Intra-articular fractures of the calcaneum. Part I: Pathological anatomy and classification.

We have studied the radiographic and CT features of 120 displaced intra-articular fractures of the calcaneum in order to define the pathological anatomy. In 96% of cases, the CT scans identified three main fragments: sustentacular, lateral joint and body. The sustentacular fragment was often rotated into varus, the lateral joint fragment into valgus and the body fragment impacted upwards, in varus and displaced laterally. The displacement of these fragments varied according to which of three fracture types was present, as defined by the composition of the fractured lateral wall of the calcaneum. In type 1 it was formed by the lateral joint fragment alone; in type 2 by both body and lateral joint fragments; and in type 3 by the body fragment alone. Fracture fragment displacement differs from that previously described, in that true uniform depression of the lateral joint fragment is rare.