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1. General Principles & Basic Science MCQs

Practice Set 371 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 7401

Topic: Biomechanics & Biomaterials

A 28-year-old male powerlifter feels a tearing sensation in his anterior chest wall while performing a heavy bench press. Examination reveals an asymmetric loss of the anterior axillary fold and marked weakness in internal rotation. MRI confirms a complete rupture of the pectoralis major tendon at its humeral insertion. Based on the biomechanics of the bench press exercise, which specific fibers of the pectoralis major are typically under the greatest tension and tear first?

. Clavicular head fibers
. Superior fibers of the sternal head
. Inferior fibers of the sternal head
. Costal fibers
. Abdominal fibers

Correct Answer & Explanation

. Clavicular head fibers

Explanation

The pectoralis major tendon twists 180 degrees before inserting on the proximal humerus, meaning the inferior fibers of the sternal head insert most superiorly and proximally. During a bench press (arm extended, abducted, and externally rotated), these inferior sternal fibers are placed under maximal stretch and have a mechanical disadvantage, making them the most common starting point for a pectoralis major tendon rupture.

Question 7402

Topic: Surgical Anatomy & Approaches

A 38-year-old weightlifter undergoes an anatomic repair of a distal biceps tendon rupture via a single-incision anterior approach. Postoperatively, he notes numbness and paresthesias along the radial and volar aspect of his forearm. Which of the following nerves was most likely injured or subjected to excessive traction during the surgical approach?

. Posterior interosseous nerve (PIN)
. Anterior interosseous nerve (AIN)
. Lateral antebrachial cutaneous nerve (LABCN)
. Superficial radial nerve
. Medial antebrachial cutaneous nerve (MABCN)

Correct Answer & Explanation

. Posterior interosseous nerve (PIN)

Explanation

The lateral antebrachial cutaneous nerve (LABCN) is a continuation of the musculocutaneous nerve and exits the deep fascia just lateral to the biceps tendon. It is highly susceptible to traction or iatrogenic transection during the anterior single-incision approach for distal biceps repair, leading to sensory deficits in the lateral forearm. The posterior interosseous nerve (PIN) is more at risk during a two-incision approach.

Question 7403

Topic: Surgical Anatomy & Approaches

A 55-year-old construction worker undergoes an open subpectoral biceps tenodesis for a symptomatic SLAP tear and biceps tendinopathy. Postoperatively, he is noted to have a new-onset neurological deficit with weakness in elbow flexion and numbness over the lateral forearm. Which of the following nerves is at greatest risk of injury during the deep retractor placement for this procedure?

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

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve is at greatest risk of injury during open subpectoral biceps tenodesis, particularly with overzealous medial retraction. The nerve usually pierces the coracobrachialis 5-8 cm distal to the coracoid process and runs between the biceps and brachialis. Medial retractors (like a Hohmann retractor) placed blindly can compress or stretch this nerve.

Question 7404

Topic: Surgical Anatomy & Approaches

A newborn infant is diagnosed with a brachial plexus birth palsy after a difficult forceps delivery. The child exhibits a shoulder that is internally rotated and adducted, an extended elbow, and a flexed wrist, commonly known as a 'waiter's tip' posture. Which nerve roots are predominantly injured in this classic presentation?

. C5, C6
. C7, C8, T1
. C5, C6, C7
. C8, T1
. C6, C7, C8

Correct Answer & Explanation

. C5, C6

Explanation

Erb's palsy involves an injury to the upper trunk of the brachial plexus, specifically the C5 and C6 nerve roots. This results in the classic 'waiter's tip' deformity due to loss of shoulder abduction and external rotation (suprascapular and axillary nerves), loss of elbow flexion (musculocutaneous nerve), and weakness of wrist extensors.

Question 7405

Topic: 1. General Principles & Basic Science

A 19-year-old male is brought to the emergency department after a high-impact rugby tackle. He complains of shortness of breath, dysphagia, and severe pain over his medial clavicle. Physical examination reveals a palpable depression over the medial aspect of the affected clavicle. After ensuring a stable airway, what is the most appropriate next step in management?

