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2. Trauma MCQs

Practice Set 91 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 1801

Topic: 2. Trauma

A surgeon is fixing a comminuted humeral shaft fracture with a neutralization plate. What is the primary role of the screws when used in a neutralization plate construct?

. To generate interfragmentary compression across the fracture site
. To share axial load equally with the plate
. To shield the fracture from bending, torsion, and shear forces
. To promote micromotion for callus formation
. To prevent screw toggling within the plate

Correct Answer & Explanation

. To shield the fracture from bending, torsion, and shear forces

Explanation

Correct Answer: CA neutralization plate is used to protect a primary lag screw or screws providing interfragmentary compression. Its main function is to shield the fracture from bending, torsional, and shear forces, allowing the lag screws to maintain compression without being subjected to disruptive stresses. The plate itself bears the majority of the external loads applied to the bone, thus 'neutralizing' these forces from reaching the fracture site. The screws fix the plate to the bone, but their primary biomechanical role in this construct is to hold the plate securely to provide the shielding effect, not to generate compression or share axial load equally in the immediate fracture zone.

Question 1802

Topic: 2. Trauma

You are performing an arthrodesis of the subtalar joint. Which type of screw is typically preferred for maximizing compression across the joint surfaces and why?

. Fully threaded cortical screws, due to their superior purchase in dense bone.
. Partially threaded cancellous screws, leveraging their larger core diameter and coarse threads.
. Locking screws, as they provide angular stability and prevent loosening.
. Headless compression screws, allowing for deeper countersinking and reduced soft tissue irritation.
. Self-tapping, self-drilling screws, for speed and efficiency.

Correct Answer & Explanation

. Partially threaded cancellous screws, leveraging their larger core diameter and coarse threads.

Explanation

Correct Answer: BFor arthrodesis, maximizing compression across the fusion surfaces is paramount to promote fusion. Partially threaded cancellous screws are ideal for lag screw fixation in cancellous bone (like the tarsals) because their coarse threads provide excellent purchase in softer bone, and the unthreaded shaft allows the near fragment to slide, generating robust interfragmentary compression as the screw is tightened. This direct application of the lag screw principle is highly effective for achieving sustained compression across joint surfaces in an arthrodesis setting. While fully threaded cortical screws can be used in a lag fashion with proper overdrilling, partially threaded cancellous screws are specifically designed for this purpose in metaphyseal/epiphyseal bone.

Question 1803

Topic: 2. Trauma

A 45-year-old male sustains a transverse midshaft femur fracture. The surgeon performs antegrade intramedullary nailing using a piriformis fossa entry portal. If the entry point is placed too far medially in the piriformis fossa, what is the most likely biomechanical consequence?

. Increased risk of nonunion due to inadequate fixation.
. Valgus malalignment of the proximal femoral fragment.
. Varus malalignment of the proximal femoral fragment.
. Increased risk of sciatic nerve injury.
. Difficulty with distal interlocking screw placement.

Correct Answer & Explanation

. Varus malalignment of the proximal femoral fragment.

Explanation

Correct Answer: CThe piriformis fossa entry portal is a common approach for antegrade femoral nailing. Proper placement is crucial to avoid malalignment. If the entry point is too far medially in the piriformis fossa, the intramedullary nail will be forced to enter the canal in a more medial position relative to the mechanical axis of the femur. As the nail is advanced, it will tend to push the proximal femoral fragment into a varus position, leading to varus malalignment. Conversely, an entry point that is too lateral (e.g., through the greater trochanter tip or a more lateral piriformis entry) can lead to valgus malalignment. While sciatic nerve injury (Option D) is a potential complication of piriformis fossa entry, it is not the most likely biomechanical consequence of amedialentry point in terms of fracture alignment. Difficulty with distal interlocking (Option E) is more often related to rotational malalignment or technical issues, not primarily the medial entry point itself causing varus.

Question 1804

Topic: 2. Trauma

A 60-year-old female sustains a transverse olecranon fracture after a fall. She is treated with tension band wiring. What is the primary biomechanical principle that makes tension band wiring an effective fixation method for this type of fracture?

. It provides absolute rigidity, preventing all micromotion at the fracture site.
. It converts tensile forces on the convex side of the fracture into compressive forces at the fracture site.
. It acts as a buttress, preventing posterior displacement of the olecranon fragment.
. It relies on bone-implant friction for stability, similar to a conventional plate.
. It allows for controlled distraction at the fracture site to promote healing.

