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2. Trauma MCQs

Practice Set 107 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 2121

Topic: 2. Trauma

A transverse olecranon fracture is treated with a tension band wiring construct. For this construct to function optimally from a biomechanical standpoint, the wire loop must be placed on the:

. Compressive surface to resist shear forces
. Tension surface to convert tensile forces into compressive forces at the articular margin
. Neutral axis to minimize bending moments
. Medial cortex to resist varus stress
. Lateral cortex to resist valgus stress

Correct Answer & Explanation

. Tension surface to convert tensile forces into compressive forces at the articular margin

Explanation

The tension band principle requires the implant to be placed on the tension (convex) side of the bone. When the joint is loaded, it converts the distraction forces into stabilizing compressive forces at the opposite (articular) cortex.

Question 2122

Topic: 2. Trauma

In the application of a bridge plate for a highly comminuted diaphyseal fracture, what is the recommended plate span ratio (plate length to fracture length) to ensure optimal biomechanical stability and minimize implant failure?

. Less than 1.0
. 1.0 to 1.5
. 2.0 to 3.0
. Greater than 8.0
. It is irrelevant in comminuted fractures

Correct Answer & Explanation

. 2.0 to 3.0

Explanation

The recommended plate span ratio is 2.0 to 3.0 for comminuted fractures and 8.0 to 10.0 for simple fractures. This properly distributes stress over a longer working length, reducing the risk of plate fatigue and catastrophic failure.

Question 2123

Topic: 2. Trauma

A straight intramedullary nail is inserted into a femur with a pronounced anterior bow. What is the most likely biomechanical complication during insertion?

. Perforation of the posterior cortex distally
. Perforation of the anterior cortex distally
. Varus malalignment of the proximal fragment
. Valgus malalignment of the distal fragment
. Torsional fracture of the femoral neck

Correct Answer & Explanation

. Perforation of the anterior cortex distally

Explanation

Inserting an intramedullary nail with a larger radius of curvature (straighter) into a femur with a prominent anterior bow (smaller radius of curvature) causes a mismatch. This can lead the tip of the nail to impinge upon and perforate the distal anterior cortex.

Question 2124

Topic: 2. Trauma

A surgeon is evaluating screw density for a locking plate construct. Screw density is defined as the number of inserted screws divided by the total number of plate holes. For a bridge plating technique, what is the generally recommended maximum screw density to balance construct stiffness and stress distribution?

. 0.1
. 0.25
. 0.4 to 0.5
. 0.75
. 1.0

Correct Answer & Explanation

. 0.4 to 0.5

Explanation

In bridge plating, a screw density of 0.4 to 0.5 is generally recommended. Leaving empty holes over the fracture site increases the working length, which prevents hardware failure from concentrated stress and allows favorable micro-motion.

Question 2125

Topic: 2. Trauma

In a simple transverse fracture, a 1 mm gap is left after fixation. During weight-bearing, there is 0.5 mm of cyclic axial movement. According to strain theory, what type of tissue will most likely form initially within this gap?

. Primary osteonal bone
. Woven bone
. Cartilage
. Granulation tissue
. Fibrous tissue

Correct Answer & Explanation

. Fibrous tissue

Explanation

Strain is the change in gap length divided by the original gap length (0.5 mm / 1.0 mm = 50%). This extreme strain environment only permits the survival and formation of fibrous or granulation tissue, invariably leading to nonunion.

Question 2126

Topic: Lower Extremity Trauma

A surgeon evaluates a slotted versus a solid intramedullary nail of identical outer diameter and material. What is the most significant biomechanical consequence of the longitudinal slot?

. Significantly decreased bending rigidity
. Significantly decreased torsional rigidity
. Increased risk of thermal necrosis during insertion
. Increased axial stiffness
. Decreased resistance to shear forces

Correct Answer & Explanation

. Significantly decreased torsional rigidity

Explanation

The primary biomechanical difference between a solid and a slotted nail is that the slotted nail has significantly decreased torsional rigidity. While bending rigidity is only slightly affected by the slot, the open section dramatically reduces the construct's ability to resist twisting forces.

Question 2127

Topic: 2. Trauma

In bridge plating of a highly comminuted femoral shaft fracture, what is the primary biomechanical rationale for leaving several screw holes empty directly over the fracture zone (increasing the working length)?

. It increases the torsional stiffness of the overall construct
. It decreases the axial stiffness of the construct to promote secondary bone healing
. It increases the bending stiffness of the plate
. It concentrates stress at the fracture site to stimulate primary bone healing
. It prevents the plate from acting as a tension band

Correct Answer & Explanation

. It decreases the axial stiffness of the construct to promote secondary bone healing

Explanation

Increasing the working length of a plate decreases the axial and bending stiffness of the construct. This increased flexibility reduces stress concentration at a single point, distributing strain across the comminuted fracture to promote secondary (callus) bone healing.

