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Biology, Genetics & Bone Healing MCQs

Practice Set 19 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 361

Topic: Biology, Genetics & Bone Healing

A 66-year-old man with symptomatic, advanced Paget's disease of the left femur is scheduled for an elective total hip arthroplasty due to severe secondary osteoarthritis. Which of the following is the most appropriate preoperative intervention to minimize surgical blood loss?

. Administration of denosumab 1 week prior to surgery
. Administration of intravenous bisphosphonates 2 months prior to surgery
. Administration of subcutaneous teriparatide 1 month prior to surgery
. Preoperative embolization of the femoral artery
. Administration of calcitonin on the day of surgery

Correct Answer & Explanation

. Administration of intravenous bisphosphonates 2 months prior to surgery

Explanation

Preoperative treatment with bisphosphonates decreases the extreme vascularity and disease activity in pagetic bone. This has been shown to significantly reduce intraoperative blood loss during elective orthopedic procedures like THA.

Question 362

Topic: Biology, Genetics & Bone Healing

A patient with active Paget's disease is treated with an intravenous nitrogen-containing bisphosphonate. At the cellular level, this medication achieves its primary therapeutic effect by inhibiting which of the following enzymes?

. Cathepsin K
. Farnesyl pyrophosphate (FPP) synthase
. Alkaline phosphatase
. Tartrate-resistant acid phosphatase (TRAP)
. Cyclooxygenase-2 (COX-2)

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway within osteoclasts. This leads to impaired prenylation of regulatory proteins, ultimately causing osteoclast apoptosis and reduced bone resorption.

Question 363

Topic: Biology, Genetics & Bone Healing

A 75-year-old woman treated with prolonged alendronate for Paget's disease presents to the ED after a low-energy fall. Radiographs demonstrate a transverse subtrochanteric femur fracture with a medial cortical spike and localized lateral cortical thickening. Following intramedullary nailing, which of the following medications is contraindicated for managing her fracture healing given her specific medical history?

. Vitamin D
. Calcium carbonate
. Teriparatide
. Denosumab
. Calcitonin

Correct Answer & Explanation

. Teriparatide

Explanation

The patient has an atypical femur fracture related to prolonged bisphosphonate use. While teriparatide is sometimes used off-label to aid healing in atypical femur fractures, it carries a black box warning and is strictly contraindicated in patients with Paget's disease due to the risk of osteosarcoma.

Question 364

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a comminuted diaphyseal tibia fracture. Which of the following factors is MOST critical in determining the rate of secondary fracture healing, assuming adequate reduction and stabilization?

. Adequate immobilization rigidity
. Presence of an intact periosteal sleeve
. Systemic vitamin D levels
. Patient's age and bone mineral density
. Degree of interfragmentary strain

Correct Answer & Explanation

. Degree of interfragmentary strain

Explanation

Correct Answer: EThe degree of interfragmentary strain is the most critical factor influencing secondary fracture healing, also known as callus healing. Too much strain (macromotion) disrupts the forming callus and inhibits healing, leading to non-union. Too little strain (excessive rigidity, as in primary healing) may prevent sufficient callus formation required for secondary healing. The optimal strain environment allows for the progression from hematoma to granulation tissue, soft callus, hard callus, and finally remodeling. While an intact periosteal sleeve is important for osteogenic cells, and immobilization rigidity contributes to managing strain, thedegreeof strain itself is the direct biomechanical determinant. Vitamin D and BMD are systemic factors but less direct than local biomechanical factors.

Question 365

Topic: Biology, Genetics & Bone Healing

A 30-year-old patient is immobilized for 6 weeks following a complex ankle fracture. During this period of disuse, bone remodeling shifts towards resorption, contributing to localized osteopenia. Which bone cell type is primarily responsible for sensing the altered mechanical environment and initiating these remodeling changes?

