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1. General Principles & Basic Science MCQs

Practice Set 393 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 7841

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties, meaning its biomechanical behavior alters depending on the rate of loading. Which of the following statements best describes the response of cortical bone to a high strain rate (e.g., a high-velocity gunshot wound)?

. It becomes more ductile and absorbs less energy before failure.
. It becomes stiffer, sustaining higher loads, and absorbs more energy before failure.
. Its ultimate tensile strength decreases significantly.
. It behaves as a purely elastic material without plastic deformation.
. Its modulus of elasticity decreases, leading to failure at lower loads.

Correct Answer & Explanation

. It becomes stiffer, sustaining higher loads, and absorbs more energy before failure.

Explanation

Bone is a viscoelastic and anisotropic material. At higher strain rates (rapid loading), bone becomes stiffer (has a higher modulus of elasticity) and its ultimate strength increases. Consequently, it can absorb more energy prior to failure compared to low loading rates. However, when the energy capacity is finally exceeded, the energy release often results in highly comminuted fractures with extensive soft tissue damage.

Question 7842

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones. Which of the following best characterizes the composition and structure of the superficial (tangential) zone?

. Highest concentration of proteoglycans and lowest water content.
. Collagen fibers oriented perpendicular to the joint surface.
. Highest water content and collagen fibers oriented parallel to the joint surface.
. Contains the largest diameter collagen fibrils.
. Chondrocytes are primarily hypertrophic and arranged in vertical columns.

Correct Answer & Explanation

. Highest water content and collagen fibers oriented parallel to the joint surface.

Explanation

The superficial (tangential) zone of articular cartilage makes up 10-20% of the cartilage thickness. It possesses the highest water content, the lowest concentration of proteoglycans, and a high concentration of collagen fibers (primarily Type II and IX) that are oriented parallel to the joint surface to maximally resist shear forces. The deep zone, in contrast, has the lowest water content, highest proteoglycan content, and vertically oriented collagen fibers to resist compressive loads.

Question 7843

Topic: Biology, Genetics & Bone Healing

Monoclonal antibodies targeting sclerostin, such as romosozumab, are utilized in the management of osteoporosis. What is the primary molecular mechanism by which sclerostin normally influences bone remodeling?

. It activates the RANKL receptor on osteoclast precursors to promote osteoclastogenesis.
. It binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway.
. It directly stimulates osteoblast differentiation by upregulating the Runx2 transcription factor.
. It inhibits the secretion of osteoprotegerin (OPG) by bone marrow stromal cells.
. It promotes chondrocyte hypertrophy during endochondral ossification.

Correct Answer & Explanation

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

Explanation

Sclerostin is a glycoprotein secreted primarily by mature osteocytes. It acts as a negative regulator of bone formation by binding to the LRP5/6 co-receptors on the surface of osteoblasts. This binding competitively blocks the Wnt/beta-catenin signaling pathway, leading to decreased osteoblastic activity and reduced bone formation. Inhibiting sclerostin results in a dual effect: increased bone formation and decreased bone resorption.

Question 7844

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) belong to the TGF-beta superfamily and play critical roles in osteoinduction. Which of the following recombinant human BMPs is FDA-approved for use with an absorbable collagen sponge in the treatment of acute, open tibial shaft fractures?

. rhBMP-2
. rhBMP-3
. rhBMP-4
. rhBMP-7
. rhBMP-9

Correct Answer & Explanation

. rhBMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for application via an absorbable collagen sponge for acute, open tibial shaft fractures, as well as for anterior lumbar interbody fusions (ALIF) with certain interbody devices. rhBMP-7 (also known as Osteogenic Protein-1 or OP-1) previously had a Humanitarian Device Exemption for recalcitrant nonunions but is no longer commercially available. BMP-3 actually acts as an antagonist to bone formation.

Question 7845

Topic: Infection, Pharmacology & VTE

When evaluating prosthetic joint infections, bacteria within a mature biofilm exhibit significantly different survival characteristics compared to planktonic bacteria. Which of the following best describes the antimicrobial resistance profile of sessile bacteria within a biofilm?

