Acute Osseous Injury to the Pelvis and Acetabulum

Prevalence, Epidemiology, and Definitions

The prognosis of a pelvic fracture depends on the severity of trauma, the stability of the injury, the adequacy of treatment, and the occurrence of complications, such as neural damage, urethral tear, or nonunion. Communication between the fracture site and the skin perineum or pelvic contents implies an open fracture, which connotes a significantly worse prognosis.

The incidence of pelvic fractures is difficult to assess but has been reported as high as 20 to 37 per 100,000. During past decades the incidence of pelvic fractures has increased because of the high rates of high-speed motor vehicle accidents and falls from heights. Two thirds of pelvic fractures occur in patients with multiple trauma. Classification systems of pelvic fractures are based on analysis of force vectors and degree of instability. Proper categorization of pelvic fractures based on these classification systems is often done using MDCT. These classification systems provide a logical approach to the multidisciplinary management of pelvic ring disruption, allowing early and appropriate treatment.

The mortality of major pelvic fracture, despite improvements in management, continues to be 10% to 20%. Open fractures have higher mortality, which may reach 50%. Morbidity and mortality mainly result from associated injuries, especially to the head, and/or from massive pelvic bleeding. Decreasing the mortality rates requires early diagnosis and aggressive treatment. Long-term complications such as nonunion, malunion, limb-length discrepancy, and low back pain result from up to 52% of fractures through the sacrum or sacroiliac joint.

Anatomy

The pelvis is composed of two innominate bones and the sacrum. The innominate bones are formed by joining of three ossification centers that form the ilium, the ischium, and the pubic bones. These are fused at the level of the acetabulum. The sacrum articulates posteriorly with the ilium through the sacroiliac joint and anteriorly with the pubis at the pubic symphysis.

The pelvic ring has no inherent stability. Stability of the pelvic ring depends on soft tissues around the pelvis. Key structures are interosseous ligaments that run between the ilium and the sacrum posteriorly and between the pubic symphysis and anterior abdominal wall anteriorly. The extremely strong posterior sacroiliac ligaments maintain the normal position of the sacrum in the pelvic ring, and the entire complex has the appearance of a suspension bridge. They can be divided into transversal and vertically oriented. Transversal ligaments include short posterior and anterior sacroiliac ligaments, iliolumbar ligament, and sacrospinous ligament, which form a tension band. Vertically oriented ligaments include long posterior sacroiliac ligaments and sacrotuberous and lateral lumbosacral ligaments. These ligaments also contribute to the pelvic floor.

Deep pelvic anatomy includes extraperitoneal organs such as rectum, bladder, urethra, uterus, vagina, and intraperitoneal intestinal structures. The two more important injuries related to pelvic trauma are direct vascular injury with hemorrhage and urologic injury (bladder or urethra). The pelvis is extremely well vascularized, with the majority of blood supply arising from the hypogastric artery. The superior gluteal artery is the most commonly injured vessel in posterior wall fractures, whereas injury to the obturator and internal pudendal arteries is related to pubic rami fractures. Nerve supply from the lumbar and sacral plexus is close to the posterior structures.

Biomechanics

The pelvic skeleton is a weight-bearing structure that transmits forces from the lumbar spine to the lower extremity. In addition, the pelvic ring serves as a protector of internal pelvic organs. The osseous pelvis acts like a ring unit. Stability depends on the anatomic structures, bones and ligaments, resisting vertical and rotational forces, depending on their orientation. Transversely oriented ligaments resist rotational instability, whereas vertically oriented ligaments oppose vertical displacement.

Pelvic muscles, rectus abdominis and its fascia, abdominal obliques, obturators, and adductors also contribute to ring stability.