. Osteoblasts
. Osteoclasts
. Osteocytes
. Mesenchymal stem cells
. Chondrocytes

Correct Answer & Explanation

. Osteocytes

Explanation

Correct Answer: COsteocytes, entrapped within the bone matrix, are the primary mechanosensors of bone. They sense mechanical strain and fluid flow through their lacunar-canalicular network. This mechanotransduction initiates signaling cascades (e.g., sclerostin, RANKL) that regulate the activity of osteoblasts (bone formation) and osteoclasts (bone resorption), thereby orchestrating bone remodeling. Osteoblasts synthesize new matrix, osteoclasts resorb bone, and progenitor cells are distinct (e.g., mesenchymal stem cells). While they indirectly contribute to calcium homeostasis through remodeling, they don't directly release calcium as their primary role.

Question 366

Topic: Biology, Genetics & Bone Healing
A 72-year-old female with severe osteoporosis is being considered for denosumab therapy. Understanding its mechanism of action, which cytokine is a potent stimulator of osteoclastogenesis and bone resorption, and is directly targeted by denosumab?
. TGF-β
. IL-6
. RANKL
. BMP-2
. PTHrP

Correct Answer & Explanation

. RANKL

Explanation

RANKL (Receptor Activator of Nuclear Factor kappa-B Ligand) is a key cytokine that binds to RANK receptors on pre-osteoclasts and mature osteoclasts, stimulating their differentiation, activation, and survival, thereby promoting bone resorption. Denosumab is a monoclonal antibody that targets and inhibits RANKL, making it a powerful antiresorptive agent. TGF-β and BMP-2 are more involved in bone formation, IL-6 has diverse inflammatory roles, and PTHrP is involved in endochondral ossification and hypercalcemia of malignancy.

Question 367

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is utilized in spine fusion and open tibia fractures. When an examiner asks about its cellular mechanism of action, you correctly state that BMP-2 initiates osteoinduction primarily by binding to cell surface receptors and subsequently activating which intracellular signaling pathway?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. JAK/STAT pathway
. SMAD 1/5/8 pathway
. Notch signaling pathway

Correct Answer & Explanation

. SMAD 1/5/8 pathway

Explanation

BMP-2 binds to serine/threonine kinase receptors on mesenchymal stem cells, which phosphorylates and activates the intracellular SMAD 1/5/8 complex. This complex translocates to the nucleus to upregulate osteogenic genes like Runx2.

Question 368

Topic: Biology, Genetics & Bone Healing

You are questioned about the physiology of fracture healing following the application of a dynamic compression plate (rigid internal fixation). This construct relies on which of the following mechanisms to achieve union?

. Endochondral ossification with a large cartilaginous callus
. Primary bone healing via Haversian remodeling and cutting cones
. Intramembranous ossification solely driven by the periosteum
. Chondrocyte hypertrophy and apoptosis leading to calcified cartilage
. Distraction osteogenesis mimicking embryonic growth plate activity

Correct Answer & Explanation

. Primary bone healing via Haversian remodeling and cutting cones

Explanation

Rigid internal fixation with absolute stability minimizes interfragmentary strain, bypassing callus formation. It instead promotes primary (direct) bone healing, which occurs via osteoclast cutting cones and subsequent osteoblast-mediated Haversian remodeling.

Question 369

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion extending to the subchondral bone of the distal femur. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered to facilitate joint-salvage surgery, which medication is most appropriate and what is its mechanism?

. Imatinib; tyrosine kinase inhibitor
. Methotrexate; folate antimetabolite
. Denosumab; RANKL inhibitor
. Zoledronic acid; osteoclast apoptosis stimulator
. Doxorubicin; DNA intercalator

Correct Answer & Explanation

. Denosumab; RANKL inhibitor

Explanation

Giant cell tumors of bone consist of neoplastic stromal cells that express RANKL, which recruits osteoclast-like giant cells. Denosumab is a monoclonal antibody against RANKL used to consolidate the tumor prior to curettage or resection.

