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Biology, Genetics & Bone Healing MCQs

Practice Set 180 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 3581

Topic: Biology, Genetics & Bone Healing

A patient with osteopetrosis suffers from severely dense, brittle bones due to defective osteoclast function. Which specific cellular component or mechanism is most commonly defective in these osteoclasts?

. Carbonic anhydrase II
. Cathepsin K
. RANK receptor
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is frequently caused by a deficiency in carbonic anhydrase II or a defect in the osteoclast's proton pump (TCIRG1). This prevents the osteoclast from creating the acidic environment necessary to dissolve bone mineral, leading to dense but brittle bones.

Question 3582

Topic: Biology, Genetics & Bone Healing

A pediatric patient with suspected X-linked hypophosphatemic rickets presents with bowing of the lower extremities. Which laboratory finding is the hallmark of this specific disease process?

. Low serum calcium
. Low serum parathyroid hormone
. Elevated FGF-23 secondary to a PHEX gene mutation
. Decreased 1,25-dihydroxyvitamin D due to renal failure
. Elevated alkaline phosphatase and elevated serum phosphorus

Correct Answer & Explanation

. Elevated FGF-23 secondary to a PHEX gene mutation

Explanation

X-linked hypophosphatemic rickets is caused by a mutation in the PHEX gene, which leads to an overproduction of FGF-23. High levels of FGF-23 inhibit renal phosphate reabsorption, causing severe hypophosphatemia and defective bone mineralization.

Question 3583

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) acts primarily through which of the following intracellular signaling pathways to promote osteoblastic differentiation?

. Wnt/beta-catenin
. SMAD 1/5/8
. MAP kinase
. JAK/STAT
. Notch/Hes

Correct Answer & Explanation

. SMAD 1/5/8

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors, leading to the phosphorylation of SMAD 1, 5, and 8, which then complex with SMAD 4 to enter the nucleus and regulate transcription of osteogenic genes like Runx2.

Question 3584

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary (direct) bone healing without callus formation requires absolute stability. What is the maximum percentage of interfragmentary strain that still permits lamellar bone to form directly across the fracture gap?

. < 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. > 50%

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory dictates that lamellar bone can only form under conditions of < 2% strain (absolute stability). Strains between 2% and 10% allow for secondary healing (callus/woven bone), while strains > 10% result in fibrous tissue or nonunion.

Question 3585

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes demineralized bone matrix (DBM) during a spinal fusion. Which of the following best describes the inherent bone grafting properties of this material?

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

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a collagen scaffold (osteoconductive) and contains active growth factors like bone morphogenetic proteins (osteoinductive). It is completely devoid of living cells, so it is not osteogenic.

Question 3586

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an expansile, purely lytic lesion in the distal femur extending to the subchondral bone without a sclerotic rim. Biopsy shows multinucleated giant cells. Which targeted medication is indicated for unresectable cases?

. Imatinib
. Denosumab
. Zoledronic acid
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL used for unresectable giant cell tumors of bone. It inhibits the RANKL-mediated differentiation and activation of the neoplastic multinucleated giant cells.

Question 3587

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is started on teriparatide. Which of the following best describes the mechanism of action of this medication?

. Inhibits osteoclast ruffled border formation
. Binds to RANKL to prevent osteoclast activation
. Acts as a recombinant PTH analog to stimulate osteoblast activity
. Directly incorporates into bone matrix to increase mineralization
. Modulates estrogen receptors to decrease bone resorption

Correct Answer & Explanation

. Acts as a recombinant PTH analog to stimulate osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it acts as an anabolic agent by directly stimulating osteoblast activity and bone formation.

Question 3588

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the primary pathologic event in the initial phase of Paget disease of bone?

. Intense localized osteoblastic activity
. Intense localized osteoclastic bone resorption
. Replacement of marrow with fibrous tissue
. Defective mineralization of osteoid
. Inadequate formation of type I collagen

Correct Answer & Explanation

. Intense localized osteoclastic bone resorption

Explanation

Paget disease initially begins with an intense, localized osteoclastic (lytic) phase characterized by massive bone resorption. This is followed by a mixed phase and ultimately a sclerotic phase with disorganized woven bone.

Question 3589

Topic: Biology, Genetics & Bone Healing

What is the correct sequence of the four histological transition zones at a direct tendon-to-bone insertion (enthesis)?

. Tendon, uncalcified fibrocartilage, calcified fibrocartilage, bone
. Tendon, calcified fibrocartilage, uncalcified fibrocartilage, bone
. Bone, calcified fibrocartilage, uncalcified fibrocartilage, tendon
. Tendon, uncalcified fibrocartilage, woven bone, lamellar bone
. Tendon, calcified fibrocartilage, woven bone, lamellar bone

Correct Answer & Explanation

. Tendon, uncalcified fibrocartilage, calcified fibrocartilage, bone

Explanation

A direct enthesis transitions through four distinct zones to gradually transfer mechanical stress. The sequence is tendon, uncalcified fibrocartilage, a basophilic tidemark, calcified fibrocartilage, and finally bone.

Question 3590

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of Rheumatoid Arthritis, which cell type is primarily responsible for the direct destruction of articular cartilage and bone within the pannus?