The anatomy of the pelvis is such that stresses placed on it by abnormal motion at any of three joints, sacroiliac or pubis, causes instability and leads to a second fracture in other structures of the pelvic ring. The loss of bone continuity or one of the joints of the pelvic arch changes the transmission of forces, increasing loads over other pelvic structures. Therefore, if the pelvic ring becomes broken in one area and the fragments become displaced, then there must be a fracture or dislocation in another portion of the ring. The orientation of the fractures and direction of displacement provide a clue to the mechanism of injury.

The major forces acting on a hemipelvis are external, internal rotation (compression), and vertical shear ( Fig. 20-1 ). In some complex high-energy injuries, the forces may defy detailed description. External rotation is caused by a direct blow on the posterior iliac spines or more commonly by forced external rotation of the legs and produces an open-book type of injury. This is characterized by disruption of the symphysis pubis and, as the force continues, by rupture of the anterior sacroiliac and sacrospinous ligaments. An end point is reached when the posterior ilium abuts against the sacrum; however, if the force continues, the hemipelvis may be sheared off, resulting in gross instability.

Internal rotation (lateral compression) may be caused by a direct blow on the lateral aspect of the iliac crest or an indirect force through the femoral head. This produces compression fractures of the posterior complex and fractures of the rami anteriorly (see Fig. 20-1 ). The posterior and anterior lesions may either be on the same side of the pelvis (ipsilateral type) or on the opposite side (bucket-handle type). This latter type is associated with major rotational deformities and may result in malunion. In some instances, a lateral compression force may stop short of rupture of the posterior structures, but in others, rupture will occur.

Imaging Techniques

Conventional radiography is the first test, after clinical assessment, for the diagnosis of pelvic fractures. Although recently under debate, anteroposterior pelvic radiography is usually included in the protocol for all multiple trauma patients once the patient's condition is stabilized. Pelvic radiography has a role in the initial trauma series in patients in whom there is a clinical suspicion of severe pelvic injury and who are hemodynamically unstable or unconscious. A portable pelvic film might help distinguish which patients need immediate external fixation, may be bleeding from a complex pelvic fracture, or might benefit from further radiographic evaluation. In hemodynamically stable patients, screening with anteroposterior radiography is debated because of the availability of cross-sectional imaging methods, especially MDCT, and the poor imaging quality of standard radiographs in a high percentage of these patients. Pelvic ring fractures are uncommon in children. In the pediatric trauma patient, routine screening radiography of the pelvis is unnecessary and is not recommended, owing to the low yield in combination with high radiation exposure.

Radiography

Anteroposterior Radiographs of the Pelvis

Analysis of the anteroposterior radiographs of the pelvis determines the mechanism of pelvic ring injury, and appropriate therapeutic approaches can be started. Additional radiographic views have allowed more precise classification but currently have been mainly replaced by CT.

Anteroposterior films should be done following a rational protocol: From inside to outside, all pelvic lines must be smooth, continuous, and symmetric. Pubic rami fractures, symphysis diastasis, dislocation or fracture-dislocation of sacroiliac joint, sacrum fractures, and iliac fractures must be ruled out.

Pubic symphysis distance should not be more than 1 cm. Diastasis of the pubis is considered when the distance is greater than 2.5 cm. The pubic rami should be at the same level when they join the symphysis; overlapping of the pubic bones is related to injuries. The lower margins of the rami are a better guide because nonalignment of the upper margins may be a normal variation. The orientation of pubic rami fractures provides a clue to the mechanism of injury. Horizontal overlapping fractures of the superior and inferior pubic rami are associated with lateral compression. Vertical fractures of the rami without cranial displacement of the hemipelvis can be seen in anteroposterior compression injuries instead of pubic symphyseal diastasis ( Fig. 20-2 ). Vertical rami fractures with cranial displacement are a hallmark of vertical shear injuries ( Fig. 20-3 ).

