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1. General Principles & Basic Science MCQs

Practice Set 706 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 14101

Topic: Biology, Genetics & Bone Healing
A 4-year-old child presents with multiple fractures, cranial nerve palsies, and pancytopenia. Radiographs demonstrate a 'bone-within-a-bone' appearance and generalized osteosclerosis. A defect in which of the following enzymes is most likely responsible for this condition?
. Alkaline phosphatase
. Tissue nonspecific alkaline phosphatase (TNSALP)
. Carbonic anhydrase II
. Lysyl oxidase
. Type I collagenase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

The patient has osteopetrosis (marble bone disease), characterized by defective osteoclast function resulting in dense but brittle bones. The autosomal recessive (malignant) form is most commonly caused by a mutation in the gene encoding carbonic anhydrase II, which is essential for osteoclasts to generate the acidic environment needed for bone resorption.

Question 14102

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy with blue sclerae, hearing loss, and a history of multiple low-energy fractures undergoes a skin biopsy. Analysis of the extracellular matrix will most likely reveal a quantitative deficiency in which of the following?

. Type I collagen
. Type II collagen
. Type X collagen
. Fibrillin-1
. Elastin

Correct Answer & Explanation

. Type I collagen

Explanation

The patient has Osteogenesis Imperfecta (OI) Type I, which is a mild form of OI characterized by a quantitative deficiency of structurally normal Type I collagen (due to mutations in COL1A1 or COL1A2). Type I collagen is the primary collagen in bone, sclerae, and ligaments.

Question 14103

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. At which point in the coagulation cascade does this medication exert its primary effect?
. Inhibition of Factor IIa (Thrombin)
. Inhibition of Factor Xa
. Activation of Antithrombin III
. Inhibition of Vitamin K epoxide reductase
. Inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. LMWH primarily activates antithrombin III, which then inhibits Factor Xa.

Question 14104

Topic: Biology, Genetics & Bone Healing

BMP-2 (rhBMP-2) is utilized in spine fusion surgery. Which of the following intracellular signaling molecules is directly phosphorylated following BMP binding to its serine/threonine kinase receptor?

. JAK/STAT
. cAMP/PKA
. Smad 1/5/8
. Wnt/beta-catenin
. MAPK/ERK

Correct Answer & Explanation

. Smad 1/5/8

Explanation

Bone Morphogenetic Proteins (BMPs) belong to the TGF-beta superfamily. When a BMP binds to its cell surface serine/threonine kinase receptor, it induces the phosphorylation of specific R-Smads (Smad 1, 5, and 8). These then form a complex with the Co-Smad (Smad 4) and translocate to the nucleus to regulate gene transcription for osteoblast differentiation.

Question 14105

Topic: Infection, Pharmacology & VTE

A 70-year-old man undergoes an extended spinal fusion lasting 6 hours. He received 2 grams of IV cefazolin 30 minutes prior to incision. According to current guidelines, what is the optimal timing for redosing the cefazolin?

. It does not need to be redosed
. 2 hours after the initial dose
. 4 hours after the initial dose
. 6 hours after the initial dose
. Only if estimated blood loss exceeds 2000 mL

Correct Answer & Explanation

. 4 hours after the initial dose

Explanation

Cefazolin has a half-life of approximately 1.8 to 2 hours. Current surgical antimicrobial prophylaxis guidelines recommend redosing cefazolin every 4 hours during the procedure to maintain adequate minimal inhibitory concentrations (MIC) in the tissues. Redosing is also recommended if estimated blood loss exceeds 1500 mL.

Question 14106

Topic: Physiology & Rehabilitation

During the lowering phase of a heavy bicep curl, the biceps brachii muscle produces force while lengthening. This type of muscle contraction is defined as:

. Isometric
. Concentric
. Eccentric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when a muscle develops tension while simultaneously lengthening (e.g., the lowering phase of a bicep curl). A concentric contraction involves muscle shortening during force production. An isometric contraction involves force production without a change in muscle length. Eccentric contractions generate the highest forces and are most commonly associated with delayed-onset muscle soreness (DOMS).

Question 14107

Topic: Biology, Genetics & Bone Healing

A 5-year-old child newly immigrated from a northern latitude presents with bowing of the legs and widening of the wrists. Laboratory evaluation reveals hypocalcemia and hypophosphatemia. Which of the following additional lab profiles is most likely present in nutritional rickets?

