Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 177 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 3521

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological treatment for preventing skeletal-related events in patients with giant cell tumor of bone and metastatic bone disease. It exerts its effect by binding directly to which of the following targets?

. Receptor activator of nuclear factor kappa-B (RANK)
. Osteoprotegerin (OPG)
. Cathepsin K
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Sclerostin

Correct Answer & Explanation

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

Explanation

Denosumab is a human monoclonal antibody that specifically binds to and inhibits RANKL. By neutralizing RANKL, it prevents the interaction with RANK receptors on osteoclasts, severely impairing osteoclast formation, function, and survival.

Question 3522

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, primary (contact) bone healing via cutting cones requires which of the following mechanical environments?

. Absolute stability with local tissue strain less than 2%
. Relative stability with local tissue strain between 2% and 10%
. Absolute stability with local tissue strain between 2% and 10%
. Relative stability with local tissue strain less than 2%
. High strain environment greater than 10% promoting initial callus formation

Correct Answer & Explanation

. Absolute stability with local tissue strain less than 2%

Explanation

Primary bone healing occurs without callus formation and relies on direct Haversian remodeling (cutting cones). This biologic process can only occur under conditions of absolute stability, requiring an interfragmentary strain of less than 2%.

Question 3523

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) induce bone formation primarily by signaling through which of the following intracellular pathways?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. JAK/STAT pathway
. Smad 1/5/8 pathway
. cAMP/PKA pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate and activate intracellular Smad proteins (specifically Smad 1, 5, and 8). These form a complex to enter the nucleus and regulate transcription of osteogenic genes.

Question 3524

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size and bilateral thigh pain. Laboratory studies show markedly elevated alkaline phosphatase with normal calcium and phosphorus. What is the primary cellular defect in this condition?

. Impaired osteoid mineralization
. Hyperactive, multinucleated osteoclasts
. Decreased osteoblastic bone formation
. Defective Type I collagen synthesis
. Parathyroid adenoma

Correct Answer & Explanation

. Hyperactive, multinucleated osteoclasts

Explanation

Paget disease of bone is driven by primary hyperactive, multinucleated osteoclasts leading to chaotic bone resorption. This is followed by disorganized osteoblastic bone formation, resulting in weak woven bone.

Question 3525

Topic: Biology, Genetics & Bone Healing

A 70-year-old female presents with severe back pain and a purely lytic lesion in the L3 vertebral body. Laboratory tests show anemia and hypercalcemia. Which of the following mechanisms is responsible for the bone destruction in this disease?

. Direct tumor cell phagocytosis of bone
. Osteoblast inhibition via decreased Wnt signaling
. Secretion of osteoclast-activating factors (e.g., RANKL) by myeloma cells
. Ectopic parathyroid hormone (PTH) secretion
. Defective osteoid mineralization due to Bence Jones proteins

Correct Answer & Explanation

. Secretion of osteoclast-activating factors (e.g., RANKL) by myeloma cells

Explanation

Multiple myeloma cells secrete osteoclast-activating factors such as RANKL, MIP-1 alpha, and IL-6, which stimulate rampant osteoclastic bone resorption. Concurrently, they inhibit osteoblast activity, resulting in purely lytic bone lesions.

Question 3526

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with a 12-year history of alendronate use presents with sudden onset thigh pain after a minor misstep. Radiographs demonstrate lateral cortical thickening and a transverse fracture with a medial spike in the subtrochanteric region. What is the primary pathophysiologic mechanism of this specific fracture type?

. Osteoclast overactivity
. Severe generalized osteopenia
. Suppression of targeted bone remodeling
. Hyperparathyroidism
. Vitamin D deficiency

Correct Answer & Explanation

. Suppression of targeted bone remodeling

Explanation

Long-term bisphosphonate use heavily suppresses osteoclast function, leading to a suppression of targeted bone remodeling. This prevents the normal repair of skeletal microdamage, resulting in the accumulation of microcracks and eventual atypical femur fractures.

Question 3527

Topic: Biology, Genetics & Bone Healing

When a diaphyseal fracture is treated with an interfragmentary lag screw and a neutralization plate to achieve absolute stability, which mode of bone healing predominates?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Robust callus formation
. Chondrogenesis

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability virtually eliminates interfragmentary strain, bypassing the callus formation phase. The fracture heals via primary (Haversian) bone healing, utilizing cutting cones composed of osteoclasts followed by osteoblasts to directly bridge the fracture.

Question 3528

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism by which Denosumab inhibits bone resorption in the treatment of osteoporosis?

