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2. Trauma MCQs

Practice Set 62 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 1221

Topic: 2. Trauma

A 60-year-old male undergoes antegrade intramedullary nailing for a mid-shaft femoral fracture. Post-operatively, he complains of persistent pain over the greater trochanter. Radiographs confirm that the proximal end of the nail protrudes approximately 1 cm above the tip of the greater trochanter. What is the most likely biomechanical cause of his pain?

. Increased stress shielding of the femoral neck due to the long nail.
. Reduced rotational stability of the nail within the medullary canal.
. Impacting the greater trochanteric bursa and surrounding soft tissues, causing irritation.
. Preventing adequate reaming of the distal canal during surgery.
. Facilitating easier subsequent implant removal due to accessibility.

Correct Answer & Explanation

. Impacting the greater trochanteric bursa and surrounding soft tissues, causing irritation.

Explanation

Correct Answer: CThe correct answer is C. A common complication of an intramedullary nail that is too long or improperly seated proximally is its protrusion beyond the tip of the greater trochanter. Biomechanically, this protruding end acts as a mechanical irritant. It can impinge on the greater trochanteric bursa and surrounding soft tissues (e.g., gluteal tendons), leading to significant pain, inflammation, and potentially greater trochanteric bursitis. This is a well-recognized cause of postoperative discomfort and often necessitates nail removal.Option A is incorrect. While stress shielding can occur, nail protrusion itself is not the primary mechanism for increased stress shielding of the femoral neck. Stress shielding is related to the stiffness of the implant relative to the bone.Option B is incorrect. Nail protrusion does not directly reduce the rotational stability of the nail within the medullary canal; rotational stability is primarily provided by interlocking screws and canal fill.Option D is incorrect. The length of the nail and its seating are determined after reaming, so protrusion is not a cause of inadequate distal reaming.Option E is incorrect. While a protruding nail might be more accessible, the primary biomechanical consequence is pain and irritation, not ease of removal.

Question 1222

Topic: 2. Trauma

A 40-year-old male sustains a comminuted subtrochanteric femoral fracture. The surgeon chooses a reconstruction (recon) intramedullary nail. What is the primary biomechanical rationale for using a recon nail design in this specific fracture pattern compared to a standard femoral shaft nail?

. Recon nails are inherently stronger in bending and torsion.
. Recon nails promote faster healing of the shaft fracture.
. Recon nails provide multi-planar locking in the femoral head/neck, offering superior stability to the proximal fragment.
. Recon nails are designed for unreamed insertion only, preserving endosteal blood supply.
. Recon nails have a lower risk of infection due to their specific design.

Correct Answer & Explanation

. Recon nails provide multi-planar locking in the femoral head/neck, offering superior stability to the proximal fragment.

Explanation

Correct Answer: CThe correct answer is C. Subtrochanteric fractures are complex, often involving significant comminution of the proximal femur, making stable fixation of the proximal fragment challenging. Standard femoral shaft nails are primarily designed for diaphyseal stabilization and offer limited or inadequate fixation for the proximal fragment in subtrochanteric fractures. Reconstruction (recon) nails are specifically designed with a unique proximal locking configuration, typically involving two or three screws that diverge into the femoral head and neck. This multi-planar locking provides enhanced stability to the proximal fragment, resisting collapse, rotation, and cutout, which is crucial for these demanding fracture patterns. This dual-stability (proximal fragment and shaft) is the key biomechanical advantage.Option A is incorrect. While recon nails are robust, their primary advantage isn't inherently greater bending/torsional strength of the nail body itself, but rather the superior fixation of the proximal fragment.Option B is incorrect. Faster healing is a biological outcome influenced by many factors, not a direct biomechanical advantage of the recon nail design over a standard nail.Option D is incorrect. Recon nails can be used with both reamed and unreamed techniques, depending on the specific nail system and surgeon preference.Option E is incorrect. The risk of infection is generally similar between different IM nail designs and is more influenced by surgical technique and patient factors.

