Os trigonum

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Os trigonum is one of the bony ossicles of the foot and can be mistaken for a fracture.

It sits posterior to the talus on the lateral foot radiograph. It is estimated to be present in ~7% of adults ¹. The ossicle usually forms between 7-13 years of age and fuses with the talus in a majority of patients, otherwise persisting as an os trigonum.

Complications

os trigonum syndrome/posterior ankle impingement (PAI) syndrome ^1-2

Differential diagnosis

General imaging differential considerations include:

~~-<a href="/articles/posterior-talar-process-fracture">avulsion fracture of lateral tubercle of talus</a> (<a href="/articles/posterior-talar-process-fracture">shepherd fracture</a>)</li>~~
+<a href="/articles/posterior-talar-process-fracture">avulsion fracture of lateral tubercle of talus</a> (<a href="/articles/posterior-talar-process-fracture">Shepherd fracture</a>)</li>

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Os trigonum

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