Which findings on radiographs are characteristic of acetabulum fractures?

Updated: Jun 25, 2019
  • Author: David S Levey, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

Answer

According to Brandser and Marsh, [20] the following radiographic observations can be used to determine the acetabular fracture pattern and  the correct classification of most acetabular fractures:

  • A fracture of the obturator ring indicates either a T-shaped or a column fracture (with the exception of the hemitransverse type of fracture). An intact obturator ring eliminates these fractures from consideration.
  • Disruption of the ilioischial line occurs in fractures involving the posterior column or fractures in the transverse group.
  • Disruption of the iliopectineal line indicates anterior column involvement or one of the transverse-type fractures.
  • Iliac wing fractures are observed in fractures involving the anterior column.
  • Posterior wall fractures may occur in isolation or in combination with posterior column or transverse fractures.
  • The spur sign is observed exclusively in the both-column fracture. The spur is a strut of bone extending from the sacroiliac joint. Usually, this strut of bone connects to the articular surface of the acetabulum. In the both-column fracture, this connection is disrupted; a fractured piece of bone that resembles a spur remains.

The spur sign is best depicted on the obturator oblique view (see the first image below). In addition, the spur sign can be appreciated on CT scans (see the second image below).

Both-column acetabular fracture. A right obturator 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.
Both-column acetabular fracture. A computed tomogr 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).

Table 1 shows the combined set of radiographic and CT scan observations that are useful in acetabular fracture classification.

Table 1. Radiographic Features of Acetabular Fracture Types [20] (Open Table in a new window)

Fracture Type

Obturator

Ring

Fracture

Ilioischial

Line

Disrupted

Iliopectineal

Line

Disrupted

Iliac

Wing

Fracture

Posterior

Wall

Fracture

Pelvis

Into

Halves

Spur

Sign

CT Scan

Fracture

Orientation

Both-column

Yes

Yes

Yes

Yes

No

Front/back

Yes

Horizontal

Anterior column

Yes

No

Yes

Yes

No

Front/back

No

Horizontal

Posterior

column

Yes

Yes

No

No

No

Front/back

No

Horizontal

Posterior

column with

posterior wall

Yes

Yes

No

No

Yes

Front/back

No

Horizontal

T-shaped

Yes

Yes

Yes

No

No

Top/bottom

No

Vertical

Transverse with

posterior wall

No

Yes

Yes

No

Yes

Top/bottom

No

Vertical

Transverse

No

Yes

Yes

No

No

Top/bottom

No

Vertical

Posterior wall

No

No

No

No

Yes

No

No

Oblique

Anterior wall

No

No

Yes

No

No

No

No

Oblique

Anterior column

with posterior

hemitransverse

No

Yes

Yes

Yes

No

N/A*

No

N/A

*N/A indicates not applicable.

By using Brandser and Marsh's system, the accurate classification of acetabular fractures is possible in almost every patient. [20]

An accessory ossification center, the os acetabulum, may mimic an acetabular wall fracture. Its differentiating features include its characteristic superolateral location and well-corticated margins. Fractures of the anterior puboacetabular junction may be observed in pelvic ring fractures. These fractures may extend into the anterior column of the acetabulum, but they are not anterior column fractures per se. Such fractures are more correctly considered to be superior pubic ramus fractures.


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