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Imaging of Pelvic Ring and Acetabular Trauma
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Imaging of Pelvic Ring and Acetabular Trauma Claire K. Sandstrom MD, Joel A. Gross MD, Ken F. Linnau MD MS
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S0037-198X(16)00034-1 http://dx.doi.org/10.1053/j.ro.2016.03.002 YSROE50551
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Seminar in Roentgenology
Cite this article as: Claire K. Sandstrom MD, Joel A. Gross MD, Ken F. Linnau MD MS, Imaging of Pelvic Ring and Acetabular Trauma, Seminar in Roentgenology, http://dx.doi. org/10.1053/j.ro.2016.03.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Imaging of Pelvic Ring and Acetabular Trauma
Authors: Claire K. Sandstrom, MD – Assistant Professor, Department of Radiology, University of Washington / Harborview Medical Center Joel A. Gross, MD – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center Ken F. Linnau, MD MS – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center
From University of Washington / Harborview Medical Center Correspondence may be sent to: [email protected], 206.744.3561, or 325 Ninth Ave, Box 359728, Seattle WA 98104
Authors: Claire K. Sandstrom, MD – Assistant Professor, Department of Radiology, University of Washington / Harborview Medical Center Ken F. Linnau, MD MS – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center Joel A. Gross, MD – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center From University of Washington / Harborview Medical Center Correspondence may be sent to: [email protected], 206.744.3561, or 325 Ninth Ave, Box 359728, Seattle WA 98104
Introduction
Blunt trauma to the pelvis can cause fractures and ligamentous injuries to the pelvic ring and can fracture the acetabulum. Pelvic and acetabular fractures often occur with high-energy blunt trauma, including motor vehicle and motorcycle crashes, car versus pedestrian accidents, and falls.1-3 Low-energy falls can also cause pelvic and acetabular fractures in elderly osteoporotic patients.1,2,4-6 Potentially life-threatening pelvic hemorrhage, urethral and bladder injuries, and additional intraabdominal injuries may accompany pelvic trauma, affecting emergent management decisions in blunt pelvic trauma patients. 3,6-9
Pelvic Ring Injuries
The presence of pelvic ring injuries affects clinical decision-making in several ways. Unstable patients with pelvic injuries may benefit from emergent angiography or retroperitoneal pelvic packing10 rather than laparotomy for control of pelvic hemorrhage. Unstable pelvic ring injuries will ultimately require internal fixation. Bladder and urethral injuries, though not common, may require surgical repair and require dedicated imaging for prompt diagnosis.
Pelvic hemorrhage Pelvic fractures commonly cause pelvic bleeding. The majority of bleeding is self-limited, arising from venous structures or bone edges. However,
5-20% of patients with pelvic fractures have potentially life-threatening arterial hemorrhage, which may be amenable to angioembolization.11 Clinical predictors of major hemorrhage related to pelvic fractures, based on initial pelvic radiograph (Fig 1), blood work, and vital signs, are shown in Table 1.11 Likelihood of pelvic hemorrhage ranges from less than 2% for those with no predictors to over 60% for those with three or four predictors of major hemorrhage.11 Thus, angiography should be prioritized for those patients with a higher probability of major pelvic hemorrhage. Patients older than 60 years of age with major pelvic fractures and those with active arterial contrast extravasation detected on CT (Fig 2) may benefit from pelvic angiography and angioembolization regardless of hemodynamic status.12,13 External pelvic stabilization decreases pelvic volume, although the degree to which this helps to tamponade bleeding from venous structures and bone edges not amenable to angioembolization remains uncertain.12 While the utility of contrast-enhanced CT for detection of active arterial hemorrhage in hemodynamically stable blunt trauma patients is well documented,14-18 the role of arterial-phase CT of the pelvis remains uncertain.19
Bladder and Urethral injuries Bladder injuries complicate less than 10% of blunt pelvic fractures. 20 Injuries are categorized as extraperitoneal, intraperitoneal, or combined. Independent multivariate predictors of bladder rupture include pubic symphyseal diastasis >1cm (RR 9.8) and obturator ring fractures displaced >1cm (RR 3.2) (Fig 3).20 All patients with bladder rupture have hematuria, with at least 3+
hematuria on dipstick urinalysis or greater than 30 red blood cells per high powered field (RBC/HPF) on microscopic urinalysis.20,21 Thus, detection of anterior pelvic ring injuries should prompt urinalysis, and CT cystogram should be performed when the hematuria threshold is exceeded.22 While the majority of bladder ruptures are associated with pelvic fractures, a smaller percentage, usually involving intraperitoneal bladder rupture, occur in the absence of osseous pelvic injury.21,23,24 Patients with bladder rupture often have other intraabdominal injuries, including hollow visceral, splenic, and hepatic injuries.24 Urethral injuries are also rare but are more likely in male patients with anterior pelvic ring disruption. Predictors of urethral injury include diastasis (≥1cm) of the pubic symphysis (OR 11.8) or of inferomedial pubic bone fractures (OR 6.4).25 The probability of urethral injury increases approximately 10% with each millimeter increase in displacement of pubic components.25 Diagnosis and characterization of male urethral injuries is performed by retrograde urethrogram,26 although this might be difficult to perform in hemodynamically unstable patients or those with spine injuries.27
Pelvic ring stability The adult osseous pelvis is formed by the sacrum posteriorly and the bilateral innominate bones (formed by fusion of the ilium, ischium, and pubic bones) (Fig 4). The osseous structures have no inherent stability, relying instead on the integrity of the sacroiliac (SI) ligaments (anterior, short interosseous, and posterior).28 The pubic symphyseal fibrocartilage and pubic ligaments of the
anterior pelvic ring reinforce the SI joints against rotation.28,29 Supplemental support is provided by the iliolumbar, lateral lumbosacral, sacrotuberous, and sacrospinous ligaments, which primarily resist rotation of the innominate bone relative to the sacrum.28 Two types of stability, rotational and vertical, are considered (Fig 5). Most commonly, rotational stability implies that pressure applied to the anterior iliac spines will not result in unlimited outward rotation of the innominate bone, akin to opening a book. Disruption of the pubic symphysis or obturator ring without sacral or SI ligament injury maintains rotational stability because the SI ligaments resist rotational forces. Conversely, if the anterior pelvic ring, the anterior SI ligaments, and the supplementary ligamentous structures are disrupted, the innominate bone can rotate posteriorly until the iliac spine abuts the sacrum, even if the posterior SI ligaments remain intact.28 In another form of rotational instability, anterior ring fractures and posterior SI ligament disruption allow inward rotation of the hemipelvis using the anterior sacrum as a hinge (even if the anterior SI ligament remains intact).30 Vertical stability implies that each side of the pelvis maintains a normal craniocaudal relationship with the sacrum with upward forces, such as from standing upright. If a patient were to attempt to stand on a vertically unstable pelvic ring, the affected hemipelvis would move superiorly relative to the intact sacrum. This usually happens through a completely disrupted SI joint but can occur through complete fractures of the ilium or the sacrum. A vertically unstable pelvis is also rotationally unstable, whereas rotational instability does not imply
vertical instability. The presence of either rotational or vertical instability requires internal fixation.30 While pelvic stability is ultimately determined on clinical examination, radiology reports tailored to describe the disrupted bony and ligamentous elements of the pelvic ring will aid the surgeon’s decision-making.
