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2. Trauma MCQs

Practice Set 49 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 961

Topic: 2. Trauma

A 35-year-old male is admitted with a highly comminuted Schatzker VI tibial plateau fracture. Overnight, he develops increasing leg pain unresponsive to opioids. Which of the following objective measurements is an absolute indication for emergency fasciotomies?

. Absolute compartment pressure greater than 20 mmHg
. Diastolic blood pressure minus compartment pressure (Delta P) less than 30 mmHg
. Mean arterial pressure minus compartment pressure less than 40 mmHg
. Systolic blood pressure minus compartment pressure less than 50 mmHg
. Loss of palpable dorsalis pedis and posterior tibial pulses

Correct Answer & Explanation

. Diastolic blood pressure minus compartment pressure (Delta P) less than 30 mmHg

Explanation

A Delta P (diastolic blood pressure minus compartment pressure) of less than 30 mmHg is the most reliable objective threshold for diagnosing acute compartment syndrome. Loss of pulses is a late and unreliable sign.

Question 962

Topic: 2. Trauma
A polytrauma patient arrives in the trauma bay with a hemodynamically unstable anteroposterior compression (APC-III) pelvic ring injury. A pelvic binder is ordered. To be most effective in reducing pelvic volume, where should the binder be centered?
. Over the iliac crests
. Midway between the iliac crests and the greater trochanters
. Directly over the greater trochanters
. At the level of the anterior superior iliac spines (ASIS)
. Below the lesser trochanters

Correct Answer & Explanation

. Directly over the greater trochanters

Explanation

A pelvic binder must be applied directly over the greater trochanters to effectively compress the pelvic ring and reduce the symphyseal diastasis. Placing it higher (over the iliac crests) is less effective and can paradoxically open the pelvis further in some fracture patterns.

Question 963

Topic: 2. Trauma

A 30-year-old industrial painter presents with a pinpoint puncture wound on his left index finger from a high-pressure paint gun. He has mild swelling and minimal pain. Radiographs show subcutaneous emphysema but no fracture. What is the most appropriate management?

. Oral antibiotics, tetanus prophylaxis, and discharge with close follow-up
. Local wound care and a short course of intravenous antibiotics in the emergency department
. Emergent wide surgical debridement and decompression of the digit
. Corticosteroid injection into the flexor sheath to reduce inflammation
. Observation overnight with elevation; debridement only if necrosis develops

Correct Answer & Explanation

. Emergent wide surgical debridement and decompression of the digit

Explanation

High-pressure injection injuries are surgical emergencies, even if the initial presentation appears benign. Paint and industrial solvents cause intense chemical inflammation and compartment syndrome, requiring immediate wide surgical debridement to prevent amputation.

Question 964

Topic: 2. Trauma
In the management of a Gustilo-Anderson Type IIIB open tibia fracture, which of the following variables has been shown in the literature to be the most critical independent predictor of preventing deep infection?
. Surgical debridement within exactly 6 hours of the injury
. Time to administration of systemic antibiotics
. Use of high-pressure pulsatile lavage over low-pressure lavage
. Immediate definitive internal fixation
. Application of a negative pressure wound therapy device in the emergency department

Correct Answer & Explanation

. Time to administration of systemic antibiotics

Explanation

Multiple studies have demonstrated that the earliest possible administration of systemic antibiotics is the single most important factor in reducing infection rates in open fractures. The rigid 6-hour rule for surgical debridement has been largely debunked, provided antibiotics are given promptly.

Question 965

Topic: 2. Trauma

A 35-year-old male polytrauma patient with a severe chest injury and bilateral femur fractures is evaluated in the ER.

His initial labs show a lactate of 4.5 mmol/L, a pH of 7.21, and a base deficit of -8. Based on principles of Damage Control Orthopedics (DCO), what is the most appropriate initial management of his femur fractures?

. Immediate bilateral reamed intramedullary nailing
. Unreamed intramedullary nailing within 24 hours
. Open reduction and internal fixation with locking plates
. Temporary external fixation of both femurs
. Skeletal traction until discharge to a rehabilitation facility

Correct Answer & Explanation

. Temporary external fixation of both femurs

Explanation

This patient is physiologically unstable (lactate > 4.0, pH < 7.24, base deficit < -6), making him a candidate for Damage Control Orthopedics (DCO). Temporary external fixation of major long bones is indicated to avoid the second hit of prolonged surgery and blood loss associated with intramedullary nailing.

Question 966

Topic: 2. Trauma

The primary biomechanical advantage of an intramedullary nail over a plate for diaphyseal long bone fractures is:

. It provides absolute stability at the fracture site.
. It promotes primary bone healing without callus formation.
. It acts as a load-sharing device along the mechanical axis.
. It completely eliminates stress shielding of the bone.
. It requires less surgical exposure for insertion.

