Orthopedics

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Radiologic Case Study 

Your Diagnosis?

Namit Mahajan, MD; Laurie M. Lomasney, MD; Terrence C. Demos, MD; Hobie Summers, MD; Michael Stover, MD

Abstract

A 25-year-old man presented with hypotension and tachycardia after a motorcycle accident. He had no large external wounds.

Figure: AP radiograph of the pelvis.

For answer click here.

Diastasis of the symphysis pubis with disruption of one or both sacroiliac joints is often referred to as an open-book pelvic fracture that is secondary to an anterior-to-posterior–directed force. An anteroposterior (AP) radiograph of the pelvis showed diastasis of the pubic symphysis >3 cm (Figure 1). In addition, there is a widening of both sacroiliac joints, left greater than right. Axial computed tomography (CT) images of the pelvis confirmed bilateral sacroiliac joint widening and pubic symphysis diastasis (Figure 2). There is asymmetric widening of the sacroiliac joints, with an apparent hinge posteriorly indicating a partial injury of the posterior sacroiliac ligamentous complex. A portion of the posterior sacroiliac joint ligaments is likely intact allowing for external rotation around the posterior joint. These images illustrate a traumatic rotationally unstable pelvic injury.

Figure 1: AP radiograph of the pelvis shows broad diastasis of pubis symphysis. There is asymmetrical widening of sacroiliac joints (left greater than right). Soft tissue gas collections at left perineum and pelvic floor indicate soft tissue disruption, likely with bladder or urethral injury.

Figure 2: Axial CT image shows diastasis of bilateral sacroiliac joints anteriorly with minimal posterior offset on the right.

The pelvis is a ring-like structure that provides critical weight-bearing support for the spine, load transfer to the extremities, and protection of internal organs and structures in the pelvic cavity. Pelvic fractures and dislocations are frequently associated with hemorrhage and injuries to the urinary tract and other viscera. All of these factors contribute to the high morbidity and mortality rates associated with bony pelvic injuries. In multitrauma, managing physicians must have a high index of suspicion for potential pelvic injuries. because findings of pelvic injuries may be subtle on physical examination. Careful examination of the perineum is essential to rule out open injuries. Imaging is critical for timely identification of unstable pelvic injuries to initiate effective medical care.

Unstable pelvic fractures such as the open-book pelvis are often the result of high-energy trauma such as motor vehicle collisions. It is important to understand the mechanism of injury and the structural anatomy of the pelvis in evaluating pelvic trauma.

The two innominate bones and the sacrum provide little if any stability through their articulations. The anterior ligaments around the pubis symphysis provide the dominant anterior stabilizers. The sacroiliac joint consists of an anteroinferior synovial joint and posterosuperior ligamentous portion.1 The vast majority of the structural stability of the posterior pelvis depends on the integrity of the ligaments around the sacroiliac joints. Disruption of these ligaments allows subluxation and dislocation of the sacroiliac joint and essentially dissociation of the axial and ipsilateral appendicular skeleton. The most important ligaments are posterosuperior to the joint and consist of short and long components.1 These ligaments are the strongest ligaments in the body, responsible for transferring axial load to the lateralized extremities.

The majority of pelvic fractures and dislocations can be classified by the mechanism of injury. The principle mechanisms of injury are lateral compression, vertical shear, and anterior compression.1

The most common mechanism is lateral compression. True lateral compression injuries typically result in internal rotation of the hemipelvis. They can be associated with fractures of the sacral ala, iliac wing (with some fractures entering the sacroiliac joint), pubic arch, body of the pubis, and disruption and/or overlap of the pubic symphysis (locked pubic symphysis).1

Vertical shear injuries are due to forces transmitted through the femur to the ipsilateral hemipelvis. Vertical shear often is associated…

The Case:

A 25-year-old man presented with hypotension and tachycardia after a motorcycle accident. He had no large external wounds.

Figure: AP radiograph of the pelvis.

Figure: AP radiograph of the pelvis.

Your Diagnosis?

For answer click here.