Pelvic ring injury classification Pelvic ring injuries are commonly classified according to the YoungBurgess classification system, summarized in Table 2. Pelvic surgeons often use the Tile/Orthopedic Trauma Association classification system,31 which is less reliable when applied by less experienced providers.32 The four injury categories in the Young-Burgess system—lateral compression, anteroposterior compression, vertical shear, and combined mechanism—are based on the estimated force trajectory and may help determine corrective forces required for pelvic stabilization.28 However, force trajectory predicted by radiographic appearance does not always correlate with actual mechanism of injury based on crash site analysis.33 Imaging findings and manual examination are combined to differentiate stable and unstable pelvic ring injuries, thus identifying which patients need internal fixation. In anteroposterior compression injuries, disruption of the pubic symphysis alone results in anterior pelvic ring widening (Fig 6). The anterior SI joint might appear slightly wide even when the anterior SI ligaments remain intact. These
patients require manual evaluation (sometimes under anesthesia) to confirm stability.30 Lateral compression injuries are characterized by obturator ring and anterior sacral impaction fractures. The obturator ring fractures may be ipsilateral and/or contralateral to the sacral injury. Obturator ring fracture orientation may be axial, coronal, or comminuted. The most common finding indicating rotational instability is a crescent fracture, which ranges in appearance from a tiny avulsion of the posterior ilium to a large iliac wing fracture (Fig 7).34,35 Complete fracture through the entire sacral wing or tear of the SI ligament without osseous injury are less commonly seen.30 These posterior injuries should be specifically sought with all lateral compression injuries, as they potentially change management from conservative to surgical. Cephalad displacement of the hemipelvis in vertical shear injuries is best assessed posteriorly, using the relationship of the sacral arcades with the sciatic buttress (Fig 8). Vertical displacement of the posterior pelvis indicates vertical instability. Young-Burgess also includes a catchall category of combined pelvic ring injuries representing a variable combination of anteroposterior, lateral, and/or vertical directed forces.28 A radiology report using the Young-Burgess classification system to describe pelvic ring disruption will reliably convey information between providers during initial clinical decision-making.
Imaging of pelvic ring injuries Optimal imaging of pelvic ring disruptions has not been validated in the literature. While it is generally accepted that CT is highly sensitive, an appropriate diagnosis can be made with radiographs in most cases. 28 The degree of rotation of the pelvic ring is best shown on inlet views, while the degree of vertical displacement in vertical shear injuries is optimally assessed on pelvic outlet radiographs.28 Virtual inlet and outlet views can be created from existing torso CT images including the pelvis, achieving similar or better quality while decreasing radiation exposure and time to acquire additional adequate radiographic views.36 Involvement of the sacrum and sacroiliac joint is most reliably assessed by CT.28,37 MRI may be useful in osteoporotic patients with anterior pelvic ring injuries to identify non-displaced posterior ring fractures.38
Acetabular Fractures
Acetabular fractures are uncommon but important injuries that frequently require surgical reconstruction. The most common fracture patterns overall are posterior wall fractures, associated both column fractures, and transverse with posterior wall fractures.2,39-42 Acetabular fractures are often related to highenergy motor vehicle crashes, but elderly patients are much more likely to injure their acetabulum in low-energy falls.2 As a result, fractures of the anterior column, including anterior column with posterior hemitransverse fractures, are more common in older patients.2 With aging of the global population, these
previously rare types of fractures are increasing in frequency.2,42,43 Though other extremity injuries commonly accompany acetabular fractures regardless of age,40 younger patients are more likely to have additional injuries to other organ systems than older patients.2 When acetabular injuries coexist with pelvic ring injuries, treatment of both is more complicated.44 Radiographic features of acetabular anatomy are highlighted in Fig 9, while CT anatomy is reviewed in Fig 10.
Acetabular fracture classification The classification system of acetabular fractures developed and refined by Emile Letournel and Robert Judet is widely used and guides surgical approach and operative fixation.45-48 Other classification systems have not gained acceptance with surgeons. While complicated, pre-operative classification of acetabular fractures is important, as different injury types necessitate different skin incisions and fixation approaches.46 The Judet and Letournel classification delineates ten types of injuries, five of which involve a single fracture plane (simple or elementary types), and five of which are more complex (associated types), as summarized in Table 3. These were recently reviewed by Scheinfeld et al.,49 who provide a beautiful and extensive review of acetabular fractures, which is not repeated here. Instead we will focus on a few key points that often cause confusion. Key Concept #1: Transverse fractures cross both columns but are simple fractures. They are not the same as associated both column fractures.
Transverse fractures were so named when viewing the acetabulum en face with the patient positioned on his side for surgery—however, in the upright anatomic position, the rim is rotated inferiorly and anteriorly (Fig 11). This rotation explains why the transverse fracture characteristically extends from superomedial to inferolateral in an oblique plane (best appreciated on axial or coronal images). On individual axial images, the fracture has a sagittal orientation, extending anteroposteriorly. However, its location shifts from medial to lateral as axial images are viewed from superior to inferior. The addition of posterior wall comminution or ischiopubic ramus involvement advances the transverse fracture from a simple/elementary type to a complex type fracture, resulting in transverse with posterior wall fracture or T-shaped fracture, respectively. Key Concept #2: An anterior wall fracture is not a mirror image of a posterior wall fracture, as anterior wall fractures disrupt the iliopectineal line (Fig 12). In comparison, posterior wall fractures (Fig 13) always spare the ilioischial line, which defines the anatomic posterior column. In anterior wall fractures, the iliopectineal line of the pelvic brim is fractured, but the anterior iliac spines and the pubic body, as well as the posterior column, remain intact and in normal anatomic position.46 In contrast, anterior column fractures extend from the ilium, crossing the acetabular roof and quadrilateral plate, to the ischiopubic ramus (Fig 14). Key Concept #3: An associated both column fracture completely separates the acetabular tectum from the sacroiliac joint (Fig 15). The posterior column fracture exiting through the sciatic notch is joined by the iliac
wing fracture defining the anterior column component. This results in an inferiorly-directed bone shard or ―spur‖ of the fractured ilium, pathognomonic of associated both column injuries and characteristically seen on the obturator oblique Judet view projecting laterally from the acetabular fragments which have been displaced medially. The other fracture patterns that involve both anatomic columns—the T-shaped fracture, the anterior column/wall with posterior hemitransverse, transverse, and transverse with posterior wall patterns—leave some part of the acetabulum attached to the ilium and SI joint. Some acetabular fracture imaging features not included in the Judet and Letournel system predict poor clinical outcome and should be reported.50-52 These findings (listed in Table 4) may lead to the development of premature post-traumatic osteoarthritis and often necessitate joint replacement.53 Many of these predictors of poor outcome are more common in elderly patients.2
Imaging of acetabular fractures Characterization of acetabular fractures was originally performed with anteroposterior and bilateral oblique Judet views (iliac oblique and obturator oblique).46 Orthopedic surgeons who treat acetabular fractures on a regular basis will reliably classify injuries based on radiography.54 Nevertheless, CT scanning of acetabular fractures is now common practice, and although some centers still acquire conventional radiographs, virtual reconstructions from CT data can also be used. Potential benefits of CT-reconstructed virtual images include the ability (1) to subtract bowel or bladder contrast, (2) to minimize
patient discomfort, time and radiation exposure from obtaining additional radiographs, (3) to optimize projections without the need for repeat exposures, and (4) to overcome difficulties in penetration in obese patients. Use of axial CT images, 3D reconstructions, or virtual radiographic pelvis images compares favorably to the use of conventional radiographs.55,56 CT images are also helpful for preoperative measurements (articular surface displacement, impaction), detection of intraarticular bone fragments, and identification of associated femoral head injuries.37,57 In general, axial CT images through the acetabulum show a coronal fracture plane for column fractures, a sagittal fracture plane for transverse fractures, and an oblique fracture in wall fractures (Fig 16).
