Menu

2. Trauma MCQs

Practice Set 466 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 9301

Topic: 2. Trauma

In the context of fracture fixation, what is the role of a 'pre-tapped' hole?

. To allow for the use of self-tapping screws without a pilot hole.
. To ensure that the screw threads will not strip the bone during insertion.
. To create threads in dense cortical bone before screw insertion.
. To guide a K-wire for cannulated screw placement.
. To prevent thermal necrosis during screw insertion.

Correct Answer & Explanation

. To create threads in dense cortical bone before screw insertion.

Explanation

Pre-tapping involves using a separate tapping instrument to cut threads into the bone after drilling the pilot hole but before inserting the screw. This is typically done in dense cortical bone where self-tapping screws might struggle or risk excessive torque, which could lead to bone necrosis or screw breakage. Pre-tapping ensures precise thread formation, reduces insertion torque, and minimizes stress on the bone, leading to better screw purchase and reducing the risk of stripping or thermal injury.

Question 9302

Topic: 2. Trauma

What is the main biomechanical difference between a variable angle locking screw and a fixed-angle locking screw?

. Variable angle screws provide greater pullout strength.
. Fixed-angle screws allow for screw trajectory customization within a cone of angulation.
. Variable angle screws allow for off-axis screw trajectory, offering more flexibility.
. Fixed-angle screws are designed for compression, while variable angle screws are for neutralization.
. Variable angle screws have a larger core diameter for increased fatigue resistance.

Correct Answer & Explanation

. Variable angle screws allow for off-axis screw trajectory, offering more flexibility.

Explanation

Variable angle locking screws allow the surgeon to insert the screw at a chosen angle (within a certain conical range) relative to the plate, and then lock it in that position. This offers greater flexibility in screw trajectory, allowing the surgeon to optimize screw placement for specific fracture patterns, avoid joint surfaces, or capture small fragments. Fixed-angle locking screws, in contrast, must be inserted at a predetermined, fixed angle to the plate. Both types, once locked, provide angular stability.

Question 9303

Topic: 2. Trauma

A 60-year-old female with osteoporosis sustains a displaced fracture of the proximal humerus. Which screw design would provide the best purchase in her compromised bone quality?

. A standard 3.5 mm cortical screw.
. A standard 4.0 mm cancellous screw.
. A locking screw used with a fixed-angle plate.
. A fully threaded headless compression screw.
. A self-tapping, self-drilling cortical screw.

Correct Answer & Explanation

. A locking screw used with a fixed-angle plate.

Explanation

In osteoporotic bone, the bone stock is poor, making traditional screw purchase unreliable. Locking screws, when used with a locking plate, do not rely on direct compression of the plate to the bone or on the screw's purchase in the near cortex. Instead, they lock into the plate, creating a fixed-angle construct that acts as an internal fixator. This angular stability significantly improves pullout strength and overall construct rigidity in poor bone quality, making it the superior choice for osteoporotic fractures.

Question 9304

Topic: 2. Trauma

What is the primary purpose of 'countersinking' a screw head?

. To increase the purchase of the screw threads in the bone.
. To allow the screw head to sit flush with or below the bone surface, reducing prominence.
. To prevent screw loosening by increasing friction at the screw head-bone interface.
. To enhance the fatigue strength of the screw.
. To facilitate the removal of the screw in the future.

Correct Answer & Explanation

. To allow the screw head to sit flush with or below the bone surface, reducing prominence.

Explanation

Countersinking involves reaming a small conical depression in the bone surface around the pilot hole. This allows the screw head to sit flush with or slightly below the bone surface. The primary purpose is to reduce soft tissue irritation and prominence of the hardware, particularly in superficial locations or near joints. It does not primarily affect screw purchase or fatigue strength directly, though a well-seated screw head contributes to overall construct stability.

Question 9305

Topic: 2. Trauma

Which type of screw is most appropriate for a unicortical fixation in the diaphyseal segment of a long bone?

. Standard bicortical cortical screw.
. Partially threaded cancellous screw.
. Locking screw (when used with a locking plate).
. Headless compression screw.
. Fully threaded lag screw.

Correct Answer & Explanation

. Locking screw (when used with a locking plate).

Explanation

Unicortical fixation, while generally less stable than bicortical, is often employed with locking plates, particularly in situations where bicortical fixation is not feasible (e.g., risk to neurovascular structures on the far cortex) or not necessary due to the fixed-angle stability of the locking construct. Locking screws, by threading into the plate, provide angular stability even with unicortical purchase, as the strength comes from the screw-plate interface, not solely from the bone-screw interface. Other screws primarily rely on bicortical purchase for optimal stability in diaphyseal bone.

Question 9306

Topic: Lower Extremity Trauma

In the context of internal fixation, what does 'stress shielding' refer to?

