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Biology, Genetics & Bone Healing MCQs

Practice Set 163 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 3241

Topic: Biology, Genetics & Bone Healing

A 45-year-old man with a history of severe alcohol use disorder presents with swollen bleeding gums, petechiae, and joint pain. Radiographs of his knees show osteopenia and a dense provisional zone of calcification. The underlying nutritional deficiency in this patient primarily impairs which of the following steps of collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Formation of the triple helix
. Cross-linking by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy caused by Vitamin C (ascorbic acid) deficiency. Vitamin C is a required cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes are responsible for the hydroxylation of proline and lysine residues in procollagen, a critical step that allows for stable hydrogen bonding and subsequent triple helix formation.

Question 3242

Topic: Biology, Genetics & Bone Healing
During active bone resorption, osteoclasts attach to the bone matrix to create an isolated microenvironment known as the sealing zone. Which of the following integrin receptors mediates this firm attachment to osteopontin and bone sialoprotein?
. Alpha-5 beta-1
. Alpha-v beta-3
. Alpha-2 beta-1
. Alpha-L beta-2
. Alpha-M beta-2

Correct Answer & Explanation

. Alpha-v beta-3

Explanation

The alpha-v beta-3 (αvβ3) integrin is highly expressed on the ruffled border and sealing zone of osteoclasts. It is the primary receptor responsible for binding to the RGD (Arg-Gly-Asp) amino acid sequences found in bone matrix proteins like osteopontin and bone sialoprotein, anchoring the osteoclast to the bone surface.

Question 3243

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is FDA-approved and primarily used as an adjunct for the treatment of 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 acute, open tibial shaft fractures treated with an intramedullary nail. BMP-7 (rhBMP-7) is typically utilized as an alternative to autograft for recalcitrant long bone nonunions.

Question 3244

Topic: Biology, Genetics & Bone Healing

Secondary bone healing (callus formation) after a fracture is driven predominantly by which physiologic process?

. Intramembranous ossification
. Endochondral ossification
. Appositional ossification
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary bone healing involves the formation of a cartilaginous callus that is subsequently mineralized and replaced by bone, a process known as endochondral ossification. Intramembranous ossification bypasses the cartilage phase and occurs in primary bone healing.

Question 3245

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a giant cell tumor extending into the metaphysis of the proximal tibia. Which targeted pharmacotherapy acts as an effective adjuvant treatment for aggressive or unresectable disease?

. Imatinib
. Denosumab
. Bisphosphonates
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab, a monoclonal antibody against RANKL, is highly effective in treating Giant Cell Tumor of Bone (GCTB). It inhibits the RANK-RANKL interaction, effectively suppressing the activation of the osteoclast-like giant cells.

Question 3246

Topic: Biology, Genetics & Bone Healing

A 40-year-old male undergoes open reduction and internal fixation of a radius fracture with a dynamic compression plate. Which type of bone healing is expected to primarily occur at the fracture site?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Chondroid metaplasia

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Rigid internal fixation with absolute stability, such as dynamic compression plating, suppresses callus formation and promotes primary (Haversian) bone healing. This process relies on osteoclast cutting cones crossing the fracture site followed by osteoblast bone deposition.

Question 3247

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with an enlarging hat size and progressively worsening right thigh pain. Radiographs of the femur show cortical thickening, coarse trabeculae, and bowing. Laboratory tests reveal an isolated, significantly elevated alkaline phosphatase. Which of the following is the primary cellular defect in this condition?

. Defective osteoid mineralization by osteoblasts
. Excessive osteoclastic bone resorption followed by disorganized osteoblastic bone formation
. Mutations in the type I collagen gene
. Autoimmune destruction of articular cartilage
. Overproduction of parathyroid hormone

Correct Answer & Explanation

. Excessive osteoclastic bone resorption followed by disorganized osteoblastic bone formation

Explanation

The patient has Paget disease of bone, characterized by an initial phase of excessive osteoclast activity followed by a compensatory, but disorganized, osteoblast response. This results in structurally weak woven bone that is prone to deformity and fracture.

Question 3248

Topic: Biology, Genetics & Bone Healing

A 60-year-old woman presents with severe back pain. Radiographs reveal a compression fracture of L2 and multiple punched-out lytic lesions in her skull. Serum protein electrophoresis shows a monoclonal spike. Which of the following is the most likely mechanism of osteolysis in this patient?

. Production of PTH-related peptide (PTHrP) by tumor cells
. Direct enzymatic degradation of bone by plasma cells
. Tumor secretion of RANK ligand (RANKL) and IL-6 stimulating osteoclasts
. Deposition of amyloid fibrils in the osteoid matrix
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Tumor secretion of RANK ligand (RANKL) and IL-6 stimulating osteoclasts

Explanation

Multiple myeloma causes osteolytic lesions primarily through the secretion of factors like RANKL, IL-6, and MIP-1 alpha by myeloma cells. These factors potently stimulate osteoclastogenesis while inhibiting osteoblast function.

Question 3249

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, which growth factor is most directly responsible for the induction of angiogenesis during the transition from a soft cartilaginous callus to a hard bony callus?

. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-beta (TGF-beta)
. Vascular Endothelial Growth Factor (VEGF)
. Fibroblast Growth Factor (FGF)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Vascular Endothelial Growth Factor (VEGF)

Explanation

Vascular Endothelial Growth Factor (VEGF) is critical for angiogenesis during the transition from a hypoxic cartilaginous soft callus to an ossified hard callus. Inhibition of VEGF halts endochondral ossification and impairs fracture healing.

Question 3250

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with generalized bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). A bone biopsy would most likely show which of the following?