Question 2128

Topic: 2. Trauma

In the application of a unilateral external fixator for a tibia fracture, which of the following modifications provides the greatest exponential increase in the bending stiffness of the construct?

. Decreasing the distance from the bone to the longitudinal rod
. Decreasing the distance between the pins within each fragment
. Increasing the pin diameter
. Adding an additional rod in parallel
. Increasing the working length of the fracture gap

Correct Answer & Explanation

. Increasing the pin diameter

Explanation

Increasing the pin diameter has the most profound effect on the bending stiffness of an external fixator because a pin's area moment of inertia is proportional to the radius raised to the fourth power (r^4). Other modifications improve stiffness linearly, rather than exponentially.

Question 2129

Topic: 2. Trauma

When utilizing a locked plating construct for a metaphyseal fracture in severely osteoporotic bone, the system primarily relies on which biomechanical principle to resist failure compared to non-locked plates?

. High plate-to-bone frictional forces
. Resistance to screw toggle via a fixed-angle interface
. Compression of the fracture gap through eccentric screw placement
. Increased cortical purchase via a smaller screw pitch
. Conversion of shear forces into tensile forces along the plate

Correct Answer & Explanation

. Resistance to screw toggle via a fixed-angle interface

Explanation

Locked plating constructs do not rely on friction between the plate and the bone. Instead, the fixed-angle construct securely locks the screw head to the plate, converting shear stresses and primarily resisting failure by preventing screw toggle and pullout in poor-quality bone.

Question 2130

Topic: 2. Trauma

The pullout strength of a bone screw is a critical factor in fracture fixation stability. Which of the following screw design modifications mathematically provides the greatest increase in pullout strength?

. Decreasing the outer (major) diameter
. Increasing the inner (minor) diameter
. Increasing the outer (major) diameter
. Increasing the thread pitch
. Decreasing the length of thread engagement in bone

Correct Answer & Explanation

. Increasing the outer (major) diameter

Explanation

Screw pullout strength is directly proportional to the outer (major) diameter, the length of engagement, and the shear strength of the bone material. Increasing the major diameter provides the largest increase in thread surface area engaging the bone, maximizing pullout resistance.

Question 2131

Topic: Lower Extremity Trauma

How does increasing the working length of an intramedullary nail (defined as the distance between the most proximal and distal points of fixation) affect its biomechanical behavior?

. Increases torsional stiffness
. Increases bending stiffness
. Decreases both torsional and bending stiffness
. Increases axial stiffness while decreasing bending stiffness
. Has no effect on stiffness, only on fatigue life

Correct Answer & Explanation

. Decreases both torsional and bending stiffness

Explanation

The working length of an IM nail is inversely proportional to its stiffness. Increasing the distance between the locking screws effectively increases the span over which the nail must bear loads, thereby decreasing both torsional and bending stiffness.

Question 2132

Topic: 2. Trauma

For a tension band plate applied to the lateral aspect of a fractured femur to be mechanically effective, which of the following prerequisite conditions is absolutely necessary?

. The medial cortex must have intact bony contact to resist compression
. The fracture must have extensive comminution on the lateral side
. The plate must be positioned exactly on the neutral axis of the bone
. The construct must utilize exclusively locking screws
. The fracture gap must be distracted to increase interfragmentary strain

Correct Answer & Explanation

. The medial cortex must have intact bony contact to resist compression

Explanation

The tension band principle relies on converting tensile forces on the convex surface into compressive forces at the fracture site. This mechanism completely fails if the opposite (compression) side lacks intact bony contact, as the plate would instead be subjected to cyclic bending and eventual fatigue failure.

Question 2133

Topic: 2. Trauma

The area moment of inertia for a rectangular fracture plate is calculated as I = (base * height^3) / 12, where height is the plate thickness. Which modification yields the greatest theoretical increase in the plate's bending stiffness?

. Doubling the plate's width
. Doubling the plate's thickness
. Halving the plate's length
. Using titanium instead of stainless steel
. Adding compression across the fracture

Correct Answer & Explanation

. Doubling the plate's thickness

Explanation

Because the height (thickness) of the plate is cubed in the area moment of inertia formula, doubling the plate's thickness increases its bending stiffness by a factor of eight. Doubling the width only doubles the stiffness.

Question 2134

Topic: Lower Extremity Trauma

An elderly patient with an exaggerated anterior bow of the femur sustains a midshaft fracture. The surgeon inserts an intramedullary nail with a larger radius of curvature (less bowed) than the patient's native anatomy. This mismatch most significantly increases the risk of which intraoperative complication?

