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1. General Principles & Basic Science MCQs

Practice Set 281 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 5601

Topic: Biomechanics & Biomaterials

When normal articular cartilage is subjected to a constant compressive load over time, it undergoes a gradual increase in deformation until it reaches an equilibrium state. This viscoelastic property is best described as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Plasticity

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property defined as the progressive deformation of a material over time under a constant load, driven primarily by the exudation of interstitial fluid in cartilage. Stress relaxation is the decrease in stress observed over time under a constant deformation.

Question 5602

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft options possesses osteoconductive and osteoinductive properties but definitively lacks osteogenic potential?

. Iliac crest bone autograft
. Demineralized bone matrix (DBM)
. Calcium phosphate ceramic
. Cancellous allograft
. Reamer-irrigator-aspirator (RIA) harvest

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

Demineralized bone matrix (DBM) provides an osteoconductive collagen scaffold and contains bone morphogenetic proteins (BMPs) that confer osteoinductive potential. However, the decalcification and processing destroy live cells, rendering it devoid of osteogenic potential.

Question 5603

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that can be tolerated for primary (direct) bone healing to occur?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary (direct) bone healing via cutting cones requires absolute stability, defined as interfragmentary strain of less than 2%. Strains between 2% and 10% prevent primary healing but allow for secondary bone healing via callus formation.

Question 5604

Topic: 1. General Principles & Basic Science

Which mode of joint lubrication is primarily responsible for minimizing articular friction during high-load, low-speed activities such as prolonged standing or the initial phase of gait?

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication protects articular surfaces during high-load, low-speed activities when a fluid film cannot be physically maintained; it relies on surface-active molecules like lubricin (PRG4). Fluid film lubrication mechanisms predominate during high-speed, lower-load activities.

Question 5605

Topic: Biology, Genetics & Bone Healing

In the systemic metabolism of Vitamin D, the conversion of 25-hydroxyvitamin D to its most biologically active form, 1,25-dihydroxyvitamin D, is primarily catalyzed by an enzyme located in which of the following organs?

. Liver
. Skin
. Kidney
. Parathyroid gland
. Intestine

Correct Answer & Explanation

. Kidney

Explanation

The enzyme 1-alpha-hydroxylase is located primarily in the proximal tubules of the kidney and catalyzes the conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol), the most active form. The liver catalyzes the initial 25-hydroxylation step.

Question 5606

Topic: 1. General Principles & Basic Science

Which of the following modifications to an orthopedic screw design will yield the greatest proportional increase in its pullout strength?

. Decreasing the outer diameter
. Increasing the inner (core) diameter
. Increasing the outer diameter
. Decreasing the length of thread engagement
. Increasing the thread pitch

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Screw pullout strength is most heavily dependent on the outer thread diameter and the length of thread engagement in the bone. Increasing the outer diameter significantly increases the shear area of bone engaged by the threads, maximizing pullout resistance.

Question 5607

Topic: 1. General Principles & Basic Science

Which of the following biochemical and biomechanical changes is characteristic of early-stage articular cartilage degeneration in osteoarthritis?

. Decreased water content and increased compressive stiffness
. Increased water content and decreased compressive stiffness
. Increased proteoglycan concentration and increased compressive stiffness
. Decreased water content and increased proteoglycan concentration
. Increased collagen cross-linking and decreased permeability

Correct Answer & Explanation

. Increased water content and decreased compressive stiffness

Explanation

In early osteoarthritis, damage to the superficial collagen network allows the hydrophilic proteoglycans to swell unconstrained, resulting in an increased tissue water content. This structural disruption leads to increased tissue permeability and markedly decreased compressive stiffness.

Question 5608

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely utilized in total joint arthroplasty. What is the primary biomechanical trade-off associated with increasing the radiation cross-linking of UHMWPE?
. Increased abrasive wear rates
. Decreased oxidation resistance
. Decreased fatigue strength and toughness
. Decreased ultimate tensile strength but increased ductility
. Increased adhesive wear but decreased abrasive wear

Correct Answer & Explanation

. Decreased fatigue strength and toughness

Explanation

While high levels of radiation cross-linking significantly improve the abrasive wear resistance of UHMWPE, it structurally restricts polymer chain mobility. This results in reduced mechanical properties, specifically diminished fatigue strength, ductility, and fracture toughness.

Question 5609

Topic: 1. General Principles & Basic Science

Osteoclasts degrade bone by creating an acidic environment. Which of the following enzymes is primarily responsible for the degradation of the organic bone matrix within the resorption pit?

. Alkaline phosphatase
. Tartrate-resistant acid phosphatase (TRAP)
. Cathepsin K
. Matrix metalloproteinase-3 (MMP-3)
. Carbonic anhydrase II

Correct Answer & Explanation

. Cathepsin K

Explanation

Osteoclasts secrete hydrogen ions via carbonic anhydrase II to dissolve inorganic hydroxyapatite, while Cathepsin K degrades the organic collagenous matrix at the ruffled border. TRAP is a marker of osteoclast activity but not the primary degrading enzyme.

Question 5610

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum interfragmentary strain that allows for the formation of lamellar bone directly without an intermediate cartilage phase?

. Less than 2%
. Between 2% and 10%
. Between 10% and 15%
. Between 15% and 25%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing (lamellar bone formation) requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary healing via callus formation.

