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2. Trauma MCQs

Practice Set 78 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 1541

Topic: 2. Trauma

A 40-year-old male with a healing transverse femoral shaft fracture, initially fixed with a statically locked intramedullary nail, shows signs of delayed union. The surgeon decides to dynamize the nail. What is the primary biomechanical goal of this procedure in the context of a delayed union?

. To increase the overall bending stiffness of the implant-bone construct.
. To convert the fixation from relative stability to absolute stability.
. To increase axial load transfer and controlled interfragmentary compression across the fracture site.
. To reduce rotational forces at the fracture site, preventing malunion.
. To minimize stress shielding by replacing the nail with a less stiff implant.

Correct Answer & Explanation

. To increase axial load transfer and controlled interfragmentary compression across the fracture site.

Explanation

Correct Answer: CDynamization, typically achieved by removing one set of locking screws (often the static screws), converts a statically locked construct into one that allows for controlled axial micromotion and telescoping. The primary biomechanical goal in a delayed union is to increase axial load transfer and controlled interfragmentary compression across the fracture site. This controlled micromotion and compression, within the appropriate biological window of strain, stimulates callus formation and maturation, thereby promoting consolidation and accelerating healing. It addresses the issue of insufficient mechanical stimulation at the fracture site.Option A is incorrectbecause dynamization generally decreases, rather than increases, the overall stiffness of the construct by allowing axial motion.Option B is incorrectbecause dynamization moves the construct further away from absolute stability (which aims to eliminate motion) by allowing controlled motion.Option D is incorrectbecause dynamization primarily affects axial motion; rotational control is generally maintained by the remaining locking screws. The goal is not to reduce rotational forces but to allow axial loading.Option E is incorrectbecause dynamization aims to reduce stress shielding by allowing the bone to bear more load, but it does so by altering the locking configuration, not by replacing the nail with a less stiff implant.

Question 1542

Topic: 2. Trauma

During the insertion of an intramedullary nail for a mid-shaft femoral fracture, the surgeon emphasizes selecting a nail with an appropriate anterior bow. What is the primary biomechanical reason for matching the nail's curvature to the natural anatomical bow of the femur?

. To facilitate easier removal of the implant post-healing.
. To increase the ultimate tensile strength of the nail material.
. To optimize nail-bone contact, reduce stress concentrations, and enhance resistance to bending forces.
. To allow for multiplanar locking screws in the distal metaphysis.
. To minimize the risk of post-operative infection by reducing surgical time.

Correct Answer & Explanation

. To optimize nail-bone contact, reduce stress concentrations, and enhance resistance to bending forces.

Explanation

Correct Answer: CThe femur has a natural anterior bow. An intramedullary nail with an appropriate matching curvature is crucial for optimizing nail-bone contact along the entire length of the nail. This close fit minimizes stress concentrations at the nail-bone interface, reduces toggling within the canal, and maximizes the load-sharing capacity of the construct. By conforming to the bone's anatomy, it enhances the construct's resistance to bending forces and prevents potential stress risers that could lead to iatrogenic fracture (e.g., anterior cortical impingement during insertion) or implant failure.Option A is incorrectbecause while a well-seated nail might be easier to remove, this is not the primary biomechanical reason for matching the bow.Option B is incorrectbecause ultimate tensile strength is an intrinsic material property and is not influenced by the nail's curvature.Option D is incorrectbecause the anatomical bow primarily relates to the diaphyseal fit, not directly to the ability to place multiplanar locking screws in the metaphysis.Option E is incorrectbecause minimizing infection risk is a surgical/biological goal, not a direct biomechanical consequence of matching the nail's curvature.

Question 1543

Topic: 2. Trauma

A 38-year-old male presents with a comminuted proximal tibial fracture extending into the metaphysis. The medullary canal is significantly wide in this region. The surgeon decides to use 'blocking screws' (Poller screws) in conjunction with an intramedullary nail. What is the primary biomechanical purpose of these blocking screws?

