Fracture Characteristics

Anterior column fractures are historically rare acetabular fractures with a suspected incidence of approximately 3.9%.¹ With increasing computed tomography (CT) diagnostics of acetabular fractures, and considering the overall demographic development, a relevant increase of the incidence has been observed. Low anterior column fractures especially were observed to have an expected frequency of approximately 6–12% (see ▶ 5).

Letournel defined four subtypes of anterior column fractures, depending on the most cranial fracture line.² In general, very low, low, intermediate, and high fractures of the anterior column were distinguished (▶ Fig. 12.1):

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  Very low fractures: the most proximal fracture line extends to the anteroinferior acetabulum involving the lowest part of the anterior horn.

  
  
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  Low fractures: the fracture ends in the “psoas groove” (psoas gutter) inferior to the anterior inferior iliac spine; part of the quadrilateral surface is attached to the main fragment; with extended involvement of the quadrilateral surface, transitions to associated anterior column plus posterior hemitransverse fractures are possible.

  
  
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  Intermediate fractures: the most cranial fracture line ends between the anterior superior and anterior inferior iliac spine; medially, the fracture line crosses the iliopectineal line near the sacroiliac (SI) joint; the quadrilateral surface is often extensively broken; the distal fracture line typically leaves the inferior obturator foramen, but can run through the upper pubic rami; incomplete fractures are possible.

  
  
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  High fractures: cranially, the fracture ends posterior to the anterior superior iliac spine at a variable point along the iliac crest, sometimes with multiple fracture lines: marginal impaction zones are relatively common; in rare cases, the fracture line extends into the SI joint, with or without additional joint instability.

  
  
  
  

  

  
  

  Fig. 12.1 Schematic drawing of the four subtypes of anterior column fractures.

12.2 Radiological–Anatomical Criteria

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  Pelvis anteroposterior (AP) view (▶ Fig. 12.2, ▶ Fig. 12.3, ▶ Fig. 12.4, ▶ Fig. 12.5). Depending on the subtype of the anterior column fracture, the iliopectineal line is disrupted at various locations. Especially in intermediate and high anterior column fractures, parts of the superior acetabulum can be displaced. The teardrop figure can be involved (subluxation, rotated) depending on the extent of involvement of the quadrilateral surface. In very low fractures, a double configuration of the teardrop figure is occasionally visible. The characteristic lines of the posterior column and wall remain intact.

  
  
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  Iliac oblique view (IOV) (▶ Fig. 12.2, ▶ Fig. 12.3, ▶ Fig. 12.4, ▶ Fig. 12.5). The integrity of the posterior column line is confirmed. The level of the cranial fracture line is recognized and involvement of the iliac fossa is visualized.

  
  
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  Obturator oblique view (OOV) (▶ Fig. 12.2, ▶ Fig. 12.3, ▶ Fig. 12.4, ▶ Fig. 12.5). The extent of displacement, the fracture characteristics with localization of fracture lines involving the pubic rami and the iliopectineal line, and their relation to the acetabular roof become visible. Occasionally, an additional fracture line lateral to the acetabulum is present. This fracture can be misinterpreted as a both-column fracture (spur sign) (see ▶ 17). The exact fracture course involving the obturator foramen is cleared. The characteristic lines of the posterior column and wall are intact.

  
  
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  Computed tomography (▶ Fig. 12.2, ▶ Fig. 12.3, ▶ Fig. 12.4, ▶ Fig. 12.5). The main fracture line is analyzed, starting cranially, to confirm the diagnosis of an anterior column fracture. Three-dimensional (3D)-CT provides an optimal view of the exact fracture morphology, analysis of the fragment size, of possible additional injuries, and the extent of involvement of the quadrilateral surface—the latter especially using a medial hemipelvic view. The most proximal fracture line is identified. Sagittal reconstructions allow analysis of quadrilateral surface involvement.

  
  
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  Transition forms to other fracture types. In the presence of extended involvement of the quadrilateral surface with incomplete fracture lines in direction to the posterior wall, transitions to associated anterior column plus posterior hemitransverse fractures are possible. Additionally, incomplete fracture lines at the proximal level of the greater sciatic notch can mimic transitions to both-column fractures. Occasionally, atypical anterior column fractures are observed, where the main fracture line starts at the iliac crest and enters the articular surface superiorly without disruption of the iliopectineal line (▶ Fig. 12.6).