. Decreased osteoclast activity
. Decreased osteoblast activity
. Increased unmineralized osteoid
. Normal bone mineralization with decreased bone mass
. Mosaic pattern of lamellar bone

Correct Answer & Explanation

. Increased unmineralized osteoid

Explanation

The clinical and laboratory picture (low Ca, low PO4, high Alk Phos, high PTH) is classic for osteomalacia, often due to Vitamin D deficiency. Bone biopsy in osteomalacia typically shows increased unmineralized osteoid (wide osteoid seams) due to a defect in bone mineralization. 'Normal bone mineralization with decreased bone mass' describes osteoporosis, and a 'mosaic pattern' is indicative of Paget's disease.

Question 3251

Topic: Biology, Genetics & Bone Healing

Which Bone Morphogenetic Protein (BMP) is FDA-approved for use in acute open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-6
. BMP-7

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for use in acute, open tibial shaft fractures when applied via an absorbable collagen sponge. BMP-7 (Osteogenic Protein-1) historically had a Humanitarian Device Exemption for recalcitrant tibial nonunions.

Question 3252

Topic: Biology, Genetics & Bone Healing
During the remodeling phase of tendon healing, which type of collagen is primarily synthesized to replace the initial provisional matrix?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

During the initial proliferative phase of tendon healing, fibroblasts rapidly deposit Type III collagen, forming a disorganized provisional matrix. In the remodeling phase, this is gradually replaced by thicker, highly organized Type I collagen, which restores the tensile strength of the mature tendon.

Question 3253

Topic: Biology, Genetics & Bone Healing

What is the primary cellular mechanism by which nitrogen-containing bisphosphonates (e.g., Alendronate) inhibit osteoclast function?

. Inhibition of RANKL binding to RANK
. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway
. Direct activation of osteoblast apoptosis
. Incorporation into ATP to form a non-hydrolyzable ATP analogue
. Binding to the estrogen receptor to modulate gene transcription

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronate) inhibit bone resorption by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins (such as Ras, Rho, and Rac) that are essential for osteoclast survival and ruffled border formation. Non-nitrogenous bisphosphonates form toxic ATP analogues.

Question 3254

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated by lamellar bone during fracture healing?

. 2%
. 10%
. 30%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

According to Perren's strain theory, lamellar bone can only tolerate up to 2% strain before failing. In contrast, cartilage tolerates up to 10% strain, and granulation tissue can withstand up to 100% strain.

Question 3255

Topic: Biology, Genetics & Bone Healing

A 70-year-old female is treated with denosumab for severe osteoporosis. Which of the following best describes the molecular mechanism of this medication?

. Bisphosphonate analogue that induces osteoclast apoptosis
. Monoclonal antibody against RANK ligand (RANKL)
. Recombinant parathyroid hormone that stimulates osteoblasts
. Monoclonal antibody against sclerostin
. Selective estrogen receptor modulator

Correct Answer & Explanation

. Monoclonal antibody against RANK ligand (RANKL)

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL, preventing it from interacting with the RANK receptor on osteoclasts. This effectively inhibits osteoclast formation, function, and survival, thereby decreasing bone resorption.

Question 3256

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used in orthopedic surgery to augment fracture healing. Which of the following best describes its primary biologic properties?

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

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a structural scaffold for new bone growth (osteoconductive) and contains bone morphogenetic proteins (BMPs) that stimulate local cells to form bone (osteoinductive). It lacks viable bone-forming cells, so it is not osteogenic.

Question 3257

Topic: Biology, Genetics & Bone Healing

A 12-year-old child with a history of recurrent fractures, delayed dentition, and anemia is diagnosed with osteopetrosis. The pathogenesis of this condition is primarily related to a defect in which of the following?

. Type I collagen synthesis
. Carbonic anhydrase II
. Fibroblast growth factor receptor 3 (FGFR3)
. Runx2 transcription factor
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, frequently due to a mutation in carbonic anhydrase II. This enzyme is crucial for generating the acidic environment required by osteoclasts to dissolve the bone mineral matrix.

Question 3258

Topic: Biology, Genetics & Bone Healing

Which of the following ultrastructural components allows for direct communication and the exchange of nutrients between adjacent osteocytes within dense cortical bone?

. Haversian canals
. Volkmann canals
. Canaliculi
. Howship lacunae
. Sharpey fibers

Correct Answer & Explanation

. Canaliculi

Explanation

Osteocytes reside within lacunae and extend long cytoplasmic processes through microscopic channels called canaliculi. These networks connect via gap junctions, facilitating essential intercellular communication and nutrient transport.

Question 3259

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary bone healing with direct lamellar bone formation can only occur if the interfragmentary strain is kept below what maximum threshold?

. 2%
. 10%
. 20%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Lamellar bone formation requires absolute stability, tolerating a maximum of 2% strain. Woven bone can tolerate up to 10% strain, while granulation tissue can withstand up to 100% strain.

Question 3260

Topic: Biology, Genetics & Bone Healing

Articular cartilage relies on a specific biochemical composition to withstand compressive and shear forces. Which of the following collagens comprises 90-95% of the collagen in normal hyaline cartilage, and which cell type is responsible for its production?

. Type I collagen / Osteoblast
. Type I collagen / Chondrocyte
. Type II collagen / Chondrocyte
. Type X collagen / Hypertrophic chondrocyte
. Type XI collagen / Fibroblast

Correct Answer & Explanation

. Type II collagen / Chondrocyte

Explanation

Type II collagen is the primary structural framework of articular cartilage, providing tensile strength. It is synthesized exclusively by resident chondrocytes within the extracellular matrix.

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