Acetabular Fractures

Epidemiology

Acetabular fractures are relatively uncommon, occurring in approximately 3 per 100,000 individuals each year. These injuries are typically associated with high-energy trauma, such as road traffic accidents or falls from height.

Neurological involvement occurs in up to 30% of cases, most commonly affecting the sciatic nerve. The peroneal division of the sciatic nerve is more frequently injured than the tibial division.

These fractures often occur in younger adults following high-energy mechanisms but can also be seen in elderly patients with osteoporotic bone after low-energy trauma. The frequency of associated systemic injuries is high due to the force involved in these mechanisms.

Anatomy

The acetabulum represents the socket portion of the hip joint, formed by the union of the ilium, ischium, and pubis. Structurally, it functions as part of a two-column system, a concept introduced by Letournel and Judet, in which the acetabulum can be visualized as an inverted “Y” composed of anterior and posterior columns that converge at the acetabular dome.

Anterior Column (Iliopubic Component)

• Extends from the iliac crest to the pubic symphysis.
• Includes the anterior wall of the acetabulum and the anterior portion of the ilium, superior pubic ramus, and pubic body.
• Fractures involving this column commonly exit below the anteroinferior iliac spine.

Posterior Column (Ilioischial Component)

• Extends from the greater sciatic notch down to the ischial tuberosity.
• Includes the posterior wall of the acetabulum and the ischial portion of the acetabular surface.
• This column forms the posterior boundary of the acetabulum and provides attachment for important gluteal and short external rotator muscles.

Acetabular Dome

• The superior weight-bearing segment of the acetabulum where the anterior and posterior columns meet.
• It bears the majority of the joint reaction forces during standing and walking.
• Anatomical restoration of this region is crucial for preserving normal hip biomechanics.

Corona Mortis

• A vascular communication between the obturator and external iliac or deep inferior epigastric vessels.
• Found in approximately 10–15% of individuals.
• It usually traverses the superior pubic ramus, about 6 cm lateral to the pubic symphysis.
• Awareness of this vessel is essential during anterior surgical approaches (e.g., modified Stoppa) to prevent severe hemorrhage.

Other Important Vascular and Neural Structures

• Ascending branch of the medial femoral circumflex artery supplies the femoral head; it lies deep to the quadratus femoris muscle.
• Superior gluteal neurovascular bundle emerges from the greater sciatic notch and is at risk during posterior approaches.

Mechanism of Injury

Acetabular fractures, much like pelvic fractures, usually result from high-energy trauma. Common causes include motor vehicle collisions, motorcycle accidents, and falls from significant heights. In elderly individuals with osteoporotic bone, these fractures can occur even from low-energy mechanisms, such as a fall from standing height.

The pattern of the fracture is influenced by:

• The position of the femoral head at the moment of impact.
• The direction and magnitude of the applied force.
• The age and bone quality of the patient.

Direct Trauma

A lateral impact to the greater trochanter with the hip in a neutral position can cause a transverse acetabular fracture.

• If the hip is abducted, the fracture tends to be lower (infratectal).
• If the hip is adducted, the fracture becomes higher (transtectal).
  An externally rotated and abducted hip directs force to the anterior column, while an internally rotated hip leads to posterior column involvement.

Indirect Trauma (Dashboard Injury)

In dashboard-type injuries, force transmitted through a flexed knee drives the femoral head posteriorly into the acetabulum.

• As hip flexion increases, the posterior wall fracture occurs lower on the acetabulum.
• As hip flexion decreases, the fracture involves the superior portion of the posterior wall.

This mechanism also explains the frequent association between posterior wall fractures and posterior hip dislocations.

Clinical Evaluation

Because acetabular fractures are commonly the result of high-energy trauma, initial evaluation must follow the Advanced Trauma Life Support (ATLS) protocol, addressing airway, breathing, circulation, disability, and exposure before proceeding to a focused orthopedic assessment.

General Assessment

• Evaluate for polytrauma, as associated injuries (head, thoracic, abdominal, or long-bone fractures) are frequent.
• Patient age, medical comorbidities, and mechanism of injury significantly influence both treatment selection and prognosis.

Neurovascular Examination

A careful neurovascular assessment is critical.

