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2. Trauma MCQs

Practice Set 467 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 9321

Topic: 2. Trauma

What is the term for the smooth, unthreaded portion of a partially threaded screw?

. Threaded shank.
. Core diameter.
. Major diameter.
. Shaft or run-out.
. Pitch.

Correct Answer & Explanation

. Shaft or run-out.

Explanation

The smooth, unthreaded portion of a partially threaded screw between the screw head and the threaded portion is referred to as the 'shaft' or 'run-out' (though run-out more technically describes the transition zone where threads fade out). In a partially threaded lag screw, this smooth shaft is critical as it allows the near bone fragment to slide along it without engaging the threads, enabling the screw head to draw the near fragment towards the far fragment and achieve interfragmentary compression.

Question 9322

Topic: Pelvic & Acetabular Trauma
In the acute resuscitation of a hemodynamically unstable patient with an anteroposterior compression (APC) type III pelvic ring injury, what is the most appropriate anatomical landmark for the application of a pelvic circumferential compression device (binder)?
. Anterior superior iliac spines
. Iliac crests
. Greater trochanters
. Pubic symphysis
. Sacral promontory

Correct Answer & Explanation

. Greater trochanters

Explanation

Pelvic binders must be placed at the level of the greater trochanters to effectively reduce pelvic volume by applying appropriate compressive forces across the pubic symphysis. Placement over the iliac crests or ASIS can paradoxically open the pelvis further in certain fracture patterns.

Question 9323

Topic: 2. Trauma
A 30-year-old male sustains a high-energy Pauwels type III femoral neck fracture. Which of the following internal fixation constructs provides the greatest biomechanical stability against vertical shear forces?
. Three parallel cancellous screws placed in an inverted triangle
. Dynamic hip screw (DHS) with an anti-rotation screw
. Two parallel cancellous screws
. Cephalomedullary nail
. Unipolar hemiarthroplasty

Correct Answer & Explanation

. Dynamic hip screw (DHS) with an anti-rotation screw

Explanation

Pauwels type III fractures have a high vertical fracture angle (>50 degrees), subjecting the fracture to significant vertical shear forces. A fixed-angle device like a DHS, often supplemented with a derotational screw, provides superior biomechanical stability against shear forces compared to multiple cancellous screws.

Question 9324

Topic: 2. Trauma

In a patient with a closed tibial shaft fracture and suspected acute compartment syndrome, which of the following pressure measurements is generally accepted as an absolute indication for fasciotomy?

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

Correct Answer & Explanation

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

Explanation

The delta P measurement is the most reliable indicator for fasciotomy. It is calculated by subtracting the intracompartmental pressure from the diastolic blood pressure. A delta P of less than 30 mmHg strongly indicates inadequate tissue perfusion and is the standard threshold for surgical intervention.

Question 9325

Topic: 2. Trauma
A 40-year-old farmer sustains an open tibial shaft fracture after his leg is caught in agricultural machinery. The wound is 12 cm long with extensive muscle stripping and gross soil contamination. According to evidence-based guidelines, what is the most appropriate initial empirical antibiotic regimen?
. First-generation cephalosporin alone
. First-generation cephalosporin + aminoglycoside
. First-generation cephalosporin + fluoroquinolone
. First-generation cephalosporin + aminoglycoside + high-dose penicillin
. Vancomycin + Piperacillin/Tazobactam

Correct Answer & Explanation

. First-generation cephalosporin + aminoglycoside + high-dose penicillin

Explanation

This is a Gustilo-Anderson Type IIIA open fracture with gross agricultural contamination, putting the patient at high risk for Clostridium perfringens infection. The standard antibiotic protocol for type III open fractures is a first-generation cephalosporin and an aminoglycoside. High-dose penicillin (or ampicillin) is added specifically for severe agricultural, fecal, or standing-water contamination to provide anaerobic coverage.

