Epidemiology

Fractures of the bony pelvis account for 3% of all fractures; however, the overall mortality from pelvic ring injuries is 10% to 15%. Motor vehicle collisions (MVCs) involving cars or cars and pedestrians cause approximately 60% of pelvic fractures.¹ Side-impact car collisions more commonly cause pelvic fractures than do head-on car collisions.² Falls and motorcycle accidents are also significant causes of pelvic ring injuries.

The blood supply and innervation of the pelvic organs and lower extremities are intimately linked to the pelvic architecture. Major disruptions lead to life-threatening blood loss, damage to urogenital organs, and neurologic deficits. The emergency physician (EP) must identify patients at risk for pelvic ring disruption and aggressively work to control bleeding.

Pathophysiology

The pelvis provides support for upright mobility by connecting the spine to the lower extremities. When viewed as a whole, the pelvis contains a major ring and two inferior rings. The triangular sacrum and two innominate bones form the major pelvic ring (Fig. 81.1). The sacrum is a fusion of the five sacral vertebrae and distributes the weight of the upper part of the body to the innominate bones. The sacrum also conducts the sacral nerve roots to the pelvic organs. Each innominate bone is a fusion of the ilium, ischium, and pubic bones. the intersection of the fusion forms the acetabulum, which articulates with the femur. Posteriorly, the innominate bones are anchored to the sacrum by the anterior and posterior iliac ligaments, two of the body’s strongest ligaments. The sacrotuberous and sacrospinous ligaments attach the sacrum to the ischial tuberosity and the ischial spines bilaterally, thus further reinforcing the posterior arch of the pelvic ring.

Fig. 81.1 Bony pelvis.

A, Anteroposterior view. B, Innominate bone (lateral view).

Anteriorly, the innominate bones are anchored to each other at the cartilaginous pubic symphysis. Because the innominates and sacrum are dense bone anchored together with equally dense connective tissue, disruption of the architecture of the major pelvic ring requires tremendous force and usually results in bony fractures or ligamentous disruptions at two or more sites in the ring. The inferior rings are formed by the pubic and ischial rami. They serve as attachments for muscles of the thighs and do not bear weight from the upper part of the body. Low-force mechanisms such as straddle injuries and falls onto the buttocks can fracture the rings, usually an isolated pubic ramus.

The left and right internal iliac arteries course in the region of the sacroiliac joints; they branch and form a network of vessels in the posterior pelvic arch. Posteriorly, the superior gluteal artery is commonly injured. Throughout the pelvis, arteries and veins are easily injured during the impact that causes the pelvic fracture, and blood collects in the retroperitoneal space.

Lateral compression, caused by injuries involving the side, crushes the pelvis inward; therefore, massive pelvic bleeding is uncommon with these types of injury. Sacral crush fractures and horizontal pubic ramus fractures can be diagnosed radiographically. Sacroiliac diastasis may also occur.

Anteroposterior compression forces cause the iliac wings to rotate outward, as when a pedestrian is struck directly anteriorly or posteriorly by a car. The fractures are unstable and pelvic volume increases, which allows massive retroperitoneal venous or arterial pelvic bleeding to occur. Diastasis of the anterior pelvic ring may be evident and is often termed an open book pelvic fracture. The posterior ligaments (as a guiding principle) can withstand about 2.5 cm of symphyseal diastasis before the sacral ligaments are disrupted. Associated acetabular fractures are commonly present in about half of cases.

Vertical shear injuries are less common and result from axial force through the legs or spine to the pelvis. The anterior and posterior rings are both disrupted. As the hemipelvis is forcibly sheared, pelvic volume increases, which results in massive bleeding.

Several classification schemes involving the direction of force applied to the pelvis, the bones injured, the degree of instability of the ring, and any associated injuries are used for pelvic ring disruptions. Fracture stability and increases in pelvic volume determine the magnitude of blood loss and potential mortality. See Box 81.1.