[Os trigonum syndrome].

The os trigonum is one of the most frequent accessory bones of the foot. It is located dorsal of the talus. Os trigonum syndrome means a typical pain syndrome localized in the back-foot caused by this ossicle. This syndrome occurs mostly in man with sports activities accompanied with intensive stress to different parts of the foot. It can be caused particularly by standing on the toe in the "en-pointe-position" in ballet dancers when the flexor hallucis tendon is under maximal tension or by activities accompanied with maximal plan-tarflexion in soccer players for instance. Typical complaints, findings and different therapeutic procedures are demonstrated in two cases. Therapy includes different non-operative methods. Resistance to non-operative procedures is indication for operative therapy. Excision of this ossicle is surgical therapy of first choice.