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Biology, Genetics & Bone Healing MCQs

Practice Set 148 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 2941

Topic: Biology, Genetics & Bone Healing

Malignant infantile osteopetrosis is a fatal genetic disorder characterized by dense, brittle bones and pancytopenia. The most common genetic defect in this condition impairs which of the following mechanisms?

. Synthesis of type I collagen
. Function of the osteoclast ruffled border via TCIRG1 mutation
. Wnt-beta catenin signaling pathway
. Differentiation of mesenchymal stem cells
. Secretion of osteoprotegerin

Correct Answer & Explanation

. Synthesis of type I collagen

Explanation

Malignant infantile osteopetrosis is most commonly caused by a mutation in the TCIRG1 gene, which encodes a subunit of the vacuolar proton pump (V-ATPase). This prevents osteoclasts from acidifying the resorption pit, leading to defective bone resorption.

Question 2942

Topic: Biology, Genetics & Bone Healing

A patient with severe nutritional deficiencies presents with bleeding gums, perifollicular hemorrhages, and impaired wound healing. The underlying enzymatic defect impairs bone formation by disrupting which step in collagen synthesis?

. Cleavage of procollagen C-terminal propeptides
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Cross-linking of collagen fibrils by lysyl oxidase
. Transcription of COL1A1 genes

Correct Answer & Explanation

. Cleavage of procollagen C-terminal propeptides

Explanation

Scurvy is caused by Vitamin C deficiency. Vitamin C acts as an essential cofactor for prolyl and lysyl hydroxylases, which are required for the hydroxylation of proline and lysine residues, a critical step for stable collagen triple helix formation.

Question 2943

Topic: Biology, Genetics & Bone Healing

Secondary bone healing is characterized by intermediate callus formation. According to Perren's strain theory, what is the maximum tissue strain that allows for the formation of lamellar bone?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 100%
. Greater than 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, lamellar bone can only form in environments with less than 2% strain. Cartilage can form in 2-10% strain, and granulation tissue forms when strain is 10-100%.

Question 2944

Topic: Biology, Genetics & Bone Healing

Which of the following processes accurately characterizes intramembranous ossification during bone formation?

. Bone formation via an intermediate cartilage model
. Direct differentiation of mesenchymal stem cells into osteoblasts
. Endochondral ossification occurring in a secondary fracture callus
. Longitudinal growth occurring at the physis
. Secondary bone healing facilitated by micro-motion

Correct Answer & Explanation

. Bone formation via an intermediate cartilage model

Explanation

Intramembranous ossification involves the direct differentiation of mesenchymal stem cells into osteoblasts, bypassing any cartilaginous intermediate. This process forms the flat bones of the skull, the clavicle, and the periosteal outer layer of long bones (appositional growth).

Question 2945

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective targeted medical therapy used in the treatment of Giant Cell Tumor of Bone. It exerts its effect by binding directly to which of the following molecules?

. RANK
. RANKL
. Osteoprotegerin
. Cathepsin K
. TNF-alpha

Correct Answer & Explanation

. RANK

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In Giant Cell Tumor of Bone, the neoplastic mononuclear stromal cells overexpress RANKL, which recruits and activates the reactive osteoclast-like giant cells. Denosumab blocks this interaction.

Question 2946

Topic: Biology, Genetics & Bone Healing

Which of the following bone grafting materials inherently possesses osteogenic, osteoinductive, and osteoconductive properties?

. Demineralized bone matrix (DBM)
. Cancellous bone allograft
. Iliac crest bone autograft
. Bone morphogenetic protein-2 (BMP-2)
. Calcium phosphate cement

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

Iliac crest bone autograft is the 'gold standard' because it is the only option listed that provides all three essential properties for bone healing: osteoconduction (scaffold), osteoinduction (growth factors like BMPs), and osteogenesis (live osteoprogenitor cells). DBM is osteoconductive and osteoinductive but lacks live cells. Allograft is only osteoconductive. BMP-2 is purely osteoinductive.

Question 2947

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a lytic, eccentrically located lesion in the distal femoral epiphysis. Biopsy confirms a Giant Cell Tumor of bone. She is treated preoperatively with denosumab to consolidate the tumor and reduce its vascularity. What is the specific molecular target of this medication?

. Vascular endothelial growth factor (VEGF)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoclastic proton pumps
. Hydroxyapatite crystals
. CD20 receptor

Correct Answer & Explanation

. Vascular endothelial growth factor (VEGF)

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts. In Giant Cell Tumor of bone, the neoplastic stromal cells express RANKL, which recruits and activates the reactive, bone-destroying multinucleated giant cells.

