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Updated: Sep 6 2023

Interdigital (Morton's) Neuroma

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  • summary
    • Interdigital Neuromas, also known as Morton's neuroma, is a compressive neuropathy of the interdigital nerve that often leads to plantar forefoot pain.
    • Diagnosis is made clinically with tenderness over the plantar aspect of the involved webspace with a palpable neuroma and a positive Mulder's click on examination. 
    • Treatment is a trial of nonoperative management with a wide shoe box with metatarsal pads. Operative management is indicated for patients with persistent symptoms who fail nonoperative management. 
  • Epidemiology
    • demographics
      • middle-aged females (9:1)
    • body location
      • most commonly involves the 3rd and 4th interdigital nerves between the metatarsal heads (3rd webspace)
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • not fully understood
          • compression/tension of the interdigital nerve around the transverse intermetatarsal ligament
          • repetitive microtrauma
      • pathoanatomy
        • perineural fibrosis and entrapment of the interdigital nerve
  • Anatomy
    • Interdigital nerve
      • location
        • lies plantar to the transverse intermetatarsal ligament between the metatarsal heads
      • components
        • confluence branches of the lateral and medial plantar nerves
  • Presentation
    • Symptoms
      • pain
        • worse with weight-bearing or wearing narrow toe box shoes (e.g. high heels)
        • relief of symptoms by removing shoes and massaging foot
      • paresthesia
        • most commonly on the plantar aspect of web space
    • Physical exam
      • palpation
        • neuroma may be palpable
        • positive web-space compression test
      • provocative tests
        • Mulder's click
          • bursal click may be elicited by squeezing metatarsals together
        • Drawer test at metatarsal phalangeal joint (MTPJ)
          • assess for MTPJ instability
  • Imaging
    • Radiographs
      • recommended views
        • weight bearing AP/lateral/oblique views
      • findings
        • usually normal
        • may see bony deformity
    • Ultrasound
      • indication
        • non-palpable neuroma with clear clinical presentation
      • findings
        • oval, hypoechoic mass oriented parallel to the metatarsal bones
      • outcomes
        • highly operator dependent
    • MRI
      • indication
        • not usually required for diagnosis
        • may be used to rule out other pathologies
  • Studies
    • Common digital nerve block
      • indication
        • confirmatory for accurate diagnosis of interdigital neuroma
      • findings
        • numbness over lateral surface of toe with relief of patient reported pain
  • Differential
    • MTP synovitis
      • consider if there is no relief of pain after well positioned digit nerve block
    • Metatarsalgia
    • Stress fracture
    • MTPJ arthritis
    • Metatarsal head osteonecrosis
    • Neoplasm
    • Lumbar radiculopathy
  • Treatment
    • Nonoperative
      • wide shoe box with firm sole and metatarsal pad
        • indications
          • first line of treatment
        • outcomes
          • results are unpredictable
            • approximately 20% of patients will have complete resolution of symptoms
          • adding anti-inflammatory medications rarely provide any benefit
      • corticosteroid injection
        • indications
          • symptomatic benefit
        • modality
          • usually approached dorsal after isolating the neuroma with palpation or ultrasound
        • outcomes
          • evidence for its effectiveness is weak
          • suggested to provide symptomatic benefit in short term randomized control studies 
    • Operative
      • neurectomy
        • indications
          • failure of nonoperative management
        • techniques
          • dorsal or plantar approach (dorsal most common)
          • neurectomy with nerve burial (bury proximal stump within intrinsic muscles)
          • transverse intermetatarsal ligament release
  • Technique
    • Dorsal neurectomy
      • approach
        • 3 to 4 cm incision just proximal to the involved webspace
        • blunt dissection to avoid injury to branches of superficial peroneal nerve
      • technique
        • spread the metatarsal bones to visualize the webspace, as well as tension the transverse intermetatarsal ligament
        • protecting the neurovacular bundle, transect the transverse intermetatarsal ligament
        • identify the interdigital nerve proximal and distal to the nerve bifurcation
        • resect the nerve at least 3 cm proximal to intermetatarsal ligament
        • reapproximate and repair the transverse intermetatarsal ligament to avoid intermetatarsal head instability
  • Complications
    • Stump neuroma
      • causes include
        • inadequate retraction (traction neuritis)
          • caused by tethering of plantar neural branches that prevent retraction following resection
        • inadequate resection (not proximal enough)
          • most common
          • nerve should be resected at least 3 cm proximal to intermetatarsal ligament
      • resect through plantar or dorsal incision
    • Painful plantar scar
      • increased risk (5%) with plantar incision
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