Question 370

Topic: Biology, Genetics & Bone Healing

You are explaining the rationale for using a compression plate for a transverse radius fracture. Absolute stability constructs, such as compression plating, promote which type of bone healing, and what is the primary prerequisite?

. Secondary bone healing; callus formation
. Intramembranous ossification; a wide gap for hematoma
. Primary bone healing; anatomic reduction and rigid fixation
. Endochondral ossification; micromotion
. Creeping substitution; bone grafting

Correct Answer & Explanation

. Primary bone healing; anatomic reduction and rigid fixation

Explanation

Absolute stability constructs prevent micromotion and rely on anatomic reduction to achieve primary (direct) bone healing. This process occurs via cutting cones crossing the fracture site without the formation of a visible fracture callus.

Question 371

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a lytic, expansile lesion in the distal femur epiphysis extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor of bone. She is started on denosumab therapy preoperatively. What is the precise mechanism of action of this medication?

. Inhibits RANKL, preventing osteoclast differentiation and function
. Directly induces apoptosis in the neoplastic mononuclear stromal cells
. Inhibits vascular endothelial growth factor (VEGF) preventing angiogenesis
. Acts as a tyrosine kinase inhibitor targeting c-kit
. Alkylates DNA, causing cross-linking in rapidly dividing cells

Correct Answer & Explanation

. Inhibits RANKL, preventing osteoclast differentiation and function

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANKL. This prevents the differentiation and function of the reactive osteoclast-like giant cells, thereby reducing osteolysis and allowing for peripheral tumor ossification.

Question 372

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a massive, unresectable recurrent Giant Cell Tumor (GCT) of the sacrum. The multidisciplinary tumor board recommends initiation of denosumab therapy. What is the specific mechanism of action of this medication in treating GCT of bone?

. Inhibition of Vascular Endothelial Growth Factor (VEGF) preventing tumor angiogenesis
. Monoclonal antibody targeting RANKL, thereby inhibiting osteoclast-like giant cell activation
. Direct cytotoxic apoptosis of the neoplastic mononuclear stromal cells
. Stimulation of aggressive osteoblast proliferation to ossify the tumor mass
. Inhibition of the mammalian target of rapamycin (mTOR) pathway

Correct Answer & Explanation

. Monoclonal antibody targeting RANKL, thereby inhibiting osteoclast-like giant cell activation

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). In GCT, neoplastic stromal cells express RANKL, which recruits and activates the osteoclast-like giant cells; denosumab breaks this cycle, halting osteolysis.

Question 373

Topic: Biology, Genetics & Bone Healing

A 34-year-old female presents with a recurrent giant cell tumor of the distal radius that is now deemed unresectable without significant morbidity. Which targeted medical therapy is most appropriate to inhibit the recruitment and activity of the osteoclast-like giant cells?

. Doxorubicin
. Denosumab
. Imatinib
. Methotrexate
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL. It prevents RANKL from binding to RANK on the osteoclast-like giant cells, thereby inhibiting their recruitment and bone-resorbing activity, making it highly effective for unresectable GCTs.

Question 374

Topic: Biology, Genetics & Bone Healing

A 70-year-old female on long-term alendronate therapy for osteoporosis presents with atraumatic thigh pain. Radiographs reveal a transverse, non-comminuted fracture of the femoral shaft with localized lateral cortical thickening. Which of the following is an expected histologic or biological feature of this specific type of fracture?

. Hyperactive osteoclast-mediated bone resorption at the fracture site
. Severely suppressed bone turnover with absent osteoclastic remodeling
. Robust cartilaginous callus formation within 2 weeks
. High levels of serum alkaline phosphatase
. A primary defect in type I collagen synthesis

Correct Answer & Explanation

. Severely suppressed bone turnover with absent osteoclastic remodeling

Explanation

Atypical femur fractures associated with bisphosphonate use are characterized by severely suppressed bone turnover. Bisphosphonates inhibit osteoclast function, leading to the accumulation of microdamage, lateral cortical hypertrophy, and eventual failure.

