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2. Trauma MCQs

Practice Set 90 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 1781

Topic: 2. Trauma

A 32-year-old male sustains a transverse mid-diaphyseal femoral fracture. He is treated with a reamed, statically locked intramedullary nail. Biomechanically, what is the primary advantage of this construct over a rigidly compressed plate for this specific fracture pattern?

. It provides absolute stability, promoting primary bone healing.
. It completely eliminates stress shielding of the femoral shaft.
. It acts as a load-sharing device, allowing controlled micromotion to stimulate secondary bone healing.
. It ensures a higher ultimate tensile strength of the overall bone-implant construct.
. It requires less surgical time and blood loss.

Correct Answer & Explanation

. It acts as a load-sharing device, allowing controlled micromotion to stimulate secondary bone healing.

Explanation

Correct Answer: CIntramedullary (IM) nails are load-sharing devices, meaning they share axial, bending, and torsional loads with the bone. This central placement along the mechanical axis minimizes bending moments and allows for controlled micromotion at the fracture site, which is a potent stimulus for secondary bone healing via callus formation (endochondral ossification). A rigidly compressed plate, conversely, aims for absolute stability and primary bone healing (direct cortical healing). While IM nailing often involves less soft tissue dissection, which is a surgical advantage, the primary biomechanical benefit in terms of healing mechanism is load sharing and relative stability. Stress shielding is reduced compared to rigid plates but not eliminated. Ultimate tensile strength is a material property, not a construct advantage over a plate.

Question 1782

Topic: 2. Trauma

A 48-year-old female with a comminuted tibial shaft fracture is undergoing intramedullary nailing. The surgeon opts for a reamed technique. What is the most significant biomechanical consequence of reaming the medullary canal in this scenario?

. It primarily preserves the endosteal blood supply, accelerating healing.
. It allows for the insertion of a larger diameter nail, significantly increasing bending and torsional stiffness.
. It reduces the risk of thermal osteonecrosis at the fracture site.
. It converts the nail into a load-bearing implant.
. It facilitates dynamic compression at the fracture site.

Correct Answer & Explanation

. It allows for the insertion of a larger diameter nail, significantly increasing bending and torsional stiffness.

Explanation

Correct Answer: BReaming the medullary canal allows for the insertion of a larger diameter intramedullary nail. The bending and torsional stiffness of a nail are highly dependent on its diameter and cross-sectional geometry (specifically, the area moment of inertia). A larger diameter nail provides a tighter fit within the canal, maximizing bone-implant contact and significantly increasing the overall stiffness of the construct. This enhanced stiffness is crucial for stabilizing comminuted fractures, where the bone itself provides little inherent stability. Reaming temporarily disrupts the endosteal blood supply and can cause thermal osteonecrosis if not performed carefully, thus option A and C are incorrect. IM nails remain load-sharing devices, not load-bearing, and reaming does not directly facilitate dynamic compression (which is achieved by specific locking screw configurations).

Question 1783

Topic: 2. Trauma

A 28-year-old male sustains a spiral mid-shaft humeral fracture. Antegrade intramedullary nailing is performed. To achieve optimal rotational stability in this fracture pattern, which biomechanical feature of the construct is most critical?

. The largest possible nail diameter to maximize canal fill.
. The use of a titanium alloy nail due to its lower Young's Modulus.
. The presence of multiple, appropriately placed interlocking screws in both the proximal and distal fragments.
. A tight fit of the nail within the isthmus of the humerus.
. The pre-bending of the nail to match the humeral curvature.

Correct Answer & Explanation

. The presence of multiple, appropriately placed interlocking screws in both the proximal and distal fragments.

Explanation

Correct Answer: CIn spiral or comminuted fractures, the bone fragments themselves cannot resist rotational forces due to the lack of inherent bony stability. Therefore, rotational stability is primarily achieved by the interlocking screws. These screws connect the intramedullary nail to both the main proximal and distal bone fragments, effectively linking them and preventing independent rotation between the implant and the bone. While nail diameter, material properties, and a tight fit contribute to overall construct stiffness, interlocking screws are the direct and most critical mechanism for resisting rotation in unstable fracture patterns. Pre-bending helps with anatomical alignment but does not directly provide rotational stability to the fracture fragments.

