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2. Trauma MCQs

Practice Set 624 of 640

This practice set contains high-yield board review questions covering key concepts in 2. Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 12461

Topic: 2. Trauma

When inserting a cortical screw for fracture fixation, which of the following geometric modifications to the screw's design would most significantly increase its pullout strength?

. Increasing the inner root diameter
. Increasing the outer thread diameter
. Decreasing the thread pitch
. Increasing the length of the screw head
. Decreasing the number of threads per inch

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

The pullout strength of a bone screw is most profoundly and exponentially affected by its outer thread diameter. Other factors that increase pullout strength include a decreased inner (root) diameter, increased length of thread engagement, and a finer thread pitch.

Question 12462

Topic: 2. Trauma

A 25-year-old male is admitted with a highly comminuted tibia fracture. He develops escalating leg pain out of proportion and paresthesias. Which of the following compartment pressure monitoring criteria is the most reliable threshold for performing an emergency fasciotomy?

. Absolute compartment pressure > 20 mmHg
. Absolute compartment pressure > 30 mmHg
. Delta P (Diastolic blood pressure - compartment pressure) < 30 mmHg
. Delta P (Mean arterial pressure - compartment pressure) < 45 mmHg
. Delta P (Systolic blood pressure - compartment pressure) < 30 mmHg

Correct Answer & Explanation

. Delta P (Diastolic blood pressure - compartment pressure) < 30 mmHg

Explanation

The Delta P value, calculated as the diastolic blood pressure minus the absolute compartment pressure, is the most reliable objective indicator of compartment syndrome. A Delta P of less than 30 mmHg signifies inadequate microvascular tissue perfusion and is a strong indication for fasciotomy.

Question 12463

Topic: 2. Trauma

You are critically evaluating a randomized controlled trial comparing a novel locking plate to standard intramedullary nailing for distal tibia fractures. The authors conclude there is no significant difference between the implants, but you note the study was severely underpowered. Accepting this conclusion risks committing which type of statistical error?

. Type I error
. Type II error
. Alpha error
. Selection bias
. Observation bias

Correct Answer & Explanation

. Type II error

Explanation

A Type II (beta) error occurs when a study fails to reject a false null hypothesis, meaning it misses a true difference that actually exists (a false-negative result). This is most commonly caused by an inadequate sample size (underpowered study).

Question 12464

Topic: 2. Trauma

Acute compartment syndrome is a devastating complication following high-energy tibial fractures. Irreversible muscle and nerve ischemia is fundamentally triggered by which of the following pathophysiological mechanisms?

. Increased arterial inflow overriding the capacitance of the deep venous system
. A decrease in the local arteriovenous pressure gradient leading to cellular hypoxia
. Direct traumatic mechanical compression of the primary nerve bundles
. Toxic accumulation of extracellular potassium resulting in vasospasm
. Premature closure of the microcapillary sphincters mediated by substance P

Correct Answer & Explanation

. A decrease in the local arteriovenous pressure gradient leading to cellular hypoxia

Explanation

The hallmark of acute compartment syndrome is a critical rise in intracompartmental pressure that exceeds venous outflow pressure. This collapses the venules, eliminating the local arteriovenous pressure gradient required for capillary perfusion, ultimately resulting in cellular anoxia and tissue death.

Question 12465

Topic: 2. Trauma

When fixing a complex diaphyseal tibia fracture with an intramedullary nail, the surgeon wishes to maximize the construct's torsional stiffness. Which of the following technical modifications will most significantly increase torsional stiffness?

. Decreasing the nail diameter
. Decreasing the working length of the nail
. Using a solid nail instead of a hollow nail
. Placing the interlocking screws farther away from the fracture site
. Using dynamic rather than static interlocking screws

Correct Answer & Explanation

. Decreasing the working length of the nail

Explanation

The torsional stiffness of an intramedullary nail is inversely proportional to its working length. Decreasing the working length (the unsupported distance between the proximal and distal locking screws closest to the fracture) significantly increases torsional rigidity.