• Sciatic nerve injury occurs in up to 40% of posterior column or posterior wall fractures, most often affecting the peroneal division.
• The sciatic nerve may occasionally become entrapped within the fracture site.
• Femoral nerve injury is uncommon but can occur with anterior column fractures or excessive traction during surgery.
• Rarely, the femoral artery may be compressed or injured by a displaced anterior column fragment.

Examination of Associated Injuries

• Ipsilateral lower limb injuries are common; particular attention should be given to the knee joint, where posterior instability or patellar fractures may coexist.
• Soft-tissue findings such as abrasions, contusions, hematomas, or Morel-Lavallée lesions (closed degloving injuries) can help determine the direction and intensity of the traumatic force.
• Pelvic stability should be assessed gently to avoid exacerbating bleeding or displacement.

Radiographic Evaluation

Accurate radiographic assessment is essential for diagnosis, classification, and surgical planning in acetabular fractures. A systematic evaluation should include both plain radiographs and computed tomography (CT) imaging.

Plain Radiographs

The standard radiographic series includes three views:

1. Anteroposterior (AP) pelvis view
2. Iliac oblique view
3. Obturator oblique view

Each view highlights different aspects of the acetabulum and helps identify fracture lines, column integrity, and displacement.

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1. Anteroposterior (AP) Pelvis View

Key anatomic landmarks visible on this view include:

• Iliopectineal line – represents the anterior column.
• Ilioischial line – corresponds to the posterior column.
• Anterior wall and posterior wall outlines.
• Teardrop – formed by the floor of the acetabular fossa and the quadrilateral plate.
• Superior acetabular dome – the primary weight-bearing surface.

Any interruption or displacement of these lines suggests column involvement. The relationship between the femoral head and acetabular outlines indicates joint congruency.

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2. Iliac Oblique View (45° External Rotation)

• Obtained by rotating the patient approximately 45° externally.
• Best demonstrates the posterior column (ilioischial line), iliac wing, and anterior acetabular wall.
• Useful for assessing posterior column displacement and integrity of the iliac bone.

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3. Obturator Oblique View (45° Internal Rotation)

• Obtained by rotating the pelvis 45° internally toward the unaffected side.
• Highlights the anterior column and posterior wall.
• Valuable for evaluating posterior wall fractures, which often accompany posterior hip dislocations.

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Computed Tomography (CT)

CT is indispensable for modern acetabular fracture evaluation. It provides:

• Detailed information on the extent, orientation, and displacement of fracture lines.
• Visualization of articular impaction or comminution.
• Identification of intra-articular bone fragments.
• Assessment of sacroiliac joint involvement or pelvic ring continuity.
• 3D reconstructions can digitally remove the femoral head, allowing a clear view of the acetabular articular surface and both columns.

CT findings often refine classification, guide approach selection, and help predict surgical difficulty.

Classification

The most widely accepted system for describing acetabular fractures is the Judet–Letournel classification, which categorizes fractures according to anatomical involvement and fracture pattern. It divides acetabular fractures into 10 types — five elementary and five associated patterns.

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Elementary Fractures

These involve a single column or wall.

1. Posterior Wall Fracture
   • Involves separation of a portion of the posterior articular surface.
   • The posterior column remains intact (ilioischial line not disrupted).
   • Commonly associated with posterior hip dislocation.
   • Obturator oblique view best demonstrates the fracture.
   • Marginal impaction (articular cartilage impacted into subchondral bone) occurs in approximately 25% of cases and is best appreciated on CT.
   • The “gull sign” on X-ray indicates dome impaction, often predicting a poorer prognosis, especially in osteoporotic bone.
2. Posterior Column Fracture
   • The fracture line starts at the greater sciatic notch, crosses the retroacetabular surface, and exits at the obturator foramen.
   • The ischiopubic ramus is fractured, and ilioischial line disruption is evident.
   • The femoral head may displace medially due to loss of posterior support.
3. Anterior Wall Fracture
   • The least common acetabular fracture type.
   • Involves only a small segment of the anterior articular surface and roof.
   • The anterior column remains largely intact, and the ischiopubic ramus is uninjured.
   • The teardrop may appear displaced medially on radiographs.
4. Anterior Column Fracture
   • Characterized by disruption of the iliopectineal line.
   • The femoral head tends to be displaced anteromedially.
   • Fractures are categorized as low, intermediate, or high, depending on where the fracture exits the ilium superiorly.
   • Higher fractures involve more of the weight-bearing dome.
   • CT is valuable for assessing the degree of articular involvement.
5. Transverse Fracture
   • The acetabulum is divided into superior and inferior halves, with the fracture line extending through the articular surface.
   • Classified according to its level:
     • Transtectal: through the acetabular dome (weight-bearing zone).
     • Juxtatectal: at the junction of the dome and acetabular fossa.
     • Infratectal: through the acetabular fossa (below the dome).
   • The higher the fracture line, the greater the dome displacement.
   • The femoral head often follows the inferior (ischiopubic) fragment, sometimes leading to central dislocation.
   • Both iliopectineal and ilioischial lines are disrupted.
   • The fracture is best evaluated with axial CT imaging.

