Morton's Neuroma

                                 Dr. KS Dhillon

Introduction

Morton neuroma is also known as interdigital neuroma. It was first described in 1876. There is perineural fibrosis and nerve degeneration of the common digital nerve in the foot [1,2].  Morton’s neuroma, or Morton neuroma, is not a true neuroma. There is neuropathic pain in the distribution of the interdigital nerve secondary to repetitive irritation of the nerve. The most common location is in the 3rd webspace between the third and fourth metatarsal bones. Less common locations are between the second and third metatarsals and, rarely, between the first and second or fourth and fifth metatarsals [3]. When conservative measures for Morton's neuroma are not successful, surgical excision of the perineural fibrosis may be necessary.

Pain episodes are intermittent. Patients can experience 2 attacks of pain in a week and then none for a year. Recurrences of pain are variable and there is a tendency to become more frequent with time. Between attacks, there are no symptoms. Between 2 to 3% of the time two neuromas coexist on the same foot. If 2 or more areas of tenderness are present then other diagnoses should be considered.

Symptoms of Morton’s neuroma

Symptoms of Morton’s neuroma include:

1. The most common presenting complaint is pain and dysesthesias in the forefoot and corresponding toes adjacent to the neuroma.

2. Pain is described as sharp and burning and may be associated with cramps.

3. Numbness is usually present in the toes adjacent to the neuroma and it occurs along with episodes of pain.

4. Pain is usually intermittent. The episodes often occur for minutes to hours at a time and have long intervals from weeks to months between a single or small group of attacks.

5. Some patients describe the sensation as walking on a marble.

6. Massage of the affected area offers significant relief.

7. Night pain is reported but is rare

8. Narrow, tight high-heeled shoes aggravate the symptoms

Physical Examination

Many acknowledge that the examination of patients with Morton's neuroma is usually negative. Studies, however, have shown that a clinical history and examination may be more sensitive than ultrasonography or magnetic resonance imaging. The sensation is wholly intact and maneuvers are unsuccessful in reproducing the characteristic pain. Palpation of the actual neuroma is usually successful. 

Firm squeezing of the metatarsal heads with one hand while applying direct pressure to the plantar and dorsal interspace with the other hand may elicit radiating neuropathic pain. Pain can be localized only to the plantar aspect of the webspace. 

The squeeze test can result in a "click" (Mulder click) as the neuroma moves between the metatarsals in the dorsal direction. Passive and active toe dorsiflexion can aggravate the symptoms. Sensory abnormalities may be observed. 

Investigations for Morton’s neuroma

Magnetic resonance imaging (MRI) is not needed in most cases for establishing a diagnosis of Morton's neuroma. It, however, has been widely studied [4,5]. The sensitivity is 87% and the specificity is as high as 100%.

Ultrasonography is gaining popularity and it may be equivalent in sensitivity to MRI [6,7,8]. Computed tomography (CT) scanning has also been used but it may not be as sensitive as ultrasonography or MRI. 

Temporary elimination of pain in the associated webspace with a common digital nerve block with an anesthetic agent will support a diagnosis of Morton's neuroma.

Management of Morton’s neuroma

Nonoperative

Nonoperative treatment is the first line of treatment. A wide shoe box with a firm sole and metatarsal pad is used. The outcome with such treatment is 

unpredictable. Approximately 20% of patients will have complete resolution of symptoms. Adding anti-inflammatory medications rarely provide any benefit. 

Corticosteroid injections have been used for symptomatic benefit. The usual approach is dorsal after isolating the neuroma with palpation or ultrasound. The evidence for its effectiveness is weak. Short-term randomized control studies show that steroid injection provides symptomatic benefit [4,5]. 

Operative

Surgical treatment would be indicated when there is failure of nonoperative management. The surgical approach can be dorsal or plantar approach [6,7]. The dorsal approach is most commonly used. A neurectomy with nerve burial and transverse intermetatarsal ligament release is done. 

To perform a dorsal neurectomy a 3 to 4 cm incision is made just proximal to the involved webspace. Blunt dissection is carried out to avoid injury to branches of the superficial peroneal nerve. The metatarsal bones are spread to visualize the webspace, as well as to tension the transverse intermetatarsal ligament. While protecting the neurovascular bundle, the transverse intermetatarsal ligament is transected. The interdigital nerve proximal and distal to the nerve bifurcation is identified. It is resected at least 3 cm proximal to the intermetatarsal ligament. The transverse intermetatarsal ligament is reapproximated and repaired to avoid intermetatarsal head instability.

Complications

The surgical complications include a stump neuroma and a painful plantar scar. There is a 5% increased risk of painful plantar scar with a plantar incision.

The causes of stump neuroma include inadequate resection of the nerve and inadequate retraction. The most common cause is inadequate resection. The nerve should be resected at least 3 cm proximal to the intermetatarsal ligament. Inadequate retraction is caused by tethering of plantar neural branches that prevent retraction following resection.

