Residency · Residency · Orthopedic Surgery

Pelvic Ring Injuries: Evaluation and Stabilization

Anatomy of the Pelvic Ring

Bony Anatomy

The pelvic ring is formed by three bones: two innominate bones (each composed of the ilium, ischium, and pubis) and the sacrum. The anterior ring consists of the pubic symphysis and bilateral pubic rami. The posterior ring comprises the sacroiliac (SI) joints and sacrum. The posterior ring bears 60-70% of the axial load transmitted from the spine to the lower extremities and is therefore the key to pelvic stability. The acetabulum is formed at the junction of all three components of the innominate bone, meeting at the triradiate cartilage.

Ligamentous Anatomy

The ligamentous structures of the pelvis determine its stability. The anterior sacroiliac ligaments are the weakest of the SI joint ligaments. The posterior sacroiliac ligaments are the strongest ligaments in the body, with the short posterior SI ligaments resisting anterior translation and the long posterior SI ligaments resisting cephalad migration. The interosseous SI ligaments resist axial and rotational forces. The sacrospinous ligament runs from the sacrum to the ischial spine, and when disrupted, permits rotational instability. The sacrotuberous ligament connects the sacrum to the ischial tuberosity, and its disruption (combined with posterior SI ligament failure) allows vertical instability. The pubic symphysis is a fibrocartilaginous joint reinforced by superior and inferior pubic ligaments.

Neurovascular Anatomy

Several critical neurovascular structures are at risk in pelvic injuries. The L5 nerve root crosses the sacral ala and is vulnerable in Denis Zone 2 sacral fractures. The internal iliac vessels lie directly anterior to the SI joint. The corona mortis, an anastomosis between the obturator and external iliac or inferior epigastric vessels, poses a hemorrhage risk during anterior surgical approaches. The superior gluteal artery exits through the greater sciatic notch and can be injured in posterior ring disruptions. The presacral venous plexus is the source of massive hemorrhage in many unstable pelvic fractures.

Classification Systems

Young-Burgess Classification

The Young-Burgess system classifies pelvic ring injuries by the mechanism of injury and vector of deforming force.

Anteroposterior Compression (APC)

APC-I injuries show symphysis diastasis less than 2.5 cm with intact posterior ring ligaments and an intact sacrospinous ligament. These are stable injuries that can bear weight as tolerated. APC-II injuries demonstrate diastasis greater than 2.5 cm with a disrupted sacrospinous ligament but intact posterior SI ligaments, creating the classic "open book" pattern that is rotationally unstable but vertically stable. APC-III injuries have complete disruption of both anterior and posterior SI ligaments, producing rotational and vertical instability with associated massive hemorrhage risk.

Lateral Compression (LC)

Lateral compression is the most common mechanism, accounting for 60-70% of pelvic ring injuries. LC-I injuries show an ipsilateral sacral buckle fracture with ipsilateral rami fractures; these are stable because the posterior ring remains intact. LC-II injuries feature a crescent (iliac wing) fracture with ipsilateral rami fractures, producing partial instability with an internal rotation deformity. LC-III injuries combine an ipsilateral LC pattern with a contralateral APC injury (the "windswept pelvis"), resulting in both rotational and vertical instability.

Vertical Shear (VS)

Vertical shear injuries demonstrate complete superior displacement of a hemipelvis with disruption through both the anterior and posterior ring. These carry the highest associated mortality. Characteristic findings include clinical leg-length discrepancy and vertical displacement visible on the AP pelvis radiograph.

Combined Mechanism (CM)

Combined mechanism injuries display features of more than one pattern.

Tile Classification

The Tile classification provides a simplified framework: Type A injuries are stable with an intact posterior ring, Type B injuries are rotationally unstable but vertically stable, and Type C injuries are both rotationally and vertically unstable.

Initial Assessment and Resuscitation

Primary Survey

Pelvic fractures are markers of high-energy trauma, and management should follow ATLS protocols. Associated injuries are extremely common: head injuries occur in approximately 50%, chest injuries in 20%, abdominal injuries in 15%, and urogenital injuries in 10-20%. Overall mortality ranges from 5-15%, rising to 40-60% in hemodynamically unstable patients.

