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1. General Principles & Basic Science MCQs

Practice Set 280 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 5581

Topic: Biomechanics & Biomaterials
Which of the following sterilization techniques for ultra-high-molecular-weight polyethylene (UHMWPE) joint components is most strongly associated with generating free radicals, leading to accelerated oxidative degradation?
. Ethylene oxide gas sterilization
. Gamma irradiation in a vacuum
. Gamma irradiation in ambient air
. Gas plasma sterilization
. Autoclaving

Correct Answer & Explanation

. Gamma irradiation in ambient air

Explanation

Gamma irradiation in an oxygen-rich environment (ambient air) generates free radicals that react with oxygen, causing chain scission and severe oxidative degradation of the polyethylene. Modern UHMWPE is cross-linked and sterilized in inert gases to prevent this.

Question 5582

Topic: Biology, Genetics & Bone Healing
A 12-year-old boy presents with a history of recurrent long bone fractures after minimal trauma, progressive hearing loss, and distinctly blue sclerae. This clinical phenotype is most likely due to a genetic mutation affecting which structural protein?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Fibrillin-1

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is classically caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode Type I collagen. Type I collagen is the primary structural protein in bone, sclerae, and the ossicles of the ear.

Question 5583

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopaedic implant materials is most susceptible to severe galvanic corrosion when placed in direct physical contact in vivo?

. Titanium alloy and cobalt-chromium alloy
. Stainless steel and titanium alloy
. Cobalt-chromium alloy and trabecular metal
. Stainless steel and cobalt-chromium alloy
. Commercially pure titanium and titanium alloy

Correct Answer & Explanation

. Stainless steel and titanium alloy

Explanation

Mixing stainless steel and titanium alloy creates a strong electrochemical potential difference, making the construct highly susceptible to galvanic corrosion. Cobalt-chromium and titanium alloys are more electrochemically compatible and are frequently used together clinically without significant galvanic issues.

Question 5584

Topic: Biomechanics & Biomaterials

During the application of a dynamic splint to a contracted joint, a constant deformation is maintained over time. The observed decrease in peak force required to maintain this constant tissue length is an example of which viscoelastic property?

. Creep
. Hysteresis
. Stress relaxation
. Strain rate dependency
. Fatigue failure

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant strain (length), resulting in a progressive decrease in the stress (force) required to maintain that deformation. In contrast, creep is the progressive deformation of a material under a constant applied load.

Question 5585

Topic: 1. General Principles & Basic Science

In which zone of normal articular cartilage are the type II collagen fibers oriented primarily perpendicular to the joint surface to maximize resistance to compressive loads?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone of articular cartilage, collagen fibers are oriented perpendicularly to the articular surface and cross the tidemark. This structural arrangement provides the greatest resistance to compressive forces across the joint.

Question 5586

Topic: Biology, Genetics & Bone Healing

Which of the following molecules acts as a soluble decoy receptor for RANKL, thereby inhibiting osteoclastogenesis and reducing bone resorption?

. Osteocalcin
. Sclerostin
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Cathepsin K

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors. By blocking this signaling cascade, OPG effectively inhibits osteoclast differentiation and function.

Question 5587

Topic: Physiology & Rehabilitation

A physical therapy protocol specifies a muscle contraction where tension remains constant while the muscle actively lengthens to control a decelerating load. Which of the following best describes this type of muscle contraction?

. Concentric
. Isometric
. Eccentric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when a muscle lengthens while simultaneously generating tension, typically acting to decelerate a joint or resist gravity. It generates the highest forces compared to other contraction types and is primarily responsible for delayed onset muscle soreness (DOMS).

Question 5588

Topic: Biomechanics & Biomaterials

Which of the following geometric structural properties most directly dictates a long bone's resistance to bending forces?

. Cross-sectional area
. Polar moment of inertia
. Area moment of inertia
. Modulus of elasticity
. Yield strength

Correct Answer & Explanation

. Area moment of inertia

Explanation

The area moment of inertia determines a structure's resistance to bending and is proportional to the distance of the material distributed from the neutral axis. Polar moment of inertia, conversely, dictates the structure's resistance to torsional (twisting) loads.

Question 5589

Topic: Biology, Genetics & Bone Healing

Absolute stability in fracture fixation with a fracture gap of less than 0.1 mm results in primary bone healing. Which of the following represents the predominant mechanism of healing under these strict biomechanical conditions?

. Endochondral ossification
. Intramembranous ossification
. Contact healing via cutting cones
. Gap healing via woven bone formation
. Fibrocartilage callus formation

Correct Answer & Explanation

. Contact healing via cutting cones

Explanation

With absolute stability and direct cortical contact (gap < 0.1 mm), primary bone healing occurs via contact healing. This process is driven by osteoclast cutting cones that tunnel across the fracture site, immediately followed by osteoblasts depositing lamellar bone without an intermediate callus.

Question 5590

Topic: Physiology & Rehabilitation

During the normal gait cycle, maximum physiological dorsiflexion of the ankle occurs at which of the following phases?

. Initial contact
. Loading response
. Midstance
. Terminal stance
. Pre-swing

Correct Answer & Explanation

. Terminal stance

Explanation

Maximum ankle dorsiflexion (approximately 10 degrees) occurs at the end of the terminal stance phase, immediately prior to heel-off. This pre-loads the gastrocsoleus complex for the rapid plantarflexion required during pre-swing (toe-off).

Question 5591

Topic: 1. General Principles & Basic Science

What is the primary biomechanical function of the aggrecan molecule within the extracellular matrix of articular cartilage?

