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1. General Principles & Basic Science MCQs

Practice Set 392 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 7821

Topic: Infection, Pharmacology & VTE

A patient develops a surgical site infection caused by Methicillin-Resistant Staphylococcus aureus (MRSA). The chosen intravenous antibiotic targets the bacterial cell wall by binding to the D-alanyl-D-alanine terminus of cell wall precursor units. What is the most significant dose-limiting toxicity of this medication?

. Ototoxicity
. Hepatotoxicity
. Nephrotoxicity
. Tendinopathy
. Peripheral neuropathy

Correct Answer & Explanation

. Nephrotoxicity

Explanation

The antibiotic described is Vancomycin, a glycopeptide that inhibits bacterial cell wall synthesis by binding to the D-ala-D-ala terminus of peptidoglycan precursors. The most significant and common dose-limiting toxicity of Vancomycin is nephrotoxicity, which requires trough level monitoring. While ototoxicity can occur, it is much rarer than renal impairment. Red Man Syndrome is a histamine-mediated infusion reaction, not a dose-limiting toxicity. Tendinopathy is associated with fluoroquinolones.

Question 7822

Topic: Biomechanics & Biomaterials

Rank the following common orthopedic implant materials in order of decreasing Young's modulus (stiffness):

. Alumina Ceramic > Cobalt-Chrome > Titanium > Cortical Bone
. Cobalt-Chrome > Alumina Ceramic > Titanium > Cortical Bone
. Titanium > Cobalt-Chrome > Cortical Bone > Cancellous Bone
. Cobalt-Chrome > Titanium > Alumina Ceramic > Cortical Bone
. Alumina Ceramic > Titanium > Cobalt-Chrome > Cortical Bone

Correct Answer & Explanation

. Alumina Ceramic > Cobalt-Chrome > Titanium > Cortical Bone

Explanation

Young's modulus is a fundamental biomechanical measure of the stiffness of a solid material. The correct order from stiffest (highest modulus) to most flexible (lowest modulus) is Alumina Ceramic (approx. 380 GPa) > Cobalt-Chrome alloys (approx. 210-240 GPa) > Stainless Steel (approx. 200 GPa) > Titanium alloys (approx. 100-110 GPa) > Cortical Bone (approx. 15-20 GPa) > PMMA bone cement (approx. 3 GPa) > Cancellous bone (approx. 0.1-2 GPa).

Question 7823

Topic: 1. General Principles & Basic Science
The structural properties of a healing tendon or ligament are heavily dependent on the remodeling phase of tissue repair. During this phase, what is the primary cellular event responsible for increasing the tensile strength of the healing tissue?
. Extensive angiogenesis establishing a highly vascular granulation tissue bed
. Replacement of type III collagen with highly organized type I collagen
. Replacement of type I collagen with highly organized type III collagen
. Increased production of glycosaminoglycans significantly raising tissue water content
. Proliferation of inflammatory macrophages causing early scar formation

Correct Answer & Explanation

. Replacement of type III collagen with highly organized type I collagen

Explanation

Tendon and ligament healing occurs in three overlapping phases: inflammation, proliferation, and remodeling. During the early proliferative phase, immature and mechanically weaker type III collagen is predominantly laid down. During the remodeling phase (which can last months to years), this type III collagen is gradually resorbed and replaced by stronger, more highly organized type I collagen. These type I collagen fibers cross-link and align parallel to the axis of mechanical stress, significantly increasing the ultimate tensile strength of the tissue.

Question 7824

Topic: Biology, Genetics & Bone Healing

Romosozumab is a monoclonal antibody utilized in the treatment of severe osteoporosis to decrease the risk of fractures. What is its exact mechanism of action at the molecular level?

. Binds and neutralizes receptor activator of nuclear factor kappa-B ligand (RANKL)
. Inhibits Cathepsin K, preventing the degradation of bone matrix
. Binds to and inhibits sclerostin, unblocking the Wnt/beta-catenin signaling pathway
. Directly stimulates the parathyroid hormone (PTH) receptor
. Inhibits farnesyl pyrophosphate synthase within osteoclasts

Correct Answer & Explanation

. Binds to and inhibits sclerostin, unblocking the Wnt/beta-catenin signaling pathway

Explanation

Romosozumab is a monoclonal antibody that targets and inhibits sclerostin. Sclerostin is a glycoprotein secreted by osteocytes that normally downregulates bone formation by inhibiting the Wnt/beta-catenin signaling pathway in osteoblasts. By inhibiting sclerostin, romosozumab exerts a dual effect: it significantly promotes bone formation and also mildly decreases bone resorption, making it a highly effective anabolic agent for severe osteoporosis.