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Associated Fractures

These patterns combine two or more elementary fractures.

1. Posterior Column with Posterior Wall Fracture
   • Combines two posterior components.
   • The posterior wall fragment is markedly rotated or displaced relative to the column.
   • Frequently associated with posterior hip dislocation and sciatic nerve injury.
2. T-Shaped Fracture
   • Formed by a transverse fracture combined with a vertical fracture line dividing the ischiopubic fragment.
   • The vertical limb (stem) may exit anteriorly, posteriorly, or inferiorly, depending on the force vector.
   • Best visualized on the obturator oblique view or CT scan.
3. Transverse with Posterior Wall Fracture
   • Involves a transverse component with an associated posterior wall fragment.
   • On CT, the femoral head is posteriorly dislocated in two-thirds of cases and centrally displaced in one-third.
   • Marginal impaction is common.
4. Anterior Column with Posterior Hemitransverse Fracture
   • Combines an anterior column fracture with a transverse component that extends through only the posterior column (hemitransverse).
   • A nondisplaced articular fragment typically serves as the key reference point during surgical reduction.
5. Both-Column Fracture
   • The most complex pattern.
   • Both anterior and posterior columns are completely separated from each other and from the axial skeleton, resulting in a “floating acetabulum.”
   • A “spur sign” (a bony projection from the intact ilium) may be seen on the obturator oblique view — this sign is pathognomonic.

Treatment

The primary goal of treatment in acetabular fractures is to achieve anatomic reduction of the articular surface, restore joint stability, and prevent post-traumatic arthritis. The choice between operative and nonoperative management depends on fracture type, displacement, hip stability, patient age, and comorbidities.

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Initial Management

• The patient is typically placed in skeletal traction to reduce pain, prevent further soft-tissue injury, and maintain femoral head position within the acetabulum.
• Traction also facilitates preoperative care and management of associated injuries.
• Early resuscitation and complete evaluation of concomitant injuries are essential before definitive fixation.

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Nonoperative Management

Nonoperative treatment is reserved for stable, congruent fractures or for patients unfit for surgery.

Radiographic Assessment: Roof Arc Concept

The roof arc angle assesses the integrity of the acetabular dome — the primary weight-bearing area.

• It is measured between a vertical line through the center of the acetabulum and a line from the fracture edge to the same center.
• Roof arc <45° indicates fracture extension into the weight-bearing dome, suggesting the need for surgery.
• These angles are evaluated on:
  • AP view → medial roof arc
  • Iliac oblique view → posterior roof arc
  • Obturator oblique view → anterior roof arc
• On CT, a fracture line within 2 cm of the dome apex corresponds to a roof arc <45° on X-ray.

Indications for Nonoperative Treatment

• Nondisplaced fractures with intact hip stability.
• Infratectal transverse or distal anterior column fractures where the medial buttress maintains femoral head congruency.
• Roof arc angles >45° in all three planes.
• Posterior wall fractures <20% of wall size and stable under fluoroscopic stress test.
• Elderly or medically unfit patients, in whom residual deformity may be accepted.

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Operative Management

Indications

• Displaced fractures involving the weight-bearing dome.
• Irreducible or unstable hip dislocations.
• Posterior wall fractures >50% or unstable under stress examination.
• Loose intra-articular fragments causing incongruity (excluding small foveal fragments).
• Inability to maintain joint congruence by closed methods.

