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2. Trauma MCQs

Practice Set 408 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 8141

Topic: 2. Trauma

A 35-year-old man sustains a closed spiral fracture of the distal third of his right humeral shaft in a motor vehicle collision (Holstein-Lewis fracture). In the emergency department, he is entirely unable to extend his wrist or digits, and has decreased sensation over the dorsal first web space. His radial and ulnar pulses are 2+ and capillary refill is brisk. A closed reduction is performed, and a coaptation splint is applied. Post-reduction radiographs show acceptable alignment, but his neurologic deficit remains completely unchanged. What is the most appropriate next step in management?

. Immediate surgical exploration of the radial nerve and open reduction internal fixation
. Observation and supportive splinting, with follow-up electromyography (EMG) at 6 weeks if no clinical improvement is seen
. Emergent MRI of the humerus to evaluate the integrity of the radial nerve
. Immediate surgical exploration, internal fixation, and primary nerve grafting
. Application of a long arm cast in 90 degrees of elbow flexion

Correct Answer & Explanation

. Immediate surgical exploration of the radial nerve and open reduction internal fixation

Explanation

The patient presents with a Holstein-Lewis fracture (spiral fracture of the distal third of the humeral shaft) complicated by a primary radial nerve palsy. The incidence of radial nerve palsy with humeral shaft fractures is approximately 11-18%, and the vast majority represent neuropraxia or axonotmesis that will recover spontaneously over 3 to 4 months. The standard of care for a closed humeral shaft fracture with a primary radial nerve palsy is conservative management with observation and supportive splinting of the wrist and digits. Surgical exploration is generally not immediately indicated for a primary palsy following a closed fracture unless the fracture itself requires surgery for other indications (e.g., open fracture, vascular injury, polytrauma), or it fails to show clinical or electromyographic (EMG) signs of recovery by 3 to 4 months. Since his palsy was present before reduction and remained unchanged, observation is the correct next step. An EMG is typically obtained at 6 weeks to establish a baseline or check for early signs of reinnervation if clinical improvement is absent.

Question 8142

Topic: 2. Trauma

A 72-year-old female sustains a 4-part proximal humerus fracture after a mechanical fall. Which of the following radiographic findings is considered the most reliable predictor of subsequent avascular necrosis (AVN) of the humeral head?

. Displaced greater tuberosity fracture > 1 cm
. Valgus impaction of the humeral head
. Metaphyseal head extension (calcar length) of < 8 mm
. Disruption of the lateral periosteal hinge
. Displacement of the bicipital groove

Correct Answer & Explanation

. Displaced greater tuberosity fracture > 1 cm

Explanation

According to Hertel's criteria, the best radiographic predictors for ischemia (and subsequent AVN) of the humeral head in proximal humerus fractures include a short metaphyseal head extension (calcar length) of < 8 mm, disruption of the medial (not lateral) periosteal hinge, and an anatomic neck fracture pattern. Valgus impacted fractures generally have a lower rate of AVN compared to displaced anatomic neck or varus angulated fractures.

Question 8143

Topic: 2. Trauma

A fracture demonstrating a 'butterfly fragment' is typically indicative of which type of loading mechanism?

. Pure tension
. Pure compression
. Pure torsion
. Bending with axial compression
. Shear force

Correct Answer & Explanation

. Pure tension

Explanation

A butterfly fragment, or wedge fragment, is characteristic of a fracture caused by a bending moment combined with axial compression. The fragment results from a combination of compressive failure on the concave side and tensile failure on the convex side of the bending bone. Pure tension results in transverse fractures, pure compression in oblique or comminuted fractures, and pure torsion in spiral fractures.

Question 8144

Topic: 2. Trauma

In the context of fracture nonunion, which type of nonunion is generally characterized by sufficient vascularity but insufficient stability?