Question 1223

Topic: 2. Trauma

A 32-year-old male sustains a distal tibia fracture with significant metaphyseal comminution and a wide medullary canal proximally. The surgeon plans for antegrade intramedullary nailing. To improve nail centralization and stability in the wide metaphyseal region, the surgeon decides to use a 'blocking screw' (Poller screw). What is the primary biomechanical function of this blocking screw?

. To prevent nail migration out of the bone.
. To increase the ultimate strength of the nail material.
. To guide the nail into a desired position within a wide canal, improving fit and stability.
. To facilitate earlier weight-bearing in unstable fractures.
. To reduce the risk of infection by occupying empty space.

Correct Answer & Explanation

. To guide the nail into a desired position within a wide canal, improving fit and stability.

Explanation

Correct Answer: CThe correct answer is C. Blocking screws, also known as Poller screws, are placed adjacent to the intramedullary nail in the medullary canal. Biomechanically, their primary purpose is to reduce the effective width of the canal in areas where it is excessively wide (e.g., metaphyseal fractures or large canals). This helps to center the nail, improve bone-implant contact, and guide the nail into a desired position, thereby increasing bending and torsional stability and reducing malalignment. They 'block' unwanted motion of the nail within the wide canal, ensuring better load transfer and stability.Option A is incorrect. While they contribute to overall stability, preventing nail migration is primarily achieved by proper nail length and interlocking screws.Option B is incorrect. Blocking screws do not alter the intrinsic material properties or ultimate strength of the nail.Option D is incorrect. While improved stability can contribute to earlier weight-bearing, that is an indirect effect, not the primary biomechanical function of the screw itself.Option E is incorrect. There is no biomechanical evidence that blocking screws reduce infection risk by occupying empty space.

Question 1224

Topic: 2. Trauma

A 25-year-old male undergoes intramedullary nailing for a mid-shaft femoral fracture. Post-operatively, a lateral radiograph reveals that the nail has a sagittal curvature that does not perfectly match the natural anterior bow of the femur, leading to cortical impingement at the anterior cortex proximally and posterior cortex distally. This mismatch can lead to what biomechanical phenomenon?

. Increased rotational stability of the construct.
. Reduced risk of periprosthetic fracture.
. The 'windshield wiper effect' and potential for malunion.
. Enhanced load sharing between the nail and the bone.
. Easier removal of the implant in the future.

Correct Answer & Explanation

. The 'windshield wiper effect' and potential for malunion.

Explanation

Correct Answer: CThe correct answer is C. Long bones, such as the femur and tibia, have natural physiological curvatures (e.g., anterior bow of the femur, anterior apex recurvatum of the tibia). Intramedullary nails are designed with specific curvatures to match these anatomical bows. If the nail's curvature does not precisely match the bone's, it can lead to cortical impingement (as described in the vignette) and a phenomenon known as the 'windshield wiper effect.' This describes the cyclical angulation or toggling motion of the intramedullary nail within the medullary canal, particularly at its ends or at points of impingement. This motion can lead to irritation of the bone, endosteal erosion, pain, and potentially contribute to delayed union or nonunion due to excessive or uncontrolled motion, and can also lead to malunion (e.g., procurvatum or recurvatum).Option A is incorrect. Cortical impingement and the windshield wiper effect indicate insufficient stability and poor fit, which would likelydecreaserotational stability.Option B is incorrect. Cortical impingement creates stress risers, whichincreasethe risk of periprosthetic fracture, not reduce it.Option D is incorrect. Poor nail fit and impingement disrupt optimal load sharing and can lead to concentrated stresses rather than enhanced load sharing.Option E is incorrect. A nail that is poorly seated or causes impingement can be more difficult to remove due to bone overgrowth or binding.

Question 1225

Topic: 2. Trauma

A 68-year-old female with a history of diabetes and peripheral vascular disease sustains an open, comminuted proximal tibia fracture (AO/OTA 41-C2). The surgeon plans for antegrade intramedullary nailing. What is the most significant biomechanical challenge associated with achieving stable fixation of the proximal fragment in this specific fracture pattern?

