Accessory navicular bone - Geist classification

Case contributed by Dr Samir Benoudina

Presentation

Accessory navicular bone - Geist classification

Accessory navicular bone - Geist classification

Case Discussion

The Geist1 classification divides accessory navicular bones into three types:

  1. type 1 accessory navicular bone
    • also known as os tibiale externum
    • 2-3 mm sesamoid bone embedded within the distal portion of the posterior tibial tendon
    • no 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
  2. type 2 accessory navicular bone
    • accounts for ~55% (range 50-60%) of all accessory navicular bones
    • triangular or heart-shaped
    • typically measures around 12 mm
    • connected to the navicular tuberosity by a 1-2 mm thick layer of either fibrocartilage or hyaline cartilage
    • eventual osseous fusion to the navicular tuberosity may take place
  3. 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

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