. Binding to the RANK receptor on osteoclasts
. Inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway
. Binding to RANKL and preventing its interaction with RANK
. Stimulating the production of osteoprotegerin (OPG) by osteoblasts
. Directly inducing apoptosis of mature osteoclasts

Correct Answer & Explanation

. Binding to RANKL and preventing its interaction with RANK

Explanation

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

Question 3529

Topic: Biology, Genetics & Bone Healing

Absolute stability constructs, such as a compression plate for a transverse radius fracture, promote which type of bone healing?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Callus formation
. Fibrous union

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability (rigid fixation with compression and no interfragmentary motion) eliminates the strain necessary to stimulate callus formation, promoting primary bone healing. This occurs via direct Haversian remodeling (cutting cones), where osteoclasts cross the fracture line followed by osteoblasts laying down new lamellar bone.

Question 3530

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. Which of the following properties does DBM inherently possess?

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

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) contains bone morphogenetic proteins (BMPs) exposed during the demineralization process, making it osteoinductive (can stimulate local mesenchymal stem cells to differentiate into osteoblasts). It also provides a scaffold for new bone growth, making it osteoconductive. It contains no living cells, so it is not osteogenic.

Question 3531

Topic: Biology, Genetics & Bone Healing

A 7-year-old child presents with gingival bleeding, petechiae, and diffuse bone pain. Radiographs reveal generalized osteopenia and widened, dense zones of provisional calcification. The underlying nutritional deficiency impairs bone formation by disrupting which of the following cellular processes?

. Cleavage of procollagen C-terminal propeptides
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen by lysyl oxidase
. Glycosylation of hydroxylysine
. Extracellular assembly of the collagen triple helix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The clinical picture describes scurvy, caused by Vitamin C deficiency. Vitamin C (ascorbic acid) is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase, the enzymes responsible for the hydroxylation of proline and lysine residues in procollagen. Without this, the collagen triple helix cannot form stable hydrogen bonds.

Question 3532

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with increasing hat size, hearing loss, and bowing of his tibiae. Serum alkaline phosphatase is markedly elevated, but calcium and phosphate are normal. Genetic testing is most likely to reveal a mutation in which of the following genes, known to play a critical role in RANK-NF-kB signaling?

. FGFR3
. COMP
. SQSTM1
. RUNX2
. COL1A1

Correct Answer & Explanation

. SQSTM1

Explanation

The patient has Paget's disease of bone. Up to 50% of familial cases and 10-20% of sporadic cases of Paget's disease are associated with mutations in the SQSTM1 gene, which encodes the p62 protein. This mutation results in osteoclast overactivity via enhanced RANK-NF-kB signaling.

Question 3533

Topic: Biology, Genetics & Bone Healing

The biological incorporation of a massive cortical bone allograft used in tumor reconstruction relies primarily on the process of 'creeping substitution'. Which of the following sequences best characterizes this process?

. Simultaneous surface apposition of new bone without prior resorption
. Osteoclasts leading cutting cones followed sequentially by osteoblastic bone deposition
. Rapid endochondral ossification originating from host marrow elements
. Intramembranous ossification independent of osteoclastic activity
. Osteoblastic woven bone formation followed by osteoclastic remodeling

Correct Answer & Explanation

. Osteoclasts leading cutting cones followed sequentially by osteoblastic bone deposition

Explanation

Cortical bone grafts incorporate via creeping substitution, which is identical to normal Haversian remodeling. This process involves osteoclasts forming a 'cutting cone' to resorb the dead allograft bone, followed by trailing osteoblasts that lay down new host bone in the cavities created.

Question 3534

Topic: Biology, Genetics & Bone Healing

External beam radiation therapy is an effective prophylactic treatment for heterotopic ossification (HO) following total hip arthroplasty. What is the primary biological mechanism of action of radiation therapy in this setting?

. Inhibition of osteoclast function and survival
. Apoptosis of mature, bone-forming osteoblasts
. Inhibition of proliferation and differentiation of pluripotent mesenchymal stem cells
. Denaturation of endogenous bone morphogenetic proteins (BMPs)
. Upregulation of sclerostin production by local osteocytes

Correct Answer & Explanation

. Inhibition of proliferation and differentiation of pluripotent mesenchymal stem cells

Explanation

Heterotopic ossification prophylaxis with low-dose radiation (typically 700 cGy in a single fraction) works by inhibiting the rapid proliferation and subsequent differentiation of pluripotent mesenchymal stem cells into osteoprogenitor cells. To be effective, it must be administered within 24 hours prior to surgery or within 48 to 72 hours postoperatively before differentiation has occurred.

