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1. General Principles & Basic Science MCQs

Practice Set 293 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 5841

Topic: Biomechanics & Biomaterials

Cortical bone is stronger in longitudinal compression than it is in transverse loading or tension. What is the biomechanical term for a material that exhibits different mechanical properties depending on the direction of loading?

. Isotropic
. Viscoelastic
. Anisotropic
. Plasticity
. Fatigue

Correct Answer & Explanation

. Anisotropic

Explanation

Anisotropy refers to a material having directionally dependent mechanical properties. Because of its osteonal structure, cortical bone is highly anisotropic, being strongest when loaded parallel to its longitudinal axis.

Question 5842

Topic: Biology, Genetics & Bone Healing

Which of the following is the primary histological finding that distinguishes osteomalacia from osteoporosis?

. Decreased cortical thickness
. Increased unmineralized osteoid seams
. Presence of empty osteocyte lacunae
. Increased woven bone formation
. Multinucleated giant cells

Correct Answer & Explanation

. Increased unmineralized osteoid seams

Explanation

Osteomalacia is characterized by a defect in bone mineralization, resulting in a classic histological appearance of thickened, unmineralized osteoid seams. Osteoporosis, by contrast, shows normal mineralization but a quantitatively decreased total bone mass.

Question 5843

Topic: 1. General Principles & Basic Science

Which of the following best describes the mechanism of action of vancomycin, an antibiotic frequently mixed into polymethylmethacrylate (PMMA) bone cement for infection prophylaxis?

. Inhibits bacterial DNA gyrase
. Binds irreversibly to the 30S ribosomal subunit
. Binds to D-alanyl-D-alanine termini of peptidoglycan precursors
. Inhibits beta-lactamase production
. Disrupts the bacterial cell membrane via rapid depolarization

Correct Answer & Explanation

. Binds to D-alanyl-D-alanine termini of peptidoglycan precursors

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits Gram-positive bacterial cell wall synthesis. It binds tightly to the D-alanyl-D-alanine portion of cell wall precursors, effectively preventing their cross-linking and weakening the cell wall.

Question 5844

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the cellular mechanism of action of nitrogen-containing bisphosphonates (e.g., alendronate)?

. Inhibiting the farnesyl pyrophosphate synthase enzyme in the mevalonate pathway
. Acting as a decoy receptor for RANKL
. Inhibiting DNA gyrase within the osteoclast nucleus
. Stimulating osteoblast differentiation through Wnt signaling
. Binding to sclerostin to prevent its inhibitory effects

Correct Answer & Explanation

. Inhibiting the farnesyl pyrophosphate synthase enzyme in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins (like Ras and Rho), ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 5845

Topic: Biology, Genetics & Bone Healing

Denosumab is a potent antiresorptive agent used in the treatment of osteoporosis and giant cell tumor of bone. What is its primary mechanism of action?

. Recombinant parathyroid hormone analog
. Monoclonal antibody against sclerostin
. Inhibitor of the mevalonate pathway
. Monoclonal antibody that binds to RANKL
. Selective estrogen receptor modulator (SERM)

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding RANKL, it prevents interaction with the RANK receptor on osteoclasts, thus inhibiting osteoclast formation and function.

Question 5846

Topic: Infection, Pharmacology & VTE

A patient undergoing treatment for an implant-associated orthopedic infection develops sudden Achilles tendon pain. The antibiotic utilized is known to inhibit DNA gyrase. Which medication was most likely prescribed?

. Rifampin
. Vancomycin
. Ciprofloxacin
. Linezolid
. Gentamicin

Correct Answer & Explanation

. Ciprofloxacin

Explanation

Fluoroquinolones, such as ciprofloxacin, work by inhibiting bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. They carry a black box warning for tendinopathy and tendon rupture, which most commonly affects the Achilles tendon.

Question 5847

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of orthopedic implants, the total area under a material's stress-strain curve represents which of the following properties?

