Morton's Neuroma

Description

Morton's Neuroma (MN) is a condition associated with the common plantar digital nerves, caused by entrapment of the nerve and repetitive traction underneath the deep transverse metatarsal ligament leading to epineural and perineural fibrous overgrowth[1]

Also known as Morton neuroma, Morton's metatarsalgia, Intermetatarsal neuroma and Intermetatarsal space neuroma[2] the benign neuroma most commonly affects the intermetatarsal plantar nerve of the second and third intermetatarsal spaces (between 2nd−3rd and 3rd−4th metatarsal heads), which results in the entrapment of the affected nerve.

The main symptoms are pain and/or numbness, sometimes relieved by removing footwear.

Clinically Relevant Anatomy

Morton's-1.png

Mechanism of Injury / Pathological Process

Some sources claim that entrapment of the plantar nerve because of compression between the metatarsal heads, as originally proposed by Morton, is highly unlikely, because the plantar nerve is on the plantar side of the transverse metatarsal ligament and thus does not come in contact with the metatarsal heads. It is more likely that the transverse metatarsal ligament is the cause of the entrapment.[3][4]

Epidemiology / Eitiology

MN occurs up to 10 times more frequently in women around the age of 50. Pain onset is often insidious, and the prevalence of neuromas in asymptomatic individuals may be as high as 25-50%

Clinical Presentation

Symptoms include: pain on weight bearing, frequently after only a short time. The nature of the pain varies widely among individuals. Some people experience shooting pain affecting the contiguous halves of two toes. Others describe a feeling like having a pebble in their shoe or walking on razor blades. Burning, numbness, and paresthesia may also be experienced.[5] The symptoms progress over time, often beginning as a tingling sensation in the ball of the foot (Mulder’s Sign).[6]

Morton's neuroma lesions have been found using MRI in patients without symptoms.[7]

Morton's-MRI.png

Diagnostic Procedures

Clinical diagnosis can be up to 99% accurate with typical complaints of plantar webspace pain, paresthesias and/or numbness aggravated by weight-bearing activities and eased by rest and massage[1] There is often no obvious deformity, erythema, sign of inflammation, or limitation of movement. Direct pressure between the metatarsal heads will replicate the symptoms, as will compression of the forefoot between the finger and thumb so as to compress the transverse arch of the foot. 

Histopathology

Microscopically, the affected nerve is markedly distorted, with extensive concentric perineural fibrosis. The arterioles are thickened and occlusion by thrombi are occasionally present.[8]

Imaging

Though a neuroma is a soft tissue abnormality and will not be visualized on standard radiographs, the first step in the assessment of forefoot pain is an X-ray in order to evaluate for the presence of arthritis and exclude stress fractures/reactions and focal bone lesions, which may mimic the symptoms of a neuroma. Ultrasound (sonography) accurately demonstrates thickening of the interdigital nerve within the web space of greater than 3mm, diagnostic of a Morton’s neuroma. This typically occurs at the level of the intermetatarsal ligament. Frequently, intermetatarsal bursitis coexists with the diagnosis. Other conditions that may also be visualized with ultrasound and can be clinically confused with a neuroma include synovitis/capsulitis from the adjacent metatarsophalangeal joint, stress fractures/reaction, and plantar plate disruption.[9][10]  MRI can similarly demonstrate the above conditions; however, in the setting where more than one abnormality coexists, ultrasound has the added advantage of determining which may be the source of the patient’s pain by applying direct pressure with the probe. Further to this, ultrasound can be used to guide treatment such as cortisone injections into the webspace, as well as alcohol ablation of the nerve.

Morton's-Xray.pngMorton's-US.png

Differential Diagnosis

There are other causes of pain in the forefoot. Too often all forefoot pain is categorized as neuroma. Other conditions to consider are capsulitis, which is an inflammation of ligaments that surrounds two bones, at the level of the joint. In this case, it would be the ligaments that attach the phalanx (bone of the toe) to the metatarsal bone. Inflammation from this condition will put pressure on an otherwise healthy nerve and give neuroma-type symptoms. Additionally, an intermetatarsal bursitis between the third and fourth metatarsal bones will also give neuroma-type symptoms because it too puts pressure on the nerve. Freiberg's disease, which is an osteochondritis of the metatarsal head, causes pain on weight bearing or compression.manula

Management / Interventions

Physiotherapy intervention

Manual therapy has been shown to be effective for pain resolution of symptoms,[1] however there is little evidence to support this. Manual therapy is hypothesized to alter afferent nociceptive barrages, normalize sensori-motor mismatches, activate descending anti-nociceptive pathways. [11] Therefore, utilizing manual therapy in case of pain seems appropriate.[1]

Extracorporeal Shockwave Therapy has been shown to be a potentially useful modality to reduce pain in patients with Morton's neuroma[12].

