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Biology, Genetics & Bone Healing MCQs

Practice Set 86 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 1701

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with a 10-year history of alendronate use presents with several weeks of vague, aching right thigh pain that worsens with weight-bearing. Radiographs reveal focal lateral cortical thickening ('cortical beaking') and a transverse radiolucent line extending partially through the lateral cortex in the subtrochanteric region of the right femur. What is the most appropriate management?

. Discontinue alendronate, prescribe calcium/vitamin D, and strictly restrict weight-bearing
. Prophylactic intramedullary nailing of the affected right femur
. Open reduction and internal fixation with a lateral locking plate
. Initiate teriparatide therapy and allow unrestricted weight-bearing
. Immediate cessation of alendronate and switch to denosumab therapy

Correct Answer & Explanation

. Prophylactic intramedullary nailing of the affected right femur

Explanation

This patient presents with a symptomatic, incomplete atypical femur fracture (AFF) associated with long-term bisphosphonate use. The presence of a radiolucent line (incomplete fracture) in the setting of thigh pain indicates an impending complete fracture. The standard of care for a symptomatic incomplete AFF with a visible radiolucent fracture line is prophylactic intramedullary nailing. This prevents completion and displacement of the fracture, which is associated with high morbidity and high rates of nonunion. Medical optimization (stopping bisphosphonates, considering teriparatide) is also important but secondary to surgical stabilization of the impending fracture.

Question 1702

Topic: Biology, Genetics & Bone Healing

An 80-year-old woman presents with acute, severe localized midthoracic back pain following a minor lifting incident 1 week ago. Neurologic exam is completely normal. Radiographs demonstrate an acute T8 osteoporotic compression fracture with a 20% loss of anterior height. What is the recommended initial management?

. Balloon kyphoplasty
. Percutaneous vertebroplasty
. Posterior spinal fusion T7-T9
. Pain management, early mobilization, and osteoporosis evaluation
. Rigid custom TLSO brace for 3 months

Correct Answer & Explanation

. Pain management, early mobilization, and osteoporosis evaluation

Explanation

The initial management for an acute, stable osteoporotic vertebral compression fracture without neurologic deficit is non-operative. This includes aggressive pain management, early mobilization to prevent deconditioning and pulmonary complications, and medical treatment of the underlying osteoporosis. Vertebral augmentation is generally reserved for patients who fail conservative management (typically after 3-6 weeks) or have intractable pain leading to hospitalization.

Question 1703

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman is diagnosed with a large, destructive, recurrent giant cell tumor of the sacrum with impending neurologic compromise. Surgical resection would result in significant morbidity, so her multidisciplinary oncology team initiates targeted medical therapy. What is the mechanism of action of the most appropriate pharmacological agent?

. Binding and neutralization of RANK Ligand (RANKL)
. Direct induction of osteoclast apoptosis
. Inhibition of vascular endothelial growth factor (VEGF) receptors
. Competitive antagonism at the estrogen receptor
. Inhibition of mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Binding and neutralization of RANK Ligand (RANKL)

Explanation

The most appropriate targeted medical therapy for an unresectable or highly morbid Giant Cell Tumor of Bone (GCTB) is denosumab. Denosumab is a fully human monoclonal antibody that specifically binds to and neutralizes RANK Ligand (RANKL). In GCTB, the neoplastic mononuclear stromal cells secrete high levels of RANKL, which recruits and activates the reactive, multinucleated osteoclast-like giant cells that cause bone destruction. By neutralizing RANKL, denosumab prevents giant cell formation and halts osteolysis.

