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1. General Principles & Basic Science MCQs

Practice Set 308 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 6141

Topic: Biomechanics & Biomaterials

A surgeon mistakenly utilizes titanium alloy screws to secure a stainless steel dynamic compression plate. This combination of dissimilar metals in an electrolytic fluid environment primarily predisposes the construct to which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct contact within an electrolytic environment (like body fluid). The less noble metal undergoes accelerated anodic corrosion.

Question 6142

Topic: Biology, Genetics & Bone Healing

Cleidocranial dysplasia is characterized by hypoplastic clavicles, delayed cranial suture closure, and supernumerary teeth. It is caused by a genetic mutation in the master transcription factor for osteoblast differentiation. Which gene is affected?

. SOX9
. RUNX2 (CBFA1)
. Osterix (SP7)
. TWIST1
. COMP

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

RUNX2 (also known as CBFA1) is the master transcription factor required for the differentiation of mesenchymal stem cells into osteoblasts. Loss-of-function mutations in RUNX2 cause cleidocranial dysplasia.

Question 6143

Topic: Biology, Genetics & Bone Healing

Primary bone healing occurs under conditions of absolute stability without radiographically visible callus formation. Which of the following is the key microscopic mechanism driving this process?

. Endochondral ossification
. Intramembranous ossification
. Cutting cone remodeling
. Fibrocartilage template calcification
. Chondrocyte apoptosis

Correct Answer & Explanation

. Cutting cone remodeling

Explanation

Primary bone healing relies on Haversian remodeling via cutting cones. Osteoclasts bore across the fracture line, immediately followed by osteoblasts laying down lamellar bone, requiring less than 2% interfragmentary strain.

Question 6144

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates serum calcium homeostasis. Which of the following accurately describes the effect of intermittent, low-dose exogenous administration of PTH (e.g., teriparatide)?

. It primarily stimulates osteoclast activity directly via RANKL expression on osteocytes
. It induces widespread apoptosis of mature osteoblasts
. It suppresses Wnt/beta-catenin signaling in the bone microenvironment
. It disproportionately stimulates osteoblast activity and extends osteoblast lifespan
. It inhibits intestinal calcium absorption by downregulating Vitamin D

Correct Answer & Explanation

. It disproportionately stimulates osteoblast activity and extends osteoblast lifespan

Explanation

While continuous PTH leads to net bone resorption, intermittent low-dose PTH (teriparatide) exerts an anabolic effect. It disproportionately stimulates osteoblastic bone formation over osteoclastic resorption and inhibits osteoblast apoptosis.

Question 6145

Topic: Biology, Genetics & Bone Healing

A researcher is evaluating markers of bone turnover in patient serum. Which of the following markers is considered the most specific indicator of mature osteoblast activity and bone formation?

. Tartrate-resistant acid phosphatase (TRAP)
. Type X collagen
. Osteocalcin
. Cathepsin K
. Matrix metalloproteinase 13 (MMP-13)

Correct Answer & Explanation

. Osteocalcin

Explanation

Osteocalcin is the most abundant non-collagenous protein in bone matrix and is highly specific to mature osteoblasts. TRAP and Cathepsin K are markers of osteoclast activity, whereas Type X collagen marks hypertrophic chondrocytes.

Question 6146

Topic: Biology, Genetics & Bone Healing

A pediatric patient with X-linked hypophosphatemic rickets presents with progressive lower extremity bowing. Pathophysiologically, this condition is driven by a mutation in the PHEX gene, leading to the overactivity of which regulatory hormone?

. Parathyroid hormone (PTH)
. 1,25-dihydroxyvitamin D
. Calcitonin
. Fibroblast growth factor 23 (FGF-23)
. Osteoprotegerin

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF-23)

Explanation

X-linked hypophosphatemia is caused by a PHEX gene mutation that fails to downregulate FGF-23. The resulting excess of FGF-23 causes massive renal phosphate wasting and impairs bone mineralization.

Question 6147

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed a medication for osteoporosis that works by binding to and inhibiting RANKL. What is the primary cellular effect of this medication?

