tc analise acetabulo

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AJR:187, October 2006 915

AJR2006; 187:915925

0361803X/06/1874915

American Roentgen Ray Society

M E D I C A L I M A G I N G

A CE N T U R Y O F

M E D I C A L I M A G I N G

A CE N T U R Y O F

rkee et al.diographic and CTssification of Acetabularctures

M u sc u l os ke l e t al I m ag i n g P i c to r i al E s sa y

Classification of CommonAcetabular Fractures:Radiographic and CT Appearances

N. Jarrod Durkee1,2

Jon Jacobson1

David Jamadar1

Madhav A. Karunakar3

Yoav Morag1

Curtis Hayes1,4

Durkee NJ, Jacobson J, Jamadar D,

Karunakar MA, Morag Y, Hayes C

Keywords: acetabular fracture, CT, musculoskeletal

imaging, pelvic imaging, radiography, trauma

DOI:10.2214/AJR.05.1269

Received July 21, 2005; accepted after revision

September 18, 2005.

1Department of Radiology, University of Michigan Medical

Center, 1500 E Medical Center Dr., TC-2910G, Ann Arbor, MI

48109-0326. Address correspondence to J. Jacobson

([email protected]).

2Present address: Department of Radiology, University of

Washington, Seattle, WA.

3Department of Orthopedic Surgery, University of Michigan

Medical Center, Ann Arbor, MI 48109-0326.

4

Present address: Department of Radiology, MedicalCollege of Virginia, Virginia Commonwealth University,

Richmond, VA.

CME

This article is available for 1 CME credit. See www.arrs.org

for more information.

OBJECTIVE. Accurate characterization of acetabular fractures can be difficult because of

the complex acetabular anatomy and the many fracture patterns. In this article, the five most

common acetabular fractures are reviewed: both-column, T-shaped, transverse, transverse with

posterior wall, and isolated posterior wall. Fracture patterns on radiography are correlated with

CT, including multiplanar reconstruction and 3D surface rendering.

CONCLUSION. In the evaluation of the five most common acetabular fractures, assessment

of the obturator ring, followed by the iliopectineal and ilioischial lines and iliac wing, for fracture

allows accurate classification. CT is helpful in understanding the various fracture patterns.

ccurate classification of acetabular

fractures is important for determin-

ing the proper surgical treatment

[1, 2]. Because of the complex ace-

tabular anatomy, various classification schemes

have been suggested [35], but the Judet-Le-

tournel classification system remains the most

widely accepted [2, 4, 6]. Although radio-

graphic examination provides essential infor-

mation for acetabular classification, CT, includ-

ing multiplanar reconstruction, is helpful in the

visualization of complex fractures [7].This article reviews the pelvic bone anat-

omy and the five most common acetabular

fractures: both-column, T-shaped, transverse,

transverse with posterior wall, and isolated

posterior wall [2]. A fracture classification al-

gorithm based on radiography is used, with

correlation made to CT.

Normal Anatomy: Columns and Walls

The acetabulum is formed by anterior and

posterior columns of bone, which join in the

supraacetabular region [2, 6, 8]. The anterior

and posterior walls extend from each respec-

tive column and form the cup of the acetabu-lum. The anterior and posterior columns con-

nect to the axial skeleton through a strut of

bone called the sciatic buttress. When looking

at the acetabulum en face, the anterior and

posterior columns have the appearance of the

Greek letter lambda (!) [2, 6] (Fig. 1A). The

anterior column represents the longer, larger

portion, which extends superiorly from the

superior pubic ramus into the iliac wing. The

posterior column extends superiorly from the

ischiopubic ramus as the ischium toward the

ilium. The anterior and posterior columns of

bone unite to support the acetabulum. In turn,

the sciatic buttress extends posteriorly from

the anterior and posterior columns to become

the articular surface of the sacroiliac joint,

A

A

Fig. 1Normal pelvic bone anatomy.A, Surface-rendering 3D CT of pelvis in lateral viewwith femur and right hemipelvis removed showsanterior column (green), posterior column (blue), andsciatic buttress (red).(Fig. 1 continues on next page)


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Durkee et al.

916 AJR:187, October 2006

which attaches the columns to the axial skel-

eton. The anterior and posterior walls, which

extend from the columns and support the hip

joint, are well seen on an axial CT (Fig. 1B).