Conclusion
Though uncommon, pelvic ring injuries and acetabular fractures are important diagnoses in blunt trauma patients. Associated injuries, including pelvic hemorrhage, bladder and urethral injuries, and other abdominal organ injuries, are frequently present. Concepts of stability and force trajectory guide decision-making regarding surgical fixation for pelvic ring injuries, and the YoungBurgess system is useful for communication of imaging findings. Orthopedic surgeons use the Judet and Letournel system to classify acetabular fractures and to guide surgical approach. Radiology reports should include features relevant for surgical decision-making.
Tables Table 1. Clinical predictors of major hemorrhage related to pelvic fractures. Predictor Displaced obturator ring fracture (≥1cm) Pubic symphyseal diastasis (≥1cm) Hematocrit ≤30% Pulse ≥130 beats / min
Odds Ratio for Major Hemorrhage 3.8 3.9 6.6 3.3
Table 2. Summary of Young-Burgess classification system for pelvic ring injuries. Injury type
Anteroposterior compression I (APC-I)
Characteristic injury of anterior pelvic ring Pubic symphyseal diastasis or sagittal pubic rami fractures
Anteroposterior compression II (APC-II)
Pubic symphyseal diastasis or sagittal pubic rami fractures
Anteroposterior compression III (APC-III)
Pubic symphyseal diastasis or sagittal pubic rami fractures
Lateral compression I (LC-I)
Pubic rami fractures in axial, coronal, or comminuted planes
Sacral impaction injury
Lateral compression II (LC-II)
Pubic rami fractures in axial, coronal, or comminuted planes
Lateral compression III, (LC-III) aka ―windswept pelvis‖ Vertical shear (VS)
Pubic rami fractures in axial, coronal, or comminuted planes
Crescent fracture of iliac wing (posterior SI ligament avulsion or tear) Ipsilateral LC-I or LC-II injury as well as contralateral open book injury (APC II or III)
Rotationally stable, vertically stable Rotationally unstable, vertically stable Rotationally unstable, vertically unstable Rotationally stable, vertically stable Rotationally unstable, vertically stable Rotationally unstable, +/vertically unstable
Vertical displacement of hemipelvis (usually at SI joint but some at iliac wing or sacral
Rotationally unstable, vertically unstable
Vertical pubic rami fractures or pubic symphyseal diastasis
Differentiating features
Typical stability
SI joints may be stretched but anterior and posterior SI ligaments are intact Anterior SI ligament torn with anterior SI joint widening; posterior SI ligament intact Anterior and posterior SI ligaments torn with diffuse SI joint widening
Combined mechanism
fracture) Variable combination of lateral compression, anteroposterior compression, and vertical shear
Variable, but often rotationally and vertically unstable
Table 3. Summary of acetabular fractures as classified by Judet and Letournel. Simple or elementary types
Complex types
Posterior wall
Transverse with posterior wall
Anterior wall
Posterior column with posterior wall
Posterior column
Associated both column
Anterior column
Anterior column or wall with posterior hemitransverse
Transverse
T-shaped
Table 4. Imaging factors that contribute to poor surgical outcome following acetabular fracture. Poor Prognostic Factors Contributing to Poor Surgical Outcome and Early Osteoarthritis Comminution of posterior wall Articular impaction (often with rotation) of posterior wall fragment(s) Articular impaction (often with rotation) of medial roof fragment(s) Hip dislocation Hip subluxation or incongruity of joint Femoral head injury
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Figures and Legends for Pelvis Paper:
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Fig. 1. Arterial hemorrhage in pelvic ring injury in a 64-year-old man who was thrown from a horse. A. The initial anteroposterior pelvic radiograph demonstrates distraction of the symphysis pubis (double headed arrow) to 2.7cm and mild right sacroiliac joint widening (black arrow). B. Coronal CT image confirms widening of the symphysis pubis and demonstrates active arterial extravasation adjacent to the left superior pubic ramus (white arrow). C. Subsequent pelvic angiography demonstrates active extravasation from the left obturator artery (white arrow), which was controlled with coil embolization.
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Fig. 2. Arterial hemorrhage detected on CT in a 75-year-old woman following ground level fall. The patient was taking warfarin. A. Semitransparent shaded surface display from CT of the pelvis demonstrates a lateral compression fracture, with left superior and inferior obturator ring fractures (white arrowheads), and left sacral impaction fracture (black arrow). B. Coronal image from contrast enhanced CT demonstrates active vascular extravasation (white arrow) near the left superior pubic ramus fracture (white arrowhead). Large pelvic hematoma displaces the bladder and Foley catheter toward the right. C. Digital subtraction catheter angiogram demonstrates arterial extravasation (white arrow) from the left pudendal artery, in this patient with multiple occluded pelvic arteries and extensive collateral vessels.
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Fig. 3. Pelvic ring disruption with extraperitoneal bladder rupture in a 38-year-old man following 40 foot fall. A. The initial anteroposterior pelvic radiograph demonstrates diastasis of the pubic symphysis (double headed arrow) measuring 1.7 cm. A fracture of the left obturator ring (white arrow) and subtle widening of the left sacroiliac joint (open black arrow) are also noted. B. Axial and C. coronal images from CT cystogram demonstrate an extraperitoneal bladder rupture (black arrowhead), with contrast extending into the extraperitoneal space (black arrows) and through the disrupted symphysis pubis to below the right pubic body (open white arrow).
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Fig. 4. Normal pelvic ring anatomy. Bony anatomy on A. anterior and B. posterior projections of shaded surface display of the bony pelvis and on C. anteroposterior pelvic radiograph. Short white lines denote the junctions of the ilium, ischium, and pubis on images A. and B. ASIS, anterior superior iliac spine. AIIS, anterior inferior iliac spine. PSIS, posterior superior iliac spine. PIIS, posterior inferior iliac spine. Pelvic ligamentous stabilizers are depicted on D. anterior and E. posterior projections of shaded surface displays of the bony pelvis. L, ligament.
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E
C
Fig. 5. Pelvic ring stability and instability. A. In a rotationally stable pelvis, the pelvic ring resists force applied to the anterior superior iliac spine (arrow). No rotation is appreciated clinically or radiologically. B. With external rotational instability, force applied to the anterior superior iliac spine (arrow) will externally rotate the innominate bone, increasing pelvic volume. This type of instability can exist with intact posterior sacroiliac ligaments. C. With internal rotational instability, force applied to the anterior superior iliac spine (arrow) will internally rotate the innominate bone, decreasing pelvic volume. This type of instability can exist with intact anterior sacroiliac ligament. D. Vertical stability implies that no vertical displacement of the innominate bone occurs when a vertical force (arrow) is applied to the affected hemipelvis. E. In vertical instability, a vertical force (arrow) applied to the affected hemipelvis results in vertical displacement of the innominate bone relative to the sacrum. This type of instability requires complete disruption of bones and/or ligaments connecting one hemipelvis and is therefore also rotationally unstable.
A
B
C
Fig. 6. Open book pelvis (APC-I) in a 64-year-old man who was bucked from a horse. A. The initial AP radiograph shows mild widening of the pubic symphysis (black arrow) measuring 1.3 cm, raising concern for an AP compression type pelvic ring disruption. B-C. Subsequently obtained axial CT images of the pelvis show a large parasymphyseal hematoma with active contrast extravasation (B, open white arrow). There is no sacroiliac joint widening in the posterior aspect of the pelvic ring (C, white arrows), confirming APC-I injury.