Question 9326

Topic: 2. Trauma
A 28-year-old male is brought to the ED after a motorcycle collision. He has an open-book pelvic fracture (APC III) with a symphyseal diastasis of 4 cm and is hemodynamically unstable despite initial fluid resuscitation (BP 80/40 mmHg, HR 130 bpm). A FAST scan of the abdomen is negative. What is the most appropriate next step in management?
. Immediate transfer for pelvic arterial embolization
. Immediate open reduction and internal fixation of the anterior ring
. Application of a pelvic binder and preperitoneal pelvic packing
. Retrograde urethrogram to rule out associated injuries
. Exploratory laparotomy

Correct Answer & Explanation

. Application of a pelvic binder and preperitoneal pelvic packing

Explanation

In a hemodynamically unstable patient with an unstable pelvic ring injury and a negative FAST scan, the source of bleeding is presumed to be the pelvis (mostly venous from the presacral plexus or cancellous bone). The immediate priority is closing the pelvic volume (using a binder or sheet) to induce a tamponade effect, often followed promptly by preperitoneal pelvic packing or angiography if packing fails or arterial bleeding is strongly suspected. Stabilization and packing take precedence over definitive ORIF or urological workup in the acute resuscitation phase.

Question 9327

Topic: 2. Trauma

A 35-year-old man sustains a closed comminuted fracture of the tibial diaphysis. He reports severe pain out of proportion to his injury, exacerbated by passive extension of his toes. The clinical suspicion for acute compartment syndrome is high, and compartment pressures are measured. Which of the following measurements is the most reliable threshold for indicating fasciotomy?

. 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 < 30 mmHg

Correct Answer & Explanation

. Diastolic blood pressure minus compartment pressure < 30 mmHg

Explanation

The 'Delta P' (Diastolic Blood Pressure minus the intracompartmental pressure) is the most reliable objective measurement for diagnosing acute compartment syndrome. A Delta P of less than 30 mmHg indicates inadequate tissue perfusion and is a strong indication for emergent fasciotomy. Absolute pressures are less reliable because perfusion pressure varies significantly between patients (e.g., hypotensive trauma patients vs. hypertensive individuals).

Question 9328

Topic: 2. Trauma

A 22-year-old soccer player sustains a non-contact twisting injury to the knee. Radiographs reveal an elliptic avulsion fracture of the lateral tibial plateau (Segond fracture). This radiographic finding is virtually pathognomonic for an anterior cruciate ligament (ACL) tear. Which specific structure is primarily responsible for generating this avulsion fracture?

. Iliotibial band
. Biceps femoris tendon
. Anterolateral ligament (ALL) and lateral capsular complex
. Fibular collateral ligament
. Popliteus tendon

Correct Answer & Explanation

. Anterolateral ligament (ALL) and lateral capsular complex

Explanation

A Segond fracture is an avulsion fracture of the lateral tibial plateau that occurs with internal rotation and varus stress. It is strongly associated with ACL tears. Anatomical and biomechanical studies have demonstrated that this bony avulsion is produced by tension from the anterolateral ligament (ALL) and the associated lateral capsular complex.

Question 9329

Topic: 2. Trauma

Which of the following internal fixation constructs relies predominantly on intramembranous and endochondral ossification (secondary bone healing) to achieve fracture union?

. Compression plating of a transverse radius fracture
. Lag screw fixation of a medial malleolus fracture
. Intramedullary nailing of a comminuted tibial shaft fracture
. Tension band wiring of an olecranon fracture
. Dual plating of a distal humerus fracture achieving absolute stability

Correct Answer & Explanation

. Intramedullary nailing of a comminuted tibial shaft fracture

Explanation

Fracture healing can be categorized into primary (direct) and secondary (indirect) healing. Primary healing occurs with absolute stability (no micro-motion) and relies on direct Haversian remodeling without a callus (e.g., compression plating, lag screws). Secondary healing occurs under conditions of relative stability and involves callus formation via endochondral and intramembranous ossification. An intramedullary nail provides relative stability and heals via secondary bone healing.

Question 9330

Topic: 2. Trauma

A 26-year-old male is admitted with bilateral closed femoral shaft fractures. On post-injury day 2, he becomes acutely hypoxic, confused, and develops a petechial rash over his axillae and conjunctivae. Which of the following pathophysiological mechanisms is most directly responsible for the development of his condition?