. The protection of the implant from excessive biomechanical forces by the surrounding bone.
. The phenomenon where an implant carries a disproportionate amount of load, reducing stress on the bone.
. The ability of an implant to withstand repetitive loading cycles without failure.
. The process of bone remodeling in response to inflammatory reactions around an implant.
. The shielding of neural structures from direct contact with the implant.

Correct Answer & Explanation

. The phenomenon where an implant carries a disproportionate amount of load, reducing stress on the bone.

Explanation

Stress shielding occurs when a rigid implant (like a plate or intramedullary nail) bears a significant portion of the physiological load that would normally be carried by the bone. This reduction in stress on the bone (in accordance with Wolff's Law) can lead to localized bone resorption and reduced bone density around the implant. While sometimes unavoidable, excessive stress shielding can weaken the bone, increasing the risk of refracture upon implant removal.

Question 9307

Topic: 2. Trauma

Which screw type is most suitable for fixing a small, intra-articular osteochondral fragment where the screw head must not protrude into the joint space?

. Standard cortical screw.
. Standard cancellous screw.
. Dynamic compression screw.
. Headless compression screw.
. Locking screw.

Correct Answer & Explanation

. Headless compression screw.

Explanation

Headless compression screws are specifically designed for applications where the screw needs to be fully buried within the bone, particularly in articular or periarticular fractures. Their lack of a prominent head prevents irritation to overlying cartilage or soft tissues. They also provide compression across the fracture due to their differential thread pitch. This makes them ideal for fixing osteochondral fragments.

Question 9308

Topic: 2. Trauma

Which type of screw is typically color-coded in orthopedic sets to indicate its compatibility with a specific plate system?

. Cortical screws.
. Cancellous screws.
. Lag screws.
. Locking screws.
. Position screws.

Correct Answer & Explanation

. Locking screws.

Explanation

Locking screws are almost always color-coded to match specific locking plate systems. This is critical because locking screws must be perfectly compatible with the threaded holes of their respective plates to ensure proper engagement and the creation of a fixed-angle construct. Using an incompatible locking screw would compromise the angular stability of the system. While some other screws might have color codes for diameter, locking screws and their corresponding plates are very commonly matched by color to ensure system integrity.

Question 9309

Topic: 2. Trauma

A surgeon is repairing a tibial plateau fracture with a buttress plate. What is the primary role of the screws placed distally and proximally to the fracture in this construct?

. To provide dynamic compression across the fracture.
. To create a fixed-angle construct.
. To fix the plate firmly to the bone, thus supporting the articular surface against axial load.
. To act as lag screws to achieve interfragmentary compression.
. To allow for controlled micromotion at the fracture site.

Correct Answer & Explanation

. To fix the plate firmly to the bone, thus supporting the articular surface against axial load.

Explanation

In a buttress plate construct for a tibial plateau fracture, the plate is placed to prevent the collapse or displacement of articular fragments under axial load. The screws fix the plate securely to the bone, effectively transmitting the axial loads through the plate rather than allowing the fragments to collapse. While lag screws might be used intra-articularly for primary reduction, the screws holding the buttress plate are primarily serving to anchor the plate and provide the buttressing effect, supporting the articular surface and preventing secondary collapse.

Question 9310

Topic: 2. Trauma

What is the function of the differential thread pitch in some headless compression screws (e.g., Herbert screw design)?

. To increase the resistance to rotational forces.
. To allow for self-drilling capability.
. To generate compression across the fracture as the screw is inserted.
. To prevent inadvertent overtightening and stripping.
. To enhance the screw's ability to be removed in the future.

Correct Answer & Explanation

. To generate compression across the fracture as the screw is inserted.

Explanation

Headless compression screws with a differential thread pitch (e.g., the Herbert screw principle) have a coarser pitch on the distal threads and a finer pitch on the proximal threads. As the screw is advanced, the distal threads engage the far fragment and pull it, while the proximal threads engage the near fragment more slowly. This differential advancement rate effectively draws the two fragments together, generating interfragmentary compression across the fracture. This compression is maintained as the screw is fully seated.

Question 9311

Topic: 2. Trauma

When using a fully threaded screw to achieve interfragmentary compression (lag screw technique), what specific step is required that is NOT needed for a partially threaded lag screw?

. Overdrilling the far cortex to create a gliding hole.
. Tapping only the far cortex.
. Using a smaller drill bit for the pilot hole.
. Creating a gliding hole in the near cortex, equal to the screw's major diameter.
. Countersinking the screw head.

Correct Answer & Explanation

. Creating a gliding hole in the near cortex, equal to the screw's major diameter.