. Decreased osteoblast apoptosis
. Inhibition of osteoclast maturation and survival
. Direct inhibition of cathepsin K
. Increased Wnt signaling
. Inhibition of farnesyl pyrophosphate synthase

Correct Answer & Explanation

. Inhibition of osteoclast maturation and survival

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts. This inhibits osteoclast maturation, function, and survival, leading to decreased bone resorption.

Question 6148

Topic: Biomechanics & Biomaterials

A 50-year-old woman undergoes total hip arthroplasty with a highly cross-linked polyethylene liner. Which of the following best describes the mechanical consequence of high cross-linking compared to conventional polyethylene?

. Increased yield strength
. Increased ductility
. Decreased wear resistance
. Decreased fatigue resistance
. Decreased elastic modulus

Correct Answer & Explanation

. Decreased fatigue resistance

Explanation

Highly cross-linked polyethylene significantly increases wear resistance by restricting polymer chain mobility. However, this alteration mechanically leads to decreased fatigue resistance, yield strength, and ductility.

Question 6149

Topic: Biology, Genetics & Bone Healing

A 40-year-old man sustains a transverse femoral shaft fracture treated with a rigid locked intramedullary nail. Which type of bone healing will predominate at the fracture site?

. Primary bone healing via cutting cones
. Intramembranous ossification
. Endochondral ossification
. Appositional bone growth
. Creeping substitution

Correct Answer & Explanation

. Endochondral ossification

Explanation

Intramedullary nailing provides relative stability, which permits micromotion at the fracture site. This mechanical environment promotes secondary bone healing via callus formation, which occurs predominantly through endochondral ossification.

Question 6150

Topic: Biology, Genetics & Bone Healing

Which of the following signaling pathways is directly stimulated by the binding of bone morphogenetic protein-2 (BMP-2) to its cell surface receptor on mesenchymal stem cells?

. Wnt/beta-catenin
. Smad 1/5/8
. JAK/STAT
. Notch/Hes
. MAPK/ERK

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMP-2 binds to serine/threonine kinase receptors and primarily transduces signals through the intracellular Smad 1/5/8 pathway. In contrast, TGF-beta primarily utilizes the Smad 2/3 signaling cascade.

Question 6151

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with short stature, frontal bossing, and bowing of the lower extremities. Laboratory tests show normal serum calcium, decreased serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. What is the primary mechanism responsible for his condition?

. Deficient hydroxylation of 25-hydroxyvitamin D
. Impaired renal reabsorption of phosphate due to elevated FGF-23
. Decreased intestinal absorption of calcium
. Lack of carbonic anhydrase II
. Overproduction of parathyroid hormone

Correct Answer & Explanation

. Impaired renal reabsorption of phosphate due to elevated FGF-23

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation, leading to the overproduction of FGF-23. Excess FGF-23 inhibits renal reabsorption of phosphate and decreases 1-alpha-hydroxylase activity, resulting in hypophosphatemia.

Question 6152

Topic: Biology, Genetics & Bone Healing

A 60-year-old man is treated with a medication that stimulates bone formation by inhibiting sclerostin. Which signaling pathway is directly upregulated by this medication?

. Wnt/beta-catenin
. OPG/RANKL
. Smad 1/5/8
. Insulin-like growth factor-1
. Fibroblast growth factor

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

Romosozumab is a monoclonal antibody against sclerostin. Sclerostin is a natural inhibitor of the Wnt/beta-catenin pathway; thus, its inhibition upregulates Wnt signaling and increases osteoblast activity.

Question 6153

Topic: Biomechanics & Biomaterials

In the context of bone biomechanics, which of the following terms best describes a material's continuous increase in strain over time when subjected to a constant load?

. Stress relaxation
. Hysteresis
. Creep
. Fatigue
. Yield

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (strain) of a viscoelastic material under a constant applied load. Stress relaxation, conversely, is the decrease in stress over time under a constant strain.

Question 6154

Topic: Biology, Genetics & Bone Healing

A researcher is evaluating the use of continuous versus intermittent parathyroid hormone (PTH) therapy on bone mass. Which of the following best describes the effect of intermittent PTH administration?

