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2. Trauma MCQs

Practice Set 368 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 7341

Topic: Lower Extremity Trauma

When a long bone is subjected to bending forces, its resistance to bending is proportional to its area moment of inertia. For a hollow cylinder, area moment of inertia is proportional to the radius raised to which power?

. 1st power
. 2nd power
. 3rd power
. 4th power
. 5th power

Correct Answer & Explanation

. 1st power

Explanation

The area moment of inertia for a cylinder is proportional to the radius to the fourth power (r^4). Thus, placing intramedullary nails with a larger radius or increasing the outer diameter of a bone exponentially increases bending rigidity.

Question 7342

Topic: 2. Trauma

According to Perren's strain theory, secondary fracture healing with abundant callus formation is optimized when the mechanical strain at the fracture gap is maintained between:

. 0% and 2%
. 2% and 10%
. 10% and 30%
. 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. 0% and 2%

Explanation

Perren's strain theory posits that secondary bone healing (callus formation) requires a moderate interfragmentary strain environment, typically between 2% and 10%. Strain below 2% promotes primary healing, while strain above 10% disrupts tissue formation, potentially leading to nonunion.

Question 7343

Topic: 2. Trauma

In the fixation of a diaphyseal fracture using a bridge plate technique, intentionally increasing the distance between the innermost screws adjacent to the fracture gap (increasing the working length) has what biomechanical effect on the construct?

. Increases the torsional stiffness of the overall construct
. Decreases the construct's flexibility, promoting primary bone healing
. Increases construct flexibility, reducing strain concentration on the implant and promoting callus formation
. Increases the risk of screw pull-out by concentrating stress at the innermost screws
. Eliminates the need for bicortical screw purchase

Correct Answer & Explanation

. Increases the torsional stiffness of the overall construct

Explanation

Increasing the working length of a plate increases the flexibility of the fixation construct. This controlled flexibility allows for beneficial interfragmentary motion that promotes secondary bone healing (callus) while decreasing the stress concentrated on any single section of the plate, preventing fatigue failure.

Question 7344

Topic: 2. Trauma

When applying a compression plate to a transverse midshaft femur fracture, the plate is ideally placed on the tension side of the bone. For the human femur, the tension side is generally located on the:

. Medial cortex
. Anterior cortex
. Lateral cortex
. Posterior cortex
. Anteromedial cortex

Correct Answer & Explanation

. Medial cortex

Explanation

In the femur, normal physiologic loading creates a bending moment that results in tension on the lateral cortex and compression on the medial cortex. Plates are most effective when acting as a tension band on the tension side.

Question 7345

Topic: 2. Trauma

The predominant blood supply to the proximal pole of the scaphoid is provided by retrograde branches entering the dorsal ridge from which artery?

. Ulnar artery
. Anterior interosseous artery
. Radial artery
. Deep palmar arch
. Superficial palmar arch

Correct Answer & Explanation

. Ulnar artery

Explanation

The primary blood supply to the scaphoid comes from the dorsal carpal branch of the radial artery. These vessels enter the distal portion of the scaphoid and supply the proximal pole in a retrograde fashion, explaining the high nonunion rate in proximal pole fractures.

Question 7346

Topic: 2. Trauma

Following a displaced subcapital femoral neck fracture, the primary blood supply to the adult femoral head is disrupted. This dominant blood supply normally arises directly from the:

. Ligamentum teres artery
. Inferior gluteal artery
. Lateral femoral circumflex artery
. Medial femoral circumflex artery
. Obturator artery

Correct Answer & Explanation

. Ligamentum teres artery

Explanation

The medial femoral circumflex artery provides the predominant blood supply to the adult femoral head via its lateral epiphyseal branches. Disruption of these retinacular vessels in displaced neck fractures leads to a high risk of avascular necrosis.

Question 7347

Topic: 2. Trauma

A 24-year-old man sustains a fracture through the proximal pole of the scaphoid. He is at high risk for avascular necrosis due to the primary blood supply of the scaphoid, which enters the bone at which anatomical location?

. Palmar surface of the proximal pole
. Dorsal ridge distal to the waist
. Volar tubercle
. Scapholunate interosseous ligament
. Radioscaphocapitate ligament

Correct Answer & Explanation

. Palmar surface of the proximal pole

Explanation

The primary vascular supply to the scaphoid enters distally at the dorsal ridge and courses retrogradely towards the proximal pole. Fractures proximal to this entry point often disrupt this retrograde blood supply, leading to ischemia.

