From the case:
Os trigonum
{"current_user":null,"step_through_annotations":true,"access":{"can_edit":false,"can_download":true,"can_toggle_annotations":true,"can_feature":false,"can_pin":false},"extraPropsURL":"/studies/10736/annotated_viewer_json?lang=us"}
Os trigonum.
Case Discussion
An os trigonum is one of the bony ossicles of the foot and can be mistaken for a fracture. it sits posterior to talus on the lateral foot radiograph.