Diagnosis:

Traumatic Pelvic Injuries: The Open-Book Pelvis

Diastasis of the symphysis pubis with disruption of one or both sacroiliac joints is often referred to as an open-book pelvic fracture that is secondary to an anterior-to-posterior–directed force. An anteroposterior (AP) radiograph of the pelvis showed diastasis of the pubic symphysis >3 cm (Figure 1). In addition, there is a widening of both sacroiliac joints, left greater than right. Axial computed tomography (CT) images of the pelvis confirmed bilateral sacroiliac joint widening and pubic symphysis diastasis (Figure 2). There is asymmetric widening of the sacroiliac joints, with an apparent hinge posteriorly indicating a partial injury of the posterior sacroiliac ligamentous complex. A portion of the posterior sacroiliac joint ligaments is likely intact allowing for external rotation around the posterior joint. These images illustrate a traumatic rotationally unstable pelvic injury.

Figure 1: AP radiograph of the pelvis shows broad diastasis of pubis symphysis

Figure 1: AP radiograph of the pelvis shows broad diastasis of pubis symphysis. There is asymmetrical widening of sacroiliac joints (left greater than right). Soft tissue gas collections at left perineum and pelvic floor indicate soft tissue disruption, likely with bladder or urethral injury.


Figure 2: Axial CT image shows diastasis of bilateral sacroiliac joints

Figure 2: Axial CT image shows diastasis of bilateral sacroiliac joints anteriorly with minimal posterior offset on the right.

Background

The pelvis is a ring-like structure that provides critical weight-bearing support for the spine, load transfer to the extremities, and protection of internal organs and structures in the pelvic cavity. Pelvic fractures and dislocations are frequently associated with hemorrhage and injuries to the urinary tract and other viscera. All of these factors contribute to the high morbidity and mortality rates associated with bony pelvic injuries. In multitrauma, managing physicians must have a high index of suspicion for potential pelvic injuries. because findings of pelvic injuries may be subtle on physical examination. Careful examination of the perineum is essential to rule out open injuries. Imaging is critical for timely identification of unstable pelvic injuries to initiate effective medical care.

Mechanism of Injury

Unstable pelvic fractures such as the open-book pelvis are often the result of high-energy trauma such as motor vehicle collisions. It is important to understand the mechanism of injury and the structural anatomy of the pelvis in evaluating pelvic trauma.

The two innominate bones and the sacrum provide little if any stability through their articulations. The anterior ligaments around the pubis symphysis provide the dominant anterior stabilizers. The sacroiliac joint consists of an anteroinferior synovial joint and posterosuperior ligamentous portion.1 The vast majority of the structural stability of the posterior pelvis depends on the integrity of the ligaments around the sacroiliac joints. Disruption of these ligaments allows subluxation and dislocation of the sacroiliac joint and essentially dissociation of the axial and ipsilateral appendicular skeleton. The most important ligaments are posterosuperior to the joint and consist of short and long components.1 These ligaments are the strongest ligaments in the body, responsible for transferring axial load to the lateralized extremities.

The majority of pelvic fractures and dislocations can be classified by the mechanism of injury. The principle mechanisms of injury are lateral compression, vertical shear, and anterior compression.1

The most common mechanism is lateral compression. True lateral compression injuries typically result in internal rotation of the hemipelvis. They can be associated with fractures of the sacral ala, iliac wing (with some fractures entering the sacroiliac joint), pubic arch, body of the pubis, and disruption and/or overlap of the pubic symphysis (locked pubic symphysis).1

Vertical shear injuries are due to forces transmitted through the femur to the ipsilateral hemipelvis. Vertical shear often is associated with unilateral, vertically-oriented fractures of the superior and inferior pubic rami, posterior injuries (eg, fractures involving the ipsilateral sacrum), and sacroiliac joint dislocations.1

Anterior compression injuries feature diastasis of the symphysis pubis and disruption of the sacroiliac joint unilaterally or bilaterally. The affected hemipelvis is usually externally rotated and appears broader on an AP radiograph. The forces may cause pubic symphysis diastasis up to 2.5 cm without causing disruption of the sacroiliac joint ligaments.1 With greater pubic separation, there is usually disruption of the sacroiliac ligament complex causing rotational instability. If the posterior sacroiliac ligament complex is disrupted, the injury is globally unstable.1

Wide disruption of the sacroiliac joint is easily visualized on an AP radiograph. However, sacroiliac joint disruption with posterior displacement may not be visible on AP images, but readily apparent on CT. In addition to sacroiliac joint injuries, direct anterior compression can result in fractures of all 4 pubic rami (ie, straddle injury).

