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Pelvic & Acetabular Trauma MCQs

Practice Set 6 of 35

This practice set contains high-yield board review questions covering key concepts in Pelvic & Acetabular Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 101

Topic: Pelvic & Acetabular Trauma

Which of the following ligaments is considered the primary static stabilizer of the pelvic ring, providing the greatest resistance against vertical shear forces?

. Anterior sacroiliac ligament
. Sacrospinous ligament
. Sacrotuberous ligament
. Interosseous sacroiliac ligament
. Iliolumbar ligament

Correct Answer & Explanation

. Interosseous sacroiliac ligament

Explanation

The posterior sacroiliac complex, specifically the interosseous sacroiliac ligament, is the strongest ligament in the body and serves as the primary static stabilizer of the pelvic ring, primarily resisting vertical shear and distraction forces.

Question 102

Topic: Pelvic & Acetabular Trauma
A 38-year-old male sustains a severe pelvic crush injury resulting in an LC-III fracture pattern (windswept pelvis). This injury pattern is characterized by which of the following combinations of forces?
. Bilateral anterior-posterior compression forces
. Lateral compression on one side and an anteroposterior compression (external rotation) injury on the contralateral side
. Unilateral vertical shear with contralateral lateral compression
. Bilateral vertical shear forces
. Pure internal rotation forces on both hemipelves

Correct Answer & Explanation

. Lateral compression on one side and an anteroposterior compression (external rotation) injury on the contralateral side

Explanation

An LC-III or 'windswept' pelvis occurs when a severe lateral compression force continues across the pelvic ring, causing an internal rotation injury on the impacted side and an external rotation (open book) injury on the contralateral side.

Question 103

Topic: Pelvic & Acetabular Trauma
A 35-year-old male sustains a high-energy pelvic ring injury. AP radiograph demonstrates 4 cm of pubic symphyseal widening and widening of the left sacroiliac joint. He is hemodynamically stable. An MRI is obtained which confirms disruption of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments. Which of the following ligamentous structures remains intact in an Anteroposterior Compression Type II (APC-II) injury but is disrupted in an APC-III injury?
. Anterior sacroiliac ligament
. Sacrospinous ligament
. Sacrotuberous ligament
. Posterior sacroiliac ligament
. Iliolumbar ligament

Correct Answer & Explanation

. Sacrotuberous ligament

Explanation

APC-II injuries involve disruption of the symphysis, anterior sacroiliac ligaments, and the sacrotuberous/sacrospinous ligaments, but the strong posterior sacroiliac ligaments remain intact. APC-III injuries involve complete disruption of both anterior and posterior sacroiliac complexes, causing complete spinopelvic instability.

Question 104

Topic: Pelvic & Acetabular Trauma

A 45-year-old female presents to the trauma bay in hemorrhagic shock following a high-speed motor vehicle collision. Her pelvis is clinically unstable to compression. The trauma team decides to place a non-invasive commercial pelvic binder. To be maximally effective at reducing pelvic volume, the binder should be centered directly over which anatomical landmark?

. Anterior superior iliac spines
. Iliac crests
. Greater trochanters
. Pubic symphysis
. Umbilicus

Correct Answer & Explanation

. Greater trochanters

Explanation

Pelvic binders should be placed centered over the greater trochanters to effectively close the pelvic ring and reduce volume. Placement over the iliac crests or ASIS is less effective and may paradoxically open the pelvic ring or cause localized pressure necrosis.

Question 105

Topic: Pelvic & Acetabular Trauma

A 30-year-old male presents with a completely unstable pelvic ring injury and gross blood at the urethral meatus. A retrograde urethrogram demonstrates a posterior urethral disruption. What is the most appropriate initial urologic management before definitive pelvic ring fixation?

. Placement of a transurethral Foley catheter
. Placement of a suprapubic catheter
. Immediate primary end-to-end urethral anastomosis
. Flexible cystoscopy and stenting
. Observation and delayed catheterization

Correct Answer & Explanation

. Placement of a suprapubic catheter

Explanation

In the setting of a posterior urethral disruption associated with a pelvic ring injury, placement of a suprapubic catheter is the standard initial management. Transurethral catheterization is contraindicated as it may convert a partial tear into a complete tear.

Question 106

Topic: Pelvic & Acetabular Trauma
A patient with a severe lateral compression pelvic fracture is noted to have a large, fluctuant swelling over the left greater trochanteric region. Skin integrity is intact, but the skin feels highly mobile over the deep fascia. If left untreated, this specific lesion most strongly predisposes the patient to which of the following complications?
. Heterotopic ossification
. Deep surgical site infection after fixation
. Avascular necrosis of the femoral head
. Sciatic nerve compression
. Refractory hypovolemic shock

Correct Answer & Explanation

. Deep surgical site infection after fixation

Explanation

A Morel-Lavallée lesion is a closed internal degloving injury where skin and subcutaneous tissue are sheared from the underlying fascia, leading to a hemolymphatic fluid collection. If not adequately decompressed/debrided before internal fixation, it carries a very high risk of deep bacterial infection.