Question 1704

Topic: Biology, Genetics & Bone Healing
A 20-year-old woman has an impending pathologic fracture of the proximal femur due to a large, ground-glass, radiolucent lesion. She also has a history of precocious puberty and café-au-lait spots with irregular borders ('coast of Maine'). The underlying cellular defect involves:
. Decreased activity of osteoclasts due to carbonic anhydrase II deficiency
. Constitutive activation of adenylate cyclase due to a G-protein mutation
. Defective mineralization of osteoid leading to rickets
. Impaired formation of type 1 collagen triple helix
. Abnormal signaling of the Wnt/beta-catenin pathway

Correct Answer & Explanation

. Constitutive activation of adenylate cyclase due to a G-protein mutation

Explanation

The clinical triad of polyostotic fibrous dysplasia, precocious puberty (or other endocrinopathies), and café-au-lait spots with irregular borders is diagnostic of McCune-Albright syndrome. This syndrome is caused by a somatic, postzygotic activating mutation in the GNAS gene, which encodes the alpha subunit of the stimulatory G-protein (Gs-alpha). This mutation causes constitutive activation of adenylate cyclase, leading to continuously elevated intracellular cyclic AMP (cAMP) levels, driving abnormal cellular proliferation and endocrine hyperfunction.

Question 1705

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with persistent knee pain. Radiographs show an eccentric, lytic epiphyseal lesion in the distal femur. A biopsy demonstrates mononuclear cells and multinucleated giant cells. Which of the following is the specific molecular target of the monoclonal antibody denosumab, which may be used in the medical management of this condition?

. Receptor Activator of Nuclear factor Kappa-B (RANK)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Osteoprotegerin
. Macrophage Colony-Stimulating Factor (M-CSF)
. Vascular Endothelial Growth Factor (VEGF)

Correct Answer & Explanation

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

Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits RANKL. In giant cell tumors of bone, the neoplastic mononuclear stromal cells express RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) responsible for aggressive bone resorption.

Question 1706

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman is diagnosed with a giant cell tumor of the distal femur. Due to the proximity of the lesion to the articular surface, she is started on a course of denosumab therapy prior to intralesional curettage. Which of the following best describes the specific mechanism of action of this medication?

. Binds to the RANK receptor directly on multinucleated osteoclasts
. Binds to RANKL, preventing its interaction with the RANK receptor
. Inhibits vascular endothelial growth factor (VEGF) signaling
. Directly induces apoptosis of the neoplastic mononuclear stromal cells
. Inhibits farnesyl pyrophosphate synthase within the osteoclast

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANK Ligand (RANKL). In Giant Cell Tumor of bone, the neoplastic mononuclear stromal cells overexpress RANKL. This overexpression recruits and activates reactive, non-neoplastic multinucleated giant cells (osteoclast-like cells) which cause bone destruction. By binding RANKL, denosumab prevents it from activating the RANK receptor on osteoclasts and their precursors, thereby halting bone resorption.

Question 1707

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with new-onset severe lower back pain and generalized fatigue. Laboratory studies reveal a normocytic anemia, elevated serum creatinine, and hypercalcemia. A skeletal survey shows multiple 'punched-out' lytic lesions in the skull and pelvis with no surrounding reactive sclerosis. Which of the following factors is most directly responsible for the uncoupled bone remodeling that leads to these purely lytic lesions?

. Overproduction of bone morphogenetic protein-2 (BMP-2) by plasma cells
. Tumor secretion of Dickkopf-1 (DKK1) and Macrophage Inflammatory Protein-1 alpha (MIP-1a)
. Systemic overexpression of osteoprotegerin (OPG)
. Increased production of fibroblast growth factor 23 (FGF23)
. Decreased levels of parathyroid hormone-related peptide (PTHrP)

Correct Answer & Explanation

. Tumor secretion of Dickkopf-1 (DKK1) and Macrophage Inflammatory Protein-1 alpha (MIP-1a)

Explanation

Multiple myeloma is characterized by purely lytic bone lesions resulting from uncoupled bone remodeling (increased osteoclast activity and suppressed osteoblast activity). Myeloma cells secrete DKK1, which inhibits the Wnt signaling pathway, severely suppressing osteoblast differentiation and preventing reactive bone formation. Additionally, they secrete MIP-1a and RANKL, which strongly activate osteoclasts, leading to unchecked bone resorption.

