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2. Trauma MCQs

Practice Set 50 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 981

Topic: 2. Trauma

A surgeon is evaluating the working length of an intramedullary nail construct for a comminuted midshaft tibia fracture. Which of the following maneuvers will decrease the working length and increase the stiffness of the construct?

. Placing the interlocking screws further away from the fracture site
. Using a smaller diameter nail
. Removing the dynamic interlocking screw
. Placing the interlocking screws as close to the fracture site as possible
. Using an unslotted rather than a slotted nail

Correct Answer & Explanation

. Placing the interlocking screws as close to the fracture site as possible

Explanation

The working length of a nail is the distance between the closest points of proximal and distal fixation. Placing screws closer to the fracture decreases the working length, which increases the construct's stiffness.

Question 982

Topic: 2. Trauma

During the treatment of a proximal third tibia fracture with an intramedullary nail, Poller (blocking) screws are utilized. What is the primary biomechanical rationale for this technique?

. To provide interfragmentary compression across the main fracture line
. To increase the effective medullary canal diameter
. To decrease the working length and restrict translation of the nail within the metaphyseal bone
. To act as a dynamic locking mechanism allowing axial telescoping
. To prevent thermal necrosis during reaming

Correct Answer & Explanation

. To decrease the working length and restrict translation of the nail within the metaphyseal bone

Explanation

Poller screws are placed adjacent to the nail to artificially narrow the medullary canal in metaphyseal regions. This guides the nail, prevents angular deformity, and increases construct stiffness by decreasing toggling.

Question 983

Topic: 2. Trauma

Which of the following reaming techniques is most effective at minimizing the potentially detrimental elevation of intramedullary pressure and subsequent fat embolization?

. Using dull reamers with a high advancement rate
. Using sharp reamers with deep flutes and a slow advancement rate
. Reaming without a tourniquet to allow venous offloading
. Rapid back-and-forth passes with a solid reamer head
. Irrigating the canal exclusively with pressurized saline during reaming

Correct Answer & Explanation

. Using sharp reamers with deep flutes and a slow advancement rate

Explanation

Intramedullary pressure is minimized by using sharp, deep-fluted reamers that provide adequate clearance for debris. Slow advancement allows the displaced marrow and fat to bypass the reamer head rather than being forced into the venous system.

Question 984

Topic: 2. Trauma

Why does a highly comminuted diaphyseal fracture treated with an intramedullary nail tolerate axial loading better, in terms of gap strain, than a simple transverse fracture with a similar gap distance?

. Comminuted fractures undergo intramembranous rather than endochondral ossification.
. The total displacement is distributed over multiple fracture gaps, lowering the strain per gap.
. Comminution inherently increases the bending stiffness of the nail construct.
. The working length is mathematically shorter in comminuted fractures.
. Vascular supply is preserved better in comminuted fractures, altering the strain threshold.

Correct Answer & Explanation

. The total displacement is distributed over multiple fracture gaps, lowering the strain per gap.

Explanation

Strain is the change in gap length divided by the original gap length. In a comminuted fracture, overall motion is shared among multiple fracture interfaces, keeping the individual strain at each gap below the 10% threshold required for granulation tissue to differentiate.

Question 985

Topic: 2. Trauma

Following reamed intramedullary nailing of a closed diaphyseal femur fracture, what is the predominant initial alteration in the cortical blood supply?

. Hyperemia of the endosteal circulation within 24 hours
. Complete reversal of flow from centrifugal to centripetal
. Immediate regeneration of medullary nutrient arteries
. Ischemic necrosis of the periosteum due to pressure changes
. Complete cessation of both periosteal and endosteal flow

Correct Answer & Explanation

. Complete reversal of flow from centrifugal to centripetal

Explanation

Reaming destroys the endosteal blood supply, which normally flows centrifugally (from inside out). The bone acutely compensates by reversing the flow to a centripetal direction, relying entirely on the periosteal blood supply until endosteal vessels reconstitute.