  
  
  
  

  

  
  

  Fig. 12.2 Example of a very low anterior column fracture with articular involvement at the inferior anterior horn.

  
  
  
  

  

  
  

  Fig. 12.3 Example of a low anterior column fracture below (distal) to the anterior inferior iliac spine.

  
  
  
  

  

  
  

  Fig. 12.4 Example of an intermediate anterior column fracture. The most proximal fracture line is between the anterior superior and anterior inferior iliac spine.

  
  
  
  

  

  
  

  Fig. 12.5 Example of a high anterior column fracture with the fracture extending at a variable area of the iliac crest.

  
  
  
  

  

  
  

  Fig. 12.6 Example of an atypical fracture of the anterior column. The fracture starts at the iliac crest and stops at the superior acetabulum. Due to its anterior course, it is classified as anterior column fracture.

12.3 Pathobiomechanics

Letournel proposed a force form lateral through the greater trochanter along the femoral neck with the hip in 25 degrees external rotation as a theoretical mechanism for anterior column fractures.² Higher external rotations lead to fractures of the anterior wall, whereas lower rotations lead to associated anterior column plus posterior hemitransverse fractures. Clinically, this mechanism leads to 8% of anterior column fractures. A dashboard mechanism was never observed to result in an anterior column fracture.

Lansinger et al confirmed Letournel’s ideas.³ Experimentally, with the hip in full extension and slight internal rotation ≤ 10 degrees or external rotation of approximately 40 degrees, fractures of the anterior column were observed. Forces of about 500 N were necessary to create the fracture.

Dakin et al only observed one single anterior column fracture choosing this mechanism (3.7%).⁴

12.4 Hip Joint Stability

The extent of fracture instability is a function of the localization of the most proximal fracture line. The lower the fracture, the more stable the joint. Clinically, the most often observed (very) low fractures at the level of the anterior horn are therefore the most stable ones. Fractures reaching the iliac crest are supposed to be most unstable.⁵

The femoral head typically follows the fragment(s) resulting in a hip subluxation.

12.5 Biomechanics of Anterior Column Fractures

There is only one biomechanical study dealing with anterior column fractures.⁶

Harnroongroj analyzed hemipelvises in a simulated single leg stance after creating defects in the anterior and posterior column. Lateral force transmission was performed.

When the posterior column was intact, maximum forces of 760 N and a stiffness of 113 N/mm were observed, whereas an intact anterior column resisted maximum forces of 2000 N and a stiffness of 300 N/mm was measured. They concluded that the posterior column had a 2.75-fold higher strength compared to the anterior column.

A disadvantage of this analysis was that the fractures were not comparable to clinical fracture situations and a lateral force transmission does not correspond to physiological loading of the hip joint.

12.6 Treatment Indications

The type of treatment depends on fracture displacement, articular modifiers, and the localization of the most proximal fracture line.

12.6.1 Conservative Treatment

Conservative treatment is especially recommended for very low, low, and the majority of intermediate anterior column fractures, depending on the extent of articular involvement, articular displacement, and resulting joint incongruence.

Undisplaced or minimally displaced high anterior column fractures and isolated fractures without additional articular injuries can as well be treated nonoperatively (conservative functional treatment with early [partial] weight bearing).

Minimally invasive procedures are an alternative for treating these fractures (see ▶ 22).

12.6.2 Operative Treatment

Operative treatment is indicated in:

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  Unstable hip joint

  
  
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  Femoral subluxation/dislocation

  
  
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  Intraarticular fragments

  
  
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  Extended superior dome involvement

  
  
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  Presence of marginal impaction

12.7 Techniques of Osteosynthesis

12.7.1 Biomechanics of Osteosynthesis

Konrath et al analyzed the effect of anatomical and nonanatomical reduction in high anterior column fractures.⁷

In six cadavers, high anterior column fractures were osteotomized and loaded in a simulated single leg stance model. Stabilization was performed with two lag screws at the iliac wing and an additional inguinal, suprapectineal reconstruction plate. Anatomical and nonanatomical joint reconstructions were created with a persistent step or gap of 3.4 mm on average.

Compared to the intact acetabulum, either after anatomical reduction and after gap malreduction, a significant reduction of the anterior and posterior contact area was observed, whereas a step malreduction led only to a significant anterior reduction of the contact area. No significant differences were observed at the superior acetabulum.

