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Biology, Genetics & Bone Healing MCQs

Practice Set 167 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 3321

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of bone healing when absolute stability is achieved with a lag screw and neutralization plate?

. Endochondral ossification
. Intramembranous ossification
. Cutting cone remodeling (Haversian remodeling)
. Callus formation via chondrocyte hypertrophy
. Fibrous tissue conversion to bone

Correct Answer & Explanation

. Cutting cone remodeling (Haversian remodeling)

Explanation

Absolute stability (strain < 2%) leads to primary bone healing, which occurs via Haversian remodeling (cutting cones) crossing the fracture site. There is no visible callus (which is characteristic of endochondral ossification/secondary healing).

Question 3322

Topic: Biology, Genetics & Bone Healing

What is the mechanism of action of denosumab in the treatment of osteoporosis?

. Inhibition of farnesyl pyrophosphate synthase
. Direct stimulation of osteoblast proliferation
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Selective estrogen receptor modulation
. Recombinant PTH analogue stimulating bone formation

Correct Answer & Explanation

. Monoclonal antibody against RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with RANK on osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

Question 3323

Topic: Biology, Genetics & Bone Healing
Which collagen type is the most abundant in normal bone matrix?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen accounts for about 90% of the organic matrix of bone. Type II is found in articular cartilage. Type III is found in skin, blood vessels, and early fracture callus. Type X is found in the hypertrophic zone of the physis.

Question 3324

Topic: Biology, Genetics & Bone Healing

A 45-year-old malnourished patient presents with bleeding gums, petechiae, and joint pain. A deficiency in which of the following vitamins is responsible for this condition, and what is its role in collagen synthesis?

. Vitamin D; mineralization of osteoid
. Vitamin K; gamma-carboxylation of osteocalcin
. Vitamin A; osteoclast function
. Vitamin C; hydroxylation of proline and lysine residues
. Vitamin E; antioxidant protection of cell membranes

Correct Answer & Explanation

. Vitamin C; hydroxylation of proline and lysine residues

Explanation

Scurvy is caused by Vitamin C deficiency. Vitamin C (ascorbic acid) is a required cofactor for prolyl hydroxylase and lysyl hydroxylase, which hydroxylate proline and lysine residues in procollagen. This step is essential for the stable triple-helix formation of collagen.

Question 3325

Topic: Biology, Genetics & Bone Healing

Which of the following cytokines is most strongly implicated as an osteoclast activating factor in the pathogenesis of lytic bone lesions in multiple myeloma?

. Interleukin-1 (IL-1)
. Interleukin-6 (IL-6)
. Tumor necrosis factor-alpha (TNF-a)
. Transforming growth factor-beta (TGF-b)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Interleukin-6 (IL-6)

Explanation

Interleukin-6 (IL-6) is a critical cytokine in multiple myeloma. It acts as a potent osteoclast-activating factor and also promotes the growth and survival of myeloma cells, leading to characteristic lytic bone lesions.

Question 3326

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and anterior bowing of the tibiae. Laboratory evaluation is most likely to show which of the following?

. Elevated serum calcium, decreased phosphorus, elevated alkaline phosphatase
. Normal serum calcium, normal phosphorus, elevated alkaline phosphatase
. Decreased serum calcium, decreased phosphorus, elevated alkaline phosphatase
. Normal serum calcium, elevated phosphorus, elevated acid phosphatase
. Elevated serum calcium, elevated phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Normal serum calcium, normal phosphorus, elevated alkaline phosphatase

Explanation

The patient has Paget's disease of bone (osteitis deformans). In Paget's disease, there is disorganized bone remodeling, leading to markedly elevated alkaline phosphatase, but serum calcium and phosphorus levels typically remain normal.

Question 3327

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) initiate intracellular signaling primarily through which of the following pathways?

. cAMP/PKA pathway
. JAK/STAT pathway
. Smad pathway
. MAPK/ERK pathway
. Wnt/beta-catenin pathway

Correct Answer & Explanation

. Smad pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase cell surface receptors, which phosphorylate intracellular Smad proteins (typically Smad 1, 5, and 8). The phosphorylated Smads complex with Smad 4 and translocate to the nucleus to regulate gene transcription.

Question 3328

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with multiple fractures and a 'rugger-jersey' spine appearance on radiographs. Labs show normal calcium, normal phosphorus, and elevated acid phosphatase. Which of the following is the underlying molecular defect most commonly associated with this condition?

. Defect in type I collagen synthesis
. Mutation in the PHEX gene
. Deficiency of carbonic anhydrase II
. Overactivity of fibroblast growth factor receptor 3 (FGFR3)
. Mutation in the COMP gene

Correct Answer & Explanation

. Deficiency of carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, leading to dense, brittle bones and a 'rugger-jersey' spine. A common mutation is a deficiency in carbonic anhydrase II, which normally produces the acidic environment required for osteoclasts to resorb bone.