Question 7348

Topic: 2. Trauma

A 35-year-old man presents with a hypertrophic nonunion of the tibial shaft 9 months after closed intramedullary nailing. The patient is otherwise healthy and non-smoker. What is the most appropriate definitive management?

. Exchange intramedullary nailing to a larger diameter nail
. Iliac crest bone grafting alone
. Platelet-rich plasma injection at the nonunion site
. Pulsed electromagnetic field stimulation
. Resection of the nonunion and circular external fixation

Correct Answer & Explanation

. Exchange intramedullary nailing to a larger diameter nail

Explanation

Hypertrophic nonunions have adequate biological healing potential (hence the 'elephant foot' callus) but fail due to excessive mechanical instability. Exchange nailing to a larger diameter provides the necessary stability, leading to predictable union without bone grafting.

Question 7349

Topic: 2. Trauma

Decreasing the working length of a bridging plate construct for a diaphyseal fracture will have which of the following biomechanical effects?

. Increases the torsional and bending stiffness
. Decreases the bending stiffness only
. Increases the micromotion at the fracture site
. Promotes secondary bone healing via increased strain
. Decreases the risk of plate failure

Correct Answer & Explanation

. Increases the torsional and bending stiffness

Explanation

Decreasing the working length (the distance between the two innermost screws on either side of the fracture) increases the stiffness of the construct in bending and torsion. This limits tolerated micromotion.

Question 7350

Topic: 2. Trauma

A 45-year-old man presents with a hypertrophic nonunion of the tibial shaft 9 months after intramedullary nailing. Radiographs show abundant bridging callus that fails to cross the fracture site (elephant shoe appearance). What is the primary underlying cause of this condition?

. Inadequate blood supply
. Low-grade infection
. Inadequate mechanical stability
. Severe malnutrition
. Genetic predisposition

Correct Answer & Explanation

. Inadequate blood supply

Explanation

Hypertrophic nonunions are characterized by excellent biology and vascularity but inadequate mechanical stability. The treatment of choice is typically improving stabilization, such as exchange nailing with a larger diameter nail.

Question 7351

Topic: 2. Trauma

The scaphoid bone is highly susceptible to avascular necrosis following a waist fracture due to its retrograde blood supply. The primary arterial supply to the proximal pole enters at which of the following anatomic locations?

. Volar tubercle
. Distal to the waist via branches of the radial artery
. Directly into the proximal pole via the ulnar artery
. Through the scapholunate interosseous ligament
. Superficial palmar arch

Correct Answer & Explanation

. Volar tubercle

Explanation

The primary blood supply to the scaphoid is retrograde, entering the dorsal ridge distal to the waist from the dorsal carpal branch of the radial artery. Fractures at the waist or proximal pole disrupt this supply, leading to ischemia of the proximal segment.

Question 7352

Topic: 2. Trauma

To maximize biomechanical stability and prevent gap formation during the internal plate fixation of a transverse fracture of the radius, the plate should ideally be applied to which aspect of the bone?

. The compression side
. The neutral bending axis
. The tension side
. The intramedullary canal
. The anterior surface regardless of load

Correct Answer & Explanation

. The compression side

Explanation

According to the tension band principle, applying a plate to the tension side of a bone converts tensile forces into compressive forces at the opposite cortex. This prevents fracture gaping and promotes stable primary bone healing.

Question 7353

Topic: 2. Trauma

Figure 46 shows the AP radiograph of a patient with right shoulder pain. What is the most likely diagnosis?

. Periosteal sleeve injury
. Acute type 2 acromioclavicular joint separation
. Rickets
. Traumatic osteolysis
. Distal clavicle fracture

Correct Answer & Explanation

. Periosteal sleeve injury

Explanation

Posttraumatic osteolysis of the distal portion of the clavicle is a condition that can be a complication of acute or repetitive trauma. The distal end of the clavicle is frayed and resorbed. Resorption may occur after weeks or months. The end of the clavicle may reconstitute over a period of months, or the acromioclavicular joint may remain widened. The differential diagnosis for distal clavicular erosion also includes rheumatoid arthritis, hyperparathyroidism, neoplastic destruction, cleidocranial dysplasia, and pyknodysostosis. Acutely, a type 2 acromioclavicular joint injury does not result in erosion or resorption of the clavicle. Periosteal sleeve injuries radiographically mimic acromioclavicular joint dislocation. Rickets occurs only in childhood.

Question 7354

Topic: 2. Trauma

Following a severe pelvic ring fracture, a patient experiences loss of perineal sensation and sphincter dysfunction. The injured nerve normally exits the pelvis through the greater sciatic foramen and re-enters the perineum through which structure?

