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Biology, Genetics & Bone Healing MCQs

Practice Set 157 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 3121

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft or graft substitute materials unequivocally possesses osteoconductive, osteoinductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous autograft
. Cortical allograft
. Bone morphogenetic protein-2 (BMP-2)
. Calcium phosphate cement

Correct Answer & Explanation

. Cancellous autograft

Explanation

Cancellous autograft is the gold standard because it provides all three properties: live cells for osteogenesis, growth factors for osteoinduction, and a scaffold for osteoconduction. Products like DBM are osteoinductive and osteoconductive, but lack live cells.

Question 3122

Topic: Biology, Genetics & Bone Healing

A patient with chronic kidney disease presents with diffuse bone pain and osteodystrophy. Laboratory results show hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH). What is the primary biochemical defect causing hypocalcemia in this patient?

. Decreased production of calcitonin
. Excessive urinary calcium loss
. Impaired 1-alpha-hydroxylase activity
. Overproduction of osteoprotegerin
. Primary hyperparathyroidism

Correct Answer & Explanation

. Impaired 1-alpha-hydroxylase activity

Explanation

In chronic kidney disease, the failing kidneys cannot produce 1-alpha-hydroxylase, which is required to convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D. This leads to impaired intestinal calcium absorption and secondary hyperparathyroidism.

Question 3123

Topic: Biology, Genetics & Bone Healing

In the incorporation of a cortical bone allograft, which of the following best describes the physiological process of creeping substitution?

. Osteoblasts synthesize new woven bone prior to any osteoclastic activity.
. Osteoclastic resorption is coupled with simultaneous osteoblastic bone formation.
. Inflammation leads to the direct transformation of fibrous tissue into lamellar bone.
. Complete allograft resorption occurs universally before any new bone formation begins.
. Chondrocytes proliferate and undergo endochondral ossification within the graft.

Correct Answer & Explanation

. Osteoclastic resorption is coupled with simultaneous osteoblastic bone formation.

Explanation

Creeping substitution is the process by which cortical bone grafts are incorporated. It involves osteoclastic resorption through cutting cones followed by osteoblastic bone formation, which can initially weaken the structural integrity of the graft.

Question 3124

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of a BMP to its cell surface receptor, which intracellular signaling proteins are directly phosphorylated to translocate to the nucleus and regulate gene expression?

. Janus kinases (JAK)
. Signal Transducers and Activators of Transcription (STAT)
. Smad proteins
. Wnt/beta-catenin
. Nuclear factor kappa B (NF-kB)

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs belong to the TGF-beta superfamily and signal through serine/threonine kinase receptors. Upon binding, they induce phosphorylation of intracellular Smad proteins (primarily Smad 1, 5, and 8), which then translocate to the nucleus.

Question 3125

Topic: Biology, Genetics & Bone Healing

Perren's strain theory dictates the type of tissue that can form in a fracture gap based on the mechanical environment. What is the maximum tissue strain tolerated by the formation of lamellar bone?

. Less than 2%
. Up to 10%
. Up to 20%
. Up to 50%
. Up to 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, lamellar bone can only form under very low strain conditions (less than 2%). Granulation tissue can tolerate up to 100% strain, and cartilage can tolerate up to 10% strain.

Question 3126

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient with untreated celiac disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low normal serum calcium, low phosphorus, high alkaline phosphatase, and elevated parathyroid hormone. What is the most likely diagnosis?

. Paget's disease of bone
. Primary hyperparathyroidism
. Osteomalacia
. Osteoporosis
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

Osteomalacia is characterized by impaired mineralization of osteoid, frequently due to vitamin D deficiency secondary to malabsorption. This leads to secondary hyperparathyroidism, resulting in low or normal calcium, low phosphorus, and elevated alkaline phosphatase.

Question 3127

Topic: Biology, Genetics & Bone Healing

A 35-year-old male undergoes locked intramedullary nailing for a transverse midshaft femur fracture. During the initial 4 weeks of healing, the construct allows for a specific amount of interfragmentary strain that promotes cartilaginous callus formation. According to Perren's strain theory, what range of strain best promotes secondary bone healing via endochondral ossification?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. 2% to 10%

Explanation

According to Perren's strain theory, the type of tissue that forms at a fracture site is dependent on the strain it can tolerate. Woven bone can tolerate up to 2% strain (promoting primary bone healing without callus), cartilage can tolerate up to 10% strain (promoting secondary bone healing via endochondral ossification), and granulation tissue can tolerate up to 100% strain. A strain of 2-10% favors cartilaginous callus formation.

