Lateral malleolus avulsion fracture with os subfibulare

Case contributed by Dr Henry Knipe


Twisted right ankle. Increased swelling.

Patient Data

Age: 33
Gender: Male

Thin bony fragments adjacent to the lateral aspect of tip of the lateral malleolus and cortical irregularity at the lateral talus, likely representing avulsion fractures. Incidental note of os subfibulare and os trigonum. Alignment has been maintained. Soft tissue swelling over the lateral malleolus.

Yellow arrow indicates os subfibulare. Blue arrow indicates avulsion fracture. 

Case Discussion

This case demonstrates why a knowledge of common anatomical variants is essential.

The small bony chips lateral to the tip of the lateral malleolus represent an avulsion fracture while the well-corticated bony fragment adjacent medial to the lateral malleolus tip could be mistaken for fracture if this wasn't the typical appearance and location for an accessory ossicle - the os subfibulare

On the lateral projection, there is an os trigonum can be appreciated. 

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Case information

rID: 26255
Published: 9th Dec 2013
Last edited: 16th Jul 2018
Inclusion in quiz mode: Included

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