[CT imaging features and misdiagnosis analysis of occult anterior calcaneal process fracture]

To explore CT imaging features and reason for missed diagnosis of clinical practice of occult anterior calcaneal process fracture.

From July 2013 to November 2018, the clinical data of 13 patients with occult an anterior calcaneal process fracture were retrospectively analyzed, including 2 males and 11 females, aged from 22 to 54 years old. Classification of fracture, displacement of fracture, direction of fracture line, size of fracture, with or without tarsal coalition, other fractures and misdiagnosis, the time from injury to diagnosis, condition of treatment and fracture healing were observed according to case history, data of X-ray and CT.

Thirteen patients were diagnosed as occult anterior calcaneal process fracture after CT examination. According to Degan classification, 9 patients were type I, 4 patients were typeII; 4 patients were occurred displacement, and 9 patients did not occurred displacement. On the horizontally CT, fracture line of 12 patients showed transverse, 1 patient oblique, and the size of fracture ranged from 0.40 to 1.72 cm; while on the sagittal view, fracture line of 12 patients showed vertical, 1 patient oblique, and the size of fracture ranged from 0.10 to 0.59 cm. No patients combined with talocalcaneal and scaphoid bridge. Six patients were simple anterior calcaneal process fracture, 7 patients combined with other fractures. Eight patients were misdiagnosed. The time from injury to diagnose ranged from 0 to 21 days. Nine patients with type Iwere performed conservative treatment, 6 patients healed well and 3 patients with fracture line less than 1 cm on horizontally view occurred fracture nonunion. Four patients with type II did not perform operation, and fracture were not union, regardless of fracture size.

Occult anterior calcaneal process fracture have high rate of missed diagnosis in clinical practice. CT imaging features of fracture showed that most fracture line were transverse on CT horizontal plane while vertical on CT sagittal plane, as well as small side of fragment on CT sagittal plane with differernt sizes of fragment on CT horizontal plane; type Ifracture with fragment less than 1 cm on CT horizontal plane and type II both have high rate of nonunion while treated with conservative treatment.