ANATOMY

The pelvic ring is comprised of three bones: the sacrum and the two innominate bones. There is no intrinsic bony stability to the ring itself. Integrity is maintained by a series of strong ligamentous complexes and the soft tissue envelope (Figure 1). Anatomic alignment is maintained primarily by a series of posterior ligaments. The strongest of these, the interosseous ligaments, connect the tuberosities of the ilium and sacrum. The posterior sacroiliac ligaments connect the superior and inferior posterior spines of the ilium to the lateral aspect of sacrum. Similarly, the anterior sacroiliac ligaments run from the anterior surface of the sacrum obliquely to the anterior surface of the ilium. The connecting ligaments are the sacrotuberous, which runs from the dorsum of the sacrum and posterior iliac spines to the ischial tuberosity; the sacrospinous, which courses from the lateral sacrum to the ischial spine; and the iliolumbar ligaments, which run from the transverse process of L5 to the iliac crest. This group of ligaments maintains the relationship between the sacrum and the sciatic buttress, which is the body’s primary weight bearing axis. Under anatomic conditions, there is only microscopic motion at the sacroiliac joint.

Figure 1 The bony pelvis and its major posterior ligaments. (A) Posterior view. (B) Anterior view.

(From Tile M, editor: Fractures of the Pelvis and Acetabulum, 3rd ed. Baltimore, Williams and Wilkins, 2003.)

The paired innominate bones meet anteriorly at the pubic symphysis, which is comprised of a hyaline cartilage interface reinforced by overlying fibrocartilage. The ligaments of pubic symphysis blend with the fibrocartilage to support the articulation superiorly and inferiorly. The anterior ring does not play an integral role in weight bearing but instead acts like a strut to maintain the posterior tension band.¹

RADIOLOGY

A single anteroposterior (AP) radiograph of the pelvis provides valuable information about the unstable pelvic ring injuries. The anterior injury is readily apparent, and displaced/unstable posterior injuries should be apparent. Once the diagnosis of pelvic ring injury has been made, further imaging should include inlet and outlet views of the pelvis. These are obtained with the patient supine. The x-ray beam is then tilted approximately 45 degrees cephalad for the inlet view. This view elucidates displacement in the AP plane as well as rotation. The outlet view is obtained with the x-ray beam tilted 45 degrees caudad, and provides information regarding vertical displacement. Laboratory studies have demonstrated that static plain radiographs underestimate the injury displacement by 80%. CT scans provide additional valuable information regarding soft tissue injury and foraminal encroachment (Figures 2 and 3).²

Figure 2 The inlet pelvic view. (A) Patient positioning. (B) Radiographic appearance.

(From Kellam JF, Browner BD: Fractures of the pelvic ring. In Browner BD, et al., editors: Skeletal Trauma. Philadelphia, WB Saunders, 1992, pp. 849–897.)

Figure 3 The outlet pelvic view. (A) Patient positioning. (B) Radiographic appearance.

(From Kellam JF, Browner BD: Fractures of the pelvic ring. In Browner BD, et al., editors: Skeletal Trauma. Philadelphia, WB Saunders, 1992, pp. 849–897.)

CLASSIFICATION

Multiple classification systems have been described in an attempt to clarify mechanisms of injury, as well as predict treatment algorithms and outcomes. The Young and Burgess classification system is based on previous systems that divided pelvic injuries by the force vector (Figure 4). Injuries are grouped into lateral compression (LC), AP compression (APC), vertical shear (VS), and combined mechanical (CM) injuries. The Young system further subdivides LC and APC injuries by degree of force with increasing grade of injury correlating with an extension of the original vector to greater forces. For example, an APC-I injury describes symphyseal widening without widening of the sacroiliac joints, while an APC-III injury involves a complete hemipelvis disruption with complete injury to the symphysis as well as disruption of both the anterior and posterior sacroiliac ligaments (Table 1).³

Figure 4 A diagrammatic depiction of the Young and Burgess classification system.

(From Baumgaertner MR, Tornetta P, editors: Orthopaedic Knowledge Update: Trauma 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2005, pp. 236–238, with permission.)

Table 1 Pelvic Ring Fracture Classification System

APC, Anteroposterior compression; CM, combined mechanical; LC, lateral compression; VS, vertical shear.

Adapted from Burgess AR, Eastridge BJ, Young JW, et al: Pelvic ring disruptions: effective classification system and treatment protocols. J Trauma 30(7):848–856, 1990.

This classification system has two major strengths. First, there is a reproducible association among the fracture classification, associated injuries, and mortality. Acute management and evaluation of the unstable patient may be guided by injury pattern. In addition, identification of the nature of the anterior ring lesion guides diagnosis of subtle posterior injuries often missed on screening imaging studies.⁴

ACUTE PATIENT MANAGEMENT

The initial evaluation of any trauma patient follows ATLS protocols. After completion of the primary survey examination proceeds to include plain radiographs of the chest and pelvis. The hemodynamic and respiratory status will direct further interventions. If possible, the injury mechanisms should be considered, as this will provide valuable insight into the nature and severity of the pelvic ring disruptions.

