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Biology, Genetics & Bone Healing MCQs

Practice Set 32 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 621

Topic: Biology, Genetics & Bone Healing

Cancellous bone autograft is considered the 'gold standard' for filling cavitary bone defects due to its rapid incorporation and optimal biological properties. Compared to cortical autograft, what is the primary histological mechanism that accounts for the faster revascularization and incorporation of cancellous bone graft?

. Rapid osteoclastic tunneling and formation of cutting cones
. Direct angiogenesis and immediate osteoblast lining of the exposed trabecular surfaces
. Primary endochondral ossification mediated by chondrocytes
. Stimulation of an inflammatory foreign-body reaction
. Spontaneous dissolution of the mineral matrix

Correct Answer & Explanation

. Direct angiogenesis and immediate osteoblast lining of the exposed trabecular surfaces

Explanation

Cancellous autografts possess an open, porous trabecular architecture with large marrow spaces. This structure allows for rapid ingrowth of host capillaries (angiogenesis) directly into the graft. Once vascularized, host osteoblasts can immediately begin depositing new woven bone on the surfaces of the dead trabeculae (a process called appositional bone formation). In contrast, dense cortical autograft lacks these large open spaces and requires a much slower process of osteoclastic resorption (cutting cones) to create channels before osteoblasts can deposit new bone, making its incorporation significantly slower.

Question 622

Topic: Biology, Genetics & Bone Healing

Following peripheral nerve injury and subsequent grafting, what is the primary role of Schwann cells during the process of Wallerian degeneration?

. Phagocytosis of myelin debris and formation of Bands of Bungner
. Producing collagen type I to recreate the epineurial sheath
. Suppressing macrophage infiltration at the injury site
. Generating action potentials directly across the non-vascularized graft
. Preventing random axonal sprouting and neuroma formation

Correct Answer & Explanation

. Phagocytosis of myelin debris and formation of Bands of Bungner

Explanation

During Wallerian degeneration, Schwann cells proliferate, assist in clearing myelin debris, and form longitudinal columns (Bands of Bungner) that guide regenerating axonal sprouts across the graft.

Question 623

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in hand and upper extremity osseous reconstruction. Which of the following best describes the biologic properties of DBM?

. Osteogenic and osteoconductive
. Osteoinductive and osteoconductive
. Purely osteogenic
. Purely osteoconductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

DBM lacks viable cells, so it is not osteogenic. However, it contains bone morphogenetic proteins (BMPs) providing osteoinductive properties, and its collagenous matrix provides an osteoconductive scaffold.

Question 624

Topic: Biology, Genetics & Bone Healing

A 32-year-old man with a recurrent giant cell tumor of the distal radius is treated with denosumab prior to surgical resection. What is the mechanism of action of this medication?

. Inhibits osteoblast differentiation via Wnt pathway
. Binds to RANKL, preventing osteoclast activation
. Directly induces apoptosis in neoplastic stromal cells
. Inhibits VEGF-mediated angiogenesis
. Blocks the mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts and osteoclast precursors. This inhibits osteoclast-mediated bone destruction, which is driven by the neoplastic stromal cells in giant cell tumors.

Question 625

Topic: Biology, Genetics & Bone Healing

Denosumab is often utilized in the management of surgically unsalvageable or metastatic Giant Cell Tumor of bone. What is the specific mechanism of action of this medication?

. Directly induces apoptosis of the neoplastic stromal cells
. Binds to RANK receptor on osteoclasts
. Binds to RANK ligand (RANKL) preventing interaction with RANK
. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits matrix metalloproteinases

Correct Answer & Explanation

. Binds to RANK ligand (RANKL) preventing interaction with RANK

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors. This inhibits the recruitment and action of osteoclast-like giant cells, halting the bone destruction characteristic of Giant Cell Tumor.

Question 626

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a large, lytic, eccentrically located lesion in the distal femur extending to the subchondral bone. Biopsy confirms Giant Cell Tumor (GCT) of bone. She is treated preoperatively with denosumab to downstage the tumor. What is the precise mechanism of action of this medication?

