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Biology, Genetics & Bone Healing MCQs

Practice Set 161 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 3201

Topic: Biology, Genetics & Bone Healing

A 40-year-old woman with celiac disease presents with diffuse bone pain and proximal muscle weakness. Radiographs reveal bilateral pseudofractures (Looser zones) in the femoral neck. Which of the following serum laboratory profiles is most consistent with her diagnosis?

. Normal calcium, normal phosphorus, elevated alkaline phosphatase
. Low calcium, low phosphorus, elevated alkaline phosphatase
. Elevated calcium, low phosphorus, elevated alkaline phosphatase
. Normal calcium, elevated phosphorus, normal alkaline phosphatase
. Elevated calcium, elevated phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Low calcium, low phosphorus, elevated alkaline phosphatase

Explanation

The patient has osteomalacia secondary to malabsorption of Vitamin D. This typically presents with low serum calcium, low serum phosphorus (due to secondary hyperparathyroidism), and elevated alkaline phosphatase.

Question 3202

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal-metaphyseal lesion in the proximal tibia extending to the subchondral bone. Biopsy shows multinucleated giant cells. The targeted therapy (denosumab) for this specific tumor inhibits which of the following?

. Vascular endothelial growth factor (VEGF)
. RANK ligand (RANKL)
. Tumor necrosis factor-alpha (TNF-a)
. Bone morphogenetic protein 2 (BMP-2)
. Transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. RANK ligand (RANKL)

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express high levels of RANKL, which recruits and activates the reactive multinucleated osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds and inhibits RANKL, effectively reducing osteoclastic bone destruction.

Question 3203

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with multiple fractures and hepatosplenomegaly. Radiographs reveal diffuse osteosclerosis and a "bone-within-a-bone" appearance. A genetic defect in carbonic anhydrase II is identified. This mutation primarily impairs which of the following cellular functions?

. Osteoblast differentiation from mesenchymal stem cells
. Production of osteoid matrix by osteoblasts
. Acidification of the Howship lacuna by osteoclasts
. Synthesis of Type I collagen
. Mineralization of the epiphyseal plate

Correct Answer & Explanation

. Acidification of the Howship lacuna by osteoclasts

Explanation

Carbonic anhydrase II deficiency causes osteopetrosis by preventing osteoclasts from generating the protons needed to acidify the resorptive pit (Howship lacuna). This leads to defective bone resorption, resulting in overly dense but brittle bones.

Question 3204

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical bone allograft, the process of "creeping substitution" is observed. Which of the following sequences best describes the initial cellular events in this process?

. Osteoblastic bone formation followed by osteoclastic resorption
. Osteoclastic resorption of Haversian canals followed by osteoblastic new bone deposition
. Chondrocyte proliferation followed by endochondral ossification
. Direct membranous ossification without prior resorption
. Fibroblast invasion followed by calcification

Correct Answer & Explanation

. Osteoclastic resorption of Haversian canals followed by osteoblastic new bone deposition

Explanation

Cortical bone grafts incorporate via creeping substitution, an extremely slow process where osteoclasts first resorb the existing Haversian canals. This is immediately followed by osteoblasts laying down new bone within these widened canals.

Question 3205

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which of the following statements regarding secondary bone healing is true?

. Woven bone can form only under conditions of high strain (>10%)
. Callus formation increases interfragmentary strain
. Granulation tissue tolerates up to 100% strain without rupturing
. Absolute stability is required for the formation of an external callus
. Cartilage forms under conditions of absolute zero strain

Correct Answer & Explanation

. Granulation tissue tolerates up to 100% strain without rupturing

Explanation

Perren's strain theory dictates that tissue will only form if the local strain is less than the tissue's tolerance. Granulation tissue can tolerate up to 100% strain, allowing it to initially bridge the fracture gap and stabilize the fragments so stiffer tissues can subsequently form.

Question 3206

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy is evaluated for bowing of the legs and short stature. Laboratory tests show low serum phosphate, normal calcium, normal PTH, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the primary pathophysiologic defect?