. To increase the overall bending stiffness of the nail itself.
. To provide direct compression across the fracture site.
. To guide the nail into a desired central position within the wide medullary canal, improving alignment and nail-bone fit.
. To prevent proximal migration of the nail after insertion.
. To reduce stress shielding of the distal tibial diaphysis.

Correct Answer & Explanation

. To guide the nail into a desired central position within the wide medullary canal, improving alignment and nail-bone fit.

Explanation

Correct Answer: CBlocking screws, also known as Poller screws, are placed parallel and close to the intramedullary nail within the medullary canal. Their primary biomechanical purpose is to effectively narrow the canal and guide the nail into a specific, desired central position. This is particularly useful in wide metaphyseal regions or in fractures with significant displacement, where the nail might otherwise 'float' or be malpositioned. By centralizing the nail, blocking screws improve nail-bone fit, prevent malalignment (e.g., varus/valgus or procurvatum/recurvatum), enhance rotational control, and ensure better biomechanical load transfer across the fracture site.Option A is incorrectbecause blocking screws do not directly increase the intrinsic bending stiffness of the nail itself; they improve the stability of the nail-bone construct by optimizing nail position.Option B is incorrectbecause blocking screws do not provide direct compression across the fracture site in the manner of a lag screw.Option D is incorrectbecause while they contribute to overall stability, their primary role is guiding, not preventing migration, which is typically handled by proximal locking screws.Option E is incorrectbecause blocking screws are used locally at the fracture site or in the metaphysis to improve nail position, not to reduce stress shielding of a distant segment like the distal diaphysis.

Question 1544

Topic: 2. Trauma

A 28-year-old male sustains a long spiral femoral shaft fracture. The surgeon is concerned about potential rotational malunion. Which biomechanical characteristic of the intramedullary nail construct is most crucial for preventing this specific complication?

. The overall length of the intramedullary nail.
. The ultimate tensile strength of the nail material.
. Effective locking screws providing robust rotational control at both proximal and distal fragments.
. A low modulus of elasticity of the nail to promote load sharing.
. The use of a cannulated nail to facilitate accurate guidewire placement.

Correct Answer & Explanation

. Effective locking screws providing robust rotational control at both proximal and distal fragments.

Explanation

Correct Answer: CIn long spiral diaphyseal fractures, the fracture pattern itself offers very little inherent stability against rotation. Therefore, the rotational stability of the entire construct relies almost entirely on the locking screws. Effective locking screws, particularly those providing robust static fixation (e.g., at least two screws in different planes if possible) at both the proximal and distal ends of the nail, are paramount for preventing the bone fragments from rotating around the nail. Without adequate rotational control, the fragments can twist, leading to a rotational malunion, which is a significant functional impairment.Option A is incorrectbecause while nail length is important for overall stability and preventing stress risers, it does not directly provide rotational control; that is the role of the locking screws.Option B is incorrectbecause ultimate tensile strength relates to the material's resistance to breaking under tension, not its ability to prevent rotational motion of bone fragments.Option D is incorrectbecause a low modulus of elasticity promotes load sharing and reduces stress shielding, which is beneficial for healing, but it does not directly provide rotational stability. Rotational stability comes from the interlocking mechanism.Option E is incorrectbecause a cannulated design facilitates accurate surgical placement but does not inherently provide rotational control; the locking screws perform this function.

Question 1545

Topic: 2. Trauma

A 48-year-old male presents to the emergency department after a high-energy motor vehicle collision. Radiographs and CT scans reveal a closed Schatzker Type VI tibial plateau fracture with a significant diaphyseal extension into the proximal third of the tibia. The articular surface is severely comminuted, and there is a large metaphyseal defect. Initial assessment confirms no neurovascular compromise and no compartment syndrome. The patient is otherwise healthy. Which of the following initial management steps is most appropriate?

. A. Immediate open reduction and internal fixation (ORIF) with dual plating.
. B. Application of a spanning external fixator across the knee joint.
. C. Placement of a long leg cast for immobilization.
. D. Immediate retrograde intramedullary nailing with percutaneous articular screw fixation.
. E. Diagnostic arthroscopy followed by definitive fixation.

