T alus bipartitus (also known as talus partitus or frontal split) is a rare anatomic variant of the talus, first described by Strehle in 1928 1 . Since then, to the best of our knowledge, only seven more cases have been described in the medical literature, and all of these cases occurred in adolescents who were between thirteen and eighteen years of age 2-7 . Three recent reports utilized a computed tomography (CT) scan for evaluation 5-7 , but none outlined the exact three-dimensional anatomy of the ossicle. A detailed follow-up has not been provided on any of the prior patients.The term talus bipartitus describes a large, separate piece of bone that constitutes about one-third of the posterior aspect of the talar body and is separated from that structure by a frontal split. A talus bipartitus is therefore considerably larger than an os trigonum, which contains part of the lateral tubercle of the posterior process of the talus. The os trigonum is not uncommon, with a calculated prevalence of 7% to 13% 8,9 .Over a period of ten years, we have observed four young adult patients with radiographic findings of talus bipartitus. The clinical and radiographic findings were different in all four cases, and treatment consequently had to be tailored individually.This is the first case series of this rare anatomic variant, and we report for the first time on the three-dimensional appearance of this separate ossicle. An average follow-up of 2.5 years after treatment was obtained. The patients were informed that data concerning the cases would be submitted for publication, and they all consented.
Case ReportsC ASE 1. A thirty-one-year-old woman presented with a fourteen-month history of occasional pain in the right ankle. She had a history of repetitive inversion sprains of both ankles during competitive sports during childhood, and the last severe sprain occurred three months prior to presentation. Pain was marked during exercise and had been increasing steadily over the last year. On clinical examination, there was chronic ligamentous laxity in both ankles. Slight edema was noted over the posterolateral aspect of the right ankle, but no pain on palpation could be elicited. Right ankle motion was restricted by 15°as compared with the motion on the left side (10°vs. 15°of dorsiflexion and 40°vs. 50°of plantar flexion), while inversion motion at the right subtalar joint was restricted only by 10°.Standard radiographs showed a bipartite talus with a separate bone on the posteromedial aspect, which appeared displaced (Fig. 1). CT and magnetic resonance imaging (MRI) revealed an accessory bone, approximately one-third the size of the talar dome, that extended into both the ankle and subtalar joints. No signs of osteonecrosis of the talar body or the additional ossicle were detected.A posteromedial approach to the talus was carried out via a longitudinal incision made approximately 4 cm parallel and 1 cm medial to the Achilles tendon. The posterior tibial neurovascular bundle was retracted medially, together with the flexor hallu...