Correct Answer & Explanation

. It acts as a load-sharing device along the mechanical axis.

Explanation

Correct Answer: CIntramedullary nails are load-sharing implants, meaning they bear a portion of the physiologic loads (axial, bending, torsion) while allowing the bone to carry the remainder. Their central placement along the mechanical axis of the bone minimizes the bending moment arm, effectively converting bending stresses into compressive forces, which is beneficial for fracture healing. Plates, conversely, are typically load-bearing (load-sparing in specific scenarios like bridging osteosynthesis) and are eccentrically placed, leading to higher bending stresses at the plate-bone interface. IM nails typically promote relative stability and secondary bone healing, not absolute stability or primary healing. While they can reduce stress shielding compared to rigid plates, they do not eliminate it entirely, and soft tissue preservation is a surgical technique advantage, not a primary biomechanical one.

Question 967

Topic: 2. Trauma

Regarding the biomechanics of reamed versus unreamed intramedullary nailing, which statement is most accurate?

. Unreamed nails offer superior rotational stability due to tighter fit.
. Reamed nails typically have a smaller diameter, increasing strain at the fracture site.
. Reaming significantly increases the bending and torsional stiffness of the construct.
. Unreamed nailing preserves the endosteal blood supply, leading to faster union biomechanically.
. Reaming always leads to higher rates of nonunion due to thermal necrosis.

Correct Answer & Explanation

. Reaming significantly increases the bending and torsional stiffness of the construct.

Explanation

Correct Answer: CReamed intramedullary nailing allows for the insertion of a larger diameter nail, which fills the medullary canal more completely. This intimate contact between the nail and the endosteal surface significantly increases the bending and torsional stiffness of the construct, providing greater mechanical stability at the fracture site. Unreamed nails, being of smaller diameter, have less canal fill and consequently lower stiffness. While reaming does cause temporary disruption of the endosteal blood supply, the long-term biomechanical benefit of increased stability often outweighs this, leading to comparable or even improved union rates in many cases. Unreamed nails do not inherently offer superior rotational stability, as this is primarily achieved through interlocking screws. Reaming does not always lead to higher nonunion rates; the effect on healing is complex and multifactorial.

Question 968

Topic: 2. Trauma

A common biomechanical rationale for using multiple interlocking screws at each end of an intramedullary nail for diaphyseal fractures is to:

. Increase the axial stiffness of the construct.
. Prevent stress shielding of the fracture fragments.
. Augment rotational and bending stability.
. Reduce the risk of intramedullary infection.
. Facilitate dynamic compression at the fracture site.

Correct Answer & Explanation

. Augment rotational and bending stability.

Explanation

Correct Answer: CInterlocking screws are crucial for providing rotational and bending stability, particularly in comminuted or segmentally unstable fractures where the bone cannot inherently resist these forces. By 'locking' the nail to the proximal and distal fragments, they prevent relative motion between the bone and the implant, thereby controlling rotation and preventing gross angulation. While they contribute indirectly to overall construct stability, their primary role is not to increase axial stiffness (which is mainly a function of nail diameter and material) or to prevent stress shielding. Dynamic compression is achieved by slotting or specific techniques that allow controlled axial shortening, not by multiple static interlocking screws. Infection risk is unrelated to the number of screws in this context.

Question 969

Topic: 2. Trauma

What biomechanical principle dictates the common recommendation for starting point selection in femoral intramedullary nailing?

. To maximize resistance to screw pullout.
. To avoid injury to the superficial femoral artery.
. To achieve an optimal load-sharing configuration.
. To minimize eccentric reaming of the piriformis fossa.
. To allow for easier subsequent implant removal.

Correct Answer & Explanation

. To achieve an optimal load-sharing configuration.

Explanation

Correct Answer: CThe ideal starting point for femoral IM nailing is crucial for proper nail alignment and load distribution. A starting point that is too medial or lateral can lead to eccentric reaming of the piriformis fossa or greater trochanter, potentially causing iatrogenic comminution, and may result in varus or valgus malalignment, respectively. An optimal starting point, typically in line with the long axis of the medullary canal in both sagittal and coronal planes, allows the nail to be inserted centrally, ensuring an optimal load-sharing configuration and reducing the risk of fracture malreduction or mechanical failure. Avoiding injury to neurovascular structures and maximizing screw pullout resistance are important considerations but not the primary biomechanical drivers of starting point selection in this context.

Question 970

Topic: 2. Trauma

In a comminuted diaphyseal fracture treated with an IM nail, what type of stability is generally aimed for biomechanically?