Correct Answer & Explanation

. B. Application of a spanning external fixator across the knee joint.

Explanation

Correct Answer: BFor high-energy, severely comminuted tibial plateau fractures with diaphyseal extension, especially those with significant soft tissue swelling or potential for compartment syndrome, initial management often involves damage control orthopedics. A spanning external fixator across the knee joint (B) provides temporary stabilization, restores length, and allows for soft tissue rest and swelling reduction before definitive fixation. This approach minimizes further soft tissue trauma and reduces the risk of infection and wound complications associated with immediate definitive ORIF in a compromised soft tissue envelope. Immediate ORIF with dual plating (A) or retrograde nailing (D) would be premature and carry high risks in this acute setting. A long leg cast (C) is inadequate for such an unstable, high-energy fracture. Diagnostic arthroscopy (E) is generally not indicated as an initial step for a severely comminuted fracture with diaphyseal extension, and definitive fixation should be delayed.

Question 1546

Topic: 2. Trauma

Following temporary external fixation for a Schatzker Type VI tibial plateau fracture with diaphyseal extension, the patient's soft tissues have improved. Preoperative planning reveals a significant posteromedial articular fragment and a long oblique diaphyseal component. The surgeon plans for a single-stage definitive fixation. Which surgical approach and fixation strategy is most appropriate for addressing both components?

. A. Anterolateral approach with a lateral locking plate for the plateau and antegrade intramedullary nail for the diaphysis.
. B. Medial approach with a medial buttress plate for the plateau and a retrograde intramedullary nail for the diaphysis.
. C. Combined anterolateral and posteromedial approaches for articular reduction, followed by a retrograde intramedullary nail for the diaphyseal extension.
. D. Single anterior approach with a hybrid external fixator.
. E. Dual plating (medial and lateral) for the entire fracture.

Correct Answer & Explanation

. C. Combined anterolateral and posteromedial approaches for articular reduction, followed by a retrograde intramedullary nail for the diaphyseal extension.

Explanation

Correct Answer: CA Schatzker Type VI fracture involves dissociation of the metaphysis and diaphysis from the articular block, often with significant posteromedial involvement. Addressing the posteromedial fragment typically requires a dedicated posteromedial approach for direct visualization and reduction. The anterolateral approach is standard for lateral plateau fragments. Therefore, combined anterolateral and posteromedial approaches (C) are often necessary to achieve anatomical articular reduction. For the diaphyseal extension, a retrograde intramedullary nail is an excellent choice as it provides rigid fixation of the shaft, allows for percutaneous or limited open reduction of the articular surface (often with rafting screws from the lateral plate), and avoids additional soft tissue stripping compared to extensive plating of the diaphysis. Option A is less ideal as an antegrade nail is not typically used for tibial shaft fractures, and a single anterolateral approach may miss the posteromedial fragment. Option B's medial approach alone is insufficient for a Type VI. Option D (hybrid external fixator) is usually for temporary or definitive fixation in highly compromised soft tissues, not typically for single-stage definitive internal fixation of both components. Option E (dual plating) is very invasive and carries high soft tissue risks for a long diaphyseal extension.

Question 1547

Topic: 2. Trauma

During definitive fixation of a Schatzker Type V tibial plateau fracture with a long diaphyseal extension, the surgeon opts for a retrograde intramedullary nail for the shaft component. Which of the following is a critical technical consideration when preparing the articular surface for nail insertion to prevent iatrogenic injury?

. A. Reaming the medullary canal to at least 2mm larger than the chosen nail diameter.
. B. Ensuring the entry portal is positioned anterior to the patellar tendon.
. C. Protecting the anterior cruciate ligament (ACL) insertion and avoiding damage to the intercondylar notch.
. D. Performing a prophylactic fibular osteotomy to facilitate nail insertion.
. E. Using a flexible guide wire to navigate around articular fragments.

Correct Answer & Explanation

. C. Protecting the anterior cruciate ligament (ACL) insertion and avoiding damage to the intercondylar notch.

