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2. Trauma MCQs

Practice Set 468 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 9341

Topic: 2. Trauma

What is the primary advantage of variable angle locking screws compared to fixed angle locking screws?

. Increased strength against bending forces.
. Ability to insert screws at desired trajectories to capture specific fragments or avoid obstacles.
. Enhanced interfragmentary compression.
. Reduced soft tissue irritation due to lower profile heads.
. Faster surgical implantation time.

Correct Answer & Explanation

. Ability to insert screws at desired trajectories to capture specific fragments or avoid obstacles.

Explanation

Variable angle locking screws allow the surgeon to adjust the angle of screw insertion (typically within a certain conical range, e.g., 15-20 degrees off-axis) while still achieving a locked, fixed-angle construct. This flexibility is crucial for adapting to complex fracture patterns, optimizing fragment capture, avoiding neurovascular structures, or navigating existing hardware, without compromising the angular stability. Increased strength (A) is not the primary advantage. Enhanced compression (C) is not their main purpose. Reduced profile (D) is a general design goal for all screws. Faster implantation (E) is unlikely due to the precision required.

Question 9342

Topic: 2. Trauma

A patient develops a sterile inflammatory reaction with localized swelling and effusion several months after fixation of an osteochondral fragment with a bioabsorbable PLLA screw. What is the most likely cause?

. Bacterial infection requiring antibiotics and debridement.
. Allergic reaction to metallic components of the screw.
. Release of acidic degradation products from the polymer.
. Mechanical irritation from screw prominence.
. Re-fracture of the osteochondral fragment.

Correct Answer & Explanation

. Release of acidic degradation products from the polymer.

Explanation

Bioabsorbable polymers like PLLA (Poly-L-lactic acid) degrade over time through hydrolysis into lactic acid, which is then metabolized. However, if the rate of degradation is too rapid or if there's a localized accumulation of these acidic byproducts, it can trigger a sterile inflammatory response, leading to effusions, swelling, and pain. This is a known complication, though less common with newer generations of implants. It is distinct from bacterial infection (A), allergic reaction to metal (B, as PLLA is not metal), mechanical irritation (D), or re-fracture (E).

Question 9343

Topic: 2. Trauma

When performing elective removal of a well-fixed screw after fracture healing, what is the most common technical challenge encountered?

. Stripping of the screw head during removal.
. Difficulty locating the screw head due to bony overgrowth.
. Breaking of the screw shaft during removal attempts.
. Significant bleeding from the screw tract.
. Post-operative infection after removal.

Correct Answer & Explanation

. Difficulty locating the screw head due to bony overgrowth.

Explanation

Bony overgrowth or fibrous tissue encapsulation around the screw head is a very common challenge during implant removal. It can obscure the screw head, making it difficult to engage the screwdriver, requiring careful dissection and often removal of some surrounding bone with an osteotome or burr. Stripping the screw head (A) can occur but often follows difficulty locating/engaging. Breaking the shaft (C) is less common with modern screws and careful technique. Significant bleeding (D) and infection (E) are potential complications but less common than bony overgrowth.

Question 9344

Topic: 2. Trauma

An oblique diaphyseal fracture is fixed with a single interfragmentary lag screw. This screw primarily provides:

. Relative stability, promoting secondary bone healing.
. Absolute stability, promoting primary bone healing.
. Neutralization of shear forces, allowing callus formation.
. Axial load-sharing with minimal interfragmentary motion.
. Distraction across the fracture site to facilitate callus.

Correct Answer & Explanation

. Absolute stability, promoting primary bone healing.

Explanation

A well-placed interfragmentary lag screw achieves absolute stability by generating significant compression across the fracture fragments. This compression eliminates interfragmentary motion, creating a stable environment conducive to primary bone healing (direct bone healing without significant callus formation). Relative stability (A) promotes secondary healing (with callus). Neutralization (C) is for a plate protecting lag screws. Axial load-sharing (D) might occur, but absolute stability and primary healing are the core functions. Distraction (E) would prevent healing.

Question 9345

Topic: 2. Trauma

In a specific scenario where an initial screw hole has been stripped in osteoporotic bone, and a larger screw is still insufficient, what is the 'screw-in-screw' technique?

