Accessory navicular bone
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
An accessory navicular bone is a bone of the foot that occasionally develops abnormally in front of the ankle towards the inside of the foot. This bone is present in approximately 10% of the general population and is usually asymptomatic. When it is symptomatic, surgery may be necessary.
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. It first appears in adolescence. It is more common in female patients. Reported prevalence of bilaterality varies from 50% to 90%.
Classification
- 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.
Diagnosis
Patient #1: MR images demonstrate bilateral type II accessory navicular bones
Patient #2: MR images demonstrate a type III accessory navicular