Correct Answer & Explanation

. It converts tensile forces on the convex side of the fracture into compressive forces at the fracture site.

Explanation

Correct Answer: BTension band wiring is a powerful biomechanical technique used for fractures subjected to eccentric tensile forces (e.g., olecranon, patella, medial malleolus). The primary principle is to convert these tensile forces, which would otherwise cause distraction at the fracture site, into compressive forces. This is achieved by placing a wire (the tension band) on the tension side (e.g., posterior aspect of the olecranon, anterior aspect of the patella) and anchoring it to the bone on the opposite side. When the muscle (e.g., triceps for olecranon) contracts, it applies a tensile force to the fragment. The tension band resists this pull, and because the fracture is on the compression side (e.g., articular surface of the olecranon), the tensile force in the wire is converted into compression across the fracture site, promoting healing and stability. It does not provide absolute rigidity (Option A) but rather relative stability with dynamic compression. It is not primarily a buttress (Option C) and does not rely on friction (Option D). It aims for compression, not distraction (Option E).

Question 1805

Topic: 2. Trauma

A 75-year-old female with an intertrochanteric hip fracture is treated with a Dynamic Hip Screw (DHS). What is the primary biomechanical advantage of the sliding barrel-plate mechanism of the DHS in this fracture pattern?

. It provides enhanced rotational stability to the femoral head fragment.
. It allows for controlled collapse and impaction at the fracture site, promoting secondary bone healing.
. It converts the implant into a load-bearing device, eliminating stress on the bone.
. It reduces the risk of avascular necrosis of the femoral head by preserving blood supply.
. It facilitates minimally invasive surgical technique, reducing soft tissue damage.

Correct Answer & Explanation

. It allows for controlled collapse and impaction at the fracture site, promoting secondary bone healing.

Explanation

Correct Answer: BThe Dynamic Hip Screw (DHS) is designed with a lag screw that is inserted into the femoral head and neck, which then slides within a barrel attached to a side plate. This sliding mechanism is the core biomechanical advantage for intertrochanteric fractures. It allows for controlled collapse and impaction of the fracture fragments under physiological loading. This impaction increases the stability of the fracture, promotes secondary bone healing by bringing the fragments into close apposition, and reduces the risk of screw cutout from the osteoporotic femoral head. While the lag screw provides some rotational stability, its primary dynamic function is axial sliding. The DHS is a load-sharing device, not load-bearing (Option C). Its design does not directly impact avascular necrosis risk (Option D) or inherently facilitate minimally invasive techniques (Option E), although some techniques can be less invasive.

Question 1806

Topic: 2. Trauma

A 50-year-old male sustains a highly comminuted distal tibia fracture (pilon fracture). He is treated with a bridging locking plate. What is the primary biomechanical principle guiding the surgical technique for this type of fixation to optimize healing?

. Achieving absolute anatomical reduction and interfragmentary compression of all fragments.
. Minimizing soft tissue dissection and preserving periosteal blood supply to promote biological healing.
. Maximizing the number of screws per fragment to achieve the stiffest possible construct.
. Using a short working length to prevent any micromotion at the fracture site.
. Applying a pre-bent plate to create axial compression across the articular surface.

Correct Answer & Explanation

. Minimizing soft tissue dissection and preserving periosteal blood supply to promote biological healing.

Explanation

Correct Answer: BFor highly comminuted fractures, especially in metaphyseal or articular regions like pilon fractures, the goal is often 'biological fixation' or 'relative stability' rather than absolute anatomical reduction and compression. Bridging locking plates are ideal for this. The primary biomechanical principle guiding the surgical technique is to minimize soft tissue dissection (e.g., using MIPO techniques) and preserve the periosteal blood supply. This approach prioritizes the biological environment for healing, allowing for callus formation (secondary bone healing) in a relatively stable, yet not rigidly compressed, environment. Attempting absolute anatomical reduction and compression (Option A) in highly comminuted fractures can lead to extensive soft tissue stripping, devascularization of fragments, and impaired healing. Maximizing stiffness (Option C) or using a short working length (Option D) would create a very rigid construct, which can inhibit callus formation and lead to stress shielding. Pre-bending (Option E) is typically for conventional compression plating of simple fractures, not bridging comminuted fractures.

Question 1807

Topic: 2. Trauma

A surgeon is fixing an oblique fibula fracture with a lag screw. What is the critical biomechanical purpose of drilling a 'glide hole' (oversized hole) in the near cortex?