Question 3535

Topic: Biology, Genetics & Bone Healing

In primary hyperparathyroidism, chronically elevated levels of parathyroid hormone (PTH) lead to net bone resorption. PTH achieves this primarily by binding directly to cell surface receptors on which of the following cell types?

. Osteocytes
. Osteoclasts
. Osteoblasts
. Chondrocytes
. Macrophages

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoclasts do not possess receptors for parathyroid hormone (PTH). PTH acts primarily on osteoblasts (and osteocytes). When PTH binds to osteoblasts, it stimulates them to increase the expression of RANK Ligand (RANKL) and decrease the expression of osteoprotegerin (OPG). RANKL then binds to RANK on osteoclast precursors, stimulating their differentiation and activation.

Question 3536

Topic: Biology, Genetics & Bone Healing

A 65-year-old postmenopausal woman undergoes dual-energy x-ray absorptiometry (DEXA) screening for osteoporosis. Her lowest T-score is -2.6. According to the World Health Organization (WHO), what is the statistical definition of a T-score of -2.6?

. Her bone mineral density is 2.6 standard deviations below the mean for age-matched and sex-matched controls
. Her bone mineral density is 2.6 standard deviations below the mean for young, healthy adults of the same sex
. Her bone mineral density is 2.6 standard errors below the mean for age-matched and sex-matched controls
. Her bone mineral density is 2.6 standard errors below the mean for young, healthy adults of the same sex
. Her fracture risk is 2.6 times higher than that of a young, healthy adult

Correct Answer & Explanation

. Her bone mineral density is 2.6 standard deviations below the mean for young, healthy adults of the same sex

Explanation

The T-score compares a patient's bone mineral density (BMD) to the optimal peak bone mass of a healthy young adult (typically 30 years old) of the same sex, expressed in standard deviations (SD). A T-score of -2.5 or lower defines osteoporosis. In contrast, the Z-score compares the patient's BMD to an age-matched and sex-matched population.

Question 3537

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Which of the following best describes the specific receptor type and intracellular signaling pathway utilized by BMP-2?

. Tyrosine kinase receptor and JAK/STAT pathway
. Serine/threonine kinase receptor and SMAD pathway
. G-protein coupled receptor and cAMP pathway
. Ion channel receptor and calcium-calmodulin pathway
. Nuclear receptor and Wnt/beta-catenin pathway

Correct Answer & Explanation

. Serine/threonine kinase receptor and SMAD pathway

Explanation

BMPs bind to cell surface serine/threonine kinase receptors. Upon binding, they induce phosphorylation of intracellular SMAD proteins (SMAD 1, 5, and 8), which then complex with SMAD 4 to translocate into the nucleus and regulate gene expression for osteoblast differentiation.

Question 3538

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis (e.g., Ilizarov bone transport) primarily forms new bone via which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional cartilaginous growth
. Physis-mediated elongation
. Creeping substitution

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis, assuming a stable fixator and appropriate distraction rate (typically 1 mm/day), forms new bone primarily through intramembranous ossification under conditions of tension. The bone forms directly from mesenchymal cells without an intermediate cartilage phase.

Question 3539

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in treating advanced or unresectable Giant Cell Tumor (GCT) of bone. What is its exact target and cellular mechanism in the context of GCT?

. Inhibits farnesyl pyrophosphate synthase in reactive osteoclasts
. Binds RANK receptor on multinucleated giant cells
. Binds RANKL expressed by the mononuclear neoplastic stromal cells
. Stimulates osteoprotegerin production by osteoblasts
. Induces direct apoptosis of multinucleated giant cells

Correct Answer & Explanation

. Binds RANKL expressed by the mononuclear neoplastic stromal cells

Explanation

In Giant Cell Tumor of bone, the mononuclear stromal cells are the true neoplastic cells, and they overexpress RANKL. Denosumab is a monoclonal antibody that binds this RANKL, preventing it from recruiting and activating the reactive osteoclast-like giant cells.

Question 3540

Topic: Biology, Genetics & Bone Healing

A pediatric patient with recurrent fractures, cranial nerve palsies, and diffuse bone sclerosis on radiographs is suspected to have osteopetrosis. The most common autosomal recessive form of this disease is linked to a deficiency in which of the following?

. Cathepsin K
. Carbonic anhydrase II
. Type I collagen
. Tissue nonspecific alkaline phosphatase
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is commonly caused by a deficiency in Carbonic Anhydrase II. This enzyme is required for osteoclasts to generate hydrogen ions, which are essential for creating the acidic environment necessary to dissolve bone mineral at the ruffled border.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page