Question 1708

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with worsening knee pain. Radiographs reveal an eccentric, purely lytic lesion in the distal femur that extends directly to the subchondral bone without a sclerotic margin. Biopsy demonstrates numerous multinucleated giant cells in a background of mononuclear stromal cells. Due to the proximity of the lesion to the joint surface and its size, she is treated with a targeted monoclonal antibody to downstage the tumor prior to surgery. What is the precise mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Inhibition of osteoprotegerin (OPG)
. Inhibition of tyrosine kinase signaling
. Binding to and inhibition of RANK Ligand (RANKL)
. Inhibition of programmed cell death protein 1 (PD-1)

Correct Answer & Explanation

. Binding to and inhibition of RANK Ligand (RANKL)

Explanation

The lesion is a Giant Cell Tumor (GCT) of bone. Denosumab is a fully human monoclonal antibody frequently used for locally advanced or unresectable GCTs. It binds and inhibits RANK Ligand (RANKL). The neoplastic mononuclear stromal cells in GCT express high levels of RANKL, which inappropriately recruits and activates the reactive multinucleated osteoclast-like giant cells that cause the characteristic massive osteolysis.

Question 1709

Topic: Biology, Genetics & Bone Healing

During fracture healing, a complex molecular cascade dictates the differentiation of multipotent mesenchymal stem cells into the specific cell lineages necessary for bone repair. Which of the following transcription factors serves as the critical 'master regulator' for committing mesenchymal stem cells to the osteoblastic lineage?

. SOX9
. Runx2 (Cbfa1)
. MyoD
. PPAR-gamma
. HIF-1 alpha

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (Runt-related transcription factor 2, also known as Cbfa1) is the master transcription factor responsible for the commitment and differentiation of multipotent mesenchymal stem cells into the osteoblastic lineage. SOX9 is the primary regulator for chondrogenic differentiation (cartilage). MyoD regulates myogenic differentiation (muscle). PPAR-gamma is the master regulator for adipogenic differentiation (fat). HIF-1 alpha regulates the cellular response to hypoxia.

Question 1710

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman with a history of postmenopausal osteoporosis sustains a fragility fracture of her distal radius. She has been on oral alendronate therapy for the past three years. Nitrogen-containing bisphosphonates, such as alendronate, inhibit osteoclast-mediated bone resorption primarily through which of the following molecular mechanisms?

. Inhibition of the Wnt/beta-catenin signaling pathway
. Binding to RANKL to prevent its interaction with the RANK receptor
. Direct stimulation of osteoprotegerin (OPG) secretion by osteoblasts
. Inhibition of farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway
. Irreversible inhibition of the enzyme cathepsin K

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate, zoledronic acid, risedronate) primarily exert their antiresorptive effects by inhibiting the enzyme farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway in osteoclasts. This inhibition prevents the prenylation of small GTPase proteins (like Ras, Rho, and Rab) that are essential for osteoclast function, ruffled border formation, and survival, ultimately inducing osteoclast apoptosis. Denosumab binds RANKL (Option B). Odanacatib inhibits cathepsin K (Option E).

Question 1711

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with multiple palpable, painless, bony prominences around his knees, ankles, and shoulders. Radiographs confirm multiple pedunculated and sessile bony outgrowths projecting away from the adjacent joints in the metaphyses of the long bones, continuous with the medullary cavity of the native bone. He is diagnosed with Multiple Hereditary Exostoses (MHE). What is the primary underlying biochemical defect associated with the genetic mutations in this disorder?

. Defective intramembranous ossification of the periosteum
. Constitutive overactivation of the Fibroblast Growth Factor Receptor 3 (FGFR3)
. Defective synthesis of heparan sulfate proteoglycans
. Failure of osteoclasts to acidify the resorption pit
. Abnormal substitution of glycine residues in collagen type I alpha chains

Correct Answer & Explanation

. Defective synthesis of heparan sulfate proteoglycans

Explanation

Multiple Hereditary Exostoses (MHE), also known as diaphyseal aclasis, is an autosomal dominant condition caused by loss-of-function mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for the biosynthesis of heparan sulfate proteoglycans. Defective heparan sulfate in the growth plate disrupts the normal diffusion and signaling of critical growth factors (such as Indian Hedgehog and PTHrP), leading to premature and disorganized chondrocyte proliferation that escapes the longitudinal axis, forming osteochondromas. FGFR3 overactivation causes achondroplasia. Defective osteoclast resorption leads to osteopetrosis. Abnormal collagen type I synthesis causes osteogenesis imperfecta.

