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Biology, Genetics & Bone Healing MCQs

Practice Set 37 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 721

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, the interfragmentary strain threshold determines the type of tissue that forms within a fracture gap. Primary (direct) bone healing without callus formation occurs when the interfragmentary strain is maintained below what percentage?

. 2%
. 10%
. 17%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that tissues cannot form if the local strain exceeds their tolerance. Granulation tissue tolerates up to 100% strain, fibrous connective tissue up to 17%, and fibrocartilage between 2% and 10%. Lamellar bone can only form directly (primary bone healing via cutting cones) when the interfragmentary strain is strictly below 2%, which is typically achieved with rigid absolute stability (e.g., compression plating).

Question 722

Topic: Biology, Genetics & Bone Healing

A massive structural cortical allograft is utilized to reconstruct a large segmental bone defect following tumor resection. The biological process by which the living host bone gradually resorbs the necrotic allograft bone via osteoclastic activity, immediately followed by new osteoblastic bone formation on the remaining allograft scaffold, is termed:

. Osteoinduction
. Osteogenesis
. Creeping substitution
. Endochondral ossification
. Intramembranous ossification

Correct Answer & Explanation

. Creeping substitution

Explanation

Creeping substitution is the classical process by which a non-vascularized cortical bone graft is incorporated. It involves the simultaneous resorption of the graft by host osteoclasts and the laying down of new host bone by osteoblasts along the haversian canals. Osteoinduction refers to the stimulation of phenotypic conversion of progenitor cells into osteoblasts. Osteoconduction provides a physical scaffold.

Question 723

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with persistent knee pain.

Radiographs demonstrate an eccentric, purely lytic lesion in the distal femur that extends directly to the subchondral bone without a distinct sclerotic margin. Core needle biopsy confirms a Giant Cell Tumor of bone. The formation of the multinucleated giant cells characteristic of this tumor is mediated by a specific signaling pathway. Which of the following systemic medications specifically targets and inhibits this pathway?

. Imatinib
. Denosumab
. Bisphosphonates
. Doxorubicin
. Methotrexate

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express RANKL. RANKL recruits osteoclast precursors and stimulates their differentiation into multinucleated, bone-resorbing giant cells via the RANK receptor. Denosumab is a human monoclonal antibody that specifically binds and inhibits RANKL, effectively halting osteoclastogenesis, reducing tumor size, and allowing for intralesional ossification. It is often used as a neoadjuvant or primary treatment for unresectable cases.

Question 724

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing in a long bone, the repair process transitions through several highly coordinated phases. Which type of collagen is predominantly synthesized during the soft callus phase, and which cell type is primarily responsible for its production?
. Type I collagen; osteoblasts
. Type II collagen; chondrocytes
. Type III collagen; fibroblasts
. Type X collagen; hypertrophic chondrocytes
. Type I collagen; chondroblasts

Correct Answer & Explanation

. Type II collagen; chondrocytes

Explanation

Secondary fracture healing involves endochondral ossification. During the soft callus phase, the hematoma is replaced by fibrocartilage, predominantly composed of Type II collagen synthesized by proliferating chondrocytes. This cartilaginous template is later calcified (involving Type X collagen) and finally replaced by woven bone (Type I collagen produced by osteoblasts) during the hard callus phase.

Question 725

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) initiate intracellular signaling through which of the following receptor types?

. Tyrosine kinase receptors
. Serine/threonine kinase receptors
. G-protein coupled receptors
. Intracellular nuclear receptors
. Ion channel-linked receptors

Correct Answer & Explanation

. Serine/threonine kinase receptors

Explanation

BMPs are members of the TGF-beta superfamily. They initiate intracellular signaling cascades by binding to specific Type I and Type II transmembrane serine/threonine kinase receptors, which leads to the phosphorylation and activation of intracellular Smad proteins.

Question 726

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a distal femur lytic lesion that is diagnosed as a Giant Cell Tumor of Bone. She is started on Denosumab prior to surgery to help downstage the tumor. What is the mechanism of action of this medication?