Question 7825

Topic: Biomechanics & Biomaterials



Ligaments and tendons exhibit viscoelastic properties, making their mechanical behavior dependent on the rate of loading. Which of the following best describes the biomechanical phenomenon of 'creep'?

. Increasing deformation over time when subjected to a constant load
. Decreasing stress over time when held at a constant deformation
. The energy lost as heat during a cyclical loading and unloading process
. The initial non-linear flattening of the collagen crimp pattern
. Permanent plastic deformation that occurs after exceeding the yield point

Correct Answer & Explanation

. Increasing deformation over time when subjected to a constant load

Explanation

Creep is a fundamental viscoelastic property defined as the progressive, time-dependent deformation of a material under a constant load (or stress). This is clinically relevant in casting and soft tissue stretching. 'Stress relaxation' is the decrease in stress over time when a material is held at a constant length or deformation. 'Hysteresis' is the loss of energy (usually as heat) between the loading and unloading curves.

Question 7826

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, highly cross-linked polyethylene is typically subjected to a remelting process above its melting temperature (approximately 150°C). What is the primary purpose of this remelting step?
. To increase the ultimate tensile strength of the polymer
. To eliminate free radicals and prevent long-term in vivo oxidation
. To increase the crystallinity of the polyethylene chains
. To enhance the yield strength of the material to prevent creep
. To increase the chain mobility to promote further cross-linking

Correct Answer & Explanation

. To eliminate free radicals and prevent long-term in vivo oxidation

Explanation

Gamma irradiation is used to induce cross-linking in UHMWPE, which vastly improves its wear resistance. However, irradiation cleaves polymer chains and generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to chain scission, oxidation, embrittlement, and catastrophic failure of the bearing. Thermal treatment (remelting or annealing) is performed to extinguish these free radicals. Remelting eliminates free radicals effectively but comes at the cost of a slight decrease in crystallinity and certain mechanical properties (like yield strength and fatigue resistance).

Question 7827

Topic: 1. General Principles & Basic Science

Which of the following best describes the structural and biochemical characteristics of the superficial (tangential) zone of normal articular cartilage?

. Highest concentration of proteoglycans and lowest water content
. Chondrocytes arranged in columnar arrays oriented perpendicular to the joint surface
. Highest concentration of collagen with fibers oriented parallel to the joint surface
. Lowest cell density with radially oriented collagen fibers
. Highest concentration of aggrecan and primarily Type X collagen

Correct Answer & Explanation

. Highest concentration of collagen with fibers oriented parallel to the joint surface

Explanation

The superficial (tangential) zone constitutes the top 10-20% of articular cartilage. It is characterized by the highest water content, the lowest concentration of proteoglycans, and the highest concentration of collagen (primarily Type II). The collagen fibers here are tightly packed and oriented parallel to the articular surface to resist shear and tensile stresses. The chondrocytes in this zone are flattened. The deep zone, in contrast, has the highest proteoglycan content, lowest water content, and collagen fibers oriented perpendicularly (radially) to resist compressive loads.

Question 7828

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant challenge in orthopedic implant-associated infections. Which genetic alteration is primarily responsible for the methicillin resistance in these organisms?

. Mutation in the rpoB gene altering the RNA polymerase target
. Acquisition of the vanA gene cluster altering cell wall precursors
. Efflux pump overexpression via the norA gene promoter
. Acquisition of the mecA gene encoding for an altered penicillin-binding protein (PBP2a)
. Production of highly active broad-spectrum beta-lactamase enzymes

Correct Answer & Explanation

. Acquisition of the mecA gene encoding for an altered penicillin-binding protein (PBP2a)

Explanation

Methicillin resistance in S. aureus is mediated by the staphylococcal cassette chromosome mec (SCCmec), which carries the mecA gene. The mecA gene encodes for an altered penicillin-binding protein, PBP2a, which has a remarkably low affinity for beta-lactam antibiotics. This allows the bacteria to continue cross-linking its peptidoglycan cell wall even in the presence of therapeutic levels of methicillin or other beta-lactams. VanA mediates vancomycin resistance, while rpoB mutations lead to rifampin resistance.

Question 7829

Topic: Biomechanics & Biomaterials

A 65-year-old patient undergoes a revision total hip arthroplasty where a cobalt-chromium (CoCr) femoral head is placed onto a titanium alloy (Ti-6Al-4V) stem. Which of the following best describes the dominant type of corrosion that is uniquely facilitated by combining these two dissimilar metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in direct electrical contact within an electrolytic solution (such as body fluids). The less noble metal acts as the anode and preferentially corrodes. While CoCr and Titanium alloys are frequently paired in orthopedics due to their closely matched electrochemical potentials and passive oxide layers, mixing dissimilar metals inherently risks galvanic corrosion. Fretting and crevice corrosion also occur at modular junctions (like the trunnion) but are mechanically and geometrically driven phenomena that occur even in monobloc or mixed metal constructs.