. The risk of superior gluteal artery injury during nail insertion.
. The difficulty in achieving sufficient purchase for locking screws in the wide, often osteoporotic, metaphyseal bone.
. The increased risk of radial nerve palsy during distal locking.
. The high incidence of implant migration into the knee joint.
. The inability to achieve rotational stability due to the nail's design.

Correct Answer & Explanation

. The difficulty in achieving sufficient purchase for locking screws in the wide, often osteoporotic, metaphyseal bone.

Explanation

Correct Answer: BThe correct answer is B. Antegrade nailing of proximal tibia fractures is biomechanically challenging. The proximal tibia has a wide medullary canal, and the bone in the metaphyseal region is primarily cancellous and often osteoporotic, especially in older patients or those with comorbidities like diabetes. This makes it difficult to achieve sufficient and stable purchase for the proximal interlocking screws. Poor screw purchase can lead to screw pullout, loss of reduction (particularly in the coronal plane, leading to varus or valgus malalignment), and construct failure. Modern proximal tibia nails often incorporate multiple, converging, or divergent locking screws, sometimes in multiple planes, and include features like blade designs or expanded proximal diameters to enhance stability in this region.Option A (superior gluteal artery injury) is a risk associated with femoral nailing, not tibial nailing.Option C (radial nerve palsy) is a risk associated with humeral nailing, not tibial nailing.Option D (implant migration into the knee joint) can occur if the nail is too long or improperly seated, but the primary biomechanical challenge forfixationof the proximal fragment is screw purchase.Option E is incorrect. While challenging, modern nail designs with multi-planar locking options are specifically developed to achieve rotational stability in these fractures.

Question 1226

Topic: 2. Trauma

A 45-year-old male sustains a comminuted distal femur fracture (33-C3) secondary to a high-energy trauma. You opt for open reduction and internal fixation with a locking plate. Based on the provided case, what is the primary biomechanical advantage of a locking plate construct in this specific fracture pattern?

. It provides increased interfragmentary compression compared to conventional plates.
. It allows for earlier weight-bearing due to absolute stability at the fracture site.
. It acts as an internal fixator, creating a fixed-angle construct that bypasses the need for plate-bone friction.
. It primarily functions as a tension band to neutralize bending forces.
. It significantly reduces the risk of stress shielding due to its compliant nature.

Correct Answer & Explanation

. It acts as an internal fixator, creating a fixed-angle construct that bypasses the need for plate-bone friction.

Explanation

Correct Answer: CIn highly comminuted fractures, such as a 33-C3 distal femur fracture, traditional plate-bone friction (as seen in conventional Dynamic Compression Plates - DCPs) is compromised due to bone loss or poor cortical contact. Locking plates create a fixed-angle construct where the threaded screw heads lock directly into the plate. This transforms the plate-screw interface into a rigid unit, effectively creating an 'internal fixator' or 'extramedullary splint' that functions independently of plate-bone compression. This mechanism preserves periosteal blood supply and promotes indirect healing (callus formation), which is desirable for comminuted fractures. Options A and B are incorrect because interfragmentary compression is not the primary mechanism in bridging comminution, and while locking plates offer stability, 'absolute stability' isn't always achievable or desirable in comminuted fractures where relative stability is preferred. Option D is incorrect as tension band principles apply differently and are not the primary function in this context. Option E is incorrect because locking plates typically increase, rather than reduce, stress shielding due to their rigid construct.

Question 1227

Topic: 2. Trauma

A 38-year-old male presents with a simple transverse midshaft tibia fracture. During open reduction and internal fixation with a Dynamic Compression Plate (DCP), the surgeon aims to achieve interfragmentary compression. Which of the following statements accurately describes the 'loading' or 'eccentric' drilling technique used for this purpose?

. The drill hole is placed centrally in the oval hole to maximize screw purchase.
. The drill hole is placed at the end of the oval hole furthest from the fracture to pull fragments together.
. The drill hole is placed at the end of the oval hole closest to the fracture to create compression upon screw tightening.
. Eccentric drilling is only performed in cancellous bone to prevent screw pull-out.
. The technique primarily aims to provide neutralization rather than compression.

Correct Answer & Explanation

. The drill hole is placed at the end of the oval hole closest to the fracture to create compression upon screw tightening.