Question 107

Topic: Pelvic & Acetabular Trauma

During radiographic evaluation of a pelvic ring injury, the 'outlet' view is best utilized to assess which of the following deformities?

. Internal rotation of the hemipelvis
. External rotation of the hemipelvis
. Anterior-posterior translation
. Vertical displacement of the hemipelvis
. Acetabular wall comminution

Correct Answer & Explanation

. Vertical displacement of the hemipelvis

Explanation

The pelvic outlet view (angled 45 degrees cephalad) projects the sacrum in its true en face orientation. It is the most accurate radiographic view for evaluating superior-inferior (vertical) displacement of the hemipelvis and sacral foraminal asymmetry.

Question 108

Topic: Pelvic & Acetabular Trauma

What is the correct anatomical landmark for the optimal placement of a pelvic circumferential compression device (binder) to most effectively reduce pelvic volume in a hemodynamically unstable trauma patient?

. Iliac crests
. Anterior superior iliac spines
. Greater trochanters
. Symphysis pubis
. Subtrochanteric femur

Correct Answer & Explanation

. Greater trochanters

Explanation

Pelvic binders should be placed centered over the greater trochanters to effectively close the pelvic ring and reduce pelvic volume. Placement over the iliac crests is incorrect and can paradoxically widen the true pelvis.

Question 109

Topic: Pelvic & Acetabular Trauma
A hemodynamically unstable patient with an Anteroposterior Compression Type III (APC-III) pelvic injury remains hypotensive despite initial fluid resuscitation, blood transfusion, and application of a pelvic binder. The FAST scan is negative. What is the next most appropriate step in management?
. CT abdomen and pelvis
. Pelvic angiography/embolization or pre-peritoneal pelvic packing
. Diagnostic peritoneal lavage
. Immediate exploratory laparotomy
. Removal of the binder to assess for expansion

Correct Answer & Explanation

. Pelvic angiography/embolization or pre-peritoneal pelvic packing

Explanation

In a hemodynamically unstable patient with a pelvic ring injury and a negative FAST scan, the source of bleeding is likely retroperitoneal. The standard of care is immediate hemorrhage control via pelvic angiography with embolization or pre-peritoneal pelvic packing.

Question 110

Topic: Pelvic & Acetabular Trauma

Which nerve root is most commonly injured in a vertical shear pelvic ring injury that involves a displaced transforaminal sacral fracture?

. L4
. L5
. S1
. S2
. S3

Correct Answer & Explanation

. L5

Explanation

The L5 nerve root is highly susceptible to traction injury during vertical shear injuries as it drapes over the sacral ala. Cephalad displacement of the hemipelvis places significant tension on this nerve.

Question 111

Topic: Pelvic & Acetabular Trauma

Which intraoperative fluoroscopic view is most critical to evaluate for anterior-posterior translation of the sacroiliac joint during percutaneous iliosacral screw fixation?

. AP pelvis
. Inlet view
. Outlet view
. Judet obturator oblique
. Judet iliac oblique

Correct Answer & Explanation

. Inlet view

Explanation

The pelvic inlet view best demonstrates anterior-posterior translation of the pelvic ring. It is essential for verifying reduction of the sacroiliac joint and confirming the screw does not violate the anterior sacral cortex.

Question 112

Topic: Pelvic & Acetabular Trauma
A patient with an APC-III pelvic ring injury develops a large, fluctuant fluid collection over the greater trochanter after a high-speed motorcycle crash. Aspiration yields serosanguinous fluid. What is the pathophysiologic mechanism of this lesion?
. Rupture of the tensor fascia lata
. Shearing of the subcutaneous tissue from the underlying fascia
. Intramuscular hematoma of the gluteus medius
. Lymphatic duct tear
. Deep venous thrombosis

Correct Answer & Explanation

. Shearing of the subcutaneous tissue from the underlying fascia

Explanation

This presentation describes a Morel-Lavallée lesion, a closed degloving injury. It results from severe shearing forces that separate the subcutaneous fat from the underlying investing fascia, creating a potential space that fills with blood and lymph.

Question 113

Topic: Pelvic & Acetabular Trauma
A 45-year-old male is treated for an APC-III pelvic ring injury. Follow-up radiographs reveal failure of the anterior symphyseal plate. What is the most common reason for failure of isolated anterior symphyseal plating in a completely unstable pelvic ring?
. Use of a 3.5mm rather than 4.5mm plate
. Failure to adequately stabilize the posterior pelvic ring
. Inadequate number of screws placed anteriorly
. Patient non-compliance with weight-bearing restrictions
. Over-reduction of the symphysis pubis

Correct Answer & Explanation

. Failure to adequately stabilize the posterior pelvic ring

Explanation

In a completely unstable pelvic ring injury (APC-III), isolated anterior fixation is biomechanically insufficient. Failure to adequately address and fix the posterior pelvic ring instability is the leading cause of anterior hardware failure.