A
B
C
Fig. 7. Lateral compression type injury (LC-II) in a 48-year-old woman who fell down a flight of stairs. A. The initial anteroposterior pelvic radiograph shows horizontally oriented fractures of the right obturator rami (black arrow) and abnormal angulation of the right arcuate line (black arrowhead) suggestive of lateral compression type pelvic ring disruption. B. On the inlet view, inward rotation of the right hemipelvis is apparent (black open arrows), which is characteristic of lateral compression injury. The buckle fracture of the anterior cortex of the sacrum is confirmed (open white arrow). Posterior elements of the pelvic ring are best evaluated on axial CT (C), which shows buckle fracture of the anterior cortex of the sacrum (white arrowhead). Additionally, there is an avulsion fracture at the iliac insertion of the posterior sacroiliac ligaments (white arrow), which raises concern about rotational instability.
A
B
C
Fig. 8. Vertical shear injury in a 14-year-old girl who fell 4 stories. A. The initial anteroposterior pelvic radiograph shows a step-off at the symphysis pubis (black arrowhead). An additional right obturator ring fracture (black arrow) is partially obscured by compression belt buckle. Posteriorly, the right hemipelvis is displaced cephalad at the level of the SI joint. This is best appreciated by comparing the relationship between the inferior margin of the posterior right ilium (black open arrow) and the right third sacral arcade (small black arrows) to the normal relationship of the left ilium (open white arrow) with the left third sacral arcade (small white arrows). Also very faintly seen is an avulsion fragment of the transverse process of L5 (white arrowhead). B. Coronal CT image illustrates the normal relationship of the uninjured left ilium (white open arrowhead) with the sacrum. On the right side, the ilium is displaced cephalad in relation to the sacrum, and there is associated avulsion of the sacral epiphyses (black open arrowheads) at the SI joint in this skeletally immature patient. C. The semitransparent shaded surface display of the CT data shows cephalad displacement of the right iliac bone (black open arrow) with associated right obturator ring fracture (black arrows) and iliolumbar ligament avulsion from L5 (white arrowhead), confirming vertical shear injury.
A
B
C
Fig. 9. Acetabular anatomy on radiographs. A. On anteroposterior radiograph, the iliopectineal line reflects the anterior column, while the posterior column is indicated by the ilioischial line. The posterior wall is well seen through the femoral head, while the anterior wall can be more difficult to visualize. B. On obturator oblique Judet view of the left hip, the obturator ring is laid out, and the iliac wing is shortened. This view best visualizes the iliopectineal line and anterior column, as well as the posterior wall, which projects more laterally. C. On iliac oblique Judet view of the left hip, the obturator ring is now closed, and the iliac wing is laid flat. This view best visualizes the elements of the posterior column, as well as helps to visualize the anterior wall.
A
B
C
D
Fig. 10. Acetabular anatomy on CT. A. Shaded surface display of pelvis viewed from lateral position. In this anatomic position, the acetabular fossa formed by the anterior and posterior walls is directed slightly inferiorly and anteriorly. It is stabilized by the anterior column (dark shading) and posterior column (light shading). The two columns are stabilized inferiorly by the ischiopubic ramus. The sciatic buttress is the dense and thick portion of the ilium connecting the posterior column to the sacroiliac joint. B. Shaded surface display is now rotated so that the rim of the acetabular fossa is viewed straight on. The entire acetabular articular surface, composed of the posterior wall and anterior wall, is visible and is lined by the soft tissue labrum along the acetabular rim. The cotyloid fossa is the nonarticular surface forming the medial border of the acetabular fossa, and the acetabular notch is the inferior gap in the articular surface. The acetabular tectum is the horizontal weight-bearing surface at the top of the acetabulum. C. Axial image through the mid left acetabulum shows the femoral head lying concentrically within the acetabular fossa, composed of the anterior wall, cotyloid fossa, and posterior wall (checkered shading). The quadrilateral plate is the medial surface of the acetabulum, which also forms the lateral wall of the pelvic cavity. D. On axial image through the acetabular tectum and anterior inferior iliac spine (AIIS), the dotted white line roughly divides the anterior and posterior columns.
A
B
C
D
E
F
Fig. 11. Transverse fracture in a 32-year-old man ejected during a motor vehicle crash. A. The initial anteroposterior pelvic radiograph shows complex pelvic ring disruption with vertical shear of the left hemipelvis and a right acetabular fracture (black arrowhead) that disrupts both the iliopectineal and ilioischial lines. B. Shaded surface display of the right innominate bone, viewed with the acetabulum directly en face, shows a transverse acetabular fracture (white arrows) crossing the anterior and posterior anatomic columns and dividing the innominate bone into superior and inferior halves. With the shaded surface display rotated into anatomic position, viewed from C. lateral and D. anterior, the fracture (white arrows) is now seen to be oblique, extending from superomedial to inferolateral. E. Axial image from bony pelvis CT shows the classic sagittal orientation of the transverse fracture (black arrows). F. On a coronal image, here through the ischium, the transverse fracture extends from medial superiorly to lateral inferiorly.
Fig. 12. The initial anteroposterior pelvic radiograph of a 21-year-old woman involved in a motor vehicle crash shows disruption of the iliopectineal line (black arrow) while the ilioischial line remains preserved. Findings suggest involvement of the anterior wall of the acetabulum.
Fig. 13. Posterior acetabular wall fracture in a 38-year-old man involved in a motorcycle crash. A. The initial anteroposterior pelvic radiograph shows a bone fragment (black arrow) originating from the posterior wall of the right acetabulum (open black arrow). The iliopectineal and ilioischial lines (black arrowheads) are intact. B. The axial image from the CT scan confirms that the fracture fragment (black arrow) originates form the posterior acetabular wall (open black arrow). Several small osseous fragments (white arrow) are entrapped in the joint space. C. The virtual iliac oblique (Judet) view, which was generated from the CT data, shows the posterior wall fracture fragment (black arrow) and confirms an intact posterior column.
Fig. 14. Anterior column fracture in a 68-year-old woman after motorcycle crash. Shaded surface display from pelvic CT, viewed from lateral orientation, demonstrates an anterior column fracture extending through the ilium (black arrow), acetabulum, and ischiopubic ramus (white arrowhead).
A
B
D
E
C
Fig. 15. Associated both column left acetabular fracture in a 72-year-old man status post motor vehicle collision. Selected axial images (A-C) from CT bony pelvis show fracture extending through A. the iliac wing (black arrowhead), B. acetabular tectum in a coronal orientation (black arrows), and C. through the left ischiopubic ramus. An additional fracture (white arrows, B) dividing the posterior column at the level of the tectum creates a vertically oriented spur of bone (asterisk) contiguous with the ilium superiorly. D. The vertically oriented spur of intact ilium (asterisk) is again seen on a shaded surface display of the pelvis, viewed from posterolateral, where the fractures of the anterior column (black arrowhead) and posterior column (white arrow) converge to completely separate the tectum from the sacroiliac joint. E. On the obturator oblique virtual Judet
view, the vertically oriented spur of bone projects posterolaterally relative to the medially displaced acetabular fragments, resulting in the spur sign (white arrowhead).
A B C Fig. 16. Acetabular fracture planes on axial CT. The acetabular roof or tectum is the slice on axial images just cephalad to the femoral head. Analysis of the tectum can be useful for categorization of acetabular fractures. A. The major fracture plane will be sagittally oriented (white arrowheads) in transverse fractures (see also Fig 11). B. When a column type fracture is present, the major fracture plane is coronally oriented (black arrowheads, see also Fig 15). C. Posterior wall fractures show a peripheral fracture plane at the tectum (open white arrowheads, see also Fig 13).
