Fig. 6.

Os calcaneus secundarius. a Sagittal FSE T1 in a 56-year-old man referred for follow-up after Achilles reconstructive surgery. As an incidental finding, an os calcaneum secundarium was noted. This is located in between the talus and the calcaneus (white arrowhead). b Axial FSE T1 demonstrates the ossicle located in the space between the talus and calcaneus, articulating with the anterior process of the calcaneus (only partially seen) and the tarsal navicular (white arrow). c Different patient, incidental finding of an os calcaneus secundarius, here visible on lateral radiographs (black arrow). Note also the presence of an os trigonum