. Immediate closed reduction in the emergency department
. CT scan of the chest and clavicle
. MRI of the brachial plexus
. Application of a figure-of-eight brace
. Emergent open reduction and internal fixation

Correct Answer & Explanation

. Immediate closed reduction in the emergency department

Explanation

The patient's clinical presentation (shortness of breath, dysphagia, and palpable medial depression) is classic for a posterior sternoclavicular joint dislocation. Because the displaced medial clavicle can compress critical mediastinal structures (trachea, esophagus, great vessels), a CT scan is the diagnostic modality of choice to accurately assess the dislocation and its proximity to these structures prior to attempting reduction, which should ideally be done with thoracic surgery backup.

Question 7406

Topic: 1. General Principles & Basic Science

A 24-year-old sustains a clean laceration to the volar index finger in Zone II. Surgical exploration reveals >60% laceration of both the FDS and FDP tendons. Following an optimal 4-strand core suture repair with a continuous epitendinous stitch, what is the best postoperative rehabilitation protocol?

. 6 weeks of strict static cast immobilization
. Immediate un-splinted active range of motion
. Early active motion within a dorsal block splint
. Dynamic extension splinting with forced passive flexion
. Passive extension and active flexion exercises without splinting

Correct Answer & Explanation

. 6 weeks of strict static cast immobilization

Explanation

For Zone II flexor tendon repairs with a robust core suture technique (4-strand or greater), early active motion (EAM) protocols utilizing a dorsal block splint are currently the standard of care. EAM improves tendon excursion, reduces adhesion formation, and yields better functional range of motion compared to strict immobilization or purely passive protocols, without significantly increasing the risk of rupture.

Question 7407

Topic: 1. General Principles & Basic Science

A 32-year-old male competitive weightlifter felt a sudden 'pop' in his anterior chest wall while performing a heavy bench press. Examination reveals loss of the normal anterior axillary fold contour and weakness with resisted internal rotation and adduction. In a complete rupture of the pectoralis major tendon, which portion of the muscle typically ruptures first, and where does it normally insert anatomically on the humerus?

. Clavicular head; inserts most distal and deep on the lateral lip of the bicipital groove
. Sternal head; inserts most proximal and superficial on the lateral lip of the bicipital groove
. Sternal head; inserts most proximal and deep on the medial lip of the bicipital groove
. Sternal head; inserts most distal and deep on the lateral lip of the bicipital groove
. Clavicular head; inserts most proximal and superficial on the lateral lip of the bicipital groove

Correct Answer & Explanation

. Clavicular head; inserts most distal and deep on the lateral lip of the bicipital groove

Explanation

The pectoralis major tendon undergoes a 180-degree twist before inserting on the lateral lip of the bicipital groove. Because of this twist, the sternal head inserts most distal and deep, while the clavicular head inserts most proximal and superficial. During heavy lifting (like a bench press in the extended and externally rotated position), the inferior fibers of the sternal head are under maximal tension and typically rupture first, with tears progressing superiorly.

Question 7408

Topic: 1. General Principles & Basic Science

An 18-year-old male is brought to the emergency department after a high-speed motor vehicle collision. He complains of severe chest pain, shortness of breath, and difficulty swallowing. Physical examination reveals a palpable depression at the right medial clavicle. A CT scan of the chest confirms a posterior sternoclavicular dislocation. What is the most appropriate next step in management?

. Immediate closed reduction in the emergency department using inline traction
. Closed reduction in the operating room with a cardiothoracic surgeon available
. Open reduction and internal fixation with Kirschner wires
. Open reduction and locking plate fixation without prior reduction attempt
. Sling immobilization and observation

Correct Answer & Explanation

. Immediate closed reduction in the emergency department using inline traction

Explanation

Posterior sternoclavicular (SC) joint dislocations are true orthopedic emergencies due to the risk of compression or injury to posterior mediastinal structures, including the trachea, esophagus, and great vessels (subclavian vein/artery, brachiocephalic vein). The standard of care is an urgent attempt at closed reduction in the operating room under general anesthesia. A cardiothoracic surgeon must be readily available because the reduction maneuver itself can dislodge a fractured clavicle from a great vessel, leading to catastrophic hemorrhage. Kirschner wires are strictly contraindicated in the SC joint due to the high risk of fatal migration into the heart or great vessels.

