Os calcaneus secundarius mimicking anterior process fracture: Diagnostic pitfall in acute ankle trauma

The os calcaneus secundarius is an accessory ossicle arising from secondary ossification centers and located near the anterior process of the calcaneus. Although usually asymptomatic, it may become clinically relevant following ankle trauma and can closely mimic an anterior calcaneal process fracture on conventional radiographs. We report the case of a 38-year-old male who presented with right ankle pain after an inversion injury sustained during a football match. Initial anteroposterior and lateral radiographs of the foot were unremarkable, while an oblique view revealed a small, well-defined ossified structure adjacent to the anterior process of the calcaneus, raising suspicion of a fracture. Computed tomography of the ankle demonstrated a well-corticated, smoothly marginated oval ossicle measuring approximately 15 mm, located between the anterior process of the calcaneus, the cuboid, and the talonavicular joint, with intact surrounding cortical outlines, allowing a definitive diagnosis of os calcaneus secundarius. The patient was treated conservatively with nonsteroidal anti-inflammatory drugs and rest, with complete resolution of symptoms within 30 days. This case emphasizes the essential role of imaging, particularly computed tomography, in distinguishing accessory ossicles from acute fractures and avoiding unnecessary treatment.