Figure 3c.  Vertical displacement sign. (a) Left lateral chest radiograph (magnified view) shows one pair of ribs projecting at the horizontal level (H). In the inferior pair of ribs (I), the posterior rib (arrow) is slightly lower than the anterior rib. In contrast, in the cranial rib pair (S), the posterior rib (arrowhead) is higher than the anterior rib. Thus, the posterior ribs are farther from the film and are on the right. (b) Left lateral chest radiograph (magnified view) obtained at a slightly different angle shows the upper anterior rib (arrowhead) cephalad and the lower anterior rib (arrow) caudad to the posterior ribs (ie, the anterior ribs are on the right). (c) Left lateral chest radiograph (magnified view) demonstrates how the vertical displacement sign is usually applicable even when the posterior ribs are partially superimposed. The higher rib (arrowhead) and lower rib (arrow) could be identified even when they overlapped.