Accessory navicular

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[edit] Discussion of Accessory navicular

  • An accessory navicular bone is located posterior to the posteromedial tuberosity of the tarsal navicular bone.
  • An accessory navicular bone is present in 4%-21% of the population.
  • First appears in adolescence.
  • More common in female patients.
  • Reported prevalence of bilaterality varies from 50% to 90%.

  • Three types of accessory navicular bone have been described.
  • Type 1 accessory navicular bone
    • AKA os tibiale externum
    • 2-3-mm sesmoid bone embedded within the distal portion of the posterior tibial tendon.
    • It does not have a cartilaginous connection to the naviculam tuberosity and may be separated from it by up to 5 mm.
    • Accounts for 30% of accessory navicular bones
    • Usually asymptomatic
  • Type 2 accessory navicular bone
    • Triangular or heart-shaped
    • Measures up to 12 mm
    • Accounts for 50%-60% of all ossicles.
    • Connected to the naviculam tuberosity by a 1-2-mm thick layer of either fibrocartilage on hyaline cartilage.
    • Eventual osseous fusion to the navicular tuberosity may take place
  • Type 3 accessory navicular bone
    • An especially prominent navicular tuberosity called a cornuate navicular
    • Thought to represent a fused type 2 and is occasionally symptomatic as a result of painful bunion formation over the bony protuberance.

[edit] Imaging Findings for Accessory navicular

  • As above

[edit] Images

Patient #1: MR images demonstrate bilateral type II accessory navicular bones

Patient #2: MR images demonstrate a type III accessory navicular

[edit] See Also

[edit] External Links

[edit] References for Accessory navicular