. Atrophic nonunion
. Hypertrophic nonunion
. Oligotrophic nonunion
. Pseudarthrosis
. Infected nonunion

Correct Answer & Explanation

. Atrophic nonunion

Explanation

Hypertrophic nonunion is characterized by abundant callus formation (indicating good biological activity and vascularity) but insufficient stability at the fracture site. The bone attempts to heal but cannot bridge the gap due to excessive motion, often resulting in an 'elephant foot' appearance on radiographs. Atrophic nonunion has poor vascularity and little callus formation. Oligotrophic is a variant of atrophic with minimal callus. Pseudarthrosis is a specific type of established nonunion with a false joint. Infected nonunion is due to infection.

Question 8145

Topic: 2. Trauma

The concept of 'tension band plating' relies on converting which type of force into a compressive force at the fracture site?

. Shear
. Torsion
. Compression
. Bending (tensile side)
. Axial

Correct Answer & Explanation

. Shear

Explanation

Tension band plating (or wiring) converts tensile forces (e.g., on the convex side of a bone under bending) into compressive forces at the fracture site. This helps stabilize the fracture and promotes healing by providing interfragmentary compression. It is commonly used for avulsion fractures or fractures on the tension side of eccentrically loaded bones (e.g., olecranon, patella, medial malleolus).

Question 8146

Topic: 2. Trauma

Which type of fracture pattern is typically associated with a high-energy rotational injury?

. Transverse fracture
. Oblique fracture
. Spiral fracture
. Comminuted fracture
. Avulsion fracture

Correct Answer & Explanation

. Transverse fracture

Explanation

Spiral fractures are characteristically caused by torsional (rotational) forces. The fracture line spirals along the shaft of the bone. Transverse fractures result from direct bending or tension. Oblique fractures can result from compression or bending. Comminuted fractures involve multiple fragments and are typically from high-energy direct trauma. Avulsion fractures occur when a tendon or ligament pulls off a piece of bone.

Question 8147

Topic: 2. Trauma

The concept of 'load sharing' in fracture fixation refers to:

. The implant bearing all the load, completely shielding the bone.
. The fracture fragments bearing some of the load, in addition to the implant.
. The use of multiple implants to fix one fracture.
. The ability of an implant to withstand cyclical loading.
. The body's natural ability to redistribute weight away from an injured limb.

Correct Answer & Explanation

. The implant bearing all the load, completely shielding the bone.

Explanation

Load sharing describes a fixation construct where the bone fragments themselves (e.g., compressed fracture fragments) contribute to bearing the mechanical load, allowing the implant to share that load rather than bearing it entirely. This promotes more physiological stress on the bone, which can encourage healing and reduce stress shielding. Examples include intramedullary nails or plates applied with lag screws and compression.

Question 8148

Topic: 2. Trauma

A 28-year-old male sustains a closed humerus shaft fracture with an immediate, complete radial nerve palsy. An EMG performed at 4 weeks demonstrates fibrillation potentials in the brachioradialis. Advanced imaging confirms preserved continuity of the endoneurium despite complete axonal disruption. According to the Sunderland classification, what grade of nerve injury does this represent?

. First-degree (Neuropraxia)
. Second-degree (Axonotmesis)
. Third-degree
. Fourth-degree
. Fifth-degree (Neurotmesis)

Correct Answer & Explanation

. First-degree (Neuropraxia)

Explanation

This is a Sunderland second-degree nerve injury (which corresponds to Seddon's axonotmesis). The axon is completely disrupted, leading to Wallerian degeneration distal to the injury (indicated by fibrillation potentials on EMG at 4 weeks), but the endoneurial tube and all supporting connective tissue (perineurium, epineurium) remain intact. This intact endoneurial tube allows the regenerating axon to reach its specific target, typically resulting in complete clinical recovery.

Question 8149

Topic: 2. Trauma

During internal fixation of a diaphyseal fracture, a surgeon considers the pullout strength of the cortical screws being used. Which of the following modifications to a screw design will most significantly increase its pullout strength?

