Os trigonum syndrome: a clinical entity in ballet dancers.

Thirteen Swedish National classic ballet dancers were surgically treated for an "os trigonum syndrome."Their main symptom was an impingement pain in the hind foot while actively plantarflexing the ankle during ballet dancing. The surgical procedure included excision of an os trigonum or a prominent lateral posterior process of the talus, together with division of the flexor hallucis tendon sheath if it was thickened. This procedure was safe and resulted in return of the dancers to the same level of ballet dancing within 5 to 10 weeks.