Explanation

Correct Answer: CWhen performing retrograde intramedullary nailing for a tibial plateau fracture, the nail entry portal is typically created in the intercondylar notch. It is absolutely critical to protect the anterior cruciate ligament (ACL) insertion and avoid iatrogenic damage to the articular cartilage of the intercondylar notch (C). An improperly placed entry portal can lead to knee pain, chondral damage, and potential ACL insufficiency. Reaming (A) is for the shaft, not the articular entry. The entry portal is typically posterior to the patellar tendon, not anterior (B). Prophylactic fibular osteotomy (D) is sometimes done for reduction of the tibia, but not specifically for nail entry. A flexible guide wire (E) is standard, but theplacementof the entry portal is the key to preventing iatrogenic injury.

Question 1548

Topic: 2. Trauma

A 35-year-old male sustains a high-energy closed tibial plateau fracture (Schatzker Type IV) with a spiral diaphyseal extension. He undergoes ORIF of the plateau with a lateral locking plate and retrograde intramedullary nailing of the diaphyseal component. Two days post-operatively, he develops increasing pain, swelling, and paresthesias in the foot. On examination, he has pain with passive dorsiflexion of the toes and a weak dorsalis pedis pulse. Which of the following is the most appropriate immediate next step?

. A. Elevate the limb and apply ice packs.
. B. Administer intravenous pain medication and reassess in 4 hours.
. C. Perform emergent compartment pressure measurements.
. D. Order a Doppler ultrasound to assess vascular flow.
. E. Loosen all dressings and splints and observe.

Correct Answer & Explanation

. C. Perform emergent compartment pressure measurements.

Explanation

Correct Answer: CThe patient's symptoms (increasing pain, swelling, paresthesias, pain with passive stretch, and a weak dorsalis pedis pulse) are highly suggestive of acute compartment syndrome. This is a surgical emergency. The most appropriate immediate next step is to perform emergent compartment pressure measurements (C) to confirm the diagnosis. If pressures are elevated (typically within 30 mmHg of diastolic pressure or absolute pressure >30-40 mmHg), an emergent fasciotomy is indicated. Elevating the limb (A) can worsen compartment syndrome by reducing perfusion pressure. Administering pain medication (B) would mask symptoms and delay diagnosis. While a Doppler ultrasound (D) might be considered if a vascular injury is suspected, the clinical picture points more strongly to compartment syndrome. Loosening dressings (E) is a good initial step but insufficient if compartment syndrome is developing; direct pressure measurement is needed for definitive diagnosis.

Question 1549

Topic: 2. Trauma

For a Schatzker Type VI tibial plateau fracture with a large metaphyseal defect after reduction and fixation of the articular surface, what is the most appropriate strategy to address the bone void and promote healing?

. A. Rely solely on the stability of the internal fixation and allow for spontaneous bone regeneration.
. B. Fill the defect with autogenous cancellous bone graft from the iliac crest.
. C. Use a synthetic bone graft substitute (e.g., calcium phosphate cement) without additional biological augmentation.
. D. Apply a bone morphogenetic protein (BMP) directly to the defect without grafting.
. E. Perform a fibular strut graft for structural support.

Correct Answer & Explanation

. B. Fill the defect with autogenous cancellous bone graft from the iliac crest.

Explanation

Correct Answer: BLarge metaphyseal defects in tibial plateau fractures, especially high-energy ones like Schatzker Type VI, often require augmentation to prevent collapse and promote healing. Autogenous cancellous bone graft from the iliac crest (B) is considered the gold standard due to its osteoconductive, osteoinductive, and osteogenic properties. It provides structural support and biological stimulus for bone formation. Relying solely on fixation (A) risks collapse and nonunion. Synthetic bone graft substitutes (C) are osteoconductive but lack osteoinductive and osteogenic properties, making them less ideal for large defects without biological augmentation. BMP (D) is osteoinductive but typically used in conjunction with a carrier or graft. A fibular strut graft (E) provides structural support but is less effective for filling large cancellous defects and has donor site morbidity.