. Direct cytotoxicity to neoplastic osteoblasts
. Monoclonal antibody against RANKL, inhibiting osteoclast formation
. Bisphosphonate that inhibits farnesyl pyrophosphate synthase
. VEGF inhibitor blocking tumor angiogenesis
. Monoclonal antibody against the RANK receptor directly

Correct Answer & Explanation

. Monoclonal antibody against RANKL, inhibiting osteoclast formation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclasts and osteoclast precursors, thereby profoundly inhibiting osteoclast formation, function, and survival.

Question 727

Topic: Biology, Genetics & Bone Healing

Romosozumab is a monoclonal antibody utilized in the treatment of severe osteoporosis. It functions by inhibiting sclerostin, thereby promoting bone formation. Sclerostin normally inhibits osteoblastogenesis by antagonizing which of the following signaling pathways?

. RANK/RANKL pathway
. Wnt/beta-catenin pathway via LRP5/6 receptors
. Transforming Growth Factor-beta (TGF-b) pathway
. Bone Morphogenetic Protein-2 (BMP-2) pathway
. Fibroblast Growth Factor (FGF) pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway via LRP5/6 receptors

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes. It acts as a negative regulator of bone formation by binding to the LRP5/6 coreceptors on osteoblasts, thereby inhibiting the canonical Wnt/beta-catenin signaling pathway. By blocking sclerostin, medications like romosozumab allow Wnt signaling to proceed, leading to increased osteoblast activity and bone formation.

Question 728

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, expansile, purely lytic lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy shows multinucleated giant cells interspersed among mononuclear spindle cells. In the pathogenesis of this tumor, the neoplastic mononuclear cells overexpress a specific surface molecule that drives the recruitment and differentiation of the reactive giant cells. Which of the following is that molecule?

. RANK
. RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand)
. Osteoprotegerin (OPG)
. Vascular Endothelial Growth Factor (VEGF)
. Fibroblast Growth Factor Receptor 3 (FGFR3)

Correct Answer & Explanation

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

Explanation

The clinical picture describes a Giant Cell Tumor (GCT) of bone. The true neoplastic cells in a GCT are the spindle-shaped mononuclear stromal cells. These cells highly express RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand). RANKL binds to the RANK receptor found on the surface of normal circulating monocyte/macrophage precursors, driving them to fuse and form the prominent, reactive osteoclast-like multinucleated giant cells that cause the extensive osteolysis. This pathway is the target of the monoclonal antibody Denosumab.

Question 729

Topic: Biology, Genetics & Bone Healing
Bone morphogenetic proteins (BMPs), particularly recombinant human BMP-2 and BMP-7, are utilized in orthopedic surgery to promote osteoinduction and bone healing. These signaling molecules exert their cellular effects primarily through which of the following intracellular signaling pathways?
. Wnt/β-catenin pathway
. JAK/STAT signaling pathway
. MAPK/ERK pathway
. Serine/threonine kinase receptors and Smad proteins
. Tyrosine kinase receptors and the Ras/Raf pathway

Correct Answer & Explanation

. Serine/threonine kinase receptors and Smad proteins

Explanation

BMPs belong to the Transforming Growth Factor-beta (TGF-β) superfamily. They bind to cell surface type I and type II serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8), which then form a complex with Smad4. This complex translocates to the nucleus to regulate transcription of osteogenic genes (e.g., Runx2, Osterix).

Question 730

Topic: Biology, Genetics & Bone Healing

Which of the following osteoinductive agents, members of the transforming growth factor-beta (TGF-beta) superfamily, is specifically FDA approved as an alternative to autogenous bone graft in acute, open tibial shaft fractures treated with an intramedullary nail?