. They share the identical Minimum Inhibitory Concentration (MIC) as planktonic bacteria.
. Their MIC is lower due to drastically reduced metabolic activity.
. They can require a Minimum Bactericidal Concentration (MBC) up to 1000 times higher than that of planktonic bacteria.
. Their resistance is exclusively mediated by the rapid acquisition of multidrug efflux pumps.
. They become strictly obligate anaerobes, conferring inherent resistance to all aminoglycosides.

Correct Answer & Explanation

. They can require a Minimum Bactericidal Concentration (MBC) up to 1000 times higher than that of planktonic bacteria.

Explanation

Bacteria residing in a biofilm (sessile state) are notoriously recalcitrant to antibiotic therapy and host immune clearance. They exist in a nutrient-depleted, stationary growth phase with low metabolic activity and are shielded by an extracellular polymeric substance (EPS) matrix. Because most antibiotics target actively dividing cells, sessile bacteria can survive antibiotic concentrations 100 to 1000 times higher than the Minimum Bactericidal Concentration (MBC) required to kill their planktonic (free-floating) counterparts.

Question 7846

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) has become standard of care in numerous orthopaedic procedures for reducing perioperative blood loss and transfusion requirements. Which of the following accurately describes its primary pharmacological mechanism of action?
. It directly inhibits Factor Xa within the common coagulation cascade.
. It reversibly binds to lysine receptor sites on plasminogen, thereby blocking its interaction with fibrin.
. It irreversibly inhibits cyclooxygenase, facilitating platelet aggregation at the site of vascular injury.
. It activates antithrombin III, leading to the rapid inhibition of thrombin.
. It stimulates the direct release of von Willebrand factor from endothelial cell Weibel-Palade bodies.

Correct Answer & Explanation

. It reversibly binds to lysine receptor sites on plasminogen, thereby blocking its interaction with fibrin.

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It functions as an antifibrinolytic agent by reversibly binding to the lysine receptor sites on plasminogen. This competitive binding prevents plasminogen from interacting with fibrin, thereby inhibiting the activation of plasminogen into plasmin by tissue plasminogen activator (tPA). Consequently, fibrin degradation (fibrinolysis) is blocked, stabilizing the pre-existing clot.

Question 7847

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit time-dependent viscoelastic properties that are clinically relevant to orthopedics. Which of the following biomechanical phenomena describes the progressive deformation of a viscoelastic material when it is subjected to a constant load over a prolonged period?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Resilience

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent, progressive deformation of a viscoelastic material under a constant load (e.g., a serial cast applied to correct a clubfoot). Stress relaxation is the decrease in stress over time when a material is held at a constant length/strain. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 7848

Topic: Biomechanics & Biomaterials

A stress-strain curve representing a typical metallic orthopedic implant under tension is analyzed.

Which of the following accurately describes the 'yield point' on this curve?

. The point at which the material undergoes complete structural failure
. The transition point from reversible elastic deformation to irreversible plastic deformation
. The total area under the elastic portion of the curve
. The maximum stress the material can withstand before necking occurs
. The linear slope of the initial portion of the curve

Correct Answer & Explanation

. The transition point from reversible elastic deformation to irreversible plastic deformation

Explanation

The yield point marks the transition from elastic deformation (where the material returns to its original shape when unloaded) to plastic deformation (where irreversible deformation occurs). The total area under the elastic curve is resilience. The maximum stress is the ultimate tensile strength. The linear slope represents Young's modulus of elasticity.

Question 7849

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe postmenopausal osteoporosis is started on teriparatide to reduce her fracture risk. Which of the following best describes the primary mechanism of action of this pharmacological agent?

. Monoclonal antibody that binds to RANKL, preventing osteoclast activation
. Inhibition of the farnesyl pyrophosphate synthase enzyme in the mevalonate pathway
. Intermittent administration of a recombinant parathyroid hormone analog that stimulates osteoblast activity
. Direct binding to hydroxyapatite crystals to prevent osteoclastic dissolution
. Inhibition of sclerostin, promoting the Wnt signaling pathway

Correct Answer & Explanation

. Intermittent administration of a recombinant parathyroid hormone analog that stimulates osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When given via daily intermittent injections, it acts as an anabolic agent, preferentially stimulating osteoblast activity over osteoclast activity to build new bone. Denosumab binds RANKL. Bisphosphonates inhibit farnesyl pyrophosphate synthase and bind hydroxyapatite. Romosozumab inhibits sclerostin.