The normal sacroiliac joint space is 2 to 4 mm wide. When the joint is analyzed for diastasis, the anterior and posterior aspects should be examined. Disruption of the sacroiliac joint with external rotation of the ipsilateral hemipelvis is characteristic of anteroposterior compression. If only the anterior sacroiliac joint is widened, the posterior ligaments are intact and preserving vertical stability. If the sacroiliac joint is anteriorly and posteriorly diastatic, the pelvis is completely unstable. Usually, the sacroiliac joint is completely disrupted in vertical shear injuries. Displaced vertical fractures through the sacrum or the iliac wing adjacent to the sacroiliac joint have the same implication as sacroiliac joint diastasis.

Buckle (anterior crush) fractures of the sacrum are the hallmark of lateral compression injuries. The fractures are usually oriented vertically. They may be isolated to the sacral ala, pass through the neural foramina, or extend centrally into the sacral spinal canal. Radiographic findings of the fractures may be subtle ( Fig. 20-4 ). The sacral promontory and arcuate foramina should be carefully examined for cortical disruption. Displaced vertical fractures through the sacrum can be seen in lieu of sacroiliac joint disruption in anteroposterior compression and vertical shear injuries. Horizontal fractures of the sacrum below the level of S2 do not affect the integrity of the pelvic ring.

The iliolumbar ligament is inserted at the tip of the L5 transverse process. An avulsion fracture at this site is associated with disruption of the posterior sacroiliac ligament complex, as seen in severe anteroposterior compression and vertical shear injuries. Hence, an L5 transverse-process avulsion fracture may indicate complete pelvic instability (see Fig. 20-4 ).

Inlet Radiographs of the Pelvis

Inlet radiographs are obtained with the patient in the supine position, with the X-ray tube positioned at the patient's head and angled 45 degrees toward the feet. The x-ray beam is perpendicular to the pelvic rim. The inlet view of the pelvis permits more accurate determination of the following: the degree of posterior displacement at the sacroiliac joint, the degree of internal or external rotation of the hemipelvis, the degree of pubic diastasis or overlap, and the presence of subtle sacral fractures.

Outlet Radiographs of the Pelvis

Outlet radiographs are obtained with the patient in the supine position, with the x-ray tube positioned at the patient's feet and angled 45 degrees toward the head. The X-ray beam is perpendicular to the sacrum. The primary purpose of the outlet view of the pelvis is to demonstrate the magnitude of vertical (cranial) displacement of the hemipelvis. In addition, some sacral and pubic rami fractures are better visualized with the outlet view than with other views. The sacral neural foramina are especially well depicted by using the outlet view.

Lateral Projection

Lateral cross-table radiographs should include the acetabulum, the ischial tuberosity, and the proximal femur. Transverse fractures of the sacrum and coccyx are best depicted. This projection also helps define dislocations of the hip posteriorly or anteriorly, which are frequently associated with acetabular fragments that are usually displaced in the same direction.

Computed Tomography

Computed tomography is widely recognized as an important adjunct to plain films in the evaluation of patients with acute pelvic trauma. In one third of patients, it provides additional information and can change classification. MDCT has improved our ability to image patients with multiple trauma; therefore, in some hospitals it has replaced additional plain film projections (see Fig. 20-4 ). The advantages are higher speed, extended anatomic volume imaging, postprocessing, and enhancement from the intravenous use of a contrast agent. The use of a contrast agent and CT angiography allows evaluation of the aorta and the major pelvic vasculature at the same moment, providing a vascular map. Active hemorrhage can be diagnosed on MDCT on the basis of increased density compared with surrounding tissue, which results from the extravasation of intravascular contrast agent; surgery or angiographic therapy might be indicated ( Fig. 20-5 ).

Postprocessing imaging tools with multiplanar and volume-rendering reconstructions give important information in transversally oriented fractures and in complex injuries about the relationship between the fragments and adjacent structures. MDCT has also replaced cystography.

If bladder rupture is suspected, CT cystography is indicated ( Fig. 20-6 ).