. Elasticity
. Yield strength
. Toughness
. Stiffness
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

The total area under the stress-strain curve represents the toughness of the material, which is the total amount of energy absorbed before structural failure. Stiffness, by contrast, is represented by the slope of the linear elastic region (Young's modulus).

Question 5848

Topic: Biology, Genetics & Bone Healing
Which of the following combinations correctly identifies the predominant collagen type and its synthesizing cell in normal hyaline articular cartilage?
. Type I collagen synthesized by osteoblasts
. Type II collagen synthesized by chondrocytes
. Type III collagen synthesized by fibroblasts
. Type IV collagen synthesized by endothelial cells
. Type X collagen synthesized by hypertrophic chondrocytes

Correct Answer & Explanation

. Type II collagen synthesized by chondrocytes

Explanation

Normal hyaline articular cartilage is primarily composed of water and Type II collagen, which is synthesized exclusively by chondrocytes. Type X collagen is localized to the calcified zone and is produced by hypertrophic chondrocytes.

Question 5849

Topic: Biology, Genetics & Bone Healing

Teriparatide is an anabolic agent utilized for the treatment of severe osteoporosis. How does its administration lead to increased bone mineral density?

. Continuous exposure directly inhibits osteoclast apoptosis
. Intermittent administration stimulates osteoblastic bone formation
. Continuous exposure suppresses parathyroid hormone-related peptide
. Intermittent administration directly binds and inhibits RANKL
. Continuous administration decreases renal calcium reabsorption

Correct Answer & Explanation

. Intermittent administration stimulates osteoblastic bone formation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. While continuous PTH exposure primarily drives osteoclast-mediated bone resorption, daily intermittent administration paradoxically stimulates robust osteoblastic bone formation.

Question 5850

Topic: Biomechanics & Biomaterials
Which of the following best defines the viscoelastic property of 'creep' in orthopedic biomaterials such as ultra-high-molecular-weight polyethylene (UHMWPE)?
. Progressive deformation of a material under a constant applied load over time
. Decreasing stress within a material held at a constant deformation over time
. Energy lost as heat during a single loading and unloading cycle
. Increased material stiffness as the rate of loading increases
. Failure of a material subjected to repetitive loading below its yield strength

Correct Answer & Explanation

. Progressive deformation of a material under a constant applied load over time

Explanation

Creep is the progressive, time-dependent deformation of a viscoelastic material when it is subjected to a constant load. Stress relaxation, conversely, is the decrease in internal stress when a material is held at a constant deformation.

Question 5851

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, primary bone healing (osteonal remodeling without callus formation) occurs only when the interfragmentary strain is maintained below what specific threshold?

. 2 percent
. 10 percent
. 25 percent
. 50 percent
. 100 percent

Correct Answer & Explanation

. 2 percent

Explanation

Perren's strain theory states that primary (absolute) bone healing occurs when interfragmentary strain is kept below 2%. Strains between 2% and 10% promote secondary bone healing via callus formation, while strains above 10% result in nonunion.

Question 5852

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently used in orthopedic surgery to reduce perioperative blood loss. Which of the following describes its primary mechanism of action?
. Directly inactivates factor Xa
. Binds to antithrombin III to inhibit thrombin
. Competitively inhibits the activation of plasminogen to plasmin
. Stimulates the release of von Willebrand factor from endothelial cells
. Inhibits cyclooxygenase, decreasing thromboxane A2 production

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively binds to the lysine-binding sites on plasminogen, preventing its activation to plasmin and thus effectively inhibiting fibrinolysis.

Question 5853

Topic: Biomechanics & Biomaterials

Review the provided biomechanical graphic.

On a standard stress-strain curve for cortical bone, what represents the point beyond which the material will no longer return to its original shape upon unloading?

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

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the end of the elastic region and the beginning of the plastic region on a stress-strain curve. Once loaded beyond the yield point, the material sustains permanent (plastic) deformation and cannot completely return to its original shape.