On radiographs, the iliopectineal (or ilio-

pubic) line represents the border of the ante-

rior column, and the ilioischial line represents

the posterior column [9] (Fig. 1C). The edges

of the anterior and posterior walls are also

identified. The obturator rings are composed

of the osseous structures that surround the ob-

turator foramen, which include the superior

B C

Fig. 1 (continued)Normal pelvic bone anatomy.B, Axial section through acetabulum shows anterior (arrowhead) and posterior (arrow) walls.C, Anteroposterior radiograph shows iliopectineal line (green), ilioischial line (blue), anterior acetabular wall (yellow), posterior acetabular wall (pink), and obturator foramen (O).

A B C

Fig. 2Illustrations of classification of five most common acetabular fractures.A, Both-column fracture.B, T-shaped fracture.C, Transverse fracture.(Fig. 2 continues on next page)


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Radiographic and CT Classification of Acetabular Fractures


pubic ramus and a combination of the inferior

pubic ramus and ischium (or ischiopubic ra-

mus). Anteroposterior and bilateral oblique

(or Judet) views of the pelvis are important to

adequately assess each of the radiographic

lines for fracture.

Fracture Patterns

The most widely accepted classification

scheme for acetabular fractures is that of

Judet and Letournel [2, 4, 6] . Although this

classification scheme describes 10 types

of acetabular fractures, we have focused

D E

Fig. 2 (continued)Illustrations of classification of five most common acetabular fractures.D, Transverse with posterior wall fracture.E, Isolated posterior wall fracture.

Fig. 3Classificationalgorithm for fivecommon acetabularfractures [2].

ACETABULAR

FRACTURE

IDENTIFIED

OBTURATOR

RING

DISRUPTION?

FRACTURE LINE

EXTENSION INTO ILIAC

WING?

ILIOISCHIAL AND

ILIOPECTINEAL LINE

DISRUPTION?

POSTERIOR

WALL

FRACTURE?

POSTERIOR

WALL

FRACTURE?

NOYES

NOYES

YES NO YES

NOYES

BOTH-COLUMN

FRACTURE

T-SHAPED

FRACTURE

TRANSVERSE

FRACTURE

TRANSVERSE +

POSTERIOR WALL

FRACTURE

ISOLATED

POSTERIOR

WALL FRACTURE

on the most common fracture patterns,

which represent 90% of acetabular frac-

tures [2, 6] (Fig. 2). The five most com-

mon fracture types may be divided into

two groups on the basis of presence or ab-

sence of obturator ring fracture (Fig. 3).

Although fracture of the obturator ringmay be seen in combination with acetabu-

lar fractures , it is important to note that ob-

turator ring fractures may be associated

with other pelvic injuries outside of the ac-

etabulum, such as lateral pelvic compres-

sion injury, where the obturator ring frac-

ture is associated with either an ipsilateral

or contralateral sacral fracture [6].

We first discuss the two acetabular frac-

ture types (both-column and T-shaped)

associated with obturator ring disruption.

Next we discuss the three acetabular frac-

tures types that spare the obturator ring

(transverse, transverse with posterior wall,and isolated posterior wall).

Both-Column Fracture

A both-column acetabular fracture (Figs. 4

and 5) involves both anterior and posterior col-

umns with extension into the obturator ring

and iliac wing, and is one of the most common

acetabular fractures [4]. On radiographs, frac-

ture involvement of the anterior and posterior

columns is characterized by disruption of the

iliopectineal line and ilioischial line, respec-

tively. However, disruption of these lines may

also be seen with other fracture patterns, such

as a transverse fracture. Obturator ring and il-iac wing involvement must also be present for

classification as a both-column acetabular

fracture. Fracture extension into the iliac wing

is not always obvious on the anteroposterior ra-

diograph; oblique Judet views or CT often re-

veal this finding.

On CT, fracture involvement of the ante-

rior and posterior columns is seen, and the

fracture may be comminuted. Fracture dis-

ruption of the obturator ring has a variable

appearance; fracture of the superior pubic

ramus may occur at the puboacetabular

junction. In addition, fracture of the inferior

pubic ramus may be difficult to identify ifnondisplaced. The principal fracture line,

which extends superiorly from the acetabu-

lum into the iliac wing, is characteristically

in the coronal plane.