Question 3128

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with a progressive bowing deformity of his tibia and increasing local warmth over the bone. Radiographs reveal cortical thickening and coarsened trabeculae. A biopsy is obtained. Which histologic finding is considered pathognomonic for the mixed phase of this disease?

. Extensive osteoid seams with a lack of mineralization
. Granulomas containing multinucleated giant cells
. Woven bone completely lacking osteocytes
. Empty lacunae with surrounding necrotic marrow
. Mosaic pattern of lamellar bone with prominent cement lines

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

The patient has Paget's disease of bone (osteitis deformans). The disease has three phases: lytic, mixed, and sclerotic. In the mixed phase, there is rapid, chaotic bone turnover characterized histologically by a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent cement lines due to irregular periods of bone resorption and formation.

Question 3129

Topic: Biology, Genetics & Bone Healing
A 7-year-old child presents with gingival bleeding, petechiae, and progressively worsening joint pain. Radiographs show a distinct radiolucent line proximal to the metaphysis (Trümmerfeld zone) and a dense zone of provisional calcification. This condition impairs bone formation primarily due to a defect in which of the following cellular processes?
. Cleavage of procollagen into tropocollagen
. Cross-linking of collagen fibers by lysyl oxidase
. Hydroxylation of proline and lysine residues
. Intracellular triple helix formation
. Mineralization of the osteoid matrix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The child is exhibiting signs of scurvy, caused by Vitamin C deficiency. Vitamin C (ascorbic acid) is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without it, the hydroxylation of proline and lysine residues on procollagen alpha chains cannot occur, leading to defective triple helix formation and structurally unstable collagen.

Question 3130

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is started on denosumab therapy. Which of the following best describes the molecular mechanism of action of this drug?

. Binds to RANKL, preventing its interaction with RANK
. Binds to RANK, preventing its interaction with RANKL
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Stimulates osteoblast differentiation via the Wnt/beta-catenin pathway
. Acts as a recombinant parathyroid hormone analog

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with RANK

Explanation

Denosumab is a fully human monoclonal antibody that directly targets and binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclasts and their precursors, thereby profoundly inhibiting osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

Question 3131

Topic: Biology, Genetics & Bone Healing

Histologically, the 'cutting cone' is a highly coordinated functional unit composed of an advancing front of osteoclasts followed by a trail of osteoblasts laying down new osteoid. This structure is the primary physiological mechanism for which of the following processes?

. Primary (haversian) bone remodeling
. Endochondral ossification
. Intramembranous ossification
. Secondary callus formation
. Hematoma organization

Correct Answer & Explanation

. Primary (haversian) bone remodeling

Explanation

The cutting cone is the functional unit of primary (haversian) bone remodeling in cortical bone. Osteoclasts at the leading edge resorb a tunnel of old bone, and osteoblasts trail behind to deposit new osteoid concentrically, eventually forming a new osteon (Haversian system). This process is seen in physiologic remodeling and in primary bone healing where rigid internal fixation allows direct bone repair without callus formation.

Question 3132

Topic: Biology, Genetics & Bone Healing

During a spinal fusion surgery, the surgeon requires a bone graft. Which of the following graft options uniquely provides osteoconductive, osteoinductive, AND osteogenic properties?

. Iliac crest autograft
. Demineralized bone matrix (DBM)
. Cancellous allograft
. Calcium phosphate cement
. Recombinant BMP-2

Correct Answer & Explanation

. Iliac crest autograft

Explanation

Autogenous bone graft (autograft), typically harvested from the iliac crest, is considered the gold standard because it provides all three properties essential for bone formation: osteoconduction (a scaffold), osteoinduction (growth factors like BMPs to stimulate progenitor cells), and osteogenesis (live osteoblasts and mesenchymal stem cells). Allografts and DBM lack live cells (osteogenesis). Synthetic matrices are typically only osteoconductive.

Question 3133

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is diagnosed with an expansile, lytic lesion in the distal femur. Biopsy reveals mononuclear cells and multinucleated giant cells. Which of the following best describes the mechanism of action of the targeted medical therapy for this lesion?

