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.
 Imaging Findings for Accessory navicular
- As above
Patient #1: MR images demonstrate bilateral type II accessory navicular bones
Patient #2: MR images demonstrate a type III accessory navicular
 See Also
 External Links
 References for Accessory navicular
- TT Miller, RB Staron, F Feldman, M Parisien, WJ Glucksman, and LH Gandolfo. The symptomatic accessory tarsal navicular bone: assessment with MR imaging. Radiology 1995 195: 849-853.