eMedicine Specialties > Radiology > Musculoskeletal
Pelvic Ring Fractures: Imaging
Updated: Feb 11, 2009
Radiography
Anteroposterior (AP) compression injury as seen on an AP radiograph of the pelvis. Characteristic features of an AP compression injury include symphyseal and sacroiliac joint diastasis. In this patient, the pubic symphysis and right sacroiliac joint are widened.
Vertical shear injury as seen on an anteroposterior radiograph of the pelvis. The left hemipelvis is displaced in a cranial direction, with associated sacroiliac joint diastasis. The vertically oriented fractures of the pubic rami usually are ipsilateral; however, in this patient, the rami fractures are contralateral.
Anteroposterior compression injury as seen on an anteroposterior radiograph of the pelvis. The symphysis pubis is wider than 2.5 cm (double arrow). The right sacroiliac joint is diastatic (single arrow). This is a type II or type III injury, depending on the status of the posterior sacroiliac ligaments.
Lateral compression injury as seen on an anteroposterior radiograph of the pelvis. Note the characteristic left sacral buckle fracture (long arrow) and the minimally overlapping left pubic rami fractures (short arrow). The sacral fractures may be subtle on radiographs.
Lateral compression injury as seen on an inlet radiograph of the pelvis. The internal rotation of the left hemipelvis is better visualized by using the inlet view. The fractures of the left sacrum (long arrow) and left pubic rami (short arrows) are shown.
Windswept pelvis (lateral compression injury) as seen on an anteroposterior radiograph of the pelvis. The patient had a left lateral compression injury. Note the internal rotation of the left hemipelvis and the overlapping left pubic rami fractures (double arrow). The pubic symphysis diastasis, rightward displacement of the pubic symphysis with external rotation of the right hemipelvis, and right sacroiliac joint diastasis (single arrow) are features of anteroposterior compression. The combination results in the characteristic appearance of the windswept pelvis.
Vertical shear injury as seen on an anteroposterior radiograph of the pelvis. The left hemipelvis is displaced in a cranial direction with associated sacroiliac joint diastasis (long arrow). The vertically oriented fractures of the pubic rami usually are ipsilateral; however, in this patient, the rami fractures are contralateral (short arrow).
Iliac wing fracture as seen on an anteroposterior radiograph of the pelvis. A fracture of the left iliac wing occurred secondary to a direct blow to the left hemipelvis. The fracture does not involve the pelvic ring; therefore, the pelvis is stable.
Findings
AP radiographs of the pelvis
Usually, the pubic symphysis is approximately 5 mm wide; it should not be more than 1 cm wide. Pubic symphysis diastasis occurs when the fibrocartilage connecting the 2 pubic bones is disrupted. Diastasis of the pubic symphysis indicates an AP compression injury. If overlap of the pubic bones at the symphysis is noted, a lateral compression injury is suggested. The superior pubic rami should be at the same level as they join at the symphysis. In a vertical shear injury, 1 side is displaced in a cranial direction. The lower margins of the rami are a better guide because nonalignment of the upper margins may be a normal variation (see Image 25).
The combination of a sacral buckle fracture and ipsilateral overlapping pubic rami fractures is characteristic of a lateral compression injury.
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 may be seen in AP compression injuries instead of pubic symphyseal diastasis. Vertical rami fractures with cranial displacement are a hallmark of vertical shear injuries. Minimally displaced fractures of the pubic rami may be seen in isolation, usually in an individual with osteoporosis after a low-velocity fall. The integrity of the pelvic ring is maintained.
The direction of hemipelvic displacement indicates the mechanism of injury. External rotation of the hemipelvis (open-book pelvis) occurs with AP compression. Internal rotation is seen in lateral compression. Vertical shear injuries result in vertical (cranial) displacement of the hemipelvis. Iliac wing fractures with extension to the vicinity of the SI joint are found in the more severe lateral compression injuries. Avulsion of the ischial spine occurs in external rotation or vertical displacement of the hemipelvis. Isolated iliac wing fractures may occur as a result of a direct blow without disruption of the pelvic ring. With iliac crest, anterior iliac spine, and ischial tuberosity avulsion fractures, the integrity of the pelvic ring is also maintained.
The normal SI joint space is approximately 2-4 mm in width. When the SI joint is analyzed for diastasis, the anterior and posterior aspects should be examined. Disruption of the SI joint with external rotation of the ipsilateral hemipelvis is characteristic of AP compression. If only the anterior SI joint is widened, the posterior ligaments are intact and preserving vertical stability. If the SI joint is anteriorly and posteriorly diastatic, the pelvis is completely unstable. Usually, the SI joint is completely disrupted in vertical shear injuries. Displaced vertical fractures through the sacrum or the iliac wing adjacent to the SI joint have the same implication as SI 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. The sacral promontory and arcuate foramina should be carefully examined for cortical disruption. Displaced vertical fractures through the sacrum may be seen in lieu of SI joint disruption in AP compression and vertical shear injuries. Horizontal fractures of the sacrum below the level of the 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 SI ligament complex, as seen in severe AP compression and vertical shear injuries. Hence, an L5 transverse-process avulsion fracture may indicate complete pelvic instability.
Inlet radiographs of the pelvis
The inlet view of the pelvis permits more accurate determination of the following: the degree of posterior displacement at the SI 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
The primary purpose of the outlet view of the pelvis is to demonstrate the magnitude of vertical (cranial) displacement of the hemipelvis. Additionally, 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.
