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1. General Principles & Basic Science MCQs

Practice Set 77 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1521

Topic: Surgical Anatomy & Approaches

During the distal extension of the Henry approach to the radius, the surgeon must carefully mobilize and retract a specific artery to safely expose the underlying pronator quadratus. Which artery is this, and in which direction is it retracted?

. Ulnar artery, retracted ulnarly
. Radial artery, retracted radially
. Ulnar artery, retracted radially
. Anterior interosseous artery, retracted radially
. Radial artery, retracted ulnarly

Correct Answer & Explanation

. Radial artery, retracted radially

Explanation

In the distal Henry approach, the radial artery lies medial to the brachioradialis. It must be carefully mobilized and retracted radially, along with the brachioradialis tendon, to expose the pronator quadratus and distal radius.

Question 1522

Topic: Surgical Anatomy & Approaches

A surgeon elects to use the dorsal Thompson approach for open reduction and internal fixation of a proximal third radial shaft fracture. This approach utilizes an internervous plane between which two muscles?

. Extensor carpi radialis brevis and Extensor digitorum communis
. Brachioradialis and Pronator teres
. Extensor carpi ulnaris and Flexor carpi ulnaris
. Extensor digitorum communis and Extensor carpi ulnaris
. Flexor carpi radialis and Palmaris longus

Correct Answer & Explanation

. Extensor carpi radialis brevis and Extensor digitorum communis

Explanation

The Thompson approach utilizes the internervous plane between the extensor carpi radialis brevis (radial nerve) and the extensor digitorum communis (posterior interosseous nerve).

Question 1523

Topic: Surgical Anatomy & Approaches

When extending the volar (Henry) approach proximally to address a fracture of the proximal third of the radius, the surgeon must carefully identify and protect a key neural structure. To do so safely, which maneuver is most appropriate?

. Identify the median nerve between the two heads of the pronator teres.
. Supinate the forearm to rotate the posterior interosseous nerve (PIN) laterally away from the surgical field.
. Pronate the forearm to move the posterior interosseous nerve (PIN) medially.
. Release the brachioradialis insertion completely to visualize the superficial radial nerve.
. Elevate the flexor digitorum profundus off the ulna to protect the anterior interosseous nerve.

Correct Answer & Explanation

. Supinate the forearm to rotate the posterior interosseous nerve (PIN) laterally away from the surgical field.

Explanation

When exposing the proximal radius via the Henry approach, the forearm must be supinated. This rotates the radius and moves the supinator muscle and the enclosed posterior interosseous nerve (PIN) laterally, protecting it from injury.

Question 1524

Topic: Biology, Genetics & Bone Healing

For highly comminuted mid-diaphyseal fractures of both the radius and ulna, bridge plating is selected instead of absolute rigid fixation. Which of the following biomechanical environments is created by bridge plating, and what is the primary mode of bone healing expected?

. Absolute stability with primary bone healing
. Relative stability with primary bone healing
. Absolute stability with secondary bone healing
. Relative stability with secondary bone healing
. Dynamic compression with intramembranous ossification

Correct Answer & Explanation

. Relative stability with secondary bone healing

Explanation

Bridge plating provides relative stability, which stimulates callus formation and leads to secondary bone healing. Absolute stability, which leads to primary bone healing without callus, is achieved through interfragmentary compression.

Question 1525

Topic: Surgical Anatomy & Approaches

During an anterior (Henry) approach to the proximal radius, the surgeon develops the internervous plane. Between which two muscles is the proximal portion of this plane located?

. Brachioradialis and flexor carpi radialis
. Brachioradialis and pronator teres
. Flexor carpi ulnaris and flexor digitorum superficialis
. Extensor carpi radialis brevis and extensor digitorum communis
. Flexor carpi radialis and palmaris longus

Correct Answer & Explanation

. Brachioradialis and pronator teres

Explanation

The proximal internervous plane for the Henry approach lies between the brachioradialis (innervated by the radial nerve) and the pronator teres (innervated by the median nerve). Distally, the plane transitions between the brachioradialis and the flexor carpi radialis.

Question 1526

Topic: Surgical Anatomy & Approaches

During a dorsal (Thompson) approach to the proximal third of the radius, the surgeon identifies the internervous plane. Which of the following describes the appropriate plane for this approach?

