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Supplement Article

Anterior Pelvic Ring: Introduction to Evaluation and Management

Marecek, Geoffrey S. MD*; Scolaro, John A. MD, MA

Author Information
Journal of Orthopaedic Trauma: September 2018 - Volume 32 - Issue - p S1-S3
doi: 10.1097/BOT.0000000000001249
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Abstract

HISTORY

Similar to other areas of orthopaedic trauma, management of pelvic ring injuries has moved from nonsurgical or limited external stabilization/traction to internal fixation. Before routine implementation of internal fixation techniques, anterior external fixation was used as definitive treatment for many lateral compression (LC) and anterior posterior compression (APC) type injuries.1,2 Internal fixation techniques were used with increasing frequency between the 1980s and 1990s, commonly with plates and screws.3 In the mid-90s, percutaneous techniques for the anterior and posterior pelvic ring were described, which fundamentally changed management of pelvic ring injuries.4–6

Injuries to the posterior pelvic ring through the sacrum or sacroiliac joints have historically been given priority with regard to stabilization. Many believed that in the setting of a pelvic ring injury, stabilization of the posterior elements alone would be sufficient. A single surgeon experience of pelvic ring injuries published in 1996 noted, “Many anterior fixations are not necessary … and add to the potential risks of pelvic surgery. Properly performed posterior fixation is sufficient in most cases.”7 Although stable and accurate posterior ring fixation remains important, a recognition that each injured pelvic ring element is a potential site of instability and deformity has driven improved evaluation and fixation of the anterior pelvis.

Recent literature on the pelvic ring has focused primarily on the development of anterior pelvic intramedullary techniques and on evaluating and predicting pelvic stability after injury. Alternative techniques, such as anterior subcutaneous fixation (ASF), bridge plating,8 and unique bridge fixators,9 have also been described as a means of stabilizing the anterior pelvic ring. Future biomechanical and clinical investigations will continue to improve the body of literature on the topic and improve care.

ANATOMY

The pelvic ring consists of 2 innominate bones, the sacrum, and multiple ligamentous attachments between them. Fractures and/or ligamentous injuries within the ring may result in instability. The anterior pelvic ring includes the 2 superior and inferior rami and their anterior midline junction at the pubic symphysis, a non-synovial amphiarthrodial joint.10 The relevant surgical anatomy along the superior ramus will be discussed.

The medial surface of each pubic bone is covered with a thin layer of hyaline cartilage and stabilized by anterior and posterior ligamentous structures. The main stabilizing ligaments are the superior and inferior arcuate ligament. Moving laterally, the pubic tubercle is a prominence that serves as the attachment of the inguinal ligament. Multiple muscle attachments exist near the symphysis, including the rectus abdominus, pyramidalis, adductor longus, and the upper border of the gracilis and adductor brevis. Lateral to the symphysis, the pectineal line is a ridge along the superior ramus. Fibers of the pectineal ligament and origin of the pectineus muscle are found here. If present, vascular communications between the external iliac and obturator or inferior epigastric system exist here.11 Continuing laterally along the pelvic brim, the iliopectineal fascia is a vertical thickening of fascia that inserts onto the iliopectineal eminence. This fascia separates the true pelvis from the false pelvis and the eminence represents the location where the ilium and pubis fuse. Medial to the fascia, the femoral artery and vein course over the superior ramus. Lateral to the eminence is a broad shallow depression where the iliacus and psoas major muscles, as well as the femoral nerve, pass. The obturator neurovascular bundle course below the superior ramus within the obturator canal but is in close opposition to the caudal cortical limit of the superior ramus along the superior lateral aspect of the obturator foramen.

Comprehension of the relevant surgical anatomy of the anterior pelvic ring is essential as trauma, surgical exposures, and implant placement can all result in injury. Although traumatic injury is unable to be prevented, iatrogenic injury must be avoided.

ANTERIOR PELVIC RING STABILIZATION TECHNIQUES

Techniques for stabilization of the anterior pelvic ring can be grouped into 3 main categories: plate fixation, intramedullary fixation, and spanning fixation. Each will be described in greater detail within the body of this supplement but will be introduced here.

Plate and screw fixation of the symphysis pubis is routinely performed in the setting of traumatic symphyseal widening. Plate fixation can also be used for ramus fixation or to span both an injured ramus and symphysis pubis.12 In most instances, plate and screw fixation requires a formal open surgical approach to the injured element(s) of the anterior ring. Although this technique allows direct visualization of the injury, and can be used regardless of osseous morphology, it does leave a surface implant in place, which may be undesirable in some clinical scenarios. Flexible 3.5-mm reconstruction-style plates and standard cortical screws are most frequently used.