. Using two parallel screws to increase fixation strength.
. Inserting a smaller-diameter screw into the pilot hole of a larger screw.
. Inserting a larger-diameter screw that has a smaller screw pre-tapped into its core.
. Reaming the stripped hole, inserting a cortical allograft dowel, then drilling and screwing into the dowel.
. Inserting a threaded barrel into the stripped hole, then inserting a screw into the barrel.

Correct Answer & Explanation

. Inserting a threaded barrel into the stripped hole, then inserting a screw into the barrel.

Explanation

The 'screw-in-screw' or 'threaded insert' technique (often called a screw-augmentation or revision screw system) involves inserting a larger, externally threaded sleeve or barrel (which is essentially a 'screw') into the stripped bone hole. This sleeve then provides a new, smaller, internally threaded lumen into which a standard or slightly larger screw can be inserted. This effectively restores screw purchase in compromised bone. Reaming and dowel (D) is a bone grafting technique. The other options (A, B, C) describe other scenarios or incorrect interpretations.

Question 9346

Topic: 2. Trauma

Why are torque-limiting screwdrivers often used, especially with small-diameter screws or in osteoporotic bone?

. To ensure all screws are tightened to the exact same rotational angle.
. To prevent overtightening, stripping of bone threads, and screw breakage.
. To increase the speed of screw insertion, reducing operative time.
. To automatically stop drilling when the far cortex is breached.
. To provide visual feedback on screw length.

Correct Answer & Explanation

. To prevent overtightening, stripping of bone threads, and screw breakage.

Explanation

Torque-limiting screwdrivers are designed to release or 'click' once a pre-set torque value is reached. This prevents the surgeon from applying excessive force, thereby minimizing the risk of overtightening, which can strip bone threads (leading to loss of purchase), fracture the bone, or even break the screw itself. This is particularly important with delicate screws or in compromised bone quality. They don't ensure the same rotational angle (A), speed (C), stop drilling (D), or measure length (E).

Question 9347

Topic: 2. Trauma

One purported advantage of locking plates (angle-stable plates) over traditional compression plates is their reduced impact on periosteal blood supply. How is this achieved?

. By using smaller diameter screws which cause less tissue disruption.
. By requiring less direct contact between the plate and the bone surface.
. By being made of bioinert materials that don't elicit an inflammatory response.
. By distributing stress more evenly along the bone shaft.
. By allowing dynamic compression across the fracture site.

Correct Answer & Explanation

. By requiring less direct contact between the plate and the bone surface.

Explanation

Traditional compression plates rely on friction between the plate and bone for stability, requiring direct, intimate contact and often compression of the plate against the bone. This can compromise the periosteal blood supply. Locking plates, however, function as internal fixators and do not require tight apposition to the bone; they provide angular stability regardless of direct compression to the bone surface. This 'non-contact' or limited-contact plating technique (achieved by specific plate designs or by simply not compressing the plate to the bone) helps preserve the periosteal blood supply, which is critical for bone healing. Smaller screws (A) are not the reason. Bioinert materials (C) is a general characteristic, not specific to this mechanism. Stress distribution (D) is a feature, but not directly related to periosteum. Dynamic compression (E) is for DCPs, not primarily locking plates.

Question 9348

Topic: 2. Trauma

When countersinking a screw for an intra-articular fracture, what is a critical consideration to avoid potential complications?

. Ensuring the countersink depth allows at least 5mm of screw head protrusion.
. Performing the countersink after final screw tightening.
. Avoiding excessive countersinking that could weaken the subchondral bone.
. Using a drill bit two sizes larger than the screw head for countersinking.
. Applying saline irrigation during countersinking to prevent bone necrosis.

Correct Answer & Explanation

. Avoiding excessive countersinking that could weaken the subchondral bone.

Explanation

Excessive countersinking, especially in intra-articular fractures, can significantly weaken the subchondral bone supporting the articular cartilage. This can lead to collapse of the articular surface, pain, and early post-traumatic arthritis. Therefore, careful and controlled countersinking to just allow the screw head to sit flush or slightly subchondral is essential. Protrusion (A) is the opposite of the goal. Countersinking before tightening (B) is ideal for accurate depth. Using a drill bit two sizes larger (D) is not a standard technique; dedicated countersink tools are used. Saline irrigation (E) is generally good practice during any drilling/reaming, but preventing subchondral bone weakening is the critical consideration here.

