Anteroposterior Compression (APC) Pelvic Injuries

Anteroposterior compression (APC) injuries are external rotation injuries of the pelvic ring, produced by a direct anterior impact or by the lower limbs being forced into external rotation. The force "opens" the ring like a book: the anterior structures fail first, and the injury progresses posteriorly as the force increases. APC injuries make up 15-20% of pelvic ring injuries, the second most common pattern after lateral compression, and they matter out of proportion to that because they carry the highest haemorrhage risk of all pelvic patterns and are the most common cause of massive pelvic haemorrhage.

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Mechanism. The force vector is anteroposterior, and the mechanisms that produce it are the ones to listen for in the history:

• Motorcycle collision, with the handlebars striking the pelvis
• Pedestrian struck anteriorly by a vehicle
• Frontal vehicle collision with an AP force vector
• Crush injury with anterior compression
• Fall with the legs forced into external rotation
• Fall from height with the legs apart

Who. Young males predominate, because the mechanism is high-energy trauma. Most have associated polytrauma, and their injury severity scores are typically higher than in lateral compression injuries.

Why the stakes are high. The haemorrhage, which the anatomy below explains, and the urological injury that follows symphysis disruption, since the bladder and urethra are directly affected by it.

The ring. The pelvis is a ring with anterior and posterior components, and its stability depends primarily on the posterior structures. Anteriorly, the pubic symphysis is a fibrocartilaginous joint with minimal inherent stability and a normal width of approximately 5mm; its disruption alone does not make the ring unstable. The pubic rami connect the symphysis to the acetabulum, fracture commonly alongside a symphysis disruption, and may fracture bilaterally.

The posterior ligaments. Each restrains something different. Force applied anteriorly makes them fail in sequence, front to back, and the Young-Burgess grades set out under Classification describe that sequence.

• Anterior SI ligaments - the first to fail in APC
• Interosseous SI ligaments - the main restraint to external rotation
• Posterior SI ligaments - the strongest, and the ultimate stability of the ring
• Sacrospinous ligament - resists external rotation
• Sacrotuberous ligament - resists vertical displacement

Why APC bleeds. Normal pelvic volume is approximately 1.5 litres; an APC-III can increase it to greater than 4 litres, so the pelvis can accommodate several litres of blood as a massive retroperitoneal haemorrhage, and the tamponade effect of an intact ring is lost once the ring opens. The vascular anatomy to know is the presacral venous plexus and the internal iliac veins, low-pressure, high-volume sources; the internal iliac branches, of which the superior gluteal artery is the most commonly involved; and the corona mortis, aberrant obturator vessels present in 30% of people.

Bleeding sources. Between 80 and 90% of the bleeding is venous, from disruption of the plexus, and 10-20% is arterial, often from the superior gluteal artery. The cancellous bone surfaces contribute as well.

The Young-Burgess classification stratifies APC injuries by severity and stability according to progressive ligamentous disruption. Symphyseal widening decides whether an injury is APC-I; the state of the posterior SI ligaments separates APC-II from APC-III. Posterior injury, not anterior widening, is what determines stability, and the grade predicts the haemorrhage risk and guides management.

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The setting. APC injuries are diagnosed in the context of major trauma, and pelvic assessment follows ATLS principles within the primary survey. The mechanisms that should raise suspicion are those set out under Overview.

Inspection. The signs to look for:

• Limb length discrepancy (APC-III)
• External rotation deformity of the lower limbs
• Perineal swelling or ecchymosis
• Scrotal or labial haematoma
• Visible symphysis widening in severe cases
• Blood at the urethral meatus

Palpation, gently and once only, is for a palpable symphysis gap, tenderness over the SI joints posteriorly and iliac crest tenderness.

Associated injuries. Three systems are always assessed:

• Urological - blood at the meatus or a high-riding prostate means urethral injury, and haematuria means bladder injury. Do not catheterise if urethral injury is suspected.
• Vascular - peripheral pulses, signs of hypovolaemic shock, an expanding haematoma.
• Neurological - L5 and S1 nerve root function and motor function from L2 to S1, sensory examination, perineal sensation (S2-4) and rectal tone, all documented.