Question 1550

Topic: 2. Trauma

A 55-year-old obese patient with a Schatzker Type V tibial plateau fracture and a short diaphyseal extension is undergoing definitive fixation. The surgeon plans to use a lateral locking plate for the plateau and a separate medial plate for the diaphyseal extension. What is the primary biomechanical advantage of using a lateral locking plate with 'rafting screws' for the articular component?

. A. To provide absolute stability for primary bone healing.
. B. To prevent varus collapse of the lateral articular segment and support the subchondral bone.
. C. To reduce the risk of infection by minimizing soft tissue dissection.
. D. To allow for early weight-bearing without risk of hardware failure.
. E. To facilitate dynamic compression at the fracture site.

Correct Answer & Explanation

. B. To prevent varus collapse of the lateral articular segment and support the subchondral bone.

Explanation

Correct Answer: BIn tibial plateau fractures, especially those involving the lateral condyle, 'rafting screws' are subchondral screws placed parallel to the articular surface and perpendicular to the plate. Their primary biomechanical advantage is to prevent varus collapse of the lateral articular segment and provide direct support to the depressed or comminuted subchondral bone (B). This creates a stable 'raft' beneath the articular cartilage, maintaining reduction and preventing subsidence. While locking plates provide stability, rafting screws specifically address the articular depression. Absolute stability (A) is not the primary goal of rafting screws, and they don't directly reduce infection risk (C) or guarantee early weight-bearing (D) without risk. They are not designed for dynamic compression (E).

Question 1551

Topic: 2. Trauma

A 62-year-old female with osteoporosis sustains a Schatzker Type IV tibial plateau fracture with a short metaphyseal extension. Given her bone quality, which of the following fixation principles is most critical to ensure stable fixation and prevent hardware failure?

. A. Using a non-locking plate to allow for load sharing.
. B. Employing a minimally invasive plate osteosynthesis (MIPO) technique to preserve periosteal blood supply.
. C. Maximizing the number of locking screws in the metaphyseal fragments and ensuring bicortical purchase where possible.
. D. Prioritizing dynamic compression at the fracture site.
. E. Utilizing a short plate that spans only the articular component.

Correct Answer & Explanation

. C. Maximizing the number of locking screws in the metaphyseal fragments and ensuring bicortical purchase where possible.

Explanation

Correct Answer: CIn osteoporotic bone, screw pullout strength is significantly reduced. Therefore, for stable fixation, it is critical to maximize the number of locking screws in the metaphyseal fragments and ensure bicortical purchase where anatomically safe (C). Locking screws provide angular stability, and multiple points of fixation distribute stress over a larger area, increasing construct stiffness and resistance to pullout. Non-locking plates (A) rely on friction and compression, which are compromised in osteoporotic bone. MIPO (B) is important for soft tissue preservation but doesn't directly address bone quality. Dynamic compression (D) is less important than angular stability in osteoporotic metaphyseal fractures. A short plate (E) would be insufficient for a Type IV fracture with metaphyseal extension.

Question 1552

Topic: 2. Trauma
A 28-year-old male sustains a Gustilo-Anderson Type IIIB open tibial plateau fracture with a comminuted diaphyseal extension. After initial debridement and external fixation, the patient is scheduled for definitive fixation. What is the most appropriate definitive fixation strategy, considering the open nature and soft tissue compromise?
. Immediate open reduction and internal fixation with dual plating.
. Staged approach: further debridement, soft tissue coverage (e.g., free flap), followed by internal fixation (e.g., IMN or plate).
. Definitive external fixation with a circular frame.
. Primary closure of the wound over a reamed intramedullary nail.
. Non-weight bearing cast immobilization for 12 weeks.

Correct Answer & Explanation

. Staged approach: further debridement, soft tissue coverage (e.g., free flap), followed by internal fixation (e.g., IMN or plate).

Explanation

A Gustilo-Anderson Type IIIB open fracture signifies significant soft tissue loss and contamination, often requiring reconstructive soft tissue coverage. The most appropriate strategy is a staged approach: repeated debridements, followed by definitive soft tissue coverage (e.g., local or free flap) once the wound is clean and viable. Only after successful soft tissue coverage and resolution of infection risk should definitive internal fixation (such as an intramedullary nail for the diaphysis and/or plates for the plateau) be performed.

