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Biology, Genetics & Bone Healing MCQs

Practice Set 85 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 1681

Topic: Biology, Genetics & Bone Healing

A surgeon decides to use demineralized bone matrix (DBM) as a bone graft substitute during a spinal fusion. Which of the following bone grafting properties is DBM most reliably recognized for possessing?

. Osteoconduction only
. Osteoinduction only
. Osteoconduction and osteogenesis
. Osteoconduction and osteoinduction
. Osteogenesis, osteoinduction, and osteoconduction

Correct Answer & Explanation

. Osteoconduction and osteoinduction

Explanation

Demineralized bone matrix (DBM) is an allograft that has been chemically processed to remove its mineral component. This processing exposes bone morphogenetic proteins (BMPs) and other inherent growth factors, conferring osteoinductive properties to the graft. Additionally, the remaining structural collagenous matrix provides a physical scaffold for new bone ingrowth, conferring osteoconductive properties. DBM does not contain living cells (like osteoblasts or mesenchymal stem cells), and therefore lacks osteogenic properties. Autograft is the only classic graft type providing all three: osteogenesis, osteoinduction, and osteoconduction.

Question 1682

Topic: Biology, Genetics & Bone Healing
Bone morphogenetic proteins (BMPs) are used clinically to promote bone healing. At the cellular level, the canonical signaling pathway for BMPs involves binding to a transmembrane receptor followed by the direct intracellular phosphorylation of which of the following?
. Beta-catenin
. Janus kinases (JAK)
. Smad proteins
. Cyclic AMP (cAMP)
. Tyrosine kinase

Correct Answer & Explanation

. Smad proteins

Explanation

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-β) superfamily. They bind to cell-surface serine/threonine kinase receptors. Upon activation, the type II receptor phosphorylates the type I receptor, which in turn phosphorylates intracellular receptor-regulated Smad proteins (typically Smads 1, 5, and 8 for BMPs). These phosphorylated R-Smads bind to a common-mediator Smad (Smad 4) to form a complex that translocates into the nucleus to regulate the transcription of target genes. Wnt signaling utilizes beta-catenin, while JAK-STAT and tyrosine kinases are associated with other cytokine and growth factor pathways.

Question 1683

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, primary (osteonal) bone healing without intermediate callus formation requires the interfragmentary strain at the fracture site to be maintained below what specific threshold?

. 2%
. 10%
. 15%
. 25%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that a specific tissue can only form in a fracture gap if the interfragmentary strain is below the critical tolerance level of that tissue. Interfragmentary strain is defined as the change in gap length divided by the original gap length. Granulation tissue can tolerate up to 100% strain, whereas cartilage can tolerate up to 10% strain, allowing for secondary bone healing via endochondral ossification (callus). For primary bone healing to occur—where osteonal cutting cones directly cross the fracture gap without callus formation—absolute stability is required, meaning the interfragmentary strain must be maintained at less than 2%.

Question 1684

Topic: Biology, Genetics & Bone Healing

Denosumab is frequently used in the treatment of osteoporosis and giant cell tumor of bone. What is the specific mechanism of action of this medication?

. Binds to the ruffled border of osteoclasts, directly causing apoptosis
. Acts as a competitive antagonist of the Wnt signaling pathway
. Binds directly to RANKL, preventing it from activating the RANK receptor on osteoclasts
. Stimulates osteoprotegerin (OPG) production by osteoblasts
. Inhibits the enzyme cathepsin K, preventing degradation of bone collagen

Correct Answer & Explanation

. Binds directly to RANKL, preventing it from activating the RANK receptor on osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding to RANKL, it prevents the interaction between RANKL and the RANK receptor on the surface of osteoclast precursors and mature osteoclasts. This leads to the inhibition of osteoclast formation, function, and survival, thereby decreasing bone resorption.

Question 1685

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, which of the following tissue types can tolerate the highest amount of strain before failure?

. Intact cortical bone
. Woven bone
. Lamellar bone
. Fibrocartilage
. Granulation tissue

Correct Answer & Explanation

. Granulation tissue

Explanation

Perren's strain theory dictates that a specific tissue type can only form and survive under a specific mechanical strain environment. Granulation tissue is highly compliant and can tolerate up to 100% strain before failure. Fibrocartilage can tolerate roughly 10-15% strain, woven bone can tolerate about 5% strain, and lamellar (cortical) bone can tolerate only about 2% strain.

Question 1686

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the management of osteoporosis and giant cell tumor of bone. Which of the following accurately describes its primary cellular mechanism of action?