Question 7409

Topic: Surgical Anatomy & Approaches

A 45-year-old male bodybuilder undergoes a single-incision anterior approach for the repair of an acute distal biceps tendon rupture. Postoperatively, he complains of numbness, tingling, and paresthesias over the anterolateral aspect of his forearm. Injury to which of the following structures is the most likely cause of his current symptoms?

. Radial nerve
. Posterior interosseous nerve
. Lateral antebrachial cutaneous nerve
. Medial antebrachial cutaneous nerve
. Musculocutaneous nerve proper

Correct Answer & Explanation

. Radial nerve

Explanation

The lateral antebrachial cutaneous nerve (LABCN), which is the terminal sensory branch of the musculocutaneous nerve, exits deep to the biceps and courses subcutaneously on the lateral forearm. It is the most commonly injured nerve during a single-incision anterior approach to the distal biceps. Injury results in lateral forearm paresthesias. The posterior interosseous nerve (PIN) is more commonly at risk during a two-incision approach.

Question 7410

Topic: 1. General Principles & Basic Science

When repairing an acute flexor tendon laceration in Zone II, early active motion protocols are utilized to minimize adhesions and optimize glide. To safely allow an early active motion protocol, what is the generally accepted minimum number of core suture strands required across the repair site?

. 2
. 4
. 6
. 8
. 10

Correct Answer & Explanation

. 2

Explanation

The ultimate tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site. Biomechanical and clinical studies have demonstrated that a 2-strand repair is typically insufficient to withstand the forces of early active motion and is prone to gap formation or rupture. A minimum of 4 core strands is required to provide adequate strength and stiffness to safely implement an early active motion rehabilitation protocol.

Question 7411

Topic: Surgical Anatomy & Approaches

A 40-year-old bodybuilder feels a sudden 'pop' in his anterior elbow while performing heavy preacher curls. Examination reveals a palpable defect in the distal biceps tendon, weakness in supination, and proximal retraction of the muscle belly. He undergoes a single-incision distal biceps tendon repair using a cortical button and an interference screw. Postoperatively, he notes weakness in extending his thumb and fingers, though wrist extension is preserved with radial deviation. Which nerve is most likely injured, and what is the mechanism?

. Lateral antebrachial cutaneous nerve; traction during retraction
. Posterior interosseous nerve; over-penetration of the drilling through the far cortex
. Median nerve; compression by the interference screw
. Radial nerve; transection during the surgical approach
. Superficial radial nerve; traction from the surgical incision

Correct Answer & Explanation

. Lateral antebrachial cutaneous nerve; traction during retraction

Explanation

The posterior interosseous nerve (PIN) is highly vulnerable during single-incision anterior approaches for distal biceps repair. The PIN wraps around the radial neck and can be injured by overly aggressive retractor placement on the radial side, or by the drill/pin exiting the posterior (far) cortex of the radius when creating the bone tunnel for a cortical button. The clinical presentation of weakness in finger and thumb extension, while maintaining wrist extension (as ECRL is innervated by the radial nerve proximal to the PIN branch), confirms a PIN neuropathy.

Question 7412

Topic: Surgical Anatomy & Approaches

A 28-year-old man sustained a closed, midshaft humerus fracture and an isolated, complete radial nerve palsy at the time of injury. He was treated in a functional fracture brace. Twelve weeks after the injury, the humerus demonstrates clinical and radiographic evidence of union, but the patient continues to have a complete wrist drop. Electromyography (EMG) shows no evidence of reinnervation of the brachioradialis or extensor carpi radialis longus. What is the most appropriate next step in management?

