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2. Trauma MCQs

Practice Set 106 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 2101

Topic: 2. Trauma

A comminuted femoral shaft fracture is stabilized with an intramedullary nail. How does placing the interlocking screws closer to the fracture site alter the biomechanical properties of the construct?

. Increases axial stiffness
. Decreases torsional rigidity
. Increases the working length
. Decreases the risk of screw cutout
. Promotes stress shielding

Correct Answer & Explanation

. Increases the working length

Explanation

Placing interlocking screws closer to the fracture site decreases the working length of the nail. A shorter working length increases the axial and torsional stiffness of the construct, reducing interfragmentary motion.

Question 2102

Topic: Lower Extremity Trauma

When comparing an unslotted to a slotted intramedullary nail of the same material and outer diameter, the unslotted nail provides a significant biomechanical advantage in resisting which of the following forces?

. Axial compression
. Bending
. Torsion
. Tension
. Shear

Correct Answer & Explanation

. Torsion

Explanation

Unslotted (closed-section) nails have significantly greater torsional rigidity compared to slotted (open-section) nails. While bending rigidity is also slightly increased, the most dramatic biomechanical difference is the resistance to torsional deformation.

Question 2103

Topic: 2. Trauma

During the application of a plate to the tension side of a fractured femur, the plate functions biomechanically to convert tensile forces into which of the following at the opposite cortex?

. Bending forces
. Torsional forces
. Compressive forces
. Shear forces
. Distraction forces

Correct Answer & Explanation

. Distraction forces

Explanation

The tension band principle dictates that a plate applied to the convex (tension) side of an eccentrically loaded bone converts tensile forces into compressive forces at the opposite (concave) cortex. This enhances fracture stability and promotes healing.

Question 2104

Topic: 2. Trauma

According to Perren's strain theory, what happens to the interfragmentary strain when the gap size of a fracture decreases while the deformation (absolute motion) remains constant?

. Strain decreases
. Strain remains unchanged
. Strain increases
. Strain becomes purely compressive
. Strain becomes purely shear

Correct Answer & Explanation

. Strain increases

Explanation

Interfragmentary strain is defined as the change in gap length divided by the original gap length. If the gap size decreases while the absolute motion remains the same, the relative strain increases significantly, which may prevent bone formation.

Question 2105

Topic: 2. Trauma

When utilizing bridge plating for a comminuted diaphyseal fracture, what is the recommended plate span ratio (plate length to fracture length) to minimize stress concentration and reduce the risk of implant failure?

. Less than 1
. Between 1 and 2
. Greater than 2 to 3
. Exactly 1.5
. Between 0.5 and 1

Correct Answer & Explanation

. Greater than 2 to 3

Explanation

The plate span ratio should be greater than 2 to 3 for comminuted fractures to provide a longer working length, which decreases stress concentration on individual screws. For simple fractures, a higher ratio greater than 8 to 10 is recommended.

Question 2106

Topic: 2. Trauma

A surgeon places a Poller (blocking) screw during the intramedullary nailing of a proximal third tibial fracture. To prevent a valgus deformity, where should the Poller screw be optimally positioned relative to the nail in the proximal fragment?

. Medial to the nail
. Lateral to the nail
. Anterior to the nail
. Poster to the nail
. Directly superior to the nail

Correct Answer & Explanation

. Lateral to the nail

Explanation

Poller screws are placed on the concave side of the anticipated deformity to narrow the canal and mechanically block the nail from translating. To prevent a valgus deformity (concavity lateral), the screw should be placed lateral to the nail.

Question 2107

Topic: 2. Trauma

Which of the following modifications will most significantly increase the bending stiffness of a unilateral external fixator construct?

. Decreasing the distance between the fracture and the nearest pin
. Increasing the distance between the fixator rod and the bone
. Increasing the pin diameter
. Using titanium instead of stainless steel pins
. Decreasing the number of pins per segment

Correct Answer & Explanation

. Increasing the pin diameter

Explanation

The bending stiffness of a pin is proportional to its radius to the fourth power (r^4). Therefore, increasing the pin diameter yields the most substantial exponential increase in the stiffness of an external fixator construct.

Question 2108

Topic: Lower Extremity Trauma

An intramedullary nail with a 1.5-meter radius of curvature (ROC) is inserted into a femur with a 1.2-meter ROC. This geometric mismatch most commonly increases the risk of which intraoperative complication?