Question 1784

Topic: 2. Trauma

A 55-year-old patient with a comminuted distal tibia fracture is treated with a supramalleolar intramedullary nail. The surgeon places two proximal and two distal interlocking screws. If the surgeon were to remove one proximal and one distal screw (converting to a single screw at each end), what would be the primary biomechanical consequence?

. Increased overall bending and torsional stiffness of the construct.
. A shorter working length, leading to less micromotion.
. A longer working length, allowing for increased controlled micromotion at the fracture site.
. Enhanced resistance to screw pullout.
. Conversion to absolute stability.

Correct Answer & Explanation

. A longer working length, allowing for increased controlled micromotion at the fracture site.

Explanation

Correct Answer: CThe 'working length' of an intramedullary nail construct is defined as the distance between the most proximal and most distal interlocking screws. Increasing this distance (by removing screws or placing them further apart) results in a longer working length. Biomechanically, a longer working length leads to a less stiff construct, allowing for increased controlled micromotion at the fracture site. This controlled micromotion can be beneficial for stimulating callus formation (secondary bone healing) but can also risk excessive motion and delayed union if the working length is too long for the fracture pattern. Conversely, a shorter working length (more screws, closer together) increases stiffness. Removing screws would decrease, not increase, resistance to screw pullout and would not convert to absolute stability.

Question 1785

Topic: 2. Trauma

A 70-year-old female with osteopenia sustains a mid-shaft femoral fracture. An IM nail is inserted, but intraoperative imaging reveals the distal tip of the nail terminates approximately 5 cm proximal to the metaphyseal flare. What is the most significant biomechanical concern with this nail length?

. Increased risk of infection due to inadequate canal fill.
. Reduced rotational stability of the distal fragment.
. Stress concentration at the nail tip, predisposing to a periprosthetic fracture.
. Impingement on the knee joint, causing pain and reduced range of motion.
. Inability to achieve dynamic compression.

Correct Answer & Explanation

. Stress concentration at the nail tip, predisposing to a periprosthetic fracture.

Explanation

Correct Answer: CA too-short intramedullary nail, especially one that terminates within the diaphysis rather than extending into the metaphysis, creates a stress riser at its tip. Biomechanically, this point becomes a site of concentrated stress where the stiff implant abruptly ends, transferring load to the adjacent bone. This significantly increases the risk of a periprosthetic fracture originating at or just beyond the nail tip, particularly in osteopenic bone where bone quality is already compromised. Optimal nail length involves extending into the metaphysis to distribute stress over a larger area and avoid these stress risers. Impingement on the knee joint would occur if the nail was too long and protruded distally. Rotational stability is primarily provided by interlocking screws, and dynamic compression is a function of screw configuration, not nail length.

Question 1786

Topic: 2. Trauma

A 60-year-old male with a subtrochanteric femoral fracture is undergoing antegrade IM nailing. The surgeon is carefully selecting the entry portal. What is the primary biomechanical rationale for ensuring the entry portal is appropriately positioned, typically at the tip of the greater trochanter or slightly medial to it?

. To maximize the length of the nail that can be inserted.
. To avoid injury to the superior gluteal artery.
. To minimize eccentric reaming and iatrogenic fracture of the trochanteric region, ensuring optimal nail trajectory.
. To facilitate easier removal of the implant in the future.
. To increase the bending stiffness of the nail itself.

Correct Answer & Explanation

. To minimize eccentric reaming and iatrogenic fracture of the trochanteric region, ensuring optimal nail trajectory.

Explanation

Correct Answer: CAn optimal entry portal for antegrade femoral nailing is crucial for proper nail alignment and to prevent iatrogenic complications. If the entry point is too medial (e.g., piriformis fossa entry with a lateral approach) or too far lateral, it can lead to eccentric reaming of the greater trochanter or piriformis fossa. This can potentially cause iatrogenic comminution or fracture, especially in subtrochanteric fractures where the bone is already compromised. A correctly placed entry portal ensures the nail follows the natural curvature of the femur, is well-centered in the medullary canal, and minimizes stress risers, thereby ensuring optimal nail trajectory and reducing the risk of malalignment. While avoiding neurovascular injury (like the superior gluteal artery) is important, the primary biomechanical rationale for thepositionof the entry portal relates to bone integrity and nail trajectory.