Timing of Surgery

• Ideally performed within 14 days of injury.
• Requires:
  • Hemodynamic stability and correction of associated injuries.
  • Preoperative CT evaluation to define fracture anatomy.
  • An experienced surgical team familiar with acetabular anatomy and approaches.

Urgent Surgical Indications

• Open acetabular fractures.
• Irreducible dislocations or medial femoral head dislocation against the ilium.
• New-onset sciatic nerve palsy after closed reduction.
• Extensive Morel-Lavallée lesion requiring debridement before definitive fixation.

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Predictors of Clinical Outcome

Not predictive of outcome:

• Specific fracture pattern
• Initial displacement magnitude
• Presence of intra-articular fragments
• Acetabular impaction
• Posterior dislocation alone

Predictive of poor outcome:

• Femoral head cartilage or bone injury
• Inaccurate reduction of articular surface
• Posterior wall comminution
• Older age, which reduces capacity for anatomic reduction and healing

Stability and Congruity

Stability

Hip joint stability depends on the integrity of the acetabular walls and columns.
Instability most often occurs in posterior fracture types, but it may also arise from fractures of the quadrilateral plate or anterior wall.

• Posterior instability is commonly seen with posterior wall or column fractures and may be evident during fluoroscopic stress testing.
• Central instability occurs when a large quadrilateral plate fragment allows medial subluxation of the femoral head. In such cases, stabilization often requires a spring plate or a buttress plate placed along the infrapectineal surface via the Stoppa approach.
• Anterior instability results from a large anterior wall fracture or an anterior column–posterior hemitransverse pattern, leading to anteromedial femoral head displacement.

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Congruity

Maintaining articular congruity between the femoral head and acetabulum is essential to prevent post-traumatic arthritis.

• Incongruity is best evaluated using CT scans.
• Minor incongruities outside the weight-bearing dome may be acceptable, but any displacement within the superior dome usually requires surgical correction.
• Displaced dome fractures seldom reduce adequately with traction alone.
• High transverse or T-shaped fractures are inherently unstable shearing injuries; they rarely achieve satisfactory closed reduction and often need surgical fixation.
• In both-column fractures, surgery is indicated if the roof fragment is displaced or if secondary congruence cannot be achieved.
• Intra-articular bone fragments may interfere with joint congruence and should be removed, except for small foveal avulsions tethered by the ligamentum teres.
• Femoral head fractures usually require open reduction and fixation to maintain joint sphericity.
• Soft-tissue interposition between fracture fragments or within the joint necessitates removal for proper reduction.

Radiographic assessment of reduction includes:

• Restoration of iliopectineal and ilioischial lines.
• Comparison of hip symmetry with the contralateral side on AP pelvis view.
• Concentric joint reduction visible on all radiographic projections.

The ultimate aim of treatment is a perfectly congruent, stable, and load-bearing joint.

Surgical Approaches

No single surgical approach can fully expose the entire acetabulum. The approach is selected according to the fracture pattern, displacement direction, and surgical objective. The major approaches include:

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1. Kocher–Langenbeck Approach

Indications

• Posterior wall fractures
• Posterior column fractures
• Combined posterior column and wall fractures
• Transverse fractures with posterior displacement
• Selected T-shaped fractures (predominantly posterior)

Exposure

• Provides access to the posterior column, ischial spine, retroacetabular surface, ischial tuberosity, and ischiopubic ramus.

Limitations

• Poor visualization of the superior dome and anterior column.
• May require a trochanteric osteotomy for extended exposure.

Complications

• Sciatic nerve palsy (~10%)
• Infection (~3%)
• Heterotopic ossification (8–25%)
  • The effectiveness of postoperative prophylaxis with NSAIDs or radiation remains uncertain.

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2. Ilioinguinal Approach

Indications

• Anterior wall and anterior column fractures
• Transverse fractures with anterior displacement
• Anterior column–posterior hemitransverse fractures
• Both-column fractures

Exposure

• Provides access to the internal iliac fossa, pelvic brim, quadrilateral surface, superior pubic ramus, and sacroiliac joint.
• Limited exposure of the external iliac wing.