Classification

The two major classification systems for describing pelvic fractures are the Young-Burgess and Tile systems. The Young-Burgess classification focuses on the mechanism of the injury while the Tile system focuses on pelvic stability.

The hallmark of anterior compression injuries is pubic symphyis diastasis with or without disruption of the sacroiliac joints. The Young-Burgess system describes 3 types of anterior compression injuries. In type I injuries, pubic diastasis is 2.5 cm, with the sacroiliac joint and posterior ligaments remaining intact. Pelvic stability is preserved. In type II injuries, pubic diastasis is >2.5 cm with diastasis of 1 or both sacroiliac joints due to anterior ligament complex disruption resulting in rotational instability. The posterior ligaments are still intact and vertical stability is preserved.2 In type III injuries, posterior sacroiliac ligaments are disrupted causing vertical and rotational instability. In all anterior compression injuries, hemipelvis displacement is seen as an external rotation deformity.

In the Young-Burgess classification system, sacroiliac joint disruption is also included in the type II lateral compression injury and vertical shear injury. In a type II lateral compression injury, there can be ipsilateral sacral buckle fractures, ipsilateral horizontal pubic rami fractures, and ipsilateral iliac wing fracture or posterior sacroiliac joint disruption.2 In vertical shear injury, there are vertical pubic rami fractures and sacroiliac joint disruption with or without adjacent fractures.

The Tile classification is based on pelvic stability. Type A fractures are stable and do not disrupt the ligamentous structures of the pelvic ring.3 Type B fractures are rotationally unstable but vertically stable. There is incomplete disruption of the posterior pelvic arch. This subset of fractures includes the open-book pelvis. More specifically, the open-book pelvis is a type B 3.1 anterior compression injury where there is pubic diastasis, bilateral sacroiliac joint diastasis, and external rotation of the pelvis.2 Type C fractures are globally unstable. There is complete disruption of the posterior arch and pelvic floor.

Imaging

Radiographs

Every severely traumatized patient with suspected pelvic injury or appropriate mechanism should have an AP radiograph of the pelvis to include the hips. Following trauma, the AP pelvis radiograph can be used to identify unstable injury patterns and help initiate treatment of the patient. In the open-book pelvis, the AP radiograph is crucial for initial evaluation of sacroiliac joint and pubic symphysis width. The normal sacroiliac joint is approximately 2 to 4 mm wide. The pubic symphysis has a normal width upper limit of approximately 5 mm.1 Gross displacement is usually easily seen on the AP image (Figures 3, 4). However, with minimal displacement, disruption of pelvic bones can be difficult to identify. This is especially true with radiographs of a trauma patient with suboptimal positioning and overlying artifacts such as bowel gas and stool.

Figure 3: Pubic symphysis diastasis Figure 4: Pen-book pelvis injury with pubic symphysis diastasis and sacroiliac joint diastasis Figure 5: Mild diastasis of pubis symphysis and borderline diastasis of both sacroiliac joints

Figure 3: AP pelvis radiograph shows pubic symphysis diastasis and sacroiliac joint diastasis (left greater than right). Right intertrochanteric fracture is incidentally noted. Figure 4: AP pelvis radiograph shows open-book pelvis injury with pubic symphysis diastasis and sacroiliac joint diastasis (right greater than left). Figure 5: AP pelvis radiograph shows mild diastasis of pubis symphysis and borderline diastasis of both sacroiliac joints in this young pregnant woman. Mineralized fetal skeleton at central pelvis.

The widths of both sacroiliac joints should be compared for asymmetry. Superior displacement of the iliac margin on the side of ligament disruption is best noted by inspecting the inferior aspect of the sacroiliac joint and comparing the positions of the anterior segments of the sacrum and ilium for symmetry.1 A fracture of the transverse process of the fifth lumbar vertebrae is sometimes associated with sacroiliac joint injury due to its ligamentous contribution at the lumbosacral junction.

