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1. General Principles & Basic Science MCQs

Practice Set 297 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 5921

Topic: Biomechanics & Biomaterials
Gamma irradiation of ultra-high molecular weight polyethylene (UHMWPE) in an inert environment (e.g., argon or vacuum) followed by remelting is primarily performed to achieve which of the following?
. Increase the crystalline content of the polyethylene
. Eliminate free radicals and reduce oxidative degradation
. Increase the elastic modulus of the bearing surface
. Decrease the cross-linking density
. Enhance water absorption for better lubrication

Correct Answer & Explanation

. Eliminate free radicals and reduce oxidative degradation

Explanation

Gamma irradiation facilitates cross-linking to improve wear resistance but also creates free radicals that can lead to oxidative degradation. Remelting the polyethylene eliminates these free radicals, stabilizing the material against oxidation at the cost of slight decreases in mechanical strength.

Question 5922

Topic: 1. General Principles & Basic Science

In the structural composition of articular cartilage, which molecule is responsible for covalently stabilizing the aggrecan core protein to the hyaluronic acid backbone?

. Chondroitin sulfate
. Type II collagen
. Fibronectin
. Link protein
. Keratan sulfate

Correct Answer & Explanation

. Link protein

Explanation

Aggrecan, the major proteoglycan in articular cartilage, interacts non-covalently with hyaluronic acid to form massive aggregates. Link protein stabilizes this interaction, securely anchoring the aggrecan monomers to the hyaluronan chain.

Question 5923

Topic: Biology, Genetics & Bone Healing
A patient with a history of recurrent fractures and dense, brittle bones on radiographs is diagnosed with malignant infantile osteopetrosis. This condition is most commonly caused by a loss-of-function mutation affecting which of the following?
. Type I collagen (COL1A1)
. Fibroblast growth factor receptor 3 (FGFR3)
. Tissue nonspecific alkaline phosphatase (TNSALP)
. TCIRG1 (V-type proton ATPase subunit)
. Core binding factor alpha-1 (Cbfa1/Runx2)

Correct Answer & Explanation

. TCIRG1 (V-type proton ATPase subunit)

Explanation

Osteopetrosis represents a failure of osteoclast-mediated bone resorption. The most common mutation in the severe autosomal recessive form involves TCIRG1, which encodes a subunit of the V-type H+ ATPase required to acidify the resorption pit.

Question 5924

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., alendronate, zoledronic acid) inhibit osteoclast function primarily by targeting which of the following enzymes in the mevalonate pathway?

. Carbonic anhydrase II
. Farnesyl pyrophosphate synthase
. HMG-CoA reductase
. Cathepsin K
. Cyclooxygenase-2

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents the prenylation of small GTP-binding proteins (like Ras and Rho), leading to osteoclast apoptosis.

Question 5925

Topic: Biomechanics & Biomaterials

Which of the following orthopaedic biomaterials has a Young's modulus of elasticity most closely matching that of human cortical bone?

. Alumina ceramic
. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Ultra-high molecular weight polyethylene

Correct Answer & Explanation

. Titanium alloy

Explanation

Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloys (~110 GPa) are closer to cortical bone than stainless steel (~200 GPa) or cobalt-chromium alloys (~220 GPa), resulting in less stress shielding.

Question 5926

Topic: 1. General Principles & Basic Science

In the synthesis of Type I collagen, the polypeptide chains form a tight triple helix. This structural conformation fundamentally relies on the presence of which amino acid at every third position?

. Proline
. Hydroxyproline
. Lysine
. Glycine
. Arginine

Correct Answer & Explanation

. Glycine

Explanation

Collagen possesses a characteristic repeating motif of Gly-X-Y, where X is often proline and Y is often hydroxyproline. Glycine, the smallest amino acid, is required at every third position to allow the three chains to pack tightly into the triple helix.

Question 5927

Topic: Biology, Genetics & Bone Healing

Sclerostin is a glycoprotein secreted by osteocytes that serves as a potent negative regulator of bone formation. It achieves this primarily by binding to which of the following cellular targets?

. RANKL
. Osteoprotegerin (OPG)
. LRP5/6 receptors
. Bone morphogenetic protein receptor type II (BMPR-II)
. Transforming growth factor-beta (TGF-b) receptor

Correct Answer & Explanation

. LRP5/6 receptors

Explanation

Sclerostin binds to the LRP5/6 coreceptors on the surface of osteoblasts. This action blocks the canonical Wnt/beta-catenin signaling pathway, effectively inhibiting osteoblast differentiation and bone formation.

Question 5928

Topic: Biology, Genetics & Bone Healing

Endochondral ossification is the primary mechanism of bone formation in fracture callus. Which of the following transcription factors is recognized as the master regulator of chondrocyte differentiation in this process?

. Sox9
. Runx2
. Osterix
. Beta-catenin
. PPAR-gamma

Correct Answer & Explanation

. Sox9

Explanation

Sox9 is the crucial transcription factor for chondrocyte differentiation and cartilage matrix production during endochondral ossification. Runx2 (Cbfa1) is the master transcription factor for osteoblast differentiation.

Question 5929

Topic: Biomechanics & Biomaterials

Figure 1 displays a stress-strain curve for a typical metallic orthopaedic implant.

The exact point on the curve where the material transitions from completely recoverable elastic deformation to non-recoverable plastic deformation is defined as the:

. Ultimate tensile strength
. Failure point
. Yield point
. Modulus of elasticity
. Endurance limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point characterizes the transition from elastic to plastic behavior on a stress-strain curve. Loading the material beyond this specific point results in permanent (plastic) deformation.