Imaging of Pelvic Ring and Acetabular Trauma Claire K. Sandstrom MD, Joel A. Gross MD, Ken F. Linnau MD MS
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PII: DOI: Reference:
S0037-198X(16)00034-1 http://dx.doi.org/10.1053/j.ro.2016.03.002 YSROE50551
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Seminar in Roentgenology
Cite this article as: Claire K. Sandstrom MD, Joel A. Gross MD, Ken F. Linnau MD MS, Imaging of Pelvic Ring and Acetabular Trauma, Seminar in Roentgenology, http://dx.doi. org/10.1053/j.ro.2016.03.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Imaging of Pelvic Ring and Acetabular Trauma
Authors: Claire K. Sandstrom, MD – Assistant Professor, Department of Radiology, University of Washington / Harborview Medical Center Joel A. Gross, MD – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center Ken F. Linnau, MD MS – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center
From University of Washington / Harborview Medical Center Correspondence may be sent to: [email protected], 206.744.3561, or 325 Ninth Ave, Box 359728, Seattle WA 98104
Authors: Claire K. Sandstrom, MD – Assistant Professor, Department of Radiology, University of Washington / Harborview Medical Center Ken F. Linnau, MD MS – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center Joel A. Gross, MD – Associate Professor, Department of Radiology, University of Washington / Harborview Medical Center From University of Washington / Harborview Medical Center Correspondence may be sent to: [email protected], 206.744.3561, or 325 Ninth Ave, Box 359728, Seattle WA 98104
Introduction
Blunt trauma to the pelvis can cause fractures and ligamentous injuries to the pelvic ring and can fracture the acetabulum. Pelvic and acetabular fractures often occur with high-energy blunt trauma, including motor vehicle and motorcycle crashes, car versus pedestrian accidents, and falls.1-3 Low-energy falls can also cause pelvic and acetabular fractures in elderly osteoporotic patients.1,2,4-6 Potentially life-threatening pelvic hemorrhage, urethral and bladder injuries, and additional intraabdominal injuries may accompany pelvic trauma, affecting emergent management decisions in blunt pelvic trauma patients. 3,6-9
Pelvic Ring Injuries
The presence of pelvic ring injuries affects clinical decision-making in several ways. Unstable patients with pelvic injuries may benefit from emergent angiography or retroperitoneal pelvic packing10 rather than laparotomy for control of pelvic hemorrhage. Unstable pelvic ring injuries will ultimately require internal fixation. Bladder and urethral injuries, though not common, may require surgical repair and require dedicated imaging for prompt diagnosis.
Pelvic hemorrhage Pelvic fractures commonly cause pelvic bleeding. The majority of bleeding is self-limited, arising from venous structures or bone edges. However,
5-20% of patients with pelvic fractures have potentially life-threatening arterial hemorrhage, which may be amenable to angioembolization.11 Clinical predictors of major hemorrhage related to pelvic fractures, based on initial pelvic radiograph (Fig 1), blood work, and vital signs, are shown in Table 1.11 Likelihood of pelvic hemorrhage ranges from less than 2% for those with no predictors to over 60% for those with three or four predictors of major hemorrhage.11 Thus, angiography should be prioritized for those patients with a higher probability of major pelvic hemorrhage. Patients older than 60 years of age with major pelvic fractures and those with active arterial contrast extravasation detected on CT (Fig 2) may benefit from pelvic angiography and angioembolization regardless of hemodynamic status.12,13 External pelvic stabilization decreases pelvic volume, although the degree to which this helps to tamponade bleeding from venous structures and bone edges not amenable to angioembolization remains uncertain.12 While the utility of contrast-enhanced CT for detection of active arterial hemorrhage in hemodynamically stable blunt trauma patients is well documented,14-18 the role of arterial-phase CT of the pelvis remains uncertain.19
Bladder and Urethral injuries Bladder injuries complicate less than 10% of blunt pelvic fractures. 20 Injuries are categorized as extraperitoneal, intraperitoneal, or combined. Independent multivariate predictors of bladder rupture include pubic symphyseal diastasis >1cm (RR 9.8) and obturator ring fractures displaced >1cm (RR 3.2) (Fig 3).20 All patients with bladder rupture have hematuria, with at least 3+
hematuria on dipstick urinalysis or greater than 30 red blood cells per high powered field (RBC/HPF) on microscopic urinalysis.20,21 Thus, detection of anterior pelvic ring injuries should prompt urinalysis, and CT cystogram should be performed when the hematuria threshold is exceeded.22 While the majority of bladder ruptures are associated with pelvic fractures, a smaller percentage, usually involving intraperitoneal bladder rupture, occur in the absence of osseous pelvic injury.21,23,24 Patients with bladder rupture often have other intraabdominal injuries, including hollow visceral, splenic, and hepatic injuries.24 Urethral injuries are also rare but are more likely in male patients with anterior pelvic ring disruption. Predictors of urethral injury include diastasis (≥1cm) of the pubic symphysis (OR 11.8) or of inferomedial pubic bone fractures (OR 6.4).25 The probability of urethral injury increases approximately 10% with each millimeter increase in displacement of pubic components.25 Diagnosis and characterization of male urethral injuries is performed by retrograde urethrogram,26 although this might be difficult to perform in hemodynamically unstable patients or those with spine injuries.27
Pelvic ring stability The adult osseous pelvis is formed by the sacrum posteriorly and the bilateral innominate bones (formed by fusion of the ilium, ischium, and pubic bones) (Fig 4). The osseous structures have no inherent stability, relying instead on the integrity of the sacroiliac (SI) ligaments (anterior, short interosseous, and posterior).28 The pubic symphyseal fibrocartilage and pubic ligaments of the
anterior pelvic ring reinforce the SI joints against rotation.28,29 Supplemental support is provided by the iliolumbar, lateral lumbosacral, sacrotuberous, and sacrospinous ligaments, which primarily resist rotation of the innominate bone relative to the sacrum.28 Two types of stability, rotational and vertical, are considered (Fig 5). Most commonly, rotational stability implies that pressure applied to the anterior iliac spines will not result in unlimited outward rotation of the innominate bone, akin to opening a book. Disruption of the pubic symphysis or obturator ring without sacral or SI ligament injury maintains rotational stability because the SI ligaments resist rotational forces. Conversely, if the anterior pelvic ring, the anterior SI ligaments, and the supplementary ligamentous structures are disrupted, the innominate bone can rotate posteriorly until the iliac spine abuts the sacrum, even if the posterior SI ligaments remain intact.28 In another form of rotational instability, anterior ring fractures and posterior SI ligament disruption allow inward rotation of the hemipelvis using the anterior sacrum as a hinge (even if the anterior SI ligament remains intact).30 Vertical stability implies that each side of the pelvis maintains a normal craniocaudal relationship with the sacrum with upward forces, such as from standing upright. If a patient were to attempt to stand on a vertically unstable pelvic ring, the affected hemipelvis would move superiorly relative to the intact sacrum. This usually happens through a completely disrupted SI joint but can occur through complete fractures of the ilium or the sacrum. A vertically unstable pelvis is also rotationally unstable, whereas rotational instability does not imply
vertical instability. The presence of either rotational or vertical instability requires internal fixation.30 While pelvic stability is ultimately determined on clinical examination, radiology reports tailored to describe the disrupted bony and ligamentous elements of the pelvic ring will aid the surgeon’s decision-making.