. Decreased PTH, decreased alkaline phosphatase
. Increased PTH, increased alkaline phosphatase
. Decreased PTH, increased alkaline phosphatase
. Increased PTH, decreased alkaline phosphatase
. Normal PTH, normal alkaline phosphatase

Correct Answer & Explanation

. Increased PTH, increased alkaline phosphatase

Explanation

In nutritional rickets (Vitamin D deficiency), reduced intestinal absorption of calcium leads to hypocalcemia. This triggers a secondary hyperparathyroidism (increased PTH), which causes phosphaturia (leading to hypophosphatemia). Increased osteoblastic activity in an attempt to form bone leads to highly elevated alkaline phosphatase.

Question 14108

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a second-degree nerve injury corresponds to which of the following descriptions?

. Myelin disruption only with intact axon (Neuropraxia)
. Axonal disruption with intact endoneurium (Axonotmesis)
. Axonal and endoneurial disruption with intact perineurium
. Axonal, endoneurial, and perineurial disruption with intact epineurium
. Complete nerve transection (Neurotmesis)

Correct Answer & Explanation

. Axonal disruption with intact endoneurium (Axonotmesis)

Explanation

Sunderland Classification: 1st degree = Neuropraxia (local myelin block, intact axon); 2nd degree = Axonotmesis (axon disrupted, endoneurium intact, Wallerian degeneration occurs but recovery is generally excellent); 3rd degree = Endoneurium disrupted, perineurium intact; 4th degree = Perineurium disrupted, epineurium intact; 5th degree = Neurotmesis (complete transection).

Question 14109

Topic: Biomechanics & Biomaterials

On a stress-strain curve for a typical orthopaedic metallic implant, the point at which the material transitions from elastic deformation to plastic deformation is known as the:

. Ultimate tensile strength
. Yield point
. Young's modulus
. Failure point
. Proportional limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point is the point on the stress-strain curve at which a material ceases to behave elastically and begins to undergo permanent (plastic) deformation. Young's modulus represents the slope of the elastic region (stiffness). Ultimate tensile strength is the maximum stress a material can withstand before failure.

Question 14110

Topic: Biology, Genetics & Bone Healing

Intermittent subcutaneous administration of Teriparatide (recombinant human PTH) is used to treat severe osteoporosis. What is the primary mechanism by which intermittent, low-dose PTH increases bone mass?

. It directly inhibits osteoclast ruffled border formation
. It stimulates osteoblast survival and bone formation via the Wnt/beta-catenin pathway
. It decreases the production of 1,25-dihydroxyvitamin D
. It binds to RANKL, preventing osteoclast activation
. It competitively inhibits sclerostin binding to LRP5/6

Correct Answer & Explanation

. It stimulates osteoblast survival and bone formation via the Wnt/beta-catenin pathway

Explanation

While continuous high levels of PTH cause bone resorption, intermittent low-dose administration of PTH (e.g., Teriparatide) has an anabolic effect on bone. It directly stimulates osteoblasts, increases their lifespan by inhibiting apoptosis, and promotes bone formation, largely through down-regulation of sclerostin and activation of the Wnt/beta-catenin signaling pathway.

Question 14111

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a ductile orthopedic implant material, the point at which the material undergoes non-reversible plastic deformation but has not yet fractured is best described by which of the following terms?

. Proportional limit
. Yield point
. Ultimate tensile strength
. Failure point
. Endurance limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the end of elastic (reversible) deformation and the beginning of plastic (irreversible) deformation. The ultimate tensile strength is the maximum stress the material can withstand on the curve, and the failure point is where the material fractures.

Question 14112

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which structural zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers that are oriented perpendicular to the joint surface?

. Superficial (Tangential) zone
. Transitional (Middle) zone
. Deep (Radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (Radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest proteoglycan concentration and the lowest water content. Its Type II collagen fibers are oriented perpendicular to the joint surface to maximally resist compressive forces and secure the cartilage to the underlying bone.

Question 14113

Topic: Biology, Genetics & Bone Healing

A 72-year-old female is treated for osteoporosis with denosumab. Which of the following best describes the precise mechanism of action of this medication?

. Binds directly to the RANK receptor on osteoclasts
. Binds to RANK-L, preventing the activation of the RANK receptor
. Inhibits the farnesyl pyrophosphate synthase pathway
. Stimulates osteoblast bone formation via the Wnt/beta-catenin pathway
. Acts as a decoy receptor similar to naturally occurring osteoprotegerin (OPG)

Correct Answer & Explanation

. Binds to RANK-L, preventing the activation of the RANK receptor

Explanation

Denosumab is a human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANK-L). This prevents RANK-L from binding to the RANK receptor on osteoclast precursors, thereby inhibiting osteoclast differentiation, function, and survival. Bisphosphonates inhibit the farnesyl pyrophosphate synthase pathway.

Question 14114

Topic: Surgical Anatomy & Approaches

During the deltopectoral approach to the shoulder, the conjoint tendon is commonly retracted medially to gain exposure to the subscapularis and anterior glenohumeral joint. Over-retraction of this structure places which of the following nerves at highest risk of injury?

. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Suprascapular nerve
. Long thoracic nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve typically enters the coracobrachialis muscle approximately 5 to 8 cm distal to the tip of the coracoid process. Vigorous medial retraction of the conjoint tendon (coracobrachialis and short head of biceps) during a deltopectoral approach can stretch and injure this nerve.

Question 14115

Topic: 1. General Principles & Basic Science
Necrotizing fasciitis is a life-threatening surgical emergency. Which of the following laboratory parameters is the most heavily weighted component of the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score?
. Creatine kinase
. Procalcitonin
. D-dimer
. C-reactive protein
. Erythrocyte sedimentation rate

Correct Answer & Explanation

. C-reactive protein

Explanation

The LRINEC score utilizes six laboratory values: C-reactive protein (CRP), total white cell count, hemoglobin, serum sodium, serum creatinine, and serum glucose. A CRP > 150 mg/L contributes the maximum points (4 points) for a single variable in this scoring system.

Question 14116

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis (e.g., via an Ilizarov frame) relies on the application of gradual, controlled tension across a corticotomy site. What is the primary histologic mechanism of bone formation in the distraction gap?

. Intramembranous ossification
. Enchondral ossification
. Appositional ossification
. Creeping substitution
. Chondrolysis

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis primarily produces new bone through intramembranous ossification. Under conditions of absolute stability and gradual distraction, osteoblasts directly lay down woven bone parallel to the axis of distraction without a cartilaginous intermediate.

Question 14117

Topic: 1. General Principles & Basic Science

Which of the following molecules is primarily responsible for boundary lubrication in normal articular cartilage, allowing for low-friction gliding under high loads and low velocities?

. Hyaluronic acid
. Type II collagen
. Aggrecan
. Lubricin (PRG4)
. Chondroitin sulfate

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Lubricin, also known as proteoglycan 4 (PRG4), is a highly glycosylated protein secreted by superficial zone chondrocytes and synoviocytes. It binds to the articular surface and provides boundary lubrication, which is critical for reducing friction and wear under high-load, low-speed conditions.

Question 14118

Topic: Surgical Anatomy & Approaches

The Watson-Jones (anterolateral) approach to the hip utilizes the interval between the tensor fasciae latae and the gluteus medius. Why is this considered an internervous plane by some authors, but technically an intranervous plane by purists?

. Both muscles are innervated by the femoral nerve
. Both muscles are innervated by the inferior gluteal nerve
. Both muscles are innervated by the superior gluteal nerve
. The plane crosses the lateral femoral cutaneous nerve distribution
. The tensor fasciae latae receives dual innervation from both the obturator and superior gluteal nerves

Correct Answer & Explanation

. Both muscles are innervated by the superior gluteal nerve

Explanation

The tensor fasciae latae (TFL) and the gluteus medius are both innervated by the superior gluteal nerve. Therefore, dissecting between them is technically an intranervous plane. However, because the nerve branches enter the muscles proximal to the operative field, it functions safely like an internervous plane if dissection is kept distal.

Question 14119

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of nerve injuries, a second-degree injury (which is equivalent to Seddon's axonotmesis) is strictly characterized by disruption of which of the following structures?

. Myelin sheath demyelination with an intact axon
. Axon disruption with intact endoneurium, perineurium, and epineurium
. Axon and endoneurium disruption with intact perineurium
. Axon, endoneurium, and perineurium disruption with intact epineurium
. Complete nerve transection involving all layers

Correct Answer & Explanation

. Axon disruption with intact endoneurium, perineurium, and epineurium

Explanation

In a Sunderland Type II injury (Seddon's axonotmesis), the axon is disrupted, leading to Wallerian degeneration distally, but the supporting connective tissue framework (endoneurium, perineurium, and epineurium) remains intact, providing a conduit for predictable nerve regeneration.

Question 14120

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for an anterior column acetabular fracture, the surgeon must carefully identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This vascular structure represents an anastomosis between which two systems?

. Internal pudendal and inferior gluteal vessels
. External iliac (or inferior epigastric) and obturator vessels
. Internal iliac and superior gluteal vessels
. Deep circumflex iliac and femoral vessels
. Superior epigastric and internal thoracic vessels

Correct Answer & Explanation

. External iliac (or inferior epigastric) and obturator vessels

Explanation

The corona mortis ('crown of death') is an important vascular anastomosis between the external iliac system (or its inferior epigastric branch) and the obturator system. It traverses the posterior aspect of the superior pubic ramus, placing it at high risk during anterior intrapelvic or ilioinguinal approaches.

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