Question 2948

Topic: Biology, Genetics & Bone Healing
During the normal biological process of tendon healing, which of the following best describes the predominant collagen type synthesized and deposited during the early proliferative phase (typically days 5 to 28)?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type III collagen

Explanation

Tendon healing occurs in overlapping phases: inflammatory, proliferative, and remodeling. During the proliferative phase, fibroblasts primarily synthesize Type III collagen, which forms a disorganized extracellular matrix. During the later remodeling phase, this is gradually replaced by the stronger, highly organized Type I collagen.

Question 2949

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a midshaft tibial fracture. Which of the following cytokines is primarily responsible for the initial recruitment of mesenchymal stem cells to the fracture site?

. Bone morphogenetic protein-2 (BMP-2)
. Platelet-derived growth factor (PDGF)
. Interleukin-1 (IL-1)
. Tumor necrosis factor-alpha (TNF-alpha)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Bone morphogenetic protein-2 (BMP-2)

Explanation

PDGF is released from degranulating platelets in the fracture hematoma immediately after injury. It acts as a powerful chemoattractant and mitogen for mesenchymal stem cells, initiating the healing cascade.

Question 2950

Topic: Biology, Genetics & Bone Healing

Which transcription factor is considered the master regulator of osteoblast differentiation and is absolutely essential for both intramembranous and endochondral ossification?

. SOX9
. Runx2 (Cbfa1)
. HIF-1 alpha
. NFATc1
. MyoD

Correct Answer & Explanation

. SOX9

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor for osteoblast differentiation. Mice lacking Runx2 have a complete lack of bone formation due to the arrest of osteoblast maturation. SOX9 is the master regulator for chondrogenesis. NFATc1 is essential for osteoclast differentiation.

Question 2951

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is primarily associated with osteoinduction via the SMAD pathway and is currently an FDA-approved adjunct for anterior lumbar interbody fusion (ALIF)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. TGF-beta

Correct Answer & Explanation

. BMP-2

Explanation

BMP-2 is FDA-approved for anterior lumbar interbody fusion (ALIF) and open tibial shaft fractures. It acts via the SMAD 1/5/8 signaling pathway to promote osteoinduction. BMP-7 (OP-1) was previously used under a humanitarian device exemption for nonunions but is not the FDA-approved agent for ALIF. BMP-3 is uniquely inhibitory to osteogenesis.

Question 2952

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the distal femur. Biopsy confirms multinucleated giant cells in a stroma of mononuclear cells. If Denosumab is utilized, what is its primary mechanism of action?

. Inhibits osteoblast proliferation
. Monoclonal antibody that binds and inhibits RANKL
. Directly inhibits matrix metalloproteinases
. Monoclonal antibody targeting VEGF
. Directly induces apoptosis of the multinucleated giant cells

Correct Answer & Explanation

. Inhibits osteoblast proliferation

Explanation

Giant Cell Tumor (GCT) of bone is driven by neoplastic mononuclear stromal cells that express RANKL. RANKL recruits and activates reactive multinucleated giant cells (which are osteoclast-like). Denosumab is a monoclonal antibody that binds RANKL, inhibiting this process and leading to tumor calcification.

Question 2953

Topic: Biology, Genetics & Bone Healing
Secondary bone healing relies on endochondral ossification to bridge a fracture gap with callus. During the transition from the soft callus stage to the hard callus stage, which major shift in collagen types takes place within the extracellular matrix?
. Type I collagen is replaced by Type II collagen
. Type II collagen is replaced by Type I collagen
. Type III collagen is replaced by Type IV collagen
. Type X collagen is replaced by Type II collagen
. Type I collagen is replaced by Type III collagen

Correct Answer & Explanation

. Type II collagen is replaced by Type I collagen

Explanation

In secondary bone healing, the soft callus primarily consists of fibrocartilage, which is rich in Type II collagen. As endochondral ossification progresses, this cartilage is calcified, resorbed, and replaced by woven bone (hard callus), which is composed predominantly of Type I collagen.

Question 2954

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is frequently used in orthopedic surgery to augment fracture healing and spinal fusion. The primary physiological mechanism by which DBM promotes bone formation is characterized by which of the following properties?