Question 1712

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, purely lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a giant cell tumor of bone. Denosumab is considered for medical management to facilitate surgery. What is the primary cellular target of this medication?

. RANK receptor on the multinucleated giant cells
. RANKL produced by the neoplastic mononuclear stromal cells
. Osteoprotegerin (OPG) produced by osteoblasts
. Vascular Endothelial Growth Factor (VEGF)
. Tumor Necrosis Factor-alpha (TNF-alpha)

Correct Answer & Explanation

. RANKL produced by the neoplastic mononuclear stromal cells

Explanation

Giant cell tumor of bone is composed of neoplastic mononuclear stromal cells and reactive multinucleated giant cells. The mononuclear cells express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates the osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds to RANKL, inhibiting this process.

Question 1713

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is FDA-approved specifically 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 when used in conjunction with an intramedullary nail. RhBMP-7 (osteogenic protein-1) was previously approved under a Humanitarian Device Exemption for recalcitrant long bone nonunions but not specifically for acute open tibial fractures.

Question 1714

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with persistent knee pain. Radiographs reveal an eccentric, purely lytic lesion in the proximal tibial epiphysis that extends to the subchondral bone. A core needle biopsy demonstrates a proliferation of mononuclear stromal cells interspersed with numerous multinucleated giant cells. For cases of this disease that are deemed unresectable or recurrent, medical therapy is often employed. What is the primary mechanism of action of the most commonly used targeted biologic agent for this condition?

. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits the mammalian target of rapamycin (mTOR) pathway
. Induces apoptosis via stabilization of p53
. Binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Acts as a broad-spectrum tyrosine kinase inhibitor

Correct Answer & Explanation

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

Explanation

The patient has a Giant Cell Tumor (GCT) of bone, which typically presents as an eccentric, lytic epiphyseal lesion in a skeletally mature patient. The neoplastic cells in GCT are the mononuclear stromal cells, which express high levels of RANKL. This recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) that cause the characteristic osteolysis. Denosumab, a fully human monoclonal antibody, specifically binds to RANKL, preventing RANK activation. This halts osteoclastogenesis and bone destruction, and is highly effective in treating recurrent or unresectable GCT of bone.

Question 1715

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic, eccentrically located lesion in the distal radius extending into the subchondral bone. Biopsy demonstrates mononuclear cells intermixed with numerous large, multinucleated osteoclast-like giant cells. The patient is prescribed a targeted medical therapy for her condition. Which of the following best describes the mechanism of action of this drug?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct binding to the RANK receptor on osteoclasts
. Binding to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. Inhibition of matrix metalloproteinases
. Activation of the Wnt/beta-catenin pathway

Correct Answer & Explanation

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

Explanation

The clinical and histologic description is classic for a giant cell tumor of bone (GCT). The neoplastic cells are the mononuclear cells, which express high levels of RANKL. This recruits and activates reactive osteoclast-like giant cells, leading to bone destruction. Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from binding to the RANK receptor on the surface of osteoclast precursors, thereby profoundly inhibiting osteoclast formation and function.

Question 1716

Topic: Biology, Genetics & Bone Healing

A 65-year-old man is incidentally found to have a substantially elevated serum alkaline phosphatase level on routine laboratory work. His serum calcium, phosphorus, and parathyroid hormone levels are strictly normal. Radiographs of his pelvis show thickened trabeculae, cortical thickening, and overall bone enlargement. A defect in which of the following cell types is considered the primary initiating event in the pathogenesis of this condition?