Question 9349

Topic: 2. Trauma

When percutaneously pinning a displaced supracondylar humerus fracture in a child with K-wires, which type of 'screw principle' is being utilized?

. Lag screw principle for interfragmentary compression.
. Position screw principle to maintain reduction.
. Tension band principle to convert tensile forces.
. Buttress principle to prevent collapse.
. Dynamic compression principle for early mobilization.

Correct Answer & Explanation

. Position screw principle to maintain reduction.

Explanation

K-wires in a supracondylar humerus fracture are typically used to maintain the reduction that has been achieved, holding the fragments in their correct anatomical position. They function as 'position pins' or 'position screws' (though they are pins), providing relative stability rather than generating interfragmentary compression. The goal is to hold the fragments in place until healing occurs, which is characteristic of a position screw. Lag screw (A) seeks compression. Tension band (C) involves wires wrapped around pins. Buttress (D) is for preventing collapse. Dynamic compression (E) for early mobilization is often not the primary goal of K-wire fixation in this context.

Question 9350

Topic: 2. Trauma

When performing an ankle arthrodesis, multiple large cancellous screws are often used. What is their primary biomechanical goal in this setting?

. To provide temporary stabilization until an external fixator is applied.
. To achieve maximal interfragmentary compression across the fusion surfaces.
. To act as position screws, allowing for controlled micromotion.
. To bridge the joint, maintaining distraction.
. To provide a scaffold for bone grafting.

Correct Answer & Explanation

. To achieve maximal interfragmentary compression across the fusion surfaces.

Explanation

The goal of arthrodesis (fusion) is to achieve solid bony union across a joint. Maximal interfragmentary compression (B) is a key principle in achieving successful arthrodesis. Large cancellous lag screws are excellent for generating and maintaining this compression, which promotes primary bone healing and accelerates fusion. Temporary stabilization (A), controlled micromotion (C), distraction (D), or scaffolding (E) are not the primary goals of these screws in arthrodesis.

Question 9351

Topic: 2. Trauma

When selecting the ideal length for a fully-threaded lag screw used to fix a comminuted fracture fragment to a main bone segment, what is the most important consideration regarding its tip?

. The screw tip should just engage the far cortex by 1-2 mm.
. The screw tip should be entirely contained within the near fragment.
. The screw tip should protrude at least 5 mm beyond the far cortex.
. The screw tip should not engage any cortex, allowing free movement.
. The screw length should be exactly the measured depth of the near fragment.

Correct Answer & Explanation

. The screw tip should just engage the far cortex by 1-2 mm.

Explanation

For afully-threadedscrew to act as a lag screw, it must be inserted into a pilot hole that has been overdrilled in the near cortex (glide hole, equal to the outer diameter of the screw) andtappedonly in the far cortex (pilot hole equal to the core diameter of the screw). For optimal purchase and to ensure the screw acts as a true lag screw by engaging the far cortex, the screw tip should just engage or protrude 1-2 mm beyond the far cortex. This ensures maximum purchase in the far cortex without being excessively prominent. If it's entirely within the near fragment (B), it won't provide far cortical purchase. Excessive protrusion (C) can cause soft tissue irritation. No cortical engagement (D) would provide no fixation. Exact near fragment depth (E) would not engage the far cortex.

Question 9352

Topic: 2. Trauma

When fixing a lateral malleolus fracture with a lag screw, what is the ideal direction of insertion for maximal interfragmentary compression?

. Perpendicular to the fracture line.
. Parallel to the long axis of the fibula.
. Perpendicular to the fibula's long axis.
. Approximately 20-30 degrees oblique to the fracture plane.
. Perpendicular to the plate being used.

Correct Answer & Explanation

. Perpendicular to the fracture line.

Explanation

For any lag screw to achieve optimal interfragmentary compression, it should be inserted as close toperpendicular to the fracture lineas possible. This vector directly pulls the fragments together. If inserted perpendicular to the bone's long axis or parallel to it, the compressive force would have a shear component, reducing effective compression across the fracture plane. Options B, C, and E describe other screw orientations or plate applications, not optimal lag screw direction relative to the fracture itself. Option D is plausible but 90 degrees is ideal.