Question 986

Topic: 2. Trauma

In cases of delayed union or nonunion treated with an intramedullary nail, hardware failure most commonly occurs at which location?

. The mid-diaphyseal portion of the nail due to maximal bending moments
. The junction of the proximal third and middle third of the nail
. Through an interlocking screw hole
. At the insertion site due to heterotopic ossification stress
. At the driving tip of the nail

Correct Answer & Explanation

. Through an interlocking screw hole

Explanation

Interlocking screw holes act as significant stress risers within the nail's structure. In the setting of nonunion, cyclic loading eventually exceeds the fatigue life of the implant, typically leading to fracture through a screw hole.

Question 987

Topic: 2. Trauma

A 35-year-old male is 4 months status post static interlocking intramedullary nailing of a transverse tibial shaft fracture. Radiographs show delayed union with no hardware failure. The surgeon considers dynamization. What biomechanical effect does dynamization primarily achieve?

. It converts shear stress into bending stress to stimulate primary bone healing.
. It removes all rotational stability, allowing robust callus formation.
. It allows axial compression and interfragmentary micro-motion at the fracture site.
. It increases the torsional rigidity of the overall construct.
. It shifts the neutral axis of the bone away from the implant.

Correct Answer & Explanation

. It allows axial compression and interfragmentary micro-motion at the fracture site.

Explanation

Dynamization involves removing static interlocking screws while leaving dynamic screws in place. This allows the nail to slide axially under load, increasing compressive interfragmentary motion and strain, which stimulates callus formation.

Question 988

Topic: Lower Extremity Trauma

When comparing a slotted hollow intramedullary nail to a non-slotted hollow intramedullary nail of the same diameter and wall thickness, the slotted nail exhibits a marked reduction primarily in which of the following mechanical properties?

. Axial stiffness
. Torsional stiffness
. Bending stiffness
. Tensile strength
. Yield strength

Correct Answer & Explanation

. Torsional stiffness

Explanation

A longitudinal slot in an intramedullary nail drastically reduces its torsional stiffness (often by more than 90% compared to a closed section). While bending stiffness is also slightly reduced, the torsional deficit is the most profound mechanical consequence.

Question 989

Topic: Lower Extremity Trauma

The formula for the area moment of inertia for a hollow tubular implant like an intramedullary nail relies heavily on the inner and outer radii. If the outer radius of a hollow nail is increased, the bending stiffness increases proportionally to which mathematical function?

. (Outer Radius)^2 - (Inner Radius)^2
. (Outer Radius)^3 - (Inner Radius)^3
. (Outer Radius)^4 - (Inner Radius)^4
. Pi * (Outer Radius - Inner Radius)
. The natural logarithm of the Outer Radius

Correct Answer & Explanation

. (Outer Radius)^4 - (Inner Radius)^4

Explanation

The bending stiffness of a hollow cylindrical implant is proportional to its area moment of inertia, calculated by the formula involving the difference of the outer and inner radii to the fourth power (r_out^4 - r_in^4).

Question 990

Topic: 2. Trauma

A surgeon plans to ream the femoral canal prior to placing an intramedullary nail. What is the standard accepted biomechanical and clinical guideline for the amount of over-reaming relative to the intended nail diameter?

. Ream to exactly the same diameter as the nail to ensure an interference fit.
. Ream 0.5 mm larger than the nail diameter.
. Ream 1.0 to 1.5 mm larger than the nail diameter.
. Ream 3.0 mm larger than the nail diameter to maximize endosteal blood flow recovery.
. Reaming diameter does not matter if a slotted nail is used.

Correct Answer & Explanation

. Ream 1.0 to 1.5 mm larger than the nail diameter.

Explanation

Standard practice dictates over-reaming the medullary canal by 1.0 to 1.5 mm larger than the intended nail diameter. This prevents incarceration of the nail during insertion and accommodates the slight bowing mismatch between the nail and bone.

