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2. Trauma MCQs

Practice Set 79 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 1561

Topic: 2. Trauma

To promote secondary bone healing via callus formation in a highly comminuted mid-shaft femur fracture treated with bridge plating, how should the surgeon manipulate the plate's working length?

. Decrease the overall plate length.
. Fill every available screw hole with bicortical screws.
. Use a thicker locking plate.
. Omit screw placement in the holes closest to the fracture site.
. Use stainless steel screws instead of titanium.

Correct Answer & Explanation

. Omit screw placement in the holes closest to the fracture site.

Explanation

In bridge plating, the working length is the distance between the innermost screws on either side of the fracture. Omitting screws near the fracture increases the working length, which decreases the construct stiffness and allows the controlled interfragmentary strain necessary for callus formation.

Question 1562

Topic: 2. Trauma

Nine months after intramedullary nailing of a femoral shaft nonunion, the patient presents with sudden thigh pain. Radiographs reveal a broken nail at the level of the nonunion. What is the most likely biomechanical cause of this hardware failure?

. Acute plastic deformation
. Ultimate tensile failure
. Fatigue failure from repetitive cyclic loading below the yield stress
. Creep failure due to prolonged static compression
. Stress shielding leading to rapid localized implant resorption

Correct Answer & Explanation

. Fatigue failure from repetitive cyclic loading below the yield stress

Explanation

In the presence of a nonunion, the bone fails to share physiological loads, placing the entire burden on the implant. Over millions of gait cycles, the implant undergoes fatigue failure, breaking from repetitive cyclic loading that is well below its ultimate tensile strength.

Question 1563

Topic: 2. Trauma

Which of the following internal fixation constructs is specifically designed to provide absolute stability and promote primary bone healing?

. Intramedullary nailing of a diaphyseal fracture
. Bridge plating of a comminuted fracture
. Circular external fixation of a nonunion
. Cast immobilization for a non-displaced fracture
. Lag screw fixation protected by a neutralization plate

Correct Answer & Explanation

. Lag screw fixation protected by a neutralization plate

Explanation

Absolute stability dictates that there is essentially zero motion at the fracture site under physiological load, preventing callus formation. A lag screw provides interfragmentary compression, and a neutralization plate protects the lag screw from bending and torsional forces, satisfying the requirement for absolute stability.

Question 1564

Topic: 2. Trauma

A 30-year-old male treated with a statically locked intramedullary nail for a tibial shaft fracture demonstrates a delayed union at 5 months with a visible fracture gap. The surgeon removes the proximal interlocking screws to "dynamize" the nail. What is the main biomechanical goal of this procedure?

. To exponentially increase torsional stiffness.
. To allow axial compression across the fracture site during weight-bearing.
. To rigidly increase bending stiffness.
. To transition the fracture to primary bone healing.
. To permanently decrease the working length of the nail.

Correct Answer & Explanation

. To allow axial compression across the fracture site during weight-bearing.

Explanation

Dynamization involves removing the locking screws from one end of a static intramedullary nail. This permits the bone fragments to compress axially during weight-bearing, stimulating secondary bone healing via Wolff's law without compromising bending alignment.

Question 1565

Topic: 2. Trauma

A 45-year-old female with osteoporotic bone undergoes open reduction and internal fixation of a distal humerus fracture. The surgeon wishes to maximize the pullout strength of the cortical screws used. According to the formula for screw pullout strength, which of the following modifications will most effectively increase pullout resistance?

. Increasing the thread pitch
. Increasing the major diameter of the screw
. Increasing the core (inner) diameter of the screw
. Decreasing the thread length engaged in the bone
. Using a screw with a smaller major diameter

Correct Answer & Explanation

. Increasing the major diameter of the screw

Explanation

Screw pullout strength is directly proportional to the major diameter of the screw and the length of thread engagement, and inversely proportional to the thread pitch. Increasing the major diameter provides the greatest increase in pullout resistance.

Question 1566

Topic: 2. Trauma

A 30-year-old male sustains a severe open tibial shaft fracture managed with a multi-planar external fixator. To maximize the bending stiffness of this construct, which of the following adjustments is most biomechanically effective?

. Increasing the distance between the bone and the longitudinal rod
. Decreasing the distance between the pins within each main fracture fragment
. Increasing the diameter of the Schanz pins
. Decreasing the diameter of the longitudinal rod
. Using pins made of a material with a lower modulus of elasticity

Correct Answer & Explanation

. Increasing the diameter of the Schanz pins

Explanation

The stiffness of an external fixator is most sensitive to the diameter of the pins, as bending stiffness is proportional to the radius raised to the fourth power (r^4). Decreasing the bone-to-rod distance and increasing the pin spread within a fragment also increase stiffness.

Question 1567

Topic: 2. Trauma

A surgeon applies a bridge plate to a comminuted midshaft femur fracture. To promote secondary bone healing via callus formation, the surgeon intentionally leaves three screw holes empty directly over the fracture site. What is the biomechanical effect of increasing the 'working length' of the plate?