Medical Intervention

Treatment often involves corticosteroid injections and surgical excision however,  these approaches do not guarantee complete relief[1] Recently, an increasing number of procedures are being performed at specialist centers which offer a range of procedures to treat Morton's neuroma under ultrasound guidance. Recent studies have shown excellent results for the treatment of Morton's neuroma with ultrasound guided sclerosing alcohol injections,[13] ultrasound guided radiofrequency ablation, and ultrasound guided cryo-ablation.[14]

Ultrasound can be used to minister the injection on the exact location of the neuroma. By using direct in-plane approach, the needle is visualized during the whole injection.[15]

Orthotics and corticosteroid injections are widely used conservative treatments for Morton’s neuroma. In addition to traditional orthotic arch supports, a small foam or fabric pad may be positioned under the space between the two affected metatarsals, immediately behind the bone ends. This pad helps to splay the metatarsal bones and create more space for the nerve so as to relieve pressure and irritation. It may however also elicit mild uncomfortable sensations of its own, such as the feeling of having an awkward object under one's foot. Corticosteroid injections can relieve inflammation in some patients and help to end the symptoms. For some patients, however, the inflammation and pain recur after some weeks or months, and corticosteroids can only be used a limited number of times because they cause progressive degeneration of ligamentous and tendinous tissues.

Sclerosing alcohol injections are an increasingly available treatment alternative if the above management approaches fail. Dilute alcohol (4%) is injected directly into the area of the neuroma, causing toxicity to the fibrous nerve tissue. Frequently, treatment must be performed 2–4 times, with 1–3 weeks between interventions. A 60-80% success rate has been achieved in clinical studies, equal to or exceeding the success rate for surgical neurectomy with fewer risks and less significant recovery. If done with more concentrated alcohol under ultrasound guidance, the success rate is considerably higher and fewer repeat procedures are needed.[16]

Radio Frequency Ablation is also used in the treatment of Morton's Neuroma.[17] The outcomes appear to be equally or more reliable than alcohol injections especially if the procedure is done under ultrasound guidance.[18]

If such interventions fail, patients are commonly offered surgery known as neurectomy, which involves removing the affected piece of nerve tissue. Postoperative scar tissue formation (known as stump neuroma) can occur in approximately 20%-30% of cases, causing a return of neuroma symptoms.[19] Neurectomy can be performed using one of two general methods. Making the incision from the dorsal side (the top of the foot) is the more common method but requires cutting the deep transverse metatarsal ligament that connects the 3rd and 4th metatarsals in order to access the nerve beneath it. This results in exaggerated postoperative splaying of the 3rd and 4th digits (toes) due to the loss of the supporting ligamentous structure. This has aesthetic concerns for some patients and possible though unquantified long-term implications for foot structure and health. Alternatively, making the incision from the ventral side (the sole of the foot) allows more direct access to the affected nerve without cutting other structures. However, this approach requires a greater post-operative recovery time where the patient must avoid weight bearing on the affected foot because the ventral aspect of the foot is more highly enervated and impacted by pressure when standing. It also has an increased risk that scar tissue will form in a location that causes ongoing pain.

Cryogenic neuroablation is a lesser known alternative to neurectomy surgery. Cryogenic neuroablation (also known as cryo injection therapy, cryoneurolysis, cryosurgery or cryoablation) is a term that is used to describe the destruction of axons to prevent them from carrying painful impulses. This is accomplished by making a small incision (~3 mm) and inserting a cryoneedle that applies extremely low temperatures of between −50 °C to −70 °C to the nerve/neuroma.[20] This results in degeneration of the intracellular elements, axons, and myelin sheath (which houses the neuroma) with wallerian degeneration. The epineurium and perineurium remain intact, thus preventing the formation of stump neuroma. The preservation of these structures differentiates cryogenic neuroablation from surgical excision and neurolytic agents such as alcohol. An initial study showed that cryo neuroablation is initially equal in effectiveness to surgery but does not have the risk of stump neuroma formation.[21]