. Inhibits osteoclast ruffled border H+-ATPase
. Binds to the RANK receptor on osteoclasts
. Binds to RANKL, preventing osteoclast activation
. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits CD99 surface antigen expression

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANK Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on osteoclasts and their precursors, thereby halting osteoclastogenesis and bone destruction.

Question 627

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with severe back pain, anemia, and hypercalcemia. A skeletal survey reveals multiple punched-out lytic lesions in the skull and spine. Which of the following imaging modalities is most likely to yield false-negative results when evaluating his bone lesions?

. Technetium-99m bone scintigraphy
. Whole-body low-dose CT
. Magnetic Resonance Imaging (MRI)
. Positron Emission Tomography (PET)
. Plain radiography

Correct Answer & Explanation

. Technetium-99m bone scintigraphy

Explanation

Technetium-99m bone scintigraphy relies on osteoblastic activity. Because multiple myeloma primarily stimulates osteoclast activity without a coupled osteoblast response, traditional bone scans are frequently negative ("cold") and are not reliable for staging.

Question 628

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with a lytic epiphyseal lesion of the distal femur. Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. In the pathogenesis of this tumor, the true neoplastic cells express high levels of which of the following?

. RANKL
. RANK receptor
. Osteoprotegerin
. Runx2
. SOX9

Correct Answer & Explanation

. RANKL

Explanation

In a Giant Cell Tumor of bone, the mononuclear stromal cells are the actual neoplastic elements. They overexpress RANKL, which recruits and activates the abundant, reactive osteoclast-like multinucleated giant cells that cause the characteristic bone destruction.

Question 629

Topic: Biology, Genetics & Bone Healing

A 30-year-old pregnant woman presents with an aggressively expanding, painful lytic lesion in the distal radius. Biopsy confirms Giant Cell Tumor (GCT) of bone. What is the primary mechanism of action of Denosumab, and why is it contraindicated in this patient?

. RANKL inhibitor; it causes fetal skeletal malformations
. Tyrosine kinase inhibitor; it causes premature closure of the fetal ductus arteriosus
. Bisphosphonate; it induces maternal renal failure
. VEGF inhibitor; it restricts placental blood flow
. RANKL inhibitor; it accelerates tumor growth during pregnancy

Correct Answer & Explanation

. RANKL inhibitor; it causes fetal skeletal malformations

Explanation

Denosumab is a monoclonal antibody against RANKL, which disrupts osteoclast function and is highly effective for GCT of bone. It is contraindicated in pregnancy because RANKL inhibition can cross the placenta and cause severe fetal skeletal malformations and impaired tooth eruption.

Question 630

Topic: Biology, Genetics & Bone Healing
When utilizing Demineralized Bone Matrix (DBM) as a bone graft substitute to fill a benign bone cyst void in a metacarpal, its primary biological mechanism relies on osteoinductivity. Which specific components retained within the DBM are responsible for this osteoinductive property?
. Living osteoblasts and osteoprogenitor cells
. Calcium hydroxyapatite crystals
. Bone morphogenetic proteins (BMPs)
. Vascular endothelial growth factors (VEGF)
. Type III collagen meshwork

Correct Answer & Explanation

. Bone morphogenetic proteins (BMPs)

Explanation

Demineralized Bone Matrix (DBM) is created by acid extraction of the mineralized component of allograft bone, which exposes and preserves the non-collagenous proteins, specifically Bone Morphogenetic Proteins (BMPs). These BMPs induce local mesenchymal stem cells to differentiate into osteoblasts, providing the osteoinductive property. DBM lacks viable cells (so it is not osteogenic) and has poor structural integrity (minimal osteoconductivity compared to cancellous bone or synthetic ceramics).

Question 631

Topic: Biology, Genetics & Bone Healing
Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is utilized as an osteoinductive graft substitute in spinal fusion and open tibia fractures. At the cellular level, BMP-2 initiates osteoblast differentiation by binding to which type of cell surface receptor to activate the SMAD signaling pathway?
. Tyrosine kinase receptor
. G-protein coupled receptor
. Serine/threonine kinase receptor
. Intracellular nuclear receptor
. Ligand-gated ion channel

Correct Answer & Explanation

. Serine/threonine kinase receptor

Explanation

Bone Morphogenetic Proteins (BMPs) are members of the Transforming Growth Factor-beta (TGF-β) superfamily. They bind to distinct Type I and Type II cell surface receptors, which are both serine/threonine kinase receptors. Upon ligand binding, these receptors form a complex that phosphorylates intracellular SMAD proteins (specifically SMADs 1, 5, and 8), which then translocate to the nucleus to upregulate osteogenic genes like Runx2.