Analysis of the peak pressures showed a significant increase at the superior acetabulum after step and gap malreduction, which was not observed after anatomical reduction.

A recent biomechanical study using a plastic bone model revealed comparable results with high anterior column fractures stabilized with two supraacetabular titanium screws with and without an additional infraacetabular titanium screw compared to conventional stabilization concepts with suprapectineal plating with and without an additional infraacetabular screw. Steel screws added only little strength.⁸

12.7.2 Approach

For operative stabilization of anterior column fractures, the intrapelvic or ilioinguinal approach is recommended.^{2,​8,​9,​10,​11,​12,​13,​14,​15}

Choosing the intrapelvic approach, in high anterior column fractures, often the first window of the ilioinguinal approach is additionally recommended.

12.7.3 Reduction Techniques

The reduction technique depends on the level of the upper end of the fracture line.

Very Low Fractures

Letournel did not refer to this fracture type in terms of reduction and further treatment.² In this fracture type, more than 80% of the articular surface remains intact, and only small parts of the anterior horn are involved, so it is questionable whether anatomical reduction is required.

Correspondingly, in isolated fractures, conservative functional treatment is recommended. When these fractures are part of a pelvic ring injury, treatment conforms to pelvic ring standards of upper pubic rami fractures. Therefore, reduction techniques for anterior pelvic ring fractures are used—depending on the pelvic ring instability, closed techniques (external fixation [see ▶ Fig. 12.22], retrograde or anterior column screw) or open techniques (retrograde screw) can be used.^16,​17

Overall, the biomechanical and the secondary biological consequences of this fracture type are unknown.

Low and Intermediate Fractures

Low and intermediate fractures are summarized in the literature.² As a significant articular part of about 30–50% is typically involved, reduction should be as anatomical as possible to avoid pressure peaks.⁷

In general, reduction techniques comparable to anterior wall fractures are recommended.

Various instruments are available for reduction. The following reduction instruments are most frequently used (▶ Fig. 12.7):

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  Long-pointed reduction forceps (Weller forceps)

  
  
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  Matta clamp

  
  
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  Ball spike pusher

  
  
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  Colinear reduction forceps

  
  
  
  

  

  
  

  Fig. 12.7 Typical reduction instruments for anterior column fractures: ball spike pusher, colinear clamp, Matta clamp, and long symmetric and asymmetric reduction forceps.

A stepwise reduction maneuver is recommended for anterior column fractures:

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  Reduction of the hip joint

  
  
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  Identification of articular fragments or marginal impactions

  
  
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  Reduction of the main fragment

Reduction of the Hip Joint

Normally, longitudinal traction alone allows reduction of the femoral head. Lateral traction by percutaneous insertion of a Schanz screw into the femoral neck can support the reduction maneuver (▶ Fig. 11.6).

Identification of the Intraarticular Pathology

It is mandatory to identify and address intraarticular fragments and/or marginal impaction zones.

Using the ilioinguinal approach, after fracture reduction, marginal impactions can be reduced through a bone window with indirect reduction of the fragment against the reduced femoral head, which acts as a template. To secure the reduced impacted fragment(s) percutaneous 3.5-mm screws can be inserted. Additionally, intraarticular fragments are difficult to control. Extension of the ilioinguinal approach with a more lateral dissection according to Ganz allows a better joint inspection.¹⁸

Using the intrapelvic approach, the option of direct reduction from an infrapectineal view allows reduction control under direct visualization.

Reduction of the Main Fragment

After fracture cleaning and reduction of marginal impactions, the reduction of the main fragment(s) against the already reduced femoral head, preferably by means of a ball spike pusher, is performed (▶ Fig. 12.8). The colinear clamp and special reduction forceps are alternatives for fracture reduction. The colinear clamp allows perpendicular orientated pressure against the intact posterior column (▶ Fig. 12.9). A temporary K-wire fixation is possible with this cannulated reduction tool.

Reduction is performed through the second window of the ilioinguinal approach; in higher anterior column fractures, the first window is used as an alternative.

Using Matta forceps, the articular fragment can be reduced through the second window by surrounding the iliopsoas with the clamp branches. The lateral branch is placed either laterally through an additional incision or more medial through the window (▶ Fig. 12.10).

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