. Posterior cortical blowout of the proximal femur
. Anterior cortical perforation of the distal femur
. Medial malleolar fracture
. Varus malalignment
. Lateral wall blowout of the greater trochanter

Correct Answer & Explanation

. Anterior cortical perforation of the distal femur

Explanation

A femur with a 1.2m ROC is more bowed than a nail with a 1.5m ROC (which is straighter). Forcing a straighter nail into a more bowed femur risks anterior cortical penetration or frank perforation in the distal femur.

Question 2109

Topic: 2. Trauma

A 28-year-old male is 4 months status post intramedullary nailing of a tibial shaft fracture. Radiographs show a delayed union. The surgeon elects to dynamize the nail by removing the proximal static interlocking screw. This procedure promotes fracture healing by increasing:

. Torsional rigidity at the fracture site
. Axial micro-motion and compression at the fracture site
. Bending stiffness of the nail
. The bending moment at the distal interlocking screws
. The gap size between the fracture fragments

Correct Answer & Explanation

. Axial micro-motion and compression at the fracture site

Explanation

Dynamization involves removing static locking screws to allow the bone fragments to axially compress during weight-bearing. This increases axial micro-motion, stimulating secondary bone healing via callus formation while maintaining rotational control.

Question 2110

Topic: 2. Trauma

Compared to a laterally applied plate, an intramedullary nail provides superior biomechanical advantage for stabilizing a mid-shaft femur fracture primarily because the nail is:

. More ductile than a conventional plate
. Positioned closer to the mechanical neutral axis of the bone
. Subject to higher bending moments
. Anchored exclusively in cancellous bone
. Designed to increase interfragmentary strain above 10%

Correct Answer & Explanation

. Positioned closer to the mechanical neutral axis of the bone

Explanation

An intramedullary nail is centrally located near the mechanical neutral axis of the long bone. This load-sharing position dramatically decreases the bending moments subjected to the implant during weight-bearing, reducing the risk of fatigue failure.

Question 2111

Topic: 2. Trauma

When utilizing absolute stability techniques (e.g., lag screw and neutralization plate) for a transverse fracture, primary bone healing is targeted. For primary bone healing (cutting cones) to occur, the interfragmentary strain must be maintained below what approximate threshold?

. 2%
. 10%
. 15%
. 20%
. 30%

Correct Answer & Explanation

. 2%

Explanation

Primary bone healing via Haversian remodeling (cutting cones) requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing, while strains above 10% lead to nonunion.

Question 2112

Topic: 2. Trauma

A surgeon spans a highly comminuted midshaft tibia fracture with a locking plate. To optimally decrease the stiffness of the construct and promote secondary bone healing by callus, the surgeon should:

. Fill every plate hole with a locking screw
. Leave screw holes empty directly over and adjacent to the fracture site
. Use a shorter plate to minimize footprint
. Place screws as close to the fracture site as possible
. Use non-locking screws exclusively

Correct Answer & Explanation

. Leave screw holes empty directly over and adjacent to the fracture site

Explanation

Leaving screw holes empty adjacent to the fracture site increases the working length of the plate. This decreases construct stiffness, allowing controlled micro-motion that stimulates secondary bone healing via robust callus formation.

Question 2113

Topic: Lower Extremity Trauma

Which of the following design modifications of an intramedullary nail will most dramatically increase its torsional stiffness?

. Increasing the wall thickness of a slotted nail
. Changing from a slotted to a solid, unslotted design
. Increasing the number of interlocking screws from two to three
. Decreasing the working length of the nail
. Applying a pre-bent curvature to the nail

Correct Answer & Explanation

. Changing from a slotted to a solid, unslotted design

Explanation

Changing an intramedullary nail from a slotted to a closed-section (unslotted) design exponentially increases torsional stiffness. While increasing the radius also increases stiffness, closing the cross-section has the most massive impact on torsional rigidity.

Question 2114

Topic: 2. Trauma

An orthopedic surgeon is designing a custom bone plate for a complex diaphyseal fracture. To maximize the plate's resistance to bending loads, which geometric change would be most effective?

. Doubling the width of the plate
. Doubling the thickness of the plate
. Increasing the length of the plate by 50%
. Switching from titanium to stainless steel
. Decreasing the screw hole diameter

Correct Answer & Explanation

. Doubling the thickness of the plate

Explanation

The bending stiffness of a rectangular plate is proportional to its width and the cube of its thickness (h^3). Therefore, doubling the thickness increases the bending stiffness by a factor of 8, making it the most effective modification.