Explanation

Correct Answer: CFor dynamic compression using a DCP, the drill hole is intentionally placed eccentrically at the end of the oval hole that is closest to the fracture line. As the screw is tightened, its spherical head slides down the inclined plane of the oval hole. This sliding motion pulls the bone fragment towards the fracture site, thereby generating interfragmentary compression across the fracture. This compression is crucial for achieving absolute stability and promoting primary bone healing. Option A is incorrect because central placement provides no compression. Option B is incorrect as placing the drill hole furthest from the fracture would pull the fragment away, causing distraction. Option D is incorrect; eccentric drilling is a technique for cortical bone. Option E is incorrect; the primary aim of this specific technique is to achieve compression, not neutralization (though a DCP can also be used for neutralization).

Question 1228

Topic: 2. Trauma

An 80-year-old female with a history of severe osteoporosis presents with a comminuted distal femur fracture. The surgeon is considering internal fixation. What is a significant disadvantage of using a conventional Dynamic Compression Plate (DCP) for internal fixation in a patient with osteopenic bone?

. It provides excessive stress shielding, leading to cortical hypertrophy.
. The screw pull-out strength is significantly reduced due to compromised bone-screw interface friction.
. It promotes undesirable relative stability, hindering primary bone healing.
. The plate contour cannot be adequately matched to the bone surface, leading to gaps.
. It typically requires a larger incision compared to modern locking plates.

Correct Answer & Explanation

. The screw pull-out strength is significantly reduced due to compromised bone-screw interface friction.

Explanation

Correct Answer: BConventional DCPs rely heavily on plate-bone friction and interfragmentary compression for stability. In osteopenic bone, the bone quality around the screw threads is poor, leading to significantly reduced screw pull-out strength. The screws may strip out, or the plate may not achieve adequate purchase or compression, leading to early construct failure. This is a major disadvantage, making conventional plates less suitable for osteoporotic bone. Locking plates are generally preferred in osteopenic bone due to their fixed-angle stability, which is independent of plate-bone friction or bone quality. Option A is incorrect; while stress shielding can occur, the immediate concern in osteopenia with DCPs is the poor bone-screw interface. Option C is incorrect; DCPs aim for absolute stability. Option D is incorrect; plate contouring is a general challenge, not specific to osteopenia. Option E is not a primary biomechanical disadvantage.

Question 1229

Topic: 2. Trauma

A resident is reviewing the fundamental principles of plate fixation. They ask about the primary biomechanical difference between a screw in a conventional plate (DCP) and a locking screw in a locking plate (LCP). Which explanation best describes this difference?

. Conventional screws provide better resistance to torsional forces.
. Locking screws have a smaller core diameter, increasing ductility.
. Conventional screws rely on plate-bone friction for stability, while locking screws create a fixed-angle construct with the plate.
. Locking screws are exclusively used in cancellous bone due to their larger thread pitch.
. Conventional screws are designed for self-tapping, whereas locking screws are not.

Correct Answer & Explanation

. Conventional screws rely on plate-bone friction for stability, while locking screws create a fixed-angle construct with the plate.

Explanation

Correct Answer: CThe fundamental difference lies in how each screw type achieves stability. Conventional screws (used in DCPs) have a smooth head that compresses the plate against the bone. Stability is achieved through plate-bone friction and interfragmentary compression. Locking screws, on the other hand, have a threaded head that screws directly into corresponding threads within the plate hole. This creates a rigid, fixed-angle construct where the screw and plate act as a single unit, independent of plate-bone friction. This fixed-angle stability is particularly advantageous in osteopenic bone or comminuted fractures where plate-bone compression is suboptimal. Option A is incorrect; locking constructs generally offer superior resistance to torsional forces. Option B is incorrect; screw core diameter varies by design, not fundamentally defining the difference. Option D is incorrect; locking screws are used in both cortical and cancellous bone. Option E is incorrect; both types can be self-tapping depending on design.

Question 1230

Topic: 2. Trauma

A resident is preparing for an orthopedic board examination and is asked to differentiate between 'absolute stability' and 'relative stability' in the context of fracture fixation with plates. Which statement best describes this distinction?

