Os trigonum syndrome

The os trigonum is a frequently encountered accessory bone of the foot. It is located at the posterior aspect of the talus, and may appear either as a separate ossicle or fused to the talus. The separate ossicle may represent an accessory bone or a fracture of the posterior process (also called the trigonal process) of the talus. The author reviews the mechanism of injury and the diagnosis and treatment. A case report of a fracture of the trigonal process is presented.