Menu

2. Trauma MCQs

Practice Set 51 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 1001

Topic: 2. Trauma

By removing the static locking screws and leaving only the dynamic screws in a locked intramedullary nail, the construct becomes least restrictive to which of the following forces during weight-bearing?

. Coronal bending
. Sagittal bending
. Torsion
. Axial compression
. Shear

Correct Answer & Explanation

. Axial compression

Explanation

Dynamic interlocking screws are placed through oblong slots in the nail. This configuration resists bending and torsion (to the limits of the slot width) but freely permits axial sliding, allowing for controlled axial compression of the fracture site.

Question 1002

Topic: 2. Trauma

Which of the following modifications will most effectively increase the torsional and bending stiffness of a statically locked intramedullary nail construct for a diaphyseal femur fracture?

. Decreasing the diameter of the nail
. Increasing the distance between the innermost interlocking screws
. Decreasing the distance between the innermost interlocking screws
. Using a slotted nail instead of a solid nail
. Using a titanium nail instead of a stainless steel nail

Correct Answer & Explanation

. Decreasing the distance between the innermost interlocking screws

Explanation

The working length of an intramedullary nail is the distance between the closest points of fixation on either side of the fracture. Decreasing the working length by placing the innermost interlocking screws closer to the fracture site significantly increases the construct's stiffness.

Question 1003

Topic: 2. Trauma

During the intramedullary nailing of a proximal third tibia fracture, a Poller (blocking) screw is placed. What is the primary biomechanical function of this screw?

. To provide interfragmentary axial compression across the fracture site
. To artificially narrow the medullary canal and decrease the construct's working length
. To increase the torsional rigidity of the primary interlocking screws
. To dynamically compress the fracture upon weight-bearing
. To induce primary membranous bone healing at the fracture gap

Correct Answer & Explanation

. To artificially narrow the medullary canal and decrease the construct's working length

Explanation

Poller screws are placed on the concavity of a potential deformity to functionally narrow the medullary canal, directing the nail into the anatomical axis. Biomechanically, they also act as surrogate cortices, decreasing the working length of the construct and increasing stiffness.

Question 1004

Topic: 2. Trauma

Following standard reamed intramedullary nailing of a diaphyseal femur fracture, the primary blood supply to the healing diaphyseal cortex initially shifts to rely predominantly on:

. The nutrient artery system
. The epiphyseal vascular complex
. The periosteal circulation via centripetal flow
. The regenerating endosteal circulation via centrifugal flow
. The metaphyseal perforators

Correct Answer & Explanation

. The periosteal circulation via centripetal flow

Explanation

Reaming inherently destroys the normal endosteal blood supply, which usually provides centrifugal flow to the inner two-thirds of the cortex. Following this disruption, cortical perfusion temporarily relies on a reversed, centripetal flow from the surrounding periosteal circulation until endosteal revascularization occurs.

Question 1005

Topic: 2. Trauma

According to Perren's strain theory, what range of interfragmentary strain is ideal for promoting secondary bone healing (callus formation) in a comminuted diaphyseal fracture treated with a locked intramedullary nail?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Secondary bone healing via endochondral ossification requires relative stability, corresponding to a strain environment optimally between 2% and 10%. Strains below 2% prompt primary bone healing, while strains above 10% typically lead to persistent granulation tissue and nonunion.

Question 1006

Topic: Lower Extremity Trauma

A patient sustains an anterior cortical perforation of the distal femur during insertion of an antegrade femoral intramedullary nail. Which of the following geometric mismatches is the most likely culprit?

. The nail has a smaller radius of curvature than the femur
. The nail has a larger radius of curvature than the femur
. The nail has a smaller area moment of inertia than the femur
. The femur has a larger radius of curvature than the nail
. The femur has a greater polar moment of inertia than the nail

Correct Answer & Explanation

. The nail has a larger radius of curvature than the femur

Explanation

A larger radius of curvature denotes a mathematically straighter object. Because the natural femur has an anterior bow (smaller radius of curvature), driving a straighter nail (larger radius of curvature) can result in impingement and perforation of the anterior distal cortex.

Question 1007

Topic: Lower Extremity Trauma

Which of the following biomechanical characteristics is most significantly and disproportionately reduced when utilizing a slotted (open-section) intramedullary nail compared to a solid (closed-section) nail of the exact same outer diameter?

. Area moment of inertia
. Bending stiffness
. Torsional rigidity
. Axial compression resistance
. Modulus of elasticity

Correct Answer & Explanation

. Torsional rigidity

Explanation

While slotting an intramedullary nail reduces both bending stiffness and torsional rigidity, its effect on torsional rigidity is much more profound. Slotted (open-section) nails demonstrate drastically lower resistance to rotational forces compared to closed-section cylinders.

