ANKLE IMPINGEMENT
(OS TRIGONUM SYNDROME)

An Os Trigonum is an accessory small bit of bone at the back of the talus (the bone in the ankle joint that moves up and down).

If, like a ballet dancer, you go up on your toes a lot, this can irritate the soft tissues and tendons, and occasionally fracture.  This can cause pain.

Symptoms may settle with rest, but sometimes surgery is required to remove the small bit of bone.