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1. General Principles & Basic Science MCQs

Practice Set 401 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 8001

Topic: 1. General Principles & Basic Science
Following a peripheral nerve transection (neurotmesis), Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin debris and facilitating the creation of endoneurial tubes to guide regenerating axons in the peripheral nervous system?
. Oligodendrocytes
. Schwann cells
. Astrocytes
. Microglia
. Ependymal cells

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Schwann cells are critical for both myelinating axons and facilitating regeneration after injury. Following nerve transection, Wallerian degeneration occurs distally. Schwann cells, along with recruited macrophages, phagocytose myelin debris. Schwann cells then proliferate and form the Bands of Bรผngner within the endoneurial tubes, which guide regenerating axons back to their targets. Oligodendrocytes serve a similar myelinating function in the central nervous system but do not aid in robust regeneration.

Question 8002

Topic: Physiology & Rehabilitation

A marathon runner relies heavily on muscle fibers adapted for prolonged endurance. Which of the following characteristics best describes the predominant muscle fiber type utilized during this activity?

. Fast twitch, anaerobic, high glycogen content
. Slow twitch, oxidative, rich in mitochondria and myoglobin
. Fast twitch, oxidative-glycolytic, intermediate fatigue resistance
. Slow twitch, anaerobic, low capillary density
. Fast twitch, relying on creatine phosphate for energy

Correct Answer & Explanation

. Slow twitch, oxidative, rich in mitochondria and myoglobin

Explanation

Marathon running requires prolonged endurance, which relies on Type I (slow-twitch) muscle fibers. These fibers are characterized by a slow contraction speed, high resistance to fatigue, and a strong reliance on aerobic (oxidative) metabolism. To support this aerobic metabolism, they have a high density of mitochondria, a rich capillary supply, and a high concentration of myoglobin, which gives them a distinct red color.

Question 8003

Topic: Infection, Pharmacology & VTE
A patient is prescribed apixaban for deep vein thrombosis (DVT) prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this anticoagulant medication?
. Direct inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Direct, selective inhibition of Factor Xa
. Vitamin K antagonism inhibiting factors II, VII, IX, and X
. Enhancement of antithrombin III activity

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Apixaban and rivaroxaban are direct oral anticoagulants (DOACs) that act as highly selective, direct inhibitors of Factor Xa (the 'xa' in their generic names denotes their target). They bind directly to Factor Xa, inhibiting both free and clot-bound Factor Xa, as well as prothrombinase activity, thereby preventing the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin inhibitor. Aspirin inhibits COX-1. Warfarin is a vitamin K antagonist.

Question 8004

Topic: 1. General Principles & Basic Science

A histologic section of healthy adult articular cartilage is analyzed. In which zone are the collagen fibers oriented primarily parallel to the joint surface to resist shear forces?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Tidemark
. Calcified zone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage makes up about 10-20% of the thickness and consists of tightly packed collagen fibers (mostly Type II) oriented parallel to the articular surface. This orientation provides the cartilage with high tensile strength to resist shear forces. The deep zone has collagen fibers oriented perpendicular to the joint surface to resist compressive forces.

Question 8005

Topic: Biomechanics & Biomaterials



A researcher is studying the failure mechanisms of orthopedic implants in an animal model. A stainless steel screw is deliberately used to secure a titanium alloy plate. What is the most likely mode of corrosion to occur at the interface of these two implants in vivo?

. Fretting corrosion
. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are placed in direct contact within an electrolytic medium, such as bodily fluids. The less noble metal becomes the anode and undergoes accelerated corrosion, while the more noble metal becomes the cathode. To prevent this, mixing dissimilar metals like stainless steel and titanium in a single construct is generally avoided.

Question 8006

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the management of osteoporosis and giant cell tumor of bone. Which of the following accurately describes its primary cellular mechanism of action?

. Binds to the RANK receptor on osteoclasts
. Inhibits the formation of sclerostin
. Acts as a soluble decoy receptor mimicking osteoprotegerin (OPG)
. Directly binds to and neutralizes RANKL
. Stimulates osteoprotegerin (OPG) production by osteoblasts

Correct Answer & Explanation

. Directly binds to and neutralizes RANKL

Explanation

Denosumab is a fully human monoclonal antibody that directly binds to and inhibits Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents RANKL from binding to the RANK receptor on the surface of osteoclasts and their precursors, thereby potently inhibiting osteoclast maturation, function, and survival. OPG is the body's natural decoy receptor for RANKL.

Question 8007

Topic: Biomechanics & Biomaterials

During the static stretching phase of a physical therapy protocol for Achilles tendinopathy, a therapist notes that when the tendon is stretched to a specific length and held constant, the internal force required to maintain that length gradually decreases over time. This specific biomechanical property is termed:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark viscoelastic property characterized by a decrease in stress (force) over time when a material is held at a constant strain (length or deformation). Creep, conversely, is the progressive increase in strain (deformation) over time when a constant stress (load) is applied. Hysteresis refers to the energy lost as heat during the loading and unloading cycles of a viscoelastic material.

