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Biology, Genetics & Bone Healing MCQs

Practice Set 145 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 2881

Topic: Biology, Genetics & Bone Healing

A 78-year-old woman has a history of chronic low back pain. She denies any extremity problems. Her pain is worse in the morning, and gets better, although it does not go away, as the day goes on. An MRI scan of the lumbar spine is shown in Figure

. She denies any acute worsening of her symptoms, although in general, her symptoms are slowly worsening. She takes nonsteroidal anti-inflammatory drugs as needed for her pain, but otherwise takes no other medications. What is the next most appropriate step in management?
. DEXA scan
. Brace treatment with a Jewett hyperextension brace
. Anterior lumbar corpectomy and arthrodesis with instrumentation
. Posterior lumbar decompression and fusion

Correct Answer & Explanation

. She denies any acute worsening of her symptoms, although in general, her symptoms are slowly worsening. She takes nonsteroidal anti-inflammatory drugs as needed for her pain, but otherwise takes no other medications. What is the next most appropriate step in management?

Explanation

โ– The patient has MRI findings throughout her lumbar spine consistent with old compression fractures. Given the imaging findings and advanced age, she is at high risk for osteoporosis and subsequent fragility fractures. Management should consist of a DEXA scan to evaluate her degree of osteoporosis and begin medical treatment as appropriate. Because acute fracture is unlikely, and she has no neurologic compromise, neither bracing nor surgical treatment is indicated.

Question 2882

Topic: Biology, Genetics & Bone Healing
Which of the following cell type-cell function pairings is false?
. Pre-osteoblasts - stem cell for osteoblasts
. Osteoblasts - synthesize organic matrix
. Osteocytes - maintain mineral homeostasis
. Osteoclasts - synthesize organic matrix
. Osteoblasts - receptors for PTH

Correct Answer & Explanation

. Osteoclasts - synthesize organic matrix

Explanation

Osteoclasts resorb bone by attaching to the bone surface, releasing enzymes, and dissolving the organic/mineral phases of bone. Osteoclasts do not have hormone receptors; osteoblasts are the cells that respond to PTH.

Question 2883

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute in orthopedic procedures. Which of the following factors or pathways is primarily responsible for the unique osteoinductive properties of DBM?

. Vascular endothelial growth factor (VEGF) secretion
. Mesenchymal stem cell (MSC) proliferation
. Exposure of endogenous Bone Morphogenetic Proteins (BMPs)
. Type I collagen structural scaffolding
. Platelet-derived growth factor (PDGF) activation

Correct Answer & Explanation

. Vascular endothelial growth factor (VEGF) secretion

Explanation

Bone graft materials can be osteogenic (contain live cells), osteoconductive (provide a scaffold), or osteoinductive (induce differentiation of stem cells into osteoblasts). Demineralized bone matrix (DBM) lacks live cells but contains the structural collagen matrix (osteoconductive) and retains the native proteinaceous growth factors of bone. The demineralization process exposes these native Bone Morphogenetic Proteins (BMPs), primarily conferring its osteoinductive capacity.

Question 2884

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with progressive knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis extending to the subchondral bone without a sclerotic margin. A biopsy is obtained and the histology is shown below.

If medical therapy is considered, which of the following best describes the targeted mechanism of action?

. Targeting osteoclasts directly via bisphosphonates to induce apoptosis
. Targeting the RANK ligand (RANKL) produced by the neoplastic mononuclear cells
. Targeting c-KIT receptors via imatinib mesylate
. Targeting rapidly dividing cells via dihydrofolate reductase inhibition
. Targeting the multinucleated giant cells directly via a monoclonal antibody

Correct Answer & Explanation

. Targeting osteoclasts directly via bisphosphonates to induce apoptosis

Explanation

The clinical and radiographic presentation is classic for a Giant Cell Tumor (GCT) of bone. In GCT, the true neoplastic cells are the mononuclear spindle cells, not the multinucleated giant cells. The neoplastic mononuclear cells secrete excessive RANKL, which recruits normal osteoclast precursors that fuse to form the characteristic giant cells, driving bone destruction. Denosumab is a monoclonal antibody that targets and binds RANKL, effectively inhibiting the recruitment and activation of the destructive giant cells.

Question 2885

Topic: Biology, Genetics & Bone Healing

When a diaphyseal fracture is treated with a perfectly applied lag screw and a neutralization plate (an absolute stability construct), bone healing primarily occurs through which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing via Haversian remodeling and cutting cones
. Secondary bone healing with soft and hard callus formation
. Chondrogenesis followed by immediate osteoclast resorption

Correct Answer & Explanation

. Endochondral ossification

Explanation

Constructs that provide absolute stability (e.g., lag screw with neutralization plate, compression plating) reduce interfragmentary strain to less than 2%. This environment prevents the formation of a fracture callus (secondary healing) and instead allows for primary (direct) bone healing. This process occurs via the direct advancement of osteoclasts forming cutting cones across the fracture site, immediately followed by osteoblasts laying down new lamellar bone (Haversian remodeling).