Question 7830

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in fracture healing by inducing the differentiation of mesenchymal stem cells into osteoblasts. BMPs primarily exert their intracellular effects through which of the following signaling pathways?

. Wnt/beta-catenin pathway
. JAK/STAT pathway
. Smad pathway
. Notch signaling pathway
. MAP kinase pathway

Correct Answer & Explanation

. Smad pathway

Explanation

BMPs are members of the Transforming Growth Factor-beta (TGF-beta) superfamily. Upon binding to their specific serine/threonine kinase cell surface receptors, they trigger the phosphorylation of intracellular receptor-regulated Smad proteins (specifically Smad1, 5, and 8). These activated Smads form a complex with the common-mediator Smad4, which then translocates into the nucleus to regulate the transcription of osteogenic target genes, notably Runx2.

Question 7831

Topic: 1. General Principles & Basic Science

A pediatric patient presents with unusually dense, fragile bones and is subsequently diagnosed with malignant infantile osteopetrosis. The pathogenesis of this disease is linked to the failure of osteoclasts to create an acidic environment in the sealing zone. Which enzyme is most commonly deficient or defective in this specific cellular process?

. Cathepsin K
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase (TRAP)
. Matrix metalloproteinase-9 (MMP-9)
. Alkaline phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclastic bone resorption, resulting in excessively dense, brittle bones. To resorb bone, osteoclasts must acidify the sealed Howship's lacuna to dissolve the inorganic hydroxyapatite. This acidification relies heavily on Carbonic Anhydrase II (CA II), which catalyzes the conversion of water and carbon dioxide into carbonic acid, yielding the protons (H+) that are subsequently pumped into the lacuna by a V-ATPase pump (TCIRG1 mutation). Cathepsin K and TRAP are involved in degrading the organic matrix (collagen) after demineralization.

Question 7832

Topic: 1. General Principles & Basic Science

Which of the following enzymes is primarily responsible for the degradation of the organic bone matrix within the Howship's lacuna during osteoclastic bone resorption?

. Alkaline phosphatase
. Matrix metalloproteinase-9
. Tartrate-resistant acid phosphatase (TRAP)
. Cathepsin K
. Carbonic anhydrase II

Correct Answer & Explanation

. Cathepsin K

Explanation

Osteoclasts resorb bone by secreting hydrogen ions (via Carbonic anhydrase II and V-ATPase) to dissolve inorganic hydroxyapatite, and proteolytic enzymes like Cathepsin K to degrade the organic matrix (primarily Type I collagen). TRAP is a marker of osteoclasts and is involved in osteopontin dephosphorylation, but Cathepsin K is the primary protease responsible for collagen degradation at the ruffled border.

Question 7833

Topic: Biomechanics & Biomaterials
The addition of Vitamin E (alpha-tocopherol) to highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) in total joint arthroplasty primarily serves to:
. Increase the crystalline structure of the polymer
. Decrease the need for irradiation
. Scavenge free radicals to prevent oxidative degradation
. Enhance the fatigue strength to levels above conventional UHMWPE
. Promote osteointegration at the cementless interface

Correct Answer & Explanation

. Scavenge free radicals to prevent oxidative degradation

Explanation

Irradiation of UHMWPE creates cross-links that improve wear resistance but also generates free radicals that can lead to oxidative degradation and embrittlement over time. Vitamin E is added as an antioxidant to scavenge these free radicals, preventing oxidation without the need to melt or anneal the plastic, thereby preserving its mechanical properties and fatigue strength.

Question 7834

Topic: 1. General Principles & Basic Science

In which zone of normal articular cartilage are the chondrocytes arranged in columns perpendicular to the joint surface, and what is the primary collagen type present?

. Superficial zone; Type II collagen
. Transitional (middle) zone; Type I collagen
. Deep zone; Type II collagen
. Calcified zone; Type X collagen
. Deep zone; Type X collagen

Correct Answer & Explanation

. Deep zone; Type II collagen

Explanation

Articular cartilage is primarily composed of Type II collagen. In the deep zone, chondrocytes are arranged in vertical columns, and collagen fibers are oriented perpendicular to the joint surface to resist compressive forces. The superficial zone has collagen parallel to the surface to resist shear, while the calcified zone contains Type X collagen and hypertrophic chondrocytes.

Question 7835

Topic: 1. General Principles & Basic Science

The pull-out strength of a cortical bone screw is most significantly increased by increasing which of the following design parameters?

