Acetabulum Fractures Workup

Updated: Sep 25, 2020
  • Author: Mihir M Thacker, MBBS, MS(Orth), DNB(Orth), FCPS(Orth), D'Ortho; Chief Editor: William L Jaffe, MD  more...
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Workup

Approach Considerations

The complicated anatomy of the acetabulum necessitates clear-cut visualization of the fracture fragments and their relationships with each other and the rest of the pelvis if anatomic reconstruction of the acetabulum is planned. The following imaging modalities can be used:

  • Plain radiographs - Pelvis with both hips (anteroposterior [AP] view), Judet views, and, if required, inlet and outlet views of the pelvis (in cases with concomitant pelvic injury)
  • Computed tomography (CT) - Plain and with three-dimensional (3D) reconstructions

Doppler ultrasonography (US) or venography may be performed in cases where deep vein thrombosis (DVT) is suspected.

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Laboratory Studies

Laboratory studies that may be helpful include the following:

  • Hemoglobin and hematocrit levels
  • Type and crossmatch blood
  • Routine evaluation of fitness for anesthesia and major surgery
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Plain Radiography

Pelvis with both hips

This is an essential radiograph and may depict the following:

  • Associated pelvic-ring fractures independent of the acetabular fracture passing through the iliac wing, obturator foramen, or the sacrum
  • Dislocation through or disruption of one or more joints in the pelvic ring
  • Bone quality
  • Rarely, a bilateral acetabular fracture
  • The acetabular fracture itself

This view enables visualization of the six fundamental radiologic landmarks of the acetabulum, as follows:

  • Borders of the anterior wall (acetabulo-obturator line) and posterior wall of the acetabulum
  • Roof or dome of the acetabulum
  • Teardrop of Köhler
  • Ilioischial line of Duverney-Parent
  • Pelvic inlet
  • Innominate line

Judet views

In the obturator oblique technique, the injured hip is raised to 45°, and the beam is centered over a point one fingerbreadth below and medial to the anterior superior iliac spine. In a correctly taken obturator oblique, the anterior and posterior iliac spines are superimposed, the iliac wing is seen in section as narrow as possible, and, correspondingly, the obturator foramen is seen as large as possible. Features to be studied include the following:

  • Pelvic brim
  • Articular surface, especially the posterior lip
  • Obturator foramen and the anterior column
  • Iliac wing in section
  • Junction of the anterior and posterior columns as seen as a line just above the roof

In the iliac oblique technique, the uninjured hip is elevated to 45°, with the injured part resting on the table. The beam is centered one fingerbreadth below the level of the anterior superior iliac spine and at the midpoint of a transverse line from the anterior superior iliac spine to the midline. In a correctly positioned iliac oblique, the iliac wing is seen widely spread out and the obturator ring is as thin as possible. Features to be studied include the following:

  • Anterior lip of the acetabulum
  • Posterior column and posterior border of the iliac bone
  • Iliac wing

Interpretation of films

Interpretation of the plain films is based on understanding the normal radiographic lines of the acetabulum and what each line represents. Disruption of any of the normal lines of the acetabulum represents a fracture involving that portion of the bone. Displacement of the articular surface is inferred by displacement of these normal lines of the acetabulum.

On the AP view, the inferior three fourths of the iliopectineal line represents the pelvic brim and is a landmark of the anterior column. The superior fourth of this line is formed by the tangency of the x-ray beam to the superior quadrilateral surface and the greater sciatic notch. The ilioischial line is formed by the tangency of the x-ray beam to the posterior portion of the quadrilateral surface and is, therefore, a radiographic landmark of the posterior column.

The teardrop and the ilioischial line both result from the tangency of the x-ray beam to a portion of the quadrilateral surface. Thus, they are always superimposed in the normal acetabulum. Separation of the teardrop and the ilioischial line indicates rotation of the hemipelvis or fracture of the quadrilateral surface.

The roof of the acetabulum is a radiographic landmark resulting from the tangency of the x-ray beam to the subchondral bone of the superior acetabulum. Interruption of the radiographic line of the roof is indicative of a fracture involving the superior acetabulum.