Anteroposterior and tangential views of the pelvis disclose most pelvic fractures. Tangential views are helpful in evaluating the sacrum and margins of the pelvis. The inlet view with 40° to 50° of caudal angulation is the best view to visualize posterior displacement of the ilium at the sacroiliac joint.1 The outlet view with 35° to 40° of cephalic angulation gives a good en face view of the sacroiliac joints in suspected disruption. In addition to inlet and outlet views, a lateral radiograph may be used to demonstrate associated fractures of the coccyx and define transverse components of sacral fractures. Forty-five degree oblique (Judet) views are useful to show other fractures, especially the anterior and posterior acetabular columns and fractures of the acetabulum.1

One mimic of ligamentous injury is perinatal ligamentous laxity. In preparation for vaginal delivery in late stage pregnancy and in the immediate postpartum period, there may be anterior sacroiliac joint widening and pubic diastasis. However, there is no ligamentous disruption. The natural history is complete restoration of pelvic ring stability. This finding only becomes clinically problematic in a few individuals (Figure 5).

Computed Tomography

Because radiographs may underestimate the severity of injury, CT is generally indicated once the patient is stable. Since a significant percentage of sacroiliac joint injuries/diastases may not be shown or may be underestimated on radiographs, CT provides great anatomical detail and avoids the problem of superimposition of structures.1 Computed tomography accurately demonstrates coexisting injuries such as acetabular fractures and hip dislocations. In addition, hematomas and other potential injuries to the regional viscera are shown. Computed tomography is also superior to other imaging modalities in evaluating implant position after surgery.

Various CT protocols are available, with universal elements consisting of narrow collimation with overlap, usually with subcentimeter reconstructions. Due to the typically emergent status of the patient, consistent imaging increments through the bony pelvis are usually obtained. Multiplanar and 3-dimensional reconstructions can clarify subtle injuries and spatial relationships prior to operative fixation.1

In open-book pelvic injuries, diastasis of the sacroiliac joint, shown as asymmetrical anteroposterior width or generalized widening, is easily seen on CT. The opposing sacral and iliac margins of the sacroiliac joint are clearly demonstrated. In particular, sacroiliac joint disruption with posterior displacement is much better depicted on CT in comparison to radiographs (Figure 6).1 Sacroiliac joint ligamentous injuries can also be identified by noting avulsion fractures at the margins of the joint. It is important to note that repeated manipulation of the multitrauma patient can result in variations in width of the injured sacroiliac joint on different modalities (Figure 7). Hemodynamically unstable patients may be stabilized with a sheet or pelvic binder, but imaging traumatized patients in these devices may result in underestimation of displacement and deformity of the pelvic ring.

Figure 6A: Bilateral anterior sacroiliac joint diastasis without posterior diastasis or offset Figure 6B: Broad diastasis of pubis symphysis shown on more inferior image

Figure 6: Axial CT image through the sacroiliac joints (A) shows bilateral anterior sacroiliac joint diastasis without posterior diastasis or offset. Broad diastasis of pubis symphysis shown on more inferior image (B).

Figure 7A: Bilateral vertical pubic rami fractures Figure 7B: Diastasis of the left sacroiliac joint

Figure 7: AP pelvis radiograph (A) shows bilateral vertical pubic rami fractures and marked elevation left pelvis. The left sacroiliac joint does not appear widened. Left posterior oblique positioning (B) shows definite diastasis of the left sacroiliac joint.

Angiography

Pelvic hemorrhage is the most serious acute complication of unstable pelvic injuries such as an open-book pelvis. Pelvic arteries or veins are disrupted in up to three-fourths of patients. Venous bleeding is usually from posterior pelvic veins or from the marrow space of broken bones.4 Arterial bleeding is usually from branches of the internal iliac artery. Posterior fractures through the greater sciatic notch commonly injure the superior gluteal artery, while anterior fractures injure the internal pudendal artery.4

The best initial treatment for an unstable pelvis in a hemodynamically unstable patient is pelvic stabilization with an external fixator, pelvic sheet, or binder. This reduces the pelvic volume, stabilizes bleeding bony surfaces, and assists in indirect tamponade of venous hemorrhage.4 If the hemorrhage is not well controlled with these measures, angiographic evaluation, and, if necessary, embolization of the transected arteries is indicated.