Pelvic ring injury classification Pelvic ring injuries are commonly classified according to the YoungBurgess classification system, summarized in Table 2. Pelvic surgeons often use the Tile/Orthopedic Trauma Association classification system,31 which is less reliable when applied by less experienced providers.32 The four injury categories in the Young-Burgess system—lateral compression, anteroposterior compression, vertical shear, and combined mechanism—are based on the estimated force trajectory and may help determine corrective forces required for pelvic stabilization.28 However, force trajectory predicted by radiographic appearance does not always correlate with actual mechanism of injury based on crash site analysis.33 Imaging findings and manual examination are combined to differentiate stable and unstable pelvic ring injuries, thus identifying which patients need internal fixation. In anteroposterior compression injuries, disruption of the pubic symphysis alone results in anterior pelvic ring widening (Fig 6). The anterior SI joint might appear slightly wide even when the anterior SI ligaments remain intact. These
patients require manual evaluation (sometimes under anesthesia) to confirm stability.30 Lateral compression injuries are characterized by obturator ring and anterior sacral impaction fractures. The obturator ring fractures may be ipsilateral and/or contralateral to the sacral injury. Obturator ring fracture orientation may be axial, coronal, or comminuted. The most common finding indicating rotational instability is a crescent fracture, which ranges in appearance from a tiny avulsion of the posterior ilium to a large iliac wing fracture (Fig 7).34,35 Complete fracture through the entire sacral wing or tear of the SI ligament without osseous injury are less commonly seen.30 These posterior injuries should be specifically sought with all lateral compression injuries, as they potentially change management from conservative to surgical. Cephalad displacement of the hemipelvis in vertical shear injuries is best assessed posteriorly, using the relationship of the sacral arcades with the sciatic buttress (Fig 8). Vertical displacement of the posterior pelvis indicates vertical instability. Young-Burgess also includes a catchall category of combined pelvic ring injuries representing a variable combination of anteroposterior, lateral, and/or vertical directed forces.28 A radiology report using the Young-Burgess classification system to describe pelvic ring disruption will reliably convey information between providers during initial clinical decision-making.
Imaging of pelvic ring injuries Optimal imaging of pelvic ring disruptions has not been validated in the literature. While it is generally accepted that CT is highly sensitive, an appropriate diagnosis can be made with radiographs in most cases. 28 The degree of rotation of the pelvic ring is best shown on inlet views, while the degree of vertical displacement in vertical shear injuries is optimally assessed on pelvic outlet radiographs.28 Virtual inlet and outlet views can be created from existing torso CT images including the pelvis, achieving similar or better quality while decreasing radiation exposure and time to acquire additional adequate radiographic views.36 Involvement of the sacrum and sacroiliac joint is most reliably assessed by CT.28,37 MRI may be useful in osteoporotic patients with anterior pelvic ring injuries to identify non-displaced posterior ring fractures.38
Acetabular Fractures
Acetabular fractures are uncommon but important injuries that frequently require surgical reconstruction. The most common fracture patterns overall are posterior wall fractures, associated both column fractures, and transverse with posterior wall fractures.2,39-42 Acetabular fractures are often related to highenergy motor vehicle crashes, but elderly patients are much more likely to injure their acetabulum in low-energy falls.2 As a result, fractures of the anterior column, including anterior column with posterior hemitransverse fractures, are more common in older patients.2 With aging of the global population, these
previously rare types of fractures are increasing in frequency.2,42,43 Though other extremity injuries commonly accompany acetabular fractures regardless of age,40 younger patients are more likely to have additional injuries to other organ systems than older patients.2 When acetabular injuries coexist with pelvic ring injuries, treatment of both is more complicated.44 Radiographic features of acetabular anatomy are highlighted in Fig 9, while CT anatomy is reviewed in Fig 10.
Acetabular fracture classification The classification system of acetabular fractures developed and refined by Emile Letournel and Robert Judet is widely used and guides surgical approach and operative fixation.45-48 Other classification systems have not gained acceptance with surgeons. While complicated, pre-operative classification of acetabular fractures is important, as different injury types necessitate different skin incisions and fixation approaches.46 The Judet and Letournel classification delineates ten types of injuries, five of which involve a single fracture plane (simple or elementary types), and five of which are more complex (associated types), as summarized in Table 3. These were recently reviewed by Scheinfeld et al.,49 who provide a beautiful and extensive review of acetabular fractures, which is not repeated here. Instead we will focus on a few key points that often cause confusion. Key Concept #1: Transverse fractures cross both columns but are simple fractures. They are not the same as associated both column fractures.
Transverse fractures were so named when viewing the acetabulum en face with the patient positioned on his side for surgery—however, in the upright anatomic position, the rim is rotated inferiorly and anteriorly (Fig 11). This rotation explains why the transverse fracture characteristically extends from superomedial to inferolateral in an oblique plane (best appreciated on axial or coronal images). On individual axial images, the fracture has a sagittal orientation, extending anteroposteriorly. However, its location shifts from medial to lateral as axial images are viewed from superior to inferior. The addition of posterior wall comminution or ischiopubic ramus involvement advances the transverse fracture from a simple/elementary type to a complex type fracture, resulting in transverse with posterior wall fracture or T-shaped fracture, respectively. Key Concept #2: An anterior wall fracture is not a mirror image of a posterior wall fracture, as anterior wall fractures disrupt the iliopectineal line (Fig 12). In comparison, posterior wall fractures (Fig 13) always spare the ilioischial line, which defines the anatomic posterior column. In anterior wall fractures, the iliopectineal line of the pelvic brim is fractured, but the anterior iliac spines and the pubic body, as well as the posterior column, remain intact and in normal anatomic position.46 In contrast, anterior column fractures extend from the ilium, crossing the acetabular roof and quadrilateral plate, to the ischiopubic ramus (Fig 14). Key Concept #3: An associated both column fracture completely separates the acetabular tectum from the sacroiliac joint (Fig 15). The posterior column fracture exiting through the sciatic notch is joined by the iliac
wing fracture defining the anterior column component. This results in an inferiorly-directed bone shard or ―spur‖ of the fractured ilium, pathognomonic of associated both column injuries and characteristically seen on the obturator oblique Judet view projecting laterally from the acetabular fragments which have been displaced medially. The other fracture patterns that involve both anatomic columns—the T-shaped fracture, the anterior column/wall with posterior hemitransverse, transverse, and transverse with posterior wall patterns—leave some part of the acetabulum attached to the ilium and SI joint. Some acetabular fracture imaging features not included in the Judet and Letournel system predict poor clinical outcome and should be reported.50-52 These findings (listed in Table 4) may lead to the development of premature post-traumatic osteoarthritis and often necessitate joint replacement.53 Many of these predictors of poor outcome are more common in elderly patients.2
Imaging of acetabular fractures Characterization of acetabular fractures was originally performed with anteroposterior and bilateral oblique Judet views (iliac oblique and obturator oblique).46 Orthopedic surgeons who treat acetabular fractures on a regular basis will reliably classify injuries based on radiography.54 Nevertheless, CT scanning of acetabular fractures is now common practice, and although some centers still acquire conventional radiographs, virtual reconstructions from CT data can also be used. Potential benefits of CT-reconstructed virtual images include the ability (1) to subtract bowel or bladder contrast, (2) to minimize
patient discomfort, time and radiation exposure from obtaining additional radiographs, (3) to optimize projections without the need for repeat exposures, and (4) to overcome difficulties in penetration in obese patients. Use of axial CT images, 3D reconstructions, or virtual radiographic pelvis images compares favorably to the use of conventional radiographs.55,56 CT images are also helpful for preoperative measurements (articular surface displacement, impaction), detection of intraarticular bone fragments, and identification of associated femoral head injuries.37,57 In general, axial CT images through the acetabulum show a coronal fracture plane for column fractures, a sagittal fracture plane for transverse fractures, and an oblique fracture in wall fractures (Fig 16).