Question 8008

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is commonly utilized to enhance posterolateral spinal fusions. BMPs induce osteoblastic differentiation primarily through which of the following intracellular signaling pathways?

. Wnt / beta-catenin pathway
. Notch signaling pathway
. Smad 1, 5, and 8 pathway
. MAP kinase pathway
. JAK-STAT pathway

Correct Answer & Explanation

. Smad 1, 5, and 8 pathway

Explanation

Bone Morphogenetic Proteins (BMPs) belong to the TGF-beta superfamily. When BMPs bind to their specific serine/threonine kinase membrane receptors, they trigger the intracellular phosphorylation of Smad proteins, specifically Smad 1, 5, and 8 (receptor-regulated Smads). These form a complex with Smad 4 (common-partner Smad) and translocate to the nucleus to regulate target gene transcription for osteoblast differentiation.

Question 8009

Topic: Biology, Genetics & Bone Healing

A patient undergoes open reduction and internal fixation (ORIF) of a transverse radial shaft fracture utilizing a dynamic compression plate to achieve absolute stability. Assuming an anatomic reduction with rigid fixation is obtained, which of the following best describes the expected primary mechanism of fracture healing?

. Endochondral ossification leading to a large cartilaginous callus
. Intramembranous ossification with abundant fibrous callus
. Direct Haversian remodeling via osteoclastic cutting cones
. Secondary bone healing mediated by early hematoma organization
. Chondrogenesis followed by rapid woven bone formation

Correct Answer & Explanation

. Direct Haversian remodeling via osteoclastic cutting cones

Explanation

Absolute stability achieved through rigid internal fixation (such as compression plating) eliminates interfragmentary motion and bypasses the callus formation seen in secondary healing. Instead, the bone heals via direct (primary) bone healing. This occurs through direct Haversian remodeling, where osteoclasts create 'cutting cones' that cross the fracture site, immediately followed by osteoblasts depositing new lamellar bone.

Question 8010

Topic: Biomechanics & Biomaterials

Which of the following statements best describes the biomechanical property of an implant that determines its rigidity and is represented by the slope of the linear portion of the stress-strain curve?

. Toughness
. Fatigue limit
. Yield strength
. Modulus of elasticity
. Ultimate tensile strength

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Modulus of elasticity (Young's modulus) is the measure of a material's intrinsic stiffness. It is calculated as the slope of the linear (elastic) portion of the stress-strain curve. A higher modulus indicates a stiffer material. Toughness is the energy absorbed up to the point of failure (area under the entire curve). Yield strength is the stress at which plastic deformation begins. Ultimate tensile strength is the maximum stress the material can withstand.

Question 8011

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone has the highest concentration of water and collagen, but the lowest concentration of proteoglycans?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Subchondral bone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest concentration of water (approx. 80%) and collagen (Type II, arranged parallel to the joint surface to resist shear stress), and the lowest concentration of proteoglycans. The deep zone contains the lowest water content and the highest concentration of proteoglycans, with collagen fibers oriented vertically to resist compressive forces.

Question 8012

Topic: Biology, Genetics & Bone Healing

During fracture healing via endochondral ossification, which transcription factor is strictly required for the differentiation of mesenchymal stem cells into chondrocytes?

. RUNX2 (Cbfa1)
. SOX9
. Osterix
. Sclerostin
. RANKL

Correct Answer & Explanation

. SOX9

Explanation

SOX9 is the master transcription factor for chondrogenesis, essential for driving mesenchymal stem cells to differentiate into chondrocytes during endochondral ossification and cartilage formation. RUNX2 (also known as Cbfa1) and Osterix are critical transcription factors for osteoblast differentiation.

Question 8013

Topic: Biology, Genetics & Bone Healing



Demineralized bone matrix (DBM) is widely used in orthopedic surgery as an adjunct for spinal fusion and fracture nonunions. Which of the following combinations of properties does DBM possess?

. Osteoinductive and osteogenic
. Osteoconductive and osteogenic
. Osteoinductive and osteoconductive
. Osteogenic only
. Osteoconductive only

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) provides a collagenous scaffold that serves as an osteoconductive matrix. Because the demineralization process preserves biologically active bone morphogenetic proteins (BMPs) and other growth factors, DBM is also osteoinductive. However, because it contains no living cells (osteoprogenitors or osteoblasts), it lacks osteogenic properties.

Question 8014

Topic: Infection, Pharmacology & VTE

A patient develops a methicillin-resistant Staphylococcus aureus (MRSA) infection following a posterior spinal fusion. Intravenous vancomycin is initiated. What is the primary mechanism of action of vancomycin?

. Inhibits DNA gyrase
. Binds to the 50S ribosomal subunit to inhibit protein synthesis
. Binds to the 30S ribosomal subunit causing mRNA misreading
. Binds to D-alanyl-D-alanine termini of peptidoglycan precursors, inhibiting cell wall synthesis
. Inhibits folic acid synthesis

Correct Answer & Explanation

. Binds to D-alanyl-D-alanine termini of peptidoglycan precursors, inhibiting cell wall synthesis

Explanation

Vancomycin is a glycopeptide antibiotic that treats Gram-positive bacterial infections, including MRSA, by inhibiting cell wall synthesis. It achieves this by binding tightly to the D-alanyl-D-alanine terminus of cell wall precursor units, effectively preventing their incorporation into the peptidoglycan matrix. Quinolones inhibit DNA gyrase, macrolides bind the 50S subunit, and aminoglycosides bind the 30S subunit.