Question 114

Topic: Pelvic & Acetabular Trauma

A trauma patient is transferred from an outside hospital with a pelvic binder in place for 36 hours. What is the most immediate clinical complication specifically associated with prolonged continuous pelvic binder application?

. Binder-induced lateral femoral cutaneous nerve palsy
. Skin necrosis and pressure ulceration
. Iatrogenic bladder rupture
. Deep vein thrombosis
. Heterotopic ossification

Correct Answer & Explanation

. Skin necrosis and pressure ulceration

Explanation

Prolonged application of a pelvic binder (especially > 24 hours) strongly increases the risk of skin necrosis and pressure ulcerations, most commonly over the greater trochanters. Binders should be removed or converted to definitive fixation as soon as hemodynamically feasible.

Question 115

Topic: Pelvic & Acetabular Trauma

Which ligamentous structure is considered the strongest in the pelvis and provides the most significant resistance to vertical shear forces acting on the sacroiliac joint?

. Sacrospinous ligament
. Sacrotuberous ligament
. Interosseous sacroiliac ligament
. Anterior sacroiliac ligament
. Iliolumbar ligament

Correct Answer & Explanation

. Interosseous sacroiliac ligament

Explanation

The interosseous sacroiliac ligament is the strongest ligament in the body and acts as the primary stabilizer against both vertical shear and anterior-posterior translational forces at the SI joint.

Question 116

Topic: Pelvic & Acetabular Trauma

In the surgical management of a completely unstable sacroiliac joint disruption, what is the primary biomechanical advantage of utilizing two iliosacral screws rather than a single screw?

. Prevention of coronal plane translation
. Increased resistance to rotational forces
. Prevention of sacral nerve root impingement
. Elimination of the need for anterior ring fixation
. Decreased risk of encountering sacral dysmorphism

Correct Answer & Explanation

. Increased resistance to rotational forces

Explanation

While a single iliosacral screw adequately resists vertical and anterior-posterior translation, a second screw provides significantly increased resistance to rotational forces, which is essential in highly unstable injuries.

Question 117

Topic: Pelvic & Acetabular Trauma

A 35-year-old male is brought in hemodynamically unstable after a motorcycle crash. A pelvic binder is applied. Which of the following anatomic structures is responsible for the vast majority (approximately 80%) of hemorrhage in pelvic ring injuries?

. Superior gluteal artery
. Internal pudendal artery
. Presacral venous plexus and cancellous bone
. External iliac artery
. Corona mortis

Correct Answer & Explanation

. Presacral venous plexus and cancellous bone

Explanation

Approximately 80% of pelvic hemorrhage following trauma originates from the presacral venous plexus and fractured cancellous bone surfaces. Arterial bleeding accounts for a smaller percentage but may require arterial embolization.

Question 118

Topic: Pelvic & Acetabular Trauma



A 45-year-old male sustains a pelvic ring injury necessitating operative fixation. When evaluating the pelvis for percutaneous iliosacral screw placement, the surgeon notes sacral dysmorphism. Which of the following radiographic features is indicative of a dysmorphic sacrum?

. Recessed sacral alae relative to the anterior sacral body
. An acute alar slope on the outlet view
. The upper sacral segment articulating completely below the iliac crests
. A collinear S1 neural foramen
. Absence of mammillary processes at the SI joint

Correct Answer & Explanation

. An acute alar slope on the outlet view

Explanation

Features of sacral dysmorphism include an acute alar slope, non-recessed (collinear) anterior sacral alae, prominent mammillary processes, and an upper sacral segment located above the iliac crests. These variations significantly narrow the safe corridor for iliosacral screw placement.

Question 119

Topic: Pelvic & Acetabular Trauma
Which radiographic view provides the best assessment of the anterior-posterior translation of the sacrum and is critical for evaluating the AP diameter of the sacral canal in suspected Denis Zone III fractures?
. Anteroposterior (AP) pelvis
. Pelvic Inlet view
. Pelvic Outlet view
. Judet Iliac oblique view
. Judet Obturator oblique view

Correct Answer & Explanation

. Pelvic Inlet view

Explanation

The Pelvic Inlet view is obtained with a caudad tilt of the x-ray beam. It looks down into the pelvic ring, providing the best view of anterior-posterior displacement of the sacrum and the pelvic brim.

Question 120

Topic: Pelvic & Acetabular Trauma

A 25-year-old male with a severe Denis Zone 2 sacral fracture and an anterior-posterior compression (APC) pelvic ring injury presents in hemorrhagic shock. A pelvic binder is applied. What is the primary source of life-threatening bleeding in this specific injury pattern?

. Internal pudendal artery
. Venous plexus and cancellous bone bleeding
. Superior mesenteric artery
. Femoral artery
. External iliac vein

Correct Answer & Explanation

. Venous plexus and cancellous bone bleeding

Explanation

In the vast majority (80-90%) of pelvic ring disruptions, life-threatening hemorrhage originates from the presacral venous plexus and bleeding from the fractured cancellous bone surfaces, which is initially managed by reducing pelvic volume.

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