Question 7850

Topic: Biomechanics & Biomaterials

Orthopedic stainless steel implants (e.g., 316L) are composed primarily of iron, chromium, and nickel. What is the primary functional reason for adding molybdenum to this alloy?

. To increase the modulus of elasticity to match cortical bone
. To improve fatigue strength and limit brittle failure
. To enhance resistance to pitting and crevice corrosion in chloride-rich environments
. To minimize the host foreign-body giant cell reaction
. To stabilize the alpha phase of the internal crystalline structure

Correct Answer & Explanation

. To enhance resistance to pitting and crevice corrosion in chloride-rich environments

Explanation

The 'L' in 316L stainless steel stands for low carbon, which prevents intergranular corrosion. The addition of molybdenum (usually 2-3%) specifically improves the alloy's resistance to pitting and crevice corrosion, which is critical in the chloride-rich physiological environment of the human body. Chromium provides a passivating oxide layer, and nickel stabilizes the austenitic face-centered cubic crystal structure.

Question 7851

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue structured in multiple histomorphologic zones.

Which of the following characteristics accurately describes the deep (basal) zone of healthy articular cartilage?

. It contains the highest concentration of water
. Collagen fibers are oriented parallel to the joint surface
. It contains the highest concentration of proteoglycans and lowest water content
. Chondrocytes are flattened and oriented horizontally
. It provides the primary resistance to shear forces

Correct Answer & Explanation

. It contains the highest concentration of proteoglycans and lowest water content

Explanation

The deep zone of articular cartilage is characterized by the highest concentration of proteoglycans and the lowest water content. The collagen fibers (mainly Type II) in this zone are large in diameter and oriented perpendicular to the joint surface to resist compressive loads. The superficial (tangential) zone has the highest water content, flattened chondrocytes, parallel collagen fibers, and provides resistance to shear forces.

Question 7852

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty due to its superior wear characteristics. However, the process of cross-linking and subsequent remelting/annealing directly diminishes which of the following mechanical properties?
. Abrasive wear resistance
. Adhesive wear resistance
. Resistance to oxidative degradation
. Galvanic corrosion resistance
. Fatigue strength and fracture toughness

Correct Answer & Explanation

. Fatigue strength and fracture toughness

Explanation

While high-dose irradiation cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) dramatically reduces adhesive and abrasive wear, the cross-linking process and subsequent thermal treatments (remelting) significantly decrease mechanical properties such as fatigue strength, fracture toughness, and ultimate tensile strength. This makes HXLPE more vulnerable to rim cracking or failure under high-stress conditions or thin components.

Question 7853

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently administered intravenously and topically in major orthopedic surgeries to reduce perioperative blood loss. By which of the following mechanisms does TXA exert its therapeutic effect?
. Direct irreversible inhibition of activated factor X (Factor Xa)
. Reversible competitive inhibition of plasminogen activation
. Irreversible binding to platelet cyclooxygenase-1 (COX-1)
. Activation of antithrombin III
. Direct binding to von Willebrand factor, stabilizing the platelet plug

Correct Answer & Explanation

. Reversible competitive inhibition of plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen. This prevents plasminogen from interacting with fibrin, thereby halting its activation into plasmin and preventing subsequent fibrin clot degradation.

Question 7854

Topic: Biology, Genetics & Bone Healing

According to Perrenโ€™s strain theory of fracture healing, the type of tissue that forms in a fracture gap is determined by the local interfragmentary strain. Lamellar bone can only form when the interfragmentary strain is below which of the following thresholds?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that a specific tissue can only form and survive in a fracture gap if the interfragmentary strain is lower than the tissue's ultimate failure strain. Granulation tissue can tolerate up to 100% strain, fibrocartilage roughly 10-15%, and woven bone about 5%. Lamellar bone requires an extremely stable environment and can only form when the strain is less than 2%.