. Bone Morphogenetic Protein-2 (BMP-2)
. Bone Morphogenetic Protein-3 (BMP-3)
. Bone Morphogenetic Protein-4 (BMP-4)
. Bone Morphogenetic Protein-7 (BMP-7)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Protein-2 (BMP-2)

Explanation

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is FDA approved for use in acute open tibial shaft fractures that have been stabilized with an intramedullary nail. Its use has been shown to reduce the need for secondary bone grafting procedures. rhBMP-7 (also known as Osteogenic Protein-1, or OP-1) was previously available under a Humanitarian Device Exemption for recalcitrant long bone nonunions, but BMP-2 is the specific agent approved for acute open tibias.

Question 731

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy reveals multinucleated giant cells in a stroma of mononuclear cells. Due to the tumor's size and location, she is started on Denosumab prior to surgical intervention. What is the mechanism of action of this medication?

. Directly inhibits osteoblast apoptosis
. Monoclonal antibody that binds to and inhibits RANKL
. Monoclonal antibody that binds directly to RANK
. Nitrogen-containing bisphosphonate analog
. Tyrosine kinase inhibitor targeting VEGF receptors

Correct Answer & Explanation

. Monoclonal antibody that binds to and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on osteoclasts and their precursors, thereby inhibiting osteoclast formation, function, and survival. It is highly effective in treating Giant Cell Tumors of bone.

Question 732

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction and fracture healing. Which of the following describes the correct intracellular signaling pathway utilized by BMP-2?

. Wnt/beta-catenin pathway
. Smad 1/5/8 pathway
. MAP kinase pathway
. JAK/STAT pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMP-2, BMP-4, and BMP-7 belong to the TGF-beta superfamily. They bind to cell-surface serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular Smad proteins, specifically Smads 1, 5, and 8. These phosphorylated Smads then form a complex with Smad 4 and translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 733

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the management of osteoporosis to stimulate bone formation. Intermittent administration of this parathyroid hormone (PTH) analog exerts its primary anabolic effect by binding to receptors on which of the following cell types?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Intermittent administration of parathyroid hormone (PTH) or its analog (teriparatide) exerts a paradoxical anabolic effect on bone by directly binding to PTH1 receptors on osteoblasts, stimulating their proliferation, increasing their lifespan by preventing apoptosis, and increasing bone formation.

Question 734

Topic: Biology, Genetics & Bone Healing
Sclerostin is a protein that negatively regulates bone formation. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) are utilized in the treatment of severe osteoporosis. Sclerostin exerts its inhibitory effect on osteoblasts primarily by antagonizing which of the following intracellular signaling pathways?
. RANK/RANKL pathway
. Wnt/β-catenin pathway
. TGF-β/SMAD pathway
. Bone Morphogenetic Protein (BMP) pathway
. Notch signaling pathway

Correct Answer & Explanation

. Wnt/β-catenin pathway

Explanation

Sclerostin is secreted by osteocytes and inhibits bone formation by binding to LRP5/6 receptors on osteoblasts. This binding blocks the coreceptor function of LRP5/6, thereby antagonizing the canonical Wnt/β-catenin signaling pathway, which is essential for osteoblast differentiation and survival.

Question 735

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are critical members of the TGF-beta superfamily that induce the differentiation of mesenchymal stem cells into osteoblasts. Which of the following recombinant BMPs is FDA-approved specifically for use in anterior lumbar interbody fusion (ALIF) with a metallic interbody cage?

. rhBMP-2
. rhBMP-3
. rhBMP-4
. rhBMP-7
. rhBMP-9

Correct Answer & Explanation

. rhBMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2, trade name Infuse) is FDA-approved for use in single-level anterior lumbar interbody fusion (ALIF) when used with an approved interbody fusion device. rhBMP-7 (OP-1) was previously approved for recalcitrant long bone nonunions under an HDE but is generally no longer commercially available in the US.

Question 736

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a critical role in osteoinduction and bone healing. Recombinant human BMP-2 (rhBMP-2) is utilized in various spine and orthopedic trauma procedures. Upon binding to its transmembrane serine/threonine kinase receptor, which intracellular signaling pathway is primarily activated by BMP-2?

