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Biology, Genetics & Bone Healing MCQs

Practice Set 77 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 1521

Topic: Biology, Genetics & Bone Healing

A researcher is studying the molecular mechanisms of bone remodeling. They identify a glycoprotein secreted primarily by osteocytes that negatively regulates bone formation by binding to the LRP5/6 coreceptor on osteoblasts, thereby inhibiting the Wnt/beta-catenin signaling pathway. Which of the following therapeutic agents is specifically designed to target and inhibit this glycoprotein?

. Denosumab
. Romosozumab
. Teriparatide
. Abaloparatide
. Burosumab

Correct Answer & Explanation

. Denosumab

Explanation

The glycoprotein described is sclerostin, which is secreted by osteocytes and inhibits the Wnt/beta-catenin pathway, reducing bone formation. Romosozumab is a monoclonal antibody that targets and inhibits sclerostin, thereby promoting osteoblast activity and bone formation.

Question 1522

Topic: Biology, Genetics & Bone Healing

In mature lamellar bone, osteons are bounded by a structurally distinct boundary that separates them from the surrounding interstitial lamellae. This histological structure is known as the:

. Volkmann canal
. Haversian canal
. Cement line
. Sharpey fiber
. Howship lacuna

Correct Answer & Explanation

. Volkmann canal

Explanation

The cement line marks the outer boundary of an osteon in cortical bone. It indicates the physiological reversal point where osteoclastic bone resorption stopped and osteoblastic new bone formation began.

Question 1523

Topic: Biology, Genetics & Bone Healing

Regarding the microscopic structure of cortical bone, which of the following statements most accurately describes Volkmann's canals?

. They run parallel to the long axis of the bone and contain osteoprogenitor cells.
. They are concentric rings of calcified matrix surrounding a central vascular channel.
. They run perpendicular to the long axis of the bone, connecting Haversian canals to the periosteum.
. They represent the boundary between older interstitial lamellae and newly formed osteons.
. They are primary sites of endochondral ossification during fracture healing.

Correct Answer & Explanation

. They run parallel to the long axis of the bone and contain osteoprogenitor cells.

Explanation

Volkmann's canals run transversely through cortical bone to connect the longitudinal Haversian canals with the periosteal and endosteal blood supplies. This network ensures adequate vascularity throughout the dense osteonal system.

Question 1524

Topic: Biology, Genetics & Bone Healing

In the process of bone remodeling, a distinct basophilic line is formed that marks the outer boundary of a newly created osteon. It is rich in osteopontin and deficient in collagen. What is this histological structure called?

. Tidemark
. Cement line (reversal line)
. Howship's lacuna
. Osteoid seam
. Lamina limitans

Correct Answer & Explanation

. Tidemark

Explanation

The cement line (reversal line) marks the outer limit of bone resorption by osteoclasts and the starting point of new bone deposition by osteoblasts. It is characteristically lacking in collagen fibers.

Question 1525

Topic: Biology, Genetics & Bone Healing

Fracture healing progresses through several overlapping phases. During the reparative phase, what type of bone is initially deposited by osteoblasts within the hard callus, characterized by a random, disorganized orientation of collagen fibers?

. Cortical bone
. Lamellar bone
. Woven bone
. Haversian bone
. Cancellous bone

Correct Answer & Explanation

. Cortical bone

Explanation

Woven bone is immature bone that is laid down rapidly during fetal development and early fracture healing (hard callus). It is eventually remodeled into highly organized, mechanically stronger lamellar bone.

Question 1526

Topic: Biology, Genetics & Bone Healing

A 12-year-old is evaluated for osteopetrosis. A genetic defect affecting osteoclast function at the ruffled border is suspected. Which cell surface integrin is essential for the sealing zone of the osteoclast to adhere to the bone surface?

. Alpha5 Beta1
. AlphaV Beta3
. Alpha2 Beta1
. Alpha1 Beta1
. AlphaIIb Beta3

Correct Answer & Explanation

. Alpha5 Beta1

Explanation

Osteoclasts utilize the AlphaV Beta3 integrin to bind to bone matrix proteins like osteopontin at the sealing zone. This creates the isolated microenvironment required for acidic bone resorption.

Question 1527

Topic: Biology, Genetics & Bone Healing

In mature diaphyseal cortical bone, vascular channels that run transversely and connect the longitudinally oriented central canals of adjacent osteons are known as:

. Canaliculi
. Howship lacunae
. Haversian canals
. Volkmann canals
. Medullary sinuses

Correct Answer & Explanation

. Canaliculi

Explanation

Volkmann canals are transverse channels that transmit blood vessels between the longitudinal Haversian canals and connect the periosteal and endosteal blood supplies. Canaliculi are the microchannels connecting osteocyte lacunae.

Question 1528

Topic: Biology, Genetics & Bone Healing

A newborn is evaluated for delayed closure of the cranial sutures and absent clavicles. Genetic testing reveals a mutation in a master transcription factor essential for osteoblast differentiation. Which gene is most likely affected?

