The signs and symptoms of os trigonum syndrome may include:
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
Tenderness in the area when touched
Swelling in the back of the ankle
Os trigonum syndrome is usually triggered by an injury, such as an ankle sprain. The syndrome is also frequently caused by repeated downward pointing of the toes, which is common among ballet dancers, soccer players and other athletes.