. Extensor carpi radialis brevis and extensor digitorum communis
. Extensor carpi radialis longus and brachioradialis
. Flexor carpi ulnaris and extensor carpi ulnaris
. Extensor digitorum communis and extensor carpi ulnaris
. Anconeus and extensor carpi ulnaris

Correct Answer & Explanation

. Extensor carpi radialis brevis and extensor digitorum communis

Explanation

The Thompson approach utilizes the internervous plane between the extensor carpi radialis brevis (radial nerve) and the extensor digitorum communis (posterior interosseous nerve). It allows exposure of the proximal and middle thirds of the radius.

Question 1527

Topic: 1. General Principles & Basic Science

When utilizing the dorsal approach to the forearm, the posterior interosseous nerve (PIN) is at risk as it passes through the supinator muscle. At what approximate distance from the radiocapitellar joint does the PIN exit the distal edge of the supinator?

. 2-3 cm
. 6-8 cm
. 10-12 cm
. 14-16 cm
. 1-2 cm

Correct Answer & Explanation

. 6-8 cm

Explanation

The posterior interosseous nerve (PIN) typically exits the distal border of the supinator muscle approximately 6 to 8 cm distal to the radiocapitellar joint. Surgeons must protect it during extensile dorsal exposures of the proximal radius.

Question 1528

Topic: Surgical Anatomy & Approaches

A surgeon elects to utilize the dorsal (Thompson) approach for open reduction and internal fixation of a proximal third radial shaft fracture. This surgical approach exploits an internervous plane between which of the following two muscle groups?

. Brachioradialis and Pronator Teres
. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis
. Extensor Carpi Ulnaris and Extensor Digiti Minimi
. Flexor Carpi Radialis and Palmaris Longus
. Brachioradialis and Flexor Carpi Radialis

Correct Answer & Explanation

. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis

Explanation

The Thompson approach utilizes the internervous plane between the extensor carpi radialis brevis (supplied by the radial nerve) and the extensor digitorum communis (supplied by the posterior interosseous nerve).

Question 1529

Topic: Biology, Genetics & Bone Healing

A 42-year-old male sustains highly comminuted midshaft fractures of both the radius and ulna. The surgeon utilizes 3.5 mm limited contact dynamic compression plates (LC-DCP) using a bridge plating technique over the comminuted segments. Which of the following best describes the biomechanical goal and expected bone healing mechanism of this construct?

. Absolute stability promoting primary bone healing
. Relative stability promoting secondary bone healing via callus formation
. Absolute stability promoting secondary bone healing
. Relative stability promoting primary bone healing
. Dynamic compression promoting intramembranous ossification

Correct Answer & Explanation

. Relative stability promoting secondary bone healing via callus formation

Explanation

Bridge plating preserves the soft tissue envelope and blood supply of comminuted fracture segments by providing relative stability. This biomechanical environment stimulates secondary bone healing through the formation of a fracture callus.

Question 1530

Topic: Surgical Anatomy & Approaches

A 24-year-old male presents to the emergency department after a football injury, complaining of severe right shoulder pain. His arm is held in slight abduction and external rotation. On inspection, the anterior aspect of his shoulder appears prominent, and there is a palpable void beneath the acromion. Which of the following physical exam findings is MOST concerning for an associated neurovascular injury in this patient?

. Loss of sensation over the lateral deltoid
. Inability to actively abduct the arm
. Weakness in wrist extension
. Absent radial pulse
. Ecchymosis over the anterior shoulder

Correct Answer & Explanation

. Absent radial pulse

Explanation

Correct Answer: DAn absent radial pulse is a critical finding indicating potential compromise of the brachial artery, which is a surgical emergency. While axillary nerve injury (loss of sensation over the lateral deltoid, weakness in abduction) is the most common nerve injury with anterior shoulder dislocations, it is rarely an acute limb-threatening condition unless it's a traction injury without spontaneous recovery. Weakness in wrist extension would suggest radial nerve involvement, which is less common. Ecchymosis is a common finding but not acutely life- or limb-threatening.

Question 1531

Topic: Surgical Anatomy & Approaches

A 68-year-old woman falls directly onto her shoulder. She presents with severe pain and an inability to move her arm. On exam, the shoulder appears abducted, and a prominent hard mass is palpable inferior to the glenoid, consistent with a Luxatio Erecta. Which neurovascular structure is at highest risk of injury in this type of dislocation?

. Axillary nerve
. Brachial plexus
. Axillary artery
. Radial nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Axillary artery

Explanation

Correct Answer: CLuxatio Erecta (inferior dislocation) involves extreme abduction, forcing the humeral head inferiorly. The head can impinge upon or stretch the neurovascular bundle in the axilla. The axillary artery is at significant risk due to its proximity and the severe displacement. While the axillary nerve and brachial plexus are also at risk, arterial compromise (axillary artery) is a more acute and limb-threatening complication associated with the extreme force and direction of displacement in luxatio erecta, often leading to intimal tears or thrombosis.