. It increases the torsional rigidity of the plate.
. It decreases the construct stiffness, allowing for more interfragmentary motion.
. It concentrates stress directly at the fracture site, risking plate fatigue.
. It increases the risk of galvanic corrosion.
. It completely eliminates axial loading across the fracture site.

Correct Answer & Explanation

. It decreases the construct stiffness, allowing for more interfragmentary motion.

Explanation

Increasing the working length of a plate (the distance between the closest screws on either side of the fracture) decreases the overall stiffness of the construct. This allows for controlled, reversible interfragmentary motion, which stimulates secondary bone healing (callus formation).

Question 1568

Topic: 2. Trauma

A 25-year-old male sustains a transverse patella fracture. The surgeon utilizes a tension band wiring technique. For this construct to successfully convert tensile forces into compressive forces at the fracture site, which anatomic requirement is essential?

. A comminuted anterior cortex
. An intact opposite (articular) cortex to act as a buttress
. Simultaneous application of a neutralization plate
. Utilization of braided cable rather than monofilament wire
. Rigid immobilization of the knee postoperatively to prevent flexion

Correct Answer & Explanation

. An intact opposite (articular) cortex to act as a buttress

Explanation

Tension band wiring applies a tensioning device on the convex (tension) side of the bone. When the joint flexes, it converts the tensile forces into compressive forces at the fracture site, which strictly requires an intact opposite cortex (concave side) to act as a buttress.

Question 1569

Topic: 2. Trauma

A surgeon inserts a 3.5 mm cortical screw as a lag screw across an oblique lateral malleolus fracture. By mistake, the surgeon uses a 2.5 mm drill bit for both the near and far cortices without overdrilling the near cortex. What is the mechanical consequence of this technical error?

. The screw will strip the far cortex immediately upon tightening.
. The fracture will undergo rigid interfragmentary compression.
. The threads will engage both cortices, preventing interfragmentary compression.
. The screw's bending strength will be significantly reduced.
. The pullout strength will be concentrated solely in the near cortex.

Correct Answer & Explanation

. The threads will engage both cortices, preventing interfragmentary compression.

Explanation

For a lag screw to compress two fragments, it must glide freely through the near cortex (gliding hole) and engage only the far cortex (thread hole). If threads engage both cortices simultaneously, the fragments are maintained at a fixed distance, preventing compression.

Question 1570

Topic: 2. Trauma

A patient with a comminuted distal femur fracture is treated with a locked plating construct. Unlike conventional non-locked plates, the stability of a locked plate construct relies primarily on which biomechanical principle?

. Friction generated between the plate and the underlying bone
. Direct interfragmentary compression via eccentric screw placement
. A fixed-angle single-beam construct independent of bone contact
. Dynamic axial compression upon weight bearing
. Decreased working length to maximize rigidity

Correct Answer & Explanation

. A fixed-angle single-beam construct independent of bone contact

Explanation

Locked plates act as internal external fixators, forming a single fixed-angle construct. Their stability depends on the rigid screw-to-plate interface rather than the friction between the plate and the bone, preserving periosteal blood supply.

Question 1571

Topic: 2. Trauma

A skier suffers a bending mechanism injury to the tibia, resulting in a fracture with a classic 'butterfly' fragment. Based on fracture mechanics, on which side of the bone was the tensile force applied?

. On the concave side of the bending force
. On the convex side, opposite the butterfly fragment
. Directly at the apex of the butterfly fragment
. Along the neutral axis of the bone
. Equally across both cortices

Correct Answer & Explanation

. On the concave side of the bending force

Explanation

In a bending injury, the bone fails first on the convex side under tension, creating a transverse fracture line. The compressive forces on the concave side cause oblique fracture lines, resulting in a butterfly fragment on the compressive side.

Question 1572

Topic: 2. Trauma

To augment fixation of a depressed tibial plateau fracture, a surgeon considers using a bone graft substitute. Calcium phosphate is chosen over calcium sulfate. Which of the following is a biomechanical characteristic of calcium phosphate cement?

. It has very high tensile strength.
. It degrades rapidly within 4 to 6 weeks.
. It sets via an exothermic reaction causing tissue necrosis.
. It has high compressive strength, similar to cancellous bone.
. It is primarily osteoinductive rather than osteoconductive.

Correct Answer & Explanation

. It has high compressive strength, similar to cancellous bone.

Explanation

Calcium phosphate cement provides high compressive strength (similar to or greater than cancellous bone), making it useful for structural support in metaphyseal defects. It sets isothermally and degrades very slowly, unlike calcium sulfate which resorbs rapidly.

Question 1573

Topic: Lower Extremity Trauma

During closed reduction and intramedullary nailing of a tibial shaft fracture, the surgeon opts for a solid intramedullary nail instead of a slotted nail of the same diameter. What is the primary biomechanical advantage of the unslotted solid nail?

. Increased ease of insertion due to higher flexibility
. Significantly higher torsional rigidity
. Decreased modulus of elasticity
. Ability to ream over a larger guide wire
. Reduction in hoop stresses on the endosteum

Correct Answer & Explanation

. Significantly higher torsional rigidity

Explanation

Slotted intramedullary nails are more flexible (less bending rigidity), making them easier to insert. However, an unslotted (closed section) nail provides significantly higher torsional rigidity and overall strength compared to a slotted nail of the same material and diameter.