If present, a pathognomonic sign of a

both-column fracture is the spur sign [2]

(Fig. 5). This sign represents posterior dis-

placement of the sciatic buttress of the iliac

wing fracture, which essentially discon-


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Durkee et al.


nects the roof of the acetabulum from the

axial skeleton. When this occurs, weight

from the torso and upper body can no longer

be supported by the acetabulum. On radio-

graphs and CT, the spur sign appears as a

shard of bone extending posteriorly at the

level of the superior acetabulum. Evaluation

of sequential CT images shows the fracture,

which separates the sciatic buttress from the

acetabular roof.

T-Shaped Fracture

A T-shaped acetabular fracture (Fig. 6) is a

combination of a transverse acetabular frac-

ture with extension inferiorly into the obtura-

tor ring. It is similar to a both-column fracture

A B

C

Fig. 445-year-old man with both-column acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT scan (D), and sagittal reconstruction CT scan (E) show acetabularfracture (straight arrows, AC), with break in obturator ring (arrowheads, AC) andextension into iliac wing (curved arrows). Note coronal plane of fracture on CT andsuperior pubic ramus fractured at puboacetabular junction.(Fig. 4 continues on next page)


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in that it disrupts the obturator ring

(Figs. 6A6C). Another similarity is disrup-

tion of both the iliopectineal and ilioischial

lines (Figs. 6A6C). However, the superior

extension of the fracture does not involve the

iliac wing, which allows differentiation from

the both-column fracture.

One area of potential confusion with the T-

shaped fracture is in regard to the transverse

component. The transverse fracture line is not

actually in the anatomic transverse plane, but

rather it is transverse relative to the acetabu-

lum. Because the cup shape of the acetabulum

is normally tilted inferiorly and anteriorly, the

transverse fracture plane assumes a similar

Fig. 4 (continued)45-year-old man with both-column acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT scan (D), and sagittal reconstruction CT scan (E) show acetabularfracture (straight arrows, AC), with break in obturator ring (arrowheads, AC) andextension into iliac wing (curved arrows). Note coronal plane of fracture on CT andsuperior pubic ramus fractured at puboacetabular junction.

ED

A

Fig. 535-year-old man with both-column acetabular fracture and spur sign.A and B, Oblique pelvic radiograph (A) and axial CT image (B) show spur sign (arrow),which represents displacement of fracture involving sciatic buttress (arrowheads).Note that sciatic buttress (arrowheads, B) no longer connects to weight-bearingportion of acetabulum.

B


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Durkee et al.


orientation. Therefore, on radiographs, the

fracture lines that disrupt the iliopectineal and

ilioischial lines course superiorly and medi-

ally in an oblique plane from the acetabulum.

This is best appreciated by looking at the ac-

etabulum en face (Fig. 6E). On CT, this trans-

verse fracture component is seen as a sagit-

tally oriented fracture coursing medially and

superiorly from the acetabulum.

Transverse Fracture

The transverse fracture of the acetabu-

lum (Fig. 7) is limited to the acetabulum,

without involvement of the obturator ring.

A transverse fracture must involve both the

anterior and posterior aspects of the acetab-

ulum, so the iliopectineal and ilioischial

lines are disrupted on radiography. Similar

to the transverse component of the T-shaped

fracture described previously, this fracture

line extends superiorly and medially from

the acetabulum. On CT, the characteristic

sagittally oriented fracture line can be seen

moving laterally to medially on subsequent

CT images when scrolling from inferior to

superior. Although not anatomically trans-

verse, the fracture plane is transverse rela-

tive to the acetabulum, which is relatively

A B

C

Fig. 640-year-old man with T-shaped acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), withright hemipelvis and femur removed, show obturator ring fractures (arrowheads) andtransverse component (arrows) through acetabulum. Note characteristicobliquesagittal orientation of transverse acetabular fracture component on CTscans that is transverse relative to acetabulum on radiographs.(Fig. 6 continues on next page)


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tilted inferiorly and anteriorly. This fracture

plane orientation is best seen on CT recon-

struction images of the acetabulum en face

(Fig. 7E).

Transverse with Posterior Wall

The transverse with posterior wall fracture

(Fig. 8) is a transverse fracture, described pre-

viously, with the addition of a comminuted

posterior wall fracture that is often displaced.