. Binds to the RANK receptor on osteoclasts
. Inhibits the formation of sclerostin
. Acts as a soluble decoy receptor mimicking osteoprotegerin (OPG)
. Directly binds to and neutralizes RANKL
. Stimulates osteoprotegerin (OPG) production by osteoblasts

Correct Answer & Explanation

. Directly binds to and neutralizes RANKL

Explanation

Denosumab is a fully human monoclonal antibody that directly binds to and inhibits Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents RANKL from binding to the RANK receptor on the surface of osteoclasts and their precursors, thereby potently inhibiting osteoclast maturation, function, and survival. OPG is the body's natural decoy receptor for RANKL.

Question 1687

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is commonly utilized to enhance posterolateral spinal fusions. BMPs induce osteoblastic differentiation primarily through which of the following intracellular signaling pathways?

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

Correct Answer & Explanation

. Smad 1, 5, and 8 pathway

Explanation

Bone Morphogenetic Proteins (BMPs) belong to the TGF-beta superfamily. When BMPs bind to their specific serine/threonine kinase membrane receptors, they trigger the intracellular phosphorylation of Smad proteins, specifically Smad 1, 5, and 8 (receptor-regulated Smads). These form a complex with Smad 4 (common-partner Smad) and translocate to the nucleus to regulate target gene transcription for osteoblast differentiation.

Question 1688

Topic: Biology, Genetics & Bone Healing

A patient undergoes open reduction and internal fixation (ORIF) of a transverse radial shaft fracture utilizing a dynamic compression plate to achieve absolute stability. Assuming an anatomic reduction with rigid fixation is obtained, which of the following best describes the expected primary mechanism of fracture healing?

. Endochondral ossification leading to a large cartilaginous callus
. Intramembranous ossification with abundant fibrous callus
. Direct Haversian remodeling via osteoclastic cutting cones
. Secondary bone healing mediated by early hematoma organization
. Chondrogenesis followed by rapid woven bone formation

Correct Answer & Explanation

. Direct Haversian remodeling via osteoclastic cutting cones

Explanation

Absolute stability achieved through rigid internal fixation (such as compression plating) eliminates interfragmentary motion and bypasses the callus formation seen in secondary healing. Instead, the bone heals via direct (primary) bone healing. This occurs through direct Haversian remodeling, where osteoclasts create 'cutting cones' that cross the fracture site, immediately followed by osteoblasts depositing new lamellar bone.

Question 1689

Topic: Biology, Genetics & Bone Healing

During fracture healing via endochondral ossification, which transcription factor is strictly required for the differentiation of mesenchymal stem cells into chondrocytes?

. RUNX2 (Cbfa1)
. SOX9
. Osterix
. Sclerostin
. RANKL

Correct Answer & Explanation

. SOX9

Explanation

SOX9 is the master transcription factor for chondrogenesis, essential for driving mesenchymal stem cells to differentiate into chondrocytes during endochondral ossification and cartilage formation. RUNX2 (also known as Cbfa1) and Osterix are critical transcription factors for osteoblast differentiation.

Question 1690

Topic: Biology, Genetics & Bone Healing



Demineralized bone matrix (DBM) is widely used in orthopedic surgery as an adjunct for spinal fusion and fracture nonunions. Which of the following combinations of properties does DBM possess?

. Osteoinductive and osteogenic
. Osteoconductive and osteogenic
. Osteoinductive and osteoconductive
. Osteogenic only
. Osteoconductive only

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) provides a collagenous scaffold that serves as an osteoconductive matrix. Because the demineralization process preserves biologically active bone morphogenetic proteins (BMPs) and other growth factors, DBM is also osteoinductive. However, because it contains no living cells (osteoprogenitors or osteoblasts), it lacks osteogenic properties.

Question 1691

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with a history of a distal radius fracture undergoes a dual-energy x-ray absorptiometry (DEXA) scan yielding a T-score of -3.0. She is prescribed denosumab. What is the precise mechanism of action of this medication?

. Binds to hydroxyapatite and inhibits osteoclast ruffled border formation
. Monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts
. Recombinant parathyroid hormone that intermittently stimulates osteoblast activity
. Selective estrogen receptor modulator (SERM) that decreases bone resorption
. Monoclonal antibody against sclerostin, promoting Wnt signaling

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that targets and binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents it from binding to the RANK receptor on the surface of osteoclasts and their precursors. This profoundly inhibits osteoclast differentiation, function, and survival, leading to decreased bone resorption.