. T-lymphocytes
. B-lymphocytes
. Fibroblast-like synoviocytes
. Polymorphonuclear leukocytes
. Mast cells

Correct Answer & Explanation

. Fibroblast-like synoviocytes

Explanation

While T-cells and macrophages drive the systemic inflammatory cascade, the fibroblast-like synoviocytes (FLS) in the pannus are primarily responsible for local joint destruction. They secrete matrix metalloproteinases (MMPs) and stimulate osteoclastogenesis via RANKL.

Question 3591

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that permits primary bone healing (cutting cone remodeling) without intermediate callus formation?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing occurs via cutting cones and requires absolute stability. Interfragmentary strain must be kept below 2%, as higher strain levels will stimulate secondary healing with callus formation or lead to nonunion.

Question 3592

Topic: Biology, Genetics & Bone Healing

Which of the following is the primary mechanism of action of Teriparatide in the treatment of osteoporosis?

. Inhibition of osteoclast RANKL binding
. Activation of the Wnt/beta-catenin pathway via sclerostin inhibition
. Direct stimulation of osteoblast activity via intermittent PTH receptor activation
. Inhibition of cathepsin K
. Incorporation into bone matrix to induce osteoclast apoptosis

Correct Answer & Explanation

. Direct stimulation of osteoblast activity via intermittent PTH receptor activation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it exerts an anabolic effect by directly stimulating osteoblast activity and new bone formation.

Question 3593

Topic: Biology, Genetics & Bone Healing

A 65-year-old female sustains a subtrochanteric femur fracture after a minor fall. She has a 10-year history of alendronate use. What is the primary mechanism of action of this medication?

. Inhibition of RANKL
. Inhibition of farnesyl pyrophosphate synthase
. Stimulation of Wnt signaling
. Decoy receptor for RANK
. Direct inhibition of cathepsin K

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This disruption causes osteoclast apoptosis and prevents bone resorption.

Question 3594

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain compatible with the formation of woven bone during secondary fracture healing?

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

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that lamellar bone forms at <2% strain, and woven bone forms at 2-10% strain. Granulation tissue is required to tolerate high strains (up to 100%) before it differentiates into stiffer tissues.

Question 3595

Topic: Biology, Genetics & Bone Healing

A 68-year-old female taking denosumab for osteoporosis is planned for an elective lumbar fusion. What is the mechanism of action of her osteoporosis medication?

. Inhibits osteoblast apoptosis
. Binds to and neutralizes RANKL
. Inhibits the mevalonate pathway
. Acts as an agonist at the estrogen receptor
. Directly inhibits cathepsin K

Correct Answer & Explanation

. Binds to and neutralizes RANKL

Explanation

Denosumab is a monoclonal antibody that binds directly to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclasts, profoundly inhibiting osteoclast formation and bone resorption.

Question 3596

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) products are commonly used in orthopedic bone grafting. Which of the following best describes the biologic properties of pure DBM?

. Osteogenic only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteoconductive and osteogenic
. Osteogenic and osteoinductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a type I collagen scaffold (osteoconductive) and retains growth factors like BMPs (osteoinductive). Because the processing removes living cells, DBM possesses no osteogenic properties.

Question 3597

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that can be tolerated for secondary bone healing via callus formation without leading to nonunion?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Perren's strain theory states that primary bone healing (direct Haversian remodeling) requires less than 2% strain. Secondary bone healing, characterized by the formation of a provisional fracture callus (initially cartilaginous), occurs in environments with 2% to 10% strain. If strain exceeds 10%, neither bone nor cartilage can form across the gap, leading to fibrous tissue interposition and potential nonunion.

Question 3598

Topic: Biology, Genetics & Bone Healing

Articular cartilage has a highly specialized extracellular matrix. Which of the following components is primarily responsible for generating the compressive stiffness of articular cartilage?

. Type I collagen
. Type II collagen
. Aggrecan
. Hyaluronic acid
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. It features heavily concentrated, negatively charged glycosaminoglycan (GAG) side chains. These repel one another and attract water (the Donnan osmotic effect), causing the molecules to swell against the restraining network of Type II collagen. This interaction provides cartilage with its characteristic compressive stiffness and resilience.

Question 3599

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is started on denosumab. What is the specific mechanism of action of this medication?

. Inhibits the enzyme farnesyl pyrophosphate synthase
. Binds to and neutralizes RANK ligand (RANKL)
. Acts as a selective estrogen receptor modulator in osteoblasts
. Stimulates osteoblast differentiation via the Wnt signaling pathway
. Directly binds to the calcium-sensing receptor on the parathyroid gland

Correct Answer & Explanation

. Binds to and neutralizes RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents RANKL from binding to the RANK receptor on osteoclast precursors, thereby profoundly inhibiting osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

Question 3600

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily and act as potent osteoinductive signaling molecules. Which specific BMP is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail?

. 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 the treatment of acute, open tibial shaft fractures stabilized with an intramedullary nail, as well as for single-level anterior lumbar interbody fusion (ALIF). rhBMP-7 (also known as Osteogenic Protein-1) was previously approved under a Humanitarian Device Exemption for recalcitrant long bone nonunions.

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