. Absolute stability, preventing all motion.
. Rigid stability, promoting primary bone healing.
. Relative stability, encouraging secondary bone healing.
. Dynamic stability, allowing significant axial micromotion.
. External stability, relying on periosteal healing.

Correct Answer & Explanation

. Relative stability, encouraging secondary bone healing.

Explanation

Correct Answer: CIntramedullary nailing, especially in comminuted diaphyseal fractures, aims for relative stability. This allows for controlled micromotion at the fracture site, which is biomechanically conducive to stimulating secondary bone healing through callus formation (endochondral ossification). Absolute stability, which aims to eliminate all motion, is typically the goal with lag screws and compression plating for simple, reducible fractures to promote primary bone healing. While some axial micromotion is desirable, 'significant axial micromotion' might lead to delayed union or nonunion. External stability isn't a classification for internal fixation.

Question 971

Topic: 2. Trauma

In a distal femur fracture requiring antegrade IM nailing, why is multi-planar distal locking biomechanically advantageous?

. It allows for dynamic compression at the fracture site.
. It reduces the risk of iatrogenic nerve injury.
. It enhances stability against both sagittal and coronal plane angulation and rotation.
. It facilitates earlier weight-bearing regardless of bone quality.
. It simplifies implant removal in the future.

Correct Answer & Explanation

. It enhances stability against both sagittal and coronal plane angulation and rotation.

Explanation

Correct Answer: CDistal femur fractures, particularly those with metaphyseal comminution, pose significant challenges for stability due to the wider canal and lack of diaphyseal purchase. Multi-planar distal locking (e.g., screws in both AP and ML planes) provides superior purchase and enhances resistance to angulation in multiple planes (sagittal and coronal) as well as improving rotational control of the distal fragment. This increased stability is critical for preventing malunion and promoting healing in these complex fracture patterns. Dynamic compression, nerve injury, and earlier weight-bearing are not directly addressed by multi-planar locking in this context, and implant removal is not a biomechanical driver.

Question 972

Topic: 2. Trauma

Considering the biomechanics of nail insertion, what is the primary purpose of pre-bending an intramedullary nail for certain fractures?

. To prevent inadvertent reaming of the medullary canal.
. To make the nail removal process easier in the future.
. To better match the natural curvature of the bone and facilitate reduction.
. To increase the ultimate tensile strength of the implant.
. To reduce the risk of intraoperative infection.

Correct Answer & Explanation

. To better match the natural curvature of the bone and facilitate reduction.

Explanation

Correct Answer: CLong bones have a natural curvature (e.g., anterior bow of the femur, anterior apex recurvatum of the tibia). Pre-bending an intramedullary nail to match this physiological curvature is critical for proper anatomical reduction and to prevent 'windshield-wiper' effect or malalignment. It helps to guide the nail through the canal and achieve optimal fracture reduction, especially in fractures with inherent angulation. Incorrect curvature matching can lead to malreduction, cortical impingement, or increased stress at the fracture site. Pre-bending does not affect reaming, tensile strength, or infection risk directly.

Question 973

Topic: 2. Trauma

What is the biomechanical significance of the 'working length' of an intramedullary nail?

. It refers to the maximum length of the nail that can be inserted.
. It represents the portion of the nail that is exposed to the external environment.
. It is the distance between the most proximal and most distal locking screws.
. It describes the effective length of the nail resisting deformation at the fracture site.
. It is the total length of the nail from end to end.

Correct Answer & Explanation

. It is the distance between the most proximal and most distal locking screws.

Explanation

Correct Answer: CThe 'working length' of an IM nail construct is defined as the distance between the most proximal and most distal interlocking screws (or between a screw and the unconstrained end of the nail). Biomechanically, this length determines the leverage arm over which forces are applied and deformation occurs. A longer working length (fewer screws, greater distance between them) generally leads to a less stiff construct and allows more micromotion at the fracture site, which can be beneficial for callus formation but also increases the risk of excessive motion and delayed union if too long. A shorter working length (more screws, closer together) results in a stiffer construct. This concept is vital for understanding load transfer and stability.

Question 974

Topic: 2. Trauma

During reaming for intramedullary nailing, what is the primary biomechanical consequence of heat generation?

. Increased rate of callus formation.
. Decreased friction between the reamer and bone.
. Potential for thermal osteonecrosis and delayed healing.
. Enhanced screw purchase in the cortical bone.
. Improved strength of the reamed bone for nail insertion.

Correct Answer & Explanation

. Potential for thermal osteonecrosis and delayed healing.

Explanation

Correct Answer: CThe mechanical action of reaming generates significant heat. If excessive, this heat can lead to thermal osteonecrosis (cell death) of the endosteal bone. Necrotic bone has compromised vascularity and cellular activity, which can delay or impair fracture healing and increase the risk of infection. While reaming does remove bone, the heat generated is a critical concern for bone viability. Strategies to mitigate this include sharp reamers, sequential reaming with gradual diameter increase, and intermittent reaming with fluid irrigation.

