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1. General Principles & Basic Science MCQs

Practice Set 605 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 12081

Topic: Surgical Anatomy & Approaches

During a standard deltopectoral approach for total shoulder arthroplasty, an inferior capsular release is performed to mobilize the proximal humerus. Which nerve is at greatest risk of iatrogenic injury during this specific step?

. Musculocutaneous nerve
. Suprascapular nerve
. Axillary nerve
. Radial nerve
. Median nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The axillary nerve passes just inferior to the shoulder capsule (closest at the 6 o'clock position). It is highly vulnerable during inferior capsular release if the surgeon strays too far from the glenoid rim or humeral neck.

Question 12082

Topic: Surgical Anatomy & Approaches

In the operative management of a displaced distal radius fracture using a volar Henry approach, the surgeon dissects through an internervous plane. This plane is located between which two structures?

. Flexor carpi radialis and Palmaris longus
. Brachioradialis and Flexor carpi radialis
. Extensor carpi radialis longus and brevis
. Flexor digitorum superficialis and Flexor carpi ulnaris
. Abductor pollicis longus and Extensor pollicis brevis

Correct Answer & Explanation

. Flexor carpi radialis and Palmaris longus

Explanation

The classic volar Henry approach to the distal radius utilizes the internervous plane between the brachioradialis (innervated by the radial nerve) and the flexor carpi radialis (innervated by the median nerve).

Question 12083

Topic: Biology, Genetics & Bone Healing

Denosumab is effectively used in the treatment of recurrent or unresectable Giant Cell Tumor (GCT) of bone. What is its specific mechanism of action?

. Inhibits osteoclast farnesyl pyrophosphate synthase
. Monoclonal antibody targeting RANK-ligand
. Directly induces apoptosis of multinucleated giant cells
. Tyrosine kinase inhibitor of VEGF receptors
. Bisphosphonate analog that binds hydroxyapatite

Correct Answer & Explanation

. Inhibits osteoclast farnesyl pyrophosphate synthase

Explanation

Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from activating RANK. In GCT, neoplastic stromal cells overexpress RANKL, and denosumab halts the resulting osteoclast-mediated osteolysis.

Question 12084

Topic: 1. General Principles & Basic Science

A 25-year-old male is involved in a motor vehicle accident and sustains a unilateral cervical facet dislocation at C5-C6. What is the most common mechanism of injury for this specific pathology?

. Extension and axial loading
. Flexion and distraction with rotation
. Hyper-extension and shear
. Lateral bending and compression
. Pure axial compression

Correct Answer & Explanation

. Extension and axial loading

Explanation

Unilateral cervical facet dislocations typically result from a mechanism of flexion, distraction, and rotation. Bilateral facet dislocations generally result from a severe flexion-distraction injury without the rotational component.

Question 12085

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, the soft callus transitions into a hard callus. Which type of collagen dominates the extracellular matrix during the hard callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The hard callus phase of secondary bone healing is characterized by the replacement of woven bone and cartilage with lamellar bone. Lamellar bone is predominantly composed of Type I collagen, unlike the soft callus which is rich in Type II collagen.

Question 12086

Topic: Biology, Genetics & Bone Healing

During the process of endochondral ossification in fracture healing, which transcription factor is considered the master regulator for differentiating mesenchymal stem cells into the osteoblast lineage?

. SOX9
. Runx2
. HIF-1 alpha
. PPAR-gamma
. Sclerostin

Correct Answer & Explanation

. SOX9

Explanation

Runx2 (CBFA1) is the primary transcription factor required for osteoblast differentiation. By contrast, SOX9 regulates chondrogenesis, and PPAR-gamma directs adipogenesis.

Question 12087

Topic: Biomechanics & Biomaterials

A 42-year-old male is involved in a high-speed motor vehicle collision and sustains an isolated extra-articular fracture of the scapular neck. Which of the following radiographic parameters is the most widely accepted absolute indication for operative internal fixation?

. Glenopolar angle of 45 degrees
. Medial/lateral translation of 5 mm
. Glenopolar angle of less than 22 degrees
. Angulation of 15 degrees in the sagittal plane
. Glenoid articular step-off of 1 mm

Correct Answer & Explanation

. Glenopolar angle of 45 degrees

Explanation

The normal glenopolar angle (GPA) is between 30 to 45 degrees. A severely decreased GPA (< 22 degrees) indicates significant rotational malalignment of the glenoid fragment relative to the scapular body, which alters rotator cuff biomechanics and glenohumeral kinematics, leading to poor clinical outcomes. Therefore, a GPA < 22 degrees is a primary indication for open reduction and internal fixation of a scapular neck fracture. Other relative indications include medial translation > 20 mm, or angular displacement > 40 degrees.

Question 12088

Topic: 1. General Principles & Basic Science

A 32-year-old male felt a pop in his anterior axilla while performing a heavy bench press. Exam reveals a loss of the anterior axillary fold. If this is a complete rupture, what is the most common pathoanatomy of this injury?