Question 7855

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection (PJI), Staphylococcus aureus utilizes the host implant surface to form a recalcitrant biofilm. Which stage of biofilm development is distinctly characterized by the production of a mature extracellular polymeric substance (EPS) matrix and the initiation of quorum sensing?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic phase

Correct Answer & Explanation

. Maturation

Explanation

Biofilm formation progresses through distinct phases: 1) Reversible attachment of planktonic bacteria. 2) Irreversible attachment mediated by adhesins. 3) Maturation, during which the bacteria multiply, form microcolonies, produce a dense extracellular polymeric substance (EPS) matrix, and engage in quorum sensing (chemical communication). 4) Dispersion (detachment), where bacteria escape to colonize new sites.

Question 7856

Topic: Biomechanics & Biomaterials

A load-deformation curve of a bone specimen is shown in Figure 1.

Which of the following parameters represents the material's toughness?

. The slope of the linear elastic region
. The peak load achieved before failure
. The area under the entire stress-strain curve
. The point at which the curve transitions from linear to non-linear
. The maximum deformation before yield

Correct Answer & Explanation

. The area under the entire stress-strain curve

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures, represented by the total area under the stress-strain curve. The slope of the linear elastic region represents the elastic modulus (stiffness). The peak load is the ultimate strength. The transition point from linear to non-linear is the yield point, marking the end of elastic deformation and the beginning of plastic deformation.

Question 7857

Topic: Biomechanics & Biomaterials
Cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) components in total joint arthroplasty is primarily performed to improve which of the following properties?
. Tensile strength
. Fatigue resistance
. Abrasive wear resistance
. Fracture toughness
. Yield strength

Correct Answer & Explanation

. Abrasive wear resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is irradiated to create free radicals that form cross-links, which significantly increases the material's abrasive wear resistance. However, this cross-linking process inherently decreases other mechanical properties, including tensile strength, fracture toughness, and fatigue resistance. Post-irradiation melting or annealing is done to extinguish remaining free radicals and prevent oxidation.

Question 7858

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the highest concentration of water and the orientation of collagen fibers parallel to the joint surface are found in which zone?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone makes up 10-20% of articular cartilage thickness. It has the highest water content (approximately 80%), the lowest proteoglycan content, and features Type II collagen fibers arranged parallel to the joint surface to resist shear and tensile stresses. The deep zone has the lowest water content, highest proteoglycan content, and collagen fibers arranged perpendicular to the surface.

Question 7859

Topic: Infection, Pharmacology & VTE

When managing a staphylococcal periprosthetic joint infection (PJI) with retention of the prosthesis, rifampin is frequently added to the antibiotic regimen due to its ability to penetrate biofilms. What is the mechanism of action of rifampin?

. Inhibition of bacterial cell wall synthesis via penicillin-binding proteins
. Binding to the 30S ribosomal subunit to inhibit protein synthesis
. Inhibition of DNA-dependent RNA polymerase
. Disruption of bacterial cell membrane potential
. Inhibition of DNA gyrase

Correct Answer & Explanation

. Inhibition of DNA-dependent RNA polymerase

Explanation

Rifampin exerts its bactericidal effect by binding to the beta subunit of bacterial DNA-dependent RNA polymerase, thereby inhibiting RNA synthesis. It is uniquely effective against slow-growing or stationary-phase staphylococci embedded in biofilms. Option A describes beta-lactams. Option B describes aminoglycosides or tetracyclines. Option D describes daptomycin. Option E describes fluoroquinolones.

Question 7860

Topic: 1. General Principles & Basic Science

Figure 2 illustrates a stage in the incorporation of a cortical bone allograft.

Which of the following is the defining characteristic of 'creeping substitution' during this process?

. Simultaneous osteoclastic resorption of necrotic bone and osteoblastic deposition of new woven bone
. Rapid vascular invasion followed by immediate enchondral ossification
. Direct transformation of mesenchymal stem cells into osteocytes without an intermediate cartilage phase
. Formation of a cartilage anlage that is subsequently calcified
. Deposition of calcium hydroxyapatite on a purely synthetic scaffold

Correct Answer & Explanation

. Simultaneous osteoclastic resorption of necrotic bone and osteoblastic deposition of new woven bone

Explanation

Creeping substitution is the biological process by which a bone graft is incorporated by the host. It involves the simultaneous invasion of vascular granulation tissue, osteoclastic resorption of the dead graft trabeculae (via cutting cones in cortical bone), and osteoblastic deposition of new viable host bone onto those same dead trabeculae. It bypasses the cartilage phase seen in secondary bone healing (enchondral ossification).

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