Anteroposterior (AP) radiograph of the pelvis (Fig. 51A) demonstrates disruption of the pubic symphysis with marked superior displacement of the left pubis and mild widening of the left sacroiliac (SI) joint. A vertically oriented fracture through the left medial/posterior iliac wing adjacent to the SI joint is present; the lateral iliac wing fragment is superiorly displaced. Coronal CT image through the femoral heads (Fig. 51B) reveals a near sagittal plane fracture through the medial posterior ilium with superior displacement of the lateral iliac wing fragment (arrow). Involvement of the inferior left sacrum was also present, only indicated on this image by the small osseous fragment inferior and medial to the left SI joint. Note the relatively superior position of the left inferior pubic ramus compared with the right inferior pubic ramus.

Vertical shear injury, AP compression fracture, isolated pubic ramus fracture.

Pelvic fractures can be classified by mechanism of injury on the basis of how they disrupt the anterior arch (pubic rami) and posterior arch (sacrum, SI joints, and posterior ileum) of the pelvis. The mechanism of injury may be a pure form, such as lateral compression, AP compression, or vertical shear, or have a combined mechanism. Vertical shear injury of the pelvis represents the most severe type of pelvic injury and may involve joint dislocations as well as fractures. A vertical shear injury occurs with disruption of both the anterior and the posterior arch, resulting in a disconnected hemipelvis. This is an unstable fracture, characterized by loss of both vertical and rotational stability of the pelvic ring; weight bearing on an unstable fracture will result in progressive displacement and may manifest as limb shortening on the affected side. Vertical shear injuries may be purely ligamentous, resulting in disruption of the pubic symphysis and one of the SI joints, or purely osseous, resulting in superior and inferior pubic ramus fractures along with either a posterior ilium or sacral ala fracture, or a combination of the two. When a fracture of the posterior ilium is involved, this form of injury has been referred to as a Malgaigne fracture. The mechanism of injury of a Malgaigne fracture is often high-energy axial loading, such as from falls or other high-energy trauma.