Pelvic fractures from blunt force trauma are broadly categorized as either “stable” or “unstable” based on the status of the pelvic ring. The pelvis is composed of three bones (the iliopubic bones and the sacrum), which are held together by strong ligaments: the symphysis pubis anteriorly and the anterior and posterior iliosacral ligament posterolaterally. A pelvic fracture is generally considered unstable if the ring is broken in two or more places.

The unstable pelvic fracture is sometimes identified during the secondary survey, when the pelvis is noted to “move” during either anteroposterior or lateral compression on physical examination. More commonly, today it is detected on plain radiograph or abdominal computed tomography (CT). However an unstable pelvic fracture is identified, once the diagnosis has been made, all further manual manipulation (i.e., “rocking the pelvis”) must cease. Although it is tempting to use an unstable pelvic exam as a prime teaching point, the unstable pelvis should not be manipulated. Each time the damaged joint is moved, the clot may be disrupted, resulting in additional bleeding from the torn veins and bony surfaces. Consumption coagulopathy may occur as coagulation factors are used for new clot formation.

Unstable pelvic fractures include disruption of the ring anteriorly at the symphysis pubis or through a pubic bone and are broadly categorized into three types: anterior-posterior (open-book) fracture, lateral compression fracture, and vertical shear (Malgaigne) fracture.