Mortons Neuroma

Mortons Neuroma is a compressive neuropathy of the interdigital nerve, usually between the third and fourth metatarsals.

Interdigital neuroma was first described in 1845 by Durlacher, and, in 1876, Morton expanded the clinical description and gave the condition its eponym, Morton Neuroma.

Females are affected more commonly than males 8:1 (most likely from wearing high heels and shoes with narrow toe boxes). The condition is usually unilateral

Pathophysiology

The pathophysiology of this condition is still poorly understood. Theories include:

1. Compression/tension around the intermetatarsal ligament,
2. Repetitive microtrauma,
3. Vascular changes,
4. Excessive bursal tissue,
5. Endoneural edema,
6. Eventual neural fibrosis.

Mortons Neuroma Symptoms

The diagnosis usually is made by careful history and physical examination, although various diagnostic studies may be helpful in selected cases.

Patients will frequently report pain and burning on the plantar aspect of the web space, with over 60% of patients noting pain radiating into the toe distally. Numbness is reported in only 40% of patients. These symptoms are exacerbated by footwear with narrow toe boxes and high heels.

Patients often note that they feel better in their bare feet and get quick relief with removal of their shoes.

Physical examination includes:

Palpation between and just distal to the metatarsal heads elicits plantar tenderness.

Tenderness in the web space is believed to be the most common finding in interdigital neuroma. Palpating the web spaces with the patient standing sometimes is helpful in differentiating a second web space neuroma from a plantar plate lesion at the second metatarsophalangeal joint. If the tenderness is mostly in the web space and not in the plantar aspect of the base of the proximal phalanx or the dorsolateral aspect of the second metatarsophalangeal joint, a neuroma is likely.

Compressing the medial and lateral aspect of the forefoot while palpating the web space structures can provoke symptoms and occasionally a bursal “click” (Mortons Neuroma Test): This click is best appreciated when the patient lies prone, and the examiner places the thumb dorsally and the index finger plantarward over the appropriate web space (usually the third) and gently rocks the hand back and forth.

Injection of the involved web space with local anesthetic is diagnostic if the neuritic symptoms are relieved temporally.

Metatarsalgia and MTP synovitis often present similarly and should be ruled out.

See Also: Mortons Neuroma Test 

Radiology Evaluation

Plain films should be performed to rule out bony masses or deformity.

Ultrasound has been reported to be 85% accurate in diagnosing of Mortons Neuroma.

MRI can be used to identify other pathologies, but not required for diagnosis.

Pathological Findings

The following list summarizes reported pathological findings of Mortons Neuroma:

1. Perineural fibrosis.
2. Increased number of intrafascicular arterioles with thickened and hyalinized walls caused by multiple layers of basement membranes.
3. Demyelinization and degeneration of nerve fibers with a decrease in the number of axis cylinders.
4. Endoneural edema.
5. Absence of inflammatory changes.
6. Frequent presence of bursal tissue accompanying the specimen.

Mortons Neuroma Treatment

The mainstay of Morton’s Neuroma treatment is surgery by neuroma excision, but nonoperative treatment is successful often enough to warrant at least a trial period.

Nonoperative treatment of Morton’s Neuroma include:

1. Shoewear modification (avoiding high heels and narrow toe boxes) is the most important and effective intervention.
2. Metatarsal pads placed proximal to the focus of pain can prevent direct pressure and widen the intermetatarsal space during weight bearing, thereby indirectly decompressing the nerve.
3. Corticosteroid injections into the affected web space can have moderate effectiveness (≈50% of patients report positive response).

Detailed preoperative examination and careful patient selection for surgery is recommended. In addition, the patient must be informed before surgery that some symptoms may remain after surgery (caused by other causes of metatarsalgia that might coexist in a patient with an interdigital neuroma).

Mortons Neuroma is treated surgically by Excision via dorsal or volar approach:

Dorsal approach:

Dorsal approach Morton’s neuroma surgery is the most common used approach. Incise the transverse intermetatarsal ligament, identify the common digital nerve and its branches, and resect the nerve 2 to 3 cm proximal to the intermetatarsal ligament (proximal to the small plantar branches), which allows the proximal stump to retract. This minimizes formation of stump neuroma, the most common complication of neuroma excision.

Difficult visualization results in a 4% rate of failure to excise the neuroma. Overall success rates approach 80%.

Plantar approach:

Plantar approach decreases the rate of missed neuroma excision. It does not require incision of the transverse intermetatarsal ligament. There is increased risk (5%) of painful plantar scar.

Typically, it’s used for revision neuroma resection.

For a recurrent interdigital neuroma, a plantar approach is recommended because the exposure is excellent.

A Randomized Controlled Trial by Christian Akermark¹ of plantar versus dorsal incisions for operative treatment of primary Morton’s neuroma, he demonstrated 87% (plantar) and 83% (dorsal) clinically good outcomes and no significant differences between the procedures in regard to pain, restrictions in daily activities, and scar tenderness.

Another prospective 2-year follow-up study² of plantar incisions in the treatment of primary intermetatarsal neuromas (Morton’s neuroma), it shows that surgery with a plantar incision seems to be a reliable and safe intervention of primary Morton’s neuromas, with only limited number of minor complications and a subjective satisfactory outcome, well in accordance with other studies, using different, surgical approaches.

Notes

• In a strict sense, the term neuroma is incorrect because the haphazard proliferation of axons seen in a traumatic
  neuroma is not found and the deposition of hyaline and collagenous material accounts for the enlargement.
• The term interdigital neuritis, rather than interdigital neuroma, has been suggested.
• The pathological process probably is degenerative, rather than proliferative, with repetitive trauma against the deep transverse intermetatarsal ligament being the most likely cause, but even this is uncertain.
• If symptoms occur after midfoot or forefoot trauma, surgical excision should only be cautiously considered because it may require several months for tissue homeostasis to return and symptoms to decrease or resolve.

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References & More

1. 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.
2. 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.
3. Campbel’s Operative Orthopaedics 12th edition Book.
4. Millers Review of Orthopaedics -7th Edition Book.