Question 9353

Topic: 2. Trauma

In which fracture pattern would a positional screw be a primary choice of fixation over a lag screw?

. A long spiral diaphyseal fracture of the tibia.
. A transverse fracture of the patella.
. A displaced medial malleolus fracture.
. A fracture of the syndesmosis with tibiofibular diastasis.
. An oblique fracture of the olecranon.

Correct Answer & Explanation

. A fracture of the syndesmosis with tibiofibular diastasis.

Explanation

A fracture of the syndesmosis with tibiofibular diastasis (D) is a classic indication for a positional screw. The goal is to maintain the anatomical reduction of the tibia and fibula without inducing excessive compression, which could restrict normal ankle motion. Lag screws (A, C, E) are used to achieve interfragmentary compression in suitable fracture patterns. A transverse patella fracture (B) is typically fixed with a tension band wiring construct.

Question 9354

Topic: 2. Trauma

When using a fully threaded screw as a lag screw (with a glide hole in the near cortex), what is the purpose of tapping only the far cortex?

. To prevent screw toggling in the near cortex.
. To ensure the screw head sits flush with the plate.
. To create threads for the screw to engage and pull the fragments together.
. To reduce friction during screw insertion.
. To allow for easier removal of the screw later.

Correct Answer & Explanation

. To create threads for the screw to engage and pull the fragments together.

Explanation

For a fully threaded screw to function as a lag screw, a glide hole (equal to the outer diameter of the screw) is drilled in the near cortex, allowing the screw shaft to pass freely. Tapping is then performedonlyin the far cortex, which creates threads for the screw to engage. As the screw is tightened, its threads purchase the far cortex, while gliding through the near cortex, thereby pulling the fragments together and creating interfragmentary compression (C). Preventing toggling (A) is related to the glide hole but not the tapping. Flush screw head (B) is countersinking. Reducing friction (D) is a secondary benefit. Easier removal (E) is not the purpose.

Question 9355

Topic: 2. Trauma

What is the primary role of a 'draw-up' screw in fracture fixation?

. To fix an articular fragment to a plate.
. To increase the length of a bone after shortening.
. To reduce a bone fragment towards a plate prior to final fixation.
. To provide dynamic compression across a fracture site.
. To act as a guide for inserting K-wires.

Correct Answer & Explanation

. To reduce a bone fragment towards a plate prior to final fixation.

Explanation

A draw-up screw (also known as a reduction screw) is used to temporarily reduce a bone fragment towards a plate or to achieve desired alignment. It typically engages the fragment and pulls it towards the pre-contoured plate, holding it in reduction while other definitive screws are inserted. It is a temporary reduction tool, not a definitive fixation screw type. Fixing to a plate (A) is general screw function. Increasing bone length (B) would be distraction. Dynamic compression (D) is a DCP function. Guiding K-wires (E) is for cannulated instruments.

Question 9356

Topic: 2. Trauma

Which type of screw is typically used for fixation of intra-articular fragments, particularly in cancellous bone, to minimize joint surface damage?

. Large diameter cortical screws.
. Fully threaded cancellous screws.
. Small diameter partially threaded cancellous (malleolar) screws.
. Locking screws with large heads.
. Self-drilling bicortical screws.

Correct Answer & Explanation

. Small diameter partially threaded cancellous (malleolar) screws.

Explanation

Small diameter, partially threaded cancellous (malleolar) screws (C) are ideal for intra-articular fragments in cancellous bone. Their small diameter minimizes cartilage and subchondral bone disruption, while their partial thread allows for effective lag compression. Large diameter cortical screws (A) would cause too much damage. Fully threaded cancellous screws (B) wouldn't provide lag compression as effectively unless carefully drilled. Locking screws (D) are generally for plates, and large heads are undesirable intra-articularly. Self-drilling bicortical screws (E) might cause too much bone trauma for small articular fragments.

Question 9357

Topic: 2. Trauma

When applying a tension band principle (e.g., for olecranon or patella fractures), what is the role of the K-wires or intramedullary screw?

