Os trigonum

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 and represents a failure of fusion of the lateral tubercle. 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. 

Related pathology

Differential diagnosis

General imaging differential considerations include:


Lower limb anatomy
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Article Information

rID: 10194
System: Musculoskeletal
Section: Anatomy
Synonyms or Alternate Spellings:
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    Figure 1
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    Os trigonum
    Case 1: os trigonum
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    Os trigonum
    Case 2: os trigonum
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    Case 3: os trigonum
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    Case 4: os trigonum (T1W MRI)
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    Case 5
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