Question 8015

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with a history of a distal radius fracture undergoes a dual-energy x-ray absorptiometry (DEXA) scan yielding a T-score of -3.0. She is prescribed denosumab. What is the precise mechanism of action of this medication?

. Binds to hydroxyapatite and inhibits osteoclast ruffled border formation
. Monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts
. Recombinant parathyroid hormone that intermittently stimulates osteoblast activity
. Selective estrogen receptor modulator (SERM) that decreases bone resorption
. Monoclonal antibody against sclerostin, promoting Wnt signaling

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that targets and binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents it from binding to the RANK receptor on the surface of osteoclasts and their precursors. This profoundly inhibits osteoclast differentiation, function, and survival, leading to decreased bone resorption.

Question 8016

Topic: 1. General Principles & Basic Science

You are evaluating a high-performance marathon runner for a tibial stress fracture. During your review of basic muscle physiology, you recall that Type I (slow-twitch) muscle fibers possess specific characteristics tailored for endurance. Which of the following best describes Type I muscle fibers compared to Type IIb fibers?

. Higher reliance on glycolytic metabolism
. Lower mitochondrial density
. Higher myoglobin content and higher fatigue resistance
. Faster contraction velocity
. Larger motor neuron size

Correct Answer & Explanation

. Higher myoglobin content and higher fatigue resistance

Explanation

Type I muscle fibers are 'slow-twitch' oxidative fibers specialized for endurance activities. They have a high myoglobin content (giving them a red appearance), high mitochondrial and capillary densities, and rely heavily on oxidative phosphorylation. They have high fatigue resistance but lower peak force, slower contraction velocity, and smaller motor neuron sizes compared to Type II (fast-twitch) fibers.

Question 8017

Topic: Biomechanics & Biomaterials



Mixed-metal constructs, such as using a stainless steel screw with a titanium plate, are generally avoided in orthopedic surgery. Which specific type of corrosion is most likely to occur in this scenario?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are placed in physical contact within a conductive electrolyte medium, such as human bodily fluid. The less noble metal becomes the anode and undergoes accelerated corrosion, while the more noble metal acts as the cathode. Fretting corrosion, by contrast, is caused by micromotion between two surfaces.

Question 8018

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key regulatory glycoprotein in bone metabolism and the target of the monoclonal antibody romosozumab. What is its primary mechanism of action at the molecular level?

. It binds to RANKL, preventing its interaction with the RANK receptor and inhibiting osteoclastogenesis.
. It competitively binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway.
. It activates the BMP-2 signaling cascade via SMAD 1/5/8 phosphorylation, suppressing osteoblast apoptosis.
. It binds to the parathyroid hormone (PTH) receptor, directly inhibiting osteoblast matrix production.
. It upregulates osteoprotegerin (OPG) expression, leading to a profound decrease in bone turnover.

Correct Answer & Explanation

. It competitively binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway.

Explanation

Sclerostin is produced primarily by mature osteocytes and acts as a negative regulator of bone formation. It functions by binding to the LRP5/6 co-receptors on the surface of osteoblasts, which competitively blocks the binding of Wnt ligands. This prevents the activation of the canonical Wnt/beta-catenin signaling pathway, leading to the phosphorylation and proteasomal degradation of beta-catenin, ultimately downregulating osteoblastogenesis and bone formation. Romosozumab is a neutralizing antibody against sclerostin that harnesses this pathway to stimulate bone formation.

Question 8019

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, a surgeon tensions the tendon graft to a specific length and fixes it. Over the next several minutes, the tension (force) required by the fixation device to maintain that exact length slowly decreases. Which of the following viscoelastic properties best describes this phenomenon?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropic degradation

Correct Answer & Explanation

. Stress relaxation

Explanation

Tendons and ligaments are viscoelastic materials, meaning their mechanical response depends on the rate and duration of loading. Stress relaxation is defined as the decrease in stress (or force) over time when the material is held at a constant strain (constant length). Conversely, creep is the progressive deformation (increase in length) over time when a material is subjected to a constant load (constant stress). Hysteresis refers to the energy lost (usually as heat) during a loading and unloading cycle.

Question 8020

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a unique structural organization to withstand both compressive and shear forces in synovial joints. Which zone of articular cartilage is characterized by the highest water content, the lowest proteoglycan concentration, and collagen fibrils oriented parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Tidemark
. Calcified cartilage zone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage comprises 10-20% of the thickness. It features densely packed Type II collagen fibrils oriented parallel to the articular surface, making it highly adept at resisting shear forces. It also contains the highest concentration of water and the lowest concentration of proteoglycans. In contrast, the deep zone contains collagen fibrils oriented perpendicular to the joint surface, the highest proteoglycan content, and the lowest water content, making it optimal for resisting compressive loads.

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