Question 632

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery to supplement fusion masses. Which of the following best describes the biological property that distinguishes DBM from purely synthetic ceramic grafts (e.g., tricalcium phosphate)?

. High compressive strength providing immediate structural support
. Presence of live, differentiating osteogenic stem cells
. Osteoinductive capacity due to retained bone morphogenetic proteins (BMPs)
. Ability to completely bypass the inflammatory phase of bone healing
. Strong osteoclastic stimulation via rapid calcium burst release

Correct Answer & Explanation

. Osteoinductive capacity due to retained bone morphogenetic proteins (BMPs)

Explanation

Demineralized bone matrix (DBM) is processed allograft bone that has had the inorganic mineral phase removed, exposing the underlying collagen matrix and trapped growth factors. While it lacks structural strength and live cells (it is NOT osteogenic), it retains osteoinductive proteins, primarily Bone Morphogenetic Proteins (BMPs), which recruit and differentiate host mesenchymal stem cells into osteoblasts. Synthetic ceramics (like TCP) are purely osteoconductive scaffolds without osteoinductive properties.

Question 633

Topic: Biology, Genetics & Bone Healing

During a corrective osteotomy for a distal radius malunion, a structural cortical bone graft is placed to maintain length. In contrast to cancellous bone grafts, which undergo rapid revascularization, cortical bone grafts incorporate primarily via a protracted process. What is the defining histologic sequence of this process?

. Osteoclastic resorption of host bone followed by osteoblastic new bone formation (creeping substitution)
. Direct intramembranous ossification from surviving transplanted osteoprogenitor cells
. Endochondral ossification beginning with a cartilaginous intermediate
. Rapid neoangiogenesis leading to direct osteoblast differentiation from endothelial cells
. Formation of woven bone directly bridging the fracture gap without prior resorption

Correct Answer & Explanation

. Osteoclastic resorption of host bone followed by osteoblastic new bone formation (creeping substitution)

Explanation

Cortical bone grafts lack the porous architecture for rapid revascularization seen in cancellous grafts. They primarily incorporate through 'creeping substitution,' a slow process where host osteoclasts first resorb the dead structural graft bone (creating cutting cones), followed immediately by host osteoblasts laying down new living bone matrix. This process temporarily weakens the graft before full incorporation occurs.

Question 634

Topic: Biology, Genetics & Bone Healing

During surgery for a highly comminuted intra-articular distal radius fracture, the surgeon utilizes an osteoconductive bone graft substitute to fill a large metaphyseal void. Which of the following best defines the primary mechanism of osteoconduction?

. Recruitment of mesenchymal stem cells via BMPs
. Providing a physical scaffold for host bone ingrowth
. Supplying viable osteoblasts to the defect site
. Inducing a sterile inflammatory response to stimulate angiogenesis
. Generating a piezoelectric effect under mechanical load

Correct Answer & Explanation

. Providing a physical scaffold for host bone ingrowth

Explanation

Bone graft properties are divided into osteoconduction, osteoinduction, and osteogenesis. Osteoconduction refers to the material's ability to act as a 3D physical scaffold or matrix for creeping substitution and ingrowth of host capillaries and osteoprogenitor cells. Osteoinduction (e.g., BMPs) recruits and stimulates cells to become osteoblasts. Osteogenesis (e.g., fresh autograft) directly supplies living bone-forming cells.