Question 2886

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, a critical transition from soft callus to hard callus occurs. During which phase of healing does this primarily take place, and what is the primary type of collagen synthesized as the matrix matures?
. Inflammatory phase; Type I transitioning to Type II collagen
. Reparative phase; Type II transitioning to Type I collagen
. Remodeling phase; Type I transitioning to Type III collagen
. Reparative phase; Type III transitioning to Type II collagen
. Remodeling phase; Type II transitioning to Type I collagen

Correct Answer & Explanation

. Reparative phase; Type II transitioning to Type I collagen

Explanation

The transition from soft to hard callus occurs during the reparative phase of secondary fracture healing. Through the process of endochondral ossification, the cartilaginous matrix (rich in Type II collagen) is replaced by woven bone (rich in Type I collagen).

Question 2887

Topic: Biology, Genetics & Bone Healing

A 65-year-old male is diagnosed with multiple myeloma and presents with hypercalcemia and extensive 'punched-out' lytic bone lesions. What is the primary molecular mechanism responsible for this accelerated osteolysis?

. Direct mechanical destruction of the bone matrix by myeloma cells
. Upregulation of RANKL and downregulation of OPG, causing massive osteoclast activation
. Secretion of parathyroid hormone-related peptide (PTHrP) by myeloma cells
. Increased production of osteoprotegerin (OPG) by the tumor microenvironment
. Secretion of transforming growth factor beta (TGF-b) stimulating osteoblasts

Correct Answer & Explanation

. Direct mechanical destruction of the bone matrix by myeloma cells

Explanation

Myeloma cells induce osteolytic lesions primarily by disrupting bone homeostasis; they secrete factors that upregulate RANKL and downregulate osteoprotegerin (OPG) in the marrow microenvironment, leading to overwhelming osteoclast activation and bone resorption.

Question 2888

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a critical role in bone healing and formation by initiating an intracellular signaling cascade. Which of the following intracellular proteins directly mediate the canonical signaling pathway of BMPs to regulate gene transcription in osteoblasts?

. Beta-catenin
. SMAD 1, 5, and 8
. NF-kappa B
. Janus kinases (JAK)
. Mitogen-activated protein kinases (MAPK)

Correct Answer & Explanation

. Beta-catenin

Explanation

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

Question 2889

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a destructive, expansile lytic lesion in her distal femur that extends to the subchondral bone. Biopsy confirms a Giant Cell Tumor (GCT) of bone. Denosumab therapy is initiated to reduce tumor size prior to intralesional curettage. Denosumab exerts its effect by directly binding to and inhibiting which of the following molecules?

. RANKL
. Osteoprotegerin (OPG)
. Vascular Endothelial Growth Factor (VEGF)
. Tumor Necrosis Factor alpha (TNF-alpha)
. Interleukin-1 (IL-1)

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This prevents RANKL from activating RANK on osteoclasts, severely inhibiting their bone-resorbing activity in Giant Cell Tumors.

Question 2890

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, which type of collagen is predominantly synthesized by chondrocytes during the soft callus phase?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

During the soft callus (cartilaginous) phase of secondary bone healing, chondrocytes primarily synthesize Type II collagen. As the cartilage calcifies and is replaced by bone in the hard callus phase, Type I collagen becomes predominant.

Question 2891

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with an eccentric, lytic lesion in the distal femoral epiphysis. Biopsy reveals neoplastic mononuclear cells expressing RANKL and reactive multinucleated giant cells. Which targeted systemic therapy is indicated if the tumor is deemed surgically unresectable?

. Imatinib
. Denosumab
. Doxorubicin
. Methotrexate
. Rituximab

Correct Answer & Explanation

. Imatinib

Explanation

Giant cell tumor of bone relies on the RANK/RANKL pathway for the recruitment of osteoclast-like giant cells by neoplastic mononuclear cells. Denosumab, a monoclonal antibody that inhibits RANKL, is utilized for advanced, recurrent, or surgically unresectable cases.

Question 2892

Topic: Biology, Genetics & Bone Healing

In the context of bone metabolism and molecular biology, which of the following accurately describes the primary function of sclerostin?

. Stimulates osteoclast differentiation via direct RANKL activation
. Inhibits Wnt/beta-catenin signaling to decrease osteoblast bone formation
. Promotes mesenchymal stem cell differentiation into chondrocytes
. Increases renal calcium reabsorption in response to hypocalcemia
. Directly binds and neutralizes endogenous parathyroid hormone

Correct Answer & Explanation

. Stimulates osteoclast differentiation via direct RANKL activation

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes that acts as a potent negative regulator of bone formation. It accomplishes this by binding to LRP5/6 receptors, thereby inhibiting the canonical Wnt/beta-catenin signaling pathway in osteoblasts.

Question 2893

Topic: Biology, Genetics & Bone Healing

Denosumab is effectively used in the treatment of recurrent or unresectable Giant Cell Tumor (GCT) of bone. What is its specific mechanism of action?