Angiography

Significant pelvic arterial injuries occur in a minority of patients with multiple high-energy injuries regardless of the fracture type, ranging from 2.5% to 10% and up to 20% in hemodynamic compromise in unstable patients. Angiography is used to diagnose and treat potentially life-threatening hemorrhage secondary to pelvic ring injury. Angiography is better than CT angiography for depicting an injury to small vessels. Pelvic angiography with transcatheter embolization has been proved to be faster, less invasive, and more successful than open surgical procedures in controlling pelvic hemorrhage, but it still remains a controversial topic ( Fig. 20-7 ; see Fig. 20-4 ).

Manifestations of the Disease

Pelvic ring fractures occur as a result of high-energy trauma. Recognition of the pattern of injury helps to diagnose associated injuries ( Table 20-1 ; see Video 20-1 ). Open fractures have higher mortality rates, with an increased risk of complications, infection, and high frequency of visceral organ lesions. Clinical skin hemorrhages and vaginal, rectal, or genitourinary bleeding must be ruled out because of the high frequency of intrapelvic hemorrhage associated with this fracture. Anteroposterior compression and vertical shear injuries have a higher incidence of pelvic vascular injury and hemorrhage. Tenderness in the parasymphyseal area, pubic rami, ileus, or sacrum is a sign often reflecting the presence of fractures. Peripheral nerve and vascular injuries are directly attributable to pelvic ring fractures. Comparative arterial palpation of the lower limbs must be done from the femoral vessels down to the dorsal foot artery to exclude vascular lesions. A complete neurologic examination to rule out nerve root injuries, from L5 through the lower sacral roots, is indicated. Fractures of sacrum or sacroiliac joint can damage adjacent sacral plexus or sacral nerve roots. Fractures extending into the region of the greater sciatic notch may damage the sciatic nerve.

Confusion in the pelvic ring classification system is due to a wide variety of classifications.

Terms such as Malgaigne, open book, or straddle fractures are in disuse. Open book fractures consist of diastasis of the symphysis pubis and external rotation of one or both iliac bones hinging at the sacroiliac joint. A Malgaigne fracture is defined as a pelvic fracture of both pubic rami plus a posterior fracture of the sacroiliac complex. Straddle fractures consist of isolated fractures of the four pubic rami.

The most common systems of classification have divided pelvic fracture as either stable or unstable, depending on the radiologic appearance and the physical findings. Stable fractures include single pelvic ring fractures and pure acetabular, pubic rami, and avulsion fractures. Unstable fractures are those in which the pelvic ring is disrupted in more than one location, particularly if the posterior complex is disrupted. The advent of external fixation systems for pelvic fracture created the need to understand the force vectors causing the fracture so that the correct countering forces can be applied to the fixation. The Young-Burgess ( Table 20-2 ) and the Tile ( Table 20-3 ) systems are two major classification schemes that have been developed for describing pelvic ring fractures. Tile initiated a classification system based on the direction of the injuring force. This concept was redefined in the Young-Burgess classification, which provides a logical approach to pelvic ring fractures and the information needed by the surgeon to plan the type of treatment and which corrective forces must be applied. The major patterns of pelvic ring fractures are anteroposterior compression, lateral compression, vertical shear, or combined mechanical injury (see Fig. 20-1 ).

Anteroposterior Compression Injury

The disruptive force is in the sagittal plane and is usually associated with vehicular accidents in blows to the front of the pelvis. Thus, this is the hallmark injury to the pubic diastasis with or without fractures of the pubic rami ( Fig. 20-8 ). Additional forces tend to open the pelvis and one or both hemipelves undergo external rotation, thus hinging and injuring the posterior sacroiliac complex ( Fig. 20-9 ). The location and degree of diastasis are correlated with the magnitude of force imparted to the pelvis and with the amount of resulting instability. Division of the symphysis pubis allows 2.5 cm of diastasis. Further diastasis is achieved if the posterior ligamentous complex is disrupted, leading to instability. Anterior sacroiliac, sacrospinous, and sacrotuberous ligament disruption results in rotational instability (APC type II) ( Fig. 20-10 ; see Fig. 20-9 ). The extension to the posterior sacroiliac ligaments leads to complete instability, both rotational and vertical (APC type III) ( Fig. 20-11 ).