Question 5854

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) plays a critical regulatory role in bone remodeling. Which of the following accurately describes its cellular source and function?

. Secreted by osteoclasts to stimulate osteoblast proliferation
. Secreted by osteoblasts to act as a decoy receptor for RANKL
. Secreted by osteocytes to inhibit Wnt signaling
. Secreted by macrophages to directly induce osteoclast apoptosis
. Secreted by the parathyroid gland to increase serum calcium

Correct Answer & Explanation

. Secreted by osteoblasts to act as a decoy receptor for RANKL

Explanation

Osteoprotegerin (OPG) is a glycoprotein secreted primarily by osteoblasts. It acts as a decoy receptor that competitively binds RANKL, preventing RANKL from activating RANK on osteoclasts and thereby inhibiting bone resorption.

Question 5855

Topic: 1. General Principles & Basic Science

Which of the following geometric properties of a standard cortical bone screw has the greatest direct influence on its pullout strength?

. Inner (minor) diameter
. Pitch
. Outer (major) diameter
. Thread length
. Core thickness

Correct Answer & Explanation

. Outer (major) diameter

Explanation

Screw pullout strength is most heavily influenced by the outer (major) diameter of the screw. While increasing thread engagement and bone quality also contribute, the major diameter is directly and most significantly proportional to pullout resistance.

Question 5856

Topic: Infection, Pharmacology & VTE

A 65-year-old male is treated with a specific antibiotic adjunct due to a staphylococcal prosthetic joint infection, chosen for its unique ability to penetrate mature biofilm. What is the mechanism of action of this drug?

. Inhibits cell wall synthesis by binding to D-alanyl-D-alanine
. Inhibits DNA-dependent RNA polymerase
. Inhibits protein synthesis by binding to the 30S ribosomal subunit
. Inhibits protein synthesis by binding to the 50S ribosomal subunit
. Disrupts the bacterial cell membrane via lipopeptide insertion

Correct Answer & Explanation

. Inhibits DNA-dependent RNA polymerase

Explanation

Rifampin is highly effective against biofilm-producing organisms like Staphylococcus species in prosthetic joint infections. Its primary mechanism of action is the inhibition of bacterial DNA-dependent RNA polymerase, thereby halting RNA transcription.

Question 5857

Topic: Biology, Genetics & Bone Healing

Which of the following cells is the primary source of receptor activator of nuclear factor kappa-B ligand (RANKL) in bone metabolism?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteoblasts and bone marrow stromal cells express RANKL on their surface in response to various stimuli. RANKL binds to RANK on osteoclast precursors, promoting their differentiation and activation.

Question 5858

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is prescribed alendronate for osteoporosis. What is the specific cellular mechanism of action of this medication?

. Inhibits osteoclast proton pumps
. Binds to RANKL to prevent osteoclast activation
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Stimulates Wnt signaling by inhibiting sclerostin
. Acts as a selective estrogen receptor modulator

Correct Answer & Explanation

. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase (FPPS) in the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

Question 5859

Topic: Biomechanics & Biomaterials

A polymer undergoes continued progressive deformation over time when subjected to a constant load. This biomechanical phenomenon is best described as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent permanent deformation of a viscoelastic material under a constant stress. Stress relaxation, in contrast, is the decrease in stress over time when a material is held at a constant strain.

Question 5860

Topic: 1. General Principles & Basic Science

Which of the following antibiotics exerts its bactericidal effect by binding to the D-alanyl-D-alanine terminus of cell wall precursor peptides and is commonly used in heat-stable polymethylmethacrylate (PMMA) cement?

. Gentamicin
. Tobramycin
. Cefazolin
. Vancomycin
. Rifampin

Correct Answer & Explanation

. Vancomycin

Explanation

Vancomycin inhibits bacterial cell wall synthesis by binding to the D-alanyl-D-alanine terminus of peptidoglycan precursors. It is heat-stable, making it highly suitable for elution from the exothermic PMMA bone cement environment.

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