Question 1787

Topic: 2. Trauma

A 35-year-old male presents with a segmental femoral shaft fracture, with a 6 cm intervening fragment. He is treated with a reamed, statically locked IM nail. Biomechanically, what is the most significant challenge posed by this fracture pattern to the IM nail construct?

. Increased risk of thermal osteonecrosis during reaming.
. Difficulty in achieving anatomical reduction of the main fragments.
. The intervening fragment acts as a stress shield, reducing load on the nail.
. Significantly increased bending and torsional forces on the nail due to the unsupported segment.
. Reduced need for interlocking screws due to the presence of multiple fragments.

Correct Answer & Explanation

. Significantly increased bending and torsional forces on the nail due to the unsupported segment.

Explanation

Correct Answer: DIn a segmental fracture, the intervening fragment effectively creates two separate fracture sites, meaning the intramedullary nail must bridge a longer span without direct bony support between the two main fragments. This significantly increases the bending and torsional moments acting on the implant, as the nail must bear a greater proportion of the physiological load across this unsupported segment. This increased loading can lead to a higher risk of implant fatigue failure, delayed union, or nonunion if the construct is not sufficiently robust. The intervening fragment does not act as a stress shield; rather, it creates a zone of instability that the nail must bridge. The need for interlocking screws is often increased, not reduced, in such unstable patterns.

Question 1788

Topic: Lower Extremity Trauma

During antegrade intramedullary nailing of a tibial shaft fracture, the surgeon encounters difficulty advancing the nail past the mid-diaphysis, with the nail tip impinging on the anterior cortex. What is the most likely biomechanical reason for this difficulty?

. The nail is too large in diameter for the reamed canal.
. The nail has a posterior apex bow, which does not match the natural anterior apex recurvatum of the tibia.
. The entry portal in the proximal tibia is too anterior.
. The interlocking screws were inserted prematurely.
. The patient has an unusually straight tibia.

Correct Answer & Explanation

. The nail has a posterior apex bow, which does not match the natural anterior apex recurvatum of the tibia.

Explanation

Correct Answer: BThe tibia naturally exhibits an anterior apex recurvatum (anterior bow) in the sagittal plane. Intramedullary nails designed for the tibia are manufactured with an anterior apex bow to match this physiological curvature. If a nail with an incorrect sagittal curvature (e.g., a posterior apex bow or a nail that is too straight) is used, or if the nail's curvature is not properly aligned with the bone's, it can impinge on the anterior or posterior cortex during insertion, making advancement difficult and potentially leading to malalignment (procurvatum or recurvatum). While an anterior entry portal can also cause anterior cortical impingement, the scenario described (nail tip impinging on the anterior cortex) is most characteristic of a nail with a posterior apex bow trying to navigate an anteriorly bowed canal.

Question 1789

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

Correct Answer: BThe 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 (Option A) is thegoalof lag screw fixation, but the 'how' is through compression. Neutralization (Option C) and buttress (Option E) are functions of plates, not the primary function of a lag screw itself. Fixation of osteochondral fragments (Option D) can be done with lag screws, but the 'non-compressive' part is incorrect if referring to a true lag screw.

Question 1790

Topic: Lower Extremity Trauma

When inserting a standard 3.5 mm cortical screw into the femoral shaft, what is the appropriate drill bit size for the pilot hole if tapping is to be performed?

. 2.0 mm
. 2.5 mm
. 2.7 mm
. 3.2 mm
. 3.5 mm

Correct Answer & Explanation

. 2.7 mm

Explanation

Correct Answer: CFor a standard 3.5 mm cortical screw, the outer (thread) diameter is 3.5 mm and the inner (core) diameter is typically 2.7 mm. When tapping is performed, the pilot hole should match the core diameter of the screw to ensure that the threads cut by the tap, and subsequently the screw, achieve maximum purchase. A 2.5 mm drill bit (Option B) is used for a 3.5 mm non-locking screw through a plate for creating compression (dynamic compression plate hole). A 2.0 mm (Option A) is for 2.7 mm screws. A 3.2 mm (Option D) is typically for larger screws like 4.5 mm cortical screws (where the core diameter is 3.2 mm). A 3.5 mm (Option E) would prevent any thread purchase.