. Decreased intestinal absorption of calcium
. Defective mineralization of the organic bone matrix due to vitamin D deficiency
. Decreased renal tubular reabsorption of phosphate driven by excess FGF-23
. Primary hyperparathyroidism
. Inability to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

Correct Answer & Explanation

. Decreased renal tubular reabsorption of phosphate driven by excess FGF-23

Explanation

The patient has X-linked hypophosphatemic rickets caused by a PHEX gene mutation, leading to unchecked elevation of FGF-23 levels. Excess FGF-23 inhibits renal phosphate reabsorption in the proximal tubule, resulting in severe renal phosphate wasting.

Question 3207

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy shows mononuclear cells interspersed with multinucleated giant cells. If pharmacological treatment is indicated, which of the following medications directly targets the pathophysiology of this lesion?

. Bisphosphonates
. Denosumab
. Methotrexate
. Imatinib
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Giant Cell Tumor of Bone is characterized by neoplastic mononuclear stromal cells that express high levels of RANKL, driving the recruitment of reactive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, directly inhibits this essential pathway.

Question 3208

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with hearing loss and increasing hat size. Radiographs show a "cotton wool" appearance of the skull. Which of the following is the primary cellular abnormality initiating this disease process?

. Overactive osteoblasts with disorganized woven bone formation
. Increased number and size of multinucleated osteoclasts
. Defective mineralization of osteoid by osteoblasts
. Deficient type I collagen synthesis
. Autonomous hypersecretion of parathyroid hormone

Correct Answer & Explanation

. Increased number and size of multinucleated osteoclasts

Explanation

Paget's disease is primarily a disorder of osteoclast function, characterized by large, multinucleated osteoclasts leading to massive bone resorption. This is followed by a secondary, disorganized osteoblastic response.

Question 3209

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, at which specific stage does the peak expression of Type II collagen occur?

. Hematoma formation
. Soft callus formation
. Hard callus formation
. Remodeling phase
. Inflammation phase

Correct Answer & Explanation

. Soft callus formation

Explanation

Type II collagen is the primary collagen type found in cartilage and reaches peak expression during the soft callus (chondrogenic) phase of secondary fracture healing. Type I collagen peaks later during hard callus formation.

Question 3210

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with progressive bowing of his lower extremities. Laboratory evaluation reveals profound hypophosphatemia, normal serum calcium, normal PTH, and elevated alkaline phosphatase. Which of the following is the most likely diagnosis?

. Vitamin D-dependent rickets type I
. Nutritional rickets
. X-linked hypophosphatemic rickets
. Osteogenesis imperfecta
. Renal osteodystrophy

Correct Answer & Explanation

. X-linked hypophosphatemic rickets

Explanation

X-linked hypophosphatemic rickets is driven by an excess of FGF-23, leading to severe renal phosphate wasting. This results in isolated hypophosphatemia with classically normal calcium and parathyroid hormone levels.

Question 3211

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman is treated for severe osteoporosis with a targeted medication that directly stimulates osteoblastic bone formation by acting as a recombinant fragment of human parathyroid hormone. Which medication was prescribed?

. Alendronate
. Denosumab
. Teriparatide
. Raloxifene
. Romosozumab

Correct Answer & Explanation

. Teriparatide

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34) that acts as a powerful anabolic agent to directly stimulate new bone formation. Unlike bisphosphonates or denosumab, it builds bone rather than primarily inhibiting resorption.

Question 3212

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft substitutes possesses osteoinductive, osteoconductive, and osteogenic properties?

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

Correct Answer & Explanation

. Cancellous autograft

Explanation

Cancellous autograft is the gold standard because it is the only option that possesses all three properties: osteogenesis (live cells), osteoinduction (growth factors like BMPs), and osteoconduction (trabecular scaffold). Demineralized bone matrix (DBM) is osteoconductive and osteoinductive but lacks live cells, meaning it is not osteogenic.

Question 3213

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive bowing of his right tibia and an increasing hat size. Radiographs show cortical thickening and altered trabecular patterns. What is the primary cellular defect initiating this condition?

. Decreased osteoblast function
. Increased osteoblast function
. Defective mineralization of osteoid
. Increased osteoclast activity with abnormal morphology
. Deficiency of Type I collagen synthesis

Correct Answer & Explanation

. Increased osteoclast activity with abnormal morphology

Explanation

Paget's disease of bone is primarily driven by abnormal, hyperactive osteoclasts that are larger and multinucleated (often containing viral inclusion bodies like paramyxovirus). This triggers a chaotic secondary osteoblastic response resulting in disorganized woven bone.