The anterior rim is the lateral margin of the anterior wall of the acetabulum and is contiguous with the inferior margin of the superior pubic ramus. The posterior rim is the lateral margin of the posterior wall of the acetabulum. Inferiorly, the posterior rim is contiguous with the posterior horn of the acetabulum.

In most cases, the fracture can be classified properly from plain films alone. Plain films are usually best for assessing the congruence between the femoral head and the roof of the acetabulum.

Measurement of roof-arc angles

Roof-arc angles are used to assess the size of the intact portion of acetabulum. [26, 27, 28, 29]  These angles are made on the AP, obturator, and iliac oblique radiographic views.

A vertical line is drawn to the geometric center of the acetabulum. Another is drawn through the point where the fracture line intersects the radiographic roof of the acetabulum and again to the geometric center of the acetabulum. The angle drawn in this way represents the medial, anterior, or posterior roof arc as seen on the AP, obturator oblique, or iliac oblique view, respectively. The roof-arc measurements roughly describe the position and orientation of the acetabular fracture and, therefore, the intact portion of superior acetabular articular surface.

A similar determination can be made from the CT scan (see Computed Tomography below). The CT scan of the superior acetabular articular surface from the vertex to 10 mm inferior to the vertex is equivalent to an area described by all three roof-arc measurements of 45°. At 10 mm below the acetabular vertex, the subchondral bone appears as a ring or arc.

If nonoperative treatment is to be considered, the head should remain congruous with the roof of the acetabulum on the three views of the pelvis with the patient out of traction, and all roof-arc measurements should be more than 45°, or there should be no displaced fracture lines involving the superior acetabular articular surface in the superior 10 mm of the acetabulum on CT.

Vrahas et al, in a cadaveric study, concluded that fractures that have a medial roof-arc angle of 45° or less, an anterior roof-arc angle of 25° or less, or a posterior roof-arc angle of 70° or less across the weightbearing portion of the acetabulum should be treated operatively. [7]

Roof-arc measurements are not commonly used. This technique is most applicable to the anterior column and less applicable to the posterior column. Roof-arc measurements are particularly helpful in evaluating the anterior column component of a T-shaped fracture. If the anterior column component is low (< 10 mm of the acetabular vertex), only the posterior portion of the fracture must be addressed surgically.

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Computed Tomography

The use of CT for acetabular fractures has revolutionized the imaging of a particularly difficult area and, with 3D reconstruction, has enormously facilitated the visualization of the fracture anatomy, the degree of comminution, and associated fracture patterns; it has also helped in the preoperative planning of the surgical reconstruction. [30, 31, 32, 33, 34, 35]

It is important to have sections taken at 2- or 3-mm intervals; incarcerated fragments may be missed if sections are taken at 5-mm intervals.

Three-dimensional CT is an invaluable tool for demonstrating the overall fracture orientation in displaced fractures, as well as for deciding the choice of operative approach to the fracture. [36] Because of smoothening artifacts, however, it may not depict minimally displaced fractures.

Special views are available that enable selective study of the details of the acetabular fracture after computer subtraction of the femoral head from the image. These provide unrestricted access for visualization of the fracture.

Axial images are more sensitive than plain radiographs for demonstrating the following:

  • Location and extent of the acetabular fracture
  • Degree of comminution, rotation of the fragments, and impaction of the weightbearing dome and the posterior wall
  • Intra-articular/incarcerated fragments (see the image below)
  • Injury to the femoral head
  • Minimally displaced iliac-wing fractures and quadrilateral plate fractures that may have been missed on plain films
  • Pelvic hematoma
  • Sacroiliac joint integrity
  • Rarely, a dislocation that is missed on a plain radiograph
Incarcerated fragment best seen on axial cuts of t Incarcerated fragment best seen on axial cuts of the CT scan.

Postoperatively, CT is an invaluable investigative tool whenever joint penetration by a fixation device is suspected (see the image below).

Intra-articular screw as seen on the axial cut of Intra-articular screw as seen on the axial cut of the CT scan.
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