. Clavicular head tearing at its musculotendinous junction
. Sternal head tearing at its musculotendinous junction
. Clavicular head tearing at its humeral insertion
. Sternal head tearing at its humeral insertion
. Combined rupture at the sternoclavicular origin

Correct Answer & Explanation

. Clavicular head tearing at its musculotendinous junction

Explanation

Pectoralis major ruptures typically occur during eccentric loading. The sternal head is most commonly injured, usually tearing near or at its tendinous insertion on the humerus because it is under maximal tension when the arm is extended and abducted.

Question 12089

Topic: 1. General Principles & Basic Science

A 28-year-old powerlifter feels a sudden "pop" in his anterior axillary fold during a heavy bench press. Examination reveals loss of the normal anterior axillary contour and marked weakness in internal rotation and adduction. What is the most common anatomical site of rupture for the pectoralis major?

. Muscle belly of the clavicular head
. Musculotendinous junction
. Sternal origin
. Humeral insertion
. Coracoid insertion

Correct Answer & Explanation

. Muscle belly of the clavicular head

Explanation

Pectoralis major ruptures almost exclusively occur in males doing heavy resistance training, most commonly failing at the tendinous insertion onto the lateral lip of the bicipital groove. Surgical repair to the humeral footprint is recommended to restore peak torque.

Question 12090

Topic: 1. General Principles & Basic Science

During a gait assessment of a patient with right hip osteoarthritis, the examiner observes the patient's pelvis dropping on the left side during the right stance phase. A positive Trendelenburg sign on the right indicates weakness of the right gluteus medius. Which nerve innervates the deficient muscle, and what is its primary spinal root contribution?

. Inferior gluteal nerve; L5, S1, S2
. Superior gluteal nerve; L4, L5, S1
. Obturator nerve; L2, L3, L4
. Femoral nerve; L2, L3, L4
. Sciatic nerve; L4, L5, S1, S2, S3

Correct Answer & Explanation

. Inferior gluteal nerve; L5, S1, S2

Explanation

The gluteus medius is innervated by the superior gluteal nerve (L4, L5, S1). Weakness of the hip abductors causes the pelvis to tilt downwards on the contralateral, unsupported side during the stance phase of the affected limb.

Question 12091

Topic: 1. General Principles & Basic Science

Articular cartilage relies on specific structural components for its unique biomechanical properties. Which of the following correctly pairs the zone of articular cartilage with its distinct collagen fiber orientation and primary function?

. Superficial zone; perpendicular collagen fibers; resists compressive forces
. Middle (transitional) zone; parallel collagen fibers; resists shear forces
. Deep zone; perpendicular collagen fibers; resists compressive forces
. Calcified zone; random collagen fibers; provides joint lubrication
. Superficial zone; random collagen fibers; high proteoglycan content

Correct Answer & Explanation

. Superficial zone; perpendicular collagen fibers; resists compressive forces

Explanation

In articular cartilage, the deep zone contains type II collagen fibers oriented perpendicularly to the articular surface. These fibers cross the tidemark to secure the cartilage to the subchondral bone, providing maximum resistance to compressive forces. The superficial zone has parallel collagen fibers to resist shear forces.

Question 12092

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman is started on teriparatide for severe osteoporosis following a fragility fracture of the distal radius. What is the mechanism of action of this medication?

. Inhibits osteoclast activity by binding to hydroxyapatite crystals
. Binds to RANK ligand, preventing the activation of osteoclasts
. Recombinant PTH analog that, when given intermittently, stimulates osteoblast activity
. Selective estrogen receptor modulator (SERM) that acts as an agonist on bone
. Sclerostin inhibitor that increases Wnt signaling in osteoblasts

Correct Answer & Explanation

. Inhibits osteoclast activity by binding to hydroxyapatite crystals

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34). While continuous elevation of PTH leads to bone resorption, intermittent daily subcutaneous administration paradoxically stimulates osteoblast activity over osteoclast activity, leading to net bone formation.

Question 12093

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, bacteria often form a biofilm that renders them highly resistant to host defenses and systemic antibiotics. Which of the following best describes the 'quorum sensing' phase of biofilm formation?

. Reversible attachment of planktonic bacteria to the implant surface via van der Waals forces
. Irreversible attachment mediated by bacterial adhesins like fibronectin-binding proteins
. Cell-to-cell communication regulating gene expression and extracellular polymeric substance (EPS) production
. Dispersal of planktonic bacteria from the mature biofilm to colonize new sites
. Phagocytosis evasion through the immediate shedding of surface antigens

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria to the implant surface via van der Waals forces

Explanation

Quorum sensing is a density-dependent mechanism of bacterial cell-to-cell communication. As bacterial density increases, autoinducers are released. Upon reaching a critical threshold, this triggers coordinated changes in gene expression across the population, leading to massive production of the extracellular polymeric substance (EPS) matrix and biofilm maturation.

