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1. General Principles & Basic Science MCQs

Practice Set 602 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 12021

Topic: 1. General Principles & Basic Science
During the remodeling phase of tendon healing, which collagen transition is most characteristic?
. Type I to Type II
. Type II to Type I
. Type III to Type I
. Type I to Type III
. Type III to Type II

Correct Answer & Explanation

. Type III to Type I

Explanation

The remodeling phase of tendon healing is characterized by the gradual replacement of immature, disorganized Type III collagen with stronger, longitudinally aligned Type I collagen. This process significantly increases the tensile strength of the tendon.

Question 12022

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is manufactured to decrease wear rates in total joint arthroplasty. What is the primary disadvantage of highly cross-linking UHMWPE?
. Increased oxidative degradation
. Decreased ultimate tensile strength
. Increased volumetric wear
. Decreased modulus of elasticity
. Increased osteolysis risk

Correct Answer & Explanation

. Decreased ultimate tensile strength

Explanation

Highly cross-linking UHMWPE significantly reduces abrasive wear but simultaneously decreases its mechanical properties, including ultimate tensile strength, yield strength, and fatigue resistance. This makes it more susceptible to catastrophic failure in high-stress applications like tibial posts.

Question 12023

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft substitutes is exclusively osteoconductive and possesses no osteoinductive or osteogenic properties?

. Demineralized bone matrix (DBM)
. Bone marrow aspirate
. Recombinant human BMP-2
. Calcium phosphate cement
. Fresh frozen allograft

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

Calcium phosphate ceramics and cements act solely as a structural scaffold (osteoconductive) for host bone ingrowth. They lack living cells (osteogenic) and bone morphogenetic proteins (osteoinductive) found in DBM or autograft.

Question 12024

Topic: Biomechanics & Biomaterials

A dynamic splint applies a constant deformation to a contracted joint over time. Which viscoelastic property explains the gradual decrease in force required to maintain this constant deformation?

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the phenomenon where a viscoelastic material experiences a decrease in stress (force) over time when subjected to a constant strain (deformation). Creep, conversely, is increasing deformation under a constant load.

Question 12025

Topic: 1. General Principles & Basic Science

A patient undergoes prolonged cast immobilization. Which skeletal muscle fiber type undergoes the most rapid and severe atrophy during this period?

. Type I (slow-twitch oxidative)
. Type IIa (fast-twitch oxidative)
. Type IIb (fast-twitch glycolytic)
. Type IIx
. Satellite cells

Correct Answer & Explanation

. Type I (slow-twitch oxidative)

Explanation

Type I (slow-twitch oxidative) muscle fibers, which are primarily responsible for postural maintenance and endurance, atrophy faster and more severely than Type II fibers during periods of immobilization.

Question 12026

Topic: 1. General Principles & Basic Science

Which molecule is primarily responsible for the boundary lubrication of articular cartilage, reducing friction during low-load, low-speed movement?

. Hyaluronic acid
. Lubricin
. Aggrecan
. Chondroitin sulfate
. Type IX collagen

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Lubricin (PRG4) is a glycoprotein that provides boundary lubrication at the articular cartilage surface, primarily effective during high-contact stress and low-speed movements. Hyaluronic acid contributes more to elastohydrodynamic lubrication.

Question 12027

Topic: Biomechanics & Biomaterials

The addition of barium sulfate or zirconium dioxide to polymethylmethacrylate (PMMA) bone cement serves which primary purpose?

. Increases the fatigue strength of the cement
. Accelerates the polymerization rate
. Decreases the exothermic reaction temperature
. Provides radiopacity
. Enhances antibiotic elution

Correct Answer & Explanation

. Increases the fatigue strength of the cement

Explanation

Barium sulfate and zirconium dioxide are added to PMMA bone cement exclusively to make the cement radiopaque, allowing for radiographic visualization. However, they act as impurities and can decrease the cement's overall mechanical strength.

Question 12028

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated by tissue before it can successfully differentiate into woven bone?

. 1%
. 2%
. 10%
. 30%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory dictates that woven bone can only form under conditions of low strain, specifically less than 10%. Granulation tissue tolerates up to 100% strain, while lamellar bone requires strictly less than 2% strain.

Question 12029

Topic: 1. General Principles & Basic Science

In which zone of articular cartilage are the collagen fibers oriented parallel to the joint surface to resist shear forces?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains densely packed collagen fibers aligned parallel to the articular surface. This specific orientation allows the cartilage to effectively resist shear stresses during joint motion.

Question 12030

Topic: Biology, Genetics & Bone Healing

Continuous endogenous secretion or excessive administration of Parathyroid Hormone (PTH) primarily leads to bone resorption by directly binding to receptors on which cell type?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoclasts

Explanation

PTH receptors are located on osteoblasts, not osteoclasts. PTH binding stimulates osteoblasts to express RANKL, which subsequently binds to RANK on osteoclast precursors, promoting their differentiation and activation for bone resorption.

Question 12031

Topic: 1. General Principles & Basic Science

In a Sunderland second-degree nerve injury (axonotmesis), which of the following structures remains intact to guide axonal regeneration?