Hemodynamic Assessment

Hemorrhage is the leading cause of death in pelvic ring injuries. Average blood loss in APC-III and VS injuries can exceed 3-4 liters. Bleeding sources include the presacral venous plexus (the most common source), branches of the internal iliac artery, and cancellous bone surfaces. Massive transfusion protocols employing a 1:1:1 ratio of packed red blood cells, fresh frozen plasma, and platelets should be activated early. Notably, performing a rectal exam to assess pelvic stability is no longer recommended as the primary assessment tool.

Mechanical Stabilization

A pelvic binder provides circumferential compression at the level of the greater trochanters, reducing pelvic volume and tamponading venous bleeding. It must be applied at the trochanter level (not the iliac crests) to be effective. The binder works well for APC and VS injuries but may worsen LC injuries by further internally rotating an already displaced hemipelvis. It is a temporary measure; definitive fixation or removal should occur within 24-48 hours to avoid skin necrosis. A sheet wrap is an acceptable alternative if a commercial binder is unavailable.

Hemorrhage Control Algorithm

The initial step is pelvic binder application combined with ATLS resuscitation. If the patient remains hemodynamically unstable despite these measures, treatment branches based on the bleeding source. For arterial bleeding (identified by contrast blush on CT angiography), angioembolization is indicated. For venous bleeding (the most common source), preperitoneal packing is increasingly used as the first-line intervention. External fixation may be applied if the patient is already in the operating room for other reasons. REBOA (Resuscitative Endovascular Balloon Occlusion of the Aorta) is an emerging option for temporizing hemorrhage control in extremis.

Preperitoneal Packing

Preperitoneal packing is performed through a lower midline or Pfannenstiel incision. Packing material is placed in the preperitoneal space and directed posteriorly toward the SI joint to compress the presacral venous plexus and fracture surfaces. It can be combined with external fixation and is increasingly used as the first-line intervention in many centers before or instead of angioembolization.

Angioembolization

Angioembolization is indicated when CT angiography identifies arterial hemorrhage (contrast extravasation). Interventional radiologists selectively embolize branches of the internal iliac artery, most commonly the superior gluteal, lateral sacral, or obturator artery branches. Empiric bilateral embolization may be required when diffuse arterial oozing is present.

Associated Injuries

Urogenital Injuries

Bladder rupture (intraperitoneal or extraperitoneal) and urethral injury are important associations. Urethral injury is more common in males and is suggested by blood at the urethral meatus or a high-riding prostate on examination. A retrograde urethrogram should be performed before catheterization if urethral injury is suspected. Vaginal or rectal lacerations in the presence of a pelvic fracture constitute an open pelvic fracture, which carries high mortality.

Neurologic Injury

L5 nerve root injury is the most common neurologic deficit, resulting from sacral fractures through the neural foramina and producing foot drop. The lumbosacral plexus can be injured in VS and LC-III patterns. Neurovascular examination must be documented before and after any reduction maneuvers.

Open Pelvic Fractures

Open fractures with wounds communicating through the perineum, vagina, or rectum carry 30-50% mortality. Rectal injuries require fecal diversion with diverting colostomy. Management includes aggressive debridement, irrigation, and hemorrhage control.

Definitive Fixation

Anterior Ring Fixation

External fixation uses pins placed in the iliac crest (with supra-acetabular placement preferred) connected by an anterior bar. It can be temporary or definitive but does not address posterior ring instability. Symphysis plating is indicated for diastasis greater than 2.5 cm and uses a superior plate with 2-3 screws on each side through a Pfannenstiel approach; dual plating (superior and anterior) provides increased stability. Rami fixation can be achieved with retrograde or antegrade intramedullary screws placed percutaneously under fluoroscopic guidance. The anterior subcutaneous internal fixator (INFIX) uses pedicle screws placed in the supra-acetabular corridor connected by a subcutaneous rod.

