Updated: 1/20/2020

Interdigital (Morton's) Neuroma

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  • Compressive neuropathy of the interdigital nerve
  • Epidemiology
    • demographics
      • middle-aged females (9:1)
    • body location
      • most commonly involves the 2nd and 3rd interdigital nerve between the metatarsal heads
  • 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 
  • Interdigital nerve
    • location
      • lies plantar to the transverse intermetatarsal ligament between the metatarsal heads
    • components  
      • confluence branches of the lateral and medial plantar nerves 
  • 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
  • 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
  • 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 diagnosis
  • 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
  • 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 
Surgical 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
  • 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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