Question 1692

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key regulatory glycoprotein in bone metabolism and the target of the monoclonal antibody romosozumab. What is its primary mechanism of action at the molecular level?

. It binds to RANKL, preventing its interaction with the RANK receptor and inhibiting osteoclastogenesis.
. It competitively binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway.
. It activates the BMP-2 signaling cascade via SMAD 1/5/8 phosphorylation, suppressing osteoblast apoptosis.
. It binds to the parathyroid hormone (PTH) receptor, directly inhibiting osteoblast matrix production.
. It upregulates osteoprotegerin (OPG) expression, leading to a profound decrease in bone turnover.

Correct Answer & Explanation

. It competitively binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway.

Explanation

Sclerostin is produced primarily by mature osteocytes and acts as a negative regulator of bone formation. It functions by binding to the LRP5/6 co-receptors on the surface of osteoblasts, which competitively blocks the binding of Wnt ligands. This prevents the activation of the canonical Wnt/beta-catenin signaling pathway, leading to the phosphorylation and proteasomal degradation of beta-catenin, ultimately downregulating osteoblastogenesis and bone formation. Romosozumab is a neutralizing antibody against sclerostin that harnesses this pathway to stimulate bone formation.

Question 1693

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, various growth factors are expressed to orchestrate cellular differentiation and matrix synthesis. Which of the following growth factors is powerfully osteoinductive, signals predominantly through serine/threonine kinase receptors, and activates intracellular Smad proteins?

. Bone morphogenetic protein 2 (BMP-2)
. Platelet-derived growth factor (PDGF)
. Insulin-like growth factor 1 (IGF-1)
. Vascular endothelial growth factor (VEGF)
. Fibroblast growth factor 2 (FGF-2)

Correct Answer & Explanation

. Bone morphogenetic protein 2 (BMP-2)

Explanation

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, are potent osteoinductive growth factors of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate and activate intracellular Smad proteins (e.g., Smad 1, 5, 8). These activated Smads form a complex with Smad 4, translocate to the nucleus, and upregulate the transcription of osteogenic genes such as Runx2.

Question 1694

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological agent used in the management of osteoporosis and giant cell tumor of bone. Which of the following describes the exact mechanism of action of this medication?

. It binds directly to the RANK receptor on osteoclasts to induce apoptosis.
. It is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor.
. It acts as a synthetic analog of osteoprotegerin (OPG) by binding to the osteoclast ruffled border.
. It inhibits cathepsin K, preventing the degradation of Type I collagen.
. It inhibits the Wnt signaling pathway by antagonizing sclerostin.

Correct Answer & Explanation

. It is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor.

Explanation

Denosumab is a fully human monoclonal antibody (IgG2) that targets and binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). RANKL is typically expressed by osteoblasts and stromal cells. By binding to RANKL, denosumab prevents the interaction between RANKL and the RANK receptor on the surface of osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival, thereby reducing bone resorption. It effectively mimics the physiological role of osteoprotegerin (OPG).

Question 1695

Topic: Biology, Genetics & Bone Healing

Which of the following factors is directly secreted by osteoblasts to inhibit osteoclastogenesis and limit bone resorption?

. RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. M-CSF (Macrophage Colony-Stimulating Factor)
. Osteoprotegerin (OPG)
. Cathepsin K
. Sclerostin

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is a decoy receptor produced by osteoblasts that binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This prevents osteoclast differentiation and activation, thereby limiting bone resorption. RANKL and M-CSF promote osteoclastogenesis. Sclerostin is produced by osteocytes to inhibit bone formation via the Wnt pathway, and Cathepsin K is an enzyme secreted by osteoclasts to degrade collagen.

Question 1696

Topic: Biology, Genetics & Bone Healing

A 45-year-old man sustains a closed midshaft femur fracture treated with a reamed, statically locked intramedullary nail. Fracture healing in this construct is predominantly expected to occur via:

. Direct osteonal remodeling without a cartilaginous intermediate
. Endochondral ossification forming a fracture callus
. Intramembranous ossification without callus formation
. Appositional bone growth exclusively
. Haversian canal widening and primary bone formation

Correct Answer & Explanation

. Endochondral ossification forming a fracture callus

Explanation

Intramedullary nailing provides relative mechanical stability rather than absolute stability. This strain environment stimulates secondary bone healing, which primarily occurs via endochondral ossification. This process progresses through stages of inflammation, soft callus (cartilaginous), hard callus, and remodeling. Primary bone healing (direct osteonal remodeling without callus) requires absolute stability and direct cortical contact, typically achieved with rigid compression plating.