Question 12094

Topic: 1. General Principles & Basic Science

During the Watson scaphoid shift test, a palpable and painful clunk is appreciated as the examiner removes thumb pressure from the scaphoid tubercle. What is the pathomechanical etiology of this clunk?

. The scaphoid subluxates dorsally over the dorsal rim of the radius
. The scaphoid reduces from a dorsally subluxated position back into the scaphoid fossa
. The lunate subluxates volarly out of the radiolunate fossa
. The scaphoid flexes volarly causing a sudden scapholunate gap
. The capitate relocates into the lunate concavity

Correct Answer & Explanation

. The scaphoid subluxates dorsally over the dorsal rim of the radius

Explanation

In a patient with scapholunate ligament disruption, applying pressure to the scaphoid tubercle during ulnar-to-radial deviation prevents normal volar flexion, causing the scaphoid to subluxate dorsally. Releasing the pressure allows the scaphoid to suddenly clunk back (reduce) into the radial fossa.

Question 12095

Topic: 1. General Principles & Basic Science

A patient presents with an inability to make a perfect "OK" sign with their fingers, instead demonstrating a flat pinch using the pulps of the thumb and index finger. Which muscle weakness is primarily responsible for this abnormal posture?

. Adductor pollicis
. Flexor digitorum profundus to the index finger and Flexor pollicis longus
. Flexor digitorum superficialis and Opponens pollicis
. First dorsal interosseous and Lumbricals
. Extensor pollicis longus and Extensor indicis proprius

Correct Answer & Explanation

. Adductor pollicis

Explanation

This deficit indicates an Anterior Interosseous Nerve (AIN) palsy. The AIN innervates the Flexor Digitorum Profundus (to the index and middle fingers), the Flexor Pollicis Longus, and the Pronator Quadratus. Weakness of the FDP and FPL prevents normal distal interphalangeal flexion, leading to a flat pinch.

Question 12096

Topic: 1. General Principles & Basic Science

A patient presents with a jammed finger. The examiner flexes the PIP joint to 90 degrees over the edge of a table and asks the patient to extend the DIP joint against resistance. The DIP joint extends rigidly and strongly. What does this positive Elson's test signify?

. Intact central slip
. Ruptured central slip
. Ruptured flexor digitorum profundus
. Intact lateral bands with an intact central slip
. Ruptured terminal extensor tendon

Correct Answer & Explanation

. Intact central slip

Explanation

Elson's test evaluates the integrity of the central slip of the extensor tendon. If the central slip is ruptured, the lateral bands displace volarly but still exert tension, allowing rigid extension of the DIP joint against resistance, while the PIP joint lacks extension force.

Question 12097

Topic: 1. General Principles & Basic Science

During a Thomas test on the right hip, the patient holds the left knee to the chest, causing the right thigh to elevate off the examination table. When the examiner extends the right knee, the right thigh drops completely to the table. Which muscle is responsible for the initial contracture?

. Psoas major
. Iliacus
. Rectus femoris
. Tensor fasciae latae
. Sartorius

Correct Answer & Explanation

. Psoas major

Explanation

The Thomas test evaluates hip flexion contractures. If the elevated thigh drops to the table upon extending the knee, the contracture is isolated to the two-joint rectus femoris muscle.

Question 12098

Topic: 1. General Principles & Basic Science

A long-distance runner presents with lateral knee pain. The examiner places the patient in the lateral decubitus position, abducts and extends the affected hip, and then allows the leg to drop passively into adduction. The leg remains abducted in the air. This positive Ober's test primarily implicates tightness in which structure?

. Gluteus maximus
. Piriformis
. Iliotibial band
. Biceps femoris
. Vastus lateralis

Correct Answer & Explanation

. Gluteus maximus

Explanation

Ober's test assesses tightness of the iliotibial band and tensor fasciae latae. A positive test occurs when the abducted hip fails to drop below horizontal into adduction.

Question 12099

Topic: 1. General Principles & Basic Science

During a gait assessment of a 60-year-old female with right hip osteoarthritis, the examiner notes that when the patient stands on her right leg, her left hemipelvis drops. This positive Trendelenburg sign is caused by weakness of which muscle group?

. Right hip adductors
. Right hip abductors
. Left hip abductors
. Right hip extensors
. Left hip flexors

Correct Answer & Explanation

. Right hip adductors

Explanation

The Trendelenburg sign results from weakness or mechanical dysfunction of the hip abductors (gluteus medius and minimus) on the stance leg. When the patient stands on the right leg, weak right abductors fail to maintain a level pelvis, causing the unsupported left side to drop.

Question 12100

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain threshold required for primary (direct) bone healing to occur without the formation of a visible fracture callus?

. Less than 2%
. 2% to 10%
. 10% to 20%
. 20% to 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing occurs via cutting cones and Haversian remodeling without the formation of an intermediate cartilaginous callus. According to Perren's strain theory, this requires absolute stability, defined as an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary bone healing (callus formation), while strains above 10% lead to nonunion.

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