. Outer (thread) diameter
. Inner (core) diameter
. Pitch length
. Screw length
. Insertion torque

Correct Answer & Explanation

. Outer (thread) diameter

Explanation

Screw pull-out strength is directly proportional to the outer (thread) diameter, the length of thread engagement in the bone, and the shear strength of the bone material, while being inversely proportional to the pitch. The outer diameter has the most mathematically significant effect on pull-out strength. The inner (core) diameter primarily determines the screw's bending strength, not pull-out strength.

Question 7836

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the mechanism of action of teriparatide in the treatment of osteoporosis?

. Binds to the RANK receptor on osteoclasts to inhibit their activation
. Inhibits the enzyme farnesyl pyrophosphate synthase in the mevalonate pathway
. Acts as a selective estrogen receptor modulator (SERM) with agonistic effects on bone
. Continuously stimulates PTH receptors leading to decreased osteoblast apoptosis
. Intermittently stimulates PTH receptors leading to preferential activation of osteoblasts over osteoclasts

Correct Answer & Explanation

. Intermittently stimulates PTH receptors leading to preferential activation of osteoblasts over osteoclasts

Explanation

Teriparatide is an anabolic agent and a recombinant human parathyroid hormone (PTH 1-34) analog. While continuous endogenous PTH elevation leads to bone resorption via osteoclast activation, intermittent (daily subcutaneous) administration of teriparatide preferentially stimulates osteoblastic bone formation, increasing bone mineral density and reducing fracture risk.

Question 7837

Topic: Biomechanics & Biomaterials
Which of the following orthopedic biomaterials possesses a Young's modulus of elasticity most closely resembling that of human cortical bone?
. Stainless steel (316L)
. Cobalt-chromium alloy
. Titanium alloy (Ti-6Al-4V)
. Ultra-high molecular weight polyethylene (UHMWPE)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Young's modulus is a measure of material stiffness. Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloy (approx. 100-110 GPa) is the closest metallic biomaterial to cortical bone compared to Stainless Steel (approx. 200 GPa) and Cobalt-Chromium (approx. 210-240 GPa). This closer modulus match helps reduce stress shielding around implants.

Question 7838

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, which type of collagen is predominantly synthesized during the soft callus phase, and which cells are primarily responsible for its production?
. Type I collagen; osteoblasts
. Type II collagen; chondrocytes
. Type III collagen; fibroblasts
. Type X collagen; hypertrophic chondrocytes
. Type I collagen; mesenchymal stem cells

Correct Answer & Explanation

. Type II collagen; chondrocytes

Explanation

Secondary fracture healing occurs via endochondral ossification. During the soft callus phase, the fracture gap is stabilized by cartilage formation in hypoxic conditions. Chondrocytes synthesize predominantly Type II collagen (along with aggrecan) to form this cartilaginous soft callus. Later, hypertrophic chondrocytes produce Type X collagen, the matrix mineralizes, and osteoblasts lay down Type I collagen to form the hard callus.

Question 7839

Topic: Infection, Pharmacology & VTE

A 65-year-old man develops a periprosthetic joint infection three months after a total knee arthroplasty. Staphylococcus epidermidis is isolated from the joint fluid. The pathogenesis of this infection involves the formation of a biofilm. Which of the following represents the critical first step in biofilm formation on the orthopedic implant?

. Quorum sensing to upregulate virulence genes
. Secretion of an extracellular polymeric substance (EPS) matrix
. Reversible attachment of planktonic bacteria to the protein-coated implant surface
. Dissemination of planktonic bacteria from a mature biofilm
. Rapid multiplication of bacteria in the local hematoma

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria to the protein-coated implant surface

Explanation

Biofilm formation begins with the immediate coating of the implant with host proteins (the conditioning film). Planktonic bacteria then undergo a phase of reversible attachment to this surface via van der Waals forces. This is followed by irreversible attachment (via adhesins like MSCRAMMs), proliferation, maturation via secretion of extracellular polymeric substance (EPS), quorum sensing, and eventual dispersion.

Question 7840

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon uses a stainless steel screw to secure a titanium plate during fracture fixation. Postoperatively, rapid degradation of the screw is observed at the interface with the plate. Which of the following best describes the primary mechanism of this implant degradation?

. Galvanic corrosion
. Fretting corrosion
. Crevice corrosion
. Pitting corrosion
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in electrical contact within an electrolytic environment (such as bodily fluids). This establishes an electrochemical potential difference, causing the less noble (more anodic) metal to undergo accelerated corrosion. To prevent this, orthopaedic constructs should typically utilize components composed of the same metal or compatible alloys.

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