Haemodynamic assessment. The unstable patient has tachycardia greater than 100 bpm, hypotension with a systolic pressure less than 90mmHg, a reduced GCS from hypoperfusion, poor peripheral perfusion, or a need for ongoing resuscitation. Presume the pelvis is the source when there is:

• Pelvic instability on examination
• No other obvious source of haemorrhage
• A high-risk mechanism
• An APC pattern on imaging

Differential diagnosis. The "open book" appearance and pelvic instability of an APC injury must be distinguished from other patterns that look similar on the AP film but demand opposite management, as the last column of the table shows. The binder that closes an externally rotated ring is not the reflex answer in lateral compression injuries, the vertically displaced hemipelvis of a vertical shear injury shares APC-III's posterior disruption but arrives by a different mechanism, and the ring principles common to all three are set out in pelvic ring injuries.

Plain radiographs. The AP pelvis is the first-line film in trauma and can be taken in the resuscitation bay. It is where the symphysis width is measured against the threshold under Classification, associated pubic rami fractures are looked for and SI joint symmetry is judged. The two further views:

• Inlet view - AP displacement, the symphysis diastasis clearly, and the anterior SI joint
• Outlet view - vertical displacement and a better view of the sacrum, which is what helps separate APC-III from APC-II

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CT. Indicated for every stable patient with a suspected pelvic injury and, in the haemodynamically stable, for surgical planning, because it defines the posterior injury pattern precisely. It gives the symphysis diastasis measurement, anterior SI joint widening, the pattern of SI joint opening from which posterior ligament integrity is inferred, associated sacral and rami fractures and, with CT angiography, contrast extravasation. CT angiography shows active arterial extravasation and guides angioembolisation.

Retrograde urethrogram. Indicated for blood at the urethral meatus, a high-riding prostate on rectal examination, a perineal haematoma, and before catheterisation whenever urethral injury is suspected. Inject 20-30mL of water-soluble contrast gently via the meatus under fluoroscopic or plain film guidance.

Cystogram. For haematuria with a pelvic fracture, once urethral integrity has been confirmed, to look for bladder rupture. An intraperitoneal rupture shows contrast around bowel; an extraperitoneal rupture gives flame-shaped extravasation, and is the more common with APC.

Bladder injury. Occurs in 15-25% of APC injuries. Extraperitoneal rupture is the more common, following the symphysis disruption; intraperitoneal rupture follows impact on a full bladder. Haematuria is the key finding. An extraperitoneal rupture is managed by catheter drainage for 10-14 days; an intraperitoneal rupture requires surgical repair.

Urethral injury. More common in males, whose membranous urethra is long. The signs and the urethrogram that must precede any catheter are under Clinical Assessment and Investigations; a complete disruption needs a suprapubic catheter.

Neurological injury. The L5 nerve root is the most vulnerable part of the lumbosacral plexus, giving foot drop and sensory loss; the S2-4 sacral roots carry bladder, bowel and sexual function.

Open pelvic fractures. Classified by Faringer according to the wound:

• Type I - iliac wing (low risk)
• Type II - perineum or buttock (moderate)
• Type III - rectum or vagina (high mortality)

Management is faecal diversion for rectal involvement, wound debridement and broad-spectrum antibiotics. Mortality is high, up to 50%.

Early complications. Haemorrhagic shock is the most common cause of early death, with massive transfusion requirements and a coagulopathy that compounds the bleeding. Venous stasis and the injury itself make the DVT risk high, and PE can be fatal, so prophylaxis starts early once it is safe. Surgical site infection occurs; osteomyelitis is rare with closed injuries.

Malunion and nonunion. Malunion means residual diastasis or SI joint malreduction, and affects gait and causes pain. Nonunion is rare with adequate fixation; a symphysis nonunion gives painful instability, and an SI nonunion may need fusion.

Hardware. Symphysis plate loosening, which is activity related, and screw pullout; removal may be needed if symptomatic.