Question 1553

Topic: Lower Extremity Trauma

Following successful ORIF of a Schatzker Type VI tibial plateau fracture with diaphyseal extension, the patient is 6 weeks post-operative. Radiographs show good alignment and early callus formation, but the articular surface remains at risk for subsidence. What is the most appropriate weight-bearing protocol at this stage?

. A. Full weight-bearing as tolerated.
. B. Partial weight-bearing with crutches, gradually increasing over 4-6 weeks.
. C. Non-weight bearing for an additional 6 weeks.
. D. Touch-down weight-bearing only, with strict avoidance of axial load.
. E. Immediate return to pre-injury activity level.

Correct Answer & Explanation

. C. Non-weight bearing for an additional 6 weeks.

Explanation

Correct Answer: CFor complex tibial plateau fractures, especially Schatzker Type VI, the articular surface and metaphyseal bone require prolonged protection from axial loading to prevent subsidence, loss of reduction, and hardware failure. Even with good fixation and early callus, the bone is not fully healed at 6 weeks. Non-weight bearing for an additional 6 weeks (C), typically until 10-12 weeks post-op, is a common and safe protocol to allow for sufficient bone healing and consolidation of the articular fragments. Full weight-bearing (A) or partial weight-bearing (B) would be too aggressive and risk collapse. Touch-down weight-bearing (D) might be considered in some less severe cases or later in the rehabilitation, but for a Type VI, strict non-weight bearing is often preferred initially. Immediate return to activity (E) is entirely inappropriate.

Question 1554

Topic: Lower Extremity Trauma

A 40-year-old male undergoes definitive fixation of a Schatzker Type V tibial plateau fracture with a long diaphyseal extension using a combined lateral locking plate for the plateau and a retrograde intramedullary nail for the diaphysis. One year post-operatively, he complains of persistent anterior knee pain, particularly with kneeling and stair climbing. Radiographs show well-healed fractures and no hardware loosening. What is the most likely cause of his symptoms?

. A. Development of post-traumatic osteoarthritis of the tibiofemoral joint.
. B. Impingement of the proximal end of the intramedullary nail or prominent locking screws on the patellar tendon.
. C. Chronic patellofemoral pain syndrome unrelated to the surgery.
. D. Avascular necrosis of the patella.
. E. Deep infection of the knee joint.

Correct Answer & Explanation

. B. Impingement of the proximal end of the intramedullary nail or prominent locking screws on the patellar tendon.

Explanation

Correct Answer: BPersistent anterior knee pain is a well-recognized and common complication following intramedullary nailing of the tibia, particularly with retrograde nails where the entry portal is through the knee joint. The most likely cause is irritation or impingement of the patellar tendon by the proximal end of the intramedullary nail or prominent proximal locking screws (B). This can be exacerbated by activities like kneeling or stair climbing. While post-traumatic osteoarthritis (A) can develop, it typically presents with more diffuse joint pain and stiffness, not isolated anterior pain. Chronic patellofemoral pain syndrome (C) could be a differential, but the direct relationship to the hardware makes impingement more likely. Avascular necrosis of the patella (D) is exceedingly rare. Deep infection (E) would typically present with more acute symptoms, systemic signs, and radiographic changes.

Question 1555

Topic: 2. Trauma

When treating a highly comminuted distal femur fracture with a locking plate, what is the primary biomechanical mechanism by which this implant provides stability?

. Friction between the plate and the bone surface
. Creation of a fixed-angle construct that resists angular deformation
. Dynamic axial compression across the fracture gap
. Relative lengthening of the plate's working distance
. Plastic deformation of the plate matching the contour of the bone

Correct Answer & Explanation

. Creation of a fixed-angle construct that resists angular deformation

Explanation

Locking plates act as single-beam, fixed-angle constructs because the screw heads thread directly into the plate holes. Unlike conventional non-locking plates, they do not rely on friction between the plate and the bone to achieve stability.

