Fracture Characteristics

Posterior column fractures are rare acetabular fractures with a suspected incidence of approximately 3.5%.¹

The fracture line typically starts in the area of the superior greater sciatic notch and extends distally into the acetabular fossa at its posterior border, separating the posterior wall and parts of the acetabular dome and reaching the obturator foramen, which can be fractured at different points.² The inferior pubic ramus is variably fractured. The teardrop figure and the obturator canal normally remain intact, whereas, in some cases, incomplete fractures are observed without fracture to the inferior ramus.

Occasionally, the most proximal part of the posterior column fracture runs transverse at the level of the ischial spine.

In the cranial part of the fracture, predominantly nonarticular comminution zones can be possible. The primary dislocation of the whole column fragment is a posterior dislocation in combination with internal rotation of the fragment, which leads to a medial displacement in direction to the true pelvis. Thus, the femoral head seems to be centrally dislocated on the pelvic anteroposterior (AP) view.

Rarely, the entire acetabular fossa remains attached to the column fragment. The teardrop figure is then shifted with the fragment and remains in relation to the posterior column.

The hip joint capsule is usually intact.

9.2 Radiological Criteria

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  Pelvic AP view (▶ Fig. 9.1a). Characteristically, the ilioischial line is disrupted and displaced centrally together with the femoral head. The lines of the anterior column (anterior wall line and iliopectineal line) remain intact, and the line of the anterior wall is often better visualized due to the lack of superposition of the posterior structures. The acetabular roof is in its normal position and shows normal density. The line of the posterior wall is usually not disrupted, but can appear with a positional change. The usually uninjured teardrop figure is in its normal position with unchanged relationship to the iliopectineal line. A proximal spur near the sacroiliac (SI) joint is often visible central to the iliopectineal line, which corresponds to the cranial border of the displaced posterior column fragment.

  
  
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  Iliac oblique view (IOV) ( ▶ Fig. 9.1b). Here, the interruption and displacement of the entire posterior column is best visualized and the most superior extend of the fracture can be identified. Fractures of the iliac wing or of the anterior roof can be excluded.

  
  
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  Obturator oblique view (OOV) ( ▶ Fig. 9.1c). The integrity of the iliopectineal line and the anterior wall is confirmed. The posterior column spur can be identified cranial and superior to the iliopectineal line, appearing smaller than on the AP X-ray.

  
  
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  Computed tomography ( ▶ Fig. 9.1d). Evaluation of accompanying injuries (e.g., intraarticular fragments and marginal impaction zones), the position of the femoral head, the extent of articular involvement, and the extent of posterior dislocation and rotation of the fragments are best seen on CT.

  
  
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  Transition forms to other fracture types. Fracture lines extending far cranially can lead to a separation of both iliac cortices at the level of the greater sciatic notch often imposing a doubled ilioischial line.² By parallel shifting of the posterior part of the iliac bone with the adherent joint surface, radiographically, a seagull wing–like structure can be seen (gull sign),³ which can represent a transition to posterior wall fractures. The gull sign is often observed in the presence of superior dome marginal impactions.

In extended fractures of the posterior column with involvement of the quadrilateral surface or incomplete fracture lines to the anterior column, transition fractures can be present to pure transverse fractures, associated posterior column posterior wall fractures, or T-type fractures.

Fractures that are not disrupting the obturator foramen represent transitions to enlarged posterior wall fractures.

9.3 Pathobiomechanics

In contrast to posterior wall fractures, the main injury vector is less defined. Letournel reported posterior column fractures as a result of a dashboard mechanism in only 2.8%, whereas in 87% a fracture of the posterior wall with or without a transverse fracture component occurred.² Impact against the greater trochanter even more rarely led to fractures of the posterior column in only 1.4%.

A more axial mechanism with force transmission of the whole leg from the foot seems to result in this fracture type—a posterior column involvement was observed in 11 of 16 patients.²

A flexion of the hip joint < 90 degrees in neutral position or slight abduction theoretically result in a posterior column fracture. Accordingly, the main fragment shows posteromedial internal rotation into the small pelvis.

Additionally, a larger fracture energy must be present to fracture the solid bone at the upper edge of the greater sciatic notch.

The hip joint capsule remains normally intact, attached to the posterior column fragment. Thus, the femoral head “follows” the fragment to a “central” dislocation.

Depending on the hip position during impact, additional injury in the area of the posterior wall, such as marginal impaction zones, can be present.

Overall, the dashboard mechanism is suitable for creating posterior column fractures. However, experimentally, only two such fractures were observed, with average forces of 5355 N.⁴ Dakin et al observed only one posterior column fractures after a dashboard mechanism.⁵

9.4 Hip Joint Stability

Hip joint instability, as frequently seen in posterior wall fractures, is usually not observed after posterior column fractures. Because the femoral head usually follows the posterior column fragment, displacement is orientated medial and posterior relative to the acetabular roof. In small posterior column fragments a subluxation or dislocation is often missing, since the femoral head is connected to the acetabular fossa through the ligament of the femoral head. Instability, therefore, is caused by the fracture itself.²

9.5 Biomechanics of Posterior Column Fractures

Only one biomechanical study analyzed a posterior column fracture.⁶ Vrahas et al simulated posterior column fractures in relation to hip joint stability.⁶ They distinguished very high fractures, extending to the superior greater sciatic notch, from intermediate, inferior, and very inferior fractures—the latter fracturing the bone at the level of the ischial spine. Radiologically, the most proximal fracture line corresponds to fractures with a roof–arc angle according to Matta⁷ of 30 degrees, 40 degrees, 50 degrees, and 60 degrees on the ala oblique view.

