Os trigonum

Changed by Joshua Yap, 13 Jul 2022

Back to revision history

Updates to Article Attributes

Body was changed:

Show markup changes

The os trigonum (plural: os trigona) is one of the 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 of the posterior process. It is estimated to be present in ~7% of adults ¹. Bilateral os trigona are seen in 2% of individuals ³. The ossicle usually forms between 7-13 years of age and fuses with the talus in a majority of patients by approximately age 17 ⁴, otherwise persisting as an os trigonum.

Related pathology

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

Differential diagnosis

General imaging differential considerations include:

-The os trigonum (plural: os trigona) is one of the <a href="/articles/accessory-ossicles">ossicles</a> 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 of the posterior process. It is estimated to be present in ~7% of adults 1. Bilateral os trigona are seen in 2% of individuals 3. The ossicle usually forms between 7-13 years of age and fuses with the talus in a majority of patients by approximately age 17 4, otherwise persisting as an os trigonum. <h4>Related pathology</h4><ul><li>
-<a href="/articles/os-trigonum-syndrome">os</a><a href="/articles/os-trigonum-syndrome"> </a><a href="/articles/os-trigonum-syndrome">trigonum</a> syndrome/<a href="/articles/posterior-ankle-impingement-syndrome">posterior ankle impingement (PAI) syndrome </a>1,2
+The os trigonum (plural: os trigona) is one of the <a href="/articles/accessory-ossicles">ossicles</a> 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 of the posterior process. It is estimated to be present in ~7% of adults 1. Bilateral os trigona are seen in 2% of individuals 3. The ossicle usually forms between 7-13 years of age and fuses with the talus in a majority of patients by approximately age 17 4, otherwise persisting as an os trigonum. <h4>Related pathology</h4><ul><li>os trigonum syndrome / <a href="/articles/posterior-ankle-impingement-syndrome">posterior ankle impingement (PAI) syndrome </a>1,2

ADVERTISEMENT: Supporters see fewer/no ads

{"current_user":null,"inclusions":[{"imageId":11956424,"studyId":36900,"caseSlug":"anatomy-of-the-talus","caption":"Figure 1","thumbnail":"https://prod-images-static.radiopaedia.org/images/11956424/a1c5a66925b021181503890f7d8a85_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"not_applicable"},{"imageId":58487500,"studyId":121011,"caseSlug":"accessory-ossicles-of-the-foot-illustration","caption":"Figure 2","thumbnail":"https://prod-images-static.radiopaedia.org/images/58487500/0._big_gallery.jpeg","isStack":false,"diagnosticCertainty":"not_applicable"},{"imageId":520944,"studyId":10736,"caseSlug":"os-trigonum","caption":"Case 1: os trigonum","thumbnail":"https://prod-images-static.radiopaedia.org/images/520944/76f7501d70eb19dbbe90729363a18ebe3adfb0b41d0d968636c5c62649153f3b_big_gallery.jpeg","isStack":false,"diagnosticCertainty":null},{"imageId":580,"studyId":8788,"caseSlug":"os-trigonum-1","caption":"Case 2: os trigonum","thumbnail":"https://prod-images-static.radiopaedia.org/images/580/a1128893e898a492ff64322c767e70_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":5049222,"studyId":25942,"caseSlug":"os-trigonum-2","caption":"Case 3: os trigonum","thumbnail":"https://prod-images-static.radiopaedia.org/images/5049222/f87086d6b4c7e510cbaac9c495c593_big_gallery.JPG","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":3251534,"studyId":22768,"caseSlug":"posterior-ankle-impingement-os-trigonum-syndrome","caption":"Case 4: os trigonum (T1W MRI)","thumbnail":"https://prod-images-static.radiopaedia.org/images/3251534/9f2f03a4a15f1ba8689df0ae137b70_big_gallery.jpg","isStack":true,"diagnosticCertainty":"confirmed_unsubstantiated"},{"imageId":15698247,"studyId":41774,"caseSlug":"os-trigonum-3","caption":"Case 5","thumbnail":"https://prod-images-static.radiopaedia.org/images/15698247/81da75c4356b397b7120c66f3f79a9_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":40872609,"studyId":69783,"caseSlug":"os-trigonum-6","caption":"Case 6","thumbnail":"https://prod-images-static.radiopaedia.org/images/40872609/51322d4cf76c9c038337b26fc2947e_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":52633988,"studyId":89651,"caseSlug":"subtalar-osteoarthritis-bilateral","caption":"Case 6: with bilateral subtalar osteoarthritis ","thumbnail":"https://prod-images-static.radiopaedia.org/images/52633988/e2cad86bb1e09f478931c0e06c313f_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_unsubstantiated"},{"imageId":54791094,"studyId":105085,"caseSlug":"posterior-ankle-impingement-os-trigonum-syndrome-4","caption":"Case 7: os trigonum syndrome","thumbnail":"https://prod-images-static.radiopaedia.org/images/54791094/annotated_1_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_unsubstantiated"},{"imageId":55720083,"studyId":109632,"caseSlug":"os-trigonum-7","caption":"Case 8","thumbnail":"https://prod-images-static.radiopaedia.org/images/55720083/Picture1_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":23220759,"studyId":50085,"caseSlug":"os-trigonum-5","caption":"Case 9","thumbnail":"https://prod-images-static.radiopaedia.org/images/23220759/0a7da50fc23f6b5cc10263cd0c01476b778e39317fd13108d4ef071643a97cb6_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"},{"imageId":61365881,"studyId":132246,"caseSlug":"os-supratalare-5","caption":"Case 10","thumbnail":"https://prod-images-static.radiopaedia.org/images/61365881/54677eb3883e7c0508a517ecb47bf029f794715ceaa3ec930cc93053b51ff251_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_substantiated"}],"ddx_inclusions":[{"imageId":15704719,"studyId":41788,"caseSlug":"posterior-talar-process-fracture","caption":"Posterior talar process fracture","thumbnail":"https://prod-images-static.radiopaedia.org/images/15704719/9180832904b0d57245950b79b082106d76f3c7e8fc66b0a70c866e98c36e6c7f_big_gallery.jpeg","isStack":false,"diagnosticCertainty":"confirmed_unsubstantiated"}],"lang":"us"}