Question 635

Topic: Biology, Genetics & Bone Healing
Bone morphogenetic proteins (BMPs) are commonly used as osteoinductive agents in bone grafting procedures. At the cellular level, BMPs initiate signal transduction by binding to cell surface receptors that possess which of the following intrinsic enzymatic activities?
. Tyrosine kinase
. Serine/threonine kinase
. Guanylyl cyclase
. Phospholipase C
. Adenylyl cyclase

Correct Answer & Explanation

. Serine/threonine kinase

Explanation

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-β) superfamily. They bind to Type I and Type II transmembrane receptors that possess intrinsic serine/threonine kinase activity. Once activated, these receptors phosphorylate downstream intracellular signaling molecules called Smads (typically Smad 1, 5, and 8), which then translocate to the nucleus to regulate gene transcription.

Question 636

Topic: Biology, Genetics & Bone Healing
Following primary repair of an acute Zone II flexor tendon laceration, the healing tendon progresses through inflammatory, fibroblastic, and remodeling phases. During the fibroblastic (proliferation) phase, which collagen type is predominantly synthesized initially by fibroblasts before being gradually replaced in the remodeling phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type IX collagen

Correct Answer & Explanation

. Type III collagen

Explanation

Tendon healing in the initial fibroblastic (proliferative) phase, which spans approximately days 5 to 28, is characterized by the production of Type III collagen. This forms a disorganized, mechanically weak matrix. During the subsequent remodeling phase, this Type III collagen is gradually replaced by the stronger, longitudinally oriented Type I collagen, increasing the tendon's tensile strength.

Question 637

Topic: Biology, Genetics & Bone Healing

A 70-year-old female on alendronate for 8 years presents with vague thigh pain. Radiographs reveal a thickened lateral cortex with a transverse radiolucent line in the subtrochanteric region of her femur. What is the most appropriate prophylactic surgical management?

. Discontinuation of alendronate and strict non-weight bearing
. Prophylactic dynamic hip screw fixation
. Prophylactic cephalomedullary nailing
. Prophylactic plating with a locking compression plate
. External beam radiation and teriparatide therapy

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture associated with long-term bisphosphonate use. The gold standard surgical management for a symptomatic, impending atypical subtrochanteric fracture is full-length intramedullary nailing (cephalomedullary nail).

Question 638

Topic: Biology, Genetics & Bone Healing

A 55-year-old male presents with chronic sacral pain and mild bowel/bladder dysfunction. Imaging reveals a large, midline, destructive lytic lesion in the sacrum. Biopsy demonstrates physaliferous cells with large cytoplasmic vacuoles. Which of the following is the most appropriate definitive management?

. Intralesional curettage and bone grafting
. Radiation therapy followed by chemotherapy
. En bloc wide surgical resection
. Radiofrequency ablation
. Denosumab therapy

Correct Answer & Explanation

. En bloc wide surgical resection

Explanation

The clinical picture and histologic finding of physaliferous cells confirm a chordoma. Chordomas are locally aggressive and largely resistant to conventional chemotherapy and radiation. The standard of care for definitive management is en bloc wide surgical excision with negative margins to prevent recurrence.

Question 639

Topic: Biology, Genetics & Bone Healing
The pathogenesis of osteoarthritis is heavily mediated by an imbalance between anabolic and catabolic factors in the joint environment. Which of the following cytokine pairs are considered the primary catabolic drivers of cartilage degradation?
. IL-4 and IL-10
. TGF-beta and IGF-1
. IL-1beta and TNF-alpha
. BMP-2 and BMP-7
. PDGF and VEGF

Correct Answer & Explanation

. IL-1beta and TNF-alpha

Explanation

Interleukin-1 beta (IL-1β) and Tumor Necrosis Factor-alpha (TNF-α) are the principal pro-inflammatory, catabolic cytokines in osteoarthritis. They upregulate matrix metalloproteinases (MMPs) and aggressively promote the breakdown of the extracellular matrix.

Question 640

Topic: Biology, Genetics & Bone Healing

The compressive resilience of articular cartilage is primarily provided by aggrecan. Aggrecan monomers achieve this massive structural and biomechanical property through non-covalent binding with which of the following substances?

. Collagen type II
. Hyaluronic acid
. Fibronectin
. Decorin
. Chondroitin sulfate

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Aggrecan monomers use link proteins to non-covalently bind to long hyaluronic acid backbones, forming massive proteoglycan aggregates. The highly negatively charged glycosaminoglycan side chains of these aggregates attract water, providing compressive stiffness via swelling pressure.

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