. Absolute stability is achieved with locking plates, while relative stability is only possible with external fixation.
. Absolute stability allows for no micromotion at the fracture site, promoting primary bone healing; relative stability allows controlled micromotion, promoting secondary bone healing.
. Relative stability is only suitable for pediatric fractures, whereas absolute stability is for adults.
. Absolute stability requires a significantly longer period of non-weight bearing compared to relative stability.
. Relative stability utilizes biodegradable plates, while absolute stability uses permanent implants.

Correct Answer & Explanation

. Absolute stability allows for no micromotion at the fracture site, promoting primary bone healing; relative stability allows controlled micromotion, promoting secondary bone healing.

Explanation

Correct Answer: BAbsolute stability, typically achieved with interfragmentary compression (e.g., lag screws, DCPs with compression), aims to eliminate all micromotion at the fracture site. This environment promotes primary bone healing, which occurs without visible callus formation. Relative stability, achieved with methods like bridging plates (locking or conventional), intramedullary nails, or external fixators, allows for controlled, limited micromotion at the fracture site. This micromotion stimulates callus formation and secondary bone healing. Both are valid approaches depending on the fracture pattern, location, and biological environment. Option A is incorrect; absolute stability can be achieved with conventional plates and lag screws, and relative stability can be achieved with bridging plates. Option C is incorrect; both types of stability are used in both pediatric and adult fractures. Option D is incorrect; weight-bearing protocols depend on the specific fracture and patient, not solely on the type of stability. Option E is incorrect; implant type (biodegradable vs. permanent) is not the defining factor for absolute vs. relative stability.

Question 1231

Topic: 2. Trauma

A 40-year-old male with a comminuted tibia fracture (42-C2) undergoes open reduction and internal fixation with a bridging locking plate. Three weeks postoperatively, he presents with increasing pain, swelling, and radiographs show loss of reduction with plate bending. Which of the following factors would most likely lead to this early failure of the plate-screw construct?

. Use of titanium instead of stainless steel.
. Excessive number of screws in the main fragments.
. Inadequate working length of the plate, making the construct too stiff.
. Improper reduction and persistent gapping at the fracture site.
. Early mobilization without weight-bearing.

Correct Answer & Explanation

. Improper reduction and persistent gapping at the fracture site.

Explanation

Correct Answer: DImproper reduction leading to persistent gapping and instability at the fracture site is a primary cause of early implant failure (pull-out, bending failure, loosening). If the fracture is not adequately reduced, the plate is subjected to excessive and repetitive forces that it was not designed to withstand, leading to premature fatigue or pull-out. In a comminuted fracture, if the bridging plate is spanning a large, unreduced gap, the plate itself bears all the load, leading to high stresses and early mechanical failure. While early weight-bearing (if not indicated) can contribute, persistent fracture gap/motion directly loads the plate in a way that leads to fatigue and failure. Option A (material choice) is less critical for early failure than surgical technique. Option B (excessive screws) would shorten the working length, making it too stiff, which can hinder secondary healing but isn't the primary cause ofearly mechanical failurein a comminuted bridging scenario. Option C (inadequate working length) can lead to stress shielding or delayed healing, but a persistent gap is a more direct cause of acute mechanical failure. Option E (early mobilization) could contribute but is secondary to the fundamental mechanical instability from poor reduction.

Question 1232

Topic: 2. Trauma

A 55-year-old male presents with a displaced intra-articular calcaneal fracture. You plan for open reduction and internal fixation. Which screw characteristic is most crucial for achieving interfragmentary compression across the fracture fragments?

. Fully threaded design with uniform pitch
. Partially threaded design with a gliding hole in the near cortex
. Self-tapping flutes on the screw tip
. Larger core diameter than thread diameter
. Cannulated shaft for K-wire guidance

Correct Answer & Explanation

. Partially threaded design with a gliding hole in the near cortex

Explanation

Correct Answer: BInterfragmentary compression, the hallmark of lag screw technique, is achieved when the screw threads purchase only in the far fragment, while the near fragment is allowed to 'lag' or slide along the smooth, unthreaded portion of the screw shaft. This requires a partially threaded screw and a gliding hole in the near cortex, which must be larger than the major (thread) diameter of the screw, allowing the screw head to draw the near fragment towards the far fragment as it tightens. A fully threaded screw, without a gliding hole, would fix both fragments equally and not generate compression.