. Anterior cortical perforation of the distal femur
. Posterior cortical perforation of the distal femur
. Proximal lateral cortex blowout
. Delayed union due to excessive dynamization
. Rotational malalignment of the distal fragment

Correct Answer & Explanation

. Anterior cortical perforation of the distal femur

Explanation

A nail with a larger radius of curvature is straighter than a highly bowed femur. Upon insertion, the straight distal tip of the nail will tend to impinge upon and potentially perforate the anterior cortex of the distal femur.

Question 2135

Topic: 2. Trauma

A surgeon increases the outer diameter of a solid titanium intramedullary nail from 10 mm to 12 mm for fixation of a midshaft femur fracture. Assuming all other factors remain constant, by approximately what factor does the bending rigidity of the nail increase?

. 1.20
. 1.44
. 1.73
. 2.07
. 2.40

Correct Answer & Explanation

. 2.07

Explanation

The area moment of inertia, which determines bending rigidity for a solid cylindrical nail, is proportional to the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm yields a factor of (12/10)^4 = 2.07, effectively doubling the bending stiffness.

Question 2136

Topic: 2. Trauma

A 25-year-old sustains a comminuted diaphyseal femur fracture treated with a statically locked intramedullary nail. To intentionally promote secondary bone healing via callus formation by decreasing the torsional and bending stiffness of the construct, the surgeon should primarily:

. Increase the outer diameter of the nail used.
. Decrease the distance between the innermost interlocking screws.
. Increase the distance between the innermost interlocking screws.
. Utilize a stainless steel nail instead of a titanium nail.
. Use fully threaded locking screws instead of partially threaded ones.

Correct Answer & Explanation

. Increase the distance between the innermost interlocking screws.

Explanation

Increasing the distance between the innermost interlocking screws increases the 'working length' of the nail. A longer working length decreases both the bending and torsional stiffness of the construct, promoting micromotion and secondary bone healing.

Question 2137

Topic: Lower Extremity Trauma

A manufacturer designs a new intramedullary nail with a longitudinal slot to allow for easier insertion and radial compression during placement. Compared to a closed-section (unslotted) nail of identical outer diameter, wall thickness, and material, the slotted nail primarily exhibits a significant reduction in:

. Bending rigidity in the anteroposterior plane.
. Bending rigidity in the coronal plane.
. Axial stiffness.
. Torsional rigidity.
. Tensile strength.

Correct Answer & Explanation

. Torsional rigidity.

Explanation

Slotted (open-section) intramedullary nails have significantly lower torsional rigidity compared to closed-section nails due to a lower polar moment of inertia. Bending rigidity is also affected but to a much lesser degree than the dramatic loss in torsional stability.

Question 2138

Topic: Lower Extremity Trauma

During the insertion of an intramedullary nail for a transverse midshaft femur fracture, the surgeon notes impending perforation of the anterior cortex of the distal femur. Biomechanically, this complication is most commonly related to the use of an intramedullary nail possessing a:

. Radius of curvature greater than that of the native femur.
. Radius of curvature less than that of the native femur.
. Significantly shorter working length.
. Smaller outer diameter.
. Higher polar moment of inertia.

Correct Answer & Explanation

. Radius of curvature greater than that of the native femur.

Explanation

The native femur has an anterior bow with a radius of curvature of approximately 1.2 meters. A nail with a greater radius of curvature is 'straighter' than the femur, causing a mismatch that frequently leads to anterior cortical impingement or perforation distally.

Question 2139

Topic: 2. Trauma

A transverse olecranon fracture is treated with a posterior tension band plate. According to biomechanical principles, placing the plate on the tension (posterior) surface of the bone ensures that tensile forces generated during active elbow flexion are converted into:

. Shear forces at the fracture site.
. Distraction forces at the articular surface.
. Compressive forces at the opposite (articular) cortex.
. Torsional forces along the ulnar diaphysis.
. Bending forces focused purely on the hardware.

Correct Answer & Explanation

. Compressive forces at the opposite (articular) cortex.

Explanation

The tension band principle states that applying fixation on the tension side of an eccentrically loaded bone resists distraction. This application dynamically converts functional tensile forces into compressive forces at the opposite (articular) cortex, enhancing fracture stability.

Question 2140

Topic: 2. Trauma

An orthopedic surgeon is applying a unilateral uniplanar external fixator to treat a severe open tibial shaft fracture. To maximize the bending and torsional stiffness of the overall fixator construct, which of the following modifications is mathematically most effective?

. Increasing the distance between the fixator bar and the bone.
. Decreasing the core diameter of the Schanz pins.
. Increasing the pin diameter.
. Decreasing the distance between the pins within each bone segment.
. Placing the pins in a completely parallel configuration.

Correct Answer & Explanation

. Increasing the pin diameter.

Explanation

The stiffness of an external fixator pin is proportional to its radius to the fourth power (r^4). Therefore, increasing the pin diameter yields the greatest mathematical increase in construct stiffness compared to modifying frame distance or pin spacing.

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