Question 1532

Topic: 1. General Principles & Basic Science

A resident is reviewing the basic anatomy of an orthopedic screw. Referring to the provided image, which labeled component is primarily responsible for providing a smooth, unthreaded link between the screw head and the threaded portion?

. A. Head
. B. Shank
. C. Thread
. D. Pitch
. E. Flutes

Correct Answer & Explanation

. B. Shank

Explanation

Correct Answer: BThe case explicitly states, 'The shank provides a smooth link between the head and thread.' The image clearly labels the shank as the unthreaded portion immediately distal to the head. The head (A) provides a connection for a screwdriver and prevents sinking. The thread (C) engages with the bone. Pitch (D) is the distance between adjacent threads. Flutes (E) provide a route for bone debris removal.

Question 1533

Topic: 1. General Principles & Basic Science

In a scenario where a surgeon aims to maximize the pull-out strength of a non-locking screw in cortical bone, which combination of screw diameter characteristics would be most advantageous?

. A. Increased outer diameter, increased core diameter.
. B. Decreased outer diameter, decreased core diameter.
. C. Increased outer diameter, decreased core diameter.
. D. Decreased outer diameter, increased core diameter.
. E. Outer diameter equal to core diameter.

Correct Answer & Explanation

. C. Increased outer diameter, decreased core diameter.

Explanation

Correct Answer: CThe case indicates that pull-out strength can be increased by 'increasing the contact surface area between screw threads and bone, either by increasing the outer diameter, decreasing the core diameter.' This combination (increased outer diameter and decreased core diameter) results in a greater thread depth, maximizing the volume of bone engaged by the screw threads and thus increasing the resistance to pull-out. Options A, B, and D would either reduce the thread depth or the overall screw-bone contact. Option E describes a smooth pin, not a screw.

Question 1534

Topic: 1. General Principles & Basic Science

A biomechanical engineer is testing various orthopedic screw designs. The primary parameter being measured when assessing a screw's "pull-out strength" is the:

. A. Torsional force required to strip the screw threads.
. B. Bending moment the screw can withstand before plastic deformation.
. C. Axial force required to remove the screw from bone.
. D. Shear stress at the screw-bone interface during cyclic loading.
. E. Compressive load the screw can bear before buckling.

Correct Answer & Explanation

. C. Axial force required to remove the screw from bone.

Explanation

Correct Answer: CThe case clearly defines pull-out strength: 'A screw's pull-out strength refers to the axial force required to remove a screw from bone.' Options A, B, D, and E describe other mechanical properties of screws (torsional strength, bending strength, fatigue strength, compressive strength) but not specifically pull-out strength, which is a measure of resistance to axial extraction.

Question 1535

Topic: Biology, Genetics & Bone Healing

A 72-year-old patient with severe osteoporosis undergoes open reduction and internal fixation of a proximal tibia fracture. The surgeon is particularly concerned about screw pull-out. Which of the following intraoperative strategies would provide the greatest cumulative benefit in maximizing screw pull-out strength in this patient?

. A. Using screws with a larger core diameter and a coarser pitch.
. B. Ensuring the pilot hole is slightly undersized, using screws with a finer pitch, and engaging as many threads as possible in the bone cortex.
. C. Employing self-drilling screws to minimize bone trauma and avoiding locking screws to allow for micro-motion.
. D. Repeatedly inserting and removing screws to create a wider bone-screw interface.
. E. Utilizing screws with a smaller outer diameter and a larger lead.

Correct Answer & Explanation

. B. Ensuring the pilot hole is slightly undersized, using screws with a finer pitch, and engaging as many threads as possible in the bone cortex.

Explanation

Correct Answer: BThis option combines multiple strategies mentioned in the case to maximize pull-out strength. The case states that pull-out strength can be increased by 'increasing the number of threads engaged in the bone cortex' and by using a 'finer' pitch. An undersized pilot hole (the opposite of 'too large a pilot hole' which reduces strength) would maximize thread purchase. Option A describes characteristics that would decrease pull-out strength (larger core, coarser pitch). Option C suggests avoiding locking screws, which the case states 'create a monobloc effect for greater stability,' and micro-motion is generally undesirable for fixation. Option D (repeated insertion/removal) is explicitly listed as a factor that reduces pull-out strength. Option E (smaller outer diameter, larger lead) would reduce thread engagement and pull-out strength.