Question 991

Topic: 2. Trauma

Intramedullary nails possess a distinct biomechanical advantage over compression plates for diaphyseal long bone fractures primarily due to their relationship with which biomechanical concept?

. Absolute stability and strain reduction below 2%
. Placement closer to the neutral bending axis of the bone
. Increased offset providing a higher moment arm
. Generation of primary bone healing through cutting cones
. Avoidance of the periosteal blood supply entirely

Correct Answer & Explanation

. Placement closer to the neutral bending axis of the bone

Explanation

IM nails act as load-sharing devices located in the medullary canal, closer to the central neutral axis of the bone. This central placement minimizes the bending moments placed on the implant, reducing the risk of fatigue failure compared to an eccentrically placed plate.

Question 992

Topic: 2. Trauma

What is the primary mechanism by which angle-stable (locking) screws enhance the performance of an intramedullary nail in metaphyseal fractures compared to standard non-locking interlocking screws?

. They allow controlled axial dynamization.
. They prevent toggling of the nail within the widened metaphyseal canal.
. They increase the inherent bending stiffness of the titanium rod.
. They eliminate the need for reaming.
. They decrease the total area moment of inertia.

Correct Answer & Explanation

. They prevent toggling of the nail within the widened metaphyseal canal.

Explanation

In the wide metaphyseal region, standard interlocking screws act essentially as a pivot, allowing the nail to toggle. Angle-stable locking mechanisms rigidly fix the screw to the nail, eliminating this toggling and maintaining alignment.

Question 993

Topic: 2. Trauma

A resident forcefully reams a sclerotic tibial diaphysis using a dull reamer and a high-speed setting. What is the most significant biological complication associated with this specific technique error?

. Excessive stimulation of endosteal bone formation
. Thermal necrosis of the diaphyseal cortex
. Immediate rupture of the popliteal artery
. Premature consolidation of the fracture gap
. Spontaneous dynamization of the implant

Correct Answer & Explanation

. Thermal necrosis of the diaphyseal cortex

Explanation

Using dull reamers at high speeds with excessive force generates tremendous friction. This leads to thermal necrosis of the surrounding cortical bone, which significantly impairs fracture healing and increases the risk of deep infection or sequestrum formation.

Question 994

Topic: 2. Trauma

An unreamed intramedullary nail relies more heavily on which type of locking construct to maintain length and rotation in a highly comminuted midshaft femur fracture compared to a tightly fit reamed nail?

. Dynamic proximal locking only
. Dynamic distal locking only
. Static locking proximally and distally
. No interlocking screws are needed if the nail is solid
. Poller screws placed centrally within the comminution

Correct Answer & Explanation

. Static locking proximally and distally

Explanation

Unreamed nails typically have a smaller diameter and do not achieve an interference fit within the isthmus. Therefore, to prevent shortening and malrotation in comminuted fractures, static interlocking (proximally and distally) is required to bear the physiological loads.

Question 995

Topic: 2. Trauma

When evaluating the structural integrity of an intramedullary nail, the 'fatigue limit' of the material refers to which of the following?

. The maximum stress the nail can withstand in a single load before permanent deformation.
. The maximum stress the nail can withstand in a single load before catastrophic failure.
. The stress level below which the implant can withstand an infinite number of cyclic loads without failure.
. The point at which the modulus of elasticity begins to decrease rapidly.
. The degree of strain at the fracture gap that induces cartilage differentiation.

Correct Answer & Explanation

. The stress level below which the implant can withstand an infinite number of cyclic loads without failure.

Explanation

The fatigue limit (or endurance limit) is the maximum cyclic stress level that a material can endure indefinitely without failing. In nonunions, repetitive physiological loading often exceeds the fatigue limit of the implant, ultimately leading to hardware breakage.