Question 975

Topic: 2. Trauma
Which of the following local factors is most detrimental to secondary fracture healing and is a primary indication for debridement and possible bone grafting?
. Small interfragmentary gap (<1mm)
. Low-energy fracture pattern
. Adequate soft tissue coverage
. Infection at the fracture site
. Early weight-bearing with stable fixation

Correct Answer & Explanation

. Infection at the fracture site

Explanation

Infection at the fracture site is profoundly detrimental to fracture healing. It directly inhibits osteoblast activity, stimulates osteoclast activity, increases local acidity, and compromises vascularity, leading to nonunion or osteomyelitis. It necessitates aggressive debridement, antibiotics, and often bone grafting once infection is controlled. A small gap and low-energy fracture generally promote healing. Adequate soft tissue is beneficial. Early weight-bearing with stable fixation can promote healing by providing beneficial micromotion.

Question 976

Topic: 2. Trauma

In the initial inflammatory phase of fracture healing, what is the primary role of the fracture hematoma?

. To provide a scaffold for direct osteon formation
. To act as a sterile medium for bacterial growth
. To serve as a source of growth factors and progenitor cells
. To mechanically stabilize the fracture fragments
. To promote immediate revascularization across the fracture site

Correct Answer & Explanation

. To serve as a source of growth factors and progenitor cells

Explanation

Correct Answer: CThe fracture hematoma, formed immediately after injury, is crucial. It contains blood cells, plasma, and necrotic tissue, but most importantly, it's a rich source of growth factors (e.g., PDGF, TGF-beta) and inflammatory cells that initiate the healing cascade. It also contains mesenchymal stem cells and sets the biological stage for repair. It does not primarily provide a scaffold for direct osteon formation, nor is its role to act as a sterile medium for bacterial growth, or to mechanically stabilize the fracture fragments, which typically requires external means. Immediate revascularization is a later event.

Question 977

Topic: 2. Trauma

For primary (direct) fracture healing to occur, what is the critical interfragmentary strain threshold generally required?

. Less than 10%
. Less than 5%
. Less than 2%
. Less than 1%
. Less than 0.5%

Correct Answer & Explanation

. Less than 2%

Explanation

Correct Answer: CPrimary bone healing requires extremely rigid fixation and minimal interfragmentary motion. The critical interfragmentary strain for direct bone formation (primary healing) is generally accepted to be less than 2%. Higher strains lead to the formation of fibrous tissue or cartilage (secondary healing). This is a foundational biomechanical principle in fracture management.

Question 978

Topic: 2. Trauma

A surgeon is inserting an intramedullary nail for a diaphyseal femur fracture. Postoperatively, radiographs reveal impingement of the nail against the anterior cortex of the distal femur. Which of the following best explains this biomechanical mismatch?

. The nail has a smaller radius of curvature than the native femur.
. The nail has a larger radius of curvature than the native femur.
. The nail was over-reamed by 2.0 mm.
. The starting point was excessively posterior.
. The nail has an excessive modulus of elasticity.

Correct Answer & Explanation

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

Explanation

The native femur has an anterior bow, typically with a radius of curvature around 1200 mm. A nail with a larger radius of curvature is straighter than the femur, leading to anterior cortical impingement or perforation distally.

Question 979

Topic: Lower Extremity Trauma

Which of the following geometric modifications to a solid intramedullary nail will most dramatically increase its bending stiffness?

. Increasing the length of the nail by 10%
. Decreasing the working length by 50%
. Increasing the radius of the nail by 20%
. Changing the material from titanium to stainless steel
. Adding an anterior slot to the nail

Correct Answer & Explanation

. Increasing the radius of the nail by 20%

Explanation

The bending stiffness of a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, even a small increase in the nail's radius provides the most exponential increase in bending stiffness.

Question 980

Topic: 2. Trauma

According to Perren's strain theory, what range of interfragmentary strain is typically generated by a statically locked intramedullary nail and what type of healing does it promote?

. Less than 2%, promoting primary intramembranous healing
. Between 2% and 10%, promoting secondary endochondral healing
. Between 10% and 30%, promoting primary cortical remodeling
. Greater than 30%, promoting robust hypertrophic callus
. 0%, resulting in contact healing through cutting cones

Correct Answer & Explanation

. Between 2% and 10%, promoting secondary endochondral healing

Explanation

Intramedullary nails provide relative stability, typically resulting in interfragmentary strain between 2% and 10%. This strain environment favors secondary fracture healing via endochondral ossification and callus formation.

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