. Increases osteoclastogenesis exclusively
. Stimulates bone formation greater than resorption
. Induces severe hypercalcemia and hypophosphatemia
. Downregulates Runx2 expression
. Causes down-regulation of IGF-1

Correct Answer & Explanation

. Stimulates bone formation greater than resorption

Explanation

Intermittent administration of PTH has an osteoanabolic effect, stimulating osteoblast-mediated bone formation more than osteoclast-mediated bone resorption. This is the mechanism of action for teriparatide.

Question 6155

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of nitrogen-containing bisphosphonates (e.g., alendronate) in the treatment of osteoporosis?

. Inhibition of osteoblast apoptosis
. Inhibition of farnesyl pyrophosphate synthase
. Direct binding to RANKL
. Stimulation of OPG production
. Inhibition of cathepsin K

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This disruption prevents the prenylation of small GTPase proteins, leading to osteoclast apoptosis.

Question 6156

Topic: 1. General Principles & Basic Science

A 35-year-old man requires a posterolateral lumbar fusion. He is a chronic smoker. Which phase of bone graft incorporation is most likely impaired by the direct effects of nicotine?

. Hemorrhage and inflammation
. Neovascularization
. Creeping substitution
. Osteonal remodeling
. Woven bone formation

Correct Answer & Explanation

. Neovascularization

Explanation

Nicotine is a potent vasoconstrictor and inhibits angiogenesis, significantly impairing the neovascularization phase of bone graft incorporation. This leads to higher rates of nonunion in smokers.

Question 6157

Topic: Biomechanics & Biomaterials

During the evaluation of a new titanium alloy for use in intramedullary nails, researchers find that it has a lower modulus of elasticity than stainless steel. What is the primary clinical advantage of this property?

. Increased resistance to galvanic corrosion
. Decreased stress shielding of the surrounding bone
. Enhanced osseointegration
. Greater ultimate tensile strength
. Resistance to fretting wear

Correct Answer & Explanation

. Decreased stress shielding of the surrounding bone

Explanation

A lower modulus of elasticity indicates greater flexibility, making the material's stiffness closer to that of cortical bone. This reduces stress shielding, which can prevent secondary osteopenia of the adjacent bone.

Question 6158

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman presents with symmetrical polyarthritis of the hands and wrists. Radiographs show periarticular osteopenia and marginal erosions. Which cytokine is the primary driver of osteoclast activation and subsequent bone erosion in this condition?

. IL-10
. TGF-beta
. TNF-alpha
. IFN-gamma
. IL-4

Correct Answer & Explanation

. TNF-alpha

Explanation

In rheumatoid arthritis, TNF-alpha and IL-1 are the key pro-inflammatory cytokines that stimulate the RANK/RANKL pathway. This overactivation drives osteoclastogenesis and the formation of characteristic marginal erosions.

Question 6159

Topic: Biology, Genetics & Bone Healing

An 8-year-old boy presents with failure to thrive and recurrent fractures. Radiographs reveal diffuse osteosclerosis and loss of the medullary canal. A defect in which of the following is most likely responsible for his condition?

. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II
. Type I collagen
. Runx2/Cbfa1 transcription factor
. Matrix metalloproteinase-13

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is characterized by dense but brittle bones due to defective osteoclast function. It is often caused by a mutation in carbonic anhydrase II or TCIRG1, preventing osteoclasts from acidifying the resorption pit.

Question 6160

Topic: Biology, Genetics & Bone Healing

A patient sustains a displaced midshaft clavicle fracture. Which type of ossification primarily formed this bone during embryogenesis?

. Endochondral ossification only
. Intramembranous ossification only
. Both intramembranous and endochondral ossification
. Appositional ossification only
. Heterotopic ossification

Correct Answer & Explanation

. Both intramembranous and endochondral ossification

Explanation

The clavicle is unique as the first bone to ossify in the embryo and does so via both intramembranous (medial and central portions) and endochondral (medial and lateral extremes) ossification.

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