Name the most widely used classification according to which the external tibial bone is classified.
The Geist classification.
Which type of accessory navicular bone is seen in this study?
This accessory navicular bone is connected to navicular tuberosity by a 1-2 mm thick layer of either fibrocartilage or hyaline cartilage and therefore is a type 2 according to the Geist classification.
What is the name of the clinical condition that can be associated with an os tibiale externum?
Accessory navicular syndrome
What is the pathological correlate seen on MRI in accessory navicular syndrome?
A stress response of the accessory navicular bone, visible as bone marrow oedema.
Who are the three authors that described the three different types of accessory navicular bones according to the Geist classification?
The os tibiale externum (type 1) was described by Gaspard Bauhin in 1605, a variation of the accessory navicular bone (type 2) was described by Hubert von Luscka in 1858 and the last version (type 3) also called cornuate navicular was described by Emil Geist in 1914, who also described the classification.
Findings:
crescent-shaped accessory navicular bone (~6 x 4 x 7 mm) adjacent to the posteromedial tuberosity of the navicular bone with a fibrocartilaginous connection partly embedded within the insertion of the tibialis posterior tendon
intense bone marrow oedema of the accessory navicular bone and adjacent oedema of the fibrocartilaginous connection as well as mild bone marrow oedema of the posteromedial aspect of the navicular tuberosity
very mild amount of fluid around the tibialis posterior tendon
Impression:
-
accessory navicular syndrome with stress response of the os tibiale externum (type 2)