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Biology, Genetics & Bone Healing MCQs

Practice Set 75 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1481

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is treated with denosumab. This biologic agent mimics the action of which naturally occurring endogenous molecule?

. RANK ligand
. Interleukin-1
. Osteoprotegerin (OPG)
. Calcitonin
. Parathyroid hormone

Correct Answer & Explanation

. RANK ligand

Explanation

Denosumab is a monoclonal antibody that specifically targets and binds to RANKL, preventing it from activating the RANK receptor on osteoclasts. This mimics the biological action of osteoprotegerin (OPG), an endogenous decoy receptor that also binds RANKL to inhibit bone resorption.

Question 1482

Topic: Biology, Genetics & Bone Healing

Which of the following represents the correct sequence of events during the incorporation of a structural cortical bone allograft?

. Osteoconduction followed by osteoinduction
. Osteoclastic resorption followed by osteoblastic formation
. Immediate revascularization followed by callus formation
. Direct intramembranous ossification without resorption
. Chondrogenesis followed by endochondral ossification

Correct Answer & Explanation

. Osteoconduction followed by osteoinduction

Explanation

Cortical allograft incorporation occurs via a process known as creeping substitution. This process begins with osteoclastic resorption of the graft material, followed subsequently by osteoblastic bone formation.

Question 1483

Topic: Biology, Genetics & Bone Healing

Which intracellular signaling pathway is directly activated by the binding of Bone Morphogenetic Proteins (BMPs) to their cell surface receptors during osteoinduction?

. Wnt/beta-catenin
. JAK/STAT
. Smad 1/5/8
. MAP kinase
. RANK/RANKL

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation and activation of Smad 1, 5, and 8. These activated Smads form a complex with Smad 4, which translocates to the nucleus to regulate the transcription of osteogenic genes.

Question 1484

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what type of tissue is expected to form in a fracture gap when the interfragmentary strain is between 2% and 10%?

. Lamellar bone
. Woven bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Lamellar bone

Explanation

Perren's strain theory dictates that tissue tolerance limits healing. Fibrocartilage can tolerate strains up to 10-15%, making it the predominant tissue in a 2-10% strain environment. Primary bone healing requires less than 2% strain.

Question 1485

Topic: Biology, Genetics & Bone Healing

Following a displaced, severely comminuted midshaft tibia fracture, the endosteal blood supply is entirely disrupted. Which vascular system provides the initial compensatory blood supply to the healing fracture callus?

. Nutrient artery system
. Metaphyseal vessels
. Epiphyseal vessels
. Periosteal vessels
. Haversian canals

Correct Answer & Explanation

. Nutrient artery system

Explanation

When the primary endosteal (nutrient artery) blood supply is disrupted by a fracture or intramedullary reaming, the periosteal blood supply undergoes transient hypertrophy. This reversed flow provides the major blood supply to the early healing callus.

Question 1486

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain compatible with the formation of lamellar bone?

. 1%
. 2%
. 10%
. 20%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory states that lamellar bone can only form under conditions of low strain, typically less than 2%. Granulation tissue tolerates up to 100% strain, while fibrocartilage tolerates up to 10% strain before tearing.

Question 1487

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing, which growth factor is primarily responsible for inducing the differentiation of mesenchymal stem cells into chondrocytes?

. BMP-2
. TGF-beta
. PDGF
. VEGF
. FGF

Correct Answer & Explanation

. BMP-2

Explanation

Bone morphogenetic proteins (such as BMP-2) are osteoinductive and strongly induce mesenchymal stem cell differentiation into chondrogenic and osteogenic lineages. TGF-beta stimulates matrix synthesis, and VEGF is essential for angiogenesis.

Question 1488

Topic: Biology, Genetics & Bone Healing

Following a displaced diaphyseal fracture of the adult tibia, what is the primary source of blood supply to the healing callus during the early stages of secondary bone healing?

. Nutrient artery
. Periosteal vessels
. Metaphyseal arteries
. Epiphyseal arteries
. Haversian canals

Correct Answer & Explanation

. Nutrient artery

Explanation

Following a fracture, the medullary nutrient artery is often disrupted. The extraosseous periosteal blood supply temporarily becomes the dominant source of blood flow to the healing fracture callus early in the reparative process.

Question 1489

Topic: Biology, Genetics & Bone Healing

The Wnt/beta-catenin signaling pathway plays a crucial role in bone homeostasis. Sclerostin (SOST) regulates bone mass by:

. Activating osteoclasts via RANKL
. Inhibiting the Wnt/beta-catenin pathway
. Stimulating osteoblast proliferation directly
. Enhancing BMP-2 expression
. Increasing VEGF secretion

Correct Answer & Explanation

. Activating osteoclasts via RANKL

Explanation

Sclerostin is produced by osteocytes and binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway. This inhibition leads to decreased osteoblastogenesis and a net reduction in bone formation.

Question 1490

Topic: Biology, Genetics & Bone Healing

The normal tendon-to-bone insertion (enthesis) consists of four zones. Following surgical repair, the regenerated insertion site typically heals by:

. Re-establishing the original four distinct zones exactly
. Formation of a fibrovascular scar tissue interface
. Direct intramembranous ossification
. Endochondral ossification
. Hyaline cartilage formation

Correct Answer & Explanation

. Re-establishing the original four distinct zones exactly

Explanation

The native enthesis consists of tendon, uncalcified fibrocartilage, calcified fibrocartilage, and bone. After surgical repair, this highly specialized transitional zone does not typically regenerate; instead, it heals via a biomechanically weaker fibrovascular scar tissue interface.