References

  1. 1.0 1.1 1.2 1.3 1.4 Sault JD, Morris MV, Jayaseelan DJ, Emerson-Kavchak AJ. Manual therapy in the management of a patient with a symptomatic Morton's Neuroma: A case report. Manual therapy. 2016 Feb 29;21:307-10.(level of evidence: 5)
  2. The Center for Morton's Neuroma: Names for Morton's neuroma, http://www.mortonsneuroma.com/names-mortons-neuroma (level of evidence: 5)
  3. Hochberg MC, Silman AJ, Smolen JS, Weinblatt ME, Weisman MH (2011). "Rheumatology, 5th Edition, Volume 1", p. 794. Mosby Elsevier, Philadelphia. ISBN 978-0-323-06551-1 (level of evidence: 5)
  4. The Center for Morton's Neuroma: A Scientific Discussion of Morton’s Neuroma, http://www.mortonsneuroma.com/mortons-neuroma-science/ (level of evidence: 5)
  5. The Center for Morton's Neuroma. "What is Morton's Neuroma?" ( level of evidence: 5)
  6. "Cryosurgery for Morton's Neuroma, UK Clinic"
  7. Bencardino J, Rosenberg ZS, Beltran J, Liu X, Marty-Delfaut E (September 2000) (level of evidence: 4) . "Morton's neuroma: is it always symptomatic?". AJR Am J Roentgenol. 175 (3): 649–53. doi:10.2214/ajr.175.3.1750649. PMID 10954445 (level of evidence: 4)
  8. Reed, RJ; Bliss, BO (February 1973) . "Morton's neuroma. Regressive and productive intermetatarsal elastofibrositis.". Archives of Pathology. 95 (2): 123–9. PMID 4118941 (article not available)
  9. Gregg JM, Schneider T, Marks P (2008). "MR imaging and ultrasound of metatarsalgia--the lesser metatarsals". Radiol Clin North Am. 46 (6): 1061–78. doi:10.1016/j.rcl.2008.09.004. PMID 19038613
  10. Gregg JM, Marks P (2007). "Metatarsalgia: an ultrasound perspective". Australas Radiol. 51 (6): 493–9. doi:10.1111/j.1440-1673.2007.01886.x. PMID 17958682.fckLR (level of evidence: 5) ^ Jump up to: a b "The Center for Morton's Neuroma" (level of evidence: 5)
  11. Jo Nijs, Boudewijn Van Houdenhove, From acute musculoskeletal pain to chronic widespread pain and fibromyalgia: Application of pain neurophysiology in manual therapy practice, In Manual Therapy, Volume 14, Issue 1, 2009, Pages 3-12, ISSN 1356-689X, https://doi.org/10.1016/j.math.2008.03.001. (http://www.sciencedirect.com/science/article/pii/S1356689X08000593) Keywords: Fibromyalgia; Central sensitisation; Whiplash; Chronic fatigue syndrome
  12. Seok H, Kim SH, Lee SY, Park SW. Extracorporeal Shockwave Therapy in Patients with Morton's Neuroma: A Randomized, Placebo-Controlled Trial. Journal of the American Podiatric Medical Association. 2016 Mar;106(2):93-9. (level of evidence: 1b)
  13. Musson RE1, Sawhney JS, Lamb L, Wilkinson A, Obaid H. (March 2012). "Ultrasound guided alcohol ablation of Morton's neuroma". Foot Ankle Int. 33 (3): 196–201. doi:10.3113/fai.2012.0196. PMID 22734280 (level of evidence: 4)
  14. Talia Friedman, MD, Daniel Richman, MD and Ronald Adler, MD. "."Sonographically Guided Cryoneurolysis Preliminary Experience and Clinical Outcomes". J Ultrasound Med. 31: 2025–2034.
  15. Ultrasound-Guided Diagnosis and Treatment of Morton’s Neuroma  Sule Sahin Onat, MD, Ayse Merve Ata, MD, and Levent Ozcakar, MD.
  16. "The Center for Morton's Neuroma" (level of evidence: 5)
  17. Chuter GS1, Chua YP, Connell DA, Blackney MC. (January 2013). "Ultrasound guided radiofrequency ablation in the management of interdigital (Morton's) neuroma". Skeletal Radiol. 42 (1): 107–11. doi:10.1007/s00256-012-1527-x. PMID 23073898 (level of evidence: 4)
  18. Hughes RJ, Ali K, Jones H, Kendall S, Connell DA (June 2007). "Treatment of Morton's neuroma with alcohol injection under sonographic guidance: follow-up of 101 cases". Acta Orthop Belg. 188 (6): 1535–9. doi:10.2214/AJR.06.1463. PMID 17515373 (level of evidence: 4)
  19. "Morton's neuroma". www.nhs.uk. NHS choices. Retrieved 15 March 2016.
  20. Cryosurgery Or Sclerosing Injections: Which Is Better For Neuromas?
  21. A Caporusso EF, Fallat LM, Savoy-Moore R (Sep–Oct 2002). "Cryogenic Neuroablation for the treatment of lower extremity neuromas". J Foot Ankle Surg. 41 (5): 286–290. doi:10.1016/S1067-2516(02)80046-1. PMID 12400711 (level of evidence: 4)