Question 5930

Topic: Biology, Genetics & Bone Healing

Continuous, chronic elevation of parathyroid hormone (PTH) leads to net bone resorption. This resorptive effect is primarily mediated by PTH initially binding to receptors on which cell type?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteoclasts lack PTH receptors. PTH binds directly to receptors on osteoblasts, causing them to increase expression of RANKL and decrease expression of OPG, which secondarily stimulates osteoclast recruitment and bone resorption.

Question 5931

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopaedic implants occurs under which of the following conditions?

. Repeated cyclic loading of a single metal component causing micro-cracks
. Mechanical wear between a metal head and a polyethylene liner
. Contact between two dissimilar metals in an electrolytic fluid environment
. Depletion of oxygen in a localized crevice such as a screw hole
. Release of metallic ions due to third-body abrasive wear

Correct Answer & Explanation

. Contact between two dissimilar metals in an electrolytic fluid environment

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct physical contact within a conductive fluid environment (e.g., body fluids). The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 5932

Topic: Biology, Genetics & Bone Healing

The primary mechanism of action of denosumab in treating osteoporosis is through binding to and inhibiting which of the following molecules?

. OPG
. RANK
. RANKL
. Osteocalcin
. Cathepsin K

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts. This effectively inhibits osteoclast formation, function, and survival.

Question 5933

Topic: Biomechanics & Biomaterials

In the context of tendon biomechanics, which of the following best describes the phenomenon of stress relaxation?

. Deformation of a material over time under a constant load
. Decrease in stress over time when a material is held at a constant length or deformation
. Energy lost as heat during a loading and unloading cycle
. Increase in stiffness with faster rates of loading
. Microscopic failure of collagen fibers prior to macroscopic failure

Correct Answer & Explanation

. Decrease in stress over time when a material is held at a constant length or deformation

Explanation

Stress relaxation is a viscoelastic property where the stress in a material decreases over time when it is held at a constant deformation. In contrast, creep is the continued deformation over time under a constant load.

Question 5934

Topic: Biomechanics & Biomaterials

A surgeon considers using a titanium screw to secure a stainless steel plate. Which of the following best describes the primary biomechanical and biologic concern regarding this construct?

. Decreased construct stiffness
. Galvanic corrosion
. Crevice corrosion
. Fretting corrosion
. Increased osteolysis from titanium debris

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Mixing different metals, such as stainless steel and titanium, in an aqueous environment like the human body sets up an electrochemical cell. This leads to galvanic corrosion, where the less noble metal undergoes accelerated corrosion.

Question 5935

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis (e.g., Ilizarov technique), new bone is formed primarily through which of the following processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional ossification
. Creeping substitution
. Osteoclastic resorption

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis under stable fixation and an appropriate distraction rate typically proceeds via intramembranous ossification. This process directly forms bone without a cartilaginous intermediate stage.

Question 5936

Topic: Biomechanics & Biomaterials

The torsional strength of a solid intramedullary nail is proportional to its radius raised to which power?

. 1
. 2
. 3
. 4
. 5

Correct Answer & Explanation

. 5

Explanation

The polar moment of inertia for a solid cylinder, which determines torsional stiffness and strength, is proportional to the radius to the fourth power (r^4). Therefore, small increases in nail diameter exponentially increase its torsional strength.

Question 5937

Topic: Biology, Genetics & Bone Healing

A patient with severe malnutrition presents with bleeding gums, petechiae, and poor wound healing. A deficiency in which of the following vitamins is responsible for these symptoms by impairing the hydroxylation of proline and lysine in collagen synthesis?

. Vitamin A
. Vitamin B12
. Vitamin C
. Vitamin D
. Vitamin K

Correct Answer & Explanation

. Vitamin C

Explanation

Vitamin C (ascorbic acid) is an essential cofactor for prolyl and lysyl hydroxylase in collagen synthesis. Deficiency causes scurvy, characterized by defective collagen cross-linking and subsequent tissue fragility.

Question 5938

Topic: 1. General Principles & Basic Science

Parona's space is a potential anatomic space in the distal forearm that can serve as a conduit for deep infections. Which of the following constitutes its dorsal border?

. Flexor digitorum profundus
. Flexor pollicis longus
. Pronator quadratus
. Interosseous membrane
. Flexor retinaculum

Correct Answer & Explanation

. Pronator quadratus

Explanation

Parona's space lies in the deep volar forearm. Its volar border is formed by the flexor digitorum profundus and flexor pollicis longus tendons, and its dorsal border is the pronator quadratus muscle and interosseous membrane.

Question 5939

Topic: Biomechanics & Biomaterials

Which of the following orthopedic materials has a Young's modulus (modulus of elasticity) that most closely matches that of cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Alumina ceramic
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a Young's modulus much closer to that of cortical bone compared to stiffer materials like stainless steel and cobalt-chromium. This closer modulus match helps reduce stress shielding around implants.

Question 5940

Topic: Biology, Genetics & Bone Healing

Sclerostin is a protein that regulates bone mass. It functions primarily by antagonizing which of the following cellular signaling pathways?

. RANKL/OPG pathway
. Wnt/beta-catenin pathway
. BMP/Smad pathway
. Notch signaling pathway
. FGF pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

Sclerostin, produced primarily by osteocytes, binds to LRP5/6 receptors on osteoblasts. This action inhibits the canonical Wnt/beta-catenin signaling pathway, leading to decreased bone formation.

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