Question 1008

Topic: 2. Trauma

Which of the following procedural elements most significantly increases the risk of thermal necrosis of the diaphyseal bone during medullary reaming?

. Using a pneumatic tourniquet during the procedure
. Using reamers with excessively deep flutes
. Advancing the reamer slowly with low thrust force
. Frequent withdrawal of the reamer to clear debris
. Utilizing highly sharpened, new reamer heads

Correct Answer & Explanation

. Using a pneumatic tourniquet during the procedure

Explanation

A pneumatic tourniquet halts intraosseous blood flow, removing its vital convective cooling effect and significantly increasing the risk of thermal necrosis during reaming. Intermittent reaming, sharp reamer heads, and deep flutes all help mitigate excessive heat generation.

Question 1009

Topic: 2. Trauma

Dynamization of an intramedullary nail for a delayed union involves removing the static interlocking screws on the longer segment side. Biomechanically, this procedure promotes fracture healing primarily by:

. Increasing the torsional rigidity of the remaining screws
. Decreasing the working length of the intramedullary nail
. Allowing controlled axial compression at the fracture site upon loading
. Shifting the healing cascade from secondary to primary bone healing
. Increasing the area moment of inertia of the entire construct

Correct Answer & Explanation

. Allowing controlled axial compression at the fracture site upon loading

Explanation

Dynamization allows the separated bone fragments to compress axially during weight-bearing by sliding along the nail. This controlled axial micromotion stimulates callus formation in delayed unions that possess rotational stability but lack interfragmentary compression.

Question 1010

Topic: 2. Trauma

In the context of intramedullary nailing, how does decreasing the working length of the nail affect the biomechanical properties of the nail-bone construct?

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

Correct Answer & Explanation

. Increases bending stiffness and increases torsional stiffness

Explanation

Working length is the distance between the closest points of fixation across the fracture. Decreasing this working length significantly increases both the bending and torsional stiffness of the overall construct.

Question 1011

Topic: 2. Trauma

A 25-year-old male undergoes reamed intramedullary nailing of a midshaft femur fracture. During the reaming process, thermal necrosis of the bone is a known risk. Which of the following factors most significantly increases the risk of thermal necrosis?

. Using sharp reamers with high rotational speed
. Using a tourniquet during the procedure
. Using dull reamers with high axial thrust
. Reaming in a pulsatile manner
. Using cannulated reamers over a ball-tipped guide wire

Correct Answer & Explanation

. Using dull reamers with high axial thrust

Explanation

Dull reamers, excessive axial thrust (pushing hard), and failure to clear the reamer flutes generate excessive heat. Osteonecrosis can occur when bone temperatures exceed 47 degrees Celsius for 1 minute.

Question 1012

Topic: 2. Trauma

A surgeon places a Poller (blocking) screw to aid in the reduction of a proximal third tibia fracture treated with an intramedullary nail. Biomechanically, what is the primary effect of this screw on the construct?

. It acts as a dynamic lag screw to compress the fracture
. It decreases the functional working length of the nail
. It expands the medullary canal to allow passage of a larger nail
. It provides an absolute stability environment for primary bone healing
. It eliminates the need for proximal interlocking screws

Correct Answer & Explanation

. It decreases the functional working length of the nail

Explanation

Poller screws act as artificial cortices that narrow the medullary canal, directing the nail path and effectively decreasing the working length. This increases the construct's stiffness and prevents angular malalignment.

Question 1013

Topic: Lower Extremity Trauma

When comparing a closed-section (solid or continuous tube) intramedullary nail to a slotted (open-section) intramedullary nail of identical outer diameter and material, the closed-section nail possesses significantly greater:

. Axial compressibility
. Working length
. Bending stiffness
. Torsional stiffness
. Notch sensitivity

Correct Answer & Explanation

. Torsional stiffness

Explanation

A closed-section intramedullary nail has a vastly higher torsional stiffness compared to an open-section (slotted) nail of the same dimensions. While bending stiffness is also higher, the most dramatic biomechanical difference is in its resistance to torsion.

Question 1014

Topic: Lower Extremity Trauma

Which of the following best describes the formula relationship for the bending stiffness (area moment of inertia) of a solid cylindrical intramedullary nail of radius (r)?

. Proportional to r squared
. Proportional to r cubed
. Proportional to r to the fourth power
. Proportional to r to the fifth power
. Inversely proportional to r to the fourth power

Correct Answer & Explanation

. Proportional to r to the fourth power

Explanation

The bending stiffness of a solid cylinder is determined by its area moment of inertia. This value is mathematically proportional to the radius raised to the fourth power.