Explanation

For a fully threaded screw to act as a lag screw and generate interfragmentary compression, a gliding hole must be specifically drilled in the near cortex. This gliding hole must be equal to or slightly larger than the major (outer) diameter of the screw. This allows the screw threads to pass freely through the near fragment without engaging, while the threads then engage the far fragment, drawing the near fragment towards the far fragment as the screw is tightened. A partially threaded lag screw inherently has a smooth shaft for the near fragment to slide along, eliminating the need to overdrill the near cortex for a gliding hole.

Question 9312

Topic: 2. Trauma

A surgeon is attempting to reduce and stabilize a severely comminuted diaphyseal fracture using a bridge plating technique. What is the primary role of the screws in this context?

. To achieve anatomical reduction and interfragmentary compression.
. To act as lag screws across the comminuted zone.
. To fix the plate to the main bone fragments, creating a splint across the comminution.
. To stimulate bone formation by creating controlled micromotion.
. To provide rotational stability by engaging only the far cortex.

Correct Answer & Explanation

. To fix the plate to the main bone fragments, creating a splint across the comminution.

Explanation

In bridge plating for comminuted diaphyseal fractures, the plate acts as an extramedullary splint. The screws are inserted bicortically into the main proximal and distal fragments, bypassing the comminuted zone. The primary role of the screws is to securely fix the plate to these main fragments, effectively 'bridging' the comminution. The goal is not anatomical reduction of the comminuted fragments or interfragmentary compression within the comminution, but rather maintenance of length, alignment, and rotation while providing a stable environment for indirect healing. The screws fix the plate to the main fragments to achieve this splinting effect.

Question 9313

Topic: 2. Trauma

What is the main reason a small fragment system (e.g., 3.5 mm screws) might be preferred over a large fragment system (e.g., 4.5 mm screws) for certain fractures, even in adults?

. Increased pullout strength due to finer threads.
. Reduced cost and easier manufacturing.
. To minimize soft tissue irritation and allow for smaller incisions.
. Greater flexibility in plate contouring.
. Reduced bone removal, which is crucial for smaller bones or fragments.

Correct Answer & Explanation

. Reduced bone removal, which is crucial for smaller bones or fragments.

Explanation

Small fragment systems are designed for smaller bones (e.g., forearm, hand, foot) or smaller fragments of larger bones (e.g., periarticular fractures). Their smaller screw and plate sizes require less bone removal, which is critical when dealing with limited bone stock, intricate anatomy, or numerous small fragments. They allow for more screws to be placed in a confined area and reduce the stress on small bone fragments. While they can lead to smaller incisions, the primary advantage stems from matching the implant size to the bone size and fragment dimensions.

Question 9314

Topic: 2. Trauma

Which of the following describes the 'neutral' position for screw placement in a Dynamic Compression Plate (DCP) hole?

. The screw is inserted at the far end of the elliptical hole, away from the fracture.
. The screw is inserted at the near end of the elliptical hole, towards the fracture.
. The screw is inserted directly in the center of the elliptical hole.
. The screw is angled to provide interfragmentary compression.
. The screw is used primarily for buttressing purposes.

Correct Answer & Explanation

. The screw is inserted directly in the center of the elliptical hole.

Explanation

When a screw is inserted directly in the center of the elliptical hole of a DCP, it acts as a 'neutral' screw. In this position, the spherical undersurface of the screw head does not slide along the inclined plane, and thus no axial compression is generated across the fracture. This position is typically used when interfragmentary compression is already achieved by lag screws, or when the plate is used primarily for neutralization or bridging, maintaining length and alignment without adding further compression.

Question 9315

Topic: 2. Trauma

A T-plate is being used for a distal tibial pilon fracture. What is the main purpose of the multiple screws directed into the epiphysis/metaphysis through the plate's 'head'?

. To provide compression across the diaphyseal fracture component.
. To act as lag screws for metaphyseal fragments.
. To stabilize and buttress articular fragments, preventing collapse and maintaining reduction.
. To facilitate bone graft incorporation into the fracture site.
. To allow for early weight-bearing without additional support.

Correct Answer & Explanation

. To stabilize and buttress articular fragments, preventing collapse and maintaining reduction.

Explanation

T-plates (or similar periarticular plates) used for pilon fractures have a broad 'head' designed with multiple screw holes to capture and stabilize small, often comminuted, articular fragments of the epiphysis/metaphysis. The primary purpose of these screws is to buttress these fragments, prevent their collapse under axial load, and maintain the reduction of the articular surface. They essentially act as 'fixed-angle' or 'buttressing' screws to reconstruct the joint block.

Question 9316

Topic: 2. Trauma

What is the major mechanical disadvantage of using a fully threaded screw as a position screw in a high-stress environment, such as a long bone fracture?

. It inherently provides less pullout strength than a partially threaded screw.
. It can over-compress soft tissues, leading to irritation.
. It prevents interfragmentary compression, which might be beneficial for healing.
. It lacks differential pitch for advanced compression.
. It is more prone to breaking due to a smaller core diameter.