. Obturator canal
. Lesser sciatic foramen
. Alcock's canal
. Inguinal canal
. Greater sciatic notch

Correct Answer & Explanation

. Obturator canal

Explanation

The pudendal nerve exits the pelvis through the greater sciatic foramen to pass posterior to the sacrospinous ligament. It then re-enters the perineum via the lesser sciatic foramen to supply the perineum and external sphincters.

Question 7355

Topic: Upper Extremity Trauma

A 21-year-old collegiate baseball pitcher undergoes an ulnar collateral ligament (UCL) reconstruction. The primary medial restraint to valgus stress of the elbow, which is targeted for reconstruction, has its distal insertion on which of the following anatomic structures?

. The radial neck
. The sublime tubercle of the ulna
. The olecranon tip
. The lesser sigmoid notch
. The anular ligament

Correct Answer & Explanation

. The radial neck

Explanation

The anterior bundle of the UCL is the primary restraint to valgus stress at the elbow from 30 to 120 degrees of flexion. It originates on the anteroinferior medial epicondyle and inserts on the sublime tubercle of the coronoid process of the ulna.

Question 7356

Topic: 2. Trauma

A trauma surgeon is performing posterior pelvic ring fixation for a vertically unstable sacral fracture. During dissection near the greater sciatic notch, the surgeon must be mindful of the ligament that defines the inferior border of the greater sciatic foramen. Which ligament is this?

. Sacrotuberous ligament
. Anterior sacroiliac ligament
. Sacrospinous ligament
. Iliolumbar ligament
. Ischiofemoral ligament

Correct Answer & Explanation

. Sacrotuberous ligament

Explanation

The sacrospinous ligament runs from the sacrum to the ischial spine, dividing the greater and lesser sciatic notches into the greater and lesser sciatic foramina. It serves as the inferior boundary of the greater sciatic foramen.

Question 7357

Topic: 2. Trauma

A patient sustains a highly comminuted rami fracture with extension into the obturator canal. On physical examination, there is weakness in hip adduction and an area of numbness over the medial aspect of the middle third of the thigh. The injured nerve directly innervates which of the following muscles?

. Pectineus
. Sartorius
. Gracilis
. Semitendinosus
. Quadratus femoris

Correct Answer & Explanation

. Pectineus

Explanation

The obturator nerve passes through the obturator canal and innervates the medial compartment of the thigh, which includes the adductor longus, brevis, magnus, obturator externus, and gracilis. It also provides sensation to the medial aspect of the middle thigh.

Question 7358

Topic: Upper Extremity Trauma

A patient with an Essex-Lopresti injury has longitudinal radioulnar dissociation. Which component of the interosseous membrane (IOM) of the forearm provides the greatest longitudinal stability and must be considered during reconstruction?

. Proximal oblique cord
. Distal oblique bundle
. Central band
. Dorsal oblique accessory cord
. Transverse radioulnar band

Correct Answer & Explanation

. Proximal oblique cord

Explanation

The central band of the interosseous membrane is the thickest and most crucial component for longitudinal stability of the forearm. It originates proximally on the radius and courses distally and ulnarly to insert on the ulna.

Question 7359

Topic: 2. Trauma

A patient develops acute compartment syndrome of the anterior leg following a tibia fracture. If left untreated, which of the following functional deficits is most likely to occur?

. Inability to plantarflex the ankle
. Inability to invert the foot
. Inability to dorsiflex the ankle and extend the toes
. Numbness over the plantar aspect of the foot
. Loss of sensation over the lateral heel

Correct Answer & Explanation

. Inability to plantarflex the ankle

Explanation

The anterior compartment of the leg contains the deep peroneal nerve, tibialis anterior, extensor hallucis longus, and extensor digitorum longus. Ischemic injury to these structures leads to a foot drop and inability to extend the toes.

Question 7360

Topic: Pelvic & Acetabular Trauma

A 40-year-old male is involved in a high-speed motor vehicle collision and sustains an unstable vertical shear pelvic ring injury. Which of the following ligaments is the strongest and provides the most stability to the posterior pelvic ring?

. Anterior sacroiliac ligament
. Sacrospinous ligament
. Sacrotuberous ligament
. Posterior interosseous sacroiliac ligament
. Iliolumbar ligament

Correct Answer & Explanation

. Anterior sacroiliac ligament

Explanation

The posterior interosseous sacroiliac ligament is the thickest and strongest ligament in the pelvis. It serves as the primary restraint against vertical and anterior-posterior translation of the sacroiliac joint.

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