acetabular fractures

AJR:187, October 2006 915

AJR 2006; 187:915–925

0361–803X/06/1874–915

© American Roentgen Ray Society

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

A C E N T U R Y O F

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

A C E N T U R Y O F

Durkee et al.Radiographic and CT Classification of Acetabular Fractures

M u s c u l o s ke l e t a l I m ag i n g • P i c t o r i a l E s s ay

Classification of Common Acetabular 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.

4Present address: Department of Radiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA.

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

OBJECTIVE. Accurate characterization of acetabular fractures can be difficult because ofthe complex acetabular anatomy and the many fracture patterns. In this article, the five mostcommon acetabular fractures are reviewed: both-column, T-shaped, transverse, transverse withposterior wall, and isolated posterior wall. Fracture patterns on radiography are correlated withCT, including multiplanar reconstruction and 3D surface rendering.

CONCLUSION. In the evaluation of the five most common acetabular fractures, assessmentof the obturator ring, followed by the iliopectineal and ilioischial lines and iliac wing, for fractureallows accurate classification. CT is helpful in understanding the various fracture patterns.

ccurate classification of acetabularfractures is important for determin-ing the proper surgical treatment[1, 2]. Because of the complex ace-

tabular anatomy, various classification schemeshave been suggested [3–5], but the Judet-Le-tournel classification system remains the mostwidely accepted [2, 4, 6]. Although radio-graphic examination provides essential infor-mation for acetabular classification, CT, includ-ing multiplanar reconstruction, is helpful in thevisualization of complex fractures [7].

This article reviews the pelvic bone anat-omy and the five most common acetabularfractures: both-column, T-shaped, transverse,transverse with posterior wall, and isolatedposterior wall [2]. A fracture classification al-gorithm based on radiography is used, withcorrelation made to CT.

Normal Anatomy: Columns and WallsThe acetabulum is formed by anterior and

posterior columns of bone, which join in thesupraacetabular region [2, 6, 8]. The anteriorand 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 ofbone called the sciatic buttress. When lookingat the acetabulum en face, the anterior andposterior columns have the appearance of theGreek letter lambda (λ) [2, 6] (Fig. 1A). Theanterior column represents the longer, largerportion, which extends superiorly from thesuperior pubic ramus into the iliac wing. The

posterior column extends superiorly from theischiopubic ramus as the ischium toward theilium. The anterior and posterior columns ofbone unite to support the acetabulum. In turn,the sciatic buttress extends posteriorly fromthe anterior and posterior columns to becomethe articular surface of the sacroiliac joint,

A

A

Fig. 1—Normal pelvic bone anatomy.A, Surface-rendering 3D CT of pelvis in lateral view with femur and right hemipelvis removed shows anterior column (green), posterior column (blue), and sciatic 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, whichextend from the columns and support the hipjoint, 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 representsthe posterior column [9] (Fig. 1C). The edges

of the anterior and posterior walls are alsoidentified. The obturator rings are composedof 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. 2—Illustrations 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)D

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Radiographic and CT Classification of Acetabular Fractures


pubic ramus and a combination of the inferiorpubic ramus and ischium (or ischiopubic ra-mus). Anteroposterior and bilateral oblique(or Judet) views of the pelvis are important toadequately assess each of the radiographiclines for fracture.

Fracture PatternsThe most widely accepted classification

scheme for acetabular fractures is that ofJudet and Letournel [2, 4, 6]. Although thisclassification scheme describes 10 typesof 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. 3—Classification algorithm for five common acetabular fractures [2].

ACETABULARFRACTUREIDENTIFIED

OBTURATORRING

DISRUPTION?

FRACTURE LINEEXTENSION INTO ILIAC

WING?

ILIOISCHIAL ANDILIOPECTINEAL LINE

DISRUPTION?

POSTERIORWALL

FRACTURE?

POSTERIORWALL

FRACTURE?

NOYES

NOYES

YES NO YES

NOYES

BOTH-COLUMNFRACTURE

T-SHAPEDFRACTURE

TRANSVERSEFRACTURE

TRANSVERSE +POSTERIOR WALL

FRACTURE

ISOLATEDPOSTERIOR

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 intotwo 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 associatedwith 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 ipsilateralor 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 FractureA both-column acetabular fracture (Figs. 4

and 5) involves both anterior and posterior col-umns with extension into the obturator ringand iliac wing, and is one of the most commonacetabular fractures [4]. On radiographs, frac-ture involvement of the anterior and posteriorcolumns is characterized by disruption of theiliopectineal line and ilioischial line, respec-tively. However, disruption of these lines mayalso be seen with other fracture patterns, suchas a transverse fracture. Obturator ring and il-iac wing involvement must also be present forclassification as a both-column acetabularfracture. Fracture extension into the iliac wingis 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 thefracture may be comminuted. Fracture dis-ruption of the obturator ring has a variableappearance; fracture of the superior pubicramus may occur at the puboacetabularjunction. In addition, fracture of the inferiorpubic ramus may be difficult to identify ifnondisplaced. The principal fracture line,which extends superiorly from the acetabu-lum into the iliac wing, is characteristicallyin the coronal plane.

If present, a pathognomonic sign of aboth-column fracture is the spur sign [2](Fig. 5). This sign represents posterior dis-placement of the sciatic buttress of the iliacwing fracture, which essentially discon-

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nects the roof of the acetabulum from theaxial skeleton. When this occurs, weightfrom the torso and upper body can no longerbe supported by the acetabulum. On radio-graphs and CT, the spur sign appears as a

shard of bone extending posteriorly at thelevel of the superior acetabulum. Evaluationof sequential CT images shows the fracture,which separates the sciatic buttress from theacetabular roof.