Chronic pain. The sources are SI joint arthritis and symphysis pain. SI joint pain affects 20-40% of APC-II and APC-III patients and symphysis pain 15-25%; a sacral fracture malunion contributes, and SI fusion may be of benefit.

Sexual and urological. Erectile dysfunction in 15-30% of males and dyspareunia in 20-40% of females, both more common with urethral injury, and chronic urethral stricture.

Leg length discrepancy. Rare with accurate reduction; it results from malreduction of a vertical component.

Mortality. Quote a source, because the grade-specific numbers in circulation are estimates. In Burgess's original 210-patient series (PMID 2381002) mortality by mechanism was APC 20.0%, lateral compression 7.0%, combined mechanical 18.0% and vertical shear 0%, against 8.6% overall. The commonly quoted grade-specific figures (APC-I under 5%, APC-II 5-15%, APC-III up to 25%) are extrapolations from this and later series rather than published sub-grade rates.

The caveat from the same paper. The cause of death was attributable to the pelvic fracture in fewer than half of cases. Most of these patients die of their associated injuries, which is why the registry data find that haemodynamics and chest injury, not the pelvic grade, predict death: population-based registry mortality for severe pelvic ring fracture is 19% (348 cases; PMID 21733513), with age 65 or over (AOR 7.6) and hypotension at scene (AOR 5.5) the dominant predictors.

Transfusion. The transfusion requirement is the number that best captures why APC bleeds: average blood replacement was 14.8 units for APC, against 9.2 for vertical shear, 8.5 for combined mechanical and 3.6 for lateral compression (PMID 2381002).

Function. Prognosis depends heavily on the initial injury severity and the associated injuries.

Global Epidemiology

• Severe pelvic ring disruption is uncommon but high-lethality. In the population-based Victorian State Trauma Registry (Australia), overall mortality after severe pelvic ring fracture was 19%, with scene/admission hypotension and age 65 years or older as the dominant predictors (Gabbe et al., 2011, PMID 21733513).
• In the original Young-Burgess cohort, the APC pattern carried the highest pattern-specific mortality (20%) and the greatest transfusion requirement (mean 14.8 units) of all pelvic patterns (Burgess et al., 1990, PMID 2381002).
• High-energy mechanisms (motor vehicle, motorcycle, pedestrian, fall from height) dominate worldwide; bimodal age distribution exists, with high-energy injuries in younger patients and lower-energy ring injuries in older patients.

Side-by-Side Guideline & System Guidance

Tranexamic Acid and Resuscitation

The CRASH-2 randomised trial established that tranexamic acid given within 3 hours of injury reduces all-cause and bleeding-related mortality in trauma haemorrhage without increasing vascular occlusive events (PMID 20554319). It is now embedded in essentially all major trauma-system massive transfusion protocols globally.

Registry & Practice-Variation Evidence

• Registry data (Victorian State Trauma Registry) show no independent association between the definitive hospital and mortality after adjustment, reinforcing that rapid physiological control rather than the receiving centre drives survival (PMID 21733513).
• A 40-year systematic review of published algorithms confirms convergence of global practice: steadily rising use of pelvic binders/sheets and CT plus angiography, external fixation as the most common stabilisation technique, and increasing incorporation of REBOA and INFIX, while diagnostic peritoneal lavage has been abandoned (PMID 39731120).
• Persistent variation remains in the first-line haemorrhage adjunct: many North American centres favour pre-peritoneal packing, while several European and Asian centres prioritise early angioembolisation - the WSES framework accommodates both within a physiology-led pathway.
• DVT/PE risk after major pelvic ring injury is universal; chemical prophylaxis with low-molecular-weight heparin is started once haemostasis is secure and typically continued for several weeks, with extended prophylaxis for prolonged immobility.

High-Yield Concepts

Key Differentiators

Hemorrhage Management Sequence

1. Recognize APC pattern and instability
2. BIND - Pelvic binder at trochanters
3. Resuscitate - MTP, TXA, permissive hypotension
4. Image - When stable enough for CT
5. Intervene - Angioembolization if arterial source
6. Fix - Definitive surgical stabilization

Surgical Fixation Principles