Question 1791

Topic: 2. Trauma

What is the primary biomechanical advantage of a locking screw construct compared to a conventional screw-plate construct in osteoporotic bone?

. Increased interfragmentary compression at the fracture site.
. Reduced stress shielding of the bone due to increased stiffness.
. Angular stability provided by a fixed-angle construct, resisting pull-out.
. Enhanced bone healing through micromotion at the fracture site.
. Superior ability to create lag compression across oblique fractures.

Correct Answer & Explanation

. Angular stability provided by a fixed-angle construct, resisting pull-out.

Explanation

Correct Answer: CLocking screws thread into the plate, creating a fixed-angle construct. This effectively turns the screw-plate interface into a 'beam' rather than relying on friction between the plate and bone for stability. This angular stability is highly resistant to screw pull-out, which is a significant problem in osteoporotic bone where screw purchase is poor. While some compression can be achieved with locking plates (e.g., with specific techniques or combi-holes), theirprimarybiomechanical advantage over conventional constructs, especially in poor bone, is angular stability and improved pull-out resistance (Option C). They generally reduce interfragmentary compression (Option A) compared to traditional lag screws. Locking plates tend to be stiffer and can increase stress shielding (Option B). They provide rigid fixation, which reduces micromotion (Option D), though some controlled micromotion can be beneficial for callus formation. Lag compression (Option E) is a function of a lag screw, and while locking screws can be used in a lag fashion through combi-holes, it's not their primary distinguishing advantage.

Question 1792

Topic: 2. Trauma

Cannulated screws are particularly advantageous in which of the following scenarios?

. Fixation of diaphyseal fractures requiring high torsional rigidity.
. Applications where precise screw placement over a guide wire is crucial.
. Situations demanding maximal cortical purchase in dense bone.
. When primary interfragmentary compression is the sole objective.
. Fixation of highly comminuted metaphyseal fractures.

Correct Answer & Explanation

. Applications where precise screw placement over a guide wire is crucial.

Explanation

Correct Answer: BCannulated screws have a hollow core, allowing them to be inserted over a guide wire. This feature is extremely useful for precise placement, especially in articular fractures, epiphyseal/metaphyseal fractures, or percutaneous applications where accurate trajectory and minimal soft tissue disruption are desired. Examples include femoral neck fractures, scaphoid fractures, or malleolar fractures. Diaphyseal fractures (Option A) typically use solid screws for torsional rigidity. Maximal cortical purchase (Option C) is achieved with solid screws matching the core diameter for the pilot hole. While theycancreate compression (Option D), their cannulation isn't formaximalcompression. Comminuted metaphyseal fractures (Option E) might use locking plates, not primarily cannulated screws for their cannulation feature alone.

Question 1793

Topic: 2. Trauma

In the context of plate and screw fixation, what is the primary role of a neutralization plate?

. To apply direct compression across the fracture site.
. To protect lag screws from bending, shear, and torsional forces.
. To provide primary load-bearing stability in comminuted fractures.
. To bridge a segmental bone defect without direct fracture contact.
. To function as a buttress, preventing collapse of articular fragments.

Correct Answer & Explanation

. To protect lag screws from bending, shear, and torsional forces.

Explanation

Correct Answer: BA neutralization plate is used in conjunction with interfragmentary lag screws. The lag screws provide the primary interfragmentary compression (absolute stability), while the neutralization plate's role is to 'neutralize' or protect these lag screws from shared forces (bending, shear, torsion) that could lead to failure of the lag screw fixation or loss of compression. It shares the load with the lag screws, but the lag screws are doing the initial compression. Direct compression (Option A) is the role of the lag screw or a DCP. Primary load-bearing in comminuted fractures (Option C) is a bridging plate function. Bridging (Option D) is also a separate plate function for comminuted fractures/defects. Buttress (Option E) plates prevent collapse, usually in metaphyseal or articular areas.