. Continue bracing and observation for an additional 12 weeks
. Tendon transfers to restore wrist and finger extension
. Surgical exploration of the radial nerve
. Open reduction and internal fixation of the humerus
. Amputation of the affected limb

Correct Answer & Explanation

. Continue bracing and observation for an additional 12 weeks

Explanation

Most radial nerve palsies associated with closed humerus fractures represent a neuropraxia or axonotmesis and will recover spontaneously. However, if there is no clinical or electromyographic (EMG) evidence of recovery by 12 weeks (3 to 4 months), surgical exploration of the nerve is indicated to evaluate for entrapment, scarring, or transection that may require neurolysis, primary repair, or nerve grafting.

Question 7413

Topic: Surgical Anatomy & Approaches

A 35-year-old man sustains a severe, closed proximal third humeral shaft fracture with extension into the surgical neck. He undergoes open reduction and internal fixation using a long proximal humeral locking plate via a standard deltopectoral approach. During the surgical approach and lateral plate placement, the surgeon must be particularly mindful of avoiding iatrogenic nerve injury. The axillary nerve is most at risk in which of the following anatomic locations?

. Crossing the anterior aspect of the subscapularis, approximately 2 cm medial to the lesser tuberosity
. Running along the inferior border of the teres major before entering the quadrangular space
. Wrapping around the surgical neck of the humerus, approximately 5 to 7 cm distal to the lateral acromial edge
. Passing anterior to the long head of the biceps tendon at the level of the bicipital groove
. Emerging from the triangular interval alongside the profunda brachii artery

Correct Answer & Explanation

. Crossing the anterior aspect of the subscapularis, approximately 2 cm medial to the lesser tuberosity

Explanation

The axillary nerve exits the quadrangular space and wraps around the posterior and lateral aspects of the surgical neck of the humerus. Anatomically, from the lateral edge of the acromion, the axillary nerve is located approximately 5 to 7 cm distally. When placing a lateral locking plate for a proximal humerus fracture, especially during minimally invasive plate osteosynthesis (MIPO) or when extending a deltopectoral approach distally, the nerve is at significant risk as it crosses the lateral humerus horizontally deep to the deltoid muscle.

Question 7414

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a diaphyseal femur fracture. Which of the following factors is most critical for the initiation of endochondral ossification during secondary fracture healing?

. Absolute rigidity of fixation
. Presence of a significant hematoma
. Presence of interfragmentary motion and adequate vascularity
. High oxygen tension at the fracture site
. Absence of inflammatory cells

Correct Answer & Explanation

. Absolute rigidity of fixation

Explanation

Endochondral ossification, characteristic of secondary fracture healing, is promoted by a degree of interfragmentary motion (relative stability) and robust vascularity. Absolute rigidity (as seen in primary healing) primarily favors intramembranous ossification. While hematoma is essential, motion and vascularity are more direct stimuli for the chondrogenic phase. High oxygen tension inhibits cartilage formation and favors bone. Inflammatory cells are critical for the initial stages of healing.

Question 7415

Topic: Biomechanics & Biomaterials

Regarding the biomechanics of cortical bone, which statement is most accurate?

. Cortical bone is stronger in tension than compression.
. The Young's modulus of cortical bone is anisotropic.
. Creep deformation is primarily due to collagen fiber slippage under rapid loading.
. Fatigue fractures occur when bone is stressed above its ultimate strength.
. Cortical bone exhibits perfect elasticity up to its yield point.

Correct Answer & Explanation

. Cortical bone is stronger in tension than compression.

Explanation

Cortical bone is an anisotropic material, meaning its mechanical properties (like Young's modulus) vary with the direction of applied load. It is significantly stronger in compression than in tension. Creep is time-dependent deformation under constant load, not primarily due to rapid loading. Fatigue fractures result from repetitive loading below the ultimate strength. Bone exhibits viscoelastic properties, not perfect elasticity, even below the yield point.

Question 7416

Topic: Biology, Genetics & Bone Healing

Which cytokine is primarily responsible for osteoclast differentiation and activation?

. Transforming Growth Factor-beta (TGF-β)
. Insulin-like Growth Factor-1 (IGF-1)
. Bone Morphogenetic Protein-2 (BMP-2)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Interleukin-6 (IL-6)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-β)

Explanation

RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand) is the primary cytokine responsible for osteoclast differentiation, activation, and survival. It is secreted by osteoblasts and stromal cells and binds to RANK receptors on pre-osteoclasts and mature osteoclasts. TGF-β and IGF-1 are generally anabolic for bone. BMP-2 is critical for osteoblast differentiation. IL-6 has multiple roles, including stimulating osteoclast activity, but RANKL is the most direct and crucial regulator.