. To allow for easier insertion of the screw into the bone.
. To prevent stripping of the screw threads in the near cortex.
. To ensure the screw head can seat flush with the bone surface.
. To allow the screw to pull the far fragment towards the near fragment, creating interfragmentary compression.
. To reduce the risk of thermal necrosis during drilling by allowing coolant flow.

Correct Answer & Explanation

. To allow the screw to pull the far fragment towards the near fragment, creating interfragmentary compression.

Explanation

Correct Answer: DThe lag screw principle is fundamental for achieving interfragmentary compression across oblique or spiral fractures. For a lag screw to function correctly, it must only engage the far cortex (the fragment being pulled) and not the near cortex (the fragment through which the screw passes). The 'glide hole' (also known as the 'oversized hole' or 'near cortex hole') is drilled with a diameter larger than the screw's outer thread diameter. This allows the screw threads to pass freely through the near cortex without engaging it. When the screw is tightened, its head compresses against the near cortex, and the threads engage only the far cortex, pulling the far fragment towards the near fragment and generating interfragmentary compression. Without a glide hole, the screw would engage both cortices, functioning as a position screw and preventing the desired compression.

Question 1808

Topic: 2. Trauma

A 25-year-old male with an open tibia fracture is treated with a unilateral external fixator. Which modification would significantly increase the bending and torsional stiffness of the external fixator construct?

. Increasing the distance between the bone and the connecting bar.
. Decreasing the diameter of the connecting pins.
. Increasing the number of pins per fragment.
. Using a single connecting bar instead of two connecting bars.
. Increasing the distance between the pins in each fragment.

Correct Answer & Explanation

. Increasing the number of pins per fragment.

Explanation

Correct Answer: CThe stiffness of an external fixator construct is crucial for fracture stability and healing. Several factors influence this stiffness:Number of pins per fragment:Increasing the number of pins per fragment significantly increases stiffness by distributing the load over more points and enhancing the bone-pin interface.Pin diameter:Larger diameter pins are stiffer and provide better purchase in the bone.Pin spacing:Spreading the pins further apart within each fragment (increasing the 'spread' or 'gauge') increases stiffness.Distance between bone and bar:Decreasing the distance between the bone and the connecting bar (reducing the 'working length' of the pins) increases stiffness.Number of connecting bars:Using two connecting bars (a biplanar or delta frame) provides significantly more stiffness than a single bar.Bar diameter and material:Larger diameter bars and stiffer materials (e.g., carbon fiber vs. aluminum) increase stiffness.Therefore, increasing the number of pins per fragment (Option C) would directly increase the stiffness. Options A, B, D, and E would all decrease the stiffness of the construct.

Question 1809

Topic: 2. Trauma

A 40-year-old male sustains a Schatzker Type II tibial plateau fracture with a depressed lateral condyle fragment. After elevation of the depressed articular fragment, a plate is applied to the lateral aspect of the tibia. What is the primary biomechanical function of this plate in this specific scenario?

. To provide interfragmentary compression across the fracture line.
. To neutralize shear forces acting on the articular surface.
. To act as a buttress, preventing re-collapse of the elevated articular fragment.
. To bridge the comminution in the metaphyseal region, promoting relative stability.
. To allow for controlled micromotion to stimulate callus formation.

Correct Answer & Explanation

. To act as a buttress, preventing re-collapse of the elevated articular fragment.

Explanation

Correct Answer: CIn a Schatzker Type II tibial plateau fracture, the lateral condyle is split and depressed. After surgical elevation of the depressed articular fragment to restore the joint surface, the bone underneath is often deficient or weakened. A buttress plate is applied to the lateral aspect of the tibia to mechanically support the elevated fragment and prevent its re-collapse under axial load. Its primary role is to provide structural support against compressive forces that would otherwise cause the articular surface to sink again. While some screws may provide compression or neutralization, the overarching function of the plate in this context is to act as a buttress. Bridging (Option D) is for comminuted diaphyseal or metaphyseal fractures without direct articular involvement, and controlled micromotion (Option E) is typically for secondary healing in diaphyseal fractures, not for maintaining articular reduction.

Question 1810

Topic: 2. Trauma

A surgeon is fixing a fracture in osteoporotic bone using conventional (non-locking) screws. Which factor is most critical in maximizing the pullout strength of these screws in this challenging bone quality?