Question 12466

Topic: 2. Trauma
A 26-year-old male sustains a high-energy Pauwels Type III femoral neck fracture. Based on biomechanical principles, which fixation construct provides the greatest stability against the high shear forces seen in this fracture pattern?
. Three parallel cancellous lag screws in an inverted triangle
. Two parallel cancellous lag screws
. A dynamic hip screw (fixed-angle device) with a derotational screw
. A single fully threaded intramedullary nail
. A fibular strut allograft alone

Correct Answer & Explanation

. A dynamic hip screw (fixed-angle device) with a derotational screw

Explanation

Pauwels Type III fractures are vertical fractures (>50 degrees) subjected to extreme shear forces rather than compressive forces. Standard multiple cancellous screws have high failure rates in this pattern due to a lack of shear stability. A fixed-angle construct, such as a sliding hip screw (dynamic hip screw), provides superior biomechanical resistance to vertical shear.

Question 12467

Topic: 2. Trauma

A Schatzker Type IV tibial plateau fracture involves the medial tibial plateau. What is the classic mechanism of injury, and what associated soft tissue injury must be highly suspected?

. Valgus stress with axial load; Lateral collateral ligament (LCL) rupture
. Varus stress with axial load; Peroneal nerve palsy
. Varus stress with axial load; Popliteal artery injury
. Direct anterior blow; Anterior cruciate ligament (ACL) rupture
. Hyperextension injury; Patellar tendon rupture

Correct Answer & Explanation

. Varus stress with axial load; Popliteal artery injury

Explanation

A Schatzker IV fracture (medial plateau) usually results from a high-energy varus force with axial loading. Because the medial bone is stronger, a fracture here implies high energy and often represents a fracture-dislocation or subluxation of the knee. Therefore, there is a very high association with vascular injury (popliteal artery) and multiple ligament injuries.

Question 12468

Topic: 2. Trauma

A 30-year-old male presents with sudden inability to actively extend the interphalangeal joint of his thumb. He had a non-displaced distal radius fracture treated in a cast 6 weeks ago. What is the most likely pathophysiologic mechanism for this new deficit?

. Missed complete laceration of the tendon at the time of injury
. Attritional rupture of the tendon over a prominent volar plate
. Ischemic rupture of the tendon at the watershed zone around Lister's tubercle
. Entrapment of the posterior interosseous nerve in the fracture callus
. Adhesive capsulitis of the trapeziometacarpal joint preventing excursion

Correct Answer & Explanation

. Ischemic rupture of the tendon at the watershed zone around Lister's tubercle

Explanation

The patient has suffered a spontaneous rupture of the Extensor Pollicis Longus (EPL) tendon, a known complication following nondisplaced or minimally displaced distal radius fractures. The mechanism is ischemic avascular necrosis of the tendon in its 'watershed' area as it passes through the tight third dorsal compartment around Lister's tubercle, exacerbated by fracture hematoma and swelling. (Attritional rupture is more common with displaced fractures or prominent hardware).

Question 12469

Topic: 2. Trauma

Bone morphogenetic proteins (BMPs) are used in orthopedics to promote bone healing. Which of the following is an FDA-approved indication for rhBMP-2?

. Open tibia shaft fractures treated with an intramedullary nail
. Nonunions of the scaphoid
. Aseptic loosening in total hip arthroplasty
. Posterior cervical spine fusion
. Symptomatic osteoarthritis of the knee

Correct Answer & Explanation

. Open tibia shaft fractures treated with an intramedullary nail

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for acute, open tibial shaft fractures treated with an intramedullary nail and for anterior lumbar interbody fusion (ALIF).

Question 12470

Topic: 2. Trauma

A 22-year-old is admitted with a closed tibia fracture. Which of the following clinical signs is considered the earliest and most reliable indicator of acute compartment syndrome in an alert patient?