Question 7417

Topic: 1. General Principles & Basic Science

Regarding articular cartilage, which statement is FALSE?

. It is primarily composed of type II collagen.
. Chondrocytes are responsible for producing the extracellular matrix.
. It is highly vascularized to facilitate nutrient exchange.
. Proteoglycans, particularly aggrecan, contribute significantly to its compressive strength.
. The tidemark separates the calcified from the uncalcified cartilage.

Correct Answer & Explanation

. It is primarily composed of type II collagen.

Explanation

Articular cartilage is avascular, aneural, and alymphatic. It relies on synovial fluid for nutrient exchange and waste removal through diffusion, not direct vascularization. It is indeed composed primarily of type II collagen, and chondrocytes synthesize the matrix. Proteoglycans like aggrecan attract water, providing turgor and compressive strength. The tidemark is a critical histological landmark separating the two layers of cartilage.

Question 7418

Topic: Biology, Genetics & Bone Healing

What is the primary role of osteoprotegerin (OPG) in bone metabolism?

. Stimulates osteoblast differentiation
. Acts as a soluble decoy receptor for RANKL, inhibiting osteoclast activity
. Promotes bone matrix mineralization
. Increases calcium reabsorption in the kidney
. Inhibits parathyroid hormone secretion

Correct Answer & Explanation

. Stimulates osteoblast differentiation

Explanation

Osteoprotegerin (OPG) is a soluble decoy receptor for RANKL. By binding to RANKL, OPG prevents RANKL from binding to its receptor (RANK) on pre-osteoclasts and osteoclasts, thereby inhibiting osteoclast differentiation, function, and survival. This effectively reduces bone resorption. It does not directly stimulate osteoblast differentiation or mineralization, nor does it affect renal calcium reabsorption or PTH secretion directly.

Question 7419

Topic: Biology, Genetics & Bone Healing

Which growth factor is most potent in inducing ectopic bone formation and is commonly used in spinal fusion procedures?

. Platelet-Derived Growth Factor (PDGF)
. Fibroblast Growth Factor (FGF)
. Vascular Endothelial Growth Factor (VEGF)
. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-alpha (TGF-α)

Correct Answer & Explanation

. Platelet-Derived Growth Factor (PDGF)

Explanation

Bone Morphogenetic Proteins (BMPs), particularly BMP-2 and BMP-7, are known for their potent osteoinductive properties and ability to induce ectopic bone formation. BMP-2 is widely used clinically in spinal fusion and fracture nonunion treatment. PDGF, FGF, and VEGF are important for angiogenesis and soft tissue healing but are not as osteoinductive. TGF-α is less relevant in this context.

Question 7420

Topic: Biology, Genetics & Bone Healing

Regarding the vascular supply of long bones, which statement is most accurate?

. The nutrient artery supplies primarily the epiphyseal regions.
. Periosteal arteries are the dominant blood supply to the inner two-thirds of the cortex.
. Metaphyseal arteries are critical for the growth plate and contribute significantly to diaphyseal vascularity in adults.
. The nutrient artery provides the main blood supply to the inner two-thirds of the cortical diaphysis.
. Venous drainage of long bones occurs exclusively through the nutrient vein.

Correct Answer & Explanation

. The nutrient artery supplies primarily the epiphyseal regions.

Explanation

The nutrient artery enters the diaphysis and branches into ascending and descending medullary arteries, supplying the inner two-thirds to three-quarters of the cortical bone via Haversian and Volkmann's canals. The periosteal arteries supply the outer one-third to one-quarter of the cortex. Metaphyseal arteries are crucial for the growth plate and also contribute to the vascularity of the adjacent diaphysis, especially after skeletal maturity. Venous drainage occurs through nutrient veins, metaphyseal veins, and periosteal veins.

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