Question 1015

Topic: 2. Trauma

A patient presents with a diaphyseal femur fracture treated with a statically locked intramedullary nail 6 months ago. Radiographs show a hypertrophic nonunion. The surgeon decides to dynamize the nail. Biomechanically, dynamization relies on:

. Converting secondary bone healing to primary bone healing
. Removing all locking screws to allow immediate unrestricted weight-bearing
. Removing interlocking screws on one side of the fracture to allow axial compression
. Increasing the torsional stiffness of the construct
. Increasing the working length to maximize bending forces

Correct Answer & Explanation

. Removing interlocking screws on one side of the fracture to allow axial compression

Explanation

Dynamization involves removing the locking screws from one end of the nail, usually on the longer fragment side. This permits the nail to slide, allowing physiological axial compression at the fracture site while maintaining rotational alignment.

Question 1016

Topic: 2. Trauma

Reamed intramedullary nailing of a long bone largely destroys the endosteal blood supply. Which of the following best describes the subsequent vascular response and healing process?

. Endosteal vessels do not regenerate, and all healing relies permanently on periosteal supply
. Endosteal blood flow is restored within 1-2 weeks, driving immediate primary cortical healing
. A compensatory hyperemic response occurs in the periosteal circulation, with endosteal regeneration occurring over several weeks
. The medullary canal becomes entirely avascular, requiring early bone grafting for union
. Nutrient artery hypertrophy compensates immediately within 48 hours to restore endosteal flow

Correct Answer & Explanation

. A compensatory hyperemic response occurs in the periosteal circulation, with endosteal regeneration occurring over several weeks

Explanation

Reaming disrupts the medullary blood supply, which prompts an immediate compensatory hyperemia in the periosteal vessels to drive early callus formation. The endosteal blood supply typically regenerates progressively over 8 to 12 weeks.

Question 1017

Topic: Lower Extremity Trauma

The anterior bow of a standard adult femur has an average radius of curvature of approximately 120 cm. If an intramedullary nail with a 200 cm radius of curvature is inserted into a femur with a 120 cm bow, what complication is most likely to occur?

. Anterior perforation of the distal femur
. Posterior perforation of the distal femur
. Anterior perforation of the proximal femur
. Medial cortical blowout at the isthmus
. Inability to pass the guide wire

Correct Answer & Explanation

. Anterior perforation of the distal femur

Explanation

A nail with a larger radius of curvature (e.g., 200 cm) is physically straighter than the native anterior bow of the femur (120 cm). During insertion, the mismatch tends to drive the distal tip of the nail anteriorly, risking anterior cortical perforation.

Question 1018

Topic: Lower Extremity Trauma

A surgeon is selecting an interlocking screw for an intramedullary nail. According to the mechanics of cylindrical structures, increasing the inner (core) diameter of the locking screw will increase its resistance to bending failure by a factor proportional to the:

. Square root of the radius
. Radius squared
. Radius cubed
. Radius to the fourth power
. Radius to the fifth power

Correct Answer & Explanation

. Radius to the fourth power

Explanation

The bending stiffness and resistance to bending failure of a cylindrical structure like a screw are dictated by the area moment of inertia. This property is directly proportional to the radius of the core to the fourth power.

Question 1019

Topic: 2. Trauma

In intramedullary nailing of a highly comminuted midshaft tibia fracture, the surgeon decides to place multiple locking screws both proximally and distally. What is the primary mechanical role of the locking screws in this specific fracture pattern?

. To provide dynamic axial compression across the fracture site
. To prevent axial telescoping and rotational instability
. To decrease the working length of the nail
. To induce primary contact bone healing
. To bypass the need for periosteal callus formation

Correct Answer & Explanation

. To prevent axial telescoping and rotational instability

Explanation

In comminuted length-unstable fractures lacking cortical contact, static interlocking screws are essential to maintain limb length by preventing axial telescoping. They also serve to control alignment by preventing rotational instability.

Question 1020

Topic: 2. Trauma

When treating a transverse midshaft humerus fracture with an intramedullary nail, leaving a 3 mm fracture gap while statically locking the nail will most likely result in:

. Immediate primary bone healing due to absolute stability
. High interfragmentary strain leading to an atrophic nonunion
. Decreased working length and early fatigue failure of the nail
. Rapid formation of cutting cones across the gap
. Increased construct stiffness leading to regional osteopenia

Correct Answer & Explanation

. High interfragmentary strain leading to an atrophic nonunion

Explanation

A statically locked IM nail provides relative stability, and a transverse pattern with a gap localizes all micromotion to a very small area. This creates an environment of excessively high interfragmentary strain, which inhibits bone bridging and risks nonunion.

Test Yourself

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

On this Page