Presentation
Twisted right ankle with swelling
Patient Data
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 to the medial aspect of the lateral malleolus tip could be mistaken for fracture if this was not the typical appearance and location for an accessory ossicle - the os subfibulare.
On the lateral projection, an os trigonum can be appreciated.
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