fibrosis as well as perivascular and sub intimal fibrosis, with the atrophic neural tissue component exhibiting demyelination and axonal damage (Wu 1996).

Surgery can be performed under general or regional anaesthesia and a dorsal or plantar approach utilised by the surgeon. A simplified description of the dorsal approach features an incision being made between the affected metatarsals down through the skin and subcutaneous tissue, retracting away the dorsal sensory branch of the intermediate dorsal cutaneous branch of the superficial peroneal nerve. Blunt dissection of the tissue continues down to the level of the intermetatarsal ligament, where the metatarsal head are spread to allow exposure of the neuroma and place the ligament under tension. This permits an elevator to go under the intermetatarsal ligament which can be transected whilst protecting the underlying neurovascular structures. The neuroma should then be capable of being identified between the metatarsal heads, adherent to the intermetatarsal bursa where it can be pulled distally permitting division of the nerve trunk as proximally as possible. The distal branches of the nerve can then be dissected with possibly phenol application to the remaining nerve trunk to resist recurrence.

Some surgeons, or circumstances, favour the plantar approach, especially in cases of recurrence where it is felt to provide better visualization of the proximal nerve trunk. In this case a plantar excision is madejust proximal to the webspace which then extends proximally. The incision is extended between the metatarsal heads to avoid scarring the bony prominences. The neuroma is usually located subcutaneously which is then resected as described above.

Conclusions

A brief description of this challenging condition, such as the current article provides, can do little more than perhaps provoke an interest in what is a multifaceted pathology that is undoubtedly worthy of greater detailed research and study, in an effort to provide even more effective treatment solutions than those currently existing.

With the exception of invasive surgery, all of the non-operative therapies are suitable for use in the primary care locations that most of podiatry is carried out in. Naturally, specialised training is required for certain treatments such as ESWT but this is available to all registered Podiatrists as is Ultrasound both diagnostic and therapeutic. Additionally courses giving licenced access to certain Prescription only medicines, or even fully independent prescribing, are available and can be wholeheartedly recommended. The HCPC website or the Institute can provide details of the latter. In order to give injections of any type an LA licence is required (even for an independent prescriber) but again, this can be studied for and gained by HCPC registered Podiatrists.

Appendix

Extract from a written report of a diagnostic ultrasound procedure performed June 2015, Female 50 years of age presenting with chronic (> 12 months) bilateral forefoot pain.

U/S Right foot: There is a 12mm low reflectivity lesion in the 2nd web space and a 10mm low reflectivity lesion in the 3rd web space. Both are consistent with Morton's Neuroma. There is no significant synovitis or fusion of the 1st through to 5th MTP joints. Normal flexor and extensor tendons. The plantar plates appear intact.

U/S Left foot: There is a 9mm low reflectivity lesion in the 2nd web space in keeping with a small neuroma. The remaining web spaces were normal. The 1st through to 5th MTP joints are normally maintained. The plantar plates appear intact and no further adverse features were seen.

Martin Harvey PGCert BSc MInstChP MCPodS Consultant Podiatrist Independent Prescriber, The Priory Hospital, Birmingham.

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Date:Nov 1, 2015
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