Question 3329

Topic: Biology, Genetics & Bone Healing

A 4-year-old girl is evaluated for bowing of the legs. Laboratory evaluation reveals normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the most appropriate medical treatment for this patient?

. High-dose Vitamin D supplementation only
. Calcitonin and bisphosphonates
. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)
. Recombinant human growth hormone
. Dietary calcium supplementation

Correct Answer & Explanation

. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)

Explanation

The patient has X-linked hypophosphatemic rickets (XLHR), caused by a PHEX mutation leading to elevated FGF-23, which wastes phosphate in the kidneys. The classic treatment requires oral phosphate repletion combined with active Vitamin D (calcitriol) to prevent secondary hyperparathyroidism. Burosumab is a newer specific therapy, but among standard options, phosphate plus calcitriol is correct.

Question 3330

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute in spine fusion surgery. Which of the following best describes the biological properties of DBM?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteogenic and osteoconductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a structural scaffold (osteoconductive) and contains retained bone morphogenetic proteins (BMPs) that stimulate bone formation (osteoinductive). Because it is sterilized and processed, it lacks live cells, so it is not osteogenic. Autograft is the only graft type that possesses all three properties.

Question 3331

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction and fracture healing. They act by binding to specific cell-surface receptors. Which of the following describes the primary intracellular signaling pathway activated directly by BMPs?

. Tyrosine kinase auto-phosphorylation leading to MAP kinase activation
. G-protein coupled receptor activation leading to cAMP production
. Serine/threonine kinase receptor activation leading to Smad 1, 5, and 8 phosphorylation
. Wnt binding to Frizzled receptors causing beta-catenin accumulation
. JAK/STAT pathway activation via cytokine receptors

Correct Answer & Explanation

. Serine/threonine kinase receptor activation leading to Smad 1, 5, and 8 phosphorylation

Explanation

BMPs belong to the TGF-beta superfamily. They bind to Type I and Type II serine/threonine kinase receptors. Upon binding, these receptors phosphorylate receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These subsequently complex with Co-Smad (Smad 4) and translocate to the nucleus to initiate osteogenic gene transcription.

Question 3332

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe bowing of the lower extremities. Laboratory tests reveal normal serum calcium, abnormally low serum phosphate, and elevated alkaline phosphatase. Genetic testing identifies a mutation in the PHEX gene. Which of the following best describes the pathophysiology of this condition?

. Decreased renal production of 1,25-dihydroxyvitamin D
. Impaired intestinal absorption of calcium
. Overproduction of FGF23 leading to renal phosphate wasting
. Defect in type I collagen synthesis
. Deficient mineralization of the growth plate due to PTH resistance

Correct Answer & Explanation

. Overproduction of FGF23 leading to renal phosphate wasting

Explanation

The patient has X-linked hypophosphatemic rickets (XLHR), the most common form of heritable rickets. A mutation in the PHEX gene leads to decreased degradation and subsequent overproduction of Fibroblast Growth Factor 23 (FGF23). Elevated FGF23 decreases renal tubular reabsorption of phosphate (causing phosphate wasting) and inhibits 1-alpha-hydroxylase, decreasing active Vitamin D levels.

Question 3333

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, purely lytic lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy shows multinucleated giant cells in a stroma of mononuclear cells. The mononuclear cells express which of the following crucial factors driving the pathogenesis of this tumor?

. RANKL
. Osteoprotegerin (OPG)
. FGF-23
. PTHrP
. Vascular Endothelial Growth Factor (VEGF)

Correct Answer & Explanation

. RANKL

Explanation

In a giant cell tumor (GCT) of bone, the true neoplastic cells are the mononuclear stromal cells. These cells overexpress Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which binds to RANK on osteoclast precursors, recruiting and activating the multinucleated, reactive osteoclast-like giant cells that cause bone resorption. This is the mechanism targeted by Denosumab.

Question 3334

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with deep, aching thigh pain and reports that his hat size has increased over the past few years. Radiographs of the femur reveal cortical thickening, coarsened trabeculae, and a prominent bowing deformity. Histological examination of the affected bone would most likely demonstrate which of the following findings?

. A mosaic pattern of lamellar bone with prominent cement lines
. Extensive replacement of bone marrow by uniform plasma cells
. Disorganized whorls of fibroblastic stroma with woven bone lacking osteoblastic rimming
. Sheets of Langerhans cells with eosinophils
. Empty lacunae with surrounding necrotic marrow

Correct Answer & Explanation

. A mosaic pattern of lamellar bone with prominent cement lines

Explanation

The clinical picture is classic for Paget's disease of bone (osteitis deformans). The hallmark histological finding is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone created by prominent, haphazard cement lines due to erratic and uncoupled osteoclast resorption and subsequent frantic osteoblast bone formation.