Question 1233

Topic: 2. Trauma

In the context of fracture fixation, what is the primary biomechanical advantage of using a locking screw in a locking plate system compared to a non-locking cortical screw?

. Increased interfragmentary compression at the fracture site
. Greater pullout strength in osteoporotic bone
. Ability to create a dynamic compression unit
. Reduced need for precise plate contouring
. Enhanced screw angulation flexibility

Correct Answer & Explanation

. Greater pullout strength in osteoporotic bone

Explanation

Correct Answer: BLocking screws thread into the plate, creating a fixed-angle construct. This effectively turns the screw-plate interface into a 'fixed-angle internal fixator', where the strength of the construct is not dependent on screw purchase into the near cortex, but rather on the angular stability created by the locked threads. This provides significantly improved pullout strength, especially beneficial in osteoporotic bone where traditional screw purchase is compromised. While reduced need for precise contouring is an advantage, the primary biomechanical benefit is the enhanced stability and pullout resistance due to the fixed-angle construct, rather than direct interfragmentary compression (which locking screws often limit).

Question 1234

Topic: 2. Trauma

What is the primary function of a position screw in fracture fixation?

. To generate interfragmentary compression between two fragments.
. To maintain the relative position of two fragments without generating compression.
. To provide angular stability in conjunction with a locking plate.
. To ream a channel for subsequent lag screw insertion.
. To act as a buttress to prevent displacement under axial load.

Correct Answer & Explanation

. To maintain the relative position of two fragments without generating compression.

Explanation

Correct Answer: BA position screw is used to hold two bone fragments together in a fixed position without actively compressing them. Unlike a lag screw, which specifically generates interfragmentary compression by threading only the far cortex (or having a gliding hole in the near cortex), a position screw threads into both the near and far cortices, or into both fragments, thus holding them at a fixed distance from each other. This is often used in syndesmotic fixation (e.g., tibiofibular syndesmosis) where excessive compression could lead to cartilage damage or loss of motion.

Question 1235

Topic: 2. Trauma

Which of the following scenarios is most appropriate for the use of a fully threaded cortical screw in a lag fashion?

. Fixation of a comminuted metaphyseal fracture where a locking plate is used.
. Stabilization of a syndesmotic injury where slight gapping is acceptable.
. Fixation of a spiral diaphyseal fracture of the tibia, requiring interfragmentary compression.
. Primary fixation of a medial malleolus fracture in osteoporotic bone.
. Anchoring a tendon graft into a bone tunnel during rotator cuff repair.

Correct Answer & Explanation

. Fixation of a spiral diaphyseal fracture of the tibia, requiring interfragmentary compression.

Explanation

Correct Answer: CA fully threaded cortical screw can be used in a lag fashion to achieve interfragmentary compression. To do this, a gliding hole (larger than the major diameter of the screw) must be drilled in the near cortex, and a smaller thread hole (matching the core diameter) drilled and tapped in the far cortex. This technique is commonly used for oblique or spiral diaphyseal fractures where strong compression is desired. For example, a spiral tibial fracture often benefits from lag screw fixation across the fracture line. Syndesmotic injuries typically use position screws, locking plates are often used for comminuted fractures, and specific headless or cannulated screws are preferred for malleolar or tendon anchor fixation.

Question 1236

Topic: 2. Trauma

A surgeon is considering the use of headless compression screws for a scaphoid fracture fixation. What is the primary advantage of a headless design in this application?

. Increased fatigue strength due to larger core diameter.
. Prevention of soft tissue irritation and ability to be fully buried within bone.
. Enhanced rotational stability in comminuted fractures.
. Superior resistance to shear forces compared to headed screws.
. Faster insertion time due to self-drilling features.