Question 1794

Topic: 2. Trauma

How does the design of a Dynamic Compression Plate (DCP) facilitate interfragmentary compression?

. By allowing locking screws to be inserted at variable angles.
. Through eccentric drilling of the pilot hole, causing the screw head to slide down an inclined plane.
. By incorporating an internal spring mechanism within each screw hole.
. Through the use of self-tapping screws with wider thread pitches.
. By requiring pre-bending of the plate to create an axial load.

Correct Answer & Explanation

. Through eccentric drilling of the pilot hole, causing the screw head to slide down an inclined plane.

Explanation

Correct Answer: BThe Dynamic Compression Plate (DCP) utilizes a specific hole design that is shaped like an inclined cylinder. When a screw is inserted through an eccentrically drilled pilot hole (i.e., drilled at one end of the oval hole), the spherical screw head contacts the inclined plane and slides down it as it is tightened. This translation of the screw head along the inclined plane pulls the bone fragment toward the plate, generating axial compression across the fracture site. Variable angle locking screws (Option A) are for locking plates, not DCPs. Internal spring mechanisms (Option C) are not part of DCP design. Self-tapping screws (Option D) simplify insertion but don't provide the compression mechanism. Pre-bending (Option E) helps prevent gapping on the far cortex but is not the primary mechanism ofinterfragmentarycompression using the plate holes.

Question 1795

Topic: 2. Trauma

A 78-year-old female with severe osteoporosis sustains a highly comminuted distal femur fracture (AO/OTA 33-C3) after a low-energy fall. You decide to proceed with open reduction and internal fixation using a locking plate. What is the primary biomechanical rationale for choosing a locking plate over a conventional Dynamic Compression Plate (DCP) in this specific patient and fracture pattern?

. Locking plates provide superior interfragmentary compression, which is crucial for comminuted fractures.
. Locking plates have a lower modulus of elasticity, thereby reducing stress shielding in osteoporotic bone.
. The fixed-angle construct of a locking plate provides stability independent of plate-bone friction, crucial for poor bone quality.
. Locking plates allow for earlier full weight-bearing due to absolute stability at the fracture site.
. Locking plates are more malleable, allowing for easier contouring to the complex distal femur anatomy.

Correct Answer & Explanation

. The fixed-angle construct of a locking plate provides stability independent of plate-bone friction, crucial for poor bone quality.

Explanation

Correct Answer: CThe primary biomechanical advantage of a locking plate in a highly comminuted fracture, especially in osteoporotic bone, is its ability to create a fixed-angle construct. The threaded screw heads lock into the plate, forming a rigid unit that functions as an 'internal fixator' or 'extramedullary splint.' This construct provides stability that is largely independent of plate-bone friction or compression, which is severely compromised in osteoporotic bone where screw pull-out strength is poor and cortical contact is minimal due to comminution. This allows for stable fixation even with poor bone quality.Option A is incorrect:Interfragmentary compression is not the primary goal or mechanism in highly comminuted fractures, where relative stability and indirect healing are preferred. Locking plates primarily bridge comminution rather than compress it.Option B is incorrect:While titanium locking plates have a lower modulus of elasticity than stainless steel, the fixed-angle construct itself is generally quite rigid and can lead to stress shielding, not reduce it. The material choice influences modulus, but the construct's rigidity is the dominant factor for stress shielding.Option D is incorrect:While locking plates provide robust stability, 'absolute stability' (no micromotion) is not always achievable or desirable in comminuted fractures, where controlled micromotion promotes secondary bone healing. Early full weight-bearing depends on many factors, not solely the plate type.Option E is incorrect:Locking plates are generally less malleable than conventional plates, and excessive bending can damage the threaded screw holes. Anatomically pre-contoured locking plates exist, but the material itself is not inherently more malleable.

Question 1796

Topic: 2. Trauma

A 35-year-old male sustains a simple transverse midshaft tibial fracture. You plan to fix this with a conventional Dynamic Compression Plate (DCP) to achieve absolute stability. When contouring the plate, what is the primary purpose of 'pre-bending' the plate slightly away from the bone at the fracture site?