Complications

• Inguinal hernia (≈1%)
• Lateral femoral cutaneous nerve paresthesia (≈23%)
• External iliac artery thrombosis (≈1%)
• Hematoma (≈5%)
• Infection (≈2%)

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3. Modified Stoppa (Intrapelvic) Approach

Indications

• Anterior wall and column fractures
• Transverse fractures with anterior displacement
• Anterior column–posterior hemitransverse fractures
• Both-column fractures

Exposure

• Allows visualization of the quadrilateral surface, pelvic brim, internal iliac fossa, superior pubic ramus, and sacroiliac joint.
• Limited exposure of the iliac wing.

Complications

• Rectus abdominis hernia
• Hematoma
• Infection
• Obturator nerve palsy

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4. Extended Iliofemoral and Combined Approaches

Indications

• Transtectal transverse with posterior wall fractures
• T-shaped fractures with wide vertical separation or associated pubic symphysis dislocation
• Both-column fractures requiring extensive exposure
• Delayed surgery (>21 days post-injury) for transverse or complex fracture patterns

Exposure

• Provides broad access to the external iliac surface, anterior column (up to the iliopectineal eminence), and posterior column (down to the upper ischial tuberosity).

Complications

• Infection: 2–5%
• Sciatic nerve palsy: 3–5%
• Heterotopic ossification: 20–50% (without prophylaxis)

Postoperative Care

Successful outcomes following acetabular fracture surgery rely not only on precise reduction and fixation but also on meticulous postoperative management.

Heterotopic Ossification (HO) Prophylaxis

• Indomethacin (NSAID) or localized low-dose radiation may be used following posterior or extended approaches to minimize HO formation.
• The benefit of routine prophylaxis remains controversial, but it is generally considered in young male patients or those undergoing extensile exposures.

Thromboembolic Prophylaxis

• Chemical anticoagulation, sequential compression devices, and compression stockings are standard preventive measures.
• Inferior vena cava (IVC) filters may be considered in patients unable to receive anticoagulants.

Mobilization and Rehabilitation

• Early out-of-bed mobilization is encouraged as soon as systemic injuries permit.
• Incentive spirometry and pulmonary exercises help prevent atelectasis and pneumonia.
• Partial weight-bearing is typically delayed until radiographic union is visible, usually at 8–12 weeks postoperatively.
• Full weight-bearing is resumed gradually, guided by pain tolerance and imaging confirmation of healing.

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Complications

Acetabular fracture surgery carries a substantial risk of both general and approach-specific complications. Awareness and prevention are key to improving long-term outcomes.

1. Surgical Wound Infection

• Risk increases with associated visceral or pelvic injuries, soft-tissue trauma, or hematoma formation.
• Closed degloving injuries (Morel-Lavallée lesions) are particularly susceptible to infection and require careful debridement before fixation.

2. Nerve Injuries

• Sciatic Nerve:
  • Most commonly injured during posterior approaches (Kocher–Langenbeck) or due to excessive traction.
  • The peroneal division is most frequently affected.
  • Reported incidence: 16–33%.
• Femoral Nerve:
  • May be stretched during ilioinguinal exposure or injured directly by an anterior column fracture.
• Superior Gluteal Nerve:
  • Vulnerable as it exits the greater sciatic notch; damage can cause abductor paralysis and Trendelenburg gait.

3. Heterotopic Ossification

• Incidence ranges from 3% to 69%, highest following the extended iliofemoral and Kocher–Langenbeck approaches.
• Risk factors include male sex, posterior/extensile approach, and muscle stripping.
• Ilioinguinal approach has the lowest incidence.
• Prophylaxis with indomethacin or radiation reduces risk.

4. Avascular Necrosis (AVN)

• Occurs in about 6–7% of cases.
• Strongly associated with posterior fracture-dislocations and delayed reduction of dislocated hips.
• Early reduction and gentle handling of soft tissues minimize risk.

5. Chondrolysis and Post-Traumatic Osteoarthritis

• Progressive cartilage loss may occur after either operative or nonoperative treatment, leading to early degenerative arthritis.
• Accurate reduction and restoration of joint congruency significantly reduce this risk.

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Summary

• The prognosis of acetabular fractures depends primarily on the accuracy of reduction, stability of fixation, and absence of complications.
• With proper management, most patients can regain pain-free mobility and functional independence, although post-traumatic arthritis remains the most common long-term concern.

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