Posterior Ring Fixation

Posterior ring fixation is the critical element because the posterior ring provides the majority of pelvic stability. Iliosacral screws are the gold standard, placed percutaneously under fluoroscopic guidance from the lateral ilium into the S1 and/or S2 vertebral body. Safe placement requires meticulous fluoroscopic technique using inlet, outlet, and lateral sacral views, as the safe corridor is narrow and nerve root injury (L5, S1) is the primary risk. CT-guided or navigation-assisted techniques reduce complication rates. Posterior tension band plates span the posterior iliac crests and are used for sacral fractures with vertical instability. Lumbopelvic fixation (triangular osteosynthesis) connects pedicle screws in L4/L5 to iliac screws and is indicated for spinopelvic dissociation patterns (bilateral sacral fractures, U-shaped sacral fractures), often combined with iliosacral screws.

Sacral Fractures -- Denis Classification

The Denis classification of sacral fractures is based on the relationship to the neural foramina. Zone 1 fractures are lateral to the foramina (alar fractures) with approximately 5% neurologic injury. Zone 2 fractures pass through the foramina with 25% neurologic injury, predominantly L5 root involvement. Zone 3 fractures are medial to the foramina (central) with 50% neurologic injury including bowel and bladder dysfunction. U-shaped and H-shaped fracture patterns represent spinopelvic dissociation requiring lumbopelvic fixation.

<image>An anteroposterior pelvic radiograph diagram showing the Young-Burgess classification of pelvic ring injuries. Illustrate APC-I (minimal symphysis widening), APC-II (open-book with widened symphysis and SI joint anteriorly), APC-III (complete disruption), LC-I (sacral buckle fracture with rami fractures), LC-II (crescent fracture), and VS (vertical displacement of hemipelvis). Label force vectors and key anatomical disruptions for each type.</image>

<image>An anatomical illustration of the posterior pelvic ring showing the sacroiliac joint and key stabilizing ligaments. Include the anterior SI ligaments, posterior SI ligaments (short and long), interosseous SI ligaments, sacrospinous ligament (ilium to ischial spine), and sacrotuberous ligament (sacrum to ischial tuberosity). Show the superior gluteal artery exiting through the greater sciatic notch and the L5 nerve root crossing the sacral ala.</image>

<image>A diagram of the hemorrhage control algorithm for unstable pelvic ring injuries. Start with pelvic binder application and ATLS resuscitation. Branch into hemodynamically stable (CT angiography, definitive fixation planning) and hemodynamically unstable (preperitoneal packing vs. angioembolization vs. external fixation). Include decision points for arterial vs. venous bleeding and the role of REBOA as a temporizing measure.</image>

Clinical Pearls

The posterior ring is the key to pelvic stability, and anterior fixation alone is insufficient for unstable injuries. Pelvic binders must be placed at the level of the greater trochanters, not the iliac crests, as incorrect placement is ineffective. LC injuries are the most common pelvic ring injury pattern, and most are stable enough for nonoperative management. In lateral compression injuries, a pelvic binder may paradoxically worsen displacement by further internally rotating the hemipelvis. Inlet and outlet pelvic radiographs should always be obtained in addition to the AP pelvis for complete evaluation. CT with 3D reconstructions is the gold standard for definitive classification and surgical planning. Iliosacral screw placement requires meticulous fluoroscopic technique because the safe corridor is narrow, especially at S2. Open pelvic fractures with perineal wounds carry a mortality rate of 30-50% and require emergent hemorrhage control, debridement, and consideration of fecal diversion.

References

• Young JWR, Burgess AR. Radiologic Management of Pelvic Ring Fractures: Systematic Radiographic Diagnosis. Urban & Schwarzenberg; 1987.
• Tile M. Pelvic ring fractures: should they be fixed? J Bone Joint Surg Br. 1988;70(1):1-12.
• Costantini TW, et al. Current management of hemorrhage from severe pelvic fractures. J Trauma Acute Care Surg. 2016;80(4):717-725.
• Routt MLC Jr, et al. Iliosacral screws: early results of treatment of posterior pelvic ring disruptions. J Orthop Trauma. 1996;10(6):395-401.
• Tosounidis TH, et al. Assessment and management of pelvic ring injuries. JBJS Rev. 2020;8(12):e20.00044.

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