Question 1556

Topic: 2. Trauma

A transverse patella fracture is fixed using a tension band wiring technique. What is the fundamental biomechanical principle of this construct during active knee flexion?

. It converts compressive forces to tensile forces across the fracture site.
. It primarily neutralizes torsional forces to allow primary bone healing.
. It provides absolute stability through pure lag screw fixation.
. It splints the fracture and prevents all motion during range of motion exercises.
. It converts tensile forces at the anterior surface to compressive forces at the articular surface.

Correct Answer & Explanation

. It converts tensile forces at the anterior surface to compressive forces at the articular surface.

Explanation

The tension band principle relies on applying a flexible band (wire) on the tension side of a bone subject to eccentric loading. As the joint flexes, the construct converts the distractive tensile forces on the anterior patella into beneficial compressive forces at the articular surface.

Question 1557

Topic: 2. Trauma

A trauma surgeon is applying a unilateral external fixator for an open tibial shaft fracture. Which of the following frame modifications will most significantly increase the bending stiffness of the construct?

. Increasing the distance between the longitudinal rod and the bone.
. Increasing the core diameter of the Schanz pins.
. Decreasing the spread between pins within the same fracture fragment.
. Decreasing the diameter of the Schanz pins.
. Increasing the distance between the innermost pins and the fracture site.

Correct Answer & Explanation

. Increasing the core diameter of the Schanz pins.

Explanation

The bending stiffness of a pin is proportional to the fourth power of its radius (area moment of inertia). Therefore, increasing the diameter of the Schanz pins provides the most exponential increase in the overall stiffness of the external fixator frame.

Question 1558

Topic: 2. Trauma

During intramedullary nailing of a comminuted mid-shaft tibial fracture, the surgeon decides to place the interlocking screws as far apart as possible. What is the biomechanical effect of increasing the working length of the nail?

. Increases torsional stiffness.
. Increases bending stiffness.
. Has no effect on construct stiffness.
. Decreases both bending and torsional stiffness.
. Decreases bending stiffness but increases torsional stiffness.

Correct Answer & Explanation

. Decreases both bending and torsional stiffness.

Explanation

The working length of an intramedullary nail is the distance between the proximal and distal points of fixation in the bone. Increasing the working length decreases both the bending and torsional stiffness of the construct, allowing for more interfragmentary motion.

Question 1559

Topic: 2. Trauma

Reaming the medullary canal of the tibia allows the placement of an intramedullary nail with a larger radius. If a surgeon places a solid nail with a radius 10% larger than originally planned, approximately how much does the nail's bending stiffness increase?

. 10%
. 21%
. 46%
. 100%
. 110%

Correct Answer & Explanation

. 46%

Explanation

The bending stiffness of a solid cylinder is proportional to its area moment of inertia, which scales to the fourth power of the radius (r^4). A 10% increase in radius (1.1) results in a 46% increase in bending stiffness (1.1^4 = 1.4641).

Question 1560

Topic: 2. Trauma

A surgeon is using a standard 3.5 mm cortical screw as a lag screw to fix an oblique fibular fracture. To achieve proper interfragmentary compression, what is the correct drilling sequence for the near (cis) and far (trans) cortices?

. 2.5 mm drill for both cortices.
. 3.5 mm drill for both cortices.
. 3.5 mm drill for the near cortex, followed by a 2.5 mm drill for the far cortex.
. 2.5 mm drill for the near cortex, followed by a 3.5 mm drill for the far cortex.
. 4.0 mm drill for the near cortex, followed by a 2.5 mm drill for the far cortex.

Correct Answer & Explanation

. 3.5 mm drill for the near cortex, followed by a 2.5 mm drill for the far cortex.

Explanation

To achieve lag screw mechanics with a fully threaded screw, the near cortex must be overdrilled (gliding hole) to the outer thread diameter (3.5 mm). The far cortex is drilled to the core diameter (2.5 mm) to allow the threads to engage and pull the far fragment toward the plate or screw head.

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