As with an isolated transverse fracture, the

key is recognizing that the obturator ring is

not disrupted, as this excludes both-column

D E

Fig. 6 (continued)40-year-old man withT-shaped acetabularfracture.AE, Anteroposteriorpelvic radiograph (A),bilateral oblique pelvicradiographs (B, C), axial

CT scan (D), and surface-rendering 3D CT scanviewed laterally (E), withright hemipelvis andfemur removed, showobturator ring fractures(arrowheads) andtransverse component(arrows) throughacetabulum. Notecharacteristicobliquesagittalorientation of transverseacetabular fracturecomponent on CT scansthat is transverse relativeto acetabulum onradiographs.

A B

Fig. 723-year-old woman with transverse acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with righthemipelvis and femur removed, show fracture (arrows) orientation transverse to acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Note characteristicsagittaloblique fracture plane on CT scan (D).(Fig. 7 continues on next page)


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Durkee et al.


and T-shaped fractures. As with the simple

transverse fracture, this fracture type does not

extend into the iliac wing.

On radiographs, disruption of both ilio-

pectineal and ilioischial lines is seen as with

the isolated transverse fracture. Unlike an iso-lated transverse fracture, however, additional

comminution of the posterior wall is seen. In

the absence of displacement, comminution of

the posterior wall may be difficult to identify

on anteroposterior radiographs because the

fragments are superimposed on the femoral

head. Oblique Judet radiographs and CT are

helpful in showing the comminuted posterior

wall component.

Isolated Posterior Wall

The isolated posterior wall fracture

(Fig. 9) is one of the most common types of

acetabular fracture, with a prevalence of

27% [8]. An isolated posterior wall fracture

does not have a complete transverse acetab-ular component. Therefore, the iliopectineal

line is not disrupted, which excludes classi-

fication of the transverse with posterior wall

fracture. However, disruption of the iliois-

chial line may or may not be present as an

extension of the comminuted posterior wall

component. Oblique (Judet) radiographs

and CT are helpful in showing the isolated

posterior wall fracture.

Conclusion

Common acetabular fractures can easily be

classified using disruption of the obturator ring

as the basis of a decision tree (Fig. 3). Fracture

of the obturator ring indicates both-column or

T-shaped fracture, with additional iliac winginvolvement differentiating the both-column

from the T-shaped fracture. Sparing of the ob-

turator ring commonly indicates transverse,

transverse with posterior wall, or isolated pos-

terior wall fracture. Disruption of both the ilio-

pectineal and ilioischial lines indicates a trans-

verse fracture, and comminution of the posterior

wall indicates a posterior wall fracture. A both-

column fracture is in the coronal plane, whereas

C

D

E

Fig. 7 (continued)23-year-old woman with transverse acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), withright hemipelvis and femur removed, show fracture (arrows) orientation transverseto acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Notecharacteristic sagittaloblique fracture plane on CT scan (D).


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A B

C

D

E

Fig. 820-year-old man showing transverse with posterior wall acetabular fracture.AE, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), withright hemipelvis and femur removed, show transverse fracture (straightarrows)disrupting iliopectineal and ilioischial lines (arrowheads) with displaced andcomminuted posterior wall fracture fragment (curved arrows).


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Durkee et al.


A B

C

D

E

Fig. 918-year-old man with isolated posterior wall acetabular fracture.AF, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B,C), axial CT images (D, E), and parasagittal reconstruction CT image (F) showdisplaced fracture fragments (curved arrows) from isolated posterior wall fracture(straight arrow, D).(Fig. 9 continues on next page)


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a transverse or T-shaped fracture is in the sagit-

tal oblique plane on CT. The addition of CT

with multiplanar reconstruction and 3D surface

rendering is helpful in understanding and clas-

sifying acetabular fractures.

Acknowledgment

We thank Robert W. Jacobson for the

illustrations.

Fig. 9 (continued)18-year-old man withisolated posterior wallacetabular fracture.AF, Anteroposteriorpelvic radiograph (A),bilateral oblique pelvicradiographs (B, C), axial

CT images (D, E), andparasagittalreconstruction CTimage (F) showdisplaced fracturefragments (curvedarrows) from isolatedposterior wall fracture(straight arrow, D).

F

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F O R Y O U R I N F O R M A T I O N

This article is available for 1 CME credit. See www.arrs.org for more information.

tc analise acetabulo

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