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Biology, Genetics & Bone Healing MCQs

Practice Set 93 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 1841

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with chronic knee pain. Imaging demonstrates an eccentric, purely lytic lesion in the distal femoral epiphysis, extending precisely to the subchondral bone plate. Biopsy reveals numerous multinucleated giant cells within a background of mononuclear stromal cells. Which of the following molecular targets is primarily expressed by the true neoplastic cells in this condition?

. Receptor Activator of Nuclear factor Kappa-B (RANK)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Osteoprotegerin (OPG)
. Runt-related transcription factor 2 (RUNX2)
. SRY-box transcription factor 9 (SOX9)

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

The clinical and histological presentation defines a Giant Cell Tumor (GCT) of bone. In GCT, the actual neoplastic elements are the mononuclear spindle-shaped stromal cells, not the giant cells themselves. These neoplastic stromal cells aberrantly express high levels of RANKL, which subsequently recruits normal monocyte-macrophage precursors and induces them to fuse into reactive, multinucleated giant cells expressing RANK. This pathway is the pharmacological target for Denosumab in unresectable GCT cases.

Question 1842

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman is evaluated for persistent right knee pain. Radiographs demonstrate an eccentrically located, purely lytic lesion in the proximal tibial epiphysis extending to the subchondral bone, with cortical thinning but no matrix calcification. Biopsy confirms a giant cell tumor of bone. Due to the proximity to the joint space and the size of the defect, she is treated preoperatively with denosumab to downstage the tumor and reconstitute the cortical rim. What is the primary mechanism of action of this pharmacological agent?

. Induction of direct apoptosis in the neoplastic mononuclear stromal cells
. Inhibition of the vascular endothelial growth factor (VEGF) pathway
. Monoclonal antibody targeting and binding to RANK ligand (RANKL)
. Selective inhibition of the tyrosine kinase c-Kit receptor
. Agonism of the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Monoclonal antibody targeting and binding to RANK ligand (RANKL)

Explanation

Giant cell tumor of bone (GCTB) is characterized by neoplastic mononuclear stromal cells that express high levels of RANK ligand (RANKL). RANKL recruits and activates non-neoplastic, multinucleated giant cells (osteoclast-like cells) which are responsible for the aggressive local bone destruction. Denosumab is a fully human monoclonal antibody that binds directly to RANKL, preventing it from interacting with the RANK receptor on the surface of osteoclast precursors. This effectively halts osteoclastogenesis and subsequent bone resorption, leading to stabilization and calcification of the tumor margin, which can facilitate surgical curettage.

Question 1843

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with generalized bone pain, profound fatigue, and a recent pathological fracture of the left humerus. Laboratory tests reveal normocytic anemia, hypercalcemia, and an elevated serum monoclonal paraprotein spike. Skeletal survey shows multiple 'punched-out' lytic lesions in the skull, spine, and pelvis. Which of the following best explains the specific mechanism driving the uncoupled bone remodeling and severe lack of osteoblastic bone formation seen in this disease process?

. Overexpression of bone morphogenetic protein 2 (BMP-2) by tumor cells
. Inhibition of the Wnt/beta-catenin signaling pathway by Dickkopf-1 (Dkk-1)
. Decreased systemic production of interleukin-6 (IL-6)
. Increased expression of osteoprotegerin (OPG) within the bone marrow microenvironment
. Activating mutation in the fibroblast growth factor receptor 3 (FGFR3)

Correct Answer & Explanation

. Inhibition of the Wnt/beta-catenin signaling pathway by Dickkopf-1 (Dkk-1)

Explanation

Multiple myeloma is characterized by purely osteolytic bone lesions due to severely uncoupled bone remodeling: there is robust osteoclast activation alongside profound suppression of osteoblast activity. Myeloma cells secrete factors such as Dickkopf-1 (Dkk-1) and sclerostin, which potently inhibit the Wnt/beta-catenin signaling pathway. The Wnt pathway is essential for osteoblast differentiation and function; its inhibition results in the failure of bone formation. Additionally, myeloma cells upregulate RANKL and downregulate osteoprotegerin (OPG), further driving osteoclast-mediated bone destruction. IL-6 is actually increased in myeloma and serves as a major growth and survival factor for the malignant plasma cells.

Question 1844

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, absolute stability constructs (such as a properly applied lag screw and neutralization plate) promote primary bone healing. What is the maximum interfragmentary strain threshold compatible with primary bone healing?

. 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 (Haversian remodeling without visible callus) requires an absolute stability environment with less than 2% interfragmentary strain. Strains between 2% and 10% result in secondary healing with callus formation.

Question 1845

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman presents with severe back pain and is found to have multiple osteolytic bone lesions. Biopsy reveals sheets of monoclonal plasma cells. Which of the following cell-signaling molecules is most directly responsible for the massive osteoclast activation seen in this disease process?

