What is the os trigonum?
The os trigonum is a tiny, additional bone in the foot. It is found on the back of the ankle and is a result of incomplete bone/ankle formation. During childhood, a part of the ankle joint called the talus bone is attached to the os trigonum by fibers. As the child grows and develops, the talus bone normally fuses with the os trigonum to create a small lump. In 3-15% of the population, however, the bones fail to fuse together and the os trigonum remains its own entity.
Read More: Os Trigonum Syndrome