Morton neuroma

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Morton neuroma (also known as an interdigital or intermetatarsal neuroma) is a benign forefoot tumor formed by thickening of the epineural and perineural tissue surrounding a plantar digital nerve. The etiology is unknown, but Morton neuroma is thought to be caused by chronic pressure on the affected plantar metatarsal structures. Manifestations include burning pain and numbness between the metatarsal heads of the foot that radiates to the adjacent toes. The third interdigital space is most commonly affected. Positive Mulder sign and Tinel sign support the clinical diagnosis of Morton neuroma. Imaging such as standing foot radiography, ultrasound, and MRI can be ordered if there is diagnostic uncertainty or to rule out alternative causes of chronic foot pain. Conservative treatment consists of avoiding activities that cause symptoms and modifying footwear by adding padding and/or using custom orthotics. Specialists may perform a corticosteroid injection or surgical excision of the nerve to help patients with persistent pain.

• Sex: ♀ > ♂ ^[3]
• Age of onset: 45–54 years
• The third interdigital space and nerve are involved in 87% of affected individuals. ^[2]

Morton neuroma is the second most common compressive neuropathy after carpal tunnel syndrome. ^[2][3]

Epidemiological data refers to the US, unless otherwise specified.

The etiology of Morton neuroma is unknown, but it is thought to be caused by chronic pressure on the affected plantar digital nerve. ^[2][3][4]

• Burning pain and numbness on plantar surface ^[2]
  • Between the involved metatarsal heads of the foot
  • Radiates to the two adjacent toes
• Patients may describe feeling a marble or pebble during weight-bearing activities. ^[5]
• Pain improves with rest and worsens with: ^[2]
  • Constrictive footwear
  • Weight-bearing activities (e.g., walking, running) ^[5]
  • Stretching the toes

Symptoms most commonly occur in the third interdigital space. ^[2][3]

Morton neuroma is a clinical diagnosis based on history and provocation testing. If there is clinical uncertainty, order imaging to confirm the diagnosis or exclude alternative causes of chronic foot pain. ^[2]

Provocation testing ^[2]

Provocation tests include:

• Mulder sign
  • The forefoot is held firmly with one hand compressing the metatarsal heads in the medial-lateral direction.
  • Pressure is applied to the sole between the affected metatarsal heads.
  • Morton neuroma is confirmed with either of the following:
    • Reproducible pain
    • Palpable click or snapping sensation (Mulder click)
• Tinel sign
  • The toes are extended with one hand while percussing the plantar surface of the affected intermetatarsal space with the other hand
  • The test is positive if pain or a tingling sensation is produced.

Imaging ^[2][6]

• Standing plain radiography of the foot: to evaluate for alternative causes of chronic foot pain
• MRI of the foot without IV contrast or US: to confirm the diagnosis or to plan treatment ^[5]

Imaging is not routinely required to diagnose intermetatarsal neuroma. ^[2]

• All patients: Initiate conservative measures to relieve pressure on the affected area and improve symptoms. ^[2][3]
  • Activity modification
  • Properly fitting footwear with additional padding ^[3]
  • Custom orthotics with metatarsal or neuronal pads
• Persistent symptoms after 6 weeks: Refer to a foot specialist for management. ^[2]
  • Interdigital corticosteroid injection with or without local anesthetic: can provide pain relief for up to 3 months ^[2][3][7]
  • Surgical excision of the affected nerve