The lateral tubercle of the posterior process of the talus is generally fused with the body of this bone, however, due to stress (forced plantar flexion) applied during the adolescent years. Also, when a partiall yossified and evenfull yossified center fractures, it causes a lack of union, giving rise to an accessory bone called Os trigonum (OT). In some cases Os trigonum syndrome or posterior impingement syndrome may occur, which is characterized by acute or chronic pain in the posterior region of the ankle. Based on the above, a retrospective study was conducted between August 2017 and May 2018, in which bilateral radiographs of 205 patients attending the Hernán Henríquez Aravena Hospital of Temuco were analyzed. Of the population studied, 154 were female and 51 were male, whose ages fluctuated between 15 and 85 years. The radiological projections used were lateral foot, lateral ankle and calcaneus lateral, to determine the prevalence of OT and provide information about its distribution in right and left foot and appearance according to sex and age. From the total sample, 24 individuals were found who had OT (11.7 %) of which 18 (75 %) corresponded to the female sex and 6 (25 %) to the male sex. In addition, measurements of the length and width of the OT were made. The data obtained is a contribution to the knowledge of the accessory bones of the foot in the Chilean population.

KEY WORDS: Anatomy; Talus; Accessory bones; Os trigonum; Imaging.