. Osteoblast
. Osteocyte
. Osteoclast
. Chondrocyte
. Fibroblast

Correct Answer & Explanation

. Osteoclast

Explanation

The patient's clinical and radiographic profile is classic for Paget's disease of bone. The disease is characterized by an isolated elevation of alkaline phosphatase with normal calcium and phosphate profiles. The primary pathologic cellular defect in Paget's disease lies in the osteoclasts, which are greatly increased in number, abnormally large, and possess numerous nuclei. This leads to a primary intense osteolytic phase, which is subsequently followed by chaotic, excessive, and structurally unsound osteoblastic bone formation.

Question 1717

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with progressive pain and swelling in her left knee. Radiographs reveal an eccentric, completely lytic lesion in the proximal tibia extending to the subchondral bone without a sclerotic margin. Biopsy shows multinucleated giant cells in a background of mononuclear stromal cells. If targeted pharmacological therapy is considered to reduce tumor burden, what is the mechanism of action of the most appropriate agent?

. Inhibition of vascular endothelial growth factor (VEGF)
. Binding to the RANK receptor on osteoclast precursors
. Binding to RANK ligand (RANKL) expressed by neoplastic stromal cells
. Inhibition of cyclooxygenase-2 (COX-2) enzyme activity
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Binding to RANK ligand (RANKL) expressed by neoplastic stromal cells

Explanation

The clinical and histologic picture describes a Giant Cell Tumor (GCT) of bone. In GCT, the mononuclear stromal cells are the true neoplastic cells, and they express high levels of RANKL. Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from interacting with RANK on the surface of osteoclast precursors. This inhibits osteoclast-mediated bone resorption and effectively reduces tumor size and progression.

Question 1718

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic lesion in the distal femur that extends to the subchondral bone. Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. She is treated with denosumab preoperatively. What is the mechanism of action of this medication?

. Direct induction of apoptosis in the multinucleated giant cells
. Inhibition of the RANK ligand (RANKL) secreted by the mononuclear stromal cells
. Binding to the osteoprotegerin (OPG) receptor on osteoclasts
. Inhibition of farnesyl pyrophosphate synthase
. Direct cross-linking of DNA leading to cell death

Correct Answer & Explanation

. Inhibition of the RANK ligand (RANKL) secreted by the mononuclear stromal cells

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express RANKL, which recruits and activates normal multinucleated giant cells (osteoclast-like cells) expressing RANK. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to RANK, thus inhibiting osteoclast-mediated bone destruction and inducing ossification of the tumor.

Question 1719

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of BMP to its cell surface receptor, which intracellular signaling molecules are primarily phosphorylated to translocate to the nucleus and regulate gene expression?

. Wnt and beta-catenin
. JAK and STAT
. Smad 1, 5, and 8
. MAP kinase
. Runx2 and Osterix

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs (part of the TGF-beta superfamily) bind to serine/threonine kinase receptors. Upon activation, they primarily phosphorylate receptor-regulated Smads (Smad 1, 5, and 8). These phosphorylated Smads then form a complex with the common-partner Smad (Smad 4) and translocate to the nucleus to regulate the transcription of osteogenic genes like Runx2.

Question 1720

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy is evaluated for multiple fractures with minimal trauma. Radiographs demonstrate diffusely increased bone density, a 'bone-within-bone' appearance in the spine, and Erlenmeyer flask deformities of the distal femora. Which of the following best describes the underlying cellular defect in this condition?

. Defective synthesis of type I collagen by osteoblasts
. Absence of a ruffled border on osteoclasts due to a defect in carbonic anhydrase II
. Increased osteoclast apoptosis due to bisphosphonate exposure
. Overexpression of fibroblast growth factor receptor 3 (FGFR3)
. Mutation in the COMP gene

Correct Answer & Explanation

. Absence of a ruffled border on osteoclasts due to a defect in carbonic anhydrase II

Explanation

The patient has osteopetrosis, characterized by dense, brittle bones due to defective osteoclastic bone resorption. A common form involves a mutation in the carbonic anhydrase II gene or the TCIRG1 gene (encoding a vacuolar proton pump), which prevents the creation of an acidic environment in the Howship lacuna, leading to the absence of the osteoclast's ruffled border and failure to resorb bone.

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