Conclusion
Though uncommon, pelvic ring injuries and acetabular fractures are important diagnoses in blunt trauma patients. Associated injuries, including pelvic hemorrhage, bladder and urethral injuries, and other abdominal organ injuries, are frequently present. Concepts of stability and force trajectory guide decision-making regarding surgical fixation for pelvic ring injuries, and the YoungBurgess system is useful for communication of imaging findings. Orthopedic surgeons use the Judet and Letournel system to classify acetabular fractures and to guide surgical approach. Radiology reports should include features relevant for surgical decision-making.
Tables Table 1. Clinical predictors of major hemorrhage related to pelvic fractures. Predictor Displaced obturator ring fracture (≥1cm) Pubic symphyseal diastasis (≥1cm) Hematocrit ≤30% Pulse ≥130 beats / min
Odds Ratio for Major Hemorrhage 3.8 3.9 6.6 3.3
Table 2. Summary of Young-Burgess classification system for pelvic ring injuries. Injury type
Anteroposterior compression I (APC-I)
Characteristic injury of anterior pelvic ring Pubic symphyseal diastasis or sagittal pubic rami fractures
Anteroposterior compression II (APC-II)
Pubic symphyseal diastasis or sagittal pubic rami fractures
Anteroposterior compression III (APC-III)
Pubic symphyseal diastasis or sagittal pubic rami fractures
Lateral compression I (LC-I)
Pubic rami fractures in axial, coronal, or comminuted planes
Sacral impaction injury
Lateral compression II (LC-II)
Pubic rami fractures in axial, coronal, or comminuted planes
Lateral compression III, (LC-III) aka ―windswept pelvis‖ Vertical shear (VS)
Pubic rami fractures in axial, coronal, or comminuted planes
Crescent fracture of iliac wing (posterior SI ligament avulsion or tear) Ipsilateral LC-I or LC-II injury as well as contralateral open book injury (APC II or III)
Rotationally stable, vertically stable Rotationally unstable, vertically stable Rotationally unstable, vertically unstable Rotationally stable, vertically stable Rotationally unstable, vertically stable Rotationally unstable, +/vertically unstable
Vertical displacement of hemipelvis (usually at SI joint but some at iliac wing or sacral
Rotationally unstable, vertically unstable
Vertical pubic rami fractures or pubic symphyseal diastasis
Differentiating features
Typical stability
SI joints may be stretched but anterior and posterior SI ligaments are intact Anterior SI ligament torn with anterior SI joint widening; posterior SI ligament intact Anterior and posterior SI ligaments torn with diffuse SI joint widening
Combined mechanism
fracture) Variable combination of lateral compression, anteroposterior compression, and vertical shear
Variable, but often rotationally and vertically unstable
Table 3. Summary of acetabular fractures as classified by Judet and Letournel. Simple or elementary types
Complex types
Posterior wall
Transverse with posterior wall
Anterior wall
Posterior column with posterior wall
Posterior column
Associated both column
Anterior column
Anterior column or wall with posterior hemitransverse
Transverse
T-shaped
Table 4. Imaging factors that contribute to poor surgical outcome following acetabular fracture. Poor Prognostic Factors Contributing to Poor Surgical Outcome and Early Osteoarthritis Comminution of posterior wall Articular impaction (often with rotation) of posterior wall fragment(s) Articular impaction (often with rotation) of medial roof fragment(s) Hip dislocation Hip subluxation or incongruity of joint Femoral head injury
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Figures and Legends for Pelvis Paper:
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Fig. 1. Arterial hemorrhage in pelvic ring injury in a 64-year-old man who was thrown from a horse. A. The initial anteroposterior pelvic radiograph demonstrates distraction of the symphysis pubis (double headed arrow) to 2.7cm and mild right sacroiliac joint widening (black arrow). B. Coronal CT image confirms widening of the symphysis pubis and demonstrates active arterial extravasation adjacent to the left superior pubic ramus (white arrow). C. Subsequent pelvic angiography demonstrates active extravasation from the left obturator artery (white arrow), which was controlled with coil embolization.
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Fig. 2. Arterial hemorrhage detected on CT in a 75-year-old woman following ground level fall. The patient was taking warfarin. A. Semitransparent shaded surface display from CT of the pelvis demonstrates a lateral compression fracture, with left superior and inferior obturator ring fractures (white arrowheads), and left sacral impaction fracture (black arrow). B. Coronal image from contrast enhanced CT demonstrates active vascular extravasation (white arrow) near the left superior pubic ramus fracture (white arrowhead). Large pelvic hematoma displaces the bladder and Foley catheter toward the right. C. Digital subtraction catheter angiogram demonstrates arterial extravasation (white arrow) from the left pudendal artery, in this patient with multiple occluded pelvic arteries and extensive collateral vessels.
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Fig. 3. Pelvic ring disruption with extraperitoneal bladder rupture in a 38-year-old man following 40 foot fall. A. The initial anteroposterior pelvic radiograph demonstrates diastasis of the pubic symphysis (double headed arrow) measuring 1.7 cm. A fracture of the left obturator ring (white arrow) and subtle widening of the left sacroiliac joint (open black arrow) are also noted. B. Axial and C. coronal images from CT cystogram demonstrate an extraperitoneal bladder rupture (black arrowhead), with contrast extending into the extraperitoneal space (black arrows) and through the disrupted symphysis pubis to below the right pubic body (open white arrow).
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Fig. 4. Normal pelvic ring anatomy. Bony anatomy on A. anterior and B. posterior projections of shaded surface display of the bony pelvis and on C. anteroposterior pelvic radiograph. Short white lines denote the junctions of the ilium, ischium, and pubis on images A. and B. ASIS, anterior superior iliac spine. AIIS, anterior inferior iliac spine. PSIS, posterior superior iliac spine. PIIS, posterior inferior iliac spine. Pelvic ligamentous stabilizers are depicted on D. anterior and E. posterior projections of shaded surface displays of the bony pelvis. L, ligament.
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Fig. 5. Pelvic ring stability and instability. A. In a rotationally stable pelvis, the pelvic ring resists force applied to the anterior superior iliac spine (arrow). No rotation is appreciated clinically or radiologically. B. With external rotational instability, force applied to the anterior superior iliac spine (arrow) will externally rotate the innominate bone, increasing pelvic volume. This type of instability can exist with intact posterior sacroiliac ligaments. C. With internal rotational instability, force applied to the anterior superior iliac spine (arrow) will internally rotate the innominate bone, decreasing pelvic volume. This type of instability can exist with intact anterior sacroiliac ligament. D. Vertical stability implies that no vertical displacement of the innominate bone occurs when a vertical force (arrow) is applied to the affected hemipelvis. E. In vertical instability, a vertical force (arrow) applied to the affected hemipelvis results in vertical displacement of the innominate bone relative to the sacrum. This type of instability requires complete disruption of bones and/or ligaments connecting one hemipelvis and is therefore also rotationally unstable.
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Fig. 6. Open book pelvis (APC-I) in a 64-year-old man who was bucked from a horse. A. The initial AP radiograph shows mild widening of the pubic symphysis (black arrow) measuring 1.3 cm, raising concern for an AP compression type pelvic ring disruption. B-C. Subsequently obtained axial CT images of the pelvis show a large parasymphyseal hematoma with active contrast extravasation (B, open white arrow). There is no sacroiliac joint widening in the posterior aspect of the pelvic ring (C, white arrows), confirming APC-I injury.