Question 3214

Topic: Biology, Genetics & Bone Healing

A diaphyseal fracture is treated with an unreamed, locked intramedullary nail, allowing micromotion at the fracture site. Which of the following best describes the predominant type of bone healing that will occur?

. Primary bone healing with cutting cones
. Intramembranous ossification only
. Endochondral ossification
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Intramedullary nailing provides relative stability, allowing micromotion that promotes secondary (indirect) bone healing. This process involves callus formation and occurs primarily via endochondral ossification (where a cartilage intermediate is formed and then replaced by bone), supplemented by intramembranous ossification at the periphery.

Question 3215

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, purely lytic, expansile lesion in the epiphysis of the proximal tibia extending to the subchondral bone. Histology shows multinucleated giant cells in a stroma of mononuclear cells. Which of the following targeted therapies acts by inhibiting RANKL in the management of this tumor?

. Imatinib
. Denosumab
. Bisphosphonates
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

The clinical, radiographic, and histologic picture is classic for a Giant Cell Tumor (GCT) of bone. Denosumab is a monoclonal antibody that binds to RANKL, preventing the activation of the RANK receptor on osteoclast-like giant cells, thereby reducing osteolysis and shrinking the tumor.

Question 3216

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the treatment of severe osteoporosis. What is its exact mechanism of action?

. Inhibits osteoclast activity via binding to hydroxyapatite
. Binds to RANKL to prevent osteoclast differentiation
. Acts as a selective estrogen receptor modulator
. Recombinant PTH analogue that stimulates osteoblast activity when given intermittently
. Inhibits sclerostin to increase bone formation

Correct Answer & Explanation

. Recombinant PTH analogue that stimulates osteoblast activity when given intermittently

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., daily subcutaneous injection), it has a paradoxical anabolic effect on bone by stimulating osteoblast activity over osteoclast activity, thereby increasing overall bone formation.

Question 3217

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy presents with multiple fractures and a history of recurrent infections. Radiographs reveal generalized osteosclerosis with a "bone-within-a-bone" appearance. A genetic defect in which of the following is most likely responsible for this condition?

. Type I collagen synthesis
. Fibroblast growth factor receptor 3
. Carbonic anhydrase II
. Cbfa1/Runx2 transcription factor
. Lysyl hydroxylase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

This patient has osteopetrosis, characterized by a failure of osteoclast function. The most common defect is a mutation in carbonic anhydrase II, which prevents the acidification of the resorption pit needed to dissolve bone mineral.

Question 3218

Topic: Biology, Genetics & Bone Healing

Which cytokine is universally considered the primary pathological mediator driving articular cartilage degradation in osteoarthritis?

. Interleukin-1 (IL-1)
. Interleukin-4 (IL-4)
. Interleukin-10 (IL-10)
. Transforming growth factor beta (TGF-b)
. Bone morphogenetic protein 2 (BMP-2)

Correct Answer & Explanation

. Interleukin-1 (IL-1)

Explanation

Interleukin-1 (IL-1) and Tumor Necrosis Factor-alpha (TNF-a) are the predominant pro-inflammatory cytokines driving articular cartilage destruction. They heavily stimulate the production of matrix metalloproteinases (MMPs) while actively inhibiting proteoglycan synthesis.

Question 3219

Topic: Biology, Genetics & Bone Healing

A severely malnourished patient presents with bleeding gums, petechiae, and severe joint pain. Radiographs show a Pelkan spur and a Wimberger ring sign. This condition is caused by a dietary deficiency that directly impairs which step of collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Formation of the triple helix
. Cross-linking of tropocollagen molecules by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Scurvy is caused by a severe Vitamin C deficiency. Vitamin C is a required cofactor for prolyl and lysyl hydroxylases, enzymes that perform the hydroxylation of proline and lysine residues necessary to stabilize the collagen triple helix.

Question 3220

Topic: Biology, Genetics & Bone Healing

During secondary (indirect) fracture healing, the cartilaginous soft callus is eventually replaced by hard woven bone. This specific biological transition most closely resembles which normal process of skeletal development?

. Intramembranous ossification
. Endochondral ossification
. Appositional bone growth
. Creeping substitution
. Osteonal remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing involves the intermediate formation of a cartilaginous soft callus that subsequently mineralizes and is replaced by bone. This process mechanically and biologically mirrors endochondral ossification observed in the physeal growth plate.

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