Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 171 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 3401

Topic: Biology, Genetics & Bone Healing

During normal bone remodeling, osteoclast differentiation and activation are primarily stimulated by the binding of RANKL to its receptor, RANK. Which of the following proteins acts as a decoy receptor to inhibit this interaction?

. Osteocalcin
. Osteopontin
. Sclerostin
. Osteoprotegerin (OPG)
. Cathepsin K

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This inhibits osteoclastogenesis and prevents excessive bone resorption.

Question 3402

Topic: Biology, Genetics & Bone Healing

In fracture fixation, increasing the working length of a bridging plate has which of the following biomechanical effects?

. Increases axial stiffness and increases torsional stiffness
. Decreases axial stiffness and decreases torsional stiffness
. Increases axial stiffness but decreases torsional stiffness
. Decreases axial stiffness but increases torsional stiffness
. Does not alter stiffness but increases yield strength

Correct Answer & Explanation

. Decreases axial stiffness and decreases torsional stiffness

Explanation

Increasing the working length of a plate decreases both its axial and torsional stiffness. This allows for increased interfragmentary motion, which promotes secondary bone healing via callus formation.

Question 3403

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute. Which of the following best describes its biological properties?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteogenic and osteoinductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM retains bone morphogenetic proteins (BMPs) providing osteoinductive properties, and its matrix acts as an osteoconductive scaffold. However, because it is acellular and lacks live osteoblasts, it does not possess osteogenic properties.

Question 3404

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis utilizing an Ilizarov frame, bone generation in the distraction gap primarily occurs via which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional bone growth
. Creeping substitution
. Osteonal remodeling

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Bone formation during distraction osteogenesis primarily occurs via intramembranous ossification, characterized by direct differentiation of mesenchymal stem cells into osteoblasts without a cartilaginous intermediate. Endochondral ossification requires a cartilage model and is classically seen in secondary fracture healing (callus formation).

Question 3405

Topic: Biology, Genetics & Bone Healing
The normal meniscus provides load distribution, shock absorption, and secondary stability to the knee. Which structural protein constitutes the vast majority (greater than 90%) of the organic dry weight of a normal meniscus?
. Type I collagen
. Type II collagen
. Type III collagen
. Type X collagen
. Aggrecan

Correct Answer & Explanation

. Type I collagen

Explanation

The meniscus is primarily composed of fibrocartilage, not hyaline cartilage. As such, type I collagen makes up > 90% of its collagen content, giving it high tensile strength. In contrast, hyaline articular cartilage is predominantly type II collagen.

Question 3406

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, lamellar bone can only form when the interfragmentary strain at the fracture gap is below which of the following thresholds?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that lamellar bone can only tolerate and form in environments with less than 2% strain. Granulation tissue tolerates up to 100% strain, while fibrocartilage can tolerate up to 10% strain.

Question 3407

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with bowed legs, widening of the physes, and metaphyseal cupping on radiographs. The primary pathophysiological defect in this condition involves:

. Defective synthesis of Type I collagen
. Failure of osteoid mineralization
. Impaired osteoclast ruffled border formation
. Defective hydroxylation of proline
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Failure of osteoid mineralization

Explanation

This presentation is classic for Rickets, which is characterized by a failure of mineralization of newly formed osteoid and growing cartilage matrix. Defective Type I collagen is seen in Osteogenesis Imperfecta, while defective hydroxylation occurs in Scurvy.

Question 3408

Topic: Biology, Genetics & Bone Healing

Scurvy leads to weakened connective tissue and bone due to a deficiency in Vitamin C. This deficiency directly impairs which of the following intracellular processes in collagen synthesis?

. Cleavage of procollagen C-terminals
. Glycosylation of hydroxylysine
. Hydroxylation of proline and lysine residues
. Formation of disulfide bonds in tropocollagen
. Extracellular cross-linking by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Vitamin C (ascorbic acid) is a required cofactor for prolyl hydroxylase and lysyl hydroxylase. Deficiency impairs the hydroxylation of proline and lysine residues, preventing the formation of stable triple-helical collagen molecules.

Question 3409

Topic: Biology, Genetics & Bone Healing

Osteoclastogenesis and subsequent bone resorption are primarily driven by the interaction of RANKL with its receptor, RANK. Which of the following proteins acts as a soluble decoy receptor to competitively inhibit this interaction?

. Cathepsin K
. Sclerostin
. Osteoprotegerin (OPG)
. Osteocalcin
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

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

Question 3410

Topic: Biology, Genetics & Bone Healing

Denosumab is a pharmacological agent utilized in the treatment of osteoporosis and giant cell tumors of bone. Its mechanism of action most closely mimics which of the following endogenous molecules?

. Osteoprotegerin (OPG)
. Parathyroid hormone (PTH)
. Bisphosphonates
. Sclerostin
. Bone morphogenetic protein-2

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Denosumab is a monoclonal antibody that binds to and neutralizes RANKL, effectively mimicking the action of endogenous Osteoprotegerin (OPG). This prevents osteoclast activation and reduces bone turnover.

Question 3411

Topic: Biology, Genetics & Bone Healing

Intermittent daily administration of teriparatide (recombinant human parathyroid hormone) exerts its beneficial effect on osteoporotic bone primarily by:

. Stimulating osteoclast apoptosis
. Inhibiting RANKL production
. Stimulating osteoblastic bone formation
. Directly mineralizing osteoid
. Increasing renal calcium excretion

Correct Answer & Explanation

. Stimulating osteoblastic bone formation

Explanation

While continuous high levels of PTH cause net bone resorption, intermittent daily administration of PTH analogs (like teriparatide) disproportionately stimulates osteoblast activity. This leads to a net increase in bone formation and mass.