. Interleukin-2 (IL-2)
. Transforming growth factor-beta (TGF-b)
. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Interferon-gamma

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Multiple myeloma cells stimulate local osteoblasts and marrow stromal cells to overexpress RANKL while downregulating OPG. RANKL binds directly to RANK on osteoclast precursors, driving extensive osteoclastogenesis and subsequent lytic bone destruction.

Question 1846

Topic: Biology, Genetics & Bone Healing



A 60-year-old man with increasing hat size and bowing of his tibiae is diagnosed with Paget's disease of bone. During the active mixed phase of this metabolic disease, which of the following is the pathognomonic histological finding?

. Empty lacunae with surrounding necrotic adipocytes
. A chaotic mosaic pattern of woven and lamellar bone with prominent cement lines
. Sheets of atypical, hyperchromatic chondrocytes
. Mononuclear cell infiltration in the synovial subintima
. Diffuse unmineralized osteoid seams thicker than 15 micrometers

Correct Answer & Explanation

. A chaotic mosaic pattern of woven and lamellar bone with prominent cement lines

Explanation

The hallmark histologic feature of Paget's disease is a chaotic "mosaic" pattern of woven and lamellar bone, separated by irregular, heavily stained cement lines. This reflects the excessively rapid, uncoordinated turnover driven by hyperactive osteoclasts and osteoblasts.

Question 1847

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized effectively for treating severe osteoporosis and preventing skeletal-related events in metastatic bone disease. What is the specific molecular mechanism of action of this pharmacological agent?

. Binds directly to bone hydroxyapatite and disrupts the osteoclast ruffled border
. Stimulates osteoblast differentiation directly via the Wnt/beta-catenin signaling pathway
. Acts as a recombinant parathyroid hormone analog to intermittently promote bone formation
. Functions as a monoclonal antibody that binds and neutralizes RANKL
. Acts as a selective estrogen receptor modulator to decrease bone resorption

Correct Answer & Explanation

. Functions as a monoclonal antibody that binds and neutralizes RANKL

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to and inhibits RANKL. By neutralizing RANKL, it prevents the activation and survival of osteoclasts, profoundly decreasing bone resorption.

Question 1848

Topic: Biology, Genetics & Bone Healing

A patient with osteopetrosis is scheduled for an elective orthopedic procedure. The pathogenesis of this disease is primarily linked to a defect in which of the following cellular mechanisms?

. Osteoblast collagen synthesis
. Osteoclast ruffled border formation
. Chondrocyte apoptosis in the physis
. Osteocyte canalicular communication
. Fibroblast excessive collagen cross-linking

Correct Answer & Explanation

. Osteoclast ruffled border formation

Explanation

Osteopetrosis is caused by impaired osteoclast function, frequently due to a defect in the formation of the ruffled border (e.g., carbonic anhydrase II deficiency). This prevents normal bone resorption and remodeling.

Question 1849

Topic: Biology, Genetics & Bone Healing

Secondary fracture healing occurs with the formation of a callus. Which of the following mechanical conditions is required for secondary fracture healing to occur rather than primary healing?

. Absolute stability and no interfragmentary strain
. Rigid internal fixation with compression plates
. Relative stability with micro-motion at the fracture site
. Anatomic reduction with an interfragmentary gap less than 0.1 mm
. Complete surgical stripping of the periosteum

Correct Answer & Explanation

. Relative stability with micro-motion at the fracture site

Explanation

Secondary healing relies on relative stability and appropriate micro-motion to stimulate robust callus formation. Primary healing requires absolute stability, compression, and virtually no interfragmentary strain.

Question 1850

Topic: Biology, Genetics & Bone Healing

Bisphosphonates are frequently used in the management of osteoporosis and metastatic bone disease. What is the primary cellular mechanism of action for nitrogen-containing bisphosphonates such as alendronate?

. Inhibition of the RANKL-RANK interaction
. Inhibition of farnesyl pyrophosphate synthase
. Stimulation of the Wnt signaling pathway
. Direct activation of osteoblast apoptosis
. Inhibition of carbonic anhydrase II

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts osteoclast cytoskeletal function, preventing ruffled border formation and promoting osteoclast apoptosis.

Question 1851

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is an FDA-approved osteoinductive agent for use as an adjunct in acute, 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 acute open tibial shaft fractures treated with an intramedullary nail. BMP-7 (OP-1) was previously approved under a humanitarian device exemption for recalcitrant long bone nonunions.

Question 1852

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient with chronic kidney disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies show low serum calcium, high parathyroid hormone (PTH), and elevated alkaline phosphatase. Histologic evaluation of this patient's bone would most likely show:

. Woven bone in a mosaic pattern
. Empty osteocyte lacunae
. Increased unmineralized osteoid seams
. Subperiosteal bone resorption
. Defective osteoclast ruffled borders

Correct Answer & Explanation

. Increased unmineralized osteoid seams

Explanation

The clinical scenario describes osteomalacia secondary to renal osteodystrophy. Osteomalacia is characterized histologically by defective mineralization, leading to thickened and increased unmineralized osteoid seams.