Question 1536

Topic: 1. General Principles & Basic Science

Referring to the provided image, the component labeled 'Depth' is crucial for a screw's pull-out strength. According to the case, how does the 'Depth' of a screw thread primarily contribute to its resistance against axial removal from bone?

. A. It dictates the linear distance the screw travels per turn.
. B. It determines the amount of contact with bone for resistance to pull-out.
. C. It provides a route for the removal of bone debris during insertion.
. D. It defines the distance between adjacent screw threads.
. E. It forms the smooth link between the head and the threaded portion.

Correct Answer & Explanation

. B. It determines the amount of contact with bone for resistance to pull-out.

Explanation

Correct Answer: BThe case states, 'the depth determines the amount of contact with bone for resistance to pull-out.' A greater thread depth allows for more bone engagement and thus a larger contact surface area, which directly increases pull-out strength. Option A describes the lead. Option C describes the function of flutes. Option D describes the pitch. Option E describes the shank.

Question 1537

Topic: Surgical Anatomy & Approaches

When performing antegrade humeral intramedullary nailing, which specific nerve is most at risk during the proximal locking screw placement?

. Axillary nerve
. Radial nerve
. Ulnar nerve
. Musculocutaneous nerve
. Median nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

Correct Answer: ADuring proximal locking screw placement for an antegrade humeral intramedullary nail, the axillary nerve is most vulnerable. It courses around the surgical neck of the humerus, deep to the deltoid, and is susceptible to injury, particularly with excessively long screws or imprecise drilling techniques in the superolateral aspect of the proximal humerus. The radial nerve is at risk more distally, especially with distal locking or in the spiral groove. The ulnar, musculocutaneous, and median nerves are typically not at high risk with proximal humeral locking screws.

Question 1538

Topic: 1. General Principles & Basic Science

What is the primary role of static locking in intramedullary nailing?

. To allow controlled micromotion at the fracture site for callus formation.
. To prevent shortening and rotational instability.
. To facilitate axial dynamization for enhanced compression.
. To reduce the risk of implant fatigue failure.
. To provide greater bending stiffness than dynamic locking.

Correct Answer & Explanation

. To prevent shortening and rotational instability.

Explanation

Correct Answer: BStatic locking, achieved by placing locking screws both proximally and distally, is primarily used to prevent shortening and rotational instability of the fracture. This is particularly important in unstable or comminuted fractures where axial loading might otherwise lead to collapse. While some controlled micromotion is desirable for callus formation, static locking aims to control excessive motion. Dynamization (removing one set of locking screws) is done to achieve compression, which is the opposite of the initial goal of static locking. Static locking does not inherently reduce implant fatigue failure more than dynamic locking, as fatigue is often due to micromotion. Bending stiffness is generally high with IM nails, and static locking maintains length and rotation, not primarily enhancing bending stiffness over dynamic locking.

Question 1539

Topic: Surgical Anatomy & Approaches

During a Latarjet procedure, the coracoid process is osteotomized and transferred to the anterior glenoid. Which two nerves are at the highest risk of iatrogenic injury during the coracoid mobilization and subsequent screw fixation?

. Axillary and suprascapular nerves
. Musculocutaneous and axillary nerves
. Radial and median nerves
. Long thoracic and spinal accessory nerves
. Thoracodorsal and subscapular nerves

Correct Answer & Explanation

. Musculocutaneous and axillary nerves

Explanation

The musculocutaneous nerve enters the conjoint tendon distally and is at risk during retraction. The axillary nerve courses inferiorly along the joint capsule and is at risk during inferior glenoid preparation and screw placement.

Question 1540

Topic: 1. General Principles & Basic Science

A 40-year-old male is struck from behind while skiing. He presents with severe chest pain, dyspnea, and a palpable void at the medial end of the right clavicle. What is the most appropriate next step in management?

. Immediate closed reduction in the emergency department
. Urgent CT scan of the chest and sternoclavicular joints
. MRI of the sternoclavicular joint
. Immediate open reduction in the operating room
. Application of a figure-of-eight brace and observation

Correct Answer & Explanation

. Urgent CT scan of the chest and sternoclavicular joints

Explanation

Posterior sternoclavicular dislocations are orthopedic emergencies due to the high risk of compression to the trachea, esophagus, and mediastinal vessels. A CT scan of the chest is critical to assess for these life-threatening injuries prior to any reduction attempts.

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