. Loss of peripheral pulses
. Pallor of the distal extremity
. Pain out of proportion to the injury and exacerbated by passive stretch
. Paresthesias in the deep peroneal nerve distribution
. Paralysis of the anterior compartment muscles

Correct Answer & Explanation

. Pain out of proportion to the injury and exacerbated by passive stretch

Explanation

Pain out of proportion to the injury, especially pain on passive stretch of the involved compartment's muscles, is the earliest and most sensitive clinical sign of acute compartment syndrome.

Question 12471

Topic: Pelvic & Acetabular Trauma
A patient arrives hypotensive after a high-speed collision, with an anteroposterior compression (APC) type III pelvic ring injury. Where is the most biomechanically effective anatomical location to apply a pelvic binder?
. Over the iliac crests
. Directly over the greater trochanters
. Superior to the anterior superior iliac spines (ASIS)
. At the level of the umbilicus
. Midway down the femoral shafts

Correct Answer & Explanation

. Directly over the greater trochanters

Explanation

A pelvic binder must be applied directly over the greater trochanters to effectively close the pelvic volume and stabilize the symphysis. Placing it higher over the iliac crests can paradoxically open the pelvis further.

Question 12472

Topic: 2. Trauma

During fracture fixation, maximizing the pullout strength of a cortical bone screw is critical. Which of the following modifications to the screw design will most significantly increase its pullout strength?

. Increasing the outer thread diameter
. Increasing the inner root diameter
. Increasing the thread pitch
. Decreasing the length of engagement
. Decreasing the thread depth

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Pullout strength is most heavily influenced by the outer diameter of the screw, as it dictates the volume of bone caught between the threads. Decreasing the inner diameter and decreasing the pitch also increase pullout strength, but to a lesser extent.

Question 12473

Topic: 2. Trauma

A patient sustains a severely displaced, closed tibial shaft fracture. Which of the following absolute pressure measurements or gradients is considered the most reliable threshold for diagnosing acute compartment syndrome?

. Absolute compartment pressure > 20 mmHg
. Absolute compartment pressure > 25 mmHg
. Diastolic blood pressure minus compartment pressure < 30 mmHg
. Mean arterial pressure minus compartment pressure > 40 mmHg
. Systolic blood pressure minus compartment pressure < 20 mmHg

Correct Answer & Explanation

. Diastolic blood pressure minus compartment pressure < 30 mmHg

Explanation

The delta pressure (diastolic blood pressure minus absolute compartment pressure) is the most reliable physiologic indicator of acute compartment syndrome. A delta pressure of less than 30 mmHg strongly indicates critical tissue ischemia requiring urgent fasciotomies.

Question 12474

Topic: Pelvic & Acetabular Trauma
A hemodynamically unstable patient arrives after a severe crush injury. Pelvic radiographs demonstrate an anterior-posterior compression (APC) Type III pelvic ring injury. After placing a pelvic binder, the patient remains hypotensive despite massive transfusion. A FAST exam is negative. What is the most appropriate next step?
. Immediate CT abdomen and pelvis
. Pre-peritoneal pelvic packing and/or angioembolization
. Exploratory laparotomy
. Application of an external fixator in the emergency department
. Bilateral lower extremity skeletal traction

Correct Answer & Explanation

. Pre-peritoneal pelvic packing and/or angioembolization

Explanation

In a hemodynamically unstable patient with a pelvic ring injury and a negative FAST exam, the pelvis is the primary source of life-threatening hemorrhage. Pre-peritoneal pelvic packing and/or pelvic angiography with embolization are the immediate interventions of choice.

Question 12475

Topic: Lower Extremity Trauma

During a total knee arthroplasty, the surgeon assesses the gaps with trial components. The knee is tight in extension and balanced in flexion. Which of the following is the most appropriate intraoperative adjustment?

