Review Question - QID 7616

Fractures of the calcaneus occur as a result of shear and compression forces. Foot position at the time of impact, the force of the impact, and bone quality all dictate the degree of comminution and fracture line orientation. Two primary fracture lines are consistently observed, one of which divides the calcaneus into medial and lateral portions. An essential feature of this fracture line is that it creates a fragment (sustentaculum tali) that remains attached to the talus by the interosseous ligament. This medial portion (constant fragment) of the posterior facet retains its normal anatomic position beneath the posterior talus. Its corresponding lateral component (labeled with an * in the figure), however, can be found displaced inferiorly within the body of the calcaneus. It is often rotated 90 degrees (as depicted in Figure 28) in relation to the remainder of the subtalar joint. This gives the appearance of what has been described as the "double-density" sign. The middle facet is more anterior and less commonly displaced. The lateral wall is nonarticular.