Question 5611

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key regulator of bone mass. By which of the following mechanisms does it primarily inhibit bone formation?

. Binding to RANKL to prevent osteoclast activation
. Inhibiting the Wnt/beta-catenin signaling pathway
. Activating the TGF-beta pathway
. Promoting Runx2 degradation
. Stimulating FGF23 production

Correct Answer & Explanation

. Inhibiting the Wnt/beta-catenin signaling pathway

Explanation

Sclerostin, secreted predominantly by osteocytes, binds to LRP5/6 receptors on osteoblasts, competitively inhibiting the Wnt/beta-catenin pathway. This decreases osteoblast differentiation and subsequent bone formation.

Question 5612

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct structural zones. Which of the following best characterizes the superficial zone?

. Highest concentration of proteoglycans
. Chondrocytes arranged in vertical columns
. Highest concentration of water and collagen fibers parallel to the joint surface
. Contains the tidemark
. Predominantly composed of Type X collagen

Correct Answer & Explanation

. Highest concentration of water and collagen fibers parallel to the joint surface

Explanation

The superficial zone of articular cartilage has the highest water content, the lowest proteoglycan content, and collagen fibers arranged parallel to the joint surface to resist shear forces. Type X collagen is primarily found in the calcified zone.

Question 5613

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is used in total joint arthroplasty to reduce wear. Which of the following is a known mechanical trade-off of increasing the cross-linking of UHMWPE?
. Increased adhesive wear
. Decreased oxidation resistance
. Decreased ultimate tensile strength and fatigue crack propagation resistance
. Increased elastic modulus
. Increased third-body wear rates

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue crack propagation resistance

Explanation

While cross-linking UHMWPE significantly reduces adhesive and abrasive wear rates, it alters the material's bulk mechanical properties, leading to a decrease in ultimate tensile strength, fatigue strength, and resistance to crack propagation.

Question 5614

Topic: Biomechanics & Biomaterials

A clinician applies a dynamic splint to a patient's contracted elbow. The splint applies a constant load over time, resulting in gradually increasing extension of the soft tissues. This phenomenon is best described by which of the following viscoelastic principles?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic deformation

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material over time when subjected to a constant load. Stress relaxation is the decrease in internal stress over time when the material is held at a constant deformation.

Question 5615

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical bone screw is directly proportional to which of the following design parameters?

. Inner core diameter
. Outer thread diameter
. Pitch of the screw
. Length of the unthreaded shaft
. Thread count per inch

Correct Answer & Explanation

. Outer thread diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement in bone, and the shear strength of the surrounding bone. It is inversely proportional to the pitch distance.

Question 5616

Topic: Biomechanics & Biomaterials

Increasing the radius of a solid circular intramedullary nail by a factor of 2 will increase its torsional rigidity by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, doubling the radius increases torsional rigidity by a factor of 16.

Question 5617

Topic: Biomechanics & Biomaterials

Stress shielding around an orthopedic implant is strongly influenced by the elastic modulus of the material. Which of the following metals has an elastic modulus closest to that of cortical bone?

. Cobalt-chromium-molybdenum alloy
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Zirconium
. Gold

Correct Answer & Explanation

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

Explanation

Titanium alloy has an elastic modulus of approximately 100-110 GPa, making it closer to cortical bone (15-20 GPa) than Cobalt-chromium (approx. 220 GPa) or Stainless steel (approx. 200 GPa). This closer matching reduces the magnitude of stress shielding.

Question 5618

Topic: 1. General Principles & Basic Science

Under high-load, short-duration impact conditions, the articular cartilage surfaces are protected primarily by which type of joint lubrication?

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

Correct Answer & Explanation

. Squeeze-film lubrication

Explanation

Squeeze-film lubrication occurs under high axial loads when opposing joint surfaces are rapidly pressed together. The viscous synovial fluid is slowly squeezed out, creating a high-pressure fluid film that separates and protects the surfaces.

Question 5619

Topic: Biology, Genetics & Bone Healing

Which transcription factor is considered the master regulator required for the differentiation of mesenchymal stem cells into chondrocytes during endochondral ossification?

. Runx2
. SOX9
. Osterix
. Beta-catenin
. PPAR-gamma

Correct Answer & Explanation

. SOX9

Explanation

SOX9 is the essential transcription factor for chondrocyte differentiation and the expression of type II collagen. Runx2 and Osterix are primarily required for osteoblast differentiation.

Question 5620

Topic: Biology, Genetics & Bone Healing

A patient presents with generalized osteosclerosis, frequent fractures, and an absence of a medullary canal on radiographs. Which of the following cellular mechanisms is most likely defective?

. Osteoblast production of osteoid
. Osteocyte regulation of sclerostin
. Carbonic anhydrase II enzyme function in osteoclasts
. Fibroblast growth factor receptor 3 (FGFR3) signaling
. Type I collagen cross-linking

Correct Answer & Explanation

. Carbonic anhydrase II enzyme function in osteoclasts

Explanation

Osteopetrosis is characterized by defective osteoclastic bone resorption. A common mutation involves Carbonic anhydrase II or the vacuolar proton pump, which prevents the acidification necessary to dissolve bone mineral.

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