. Decreasing the outer diameter
. Increasing the pitch
. Increasing the inner (root) diameter
. Increasing the outer diameter
. Decreasing the thread depth

Correct Answer & Explanation

. Decreasing the outer diameter

Explanation

Pullout strength of a screw is directly proportional to the outer diameter, thread depth, and length of engagement in the bone, and inversely proportional to the pitch. Increasing the outer diameter has the most profound effect on increasing pullout strength.

Question 8150

Topic: 2. Trauma

A 28-year-old man sustains a closed spiral fracture of the middle third of the humerus. On examination, he is unable to extend his wrist or digits. Based on the Seddon classification, if this injury is an axonotmesis, what is the expected microscopic state of the nerve at the zone of injury?

. Focal demyelination with intact axons and intact endoneurium
. Disruption of the axon and myelin sheath with intact endoneurium
. Disruption of the axon, myelin sheath, and endoneurium with intact perineurium
. Disruption of all fascicular structures with an intact epineurium
. Complete physical transection of the entire nerve trunk

Correct Answer & Explanation

. Focal demyelination with intact axons and intact endoneurium

Explanation

In the Seddon classification, Axonotmesis refers to a nerve injury where the axon and its myelin sheath are disrupted, leading to Wallerian degeneration distally. However, the supporting connective tissue framework—specifically the endoneurium, perineurium, and epineurium—remains intact. This intact framework provides a clear pathway for axonal regeneration. Neuropraxia involves focal demyelination with intact axons. Sunderland classification further divides these, but axonotmesis corresponds primarily to Sunderland 2nd degree (intact endoneurium).

Question 8151

Topic: 2. Trauma

An 8-year-old boy sustains a minor fall and presents with a pathologic fracture of the proximal humerus. Radiographs demonstrate a centrally located, completely radiolucent metaphyseal lesion extending to the physis, with a small cortical fragment resting at the dependent portion of the cyst ('fallen leaf' sign). Once the fracture heals, the cyst remains persistent and active. What is the most appropriate initial management for the cyst?

. Wide surgical resection and allograft reconstruction
. Extralesional curettage using high-speed burr
. Radiation therapy
. Aspiration and injection of methylprednisolone or bone marrow aspirate
. Neoadjuvant chemotherapy followed by marginal excision

Correct Answer & Explanation

. Wide surgical resection and allograft reconstruction

Explanation

The lesion is a Unicameral Bone Cyst (UBC), which classically presents as a central, radiolucent lesion in the metaphysis of long bones (most commonly proximal humerus and proximal femur) in children. The 'fallen leaf' sign is pathognomonic. Initial management of an active, persistent UBC with a risk of refracture after fracture healing is typically minimally invasive, most commonly aspiration and injection of a corticosteroid (methylprednisolone) and/or bone marrow aspirate. Open curettage and bone grafting is reserved for refractory cases or specific locations (like the proximal femur where fracture risk is critical). Resection, radiation, and chemotherapy are entirely inappropriate for this benign fluid-filled cyst.

Question 8152

Topic: 2. Trauma

An 8-year-old boy presents with mild arm pain after throwing a baseball. Radiographs of the humerus reveal a central, lytic lesion in the proximal diaphysis with a small piece of cortical bone resting at the dependent portion of the lesion. There is mild expansile remodeling but no other cortical breach. What is the most appropriate initial management for this patient?

. Wide surgical resection and endoprosthetic reconstruction
. Neoadjuvant chemotherapy followed by curettage
. Immobilization in a sling followed by observation or percutaneous injection
. Immediate open curettage and bone grafting
. Radiation therapy

Correct Answer & Explanation

. Wide surgical resection and endoprosthetic reconstruction

Explanation

The presentation is classic for a simple (unicameral) bone cyst with a pathologic fracture. The 'fallen leaf' or 'fallen fragment' sign is pathognomonic. Unicameral bone cysts are benign, fluid-filled lesions that commonly occur in the proximal humerus and femur of children. The initial treatment for a non-displaced fracture through a UBC is immobilization (e.g., a sling) to allow the fracture to heal. Subsequent treatment, if the cyst does not consolidate after the fracture heals, typically involves percutaneous injections (corticosteroids, bone marrow aspirate) before considering more invasive options like curettage and bone grafting.

