Pelvic Shear Fractures

Hema N. Choudur, Anthony G. Ryan, and Peter L. Munk

A young man who fell from a three-story building was brought to the radiology department on a stretcher, unable to move.

Figure 83A

Figure 83B

Pelvic shear fracture type 3.

None.

Fractures of the pelvis account for 3% of all fractures. The classification of these fractures is based on the direction of the vector and the degree of disruption resulting from applied force. These fractures are classified as lateral compression, AP compression, vertical shear, and combined mechanical injury.

These injuries occur as a result of road traffic accidents or falls from a height. A high-impact vector directs the type of injury.

The major types of fractures are due to the following:

1. External rotation resulting in an open-book type of fracture: the pubic symphysis is diastased due to an externally rotating force acting on the femora and anterosuperior iliac spines. The anterior SI joint ligaments may be severed, but not the posterior. The force may also be applied to the posterosuperior iliac spines.
   
2. Vertical shear force acting perpendicular to the posterior pelvis may cause anterior and posterior pelvic fractures in addition to soft-tissue injury (bladder, urethra, etc).
   
3. A lateral compression force causes an internal rotation of the hemipelvis, resulting in fractures of the pubic rami and SI joint on the same side of the sacrum. Sometimes, an impaction can occur at the sites of the fracture and at the SI joints.
   
4. Complex injury may result from a combination of all of the above.