. Osteogenesis
. Osteoinduction
. Osteoconduction
. Angiogenesis
. Chondrogenesis

Correct Answer & Explanation

. Osteogenesis

Explanation

DBM is primarily osteoinductive. The manufacturing process of acid demineralization exposes bone morphogenetic proteins (BMPs) and other growth factors hidden within the bone matrix. These factors recruit host mesenchymal stem cells and induce them to differentiate into osteoblasts (osteoinduction). DBM is not osteogenic because it contains no viable cells.

Question 2955

Topic: Biology, Genetics & Bone Healing

Which of the following intracellular signaling proteins is directly phosphorylated by the Type I bone morphogenetic protein (BMP) receptor following ligand binding?

. STAT3
. beta-catenin
. SMAD 1/5/8
. ERK 1/2
. NF-kappaB

Correct Answer & Explanation

. STAT3

Explanation

BMPs bind to serine/threonine kinase receptors, causing phosphorylation of SMAD 1, 5, and 8. These receptor-regulated SMADs then form a complex with SMAD 4 to translocate to the nucleus and regulate gene transcription.

Question 2956

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a destructive, lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor of bone. She is prescribed denosumab prior to surgical intervention. What is the mechanism of action of this medication?

. Inhibits VEGF, preventing tumor angiogenesis
. Binds to RANKL, preventing activation of osteoclasts
. Directly induces apoptosis in neoplastic stromal cells
. Inhibits tyrosine kinase activity
. Binds to the RANK receptor on osteoblasts

Correct Answer & Explanation

. Inhibits VEGF, preventing tumor angiogenesis

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts and their precursors. This halts osteoclastogenesis and bone resorption in Giant Cell Tumors.

Question 2957

Topic: Biology, Genetics & Bone Healing

Following a rigid open reduction and internal fixation of a transverse radius fracture using a compression plate, bone healing occurs primarily via which of the following mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing via cutting cones
. Callus formation
. Chondrocyte hypertrophy and calcification

Correct Answer & Explanation

. Endochondral ossification

Explanation

Absolute stability achieved by rigid compression plating prevents interfragmentary motion, leading to primary (direct) bone healing. This occurs via Haversian remodeling where osteoclast "cutting cones" cross the fracture site.

Question 2958

Topic: Biology, Genetics & Bone Healing
A 4-year-old boy with Osteogenesis Imperfecta (OI) Type III is treated with intravenous pamidronate. What is the primary cellular mechanism of action of this medication in this patient population?
. Stimulates osteoblast proliferation and differentiation
. Inhibits osteoclast-mediated bone resorption
. Increases intestinal calcium absorption
. Enhances type I collagen cross-linking
. Promotes mineralization of uncalcified osteoid

Correct Answer & Explanation

. Inhibits osteoclast-mediated bone resorption

Explanation

Bisphosphonates, such as pamidronate, are structural analogs of pyrophosphate that bind to hydroxyapatite crystals in bone. They are ingested by osteoclasts and induce osteoclast apoptosis, thereby inhibiting osteoclast-mediated bone resorption. In OI, this increases bone mineral density and cortical thickness, reducing fracture frequency.

Question 2959

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with multiple fractures, blue sclerae, and dentinogenesis imperfecta. Genetic testing reveals a mutation in the COL1A1 gene. Which of the following is the primary mechanism of action of the most commonly prescribed medical therapy for this condition?

. Inhibition of osteoclast-mediated bone resorption
. Stimulation of osteoblast differentiation
. Supplementation of defective type 1 collagen
. Inhibition of matrix metalloproteinases
. Stimulation of calcium absorption in the gut

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates are the medical treatment of choice for Osteogenesis Imperfecta. They work by inhibiting osteoclast-mediated bone resorption, which increases bone density and decreases fracture rates.

Question 2960

Topic: Biology, Genetics & Bone Healing

A 32-year-old female complains of knee pain. Radiographs demonstrate an eccentric, lytic, epiphyseal lesion in the proximal tibia extending to the subchondral bone without a sclerotic margin. Histology shows multinucleated giant cells in a stroma of mononuclear cells. Which of the following medical treatments can be used as an adjuvant to surgery or for unresectable disease?

. Imatinib
. Denosumab
. Doxorubicin
. Methotrexate
. Rituximab

Correct Answer & Explanation

. Imatinib

Explanation

The presentation is classic for a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody that acts as a RANKL inhibitor, is highly effective in treating GCT by preventing the RANKL-mediated maturation and activation of osteoclast-like giant cells, leading to tumor consolidation.

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