. To reduce the overall stiffness of the construct, promoting secondary bone healing.
. To ensure uniform screw purchase along the entire length of the plate.
. To prevent gapping on the far (trans) cortex when the plate is tightened, ensuring interfragmentary compression.
. To facilitate minimally invasive plate osteosynthesis (MIPO) by creating space for instruments.
. To reduce the risk of stress shielding by allowing more physiological load transfer to the bone.

Correct Answer & Explanation

. To prevent gapping on the far (trans) cortex when the plate is tightened, ensuring interfragmentary compression.

Explanation

Correct Answer: CPre-bending a conventional plate, particularly for transverse or short oblique fractures, is a critical technique to achieve effective interfragmentary compression across the entire fracture plane. When the plate is slightly pre-bent away from the bone at the fracture site, tightening the screws on either side pulls the plate flat against the bone. This action drives the fracture fragments together, creating compression on both the near and, crucially, the far (trans) cortex. Without pre-bending, tightening the screws would primarily compress the near cortex, potentially causing the far cortex to gap open, leading to an unstable construct and impaired healing.Option A is incorrect:Pre-bending is done to enhance compression and absolute stability, which increases stiffness, not reduces it.Option B is incorrect:Screw purchase is primarily determined by screw length, diameter, and bone quality, not plate pre-bending.Option D is incorrect:Pre-bending is a technique for open plating to achieve compression, not specifically for MIPO.Option E is incorrect:Pre-bending is about achieving compression, not directly reducing stress shielding. Rigid compression constructs can still cause stress shielding.

Question 1797

Topic: 2. Trauma

A 28-year-old male sustains a long oblique fracture of the midshaft humerus. After achieving interfragmentary compression with two lag screws, a plate is applied to the lateral aspect of the humerus. What is the primary biomechanical role of this plate in this specific construct?

. To provide additional interfragmentary compression across the fracture site.
. To act as a buttress, preventing axial collapse of the fracture fragments.
. To bridge the comminuted segment, promoting relative stability.
. To neutralize bending, torsional, and shear forces acting on the lag screws.
. To apply tension across the fracture site, promoting distraction osteogenesis.

Correct Answer & Explanation

. To neutralize bending, torsional, and shear forces acting on the lag screws.

Explanation

Correct Answer: DWhen lag screws are used to achieve interfragmentary compression in an oblique or spiral fracture, they provide absolute stability against shear forces. However, lag screws alone are weak against bending and torsional forces. A 'neutralization plate' is applied over the lag screws to protect them from these bending, torsional, and shear stresses that would otherwise cause the lag screws to fail or the fracture to displace. The plate 'neutralizes' these forces, allowing the lag screws to maintain their interfragmentary compression and promote primary bone healing.Option A is incorrect:The lag screws already provide the primary interfragmentary compression. The plate's role is not to add more compression but to protect the existing compression.Option B is incorrect:Buttress plates are typically used in metaphyseal or articular fractures to prevent axial collapse or displacement of fragments, not for diaphyseal oblique fractures fixed with lag screws.Option C is incorrect:Bridging plates are used for comminuted fractures where anatomical reduction and compression are not feasible, promoting relative stability. This scenario describes absolute stability with lag screws.Option E is incorrect:Tension band principles convert tensile forces into compression and are used for specific eccentric loading fractures (e.g., olecranon), not for protecting lag screws.

Question 1798

Topic: 2. Trauma
A 40-year-old male presents with a Gustilo-Anderson Type IIIA open fracture of the midshaft tibia. He has significant soft tissue loss and contamination. While considering definitive fixation, which of the following is a relative contraindication for immediate minimally invasive plate osteosynthesis (MIPO) in this scenario?
. The fracture is a simple transverse pattern.
. The patient is a polytrauma victim requiring rapid stabilization.
. The presence of significant soft tissue stripping and contamination.
. The need for a long working length to promote secondary healing.
. The fracture is located in the distal third of the tibia.

Correct Answer & Explanation

. The presence of significant soft tissue stripping and contamination.