Intramedullary fixation uses the osseous fixation pathway (OFP) of the superior ramus that exists between the pubic symphysis and supra-acetabular region.13 It can be used for simple and complex rami fractures but is not used for fixation across a symphyseal disruption. Screws are placed in an antegrade or retrograde direction; terminology that refers to whether screw insertion begins in the supra-acetabular region or near the pubic symphysis, respectively. Unless a reduction requires an open approach, intramedullary fixation has the advantage of leaving a small biological footprint; it also does not leave a surface implant on the bone. Anatomical variation exists and some patients do not possess a safe corridor for intramedullary fixation due to the size and/or shape of the OFP. The technique also requires an understanding of not only the relevant anatomy of the bony pelvis and surrounding soft tissue structures but also their fluoroscopic representations.

Finally, spanning fixation describes both pelvic external fixation and ASF. Both external fixation and ASF provide an indirect reduction to the anterior pelvic ring.1,14,15 External fixation can be used for provisional or definitive stabilization and can be used in both APC or LC type injuries. External fixation pins are commonly placed in 1 of 2 positions: (1) between the inner and outer tables of the ilium within the gluteus medius pillar16 or (2) anteriorly, starting about the anterior inferior iliac spine and heading posteriorly within the OFP in the supra-acetabular region toward the sciatic notch or posterior superior iliac spine.17 ASF uses the anterior supra-acetabular pin trajectory exclusively. External fixation and ASF also leave a limited biological footprint and can be used when osseous morphology or surgical field contamination prohibit internal fixation. Both techniques do have associated morbidity and limitations.14,18

Anterior pelvic ring fixation can be accomplished in multiple ways. Before considering the various techniques, proper evaluation of anterior pelvic ring stability is performed to determine both the need and the type of fixation applied.

ASSESSMENT OF STABILITY

Mechanical instability is obvious in certain cases (Fig. 1, widely displaced ring). However, for many cases, identifying and quantifying instability is challenging (Figs. 2A–C). Physical examination of the patient is a critical first step, as patients with pelvic ring instability are often reluctant to move in bed, intolerant of pelvic compression, and difficult to mobilize.

FIGURE 1.
FIGURE 1.:
Anteroposterior (AP) radiograph of pelvic ring with obvious mechanical instability.
FIGURE 2.
FIGURE 2.:
A 60 year old woman who sustained a fall at home. She was discharged from an outside hospital and was walking several days after injury when she presented with this AP radiograph (A) and axial CT scan (B). One week later, mechanical instability was evident on repeat AP pelvis (C).

Radiographs and computed tomography scans are commonly used studies to begin evaluation of the pelvic ring but both are static images that may not demonstrate maximum or potential displacement of the ring.19 Some surgeons have attempted to identify markers of mechanical instability that can predict later displacement. Bruce et al20 reviewed 117 LC type injuries managed nonoperatively. Patients with complete sacral fractures displaced more than 1 cm in any plane during treatment in 50% of cases. Anterior ring injuries were important as patients without ramus fractures did not displace, whereas those with unilateral or bilateral ramus fractures displaced in 8.8% and 39% of cases, respectively. However, the functional impact of this displacement is unknown. Moreover, these data provide an estimate of the risk of displacement but cannot determine the presence of mechanical instability in any given patient.

Consequently, surgeons have turned to dynamic assessments of mechanical stability in equivocal cases. Sagi et al21 described a 15-step examination under anesthesia (EUA) to identify mechanical instability in LC and APC type injuries that was used to direct treatment preoperatively and intraoperatively. In many cases, a simple internal rotation or external rotation force is sufficient to identify the presence of instability, although the surgeon may desire more information from the remainder of the examination. In a later study, Whiting et al22 subsequently documented the results of nonoperative treatment in patients with negative EUA. The study included patients with LC1, LC2, and APC1 injuries who were permitted weight-bearing as tolerated after a negative EUA. Patients had a maximal increase in displacement of 2 mm at the final follow-up and achieved uneventful union.

Dynamic evaluation can help guide decision-making intraoperatively. There is frequently debate about the role of anterior ring fixation after adequate posterior stabilization.7 Avilucea et al23 proposed a sequential examination for mechanical instability after posterior ring fixation. Half of the 74 patients demonstrated mechanical ring instability after posterior fixation and received anterior ring fixation, whereas those patients who were deemed stable did not. All patients who received fixation went on to uneventful union. Of the 36 patients who did not receive fixation, only 9 with bilateral ramus fractures had early displacement up to 12 mm. The study highlights the frequency with which mechanical instability persists after isolated posterior fixation and that special consideration may be given to patients with bilateral ramus fractures.

CONCLUSIONS

The management of the anterior pelvic ring has evolved a great deal but remains controversial. Not only are the indications for fixation of the anterior ring debated but multiple options for fixation also exist. The anterior pelvic ring, composed of the pubic symphysis and bilateral superior and inferior rami provide important contributions to ring structure, with each disruption representing a potential location of instability. Static imaging provides information about injury location and pattern but recent evidence has reinforced the fact that pelvic instability is dynamic and that appropriate measures should be taken to identify and then address it.

REFERENCES

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Keywords:

anterior pelvic ring; pelvis; instability; ramus; fracture; disruption

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