Os trigonum injuries

Abstract

Os trigonum and posterior talar process injuries are common in sports, especially soccer, football, and basketball, along with dancers, particularly those who go “en pointe.”1-3 Symptoms can be precipitated by an ankle sprain, with hyper-plantarflexion often causing a “nutcracker” effect displacing the os trigonum or creating a posterior talar fracture. The os trigonum occurs in up to 30% of the population as a normal variant.2 It lies intra-articularly adjacent to the posterior talar process. Both the posterior ankle and subtalar joint capsules adhere to this bone. The flexor hallucis longus (FHL) tendon generally courses medial to it and can be aggravated by injury to this ossicle or the posterior talus itself. The injury should be differentiated from stenosing tenosynovitis of the FHL tendon.