. SOX9
. RUNX2 (Cbfa1)
. COL1A1
. FGFR3
. COMP

Correct Answer & Explanation

. SOX9

Explanation

The patient has cleidocranial dysplasia, which is caused by a mutation in RUNX2 (Cbfa1). RUNX2 is the master transcription factor required for the commitment of mesenchymal stem cells to the osteoblast lineage.

Question 1529

Topic: Biology, Genetics & Bone Healing

A military recruit develops a tibial stress fracture during week 4 of basic training. At a cellular level, fatigue failure in cortical bone under cyclical loading initially propagates through the formation of microcracks. What is the primary biological mechanism that attempts to repair this microdamage before macroscopic failure occurs?

. Endochondral ossification
. Targeted remodeling via basic multicellular units (BMUs)
. Woven bone deposition by the periosteum
. Direct primary bone healing via cutting cones
. Intramembranous ossification within the Haversian canals

Correct Answer & Explanation

. Endochondral ossification

Explanation

Microdamage in cortical bone triggers targeted remodeling by basic multicellular units (BMUs). Osteoclasts resorb the damaged matrix, followed by osteoblasts depositing new bone; a stress fracture occurs when repetitive loading outpaces this targeted repair.

Question 1530

Topic: Biology, Genetics & Bone Healing

A bone biopsy from a patient with a suspected metabolic bone disorder is examined under microscopy. The pathologist identifies multiple vascular channels running longitudinally through the center of osteons, surrounded by concentric lamellae. What are these specific anatomical structures called?

. Volkmann canals
. Haversian canals
. Canaliculi
. Howship lacunae
. Cement lines

Correct Answer & Explanation

. Volkmann canals

Explanation

Haversian canals are the longitudinally oriented central vascular channels within osteons (Haversian systems) in cortical bone. Volkmann canals are transversely oriented and connect adjacent Haversian canals to each other and the periosteum.

Question 1531

Topic: Biology, Genetics & Bone Healing

A pathologist evaluates a bone biopsy from a healing fracture callus in a 19-year-old patient. The tissue is identified as primary woven bone. Compared to mature lamellar bone, which of the following histological or material properties is characteristic of woven bone?

. Highly organized concentric collagen fibrils
. Lower osteocyte density per unit volume
. Higher mineral content
. Randomly oriented collagen fibrils with higher cell turnover
. Presence of perfectly aligned Haversian systems

Correct Answer & Explanation

. Highly organized concentric collagen fibrils

Explanation

Woven bone is immature or reactive bone formed rapidly during early fracture healing. It is characterized by randomly oriented collagen fibrils, a higher osteocyte density, and lower mineral content compared to highly organized mature lamellar bone.

Question 1532

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman on long-term bisphosphonate therapy presents with progressive thigh pain for several weeks. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur. What is the recommended management?

. Discontinue bisphosphonates and observe
. Switch to teriparatide and prescribe crutches
. Prophylactic intramedullary nailing of the femur
. Open biopsy of the lesion to rule out malignancy
. Application of an external bone stimulator

Correct Answer & Explanation

. Discontinue bisphosphonates and observe

Explanation

The patient has an impending atypical femur fracture associated with bisphosphonate use. The presence of a cortical radiolucency combined with prodromal thigh pain is an absolute indication for prophylactic intramedullary nailing to prevent a complete, displaced fracture.

Question 1533

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with a 10-year history of alendronate use presents with vague thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur. Which of the following is the most appropriate management?

. Immediate cessation of alendronate and observation
. Switch to teriparatide and partial weight-bearing
. Prophylactic intramedullary nailing of the femur
. Prophylactic compression plating
. Core decompression

Correct Answer & Explanation

. Immediate cessation of alendronate and observation

Explanation

The presence of a radiolucent line (incomplete fracture) in a bisphosphonate-induced atypical femur fracture with persistent pain is an indication for prophylactic intramedullary nailing. This prevents complete displacement and catastrophic failure.

Question 1534

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman taking alendronate for 8 years presents with severe right thigh pain after a minor trip. Radiographs show a transverse fracture in the subtrochanteric region with lateral cortical thickening and a medial spike. What is the most appropriate management?

. Discontinue alendronate, use a full-length intramedullary nail, and obtain contralateral femur radiographs
. Continue alendronate and perform open reduction internal fixation with a dynamic hip screw
. Discontinue alendronate and treat nonoperatively in a hip spica cast
. Switch to denosumab and perform bipolar hemiarthroplasty
. Discontinue alendronate and use a short cephalomedullary nail

Correct Answer & Explanation

. Discontinue alendronate, use a full-length intramedullary nail, and obtain contralateral femur radiographs

Explanation

This is a classic bisphosphonate-associated atypical femur fracture. Management requires stopping the drug, utilizing a full-length intramedullary nail to protect the entire bowed femur, and evaluating the contralateral side for impending lesions.

Question 1535

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman who has been taking alendronate for 10 years presents with atraumatic thigh pain. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region. What is the primary pathophysiologic mechanism of this fracture?