Pathophysiology

Interdigital nerves are composed of communicating branches from the medial and lateral plantar nerves. The interdigital nerve traverses inferior to the intermetatarsal ligament at the level of the metatarsal heads. Here the nerve can be compressed or stretched from repetitive toe flexion and extension. There are studies that have shown perineural fibrosis and demyelination at the level of the metatarsal head. This indicates that the damage in Morton's neuroma may be more distal than the intermetatarsal ligament [8].

Epidemiology

Morton's neuroma is a common disease entity of the foot. The female-to-male ratio for Morton's neuroma is 5:1. The highest prevalence of Morton's neuroma is found in patients aged 15-50 years, but the condition may occur in any ambulatory patient.

Causes

There are several factors that have been implicated in the precipitation of Morton's neuroma. Morton's neuroma can develop as a result of chronic nerve irritation, especially with excessive toe dorsiflexion. Poorly fitting and constricting shoes and shoes with heel lifts often contribute to Morton's neuroma. Women who wear high-heeled shoes for a number of years are at risk. Men who wear constrictive shoes are also at risk.

A biomechanical theory of causation also exists. Individuals with tight gastrocnemius-soleus muscles and those who excessively pronate the foot may compensate by dorsiflexion of the metatarsals which leads to irritation of the interdigital nerve.

Certain activities carry an increased risk of excessive toe dorsiflexion, such as prolonged running, walking, squatting, and demi-pointe position in ballet. This can predispose to Morton’s neuroma [9].

Diagnostic Considerations

Metatarsophalangeal (MTP) joint synovitis is the most common condition that is misdiagnosed as Morton's neuroma. When pain occurs in the third webspace, the clinician may misdiagnose the condition as Morton's neuroma instead of MTP synovitis. In patients with MTP synovitis, there is swelling around the joint, the pain is localized mainly within the joint, and there is pain with forced toe flexion. There will be joint tenderness as well.

Other conditions that are often misdiagnosed as Morton's neuroma include:

• Stress fracture of the neck of the metatarsal

• Hammertoe

• Metatarsalgia (ie, plantar tenderness over the metatarsal head)

• Rheumatoid arthritis and other systemic arthritic conditions

Less common conditions that have overlapping symptoms with Morton's neuroma include:

• Freiburg osteochondrosis

• Ganglion cysts

• Neoplasms

• Metatarsal head osteonecrosis

• Intermetatarsal bursal fluid collections

• True neuromas

Prognosis

The prognosis for recovery is good with conservative treatment. Some patients may require surgical intervention [10]. Recurrence rate after surgery can be as high as 50%. 

 

References

1. Morton TG. Peculiar painful affection of fourth metatarsophalangeal articulation. Am J Med Sci. 1876. 71:37.

2. Munir U, Morgan S. Morton Neuroma. StatPearls. 2020 Jan. 

3. Valero J, Gallart J, Gonzalez D, Deus J, Lahoz M. Multiple interdigital neuromas: a retrospective study of 279 feet with 462 neuromas. J Foot Ankle Surg. 2015 May-Jun. 54 (3):320-2.

4. Gurdezi S, White T, Ramesh P. Alcohol injection for Morton's neuroma: a five-year follow-up. Foot Ankle Int. 2013 Aug;34(8): 1064-7. doi: 10.1177/1071100713489555. Epub 2013 May 13. PMID: 23669161.

5. Lizano-Díez X, Ginés-Cespedosa A, Alentorn-Geli E, Pérez-Prieto D, González-Lucena G, Gamba C, de Zabala S, Solano-López A, Rigol-Ramón P. Corticosteroid Injection for the Treatment of Morton's Neuroma: A Prospective, Double-Blinded, Randomized, Placebo-Controlled Trial. Foot Ankle Int. 2017 Sep;38(9):944-951. doi: 10.1177/1071100717709569. Epub 2017 Jun 15. PMID: 28617064.

6. Akermark C, Saartok T, Zuber Z. A prospective 2-year follow-up study of plantar incisions in the treatment of primary intermetatarsal neuromas (Morton's neuroma). Foot Ankle Surg. 2008;14(2):67-73. doi: 10.1016/j.fas.2007.10.004. Epub 2008 Feb 21. PMID: 19083618.

7. Akermark C, Crone H, Skoog A, Weidenhielm L. A prospective randomized controlled trial of plantar versus dorsal incisions for operative treatment of primary Morton's neuroma. Foot Ankle Int. 2013 Sep;34(9):1198-204. doi: 10.1177/1071100713484300. Epub 2013 Apr 5. PMID: 23564425.

8. Kim JY, Choi JH, Park J, et al. An anatomical study of Morton's interdigital neuroma: the relationship between the occurring site and the deep transverse metatarsal ligament (DTML). Foot Ankle Int. 2007 Sep. 28(9):1007-10.

9. O'Connor FG, Wilder RP, Nirschl R. Foot Injuries in the Runner. In:Textbook of Running Medicine. New York: McGraw-Hill; 2001. 258-260.

10. Mahadevan D, Salmasi M, Whybra N, Nanda A, Gaba S, Mangwani J. What factors predict the need for further intervention following corticosteroid injection of Morton's neuroma?. Foot Ankle Surg. 2016 Mar. 22 (1):9-11.