. Inhibits RANK ligand (RANKL), preventing osteoclast formation
. Binds directly to RANK on osteoclasts, inducing apoptosis
. Inhibits vascular endothelial growth factor (VEGF), reducing tumor angiogenesis
. Cross-links DNA, preventing tumor cell replication
. Activates the Wnt/beta-catenin pathway, stimulating osteoblastic differentiation

Correct Answer & Explanation

. Inhibits RANK ligand (RANKL), preventing osteoclast formation

Explanation

Denosumab is highly effective for Giant Cell Tumor (GCT) of bone. It is a monoclonal antibody that binds to RANKL (produced by the neoplastic mononuclear stromal cells), preventing it from binding to RANK on the normal osteoclast-like giant cells. This inhibits the maturation and activity of osteoclasts, leading to massive ossification of the tumor.

Question 3134

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is prescribed teriparatide for the treatment of severe osteoporosis. Which of the following best describes its mechanism of action?

. Recombinant PTH analogue that stimulates osteoblast activity
. Inhibits osteoclast ruffled border formation
. Monoclonal antibody against RANKL
. Inhibitor of the Wnt/beta-catenin pathway
. Sclerostin inhibitor

Correct Answer & Explanation

. Recombinant PTH analogue that stimulates osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it acts as an anabolic agent by strongly stimulating osteoblast activity over osteoclast activity.

Question 3135

Topic: Biology, Genetics & Bone Healing

Which of the following cytokines is the primary stimulator of osteoclastogenesis and acts by directly binding to receptors on the surface of osteoclast precursors?

. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Interleukin-10 (IL-10)
. Transforming growth factor-beta (TGF-beta)
. RANKL

Correct Answer & Explanation

. RANKL

Explanation

RANKL is secreted by osteoblasts and binds to the RANK receptor on osteoclast precursors, stimulating their differentiation, fusion, and activation. Osteoprotegerin (OPG) acts as a decoy receptor to bind RANKL and inhibit this process.

Question 3136

Topic: Biology, Genetics & Bone Healing

In cortical bone healing following rigid plate fixation with absolute stability, primary bone healing occurs without cartilaginous callus formation. Which of the following is the key cellular mechanism driving this process?

. Endochondral ossification
. Intramembranous ossification
. Cutting cones crossing the fracture site
. Chondrocyte hypertrophy and apoptosis
. Mesenchymal stem cell differentiation into osteoblasts

Correct Answer & Explanation

. Cutting cones crossing the fracture site

Explanation

Primary bone healing occurs via Haversian remodeling, where osteoclasts at the head of cutting cones cross the fracture site, followed by osteoblasts laying down new bone. This requires absolute stability and direct bone-to-bone contact.

Question 3137

Topic: Biology, Genetics & Bone Healing

Articular cartilage derives its compressive stiffness primarily from the interaction between water and which of the following macromolecular structures?

. Type II collagen
. Type I collagen
. Aggrecan
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a major proteoglycan in articular cartilage, contains highly negatively charged glycosaminoglycan chains that draw in water via Donnan osmotic pressure. This swelling pressure is resisted by the Type II collagen network, providing compressive stiffness.

Question 3138

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman with a history of Roux-en-Y gastric bypass presents with generalized bone pain and a Looser zone on pelvic radiographs. Which of the following laboratory profiles is most consistent with her underlying metabolic bone disease?

. Normal Calcium, Normal Phosphate, Normal ALP
. Low Calcium, Low Phosphate, High ALP
. High Calcium, Low Phosphate, High ALP
. Normal Calcium, High Phosphate, High ALP
. Low Calcium, High Phosphate, Low ALP

Correct Answer & Explanation

. Low Calcium, Low Phosphate, High ALP

Explanation

The patient has osteomalacia secondary to vitamin D deficiency from malabsorption. This typically presents with low or low-normal calcium, low phosphate (due to secondary hyperparathyroidism), and elevated alkaline phosphatase (ALP).

Question 3139

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates are frequently used in the management of osteoporosis. What is the primary intracellular mechanism of action of these medications?

. Inhibition of cathepsin K
. Inhibition of farnesyl pyrophosphate synthase
. Activation of the Wnt/beta-catenin pathway
. Binding to RANK ligand
. Stimulation of osteoprotegerin production

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

Question 3140

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedics as a bone graft substitute. Which of the following combinations of properties best describes DBM?

. Osteogenic and osteoconductive
. Osteoinductive and osteoconductive
. Osteogenic and osteoinductive
. Purely osteoinductive
. Purely osteoconductive

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) provides a collagen scaffold (osteoconductive) and retains bone morphogenetic proteins (BMPs) that stimulate local cells to form bone (osteoinductive). It lacks live cells, meaning it is not osteogenic.

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