Explanation

Minimally invasive plate osteosynthesis (MIPO) is designed to preserve soft tissue and periosteal blood supply, which is beneficial for fracture healing. However, in an open fracture with significant soft tissue stripping and contamination (Gustilo-Anderson Type IIIA), direct visualization of the fracture site is often critical for thorough debridement, irrigation, and assessment of fracture geometry and contamination. Attempting MIPO in such a compromised environment might hinder adequate debridement, increase the risk of infection, and potentially worsen the soft tissue envelope. In these cases, initial external fixation followed by delayed definitive fixation is often preferred.

Question 1799

Topic: 2. Trauma

A 50-year-old female sustains a transverse fracture of the olecranon. You decide to fix this using a tension band construct. What is the fundamental biomechanical principle underlying the use of a tension band in this specific fracture?

. To provide absolute stability by eliminating all micromotion at the fracture site.
. To convert tensile forces on the posterior aspect of the olecranon into compressive forces across the fracture site.
. To bridge the comminuted fracture fragments, promoting relative stability.
. To buttress the articular surface, preventing collapse of the fragments.
. To neutralize torsional forces acting on the ulna.

Correct Answer & Explanation

. To convert tensile forces on the posterior aspect of the olecranon into compressive forces across the fracture site.

Explanation

Correct Answer: BThe tension band principle is most effectively applied to eccentric loading fractures where one side is under tension and the other under compression during physiological loading. The olecranon is a classic example: during elbow flexion, the triceps pulls on the olecranon, creating tensile forces on its posterior (subcutaneous) surface. A tension band construct (typically K-wires and a figure-of-eight wire, or sometimes a small plate) is placed on this tension side. As the elbow flexes, the tension band converts these tensile forces into compressive forces across the fracture site, thus stabilizing the fracture and promoting healing.Option A is incorrect:While it provides stability, the primary mechanism is force conversion, not simply eliminating all micromotion, which is often the goal of absolute stability with lag screws or DCPs.Option C is incorrect:Bridging is for comminuted fractures where anatomical reduction is not possible or desired. The olecranon fracture is typically reduced anatomically.Option D is incorrect:Buttressing is for articular fractures to prevent collapse under axial load, not the primary mechanism for an olecranon tension band.Option E is incorrect:While it contributes to overall stability, the primary principle is the conversion of tensile forces, not solely neutralizing torsion.

Question 1800

Topic: 2. Trauma

A 30-year-old male sustains a simple transverse midshaft femoral fracture. The surgeon decides to treat this with an intramedullary (IM) nail. If plate fixation were considered as an alternative, what is the primary biomechanical advantage of an IM nail over a plate for this specific diaphyseal fracture?

. IM nails provide absolute stability, eliminating all micromotion at the fracture site.
. IM nails are inherently stiffer in bending and torsion than plates.
. IM nails provide central load-sharing, reducing eccentric loading and stress shielding.
. Plates require extensive soft tissue stripping, which is avoided with IM nailing.
. IM nails promote primary bone healing, whereas plates always lead to secondary healing.

Correct Answer & Explanation

. IM nails provide central load-sharing, reducing eccentric loading and stress shielding.

Explanation

Correct Answer: CFor diaphyseal fractures, intramedullary nails are biomechanically superior to plates primarily because they provide central load-sharing. The nail is placed within the medullary canal, close to the neutral axis of the bone. This allows the nail to share the physiological load with the bone more efficiently, reducing the eccentric loading seen with plates (which are external to the bone). This central load-sharing can lead to less stress shielding and more physiological loading of the healing bone. While soft tissue preservation (Option D) is also an advantage of nailing, the central load-sharing is the fundamental biomechanical superiority for diaphyseal fractures.Option A is incorrect:IM nails typically provide relative stability, allowing for controlled micromotion and promoting secondary bone healing. Absolute stability is not their primary mechanism.Option B is incorrect:While IM nails are very strong, their stiffness relative to plates depends on many factors (nail diameter, plate size, working length). The primary advantage ishowthey bear load, not necessarily always being stiffer in absolute terms.Option D is incorrect:While IM nailing often involves less soft tissue stripping than traditional open plating, this is a surgical technique advantage, not a fundamental biomechanical one.Option E is incorrect:IM nails typically promote secondary bone healing. Plates can achieve either primary (with absolute stability) or secondary (with relative stability/bridging) healing, depending on the construct.

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