Fig. 7

Differential diagnosis of os calcaneus secundarius. 44-year-old man referred with the suspicion of Achilles tendinopathy. a Sagittal FSE T1 incidentally demonstrates a small ossified body present in the typical location of an os calcaneus secundarius (white arrow). Patient cannot recall trauma or pain in the lateral aspect of the foot. In these cases, it is occasionally very difficult to establish the diagnosis and distinguish a sequel of an old fracture from a true small ossicle. b On axial FSE T1, the bone fragment is elongated and has irregular margins (black arrow). It corresponds to a defect in contour of the calcaneus. This orientates towards a sequel of old fracture as opposed to an accessory ossicle