. Direct pulmonary contusion from the initial trauma
. Release of marrow fat into the venous circulation leading to mechanical occlusion and biochemical endothelial damage
. Deep vein thrombosis embolizing to the pulmonary arterial tree
. Over-resuscitation with crystalloid fluids leading to acute respiratory distress syndrome (ARDS)
. Severe systemic inflammatory response syndrome (SIRS) primarily driven by bowel ischemia

Correct Answer & Explanation

. Release of marrow fat into the venous circulation leading to mechanical occlusion and biochemical endothelial damage

Explanation

The patient is presenting with the classic triad of Fat Embolism Syndrome (FES): hypoxemia, neurological abnormalities, and a petechial rash. FES typically occurs 24-72 hours after long bone fractures. The pathophysiology is bi-modal: mechanical obstruction of the pulmonary capillaries by marrow fat globules, followed by a biochemical phase where free fatty acids cause direct toxic damage to the pulmonary capillary endothelium, leading to ARDS-like pulmonary edema.

Question 9331

Topic: 2. Trauma

Which statement best describes the primary biomechanical function of a lag screw?

. To provide absolute stability by preventing any motion at the fracture site.
. To create compression across a fracture by engaging the far cortex and gliding through the near cortex.
. To act as a neutralization screw, sharing load with a plate.
. To fix osteochondral fragments in a non-compressive manner.
. To provide fixation in a buttress fashion, supporting metaphyseal bone.

Correct Answer & Explanation

. To create compression across a fracture by engaging the far cortex and gliding through the near cortex.

Explanation

The lag screw principle is fundamental to fracture fixation. It works by converting the rotational torque of screw insertion into axial compression across a fracture. This is achieved by having the screw threads engage only the far cortex (or the fragment to be compressed), while the screw shaft glides freely through a larger pilot hole (glide hole) in the near cortex (or the fragment through which compression is desired). This differential engagement pulls the fragments together, generating interfragmentary compression. Absolute stability (A) is thegoalof lag screw fixation, but the 'how' is through compression. Neutralization (C) and buttress (E) are functions of plates, not the primary function of a lag screw itself. Fixation of osteochondral fragments (D) can be done with lag screws, but the 'non-compressive' part is incorrect if referring to a true lag screw.

Question 9332

Topic: 2. Trauma

During open reduction and internal fixation of a tibial shaft fracture, a cortical screw is noted to be 'stripped' (losing purchase). What is the most appropriate initial management step?

. Replace the screw with one of the same size, but longer.
. Remove the screw and insert a larger diameter screw.
. Augment the screw hole with bone cement before re-inserting the screw.
. Reposition the plate and attempt screw insertion in an adjacent hole.
. Immediately change the fixation strategy to intramedullary nailing.

Correct Answer & Explanation

. Remove the screw and insert a larger diameter screw.

Explanation

When a screw strips, the threads in the bone have been destroyed, resulting in a loss of purchase. The most common and appropriate initial solution is to remove the stripped screw and insert a screw of a larger diameter, if available and biomechanically appropriate. This allows the new, larger screw threads to engage fresh bone. Replacing with a longer screw of the same size (A) will not solve the stripped threads. Augmenting with bone cement (C) is a valid option, often used in revision surgery or osteoporotic bone when larger screws are not feasible or fail, but a larger screw is the primary step. Repositioning the plate (D) might not be possible or ideal for the fracture fixation. Changing to IM nailing (E) is a drastic step and likely overkill for a single stripped screw, unless there are other issues with the entire construct.

Question 9333

Topic: 2. Trauma

What distinguishes a malleolar screw from a standard cortical or cancellous screw?

. It is typically fully threaded with a small core diameter.
. It is partially threaded with a coarse pitch and usually a blunt tip.
. It has a large core diameter and fine pitch, always self-tapping.
. It is a small diameter, partially threaded screw designed for interfragmentary compression in cancellous bone.
. It is exclusively used for fixation of the medial malleolus.

Correct Answer & Explanation

. It is a small diameter, partially threaded screw designed for interfragmentary compression in cancellous bone.