Question 8153

Topic: 2. Trauma

During the process of secondary fracture healing, the differentiation of mesenchymal stem cells is highly dependent on the local mechanical and biological environment. According to Carter's mechanobiology principles and Perren's strain theory, which of the following environments most strongly favors the differentiation of these cells into chondrocytes (cartilage formation)?

. High oxygen tension and mechanical strain less than 2%
. Low oxygen tension and mechanical strain between 2% and 10%
. Low oxygen tension and mechanical strain less than 2%
. High oxygen tension and mechanical strain greater than 20%
. Low oxygen tension and mechanical strain greater than 20%

Correct Answer & Explanation

. High oxygen tension and mechanical strain less than 2%

Explanation

The differentiation of tissue in a fracture gap is regulated by both mechanical strain and oxygen tension. According to Perren's strain theory, tissues can only form if they can withstand the local mechanical strain without rupturing: bone can tolerate up to 2% strain, cartilage up to 10% strain, and granulation/fibrous tissue >10-20%. Furthermore, Carter's principles dictate that low oxygen tension (hypoxia) combined with moderate mechanical strain or hydrostatic compressive stress favors chondrogenesis. Conversely, low strain and high oxygen tension favor direct osteogenesis. Extremely high strain prevents both bone and cartilage formation, leading to a fibrous nonunion.

Question 8154

Topic: 2. Trauma

When inserting a fully threaded cortical screw to provide interfragmentary compression across an oblique fracture, what mechanical parameter is directly optimized by overdrilling the near cortex to create a 'glide hole'?

. Pull-out strength
. Torsional rigidity
. Bending stiffness
. Lag effect (interfragmentary compression)
. Thread purchase in the near cortex

Correct Answer & Explanation

. Pull-out strength

Explanation

Creating a glide hole in the near cortex (overdrilling so the hole is the size of the screw's outer thread diameter) prevents the threads from engaging the near fragment. As the screw head engages the near cortex, the threads engaging the far cortex pull the far fragment towards the near fragment, generating interfragmentary compression. This mechanism is known as the lag effect. If the near cortex is not overdrilled, the threads engage both cortices simultaneously, maintaining the gap without generating compression.

Question 8155

Topic: 2. Trauma

When selecting a cortical bone screw for fracture fixation, a surgeon opts for a screw with a larger inner (core) diameter while keeping the outer diameter constant. Which of the following biomechanical effects will this design change have?

. Increases the bending strength
. Increases the pullout strength
. Decreases the resistance to pullout
. Increases the thread depth
. Decreases the frictional resistance during insertion

Correct Answer & Explanation

. Increases the bending strength

Explanation

The bending strength (and stiffness) of a screw is proportional to the inner (core) diameter. Specifically, bending stiffness is proportional to the core radius to the 4th power (area moment of inertia), and bending strength is proportional to the core radius to the 3rd power. Increasing the core diameter while keeping the outer diameter constant decreases the thread depth, which would actually decrease pullout strength.

Question 8156

Topic: 2. Trauma

A 32-year-old man sustains a transverse midshaft humerus fracture. The surgeon plans to use a lag screw and neutralization plate. To maximize the pull-out strength of the cortical screw in the diaphysis, which of the following changes to the screw design should be utilized?

. Decrease the outer diameter
. Increase the inner core diameter
. Decrease the thread pitch
. Increase the thread pitch
. Decrease the thread depth

Correct Answer & Explanation

. Decrease the outer diameter

Explanation

The pull-out strength of a bone screw is directly proportional to the outer diameter of the thread, the thread depth (outer diameter minus inner/core diameter), the length of thread engagement, and the number of threads engaged in the cortex. Thread pitch is the distance between adjacent threads; therefore, decreasing the thread pitch increases the number of threads per unit length of the screw, which increases the total cortical engagement and maximizes pull-out strength.