Question 1491

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) products primarily rely on which of the following components for their osteoinductive properties?

. Mesenchymal stem cells
. Hydroxyapatite scaffolding
. Bone morphogenetic proteins (BMPs)
. Platelet-derived growth factor (PDGF)
. Type I collagen network

Correct Answer & Explanation

. Mesenchymal stem cells

Explanation

Demineralized bone matrix (DBM) is processed by removing the mineral component of bone, which exposes the underlying osteoinductive proteins, primarily Bone Morphogenetic Proteins (BMPs). DBM serves as an osteoconductive and osteoinductive graft but inherently lacks live osteogenic cells.

Question 1492

Topic: Biology, Genetics & Bone Healing

According to Perrenโ€™s strain theory, what is the maximum interfragmentary strain that can be tolerated for the formation of lamellar bone without an intervening cartilage stage?

. 1%
. 2%
. 10%
. 15%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Primary bone healing occurs without a cartilaginous callus when interfragmentary strain is strictly below 2%. Strain between 2% and 10% allows for secondary healing via endochondral ossification.

Question 1493

Topic: Biology, Genetics & Bone Healing

Which of the following terms best describes the process by which a structural cortical allograft is slowly resorbed by osteoclasts and replaced by host osteoblasts?

. Osteoinduction
. Osteoconduction
. Creeping substitution
. Distraction osteogenesis
. Endochondral ossification

Correct Answer & Explanation

. Osteoinduction

Explanation

Creeping substitution is the simultaneous process of bone resorption by host osteoclasts and deposition by host osteoblasts into a graft. Cortical allografts undergo this process slowly, initially losing structural strength before full incorporation.

Question 1494

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is an FDA-approved osteoinductive agent for use in open tibial shaft fractures treated with intramedullary nailing?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute open tibial shaft fractures treated with an IM nail, as well as anterior lumbar interbody fusion. BMP-7 (OP-1) was previously utilized for recalcitrant tibial nonunions under an HDE.

Question 1495

Topic: Biology, Genetics & Bone Healing

Activation of the Wnt/beta-catenin signaling pathway in osteoblasts primarily results in which of the following effects?

. Increased bone resorption via RANKL expression
. Inhibition of osteoblast differentiation
. Increased bone formation and osteoblast survival
. Differentiation of mesenchymal stem cells into chondrocytes
. Apoptosis of osteocytes

Correct Answer & Explanation

. Increased bone resorption via RANKL expression

Explanation

The Wnt/beta-catenin signaling pathway promotes osteoblast differentiation, proliferation, and survival, leading to increased bone formation. Sclerostin, targeted by drugs like romosozumab, is a natural inhibitor of this pathway.

Question 1496

Topic: Biology, Genetics & Bone Healing

Primary (strain-free) bone healing is characterized by which of the following processes?

. Endochondral ossification
. Formation of a cartilaginous soft callus
. Direct osteoclastic cutting cones crossing the fracture site
. High strain environment (>10%)
. Woven bone formation bridging the fracture gap

Correct Answer & Explanation

. Endochondral ossification

Explanation

Primary bone healing occurs under conditions of absolute stability (strain <2%) and involves direct intramembranous healing via osteoclastic cutting cones. Subsequent osteoblast bone deposition occurs without intermediate callus formation.

Question 1497

Topic: Biology, Genetics & Bone Healing

Increasing the working length of a bridging plate construct leads to which of the following biomechanical changes?

. Increased axial stiffness
. Decreased axial stiffness
. Increased torsional stiffness
. Decreased construct micromotion
. Increased risk of implant failure due to stress shielding

Correct Answer & Explanation

. Increased axial stiffness

Explanation

Increasing the working length (the distance between the innermost screws on either side of the fracture) decreases the axial stiffness of the construct. This makes the fixation more flexible, promoting secondary bone healing through callus formation.

Question 1498

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) primarily induce osteoblast differentiation through which of the following intracellular signaling molecules?

. Beta-catenin
. Smad
. RANKL
. NF-kappa B
. STAT3

Correct Answer & Explanation

. Beta-catenin

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate intracellular Smad proteins (typically Smad 1, 5, and 8). These proteins then translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 1499

Topic: Biology, Genetics & Bone Healing

During the repair phase of secondary fracture healing, the soft callus is gradually replaced by hard callus primarily through which of the following processes?

. Intramembranous ossification
. Endochondral ossification
. Osteoclastic cutting cones
. Apoptosis of osteoblasts
. Wnt/beta-catenin inhibition

Correct Answer & Explanation

. Intramembranous ossification

Explanation

In secondary fracture healing, the initial cartilaginous soft callus undergoes endochondral ossification. Chondrocytes hypertrophy, the matrix is calcified, and it is subsequently replaced by woven bone to form the hard callus.

Question 1500

Topic: Biology, Genetics & Bone Healing

Sclerostin, a glycoprotein produced by osteocytes, regulates bone mass by inhibiting which of the following pathways?

. RANK/RANKL pathway
. Wnt/beta-catenin pathway
. TGF-beta signaling
. BMP/Smad pathway
. Notch signaling

Correct Answer & Explanation

. RANK/RANKL pathway

Explanation

Sclerostin inhibits the Wnt/beta-catenin pathway by binding to LRP5/6 receptors on osteoblasts, thereby decreasing osteoblast differentiation and bone formation. Romosozumab is a monoclonal antibody that targets sclerostin to treat osteoporosis.

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