Question 996

Topic: 2. Trauma

In the biomechanical assessment of a statically locked intramedullary nail spanning a highly comminuted diaphyseal fracture, how is the "working length" defined?

. Total length of the intramedullary nail minus the threaded lengths
. Distance between the innermost proximal and innermost distal interlocking screws
. Distance from the nail entry portal to the fracture epicenter
. Ratio of the outer diameter of the nail to its total length
. Distance from the fracture site to the most distal interlocking screw

Correct Answer & Explanation

. Distance between the innermost proximal and innermost distal interlocking screws

Explanation

The working length of an intramedullary nail is the unsupported segment of the implant, defined as the distance between the closest proximal and distal points of fixation (typically the innermost interlocking screws). A longer working length increases construct flexibility.

Question 997

Topic: 2. Trauma

According to Perren's strain theory, what happens to the interfragmentary environment of a midshaft femur fracture when a statically locked nail is dynamized by removing the static proximal screws?

. Bending strain increases significantly causing hypertrophic nonunion
. Shear strain decreases facilitating primary bone healing
. Axial compression is permitted, bringing interfragmentary strain into a range favorable for callus formation
. Torsional strain is completely eliminated
. Axial strain increases to over 100%, inducing membranous ossification

Correct Answer & Explanation

. Axial compression is permitted, bringing interfragmentary strain into a range favorable for callus formation

Explanation

Dynamization allows the nail to slide axially within the dynamic slot, permitting axial compression during weight-bearing. This optimizes interfragmentary strain to a level (typically 2% to 10%) that stimulates secondary bone healing via callus formation.

Question 998

Topic: 2. Trauma

Which of the following best describes the physiologic effect of intramedullary reaming on the blood supply of a long bone diaphysis?

. Immediate destruction of the endosteal supply with a transient reversal to centripetal flow
. Complete and irreversible devascularization of the entire diaphysis for 12 weeks
. Hypertrophy of the nutrient artery within 24 hours of reaming
. Sparing of the endosteal circulation if reamer size is limited to 1 mm over nail size
. Immediate stimulation of purely centrifugal flow driven by increased intramedullary pressure

Correct Answer & Explanation

. Immediate destruction of the endosteal supply with a transient reversal to centripetal flow

Explanation

Normal cortical blood flow is centrifugal (from endosteum to periosteum). Reaming destroys the endosteal circulation, causing a transient reversal to centripetal flow (periosteal to endosteal) to maintain the viability of the inner cortex.

Question 999

Topic: 2. Trauma

When placing a tibial intramedullary nail for a proximal third fracture, what is the primary biomechanical function of a Poller (blocking) screw placed adjacent to the intended nail path?

. To increase the torsional rigidity of the final construct
. To act as a surrogate cortex to narrow the metaphyseal canal and correct nail trajectory
. To compress the fracture fragments directly to induce primary bone healing
. To dynamically lock the nail preventing all axial translation
. To biologically stimulate local periosteal callus formation

Correct Answer & Explanation

. To act as a surrogate cortex to narrow the metaphyseal canal and correct nail trajectory

Explanation

In the wide metaphyseal region, a nail tends to follow the path of least resistance, leading to malalignment (commonly valgus and apex anterior in the proximal tibia). Poller screws artificially narrow the canal, forcing the nail into a central trajectory and maintaining alignment.

Question 1000

Topic: Lower Extremity Trauma

If the diameter of a solid cylindrical intramedullary nail is increased by 50% (e.g., from 10 mm to 15 mm), the bending stiffness of the implant increases by a factor of approximately:

. 1.50
. 2.25
. 3.37
. 5.06
. 16.0

Correct Answer & Explanation

. 5.06

Explanation

The bending stiffness of a solid cylinder is proportional to the area moment of inertia, which scales with the radius to the fourth power (r^4). Increasing the diameter by 1.5 times results in a stiffness increase of 1.5^4, which equals 5.06.

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