. Increasing the screw's core diameter.
. Decreasing the screw's thread pitch (finer threads).
. Increasing the screw's thread depth.
. Maximizing the number of cortices engaged by the screw.
. Using a self-tapping screw design.

Correct Answer & Explanation

. Maximizing the number of cortices engaged by the screw.

Explanation

Correct Answer: DIn osteoporotic bone, screw purchase and pullout strength are significantly compromised. While all the listed factors can influence screw strength to some degree, maximizing the number of cortices engaged by the screw is the most critical factor for conventional (non-locking) screws. Engaging two cortices (bicortical purchase) provides significantly greater pullout resistance than engaging only one (monocortical purchase) because it effectively doubles the amount of bone-screw interface and creates a more stable construct. While a larger core diameter (Option A) can increase strength, and a finer thread pitch (Option B) and increased thread depth (Option C) are features of cortical screws designed for dense bone, the overall engagement with multiple cortical layers provides the most substantial increase in pullout strength, especially in poor bone quality. Self-tapping design (Option E) facilitates insertion but does not inherently increase pullout strength compared to pre-drilled screws.

Question 1811

Topic: 2. Trauma

A 30-year-old male sustains a long spiral midshaft tibia fracture. He is treated with a reamed, statically locked intramedullary nail. What is the primary mechanism by which the interlocking screws provide rotational stability in this construct?

. By creating a tight fit between the nail and the endosteal surface of the bone.
. By preventing axial shortening of the fracture fragments.
. By resisting relative rotation between the nail and the bone fragments.
. By increasing the overall bending stiffness of the nail.
. By converting tensile forces into compressive forces at the fracture site.

Correct Answer & Explanation

. By resisting relative rotation between the nail and the bone fragments.

Explanation

Correct Answer: CIn a statically locked intramedullary nail, the interlocking screws (both proximal and distal) serve two primary biomechanical functions: preventing axial shortening/lengthening and preventing rotation. For a long spiral fracture, the fracture pattern itself offers very little inherent rotational stability. While reaming and a tight fit between the nail and the endosteal surface (Option A) contribute to some rotational stability, it is often insufficient for unstable fracture patterns like long spirals. The interlocking screws pass through holes in the nail and engage the bone cortices, effectively 'locking' the nail to the bone fragments. This direct mechanical interlock prevents relative rotation between the nail and each bone fragment, thereby providing crucial rotational stability to the overall construct. Preventing axial shortening (Option B) is also a function of static locking, but rotational stability is particularly critical for spiral fractures. Increasing bending stiffness (Option D) is primarily a function of nail diameter and material, not the screws themselves. Converting forces (Option E) describes tension band principles, not IM nailing.

Question 1812

Topic: 2. Trauma
A 45-year-old female sustains a comminuted distal femur fracture treated with a locking plate. To decrease construct stiffness and promote secondary bone healing via callus formation, which modification is most appropriate?
. Use larger diameter locking screws
. Place screws in all available plate holes
. Increase the working length by leaving holes empty near the fracture
. Use a thicker stainless steel plate
. Decrease the working length by placing screws as close to the fracture as possible

Correct Answer & Explanation

. Increase the working length by leaving holes empty near the fracture

Explanation

Increasing the working length of a plate (the distance between the two closest screws on either side of the fracture) decreases the overall stiffness of the construct. This allows for relative stability and micromotion, which promotes secondary bone healing.

Question 1813

Topic: 2. Trauma

A 30-year-old male with an open tibia fracture is managed with a uniplanar external fixator. Which structural modification most significantly increases the bending stiffness of this construct?

. Decreasing the distance between the pin and the fracture site
. Increasing the distance between the connecting rod and the bone
. Using smaller diameter pins
. Decreasing the number of connecting rods
. Increasing the distance between the pins on the same segment

Correct Answer & Explanation

. Decreasing the distance between the pin and the fracture site

Explanation

Bending stiffness of an external fixator is most significantly improved by placing pins closer to the fracture site, moving the connecting rod closer to the bone, and increasing pin diameter. Decreasing the pin-to-fracture distance minimizes the unsupported bone segment.

Question 1814

Topic: 2. Trauma

A 55-year-old male undergoes fixation of a short oblique tibial shaft fracture with a single lag screw and a neutralization plate. According to Perren's strain theory, this specific construct requires what level of strain at the fracture gap for successful healing?