Explanation

Malleolar screws are essentially small cancellous lag screws. They are partially threaded, meaning the threads engage only the far fragment, allowing the screw to glide through the near fragment and generate compression. They have a coarse thread pitch suitable for the cancellous bone of the malleoli. They typically have a small diameter (e.g., 4.0mm). While theyareused for malleoli (E), they are notexclusivelyfor the medial malleolus and can be used for other cancellous bone fractures where lag compression is desired. Fully threaded (A) or large core/fine pitch (C) are characteristics of cortical screws. Blunt tip (B) is not a defining feature.

Question 9334

Topic: 2. Trauma

The primary biomechanical function of a buttress plate is to:

. Achieve absolute stability through interfragmentary compression.
. Bridge a zone of comminution, supporting the fracture fragments.
. Prevent shear forces from displacing the fracture fragments.
. Provide a rigid scaffold to counteract axial collapse or collapse under compressive loads.
. Act as a tension band, converting tensile forces into compressive forces.

Correct Answer & Explanation

. Provide a rigid scaffold to counteract axial collapse or collapse under compressive loads.

Explanation

A buttress plate is positioned on the tension side of a fracture (or the side preventing collapse) and acts as a mechanical stop to prevent fragments from collapsing under axial or compressive loads. This is particularly relevant in metaphyseal fractures (e.g., tibial plateau, distal radius) where articular fragments might otherwise collapse into the cancellous bone void. Bridging (B) is for comminuted diaphyseal fractures, tension band (E) is a specific application, and absolute stability (A) is for lag screws. Preventing shear (C) can be a secondary effect, but the primary role is axial collapse resistance.

Question 9335

Topic: 2. Trauma

For optimal lag screw compression, what is the purpose of overdrilling the near cortex with a drill bit the size of the screw's outer diameter?

. To reduce surgical time by eliminating the need for tapping the near cortex.
. To allow the screw threads to purchase only the far cortex.
. To prevent thermal necrosis of the near cortex during screw insertion.
. To ensure adequate pilot hole preparation for the screw's core diameter.
. To facilitate easier screw removal in the future.

Correct Answer & Explanation

. To reduce surgical time by eliminating the need for tapping the near cortex.

Explanation

Overdrilling the near cortex with a drill bit equal to the screw'souter diametercreates a glide hole. This glide hole allows the screw's threads to pass freely through the near fragment without engaging it. This ensures that when the screw is tightened, its threads only engage the far fragment, pulling it towards the near fragment and generating interfragmentary compression. Without the glide hole, the screw would purchase both fragments, acting as a position screw rather than a lag screw. Reducing surgical time (A) or preventing thermal necrosis (C) are not the primarypurposeof the glide hole. Adequate pilot hole preparation (D) refers to the core diameter drill for the far cortex. Easier screw removal (E) is not the goal.

Question 9336

Topic: 2. Trauma

In a syndesmotic injury, screws are often used to maintain the anatomical relationship between the tibia and fibula. What is the primary biomechanical function of such a syndesmotic screw?

. To provide direct interfragmentary compression across the syndesmosis.
. To act as a lag screw, pulling the fibula tightly to the tibia.
. To maintain the anatomical position of the bones without applying significant compression.
. To allow controlled micromotion to stimulate fibrous tissue healing.
. To provide dynamic stability through a tension band mechanism.

Correct Answer & Explanation

. To maintain the anatomical position of the bones without applying significant compression.

Explanation

Syndesmotic screws are primarily 'position screws.' Their main goal is to hold the tibia and fibula in their correct anatomical relationship (reduction) and prevent diastasis. While some incidental compression may occur, the intent isnotto create significant interfragmentary compression like a lag screw (A, B). Excessive compression across the syndesmosis can lead to non-physiologic stiffness, pain, and potentially bone resorption. The goal is to maintain position. Controlled micromotion (D) is not the primary goal of screw fixation for syndesmosis, which is often considered rigid fixation. Tension band (E) is a separate biomechanical concept.