Question 375

Topic: Biology, Genetics & Bone Healing

A 15-year-old boy presents with a painless, bony prominence on the distal medial aspect of his thigh. Radiographs demonstrate a pedunculated osseous lesion pointing away from the joint line with distinct corticomedullary continuity. What is the histologic composition of the cartilaginous cap covering this lesion?

. Fibrocartilage
. Hyaline cartilage
. Elastic cartilage
. Woven bone
. Lamellar bone

Correct Answer & Explanation

. Hyaline cartilage

Explanation

Osteochondromas are developmental lesions characterized by corticomedullary continuity and a cartilaginous cap. The cap is composed of hyaline cartilage, which undergoes endochondral ossification similar to a normal physis.

Question 376

Topic: Biology, Genetics & Bone Healing

A 12-year-old female with a family history of multiple bony deformities is diagnosed with Hereditary Multiple Exostoses (HME). Genetic testing is most likely to reveal a mutation affecting which of the following cellular processes?

. Collagen type I synthesis
. Fibroblast growth factor receptor 3 (FGFR3) signaling
. Heparan sulfate synthesis
. Wnt/beta-catenin signaling
. Matrix metalloproteinase activity

Correct Answer & Explanation

. Heparan sulfate synthesis

Explanation

HME is an autosomal dominant condition typically caused by mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for heparan sulfate synthesis, leading to abnormal chondrocyte proliferation.

Question 377

Topic: Biology, Genetics & Bone Healing

A 72-year-old female on long-term alendronate therapy sustains a low-energy, transverse subtrochanteric femur fracture with a medial cortical spike. What is the primary cellular mechanism by which bisphosphonates increase the risk of this specific atypical fracture pattern?

. Stimulation of osteoblast-mediated woven bone formation
. Direct inhibition of osteocyte apoptosis
. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Reduction of parathyroid hormone secretion
. Inhibition of the RANKL pathway

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate synthase in the mevalonate pathway, leading to osteoclast apoptosis and profound suppression of bone remodeling. Over time, this allows microdamage accumulation, leading to atypical femur fractures.

Question 378

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic, epiphyseal lesion of the proximal tibia extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor. Prior to joint-sparing curettage, she is given a medication that targets the RANKL pathway. What is the mechanism of this drug?

. Inhibits osteoblast apoptosis
. Monoclonal antibody against RANKL preventing osteoclast activation
. Directly induces apoptosis of the neoplastic mononuclear cells
. Bisphosphonate that inhibits osteoclast ruffled border formation
. Antagonist of the Wnt/beta-catenin pathway

Correct Answer & Explanation

. Monoclonal antibody against 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 their precursors. In Giant Cell Tumors, this reduces osteoclast-mediated bone destruction and helps ossify the tumor margins to facilitate curettage.

Question 379

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy reveals mononuclear cells and multinucleated giant cells. Which of the following describes the mechanism of action of the targeted biologic therapy commonly used for this condition?

. Inhibits vascular endothelial growth factor (VEGF)
. Binds to and inhibits RANK ligand (RANKL)
. Blocks the mammalian target of rapamycin (mTOR)
. Acts as an antagonist to the estrogen receptor
. Inhibits platelet-derived growth factor receptor (PDGFR)

Correct Answer & Explanation

. Binds to and inhibits RANK ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing the activation of osteoclast-like giant cells by the neoplastic mononuclear stromal cells in Giant Cell Tumor of Bone. This leads to tumor necrosis and woven bone formation.

Question 380

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion in the distal femur without a sclerotic rim. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, denosumab acts by directly inhibiting which of the following?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Vascular endothelial growth factor (VEGF)
. Tumor necrosis factor alpha (TNF-alpha)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from interacting with RANK on the surface of osteoclasts and osteoclast precursors. This inhibits the recruitment and activation of the multinucleated giant cells characteristic of this tumor.

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