Chapter 17: Pelvis

Introduction

Pelvic fractures represent 3% of all skeletal fractures and are exceeded only by skull fractures in their associated complications and mortality.¹ Pelvic fractures range from low-energy stable fractures to high-energy unstable injuries, associated with abdominal injuries, need for major blood transfusion, and even death.² The mortality rate for high-energy pelvic fractures ranges from 10% to 20%, but in hemodynamically unstable patients or after open fractures, it increases to 50%.^3,4 Motor vehicle collisions account for approximately two-thirds of all pelvic fractures. Pedestrians struck by automobiles are responsible for 15% of cases. Crush injuries, motorcycle crashes, and falls each account for an additional 5%.⁵

Pubic rami fractures are the most common pelvic fractures with the superior ramus more frequently involved than the inferior ramus. Pubic rami fractures account for over 70% of all pelvic fractures.⁶ The incidence of fractures of the remaining pelvic bones in descending order is the ilium, ischium, and acetabulum. Sacroiliac (SI) fractures are associated with the most significant bleeding. Both the mechanism of injury and the fracture pattern identified on imaging studies are important in predicting associated injuries.

Essential Anatomy

In humans, the pelvic ring serves two important functions: weight support (stability) and protection of the viscera. There are essentially three bones that combine to form the pelvic ring: two innominate bones (composed of the ischium, ilium, and pubis) and the sacrum (Fig. 17–1). The coccyx is a fourth bone, but it is not incorporated into the pelvic ring. The two innominate bones and the sacrum are united by the formation of three joints (the symphysis pubis and the two SI joints). The ligaments that form the pelvic ring are the strongest in the body.

Weight bearing is transmitted through the bony pelvis along two pathways (Fig. 17–2). When standing, weight is transmitted through the spine to the sacrum, SI joints, and along the arcuate line to the superior dome of the acetabulum and down the femur. In the sitting position, the force is transmitted down the spine to the sacrum and the SI joints and to the ischium by way of the inferior ramus. The bone is very strong in these areas and the anteroposterior (AP) radiograph of the pelvis clearly demonstrates the thick trabecular pattern along these lines of stress. As a result, pelvic fractures more commonly interrupt the ring in areas not involved in weight transmission. A greater force is required to fracture a “weight-bearing” area of the pelvis. In addition, fractures involving the weight-bearing arches are associated with much more pain when stressed than those fractures that do not involve these arches. A good example is the superior ramus fracture. Because this structure is a nonweight-supporting area, it is ...