Initial examination must include assessment for open fractures. Despite advances in treatment and diagnosis, open pelvic fractures confer markedly increased risk for sepsis and overall mortality. A gentle but thorough rectal exam, careful inspection of perineum, and in the female patient, a vaginal exam, are critical to a complete initial evaluation.

Unstable anterior pelvic fractures are commonly associated with genitourinary injury particularly in male patients. Blood at the urethral meatus may signify a urologic injury including urethral tear or bladder rupture. Inability to pass a Foley catheter easily should prompt a retrograde urethragram and consultation of a urologic surgeon.

A complete neurologic examination of the lower extremities with documentation of sensation and muscle grading is another critical component of the evaluation. Neurologic injuries increase in frequency and severity with increasing instability of the pelvic fracture. The nature of the nerve injury may help dictate the appropriate surgical intervention, as well as provide useful prognostic information.

HEMODYNAMIC INSTABILITY

In the acute setting, the pelvic ring injury may be source of significant hemorrhage; however, biomechanically unstable pelvic ring injuries do not necessarily result in a hemodynamic compromise. Patients with pelvic ring injuries can be divided into two broad groups based on hemodynamic stability. While overall mortality rates for pelvic ring fractures are reported as 13%, the mortality rate among patients who present with a systolic blood pressure less than 90 mm Hg is as high as 52% in some series. Determining whether the pelvis is a contributor to a patient’s hemodynamic status can be problematic.

Persistent hemodynamic instability should raise concern for arterial bleeding; however, this is uncommonly the source of blood loss in patients with pelvic fractures (approximately 15%). Large-volume hemorrhage from low-pressure sources, such as the pelvic venous plexus and cancellous bone, commonly accounts for the massive blood loss seen in unstable patients. The pelvic ring injury creates a disruption of the boundaries of the retroperitoneal space allowing for massive extravasation. Despite large-volume blood loss, the unconfined space is often inadequate to generate tamponade. Further manipulation through patient transfer and physical exam in the trauma bay contributes to clot disruption and further extravasation.

MODALITIES FOR INITIAL TREATMENT

Early interventions for management of pelvic hemorrhage have been the subject of extensive debate and study. Options include angiography/embolization, laparotomy with pelvic packing, and stabilization of pelvic fractures. The keys to early management are prompt recognition of the pelvis as the source of hemorrhage and rapid implementation of an institution specific protocol for systematic stepwise intervention (Figure 5). Each intervention may have a role depending on the nature of the injury and the availability of qualified personnel.⁵

Figure 5 Acute management algorithm for unstable pelvic fractures.

(From Baumgaertner MR, Tornetta P, editors: Orthopaedic Knowledge Update: Trauma 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2005, pp. 236–238, with permission.)

TREATMENT AND OUTCOMES

Definitive reconstruction of unstable pelvic ring injuries is pursued once the acute inflammatory and resuscitation period has concluded. Stabilization of the ring allows early patient mobilization, improved pulmonary toilet, and decreased long-term morbidity. Many posterior ring injuries may be stabilized with percutaneous screw fixation following open or closed reduction. This avoids prominent hardware and decreases the risk of infection and soft tissue complication. The anterior injury pattern will dictate the need for and the type of operative stabilization. Anatomic restoration of the posterior ring injury is most critical for avoiding sitting imbalance and leg length discrepancy. In modern series, the majority of patients with anatomic fracture reductions maintained to union are able to return to their preinjury occupation, perform all activities of daily living, and walk without assistive devices. The minority of patients with good reductions who have suboptimal outcomes have one of several complications related to their initial injury complex.

The most significant factor in a patient’s overall outcome score is the severity of the initial neurologic injury. Partial and complete injuries to the lumbosacral plexus result in muscle weakness, sensory deficits, and neurogenic pain. Reduction of the bony injury will not improve the neurologic prognosis. A large percentage of patients with significant nerve injury will not return to their preinjury occupation or functional status.

Genitourinary complications are a common complaint amongst patients with unstable pelvic fractures. Injuries to the urethra and perineum result in long-term complications such as stricture, incontinence, and erectile dysfunction. Female patients commonly develop incontinence and dyspareuenia. There is also an increased rate of cesarean section in female patients following pelvic injury.

Studies of overall outcomes in patients with pelvic fractures have documented small but significant impacts on mental and physical well-being over the long term. Although the vast majority of patients are able to return to work and ambulation, the residual effects of these devastating injuries continue to impact day-to-day life.⁷

SUMMARY

Unstable pelvic ring injuries are a relatively common problem in the trauma population. A multidisciplinary approach to initial management is effective at reducing both morbidity and mortality. Every institution should establish a specific pathway for the management of hemodynamic instability based on the availability of qualified personnel and facilities. Prompt recognition of the pelvic injury and its associated complications will guide appropriate therapeutic interventions.