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Answer
For the patient with a traumatized acetabulum, accurate radiographic diagnosis and classification are the cornerstones of effective clinical care. Acetabular fractures are caused by high kinetic energy, and satisfactory management requires differentiation of the fracture types. The classification system of Judet and Letournel has led to improved management of such injuries. [1, 2, 3, 4] However, trauma-related acetabular fractures are often complex, with multiple fragments and secondary fracture lines. Computed tomography (CT) provides information regarding the extent of the fracture and is complementary to radiography for ascertaining the spatial arrangement of fracture fragments. Three-dimensional (3D) reconstruction of CT data can be helpful in understanding the complex fracture patterns.
Acetabular fractures are often complex injuries and the result of high-energy trauma with associated injuries. Understanding and classification of these rare injuries using radiography can be difficult and are much facilitated by the addition of CT. Using multidetector CT (MDCT) with two-dimensional (2D) multiplanar reformatted (MPR) images and 3D volume-rendered images, the supplemental oblique radiographic Judet views can usually be omitted. MDCT is an indispensable tool in preoperative imaging of acetabular fractures, as well as postoperative imaging in complicated cases. MDCT is excellent for detailed imaging of fracture extent, joint congruency, step-offs or gaps in the joint surface, and entrapped osteochondral fragments. [1, 5, 6]
Most acetabular fractures occur in the setting of significant trauma secondary to either a moving vehicular accident or a high-velocity acute-deceleration injury. Blunt force is exerted on the femur, is transmitted through the femoral head, and is transferred to the acetabulum. The direction and magnitude of the force, as well as the position of the femoral head, determine the pattern of acetabular injury. The determination of the pattern of injury is key to the classification of an acetabular fracture, which, in turn, is critical to yield the highest quality orthopedic surgical treatment and therapy.
Once the acetabular fracture is classified, appropriate therapy may be planned and implemented. [7, 8, 9, 10, 11] The anatomy of the acetabulum and computed tomography (CT) images of fractures are depicted below.
Lateral view of the left acetabulum. The left femur has been removed. The articular surface of the acetabulum is in the shape of an inverted horseshoe (outlined in red). The anterior column of the acetabulum includes most of the iliac wing, the anterior acetabulum, and the superior pubic ramus. The posterior column begins at the sciatic notch and includes the posterior portion of the acetabulum and the ischium.
Acetabular fracture orientation with a computed tomography (CT) scan. A CT scan of the left acetabulum obtained at the level of the dome shows that transverse-type acetabular fractures have a vertical (sagittal) orientation. Column-type fractures have a horizontal (coronal) orientation.
Acetabular fracture orientation with a computed tomography (CT) scan. A CT scan of the left midacetabulum shows that wall fractures have an oblique orientation.
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Lateral view of the left acetabulum. The left femur has been removed. The articular surface of the acetabulum is in the shape of an inverted horseshoe (outlined in red). The anterior column of the acetabulum includes most of the iliac wing, the anterior acetabulum, and the superior pubic ramus. The posterior column begins at the sciatic notch and includes the posterior portion of the acetabulum and the ischium.
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Anteroposterior view of the pelvis. The left femur has been removed for illustration purposes. The iliopectineal, or iliopubic, line is an important landmark for examining the anterior column of the acetabulum. The ilioischial line demarcates the medial border of the posterior column. The posterior wall of the acetabulum is larger and projects more laterally than does the anterior wall.
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Anteroposterior (AP) radiograph of the pelvis. The iliopectineal (or iliopubic) and ilioischial lines serve as landmarks for the anterior and posterior columns, respectively. The larger and more lateral posterior wall is visualized more easily than is the smaller, more medial anterior wall. The acetabular tear figure is a composite shadow of the inferomedial structures that compose the acetabulum. The ilioischial line should pass through the teardrop on a true AP view of the pelvis.
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Left obturator oblique view of the pelvis. The left obturator ring is seen en face. The anterior column and posterior wall of the left acetabulum are profiled in this position.
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Left iliac oblique view of the pelvis. The left iliac wing is demonstrated en face. The left posterior column and the anterior wall are seen in profile.
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Acetabular fracture classification system. Judet and colleagues (1964) described the classification scheme that is most commonly used today. Of the 10 types, 5 are elementary fractures (top row), and 5 are associated fractures (bottom row). Elementary types involve 1 primary fracture plane. Associated types involve more than 1 fracture plane.
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Acetabular fracture orientation with a computed tomography (CT) scan. A CT scan of the left acetabulum obtained at the level of the dome shows that transverse-type acetabular fractures have a vertical (sagittal) orientation. Column-type fractures have a horizontal (coronal) orientation.
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Acetabular fracture orientation with a computed tomography (CT) scan. A CT scan of the left midacetabulum shows that wall fractures have an oblique orientation.
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Anterior wall acetabular fracture. A computed tomography (CT) scan demonstrates an oblique fracture through the anterior wall of the left acetabulum (arrow). Such fractures are uncommon in isolation. The patient had other pelvic injuries.
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Posterior wall acetabular fracture. Anteroposterior radiograph of the pelvis. The posterior wall of the left acetabulum is disrupted (arrow).