Contrast-enhanced CT is often completed prior to angiography for evaluation of the abdomen, and can also serve as an accurate, noninvasive way to indicate the general site of pelvic hemorrhage. Contrast extravasation can be reliably detected with relatively high sensitivity and specificity. Active contrast extravasation has a range of 85 to 370 Hounsfield units (HU), similar to the opacified arteries. However, clotted blood in a hematoma has a range of 40 to 70 HU.4 Often, the site of extravasation on CT corresponds to the bleeding site shown on angiography. Localization by CT can save valuable time in the angiography suite.

In patients with significant hemorrhage associated with pelvic injury, transcatheter arterial embolization is now considered the treatment of choice (Figure 8). Ideally, embolization should be performed within 3 hours.4 This can significantly reduce the transfusion requirement, minimize organ failure, and decrease mortality. Although the initial survey aortogram may not reveal extravasation, selective injection of the internal iliac artery should be performed because bleeding may be intermittent. In addition, the contralateral side should be injected to look for additional sites of extravasation as well as possible collateral flow as a source of hemorrhage.4

Figure 8A: Opacification of right common iliac artery Figure 8B: Cut-off of internal iliac artery Figure 8C: Embolization coil overlying the sacroiliac joint

Figure 8: Frontal digital subtraction angiographic image (A) shows opacification of right common iliac artery with multifocal contrast extravasation (arrows) representing active hemorrhage. Imaging after embolization (B) shows cut-off of internal iliac artery and subtotal resolution of extravasation. Postprocedural AP pelvis radiograph (C) shows embolization coil (arrow) overlying the sacroiliac joint.

Retrograde Urethrogram

Injuries to the urethra and bladder often occur with traumatic pelvic injuries. Urethral injury results from pelvic fracture fragments or shearing forces near the base of the bladder. These injuries may also be associated with extraperitoneal bladder rupture.

The most common location for urethral injury is at the urogenital diaphragm due to the anterior support structures causing stretching at this site. Males have more urethral injuries due to the fact that the male urethra is longer and more mobile in comparison to females.5 It is critical to obtain a retrograde urethrogram prior to inserting a Foley catheter.

A retrograde urethrogram is the imaging study of choice for diagnosing urethral injury. Following cannulation of the meatus, approximately 20 to 30 cc of contrast is injected through a small caliber catheter under fluoroscopic guidance.5 The urethra is observed in AP and oblique projections to confirm patency to the bladder and exclude extravasation of contrast.

In general, there are 3 types of urethral injuries. In type I urethral injuries, the membranous urethra above the urogenital diaphragm is stretched and narrowed. In type II urethral injuries, the membranous urethra is disrupted near the base of the bladder. In type III urethral injuries, the membranous urethra is disrupted below the urogenital diaphragm and involves the bulbous urethra (Figure 9).2

Figure 9: Retrograde urethrogram Figure 10: Anterior and posterior stabilization following open-book pelvis injury

Figure 9: Retrograde urethrogram shows contrast extravasation (arrow) at the base of penile urethra with abundant contrast at the pelvic floor soft tissues and scrotum from transection of the urethra. Figure 10: AP pelvis radiograph shows anterior and posterior stabilization following open-book pelvis injury.

Orthopedic Management

In unstable pelvic fractures such as an open-book pelvis, open reduction and internal fixation (ORIF) is the preferred definitive management. The majority of these fractures are a result of significant trauma. Therefore, definitive internal fixation is usually not performed until the patient is stable.

In the emergent setting when the patient is hemodynamically unstable, external fixation or pelvic sheeting is indicated. External fixation can be helpful in controlling hemorrhage and as a temporary measure for fracture reduction and stabilization.6 Pins are usually placed along the iliac crest or in the supra-acetabular region. The iliac crest approach is usually fairly quick. The optimal starting point is the medial one-third of the anterior pillar, the thickest bone for pin insertion.3

With the supra-acetabular approach, pins are placed at the level of the anterior inferior iliac spine, perpendicular to the floor,3 taking care to avoid the hip joint. Placement under fluoroscopic imaging is recommended if time and patient status allows. In both settings, the external fixator frame should be far enough away from the abdomen to allow for distention and future surgical approaches.

If the patient is hemodynamically stable, internal fixation is preferred. If the posterior fibrous ligaments are intact, anterior stabilization alone is completed. When pubic symphysis disruption is associated with posterior ring disruption, ORIF is preferred for reduction of the pubic symphysis. Usually, a 4- to 6-hole pelvic reconstruction or symphyseal plate is placed on the superior surface of the symphysis.6 Iliosacral screws, interfragmentary screw or plate techniques can be used for treating sacroiliac dislocations and any associated crescent or sacral fractures (Figure 10).