Question 1574

Topic: 2. Trauma

A surgeon removes the proximal static locking screw from an intramedullary nail in a femur fracture at 12 weeks post-op to 'dynamize' the construct. What is the primary biomechanical goal of this procedure?

. To increase torsional stability at the fracture site
. To allow the fracture ends to compress axially during weight-bearing
. To decrease the bending moment of the nail
. To completely eliminate interfragmentary strain
. To shift from secondary bone healing to primary bone healing

Correct Answer & Explanation

. To allow the fracture ends to compress axially during weight-bearing

Explanation

Dynamization involves removing interlocking screws from one end of a statically locked nail. This converts it to a dynamic construct, allowing axial translation and compression at the fracture site upon weight-bearing, which stimulates callus formation.

Question 1575

Topic: 2. Trauma

To maximize the rigidity of a unilateral external fixator construct for a tibial shaft fracture, which biomechanical modification is most effective?

. Increasing the bone-to-rod distance
. Decreasing the pin diameter
. Placing the pins closer together within a segment
. Increasing the pin diameter
. Using a single connecting rod instead of two

Correct Answer & Explanation

. Increasing the pin diameter

Explanation

Increasing the pin diameter has the most profound effect on external fixator stability, as bending stiffness is proportional to the radius of the pin to the fourth power (r^4). Decreasing bone-to-rod distance and maximizing the spread of pins in each segment also improve stability.

Question 1576

Topic: 2. Trauma

For a tension band wire construct to function optimally in treating a transverse patella fracture, the wire must be placed on which surface, and what biomechanical conversion occurs during knee flexion?

. Articular surface; converts tension to compression
. Anterior surface; converts tension to compression
. Articular surface; converts compression to tension
. Anterior surface; converts compression to tension
. Central axis; neutralizes shear and bending

Correct Answer & Explanation

. Anterior surface; converts tension to compression

Explanation

The tension band principle requires the implant to be placed on the tension side of the bone (the anterior surface of the patella). During knee flexion, the anterior tension forces are converted into dynamic compressive forces at the articular surface.

Question 1577

Topic: 2. Trauma

When applying a multi-pin unilateral external fixator, which pin placement configuration maximizes the overall stiffness and stability of the construct?

. Placing all pins as close to the fracture site as possible
. Placing all pins as far from the fracture site as possible
. Placing pins widely spaced within each fragment (near-far technique)
. Placing pins narrowly spaced in the middle of each fragment
. Using uniplanar pins converging at exactly a 45-degree angle

Correct Answer & Explanation

. Placing pins widely spaced within each fragment (near-far technique)

Explanation

To maximize stability in an external fixator, pins should have a wide spread within each main bone fragment. This involves placing one pin close to the fracture and one far from the fracture (the 'near-near, far-far' configuration).

Question 1578

Topic: 2. Trauma

Which of the following fracture fixation techniques relies strictly on providing absolute stability, thereby dictating primary bone healing without callus formation?

. Bridge plating of a highly comminuted diaphyseal femur fracture
. Reamed intramedullary nailing of a closed tibial shaft fracture
. Compression plating of a transverse radius shaft fracture
. Spanning external fixation of a complex pilon fracture
. Circular frame fixation of a hypertrophic nonunion

Correct Answer & Explanation

. Compression plating of a transverse radius shaft fracture

Explanation

Compression plating creates absolute stability with negligible interfragmentary strain, leading to direct (primary) bone healing by Haversian remodeling. Intramedullary nails and bridge plates provide relative stability, promoting secondary bone healing with a callus.

Question 1579

Topic: 2. Trauma

During open reduction and internal fixation of an oblique fibula fracture, a lag screw is utilized. To achieve maximal interfragmentary compression and minimize shear forces across the fracture line, the screw should be inserted:

. Parallel to the fracture plane
. At exactly 45 degrees to the fracture plane
. Perpendicular to the long axis of the bone
. Perpendicular to the fracture plane
. At a 30-degree angle to the long axis

Correct Answer & Explanation

. Perpendicular to the fracture plane

Explanation

For optimal lag screw mechanics, the screw must be placed perpendicular to the fracture plane. If inserted at any other angle, tightening the screw will create shear forces that cause the bone fragments to glide and displace.

Question 1580

Topic: 2. Trauma

In the setting of a highly comminuted midshaft femur fracture with no cortical contact, the working length of an inserted static locked intramedullary nail is defined biomechanically as the distance between:

. The entry portal and the distal tip of the nail
. The proximal locking screws and the distal locking screws
. The proximal fracture line and the distal fracture line
. The isthmus of the canal and the distal locking screws
. The entry portal and the center of the fracture gap

Correct Answer & Explanation

. The proximal locking screws and the distal locking screws

Explanation

The working length of an implant is the unsupported span across which loads are distributed. In a highly comminuted fracture with no inherent bone support, the nail's working length spans entirely between its proximal and distal locking screws.

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