Correct Answer & Explanation

. It prevents interfragmentary compression, which might be beneficial for healing.

Explanation

A fully threaded screw, when used as a position screw (i.e., threading both cortices/fragments equally without a gliding hole), holds fragments in a fixed position but does not generate interfragmentary compression. In many long bone fractures, interfragmentary compression is a highly desirable biomechanical principle that promotes primary bone healing by reducing motion at the fracture site. The disadvantage is not that it's inherently weaker or causes soft tissue irritation, but that it misses the opportunity to apply active compression, which is often biomechanically superior for healing.

Question 9317

Topic: 2. Trauma

A surgeon is performing an acetabular fracture fixation. What type of screw is generally considered safest and most effective for anterior column fixation where the inner table of the pelvis is the far cortex?

. Long, fully threaded cortical screws bicortically.
. Short, partially threaded cancellous screws.
. Locking screws with a locking plate, potentially unicortically.
. Cannulated screws engaging only the near cortex.
. Self-drilling, self-tapping screws for speed.

Correct Answer & Explanation

. Locking screws with a locking plate, potentially unicortically.

Explanation

In complex pelvic and acetabular fracture fixation, particularly anterior column fractures, the proximity of vital structures (e.g., obturator nerve, external iliac vessels) makes bicortical fixation risky. Locking plates with locking screws offer a significant advantage here. Their ability to provide angular stability even with unicortical purchase minimizes the risk of far cortical perforation and associated neurovascular injury, making them safer while still providing adequate stability for fixation. This approach significantly reduces iatrogenic complications.

Question 9318

Topic: 2. Trauma

Which of the following scenarios is LEAST likely to benefit from the use of a locking screw?

. Fixation of a comminuted metaphyseal fracture in osteoporotic bone.
. Bridge plating of a severely comminuted diaphyseal fracture.
. Fixation of a simple, transverse diaphyseal fracture using a lag screw and neutralization plate.
. Stabilization of a proximal humeral fracture in an elderly patient.
. Repair of a periarticular fracture with multiple small fragments.

Correct Answer & Explanation

. Fixation of a simple, transverse diaphyseal fracture using a lag screw and neutralization plate.

Explanation

Locking screws excel in situations where bone quality is poor, or when a fixed-angle construct is desired (e.g., comminuted fractures, bridge plating, osteoporotic bone, periarticular fractures). In a simple, transverse diaphyseal fracture, the primary goal is often to achieve strong interfragmentary compression, which is best accomplished with a lag screw. A neutralization plate with non-locking cortical screws provides adequate stability by protecting the lag screw. Using locking screws in this specific scenario wouldn't offer a significant advantage over a well-executed lag screw + neutralization plate, and in fact, locking plates generally limit interfragmentary compression compared to traditional DCPs used in compression mode.

Question 9319

Topic: 2. Trauma

A surgeon is planning to fix a distal femoral fracture with a long plate. What is the advantage of using 'far cortical locking' screws in the diaphysis for bridge plating?

. They provide maximal interfragmentary compression.
. They allow for dynamic motion at the fracture site while maintaining alignment.
. They eliminate the need for bicortical screw purchase.
. They offer superior angular stability compared to traditional locking screws.
. They prevent soft tissue irritation by being fully buried.

Correct Answer & Explanation

. They allow for dynamic motion at the fracture site while maintaining alignment.

Explanation

Far Cortical Locking (FCL) screws are a specialized type of locking screw that engage only the far cortex in a diaphyseal bridge plating construct. They provide flexible stability, allowing for controlled micromotion at the fracture site. Unlike traditional rigid locking screws that create a stiff, fixed-angle construct, FCL screws permit slight physiological loading and movement, which is believed to promote secondary bone healing (callus formation) in comminuted fractures by reducing stress shielding while still maintaining alignment and length. They are not designed for interfragmentary compression or superior angular stability in the same way traditional locking screws are.

Question 9320

Topic: 2. Trauma

Which biomechanical principle is primarily applied when using screws in a 'tension band' construct?

. Neutralization of shear forces.
. Interfragmentary compression through lag effect.
. Conversion of tensile forces into compressive forces.
. Buttressing against axial collapse.
. Fixed-angle stability against bending.

Correct Answer & Explanation

. Conversion of tensile forces into compressive forces.

Explanation

The tension band principle is designed to convert distractive (tensile) forces acting on one side of a bone into compressive forces on the opposite side (the compression side) during functional loading. This is typically achieved with a wire (often supplemented by K-wires or screws) placed on the tension side of a fracture (e.g., patella, olecranon, medial malleolus). As the joint moves or load is applied, the tension band resists the distraction, thereby compressing the fracture fragments on the opposite side, promoting healing.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page