. Myelin sheath only
. Axon and myelin sheath
. Endoneurium
. Perineurium only
. Epineurium only

Correct Answer & Explanation

. Myelin sheath only

Explanation

A Sunderland second-degree injury involves disruption of the axon and myelin sheath, but the endoneurial tube remains intact. This intact endoneurium provides a critical pathway to guide regenerating axons back to their target organs.

Question 12032

Topic: Biology, Genetics & Bone Healing

How does increasing the working length of a plate affect its mechanical properties during fracture fixation?

. Decreases the construct's torsional stability only
. Increases the construct's overall stiffness
. Decreases the construct's stiffness and increases interfragmentary strain
. Increases the pull-out strength of the screws
. Reduces the bending moment on the plate

Correct Answer & Explanation

. Decreases the construct's torsional stability only

Explanation

The working length of a plate is the distance between the two closest screws across the fracture site. Increasing the working length makes the construct more flexible (decreases stiffness), which can increase interfragmentary strain and promote secondary bone healing via callus.

Question 12033

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, wear debris generated by particles of bone cement caught between the femoral head and polyethylene liner is best classified as:

. Adhesive wear
. Abrasive wear
. Third-body wear
. Fretting wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Third-body wear occurs when hard, loose particles (such as bone fragments, PMMA cement, or metal debris) become trapped between the two articulating bearing surfaces. This significantly accelerates the wear of the softer polyethylene component.

Question 12034

Topic: Biology, Genetics & Bone Healing

A patient with severe vitamin C deficiency (scurvy) presents with poor wound healing and joint effusions. The biochemical defect is a failure of hydroxylation of which amino acids?

. Glycine and alanine
. Proline and lysine
. Arginine and histidine
. Glutamate and aspartate
. Leucine and isoleucine

Correct Answer & Explanation

. Glycine and alanine

Explanation

Vitamin C is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without it, the hydroxylation of proline and lysine residues fails, preventing the formation of stable triple-helical collagen molecules.

Question 12035

Topic: Biomechanics & Biomaterials

Which metal alloy used in orthopedic implants possesses a modulus of elasticity most closely matching that of cortical bone?

. Cobalt-chromium-molybdenum
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Tantalum
. Commercially pure titanium

Correct Answer & Explanation

. Cobalt-chromium-molybdenum

Explanation

Titanium alloys (like Ti-6Al-4V) have a modulus of elasticity approximately half that of cobalt-chromium or stainless steel, making them the closest match to cortical bone among standard solid metals. This helps reduce stress shielding.

Question 12036

Topic: 1. General Principles & Basic Science

Which enzyme, highly expressed by osteoblasts, is essential for bone mineralization by cleaving inorganic pyrophosphate, an inhibitor of calcification?

. Tartrate-resistant acid phosphatase
. Matrix metalloproteinase-9
. Carbonic anhydrase II
. Tissue-nonspecific alkaline phosphatase (TNAP)
. Cathepsin K

Correct Answer & Explanation

. Tartrate-resistant acid phosphatase

Explanation

Tissue-nonspecific alkaline phosphatase (TNAP) is produced by osteoblasts and promotes mineralization by hydrolyzing inorganic pyrophosphate. Pyrophosphate normally acts as a potent inhibitor of hydroxyapatite crystal formation.

Question 12037

Topic: Biology, Genetics & Bone Healing

Osteopetrosis represents a group of genetic disorders characterized by dense, brittle bones. The most severe autosomal recessive form is commonly associated with a defect in:

. RANKL expression
. Osteoprotegerin (OPG) production
. Carbonic anhydrase II
. Type I collagen synthesis
. Fibroblast growth factor receptor 3

Correct Answer & Explanation

. RANKL expression

Explanation

Autosomal recessive osteopetrosis is frequently caused by mutations affecting osteoclast function, notably a deficiency in Carbonic Anhydrase II or the TCIRG1 proton pump. This prevents the acidification of the resorption pit necessary for dissolving bone mineral.

Question 12038

Topic: Biology, Genetics & Bone Healing

Bisphosphonates inhibit osteoclast-mediated bone resorption. Nitrogen-containing bisphosphonates (e.g., alendronate) achieve this by inhibiting which specific intracellular enzyme?

. Cathepsin K
. Farnesyl pyrophosphate (FPP) synthase
. Cyclooxygenase-2
. Tyrosine kinase
. HMG-CoA reductase

Correct Answer & Explanation

. Cathepsin K

Explanation

Nitrogen-containing bisphosphonates act by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins essential for osteoclast survival and ruffled border formation, leading to osteoclast apoptosis.

Question 12039

Topic: Biology, Genetics & Bone Healing

Which of the following molecules acts as a decoy receptor for RANKL, thereby inhibiting osteoclastogenesis?

. Osteocalcin
. Sclerostin
. Osteoprotegerin
. Cathepsin K
. Osteopontin

Correct Answer & Explanation

. Osteocalcin

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from binding to RANK on osteoclast precursors. This effectively inhibits osteoclast differentiation and bone resorption.

Question 12040

Topic: 1. General Principles & Basic Science

During endochondral ossification, which type of collagen is uniquely and predominantly synthesized by chondrocytes in the hypertrophic zone?

. Type I
. Type II
. Type IX
. Type X
. Type XI

Correct Answer & Explanation

. Type I

Explanation

Type X collagen is uniquely produced by hypertrophic chondrocytes during endochondral ossification. It plays a crucial role in cartilage mineralization and the transition to bone.

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