. Hyperparathyroidism leading to severe cortical thinning
. Impaired osteoblast differentiation from systemic toxicity
. Severely suppressed bone turnover causing accumulation of microdamage
. Severe vitamin D deficiency resulting in osteomalacia
. Increased RANKL expression leading to aggressive focal osteolysis

Correct Answer & Explanation

. Hyperparathyroidism leading to severe cortical thinning

Explanation

Long-term bisphosphonate use heavily suppresses osteoclast activity, leading to adynamic bone that cannot remodel or repair physiologic microdamage. This directly results in the characteristic transverse atypical femur fractures at the subtrochanteric or diaphyseal lateral cortex.

Question 1536

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a diaphyseal femur fracture. Which of the following factors is most critical for the initiation of endochondral ossification during secondary fracture healing?

. Absolute rigidity of fixation
. Presence of a significant hematoma
. Presence of interfragmentary motion and adequate vascularity
. High oxygen tension at the fracture site
. Absence of inflammatory cells

Correct Answer & Explanation

. Absolute rigidity of fixation

Explanation

Endochondral ossification, characteristic of secondary fracture healing, is promoted by a degree of interfragmentary motion (relative stability) and robust vascularity. Absolute rigidity (as seen in primary healing) primarily favors intramembranous ossification. While hematoma is essential, motion and vascularity are more direct stimuli for the chondrogenic phase. High oxygen tension inhibits cartilage formation and favors bone. Inflammatory cells are critical for the initial stages of healing.

Question 1537

Topic: Biology, Genetics & Bone Healing

Which cytokine is primarily responsible for osteoclast differentiation and activation?

. Transforming Growth Factor-beta (TGF-β)
. Insulin-like Growth Factor-1 (IGF-1)
. Bone Morphogenetic Protein-2 (BMP-2)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Interleukin-6 (IL-6)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-β)

Explanation

RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand) is the primary cytokine responsible for osteoclast differentiation, activation, and survival. It is secreted by osteoblasts and stromal cells and binds to RANK receptors on pre-osteoclasts and mature osteoclasts. TGF-β and IGF-1 are generally anabolic for bone. BMP-2 is critical for osteoblast differentiation. IL-6 has multiple roles, including stimulating osteoclast activity, but RANKL is the most direct and crucial regulator.

Question 1538

Topic: Biology, Genetics & Bone Healing

What is the primary role of osteoprotegerin (OPG) in bone metabolism?

. Stimulates osteoblast differentiation
. Acts as a soluble decoy receptor for RANKL, inhibiting osteoclast activity
. Promotes bone matrix mineralization
. Increases calcium reabsorption in the kidney
. Inhibits parathyroid hormone secretion

Correct Answer & Explanation

. Stimulates osteoblast differentiation

Explanation

Osteoprotegerin (OPG) is a soluble decoy receptor for RANKL. By binding to RANKL, OPG prevents RANKL from binding to its receptor (RANK) on pre-osteoclasts and osteoclasts, thereby inhibiting osteoclast differentiation, function, and survival. This effectively reduces bone resorption. It does not directly stimulate osteoblast differentiation or mineralization, nor does it affect renal calcium reabsorption or PTH secretion directly.

Question 1539

Topic: Biology, Genetics & Bone Healing

Which growth factor is most potent in inducing ectopic bone formation and is commonly used in spinal fusion procedures?

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

Correct Answer & Explanation

. Platelet-Derived Growth Factor (PDGF)

Explanation

Bone Morphogenetic Proteins (BMPs), particularly BMP-2 and BMP-7, are known for their potent osteoinductive properties and ability to induce ectopic bone formation. BMP-2 is widely used clinically in spinal fusion and fracture nonunion treatment. PDGF, FGF, and VEGF are important for angiogenesis and soft tissue healing but are not as osteoinductive. TGF-α is less relevant in this context.

Question 1540

Topic: Biology, Genetics & Bone Healing

Regarding the vascular supply of long bones, which statement is most accurate?

. The nutrient artery supplies primarily the epiphyseal regions.
. Periosteal arteries are the dominant blood supply to the inner two-thirds of the cortex.
. Metaphyseal arteries are critical for the growth plate and contribute significantly to diaphyseal vascularity in adults.
. The nutrient artery provides the main blood supply to the inner two-thirds of the cortical diaphysis.
. Venous drainage of long bones occurs exclusively through the nutrient vein.

Correct Answer & Explanation

. The nutrient artery supplies primarily the epiphyseal regions.

Explanation

The nutrient artery enters the diaphysis and branches into ascending and descending medullary arteries, supplying the inner two-thirds to three-quarters of the cortical bone via Haversian and Volkmann's canals. The periosteal arteries supply the outer one-third to one-quarter of the cortex. Metaphyseal arteries are crucial for the growth plate and also contribute to the vascularity of the adjacent diaphysis, especially after skeletal maturity. Venous drainage occurs through nutrient veins, metaphyseal veins, and periosteal veins.

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