Degree of Confidence
In most patients, an analysis of the AP radiographs of the pelvis results in the correct determination of the mechanism of pelvic ring injury. Appropriate therapeutic maneuvers may be initiated immediately. Additional radiographic views (eg, inlet and outlet views) and pelvic CT scans allow more precise classification when definitive treatment is considered.
Multidetector CT is now routinely used to evaluate trauma patients; some authors have questioned whether pelvic radiographs should be routinely used for patients who are destined to undergo a CT scan.1,14
False Positives/Negatives
True pelvic ring fractures must be distinguished from pelvic fractures that do not affect pelvic stability (eg, Tile type A injury).
Pelvic ring fractures should be distinguished from acetabular fractures, which may also occur with pubic rami and iliac wing fractures. The sites that are important for pelvic stability (eg, pubic symphysis, SI joints, sacrum) should be examined to exclude a pelvic ring fracture.
An acetabular fracture may be present in addition to a pelvic ring fracture. With both types, fractures should be analyzed individually.
Computed Tomography
Windswept pelvis (lateral compression injury) as seen on a pelvic CT scan. The patient sustained a left lateral compression injury with internal rotation of the left hemipelvis and a characteristic sacral buckle fracture. Note the concomitant left sacroiliac joint diastasis. The lateral force vector continued across the pelvis to produce external rotation of the right hemipelvis and diastasis of the right sacroiliac joint. The combination of injuries resulted in a windswept pelvis.
Anteroposterior (AP) compression injury as seen on a pelvic CT scan. The location and degree of sacroiliac disruption is better seen on CT scans than on radiographs. The external rotation of the right hemipelvis is a characteristic finding in AP compression. A slight posterior displacement of the right, iliac side of the sacroiliac joint suggests ligamentous disruption (arrow). This represents a type III AP compression injury.
Lateral compression injury as seen on a pelvic CT scan. The left sacral buckle (anterior crush) fracture is more readily apparent on the CT scan than on other images.
Windswept pelvis (lateral compression injury) as seen on a pelvic CT scan. The features of each component of the injury are seen to better advantage with CT. Note the internal rotation of the left hemipelvis and external rotation of the right hemipelvis (long arrows). Note also the left sacral buckle fracture (short white arrow) and the right sacroiliac joint diastasis (short black arrow). The left sacroiliac joint also is disrupted.
Vertical shear injury as seen on a pelvic CT scan. A displaced vertically oriented fracture of the ilium extends to the left sacroiliac joint.
Findings
All radiographic findings should be further assessed on pelvic CT scans (see Radiograph) because subtle fractures and disruptions may be more apparent on CT scans. In particular, sacral fractures may be difficult to detect on radiographs (see Images 24, 26).16,20,21
Diastasis of the symphysis pubis, which most commonly indicates an anteroposterior compression injury.
Avulsion fractures of the pelvis (eg, from the anterior inferior aspect of the iliac spine) do not affect the integrity of the pelvic ring. Isolated iliac wing fractures may occur as a result of a direct blow without disruption of the pelvic ring. With iliac crest, anterior iliac spine, and ischial tuberosity avulsion fractures, the integrity of the pelvic ring is also maintained.
The spatial relationship of fracture fragments is often easier to assess with CT scans than with radiographs. Axial CT images may be reformatted into the coronal and sagittal planes. Three-dimensional images of the pelvis may also be reconstructed. Reformatted images are more useful in assessing acetabular fractures than in evaluating pelvic ring fractures.
In addition to the osseous structures, the soft tissues of the pelvis should be examined. The size of a pelvic hematoma secondary to a pelvic ring fracture may be determined. If contrast material is intravenously administered for pelvic CT, active arterial bleeding may be demonstrated, and the information may be used to guide the clinical decision to incorporate angiography into the patient's treatment plan.20
Degree of Confidence
The combination of the pelvic CT scans and the AP radiographs with inlet and/or outlet views permits accurate classification of pelvic ring fractures in virtually every patient.
Magnetic Resonance Imaging
Findings
Magnetic resonance imaging (MRI) is not used to evaluate pelvic ring fractures. Research is currently underway to evaluate the use of MRI in the evaluation of deep venous thrombosis in orthopedic patients. MR venography may prove useful in depicting lower extremity and pelvic venous thrombosis.22
Ultrasonography
Findings
Ultrasound (US) is not used to evaluate pelvic ring fractures. Lower-extremity Doppler US is used to assess for the presence of lower-extremity DVT.
Nuclear Imaging
Findings
Nuclear medicine studies are not used to evaluate acute pelvic ring fractures.
Angiography
Findings
Angiography is used to diagnose and treat potentially life-threatening hemorrhage secondary to pelvic ring injury. Pelvic arteriography demonstrates the injured vessels responsible for the hemorrhage. The vessels may then be embolized to control or stop the bleeding.
More on Pelvic Ring Fractures |
| Overview: Pelvic Ring Fractures |
 Imaging: Pelvic Ring Fractures |
| Follow-up: Pelvic Ring Fractures |
| Multimedia: Pelvic Ring Fractures |
| References |
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References
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Further Reading
Keywords
pelvic ring fracture, pelvis fracture, blunt trauma, bladder rupture, vertical shear injury, anteroposterior compression injury, AP compression injury, lateral compression injury, pelvic hemorrhage, osseous pelvis, Young-Burgess classification, Tile classification, pubic diastasis, sacral buckle fracture, pubic rami fracture, iliac wing fracture