. To provide interfragmentary compression directly.
. To prevent distraction and act as a fulcrum for the tension band wire.
. To create absolute stability by rigidly joining fragments.
. To enhance the pull-out strength of the cerclage wire.
. To stimulate bone healing through micromotion.

Correct Answer & Explanation

. To prevent distraction and act as a fulcrum for the tension band wire.

Explanation

In a tension band construct, the K-wires (or intramedullary screw) are inserted parallel to the long axis of the bone and provide anchorage. Their primary role is to prevent distraction of the fracture fragments on the tension side and act as a fulcrum around which the cerclage wire (the actual 'tension band') can convert tensile forces into compressive forces on the opposite, convex side of the bone. They do not provide direct interfragmentary compression (A) themselves, but enable the wire to do so. They contribute to stability but don't solely provide absolute stability (C). Enhancing pull-out strength of the wire (D) is a secondary effect. Micromotion (E) is not the goal of tension banding.

Question 9358

Topic: 2. Trauma

A surgeon uses a 'pull-out' screw technique for reduction of a fracture fragment. What does this technique typically involve?

. Inserting a screw into the fragment and using it as a lever to manipulate the fragment.
. Using a small cortical screw as a lag screw to compress the fragment.
. Attaching a wire to a screw head to apply traction and reduce the fragment.
. Drilling a pilot hole larger than the screw to allow for easy repositioning.
. Inserting a screw and then immediately removing it to clean the fracture site.

Correct Answer & Explanation

. Attaching a wire to a screw head to apply traction and reduce the fragment.

Explanation

A 'pull-out' screw (or reduction screw with a wire) technique involves inserting a screw (often a small fragment or cortical screw) into a fracture fragment, then attaching a strong wire (e.g., cerclage wire) to the head of this screw. This wire is then pulled or tensioned via an external device or another screw in a plate, to manipulate and reduce the fragment into its desired anatomical position. The screw serves as an anchor point for applying controlled traction. Using a lever (A) is manipulation. Lag screw (B) is for compression. Larger pilot hole (D) is for gliding. Immediate removal (E) is not a reduction technique.

Question 9359

Topic: 2. Trauma

What type of screw fixation would be typically seen in a periacetabular osteotomy for acetabular repositioning?

. Cannulated lag screws for articular fragment compression.
. Long cortical screws for bridging segmental defects.
. Large diameter cancellous screws for securing osteotomy fragments.
. Self-tapping locking screws for angular stability.
. Tension band wiring for dynamic stabilization.

Correct Answer & Explanation

. Large diameter cancellous screws for securing osteotomy fragments.

Explanation

Periacetabular osteotomies involve cutting the pelvis around the acetabulum and repositioning the fragment. This fragment is then fixed to the rest of the pelvis. Given the large cancellous bone mass of the ilium and ischium involved, large diameter cancellous screws are commonly used to securely fix the osteotomy fragments (C), providing robust initial stability for healing. Cannulated lag screws (A) could be used for specific articular fragments but not the main osteotomy fixation. Cortical screws (B) are less suited for large cancellous bone. Locking screws (D) are not the primary mode of fixation here. Tension band wiring (E) is not used for this type of pelvic osteotomy.

Question 9360

Topic: 2. Trauma

What is the primary risk of using an excessively long screw in a metaphyseal or epiphyseal region?

. Loss of bone-screw interface compression.
. Soft tissue irritation or damage to adjacent neurovascular structures.
. Increased likelihood of screw breakage due to fatigue.
. Compromise of the fracture reduction.
. Reduced overall construct stiffness.

Correct Answer & Explanation

. Soft tissue irritation or damage to adjacent neurovascular structures.

Explanation

An excessively long screw, particularly in metaphyseal or epiphyseal regions, risks protruding beyond the bone, potentially irritating or damaging surrounding soft tissues (tendons, muscles) or, more critically, adjacent neurovascular structures. This can lead to pain, functional deficits, or serious complications. Loss of compression (A) and reduced stiffness (E) are not direct results of excessive length. Screw breakage (C) is typically from fatigue at stress risers. Compromise of reduction (D) is related to poor placement, not just length.

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