. Upsize the femoral component
. Downsize the femoral component
. Resect more distal femur
. Resect more proximal tibia
. Recut the posterior femoral condyles

Correct Answer & Explanation

. Resect more distal femur

Explanation

A tight extension gap with a balanced flexion gap indicates that the distal femur is under-resected. Resecting more distal femur will increase the extension space without altering the balanced flexion gap.

Question 12476

Topic: 2. Trauma

In the pathophysiology of acute compartment syndrome, the initial cascade of tissue ischemia is triggered by which of the following microvascular hemodynamic alterations?

. Arterial occlusion
. Arteriolar collapse
. Venous outflow obstruction
. Capillary leak syndrome
. Lymphatic obstruction

Correct Answer & Explanation

. Venous outflow obstruction

Explanation

Acute compartment syndrome initially develops when increased intracompartmental pressure exceeds the pressure of post-capillary venules, causing venous outflow obstruction. This leads to a backup of pressure, capillary transudation, and eventual microcirculatory collapse.

Question 12477

Topic: 2. Trauma
A 34-year-old male is brought to the trauma bay after a motorcycle accident. He is hypotensive with a mechanically unstable anteroposterior compression type III (APC III) pelvic ring injury. Application of a pelvic circumferential compression device is planned. At which anatomical landmark should this device be centered?
. Iliac crests
. Greater trochanters
. Anterior superior iliac spines
. Pubic symphysis
. Sacral promontory

Correct Answer & Explanation

. Greater trochanters

Explanation

To effectively reduce pelvic volume and control hemorrhage in open-book pelvic fractures, a pelvic binder must be placed at the level of the greater trochanters. Placement higher over the iliac crests is less effective and may inadvertently worsen the deformity.

Question 12478

Topic: 2. Trauma

A 7-year-old child sustains a Bado Type I Monteggia fracture-dislocation. Which of the following nerve injuries is most classically associated with this specific injury pattern?

. Anterior interosseous nerve
. Posterior interosseous nerve
. Ulnar nerve
. Superficial sensory radial nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Posterior interosseous nerve

Explanation

Monteggia fracture-dislocations involve a proximal ulna fracture with radial head dislocation. The posterior interosseous nerve (PIN) is anatomically tethered at the arcade of Frohse and is highly susceptible to traction or direct injury, particularly in anterior and lateral dislocations.

Question 12479

Topic: 2. Trauma

Which of the following biomechanical characteristics most accurately describes a locking plate construct compared to a conventional non-locking plate construct?

. It requires perfect contouring to the bone surface to maintain fracture reduction.
. It acts as a load-sharing device that relies on plate-to-bone friction.
. It functions as a single-beam construct with fixed-angle stability.
. It inherently applies dynamic compression to the fracture site upon screw insertion.
. It has a lower resistance to screw pull-out in osteoporotic bone.

Correct Answer & Explanation

. It functions as a single-beam construct with fixed-angle stability.

Explanation

A locking plate functions as a single-beam construct because the screw heads thread directly into the plate, creating fixed-angle stability. This eliminates the need for plate-to-bone friction, preserves the periosteal blood supply, does not require perfect contouring, and significantly increases pull-out strength in osteoporotic bone.

Question 12480

Topic: 2. Trauma

In the diagnosis of acute compartment syndrome, the 'delta P' (Delta Pressure) is often used as a threshold for fasciotomy. How is Delta P calculated?

. Systolic blood pressure minus compartment pressure
. Mean arterial pressure minus compartment pressure
. Diastolic blood pressure minus compartment pressure
. Compartment pressure minus venous pressure
. Capillary refill pressure minus compartment pressure

Correct Answer & Explanation

. Diastolic blood pressure minus compartment pressure

Explanation

Delta P is calculated as Diastolic Blood Pressure minus the Absolute Compartment Pressure. A Delta P of less than 30 mmHg is the widely accepted threshold that indicates inadequate tissue perfusion and is an absolute indication for emergency fasciotomy.

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