Question 9337

Topic: 2. Trauma

A screw with a larger core diameter relative to its outer diameter (i.e., smaller thread depth) would typically be favored for:

. Maximizing bone purchase in soft cancellous bone.
. Achieving optimal interfragmentary compression with a lag screw.
. Enhancing resistance to shear and bending forces within the screw itself.
. Reducing the risk of stripping in osteoporotic bone.
. Facilitating self-tapping capabilities in dense cortical bone.

Correct Answer & Explanation

. Enhancing resistance to shear and bending forces within the screw itself.

Explanation

A larger core diameter (and thus a smaller thread depth) means the screw itself has a thicker shaft. This increases the screw's own strength and its resistance to bending and shear forces (C). However, a smaller thread depthreducesthe bone-screw interface area, which can compromise bone purchase (A) and the ability to generate strong interfragmentary compression (B). Reducing the risk of stripping (D) is often achieved by increasing thread depth and using correct technique, not reducing it. Self-tapping (E) is a tip feature, not related to core/outer diameter ratio itself in this context.

Question 9338

Topic: 2. Trauma

In a plate and screw construct for a mid-diaphyseal femoral fracture, which of the following is the most common cause of early screw loosening?

. Corrosion of the screw material.
. Infection at the plate-bone interface.
. Inadequate reduction of the fracture fragments.
. Cyclic loading exceeding the screw-bone interface strength.
. Biodegradation of the implant material.

Correct Answer & Explanation

. Cyclic loading exceeding the screw-bone interface strength.

Explanation

Early screw loosening is most frequently caused by mechanical failure due to cyclic loading at the bone-screw interface. If the fixation is not sufficiently stable or the bone quality is poor, repetitive physiological stresses (walking, weight-bearing) can cause the bone around the screw to resorb or microfracture, leading to loss of screw purchase and subsequent loosening. Corrosion (A) is rare with modern implants. Infection (B) can cause loosening but is less common than mechanical factors. Inadequate reduction (C) may lead to construct failure but not directly screw loosening itself, unless it leads to excessive stress on the screws. Biodegradation (E) is only relevant for bioabsorbable implants, which are not typical for mid-diaphyseal femoral fractures.

Question 9339

Topic: 2. Trauma

What is the primary benefit of counter-sinking a screw head, particularly in articular or subcutaneous locations?

. To increase the pull-out strength of the screw.
. To reduce the profile of the screw head, preventing soft tissue irritation.
. To enhance the interfragmentary compression across the fracture site.
. To facilitate easier screw removal in the future.
. To provide greater stability against torsional forces.

Correct Answer & Explanation

. To reduce the profile of the screw head, preventing soft tissue irritation.

Explanation

Counter-sinking involves creating a small recess in the bone so that the screw head sits flush with or slightly below the bone surface. Its primary purpose is to reduce the prominence of the screw head, thereby minimizing soft tissue irritation, impingement, and discomfort, especially in areas with thin soft tissue coverage or near joints. It does not directly increase pull-out strength (A), enhance compression (C), facilitate removal (D), or provide greater torsional stability (E).

Question 9340

Topic: 2. Trauma

If a fracture fixed with a lag screw fails to achieve union, what type of screw loosening is most likely to be observed initially?

. Stripping of the screw threads in the far cortex.
. Backing out (unwinding) of the screw from the bone.
. Fracture of the screw shaft at the near cortex.
. Corrosion of the screw material leading to aseptic loosening.
. Excessive compression leading to non-union.

Correct Answer & Explanation

. Backing out (unwinding) of the screw from the bone.

Explanation

In the context of a non-union after lag screw fixation, the screws are subjected to repetitive micromotion and cyclic loading. This often leads to bone resorption around the threads, particularly in the near cortex (if not overdrilled properly, or if there's significant motion). As the bone around the threads resorbs, the screw loses purchase and can progressively unwind or 'back out' from the bone. Stripping (A) usually happens during insertion. Fracture of the screw shaft (C) is a later stage of failure after significant cyclic fatigue. Corrosion (D) is rare. Excessive compression (E) is not a direct mechanism for non-union itself, and if it leads to it, the screws would still fail mechanically first.

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