Correct Answer & Explanation

. Prevention of soft tissue irritation and ability to be fully buried within bone.

Explanation

Correct Answer: BHeadless compression screws are particularly advantageous in articular and periarticular fractures (like the scaphoid) because their design allows them to be completely buried beneath the cartilage or cortical surface. This eliminates prominence of the screw head, preventing soft tissue irritation, damage to articular cartilage, and making them suitable for intra-articular placement. They also provide compression across the fracture line due to differential pitch (distal threads have a coarser pitch than proximal threads, pulling the fragments together).

Question 1237

Topic: 2. Trauma

When applying a dynamic compression plate (DCP), the 'load' or 'eccentric' hole is designed to achieve what specific biomechanical effect?

. To provide angular stability by locking the screw head to the plate.
. To allow for variable angle screw insertion for greater flexibility.
. To convert axial stress into interfragmentary compression at the fracture site.
. To act as a neutralization plate, shielding lag screws.
. To distribute bone grafting material evenly around the fracture.

Correct Answer & Explanation

. To convert axial stress into interfragmentary compression at the fracture site.

Explanation

Correct Answer: CThe dynamic compression plate (DCP) utilizes a specific elliptical screw hole design. When a screw is inserted eccentrically (at one end of the ellipse) and tightened, the spherical undersurface of the screw head slides along the inclined plane of the hole. This causes the bone fragment attached to that segment of the plate to translate towards the fracture site, generating interfragmentary compression across the fracture. This mechanism converts the tightening of the screw into axial compression at the fracture.

Question 1238

Topic: 2. Trauma

A patient presents with a severe osteoporotic distal radius fracture requiring plate fixation. Which type of screw-plate construct would offer the most stable fixation against pullout forces?

. Standard cortical screws in a dynamic compression plate.
. Standard cancellous screws in a limited contact dynamic compression plate.
. Lag screws used in conjunction with a neutralization plate.
. Locking screws in a volar locking plate.
. Headless compression screws in a buttress plate.

Correct Answer & Explanation

. Locking screws in a volar locking plate.

Explanation

Correct Answer: DIn osteoporotic bone, the bone quality is compromised, significantly reducing the pullout strength of traditional screws. Locking plates with locking screws create a fixed-angle construct, essentially acting as an internal fixator. The screws lock into the plate, and the strength of the construct comes from the rigidity of this screw-plate interface, rather than solely relying on the purchase of the screw threads in the often poor-quality bone. This provides superior stability and pullout resistance in osteoporotic bone compared to non-locking constructs.

Question 1239

Topic: 2. Trauma

A 45-year-old female undergoes bridge plating for a highly comminuted midshaft femur fracture. The surgeon purposefully leaves three screw holes empty over the fracture site. Biomechanically, how does increasing the plate's working length in this manner affect the construct?

. It increases the torsional stiffness of the construct.
. It decreases construct stiffness and promotes secondary bone healing.
. It increases the risk of plate failure due to elevated stress concentration at a single hole.
. It forces primary osteonal reconstruction by providing absolute stability.
. It minimizes micromotion at the fracture site.

Correct Answer & Explanation

. It decreases construct stiffness and promotes secondary bone healing.

Explanation

Increasing the working length of a bridge plate decreases its overall stiffness, allowing controlled micromotion. This relative stability promotes callus formation and secondary bone healing while reducing the risk of plate fatigue failure.

Question 1240

Topic: 2. Trauma

A surgeon exchanges a 10 mm solid intramedullary nail for a 12 mm solid intramedullary nail during preoperative templating for a femur fracture. According to the polar moment of inertia, how does this size increase affect the bending stiffness of the nail?

. Increases by approximately 20%.
. Increases by approximately 44%.
. Increases by approximately 100% (doubles).
. Increases by approximately 300%.
. Remains unchanged as bending stiffness is determined solely by the working length.

Correct Answer & Explanation

. Increases by approximately 100% (doubles).

Explanation

The bending stiffness of a solid cylinder is proportional to the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm increases the stiffness by a factor of (1.2)^4, which is approximately 2.07, meaning it roughly doubles.

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