. To provide high tensile strength to the superficial zone
. To anchor chondrocytes firmly to the subchondral bone
. To draw water into the matrix via osmotic pressure
. To chemically cross-link type II collagen fibers
. To secrete lubricin for boundary joint lubrication

Correct Answer & Explanation

. To draw water into the matrix via osmotic pressure

Explanation

Aggrecan is a heavily glycosylated proteoglycan with a high concentration of negatively charged chondroitin and keratan sulfate chains. This creates a strong fixed charge density that draws water into the cartilage via the Donnan osmotic effect, conferring compressive stiffness.

Question 5592

Topic: Biology, Genetics & Bone Healing

Fibroblast growth factor 23 (FGF23) is a critical endocrine regulator of phosphate homeostasis. Which of the following accurately describes the primary physiological mechanism of FGF23?

. Increases intestinal phosphate absorption via up-regulation of vitamin D
. Increases renal phosphate reabsorption via NaPi-IIa up-regulation
. Decreases renal phosphate reabsorption by down-regulating NaPi-IIa cotransporters
. Stimulates 1-alpha-hydroxylase activity in the proximal convoluted tubule
. Inhibits osteoclast activity to prevent phosphate release from trabecular bone

Correct Answer & Explanation

. Decreases renal phosphate reabsorption by down-regulating NaPi-IIa cotransporters

Explanation

FGF23 is secreted by osteocytes in response to elevated serum phosphate levels. It acts on the kidneys to decrease phosphate reabsorption by down-regulating the NaPi-IIa cotransporters and inhibits 1-alpha-hydroxylase, reducing active Vitamin D levels.

Question 5593

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a third-degree injury is defined by the disruption of the axon and which of the following connective tissue structures?

. Myelin sheath only
. Endoneurium only
. Endoneurium and perineurium
. Perineurium and epineurium
. All supporting connective tissues including the epineurium

Correct Answer & Explanation

. Endoneurium and perineurium

Explanation

In a Sunderland third-degree injury, both the axon and the endoneurium are disrupted, but the perineurium and epineurium remain intact. The loss of the endoneurial tubes increases the risk of intrafascicular scarring and aberrant axonal regeneration.

Question 5594

Topic: Biology, Genetics & Bone Healing

Which of the following transcription factors serves as the essential master regulator required for the differentiation of mesenchymal stem cells into the osteoblast lineage?

. SOX9
. Runx2 (Cbfa1)
. Osterix
. PPAR-gamma
. MyoD

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the essential master transcription factor for osteoblast differentiation and subsequent bone formation. Loss-of-function mutations in the Runx2 gene are responsible for the clinical phenotype of cleidocranial dysplasia.

Question 5595

Topic: 1. General Principles & Basic Science

Which physiological mechanism of joint lubrication is most actively relied upon by the native knee under conditions of high compressive loading and extremely low velocity?

. Elastohydrodynamic lubrication
. Squeeze-film lubrication
. Hydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication predominates under high load and low sliding velocity conditions. It relies on a monomolecular layer of surface-active molecules, specifically lubricin (PRG4), which binds directly to the articular surface to reduce friction and wear.

Question 5596

Topic: Biomechanics & Biomaterials

In the evaluation of orthopedic biomaterials, the total area under the stress-strain curve up to the point of structural failure represents which of the following mechanical properties?

. Stiffness
. Yield strength
. Ductility
. Toughness
. Ultimate tensile strength

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the total amount of energy a material can absorb before catastrophic failure, represented by the total area under the stress-strain curve. Stiffness is indicated by the slope of the elastic region (Young's modulus).

Question 5597

Topic: 1. General Principles & Basic Science

Which of the following best describes the structural and biochemical composition of the superficial zone of normal articular cartilage?

. Highest proteoglycan content and perpendicular collagen fibers
. Lowest water content and random collagen fibers
. Highest water content and collagen fibers parallel to the joint surface
. Lowest collagen content and vertical collagen fibers
. Highest chondrocyte metabolic activity and thickest collagen fibrils

Correct Answer & Explanation

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

Explanation

The superficial zone of articular cartilage has the highest water content, lowest proteoglycan content, and collagen fibers oriented parallel to the joint surface to resist shear forces. The deep zone possesses the highest proteoglycan concentration and perpendicular collagen fibers.

Question 5598

Topic: Biology, Genetics & Bone Healing

Sclerostin regulates bone mass by binding to LRP5/6 receptors on osteoblasts. This binding directly inhibits which of the following intracellular signaling pathways?

. RANKL/OPG
. Wnt/beta-catenin
. TGF-beta/Smad
. Notch/Hes
. BMP/Smad

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

Sclerostin is produced by osteocytes and negatively regulates bone formation by binding to LRP5/6, which competitively inhibits the Wnt/beta-catenin signaling pathway. Monoclonal antibodies against sclerostin (e.g., romosozumab) exploit this to therapeutically increase bone mass.

Question 5599

Topic: Biomechanics & Biomaterials

A retrieved modular total hip arthroplasty demonstrates significant black macroscopic debris and surface damage at the head-neck taper junction. Which type of corrosion is most likely responsible for this specific damage pattern?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs due to micromotion between two closely apposed surfaces (such as the modular head-neck taper of a THA), which repeatedly disrupts the passive oxide layer. Galvanic corrosion requires two dissimilar metals placed in an electrolytic solution.

Question 5600

Topic: Biology, Genetics & Bone Healing

During bone resorption, osteoclasts create a sealed zone and secrete hydrogen ions to dissolve the inorganic mineral matrix. Which of the following intracellular enzymes is primarily responsible for generating these hydrogen ions?

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

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II catalyzes the conversion of CO2 and H2O into carbonic acid, which dissociates into bicarbonate and hydrogen ions; the H+ is then pumped into the resorption pit. Enzymes like Cathepsin K and MMPs function subsequently to degrade the organic collagen matrix.

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