Definition: An os trigonum is a small, round bone that sits just behind the ankle joint. The os trigonum is present in about 5-15% of normal feet. An os trigonum occurs when one area of bone does not fuse with the rest of the talus (ankle bone) during growth.
Normally, having an os trigonum is of no consequence. In some people, however, this small bone can get caught in the ankle, and even prevent normal motion. This is most commonly seen in ballet dancers who assume pointe and demipointe positions.
For the person who has an os trigonum, pointing the toes downward can result in a “nutcracker injury.” Like an almond in a nutcracker, the os trigonum is crunched between the ankle and heel bones. As the os trigonum pulls loose, the tissue connecting it to the talus is stretched or torn and the area becomes inflamed. Deep, aching pain in the back of the ankle, occurring mostly when pushing off on the big toe (as in walking) or when pointing the toes downward.
Surgery can remove the os and patient can be pain free.
Video Montage of Christine's Surgery