. Smad 2 and 3
. Smad 1, 5, and 8
. Wnt/Beta-catenin
. MAP kinase (MAPK)
. JAK/STAT

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMP-2 and BMP-7 act via cell surface receptors that have intrinsic serine/threonine kinase activity. Once activated, these receptors phosphorylate the intracellular R-Smads (Receptor-regulated Smads), specifically Smad 1, Smad 5, and Smad 8. These complex with Co-Smad (Smad 4) to translocate to the nucleus and induce osteogenic gene transcription. Smad 2 and 3 are primarily associated with the TGF-beta signaling pathway, not BMP.

Question 737

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a transverse midshaft radius fracture. He undergoes open reduction and internal fixation with a 3.5 mm dynamic compression plate placed in absolute stability. Which of the following best describes the predominant mechanism of bone healing expected in this scenario?

. Endochondral ossification with a cartilaginous intermediate
. Primary bone healing characterized by osteoclast-led cutting cones followed by osteoblasts
. Intramembranous ossification with robust callus formation
. Chondroid metaplasia within the fracture hematoma
. Secondary bone healing driven by micromotion at the fracture site

Correct Answer & Explanation

. Primary bone healing characterized by osteoclast-led cutting cones followed by osteoblasts

Explanation

Absolute stability (rigid fixation with anatomic reduction and no gap) eliminates interfragmentary strain, bypassing callus formation. It leads to primary (direct) bone healing, which occurs via Haversian remodeling driven by osteoclast-led cutting cones followed immediately by osteoblasts laying down new bone.

Question 738

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological agent used in the management of osteoporosis. What is its specific mechanism of action?

. Binds to RANKL and inhibits osteoclast activation
. Directly induces osteoclast apoptosis
. Stimulates osteoblast activity via PTH receptor
. Inhibits farnesyl pyrophosphate synthase
. Binds to sclerostin to promote bone formation

Correct Answer & Explanation

. Binds to RANKL and inhibits osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), preventing it from interacting with RANK on osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

Question 739

Topic: Biology, Genetics & Bone Healing

A 72-year-old female who has been taking a medication for osteoporosis for 8 years presents with a low-energy fracture of the femoral shaft.

What is the primary mechanism by which bisphosphonates increase the risk of these atypical femur fractures?

. Inhibition of osteoblast differentiation
. Disruption of the vascular supply to the diaphysis
. Direct toxicity to osteocytes
. Suppression of bone turnover leading to accumulation of microdamage
. Stimulation of parathyroid hormone secretion

Correct Answer & Explanation

. Suppression of bone turnover leading to accumulation of microdamage

Explanation

Long-term bisphosphonate therapy heavily suppresses osteoclast activity, which severely blunts normal targeted bone remodeling. Over time, normal physiological microdamage in the cortical bone is not repaired and accumulates. This leads to altered biomechanical properties and eventually the propagation of microcracks into a stress fracture and completed atypical femur fracture.

Question 740

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient with a highly comminuted diaphyseal femur fracture is treated with a bridging locked intramedullary nail. The resulting mechanical construct provides relative stability. Which of the following predominantly characterizes the bone healing process in this mechanical environment?

. Primary bone healing via Haversian remodeling and cutting cones
. Secondary bone healing via endochondral ossification
. Intramembranous ossification directly without a cartilage intermediate
. Creeping substitution
. Appositional direct bone growth only

Correct Answer & Explanation

. Secondary bone healing via endochondral ossification

Explanation

A bridging construct (such as an IM nail or a bridge plate for a comminuted fracture) provides relative stability rather than absolute stability. This allows for micromotion at the fracture site, which stimulates secondary bone healing. Secondary bone healing is characterized by the formation of a soft callus (cartilage intermediate) that subsequently undergoes endochondral ossification into woven bone and then remodeling into lamellar bone. Primary bone healing (cutting cones) requires absolute stability (e.g., lag screw and compression plating).

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