Percutaneous internal fixation is commonly used for complete sacroiliac joint disruption and can be done in either the prone or supine position. Cannulated screws are placed under fluoroscopic guidance from the lateral ilium into the lateral sacrum or body of S1 and/or S2.6 This approach is technically demanding, and a thorough understanding of the radiographic anatomy is required.3 For sacroiliac joint dislocations in particular, cancellous lag screws are usually used to achieve compression.

For ORIF of the sacroiliac joints, an anterior or posterior approach can be used, with the posterior approach preferred. The gluteus maximus and multifidus muscles are elevated to expose the sacrum and ilium adequately.3 C-arm fluoroscopy guides hardware placement. In the anterior approach, the iliacus muscle is elevated from the internal iliac wing to expose the sacroiliac joint. With this approach, careful attention must be paid to the L5 nerve root, which lies only 2 cm medial to the sacroiliac joint on the sacral ala.2 The anterior approach is technically demanding and is more likely to exacerbate hemorrhage in the acute setting.6 Following operative fixation, patients should have radiographic evaluation at 2, 6, and 12 weeks after surgery.

Summary

Multitrauma patients can have serious injuries that may be readily apparent or occult. Unstable pelvic fractures may be difficult to diagnose with physical examination alone. Therefore, radiographic evaluation is critical in evaluating the bony pelvis.

Radiographs are the primary initial imaging modality. In the open-book pelvis, it is important to evaluate the sacroiliac joints and pubic symphysis for diastasis. In addition, a thorough evaluation should be performed for possible fractures. If there is any suspicion of pelvic injury on radiographs, CT scan of the pelvis is indicated. Computed tomography is the most accurate method for evaluating pelvic injuries and can be used for preoperative planning. Also, CT can demonstrate visceral and vascular injuries. If there is active pelvic hemorrhage and/or the patient is unstable with no other injuries to account for blood loss, urgent stabilization and angiography to identify bleeding vessels and embolization of bleeding vessels can be completed to achieve hemodynamic control. If urethral injury is possible, a retrograde urethrogram is necessary for further evaluation and before catheterizing the bladder.

The information provided by these imaging modalities may prove critical to management of patients with open-book injuries of the pelvis.

References

  1. Rogers LF. Radiology of Skeletal Trauma. New York, NY: Churchill Livingstone; 2001.
  2. Thornton DD. Pelvic ring fractures. eMedicine Web site. http://www.emedicine.medscape.com/article/1247426-followup. Updated November 27, 2007. Accessed December 20, 2008.
  3. Graf KW Jr, Karunakar M. Unstable pelvic fractures. eMedicine Web site. http://www.emedicine.medscape.com/article/394515-overview. Updated January 18, 2008. Accessed December 1, 2008.
  4. Yoon W, Kim JK, Jeong YY, Seo JJ, Park JG, Kang HK. Pelvic arterial hemorrhage in patients with pelvic fractures: detection with contrast-enhanced CT. Radiographics. 2004; 24(6):1591-1605.
  5. Cummings JM, Boullier J. Urethral trauma. eMedicine Web site. http://www.emedicine.medscape.com/article/451797-overview. Updated July 13, 2006. Accessed November 20, 2008.
  6. Heckman JD, Bucholz RW, Beaty JH. Rockwood, Green and Wilkins’ Fractures. Philadelphia: Lippincott Williams & Wilkins, 2001.

Authors

Namit Mahajan, MD; Laurie M. Lomasney, MD; Terrence C. Demos, MD; Hobie Summers, MD; Michael Stover, MD

Drs Mahajan, Lomasney, and Demos are from the Department of Radiology, and Drs Summers and Stover are from the Department of Orthopedics, Loyola University Medical Center, Maywood, Illinois.

Drs Mahagan, Lomasney, Demos, Summers, and Stover have no relevant financial relationships to disclose.

Correspondence should be addressed to: Terrence C. Demos, MD, Department of Radiology, Loyola University Medical Center, 2160 S First Ave, Maywood, IL 60153.

10.3928/01477447-20090502-04

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