Question 8157

Topic: 2. Trauma

A 24-year-old man sustains bilateral closed femoral shaft fractures in a motorcycle collision. Twelve hours post-admission, he becomes confused, tachypneic, and develops a petechial rash over his axillae. Arterial blood gas analysis reveals a PaO2 of 55 mm Hg. What is the primary pathophysiological mechanism underlying this patient's hypoxemia?

. Ventilation-perfusion (V/Q) mismatch due to microvascular obstruction and endothelial damage
. Alveolar hypoventilation secondary to central nervous system depression
. Cardiogenic pulmonary edema from myocardial contusion
. Direct toxic effect of free fatty acids on the respiratory center
. Bronchospasm resulting from systemic inflammatory response syndrome (SIRS)

Correct Answer & Explanation

. Ventilation-perfusion (V/Q) mismatch due to microvascular obstruction and endothelial damage

Explanation

The classic triad of respiratory insufficiency, neurologic changes, and a petechial rash following long bone fractures indicates Fat Embolism Syndrome (FES). Hypoxemia in FES primarily results from ventilation-perfusion (V/Q) mismatch. This is initially caused by fat globules mechanically obstructing the pulmonary microvasculature, which is subsequently followed by a chemical pneumonitis triggered by the breakdown of fat into toxic free fatty acids, leading to severe endothelial damage and ARDS.

Question 8158

Topic: 2. Trauma

During fracture fixation, maximizing the pullout strength of a cortical bone screw is often desired, particularly in osteoporotic bone. Which of the following modifications to a screw's design would most significantly increase its pullout strength?

. Decreasing the outer (thread) diameter
. Increasing the inner (core) diameter
. Decreasing the thread pitch
. Increasing the thread pitch
. Cannulating the screw

Correct Answer & Explanation

. Decreasing the outer (thread) diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement in the bone, and the thread density (which is inversely related to thread pitch). Therefore, decreasing the thread pitch increases the number of threads engaged per unit length, thereby increasing pullout strength. Increasing the inner (core) diameter increases the screw's bending strength but decreases the thread depth, which can actually lower pullout strength. Cannulation primarily decreases the bending strength.

Question 8159

Topic: 2. Trauma

According to Perren's strain theory of fracture healing, the differentiation of mesenchymal stem cells into specific tissue types is dictated by the mechanical strain environment. What is the maximum tissue strain that allows for the formation of lamellar bone?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory postulates that a specific tissue type cannot form if the strain in the fracture gap exceeds the elongation at which that tissue ruptures. Lamellar bone is rigid and can only form and survive under conditions of very low strain, typically less than 2%. Absolute stability constructs (e.g., lag screw and neutralization plate) aim to keep strain below 2% to allow for primary bone healing. Woven bone can form in strain environments up to 10%, cartilage up to 10-30%, and granulation tissue can tolerate strains up to 100%.

Question 8160

Topic: 2. Trauma

A 35-year-old man sustains a closed midshaft humerus fracture and presents with an immediate wrist drop. At 4 weeks, an EMG shows fibrillations, and a nerve conduction study shows no action potentials across the injury site. If the pathology involves complete axonal disruption with distal Wallerian degeneration, but the endoneurium, perineurium, and epineurium remain completely intact, what is the Sunderland classification of this injury?

. First degree
. Second degree
. Third degree
. Fourth degree
. Fifth degree

Correct Answer & Explanation

. First degree

Explanation

This scenario describes a Sunderland second-degree nerve injury (equivalent to Seddon's axonotmesis). In a second-degree injury, the axon is disrupted, leading to distal Wallerian degeneration, but all connective tissue sheaths (endoneurium, perineurium, epineurium) are preserved. This intact framework allows for excellent potential for spontaneous regeneration at a rate of roughly 1 mm/day. First-degree is neuropraxia (myelin injury). Third-degree involves endoneurium disruption; fourth-degree involves perineurium disruption; fifth-degree is complete nerve transection.

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