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Interdigital (Morton's) Neuroma

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Topic updated on 06/16/14 10:07pm
Introduction
  • Compressive neuropathy of the interdigital nerve
  • Epidemiology
    • demographics
      • more common in females (9:1)
    • location
      • most frequently between the 3rd and 4th metatarsals
      • 2nd most common is between 2nd and 3rd metatarsal
  • Pathophysiology
    • poorly understood
      • compression/tension around the transverse intermetatarsal ligament 
      • repetitive microtrauma
      • excessive bursal tissue
      • endoneural edema
      • all the above can lead to neural fibrosis
Anatomy
  • 3rd and 4th inter-metatarsal space
    • unique anatomy in that medial branch of LPN and lateral branch of MPN merge and share a common perineurium 
Presentation
  • Symptoms
    • pain
      • 60% of patients report pain radiating into toe distally
      • often pain elicited during push-off phase of running athletes and demi-pointe position in dancers
      • shoes with narrow toe box or high heels can make symptoms worse 
      • patients often complain of feeling like there is a stone or similar under the ball of their foot
    • paresthesia
      • 40% report numbness or dysesthesia in plantar aspect of web space
  • Physical exam
    • plantar tenderness with palpation just distal to metatarsal heads
    • check sensation in affected region as it may be altered in some patients
    • a bursal click (Mulder's click) may be elicited by squeezing metatarsals together
    • metatarsalgia and MTP synovitis or instability must be ruled out (use drawer test at MTPJ)
Imaging
  • Radiographs
    • recommended views
      • three weight bearing views of foot to rule out bony deformity
  • MRI
    • indications
      • rule out other pathology
      • not required for diagnosis
  • Ultrasound
    • Many find helpful to evaluate nerve
    • dependent on size
    • also not necessary for diagnosis
Studies
  • Pathology shows 
    • perineural fibrosis
    • thickened and hyalinized walls 
    • demyelination
    • degeneration of nerve fibers
    • endoneural edema
    • absence of inflammatory cells
    • frequent bursal tissue
Differential
  • MTP synovitis
    • can mimic an interdigital neuroma
    • important to differentiate between the two because treatment of interdigital neuroma with a steroid injection can exacerbate pathologic condition at the MTP joint
Treatment
  • Nonoperative
    • wide shoe box with firm sole and metatarsal pad
      • indications
        • first line of treatment
    • corticosteroid injection
      • usually approached dorsal
      • nerve is below intermetatarsal ligament
      • avoid injection of MTPJ due to risk of iatrogenic instability
  • Operative
    • neuroma resection
      • indications
        • when nonoperative management fails
      • technique
        • dorsal incision used most commonly
        • resection of neuroma 2-3 cm proximal to deep transverse intermetatarsal ligament (incise transverse intermetatarsal ligament)
        • bury proximal stump within intrinsic muscles
    • neuroma decompression
      • alternative to resection, especially if adjacent neuromas
        • resection of adjacent neuromas will lead to complete numbness of toe
Complication
  • Stump neuroma
    • causes include
      • inadequate retraction (traction neuritis)
        • most common
        • caused by tethering of plantar neural branches that prevent retraction following resection
      • inadequate resection (not proximal enough)
    • resect through plantar or dorsal incision
  • Painful plantar scar
    • increased risk (5%) with plantar incision

 

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