The pubic symphysis, which is the weakest portion of the pelvic ring, is stabilized by the superior and inferior pubic ligaments.

The posterior arch is stabilized by the anterior and posterior interosseous SI ligaments. The anterior SI ligaments resist internal rotation, while the stronger posterior SI ligaments resist external rotation and vertical displacement.

Associated injuries may be caused by primary impact, osseous fragments, or secondary to shear forces, and include vascular disruption, hemorrhage, urogenital injury, lumbosacral plexus disruption, and long bone fracture.

As in other complex fracture scenarios, understanding the mechanism of injury can refine the search for additional injuries. Analogous to injury of other ring structures such as the mandible, fracture in one portion of the pelvic ring should prompt a search for fracture or ligamentous injury in a second location.

The inlet view is useful for characterizing anterior–posterior fracture displacement, while the outlet view is useful for identifying vertical displacement.

CT or CT cystography is useful for evaluation of the pelvic organs in severe trauma, and for further evaluation of pelvic fractures identified by radiography.

In the emergency setting, pelvic MRI image can be abbreviated to coronal STIR and coronal T1-weighted imaging. These limited sequences have high sensitivity for fracture, avascular necrosis of femoral head, and soft tissue injury. MRI should be considered when radiographically occult or insufficiency-type fractures are suspected.

APC injury results from head-on motor vehicle collisions where the force vector is directed in the anterior to posterior direction in the sagittal plane. This force causes external rotation at one or both SI joints, resulting in open-book type injury. Injury may be unilateral or bilateral. An associated finding is broadening of the iliac wing on the AP view. A summary of the features of APC injuries by grade is presented in the table below.