Question 2115

Topic: 2. Trauma

During fracture fixation, a surgeon aims to maximize the pullout strength of a cortical screw. Which of the following factors exerts the greatest influence on screw pullout strength?

. Inner (root) diameter of the screw
. Thread pitch
. Outer thread diameter
. Length of the screw head
. Insertion torque

Correct Answer & Explanation

. Outer thread diameter

Explanation

Screw pullout strength is most heavily influenced by the outer thread diameter, followed by the shear strength of the bone and the length of thread engagement. Increasing the outer diameter directly increases the volume of bone caught between the threads.

Question 2116

Topic: 2. Trauma

A multi-trauma patient with an open tibial shaft fracture undergoes application of a unilateral external fixator. To increase the bending stiffness of this construct in the sagittal plane, which of the following adjustments is most effective?

. Increasing the distance between the bone and the longitudinal rod
. Decreasing the diameter of the half-pins
. Increasing the distance between the innermost pins
. Increasing the diameter of the half-pins
. Using a titanium rod instead of a carbon fiber rod

Correct Answer & Explanation

. Increasing the diameter of the half-pins

Explanation

The stiffness of an external fixator pin is proportional to the fourth power of its radius (r^4). Therefore, increasing the half-pin diameter is the single most effective way to increase the overall stiffness of the external fixator construct.

Question 2117

Topic: 2. Trauma

A comminuted femoral shaft fracture is treated with a bridge plating technique. How does decreasing the working length of the plate (placing screws closer to the fracture site) affect the biomechanical environment?

. It decreases construct stiffness and promotes secondary bone healing
. It increases construct stiffness and concentrates strain at the fracture site
. It increases construct stiffness and diffuses strain across multiple plate holes
. It decreases construct stiffness and increases the risk of plate breakage
. It eliminates axial micro-motion and promotes primary bone healing

Correct Answer & Explanation

. It increases construct stiffness and concentrates strain at the fracture site

Explanation

Decreasing the working length of a plate (the distance between the innermost screws) increases the stiffness of the construct. This can unfavorably concentrate strain at the fracture site in comminuted fractures, potentially leading to nonunion or hardware fatigue.

Question 2118

Topic: 2. Trauma

When evaluating the biomechanics of an interlocked intramedullary nail, the "working length" is defined as the distance between:

. The most proximal and most distal interlocking screws
. The fracture site and the most distal interlocking screw
. The points of intimate contact between the nail and the endosteal cortex
. The proximal entry portal and the distal tip of the nail
. The most proximal screw and the fracture site

Correct Answer & Explanation

. The points of intimate contact between the nail and the endosteal cortex

Explanation

The working length of an intramedullary nail is defined biomechanically as the distance between the primary points of proximal and distal fixation. This is dictated by either the interlocking screws or the regions of intimate bone-nail contact.

Question 2119

Topic: 2. Trauma

A patient with a tibial shaft fracture treated with a statically locked intramedullary nail demonstrates delayed union at 4 months. The surgeon elects to dynamize the nail. Biomechanically, what is the primary goal of this procedure?

. To increase the torsional stiffness of the construct
. To decrease the bending stiffness of the construct
. To allow controlled axial compression at the fracture site
. To increase the working length of the nail
. To prevent translation in the coronal plane

Correct Answer & Explanation

. To allow controlled axial compression at the fracture site

Explanation

Dynamization involves removing static interlocking screws to allow the nail to slide along the dynamic slot. This permits controlled axial micro-motion and compression at the fracture site during weight-bearing, stimulating secondary bone healing.

Question 2120

Topic: 2. Trauma

When utilizing the lag screw technique to achieve interfragmentary compression across an oblique fracture, the diameter of the gliding hole in the near cortex must be:

. Equal to the core diameter of the screw
. Smaller than the core diameter of the screw
. Equal to or slightly larger than the outer thread diameter of the screw
. Equal to the thread pitch of the screw
. Half the outer diameter of the screw

Correct Answer & Explanation

. Equal to or slightly larger than the outer thread diameter of the screw

Explanation

To achieve lag compression, the gliding hole in the near cortex must be equal to or slightly larger than the screw's outer thread diameter. This prevents the threads from engaging the near cortex, allowing the screw head to compress the fragments.

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