Using forces of 800 N in 25 degrees flexion and 20 degrees abduction, dislocation occurred in all fracture types. At forces of 1200 N, two further inferior fractures showed displacement and inferior fracture occurred at 1600 N.

9.6 Treatment Indications

Type of treatment depends on the fracture dislocation and thus instability of the fracture as well as the presence of accompanying articular injury.

9.6.1 Conservative Treatment

Conservative treatment is only recommended in undisplaced fractures with no additional articular injuries, such as marginal impactions or intraarticular fragments. As described, joint stability can be present in inferior column fractures at the level of the ischial spine (▶ Fig. 9.4).

Conservative treatment includes a physiotherapeutic treatment with muscle strength support, gait training, and coordination exercises. A partial weight bearing is allowed with one-fifth body weight for 6–12 weeks with subsequent increase. Full weight bearing is normally possible normally after 8–10 weeks.

9.6.2 Operative Treatment

Indications for operative treatment are:

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  Unstable hip joint

  
  
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  Incongruence of the hip joint

  
  
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  Intraarticular fragments

  
  
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  Increasing sciatic nerve lesions

  
  
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  Presence of an acetabular impaction area

In the presence of severely unstable situations, emergency closed reduction is performed using one of the known reduction maneuvers (see ▶ 8).

Supracondylar traction is performed in nondislocated femoral heads with one-seventh to one-tenth body weight to reduce medial displacement.

In order to avoid shearing injuries of the acetabular and femoral head cartilage to the fragment, gentle reduction maneuvers under general anesthesia are recommended.

If reduction is impossible, then a relative emergency indication exists for open reduction and primary osteosynthesis of the fracture.

9.7 Techniques of Osteosynthesis

9.7.1 Biomechanics of Osteosynthesis

Schopfer et al analyzed various osteosynthesis techniques in simulated fractures of the posterior column.⁸ Typical fracture types were created in 10 cadavers and loaded in 30 degrees flexion and 60 degrees flexion. Stabilization was performed with a 3.5-mm reconstruction plate, with two reconstruction plates, and a combined reconstruction plate with additional 4.5-mm lag screw, respectively.

All three osteosyntheses led to a reconstruction of 80% of the strength of the intact pelvis. In 30 degrees flexion, no significant differences were observed between the three procedures. In 60 degrees flexion, the combined plate and screw osteosynthesis showed significantly lower fracture site movements compared to other two stabilization techniques.

9.7.2 Approach

Operative stabilization of posterior column fractures is performed using the Kocher-Langenbeck approach.

9.7.3 Reduction Techniques

Various instruments are available for reduction. The following reduction instruments are most frequently used (▶ Fig. 9.5):

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  Large pointed reduction forceps (Weller clamp)

  
  
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  Small pelvic reduction forceps for use with cortex screws (Farabeuf clamp)

  
  
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  Small pelvic reduction forceps for use with cortex screws (Jungbluth clamp)

  
  
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  Universal chuck with T-handle for 5-mm Schanz screws

  
  
  
  

  

  
  

  Fig. 9.5 Various common reduction aids (from left to right: T-handle, Schanz screw, Farabeuf forceps, Jungbluth forceps).

A stepwise reduction maneuver is recommended for posterior column fractures:

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  Distraction of the femoral head

  
  
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  Identification of (intra-)articular pathology

  
  
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  Reduction of the main fragment

Distraction of the Femoral Head

Distraction of the femoral head along the femoral neck axis is performed using a universal chuck with T-handle and a 5-mm Schanz screw inserted from the greater trochanter into the femoral neck to allow intraarticular visualization, debridement, and identification of intraarticular fragments, respectively (see ▶ 8).

Care must be taken to avoid injury of the superior gluteal neurovascular bundle with too extensive manipulation of fractures extending superior to the greater sciatic notch.

Identification of the (Intra-)Articular Pathology

In the presence of an intraarticular pathology—such as, intraarticular fragments, marginal impactions zones, avulsion of the ligament of the head of the femur—all methods are performed as described in ▶ 8.

Reduction of Marginal Impactions

Reduction of identified marginal impactions is then performed. Fragment release out of the cancellous bone must be carefully performed without damaging these fragments using a raspatory or chisel. These fragments are then reduced against the reduced femoral head, the latter acting as a template. The created cancellous defect should be filled up (see ▶ Fig. 8.16). Autogenous cancellous bone from the greater trochanter⁹ or alternatively from the anterior/middle iliac crest can be used. It may be helpful to perform a temporary fixation of these reduced impacted fragments with K-wires parallel to the joint surface (e.g., 1.4-mm diameter). Alternatively, screws or resorbable pins can be used.

In elderly patients with poor bone quality, reduction can be supported by special bone cements to fill up the resulting defects.¹⁰ Free articular fragments should also be reduced anatomically.

Reduction of the Main Posterior Column Fragment(s)

Various techniques are available for reduction of the main posterior column fragment. Primary to this maneuver, additional articular or extraarticular fragments (see ▶ Fig. 9.2) have to be addressed. These have to be reduced and temporarily or definitively fixed with K-wires, pins, or comparable implants.

Protection of the superior gluteal neurovascular bundle is mandatory when manipulation of the posterior column fragment is performed. After fracture debridement and complete visualization, insertion of a Schanz screw into the ischial tuberosity under direct visualization is helpful for manipulating the fragment and controlling rotational displacement (▶ Fig. 9.6). This can be supported by digital manipulation of the fragment at the greater sciatic notch. The course of the sciatic nerve has to be respected.

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