The Geist classification of the types of accessory navicular bones was first described by the orthopedic surgeon Dr Emil Geist, MD from the Department of Orthopedic Surgery at the University of Minnesota in 1914:
Geist ES. Supernumerary bone of the foot: A roentgen study of the feet of 100 normal individuals. Am J Orthop Surg. 1914;12:403 (link).
There are several classifications that can be used for the different types of accessory navicular, with this Geist classification is probably the most widely used.
The Geist classification divides the types of accessory navicular into three types:
Type 1 accessory navicular bone:
This type usually also is known as os tibiale externum. This is a free standing ossicle or sesamoid bone, spherical in shape about 2-3mm in size that is embedded in the tendon of the posterior tibial muscle. It has no cartilaginous connection to the main body of the navicular. This makes up to about 30% of the accessory navicular bones and is usually not painful.
Type 2 accessory navicular bone:
This is a triangular or heart-shaped sesamoid bone that is up to 12 mm in size and accounts for 50-60% of all accessory naviculars and most of the symptomatic ones. It is connected to the navicular by a 1-2-mm thick layer of cartilaginous or fibrocartilaginous tissue. It may eventually fuse with the navicular tuberosity to create a Type 3.
Type 3 accessory navicular bone:
This is a very prominent navicular tuberosity that is also sometimes called a cornuate navicular because of the hook like shape of the bone. It is probably a fused type 2 and can be symptomatic due to the prominence of the bone.
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