Lateral Compression Injury

The force of the injury is from the side and is associated with horizontally oriented pubic fractures and impacted fractures of the sacrum (see Fig. 20-4 ). Lateral compression (LC) injury results in internal rotation of the affected hemipelvis. This internal rotation decreases rather than increases the pelvic volume. Consequently, pelvic vascular injuries and resulting hemorrhage are less common. The most common injury and the least destructive, LC type I results in an ipsilateral sacral buckle fracture and pubic rami fracture. Sacral bucket fractures are usually vertically oriented and can be isolated to the sacral ala or extend centrally into the sacral spinal canal ( Fig. 20-12 ). If lateral force is increased and is more anterior, internal displacement of the anterior hemipelvis may result and, thus, potentially external rotation of posterior hemipelvis, with the joint acting as a pivot (LC type II) ( Fig. 20-13 ). When the force continues and affects the contralateral hemipelvis, the pelvis becomes severely unstable. The ipsilateral hemipelvis sustains either a type I or type II injury with associated internal rotation, whereas the contralateral pelvis undergoes external rotation (LC type III).

Vertical Shear Injury

This injury results from a fall from height onto the lower limbs. At the anterior aspect, vertically oriented fractures of the pubic rami with cranial displacement are the hallmark of this injury ( Fig. 20-14 ). Posteriorly, the sacroiliac joint is completely disrupted and therefore associated with complete instability (see Fig. 20-3 ).

Complex Injury

Complex or mixed pattern pelvic fractures are due to a combination of fracture forces. The specific findings of each pattern still are present. Pelvic stability can be determined by using the criteria outlined earlier (see Figs. 20-5 and 20-6 ).

The Young-Burgess classification does not include ring-sparing injury, which is included in the Tile classification system, such as avulsion fractures, iliac wing ( Fig. 20-15 ) or sacral fractures that do not involve the sacroiliac joint, or minimally displaced pubic rami fractures (Tile type A).

Synopsis of Treatment Options

Hemodynamic stabilization in patients with unstable pelvic ring fractures must first be achieved. Immediate resuscitation protocols must kick into action in unstable fractures. The key to treatment success is an experienced balanced multidisciplinary team that makes decisions rapidly.

Starting with mechanical measures such as a bandage around the pelvis and knees reduces the pelvis temporarily and controls hemorrhage without major limitations to patient accessibility. Antishock therapy also includes intravenous fluid administration. After completing hemostasis, the choice of orthopedic management will rely on the associated visceral (neurologic, thoracic, or abdominopelvic) or osseous (femoral or acetabular) lesions. Treatment can be divided into provisional and definitive.

Lateral Compression Injuries

In the Young-Burgess LC type II or Tile type B2 injury, in most cases the elastic recoil of the pelvis restores the anatomy to near normal and no form of stabilization is required. In the Tile type B3 (bucket-handle injury), the posterior complex is commonly compressed, rendering the ring stable. It may be impossible to reduce the displacement by closed manipulation under general anesthesia, and in most cases, no stabilization is required. If the leg-length discrepancy is greater than 1.5 cm, or if the pelvic deformity is excessive, more aggressive management may be indicated. Reduction may then be obtained by external rotation of the hemipelvis by pins in the iliac crest ( eFig. 20-1 ). When reduction has been achieved, the anterior frame is completed to hold the necessary external rotation. In the rare case of a “tilt” fracture in which bone is protruding into the perineum, open reduction and internal fixation may be required.

In complex instability fractures, with rotational and vertical instability (Young-Burgess APC type III) and vertical shear fractures (Tile type III) there is a need for definitive fixation with external frames with or without skeletal traction and open reduction with internal fixation.