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Fig. 7. Lateral compression type injury (LC-II) in a 48-year-old woman who fell down a flight of stairs. A. The initial anteroposterior pelvic radiograph shows horizontally oriented fractures of the right obturator rami (black arrow) and abnormal angulation of the right arcuate line (black arrowhead) suggestive of lateral compression type pelvic ring disruption. B. On the inlet view, inward rotation of the right hemipelvis is apparent (black open arrows), which is characteristic of lateral compression injury. The buckle fracture of the anterior cortex of the sacrum is confirmed (open white arrow). Posterior elements of the pelvic ring are best evaluated on axial CT (C), which shows buckle fracture of the anterior cortex of the sacrum (white arrowhead). Additionally, there is an avulsion fracture at the iliac insertion of the posterior sacroiliac ligaments (white arrow), which raises concern about rotational instability.
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Fig. 8. Vertical shear injury in a 14-year-old girl who fell 4 stories. A. The initial anteroposterior pelvic radiograph shows a step-off at the symphysis pubis (black arrowhead). An additional right obturator ring fracture (black arrow) is partially obscured by compression belt buckle. Posteriorly, the right hemipelvis is displaced cephalad at the level of the SI joint. This is best appreciated by comparing the relationship between the inferior margin of the posterior right ilium (black open arrow) and the right third sacral arcade (small black arrows) to the normal relationship of the left ilium (open white arrow) with the left third sacral arcade (small white arrows). Also very faintly seen is an avulsion fragment of the transverse process of L5 (white arrowhead). B. Coronal CT image illustrates the normal relationship of the uninjured left ilium (white open arrowhead) with the sacrum. On the right side, the ilium is displaced cephalad in relation to the sacrum, and there is associated avulsion of the sacral epiphyses (black open arrowheads) at the SI joint in this skeletally immature patient. C. The semitransparent shaded surface display of the CT data shows cephalad displacement of the right iliac bone (black open arrow) with associated right obturator ring fracture (black arrows) and iliolumbar ligament avulsion from L5 (white arrowhead), confirming vertical shear injury.
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Fig. 9. Acetabular anatomy on radiographs. A. On anteroposterior radiograph, the iliopectineal line reflects the anterior column, while the posterior column is indicated by the ilioischial line. The posterior wall is well seen through the femoral head, while the anterior wall can be more difficult to visualize. B. On obturator oblique Judet view of the left hip, the obturator ring is laid out, and the iliac wing is shortened. This view best visualizes the iliopectineal line and anterior column, as well as the posterior wall, which projects more laterally. C. On iliac oblique Judet view of the left hip, the obturator ring is now closed, and the iliac wing is laid flat. This view best visualizes the elements of the posterior column, as well as helps to visualize the anterior wall.
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Fig. 10. Acetabular anatomy on CT. A. Shaded surface display of pelvis viewed from lateral position. In this anatomic position, the acetabular fossa formed by the anterior and posterior walls is directed slightly inferiorly and anteriorly. It is stabilized by the anterior column (dark shading) and posterior column (light shading). The two columns are stabilized inferiorly by the ischiopubic ramus. The sciatic buttress is the dense and thick portion of the ilium connecting the posterior column to the sacroiliac joint. B. Shaded surface display is now rotated so that the rim of the acetabular fossa is viewed straight on. The entire acetabular articular surface, composed of the posterior wall and anterior wall, is visible and is lined by the soft tissue labrum along the acetabular rim. The cotyloid fossa is the nonarticular surface forming the medial border of the acetabular fossa, and the acetabular notch is the inferior gap in the articular surface. The acetabular tectum is the horizontal weight-bearing surface at the top of the acetabulum. C. Axial image through the mid left acetabulum shows the femoral head lying concentrically within the acetabular fossa, composed of the anterior wall, cotyloid fossa, and posterior wall (checkered shading). The quadrilateral plate is the medial surface of the acetabulum, which also forms the lateral wall of the pelvic cavity. D. On axial image through the acetabular tectum and anterior inferior iliac spine (AIIS), the dotted white line roughly divides the anterior and posterior columns.
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Fig. 11. Transverse fracture in a 32-year-old man ejected during a motor vehicle crash. A. The initial anteroposterior pelvic radiograph shows complex pelvic ring disruption with vertical shear of the left hemipelvis and a right acetabular fracture (black arrowhead) that disrupts both the iliopectineal and ilioischial lines. B. Shaded surface display of the right innominate bone, viewed with the acetabulum directly en face, shows a transverse acetabular fracture (white arrows) crossing the anterior and posterior anatomic columns and dividing the innominate bone into superior and inferior halves. With the shaded surface display rotated into anatomic position, viewed from C. lateral and D. anterior, the fracture (white arrows) is now seen to be oblique, extending from superomedial to inferolateral. E. Axial image from bony pelvis CT shows the classic sagittal orientation of the transverse fracture (black arrows). F. On a coronal image, here through the ischium, the transverse fracture extends from medial superiorly to lateral inferiorly.
Fig. 12. The initial anteroposterior pelvic radiograph of a 21-year-old woman involved in a motor vehicle crash shows disruption of the iliopectineal line (black arrow) while the ilioischial line remains preserved. Findings suggest involvement of the anterior wall of the acetabulum.
Fig. 13. Posterior acetabular wall fracture in a 38-year-old man involved in a motorcycle crash. A. The initial anteroposterior pelvic radiograph shows a bone fragment (black arrow) originating from the posterior wall of the right acetabulum (open black arrow). The iliopectineal and ilioischial lines (black arrowheads) are intact. B. The axial image from the CT scan confirms that the fracture fragment (black arrow) originates form the posterior acetabular wall (open black arrow). Several small osseous fragments (white arrow) are entrapped in the joint space. C. The virtual iliac oblique (Judet) view, which was generated from the CT data, shows the posterior wall fracture fragment (black arrow) and confirms an intact posterior column.
Fig. 14. Anterior column fracture in a 68-year-old woman after motorcycle crash. Shaded surface display from pelvic CT, viewed from lateral orientation, demonstrates an anterior column fracture extending through the ilium (black arrow), acetabulum, and ischiopubic ramus (white arrowhead).
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Fig. 15. Associated both column left acetabular fracture in a 72-year-old man status post motor vehicle collision. Selected axial images (A-C) from CT bony pelvis show fracture extending through A. the iliac wing (black arrowhead), B. acetabular tectum in a coronal orientation (black arrows), and C. through the left ischiopubic ramus. An additional fracture (white arrows, B) dividing the posterior column at the level of the tectum creates a vertically oriented spur of bone (asterisk) contiguous with the ilium superiorly. D. The vertically oriented spur of intact ilium (asterisk) is again seen on a shaded surface display of the pelvis, viewed from posterolateral, where the fractures of the anterior column (black arrowhead) and posterior column (white arrow) converge to completely separate the tectum from the sacroiliac joint. E. On the obturator oblique virtual Judet
view, the vertically oriented spur of bone projects posterolaterally relative to the medially displaced acetabular fragments, resulting in the spur sign (white arrowhead).
A B C Fig. 16. Acetabular fracture planes on axial CT. The acetabular roof or tectum is the slice on axial images just cephalad to the femoral head. Analysis of the tectum can be useful for categorization of acetabular fractures. A. The major fracture plane will be sagittally oriented (white arrowheads) in transverse fractures (see also Fig 11). B. When a column type fracture is present, the major fracture plane is coronally oriented (black arrowheads, see also Fig 15). C. Posterior wall fractures show a peripheral fracture plane at the tectum (open white arrowheads, see also Fig 13).