Question 3412

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum strain environment that allows for primary bone healing (direct osteonal remodeling) without intermediate callus formation?

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

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which correlates to a tissue strain of less than 2%. Under these conditions, osteoclasts create cutting cones across the fracture followed immediately by osteoblasts laying down lamellar bone.

Question 3413

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is prescribed teriparatide. What is the primary mechanism of action of this medication?

. Inhibits osteoclast activity by binding to hydroxyapatite
. Binds RANK ligand to prevent osteoclast activation
. Recombinant PTH analog that stimulates osteoblast-mediated bone formation
. Selective estrogen receptor modulator that reduces bone resorption
. Sclerostin inhibitor that enhances Wnt signaling

Correct Answer & Explanation

. Recombinant PTH analog that stimulates osteoblast-mediated bone formation

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34). When administered via daily intermittent subcutaneous injections, it paradoxically acts as a potent anabolic agent by stimulating osteoblast activity over osteoclast activity.

Question 3414

Topic: Biology, Genetics & Bone Healing

Which of the following growth factors is primarily responsible for inducing the differentiation of mesenchymal stem cells into osteoblasts during early fracture healing?

. Insulin-like Growth Factor-1 (IGF-1)
. Fibroblast Growth Factor-2 (FGF-2)
. Bone Morphogenetic Protein-2 (BMP-2)
. Vascular Endothelial Growth Factor (VEGF)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Protein-2 (BMP-2)

Explanation

Bone Morphogenetic Proteins (especially BMP-2 and BMP-7) belong to the TGF-beta superfamily and strongly induce osteoblastic differentiation from mesenchymal stem cells. They are highly osteoinductive and critical for the early phases of bone regeneration.

Question 3415

Topic: Biology, Genetics & Bone Healing

Rigid internal fixation utilizing compression plating for a transverse radius fracture primarily facilitates which specific type of bone healing?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with robust callus formation
. Chondrogenesis and subsequent enchondral bridging

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Rigid internal fixation with absolute stability (strain less than 2%) entirely bypasses callus formation, resulting in primary bone healing. This process occurs via direct Haversian remodeling where osteoclastic cutting cones traverse the fracture site, followed by osteoblastic bone deposition.

Question 3416

Topic: Biology, Genetics & Bone Healing

Articular cartilage derives its unique biomechanical properties from its extracellular matrix composition. Which component is primarily responsible for the tissue's high resistance to compressive forces?

. Type I collagen
. Type II collagen
. Aggrecan
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a large proteoglycan, binds to hyaluronic acid and entraps large amounts of water within the cartilage matrix. This osmotic swelling pressure provides the primary resistance to compressive loads, whereas Type II collagen resists tensile forces.

Question 3417

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly used as an adjuvant treatment for Giant Cell Tumor of Bone (GCTB). By which precise mechanism does this drug act to reduce tumor progression?

. Inhibiting the Wnt/beta-catenin signaling pathway
. Binding and neutralizing RANKL to prevent osteoclastogenesis
. Directly inducing apoptosis of the neoplastic mononuclear stromal cells
. Stimulating osteoprotegerin (OPG) production from osteoblasts
. Inhibiting vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Binding and neutralizing RANKL to prevent osteoclastogenesis

Explanation

Denosumab is a human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents the recruitment and maturation of giant cell osteoclasts, severely limiting the osteolytic behavior of the tumor.

Question 3418

Topic: Biology, Genetics & Bone Healing

In the biology of secondary fracture healing, the process is dependent on a specific sequence of overlapping phases. During which phase is endochondral ossification most active?

. Hematoma formation
. Inflammatory phase
. Soft callus formation
. Hard callus formation
. Remodeling phase

Correct Answer & Explanation

. Hard callus formation

Explanation

Hard callus formation represents the phase where the cartilaginous (soft) callus is converted into woven bone via endochondral ossification. This phase significantly increases the biomechanical stability of the healing fracture.

Question 3419

Topic: Biology, Genetics & Bone Healing

Which of the following orthopedic procedures relies primarily on intramembranous ossification for bone formation?

. Rigid plate fixation of a forearm fracture
. Cast immobilization of a distal radius fracture
. Distraction osteogenesis (Ilizarov technique)
. Intramedullary nailing of a femur fracture
. Secondary bone callus formation in a non-union

Correct Answer & Explanation

. Distraction osteogenesis (Ilizarov technique)

Explanation

Distraction osteogenesis primarily occurs via intramembranous ossification, which is characterized by the direct differentiation of mesenchymal stem cells into osteoblasts without a cartilaginous intermediate. Rigid fixation undergoes primary bone healing (cutting cones), while cast immobilization and IM nailing undergo secondary bone healing via endochondral ossification.

Question 3420

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum percentage of tissue strain that permits the direct formation of lamellar bone without an intermediate cartilaginous or fibrous phase?

. Less than 2%
. 2% to 10%
. 10% to 30%
. Greater than 30%
. Strain level does not affect the histological path of bone formation

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that tissues dictate the type of healing based on the strain they can tolerate. Lamellar bone can only tolerate <2% strain. Therefore, primary (direct) bone healing requires absolute stability (strain <2%). Woven bone can tolerate up to 10% strain, while cartilage tolerates 10-30% strain, and granulation tissue tolerates up to 100% strain, which defines the secondary (callus) healing pathway under relative stability.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page