Question 1697

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman is prescribed romosozumab, a monoclonal antibody, for the treatment of severe postmenopausal osteoporosis. What is the primary molecular mechanism by which this medication exerts its osteoanabolic effect?

. Inhibition of RANKL, preventing osteoclast activation and survival.
. Direct binding to the Wnt co-receptor LRP5/6 to stimulate osteoblast differentiation.
. Neutralization of a negative regulator of the Wnt/beta-catenin signaling pathway.
. Upregulation of osteoprotegerin (OPG) secretion from osteoblasts.
. Direct stimulation of parathyroid hormone (PTH) receptors on osteoblasts.

Correct Answer & Explanation

. Neutralization of a negative regulator of the Wnt/beta-catenin signaling pathway.

Explanation

Romosozumab is a monoclonal antibody that targets and neutralizes sclerostin. Sclerostin is a glycoprotein secreted primarily by osteocytes that acts as a negative regulator of bone formation by binding to the LRP5/6 co-receptors on osteoblasts, thereby inhibiting the canonical Wnt/beta-catenin signaling pathway. By neutralizing sclerostin, romosozumab disinhibits this pathway, leading to a potent osteoanabolic (bone-building) effect.

Question 1698

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with a 10-year history of alendronate use presents with a 3-month history of dull, aching right thigh pain. Plain radiographs reveal localized periosteal thickening of the lateral cortex of the subtrochanteric femur with a subtle transverse radiolucent line, but no complete fracture. What is the most appropriate prophylactic management?

. Discontinue alendronate, begin teriparatide, and observation
. Discontinue alendronate, begin denosumab, and protected weight-bearing
. Prophylactic cephalomedullary nailing of the right femur
. Open reduction and internal fixation with a dynamic hip screw
. Initiate a bisphosphonate holiday for 6 months, then resume

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing of the right femur

Explanation

This patient presents with signs of an impending atypical femur fracture (AFF), which is strongly associated with long-term bisphosphonate use. Radiographic criteria include lateral cortical thickening (the 'beak') and a transverse radiolucent line. Because she has prodromal thigh pain and radiographic evidence of an incomplete fracture (radiolucent line), the risk of completion is extremely high. The standard of care is prophylactic intramedullary nailing to prevent a complete fracture. Medical management includes discontinuing the bisphosphonate; initiating anabolic agents like teriparatide may help healing, but mechanical stabilization with a cephalomedullary nail is the primary required intervention for symptomatic incomplete AFFs.

Question 1699

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with a history of osteoporosis and 7 years of alendronate therapy presents with progressively worsening thigh pain. Radiographs reveal a transverse, non-comminuted fracture of the lateral cortex of the subtrochanteric femur with localized periosteal thickening ('beaking'). What is the most appropriate prophylactic surgical treatment?

. Dynamic hip screw (DHS)
. Cephalomedullary nailing
. Proximal femoral locking plate
. Retrograde intramedullary nail
. Total hip arthroplasty

Correct Answer & Explanation

. Cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use. Cephalomedullary (full-length) nailing is the prophylactic and therapeutic treatment of choice for subtrochanteric atypical femur fractures. Plates have a significantly higher rate of failure.

Question 1700

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with a 10-year history of alendronate use presents with a 2-month history of insidious onset, aching pain in her right thigh. She denies any recent trauma. Radiographs of the right femur demonstrate a localized periosteal reaction with lateral cortical thickening and a transverse radiolucent line spanning approximately 30% of the lateral cortex in the subtrochanteric region. What is the most appropriate next step in management?

. Discontinue alendronate, begin teriparatide, and allow protected weight-bearing
. Prophylactic stabilization with a cephalomedullary or intramedullary nail
. Discontinue alendronate and switch to denosumab therapy
. Open reduction and internal fixation with a lateral locked plate
. Core decompression of the subtrochanteric femur

Correct Answer & Explanation

. Prophylactic stabilization with a cephalomedullary or intramedullary nail

Explanation

This patient presents with a painful, incomplete atypical femur fracture (AFF) associated with long-term bisphosphonate use. Given the presence of prodromal thigh pain combined with an incomplete fracture line (radiolucent line on the lateral cortex), the risk of progression to a complete fracture is extremely high. The standard of care for a painful incomplete AFF with a visible fracture line is prophylactic stabilization, most commonly with a cephalomedullary or intramedullary nail. Medical management alone is insufficient for symptomatic impending complete fractures.

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