T-Shaped FractureA 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. 4—45-year-old man with both-column acetabular fracture.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and sagittal reconstruction CT scan (E) show acetabular fracture (straight arrows, A–C), with break in obturator ring (arrowheads, A–C) and extension into iliac wing (curved arrows). Note coronal plane of fracture on CT and superior pubic ramus fractured at puboacetabular junction.(Fig. 4 continues on next page)

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in that it disrupts the obturator ring(Figs. 6A–6C). Another similarity is disrup-tion of both the iliopectineal and ilioischiallines (Figs. 6A–6C). However, the superiorextension of the fracture does not involve the

iliac wing, which allows differentiation fromthe both-column fracture.

One area of potential confusion with the T-shaped fracture is in regard to the transversecomponent. The transverse fracture line is not

actually in the anatomic transverse plane, butrather it is transverse relative to the acetabu-lum. Because the cup shape of the acetabulumis normally tilted inferiorly and anteriorly, thetransverse fracture plane assumes a similar

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

ED

A

Fig. 5—35-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-bearing portion of acetabulum.

B

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orientation. Therefore, on radiographs, thefracture lines that disrupt the iliopectineal andilioischial 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 andsuperiorly from the acetabulum.

Transverse FractureThe 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 theanterior and posterior aspects of the acetab-ulum, so the iliopectineal and ilioischiallines are disrupted on radiography. Similarto the transverse component of the T-shaped

fracture described previously, this fractureline extends superiorly and medially fromthe acetabulum. On CT, the characteristicsagittally oriented fracture line can be seenmoving laterally to medially on subsequentCT images when scrolling from inferior tosuperior. Although not anatomically trans-verse, the fracture plane is transverse rela-tive to the acetabulum, which is relatively

A B

C

Fig. 6—40-year-old man with T-shaped acetabular fracture.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with right hemipelvis and femur removed, show obturator ring fractures (arrowheads) and transverse component (arrows) through acetabulum. Note characteristic oblique–sagittal orientation of transverse acetabular fracture component on CT scans that is transverse relative to acetabulum on radiographs.(Fig. 6 continues on next page)

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tilted inferiorly and anteriorly. This fractureplane orientation is best seen on CT recon-struction images of the acetabulum en face(Fig. 7E).

Transverse with Posterior WallThe 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, thekey is recognizing that the obturator ring isnot disrupted, as this excludes both-column

D E

Fig. 6 (continued)—40-year-old man with T-shaped acetabular fracture.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with right hemipelvis and femur removed, show obturator ring fractures (arrowheads) and transverse component (arrows) through acetabulum. Note characteristic oblique–sagittal orientation of transverse acetabular fracture component on CT scans that is transverse relative to acetabulum on radiographs.

A B

Fig. 7—23-year-old woman with transverse acetabular fracture.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with right hemipelvis and femur removed, show fracture (arrows) orientation transverse to acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Note characteristic sagittal–oblique fracture plane on CT scan (D).(Fig. 7 continues on next page)D

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and T-shaped fractures. As with the simpletransverse fracture, this fracture type does notextend into the iliac wing.

On radiographs, disruption of both ilio-pectineal and ilioischial lines is seen as withthe isolated transverse fracture. Unlike an iso-lated transverse fracture, however, additionalcomminution of the posterior wall is seen. Inthe absence of displacement, comminution ofthe posterior wall may be difficult to identifyon anteroposterior radiographs because thefragments are superimposed on the femoralhead. Oblique Judet radiographs and CT arehelpful in showing the comminuted posteriorwall component.

Isolated Posterior WallThe isolated posterior wall fracture

(Fig. 9) is one of the most common types ofacetabular fracture, with a prevalence of27% [8]. An isolated posterior wall fracturedoes not have a complete transverse acetab-ular component. Therefore, the iliopectinealline is not disrupted, which excludes classi-fication of the transverse with posterior wallfracture. However, disruption of the iliois-chial line may or may not be present as anextension of the comminuted posterior wallcomponent. Oblique (Judet) radiographsand CT are helpful in showing the isolatedposterior wall fracture.

ConclusionCommon acetabular fractures can easily be

classified using disruption of the obturator ringas the basis of a decision tree (Fig. 3). Fractureof the obturator ring indicates both-column orT-shaped fracture, with additional iliac winginvolvement differentiating the both-columnfrom 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 posteriorwall 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.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with right hemipelvis and femur removed, show fracture (arrows) orientation transverse to acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Note characteristic sagittal–oblique fracture plane on CT scan (D).

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A B

C

D

E

Fig. 8—20-year-old man showing transverse with posterior wall acetabular fracture.A–E, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT scan (D), and surface-rendering 3D CT scan viewed laterally (E), with right hemipelvis and femur removed, show transverse fracture (straight arrows) disrupting iliopectineal and ilioischial lines (arrowheads) with displaced and comminuted posterior wall fracture fragment (curved arrows).

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A B

C

D

E

Fig. 9—18-year-old man with isolated posterior wall acetabular fracture.A–F, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT images (D, E), and parasagittal reconstruction CT image (F) show displaced 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 CTwith multiplanar reconstruction and 3D surfacerendering is helpful in understanding and clas-sifying acetabular fractures.

AcknowledgmentWe thank Robert W. Jacobson for the

illustrations.

Fig. 9 (continued)—18-year-old man with isolated posterior wall acetabular fracture.A–F, Anteroposterior pelvic radiograph (A), bilateral oblique pelvic radiographs (B, C), axial CT images (D, E), and parasagittal reconstruction CT image (F) show displaced fracture fragments (curved arrows) from isolated posterior 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.

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