. Inhibits osteoclast farnesyl pyrophosphate synthase
. Monoclonal antibody targeting RANK-ligand
. Directly induces apoptosis of multinucleated giant cells
. Tyrosine kinase inhibitor of VEGF receptors
. Bisphosphonate analog that binds hydroxyapatite

Correct Answer & Explanation

. Inhibits osteoclast farnesyl pyrophosphate synthase

Explanation

Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from activating RANK. In GCT, neoplastic stromal cells overexpress RANKL, and denosumab halts the resulting osteoclast-mediated osteolysis.

Question 2894

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, the soft callus transitions into a hard callus. Which type of collagen dominates the extracellular matrix during the hard callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The hard callus phase of secondary bone healing is characterized by the replacement of woven bone and cartilage with lamellar bone. Lamellar bone is predominantly composed of Type I collagen, unlike the soft callus which is rich in Type II collagen.

Question 2895

Topic: Biology, Genetics & Bone Healing

During the process of endochondral ossification in fracture healing, which transcription factor is considered the master regulator for differentiating mesenchymal stem cells into the osteoblast lineage?

. SOX9
. Runx2
. HIF-1 alpha
. PPAR-gamma
. Sclerostin

Correct Answer & Explanation

. SOX9

Explanation

Runx2 (CBFA1) is the primary transcription factor required for osteoblast differentiation. By contrast, SOX9 regulates chondrogenesis, and PPAR-gamma directs adipogenesis.

Question 2896

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman is started on teriparatide for severe osteoporosis following a fragility fracture of the distal radius. What is the mechanism of action of this medication?

. Inhibits osteoclast activity by binding to hydroxyapatite crystals
. Binds to RANK ligand, preventing the activation of osteoclasts
. Recombinant PTH analog that, when given intermittently, stimulates osteoblast activity
. Selective estrogen receptor modulator (SERM) that acts as an agonist on bone
. Sclerostin inhibitor that increases Wnt signaling in osteoblasts

Correct Answer & Explanation

. Inhibits osteoclast activity by binding to hydroxyapatite crystals

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34). While continuous elevation of PTH leads to bone resorption, intermittent daily subcutaneous administration paradoxically stimulates osteoblast activity over osteoclast activity, leading to net bone formation.

Question 2897

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain threshold required for primary (direct) bone healing to occur without the formation of a visible fracture callus?

. Less than 2%
. 2% to 10%
. 10% to 20%
. 20% to 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing occurs via cutting cones and Haversian remodeling without the formation of an intermediate cartilaginous callus. According to Perren's strain theory, this requires absolute stability, defined as an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary bone healing (callus formation), while strains above 10% lead to nonunion.

Question 2898

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with an expansile, eccentric, lytic lesion in the epiphysis of the distal femur. A biopsy confirms the diagnosis of giant cell tumor (GCT) of bone. If she requires systemic medical therapy for unresectable disease, she may be treated with Denosumab. What is the mechanism of action of this drug?

. It binds to the RANK receptor directly on osteoclasts
. It is a monoclonal antibody that binds and inhibits RANKL
. It inhibits Vascular Endothelial Growth Factor (VEGF)
. It stimulates the production of Osteoprotegerin (OPG)
. It inhibits tyrosine kinase receptors on neoplastic stromal cells

Correct Answer & Explanation

. It binds to the RANK receptor directly on osteoclasts

Explanation

Giant cell tumor of bone consists of neoplastic stromal cells that express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclasts) responsible for the bone destruction. Denosumab is a human monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on osteoclasts, thereby halting tumor-associated osteolysis.

Question 2899

Topic: Biology, Genetics & Bone Healing
During secondary bone healing via endochondral ossification, a soft cartilaginous callus is formed and subsequently replaced by woven bone. Which type of collagen predominates in the soft cartilaginous callus prior to its replacement?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

During endochondral ossification, the initial soft callus is composed primarily of cartilage, which is characterized by Type II collagen. As mineralization occurs and the hard callus forms, Type II collagen is replaced by Type I collagen.

Question 2900

Topic: Biology, Genetics & Bone Healing

A 35-year-old female is diagnosed with an aggressive giant cell tumor of the proximal tibia. She is started on denosumab therapy prior to surgery. What is the precise mechanism of action of this medication?

. Monoclonal antibody against the RANK receptor on osteoblasts
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Direct inhibition of matrix metalloproteinases
. Stimulation of osteoblast apoptosis via the Wnt pathway
. Inhibition of the bisphosphonate-sensitive farnesyl pyrophosphate synthase

Correct Answer & Explanation

. Monoclonal antibody against the RANK receptor on osteoblasts

Explanation

Denosumab is a monoclonal antibody that binds to RANK Ligand (RANKL), preventing it from interacting with the RANK receptor on osteoclasts and giant cells. This effectively halts osteoclast-mediated bone resorption and promotes tumor consolidation.

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