Question 3335

Topic: Biology, Genetics & Bone Healing

A 72-year-old man presents with increasing head size (reports needing a larger hat) and deep aching bone pain in his right femur. Laboratory testing shows a significantly elevated alkaline phosphatase but normal calcium and phosphorus. Histological examination of the bone is most likely to show:

. Woven bone with empty lacunae
. Mosaic pattern of lamellar bone with prominent cement lines
. Thickened osteoid seams with poor mineralization
. Sheets of plasma cells with clock-face nuclei
. Proliferation of giant cells in a stroma of mononuclear cells

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

Paget disease (osteitis deformans) is characterized by increased, disorganized bone turnover. The hallmark histologic finding is a 'mosaic pattern' of lamellar bone with irregular, prominent cement lines indicating haphazard bone resorption and formation.

Question 3336

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis and multiple vertebral compression fractures is started on teriparatide. Which of the following best describes the mechanism of action of this medication?

. Inhibits osteoclast activity via RANKL binding
. Stimulates bone formation through intermittent PTH receptor activation
. Inhibits farnesyl pyrophosphate synthase in osteoclasts
. Selective estrogen receptor modulation
. Neutralizes sclerostin to promote Wnt signaling

Correct Answer & Explanation

. Stimulates bone formation through intermittent PTH receptor activation

Explanation

Teriparatide is a recombinant parathyroid hormone (PTH 1-34) analog. When administered intermittently (daily subcutaneous injection), it has an anabolic effect, directly stimulating osteoblastic bone formation. Continuous endogenous PTH, however, leads to bone resorption. Bisphosphonates inhibit farnesyl pyrophosphate synthase, and denosumab binds RANKL.

Question 3337

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain and muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). Radiographs show pseudofractures (Looser zones) in the femoral neck. What is the most likely diagnosis?

. Primary hyperparathyroidism
. Osteoporosis
. Osteomalacia
. Paget disease
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

The clinical and laboratory profile (low calcium, low phosphate, high ALP, high PTH) along with Looser zones (pseudofractures) is classic for osteomalacia, typically due to severe vitamin D deficiency. Secondary hyperparathyroidism occurs as a physiological response to the hypocalcemia.

Question 3338

Topic: Biology, Genetics & Bone Healing
A midshaft tibia fracture is treated with a cast. Callus formation is noted on radiographs at 4 weeks. Which type of collagen is the predominant structural component of the soft callus prior to its replacement by woven bone?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Secondary bone healing occurs via endochondral ossification. During the soft callus phase, chondrocytes produce a cartilaginous matrix predominantly composed of Type II collagen. This is subsequently replaced by woven bone (Type I collagen) during the hard callus phase.

Question 3339

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femur extending to the subchondral bone without a sclerotic margin. Biopsy reveals multinucleated giant cells interspersed among mononuclear stromal cells. Denosumab is considered for treatment. What is the molecular target of this medication in this specific tumor?

. RANK receptor on the giant cells
. RANKL produced by the mononuclear stromal cells
. Osteoprotegerin (OPG) in the surrounding matrix
. Vascular endothelial growth factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. RANKL produced by the mononuclear stromal cells

Explanation

In Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which produce copious amounts of RANK Ligand (RANKL). This RANKL recruits normal macrophages and induces their fusion into osteoclast-like multinucleated giant cells. Denosumab binds and inhibits RANKL produced by the stromal cells.

Question 3340

Topic: Biology, Genetics & Bone Healing

The ruffled border of osteoclasts represents the highly folded cell membrane where active bone resorption takes place. Which of the following is primarily responsible for the active acidification of the resorption lacuna at this site?

. Na+/K+ ATPase pump
. Voltage-gated calcium channels
. Carbonic anhydrase II
. Vacuolar-type H+ ATPase (V-ATPase)
. Cathepsin K

Correct Answer & Explanation

. Vacuolar-type H+ ATPase (V-ATPase)

Explanation

Acidification of the resorption pit (Howship's lacuna) is essential for bone resorption. This is primarily achieved by the vacuolar-type H+ ATPase (V-ATPase) proton pump located heavily on the ruffled border. Carbonic anhydrase II generates the protons intracellularly, but the V-ATPase actively pumps them into the lacuna. Cathepsin K is a lysosomal enzyme that degrades the organic matrix (type I collagen) once the mineral is dissolved by the acidic environment.

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