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Posterior wall acetabular fracture. A left obturator oblique radiograph of the pelvis. The posterior wall fracture (arrow) is better depicted on this view than on the anteroposterior view.
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Computed tomography (CT) scan of a posterior wall acetabular fracture. The oblique fracture of the left acetabulum is clearly depicted. The degree of displacement and marginal impaction can be determined more accurately with CT scanning than with radiography.
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Transverse with posterior wall acetabular fracture. An anteroposterior radiograph of the pelvis shows that the central dislocation of the left femoral head results in the disruption of the iliopectineal and ilioischial lines. In addition, the left posterior acetabular wall is disrupted.
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Transverse fracture with a posterior wall acetabular fracture. Compared with the anteroposterior view, this left obturator oblique view of the pelvis view better demonstrates the anterior column and posterior wall disruption. The obturator ring is intact.
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Computed tomography (CT) scan of a transverse fracture with a posterior wall acetabular fracture. The vertically oriented transverse fracture (arrow) of the left acetabulum is well depicted on CT scans. Note the oblique posterior wall fracture (arrowhead). Posterior wall fractures often are associated with femoral head dislocation.
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T-shaped acetabular fracture. An anteroposterior radiograph of the pelvis shows that a transverse fracture (arrows) disrupts the left iliopectineal and ilioischial lines. The obturator ring also is interrupted (arrowheads). No iliac wing fracture is seen above the level of the acetabulum.
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Computed tomography (CT) scan of T-shaped acetabular fracture. The transverse portion of the fracture has a vertical (sagittal) orientation (arrow). The extension of the fracture through the medial wall represents the stem of the T (arrowhead). More inferior CT scans demonstrated the obturator ring fractures.
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Posterior column acetabular fracture. An anteroposterior radiograph of the pelvis shows that the left femoral head is dislocated posteriorly. The ilioischial line is broken, but the iliopectineal line remains intact.
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Posterior column acetabular fracture. Compared with the anteroposterior view, the left obturator oblique radiograph of the pelvis better depicts the posteriorly displaced posterior column, posterior wall, and femoral head.
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Posterior column acetabular fracture. A left iliac oblique radiograph of the pelvis shows that the posterior column is markedly displaced.
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Computed tomography (CT) scan of a posterior column acetabular fracture at the level of the acetabular dome. The characteristic horizontal (coronal) orientation of the column fracture is appreciated easily by using CT scanning.
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Posterior column acetabular fracture. A computed tomography (CT) scan obtained at the level of the midacetabulum shows the horizontally oriented column fracture. The femoral head is relocated, but the recent posterior dislocation is evident in the anterior impaction fracture (arrow).
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Posterior column acetabular fracture. A computed tomography (CT) scan obtained at the level of the ischial tuberosities shows that posterior column fractures sometimes can exit through the ischial tuberosity (arrow) rather than through the obturator ring.
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Both-column acetabular fracture. An anteroposterior radiograph of the pelvis shows that the right ilioischial and iliopectineal lines are completely disrupted. A right iliac wing fracture is noted above the level of the acetabulum (arrow). A nondisplaced fracture of the right inferior pubic ramus is subtle.
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Both-column acetabular fracture. A right iliac oblique radiograph of the pelvis. The posterior column (arrowhead) and iliac wing disruptions are shown.
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Both-column acetabular fracture. A right obturator oblique radiograph of the pelvis best depicts nondisplaced fractures of the obturator ring (arrowheads). The iliopectineal line disruption (short arrow) signifies anterior column involvement. The pathognomonic spur sign (long arrow) of the both-column fracture is best appreciated on this view. The spur represents a strut of bone extending from the sacroiliac joint. The fracture of both columns disconnects this piece of bone from the acetabulum and causes its spurlike appearance.
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Both-column acetabular fracture. A computed tomography (CT) scan obtained at the level of the sacroiliac joints shows that the horizontal (coronal) column fracture begins superiorly at the iliac wing in the both-column fracture. The CT scan equivalent of the spur sign can be seen (arrow).
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Both-column acetabular fracture. A computed tomography (CT) scan obtained just above the level of the acetabular dome shows that the CT scan spur sign is present (arrow).
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Both-column acetabular fracture. A computed tomography (CT) scan obtained at the level of the acetabular dome shows the CT scan spur sign (arrow). Note how this spur does not connect to the articular portion of the acetabulum. In a both-column fracture, the articular surface of the acetabulum is completely disconnected from the axial skeleton.
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Anterior column fracture with a posterior hemitransverse acetabular fracture. An anteroposterior radiograph of the pelvis shows disruption of the iliopectineal (long arrow) and ilioischial (short arrows) lines. The obturator ring is intact.
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Anterior column fracture with a posterior hemitransverse acetabular fracture, as depicted on computed tomography (CT) scans obtained above and at the level of the right acetabulum. Left: The image shows an iliac wing fracture (arrow) that was not appreciated on the anteroposterior radiograph. (The oblique radiographs were not of good quality.) Middle: The image clearly depicts a column-type fracture (arrow) that is oriented horizontally on the CT scans. Right: The image again demonstrates the column fracture (long arrow), but now a transverse (vertically oriented) fracture can be seen posteriorly (short arrow).
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