. Less than 2%
. Between 2% and 10%
. Between 10% and 15%
. Between 15% and 20%
. Greater than 20%

Correct Answer & Explanation

. Less than 2%

Explanation

A lag screw and neutralization plate provide absolute stability, which relies on primary bone healing. Primary bone healing requires the strain at the fracture site to be less than 2% to allow osteoclasts and osteoblasts to cross the gap without disrupting the Haversian systems.

Question 1815

Topic: 2. Trauma

A surgeon uses a fully threaded cortical screw as a lag screw to fix a lateral malleolus fracture by overdrilling the near cortex. The pullout strength of this screw is biomechanically most dependent on which of the following variables?

. Core diameter
. Pitch depth
. Outer thread diameter
. Screw head diameter
. Distance from the fracture line

Correct Answer & Explanation

. Outer thread diameter

Explanation

Pullout strength is directly proportional to the square of the outer thread diameter, the length of thread engagement, and the shear strength of the bone material. Increasing the outer thread diameter has the most profound effect on pullout resistance.

Question 1816

Topic: 2. Trauma

A 22-year-old male with a transverse midshaft humerus fracture is treated with a narrow dynamic compression plate (DCP). The plate is placed on the lateral aspect of the humerus. Which biomechanical principle explains the plate's ability to resist bending forces effectively in this position?

. Load-sharing principle
. Tension band principle
. Stress shielding
. Viscoelasticity
. Galvanic corrosion

Correct Answer & Explanation

. Tension band principle

Explanation

Placing a plate on the tension side of a bone converts tensile forces into compressive forces at the fracture site, utilizing the tension band principle. The lateral aspect of the humerus and femur are classic tension sides during physiological loading.

Question 1817

Topic: 2. Trauma

A hypertrophic nonunion of a tibial shaft fracture, initially treated with a statically locked intramedullary nail, undergoes dynamization. Removing the interlocking screws furthest from the fracture promotes healing by allowing what primary biomechanical change?

. Increased torsional stiffness
. Increased axial micromotion
. Decreased bending loads
. Conversion from relative to absolute stability
. Increased radial preload

Correct Answer & Explanation

. Increased axial micromotion

Explanation

Dynamization involves removing the static locking screws to allow the bone ends to slide along the nail and compress under physiological loads. This increased axial micromotion stimulates secondary bone healing in a hypertrophic nonunion.

Question 1818

Topic: 2. Trauma

A surgeon aims to increase the bending stiffness of a conventional compression plate used for a diaphyseal fracture. Biomechanically, the bending stiffness of the plate is proportional to its thickness raised to what power?

. 1
. 2
. 3
. 4
. 5

Correct Answer & Explanation

. 4

Explanation

The bending stiffness of a plate with a rectangular cross-section depends on its area moment of inertia, calculated as (base * height^3) / 12. Therefore, bending stiffness is proportional to the thickness (height) cubed.

Question 1819

Topic: 2. Trauma

Bilateral femur fractures are treated with an 11 mm solid nail on the right and an 11 mm cannulated nail (inner diameter 5 mm) on the left. Assuming identical materials, how does the bending rigidity of the solid nail compare to the hollow nail?

. The solid nail is exactly twice as rigid
. The solid nail is more than 50% more rigid
. They have nearly identical bending rigidity (less than 10% difference)
. The hollow nail is significantly more rigid
. Cannulation halves the bending rigidity

Correct Answer & Explanation

. They have nearly identical bending rigidity (less than 10% difference)

Explanation

The area moment of inertia for a hollow cylinder subtracts the inner radius to the fourth power. Because the inner radius is small (2.5 mm) compared to the outer (5.5 mm), the inner core contributes very little to overall rigidity, making the difference less than 5%.

Question 1820

Topic: 2. Trauma

A transverse olecranon fracture is treated with tension band wiring. For this construct to successfully function as a dynamic tension band, which mechanical condition is absolutely required during active elbow flexion?

. The articular surface must be placed under continuous tension
. The intact bone opposite the implant must be able to withstand compressive forces
. The wire must be stretched past its yield point
. The construct must eliminate all compressive forces at the fracture
. The fracture must heal exclusively via endochondral ossification

Correct Answer & Explanation

. The intact bone opposite the implant must be able to withstand compressive forces

Explanation

A tension band converts tensile forces on the convex surface into compressive forces at the fracture site. For this to work without construct failure, the opposite cortex (the articular/concave side) must be intact to buttress and withstand these compressive forces.

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