Question 1853

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy shows multinucleated giant cells and mononuclear stromal cells. The neoplastic cells in this tumor strongly express:

. RANKL
. RANK
. Osteoprotegerin (OPG)
. CD68
. S-100

Correct Answer & Explanation

. RANKL

Explanation

In a Giant Cell Tumor of bone, the spindle-shaped mononuclear stromal cells are the true neoplastic cells and they express RANKL. The giant cells are reactive, non-neoplastic osteoclasts that express the RANK receptor.

Question 1854

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show mixed lytic and sclerotic changes in his skull and pelvis. Which of the following is the primary cellular abnormality initiating this condition?

. Defective osteoblast mineralization
. Excessive and disorganized osteoclast activity
. Decreased osteocyte apoptosis
. Increased chondrocyte proliferation
. Mutation in Type I collagen synthesis

Correct Answer & Explanation

. Excessive and disorganized osteoclast activity

Explanation

Paget disease of bone begins with an intensely destructive osteolytic phase driven by highly abnormal, multinucleated osteoclasts. This is followed by a disorganized blastic phase leading to structurally weak woven bone.

Question 1855

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman undergoes biopsy of a lytic epiphyseal lesion in the proximal tibia. Pathology demonstrates multinucleated giant cells interspersed among mononuclear stromal cells. If systemic therapy is considered, which of the following is the primary cellular target of the most commonly used pharmacologic agent?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Vascular endothelial growth factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab, a monoclonal antibody used for giant cell tumors, binds to RANKL. RANKL is produced by the neoplastic mononuclear stromal cells and recruits/activates the non-neoplastic osteoclast-like giant cells.

Question 1856

Topic: Biology, Genetics & Bone Healing

During the endochondral ossification process of fracture healing, mesenchymal stem cells must differentiate into chondrocytes to form the soft callus. Which of the following transcription factors is the essential master regulator for this specific chondrocytic differentiation?

. Runx2
. SOX9
. Osterix
. Sclerostin
. RANKL

Correct Answer & Explanation

. SOX9

Explanation

SOX9 is the primary transcription factor required for the differentiation of mesenchymal stem cells into chondrocytes. In contrast, Runx2 and Osterix are the key transcription factors necessary for osteoblastic differentiation.

Question 1857

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the proximal tibial epiphysis extending to the subchondral bone.

Histology shows multinucleated giant cells in a stroma of mononuclear cells. The neoplastic cells in this lesion primarily express which of the following?

. Osteoprotegerin
. RANKL
. SOX9
. CD68
. p53

Correct Answer & Explanation

. RANKL

Explanation

In a Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which heavily express RANKL. This overexpression stimulates the recruitment and fusion of normal host osteoclast precursors into the characteristic reactive multinucleated giant cells.

Question 1858

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show profound cortical thickening and coarsened trabeculae of the skull.

The primary cellular defect initiating this condition involves which of the following?

. Decreased osteoblast function
. Abnormal osteoclast activity
. Malignant transformation of chondrocytes
. Defective mineralization of osteoid
. Impaired type I collagen synthesis

Correct Answer & Explanation

. Abnormal osteoclast activity

Explanation

Paget's disease is initiated by an overactive, abnormal osteoclastic phase featuring large, hypermultinucleated osteoclasts. This intense resorption is followed by a disorganized compensatory osteoblastic response, resulting in weak, architecturally abnormal woven bone.

Question 1859

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed alendronate for the management of severe osteoporosis. At the cellular and molecular level, nitrogen-containing bisphosphonates inhibit osteoclast function primarily by disrupting which of the following metabolic pathways?

. Wnt/beta-catenin pathway
. Mevalonate pathway
. RANKL-RANK interaction
. Cytochrome P450 pathway
. Cyclooxygenase pathway

Correct Answer & Explanation

. Mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate) inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of essential small GTP-binding proteins (like Ras and Rho), leading to osteoclast apoptosis and decreased bone resorption.

Question 1860

Topic: Biology, Genetics & Bone Healing

A 2-year-old boy presents with progressive lower extremity bowing and widened wrists. Laboratory tests show normal serum calcium, significantly low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. This specific genetic defect leads to excessive production of which of the following?

. Parathyroid hormone (PTH)
. Vitamin D3
. Fibroblast growth factor 23 (FGF23)
. Calcitonin
. RANKL

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF23)

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation, which leads to pathologically elevated levels of FGF23. Excess FGF23 causes severe renal phosphate wasting and decreases 1,25-dihydroxyvitamin D production, ultimately resulting in defective bone mineralization.

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