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Biology, Genetics & Bone Healing MCQs

Practice Set 117 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 2321

Topic: Biology, Genetics & Bone Healing

A novel orthopedic implant is being developed with a surface modification designed to enhance osteointegration by mimicking the natural extracellular matrix. Which of the following strategies would be most effective at promoting specific cell adhesion and differentiation?

. Creating a smooth, polished surface to minimize bacterial colonization.
. Coating the surface with an inert polymer to reduce immune response.
. Incorporating RGD (Arginine-Glycine-Aspartic acid) peptides into the surface.
. Increasing the overall hydrophobicity of the implant material.
. Developing a microporous surface solely for enhanced nutrient diffusion.

Correct Answer & Explanation

. Incorporating RGD (Arginine-Glycine-Aspartic acid) peptides into the surface.

Explanation

Incorporating RGD (Arginine-Glycine-Aspartic acid) peptides into the implant surface is a highly effective strategy for promoting specific cell adhesion and differentiation. The RGD sequence is a common recognition motif for integrins, which are cell-surface receptors that mediate cell-extracellular matrix interactions. By providing RGD motifs, the implant surface can selectively bind to host cells (e.g., osteoblasts, mesenchymal stem cells) and trigger intracellular signaling pathways that promote osteointegration. Smooth surfaces can hinder cell adhesion, inert polymers might lack bioactivity, hydrophobicity generally discourages cell adhesion, and while microporosity is helpful, specific biological cues are more potent for directed cell behavior.

Question 2322

Topic: Biology, Genetics & Bone Healing

In the advanced stages of intervertebral disc degeneration, what is the primary change in the nucleus pulposus extracellular matrix that compromises its ability to withstand compressive loads?

. Increased collagen Type I content and reduced proteoglycans.
. Increased water content due to osmotic swelling.
. Decreased production of aggrecan and increased catabolism of proteoglycans.
. Hypertrophy of chondrocytes and mineralization.
. Proliferation of fibroblasts and increased vascularization.

Correct Answer & Explanation

. Decreased production of aggrecan and increased catabolism of proteoglycans.

Explanation

In advanced intervertebral disc degeneration, the primary change in the nucleus pulposus is a progressive decrease in the production of aggrecan (the main proteoglycan) and an increase in its catabolism. This leads to a reduction in the overall proteoglycan content, which in turn reduces the disc's ability to retain water. The loss of water-retaining capacity significantly compromises the nucleus pulposus's osmotic pressure and its ability to withstand compressive loads, leading to disc height loss and instability. While some collagen changes occur, the fundamental issue for load-bearing is proteoglycan loss and subsequent dehydration. Mineralization, vascularization, and chondrocyte hypertrophy are more characteristic of endplate changes or other tissues.

Question 2323

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the molecular basis for the 'stress-shielding' phenomenon observed in bone adjacent to stiff metallic orthopedic implants?

. Direct mechanical trauma from the implant to the bone.
. Reduced bone remodeling due to a lack of strain-induced osteocyte signaling.
. Increased osteoclast activity in response to foreign body reaction.
. Enhanced osteoblast proliferation leading to cortical thinning.
. Conversion of compact bone into cancellous bone due to altered stress distribution.

Correct Answer & Explanation

. Reduced bone remodeling due to a lack of strain-induced osteocyte signaling.

Explanation

Stress-shielding occurs when a stiff orthopedic implant carries a disproportionately high share of the mechanical load, thereby reducing the stress (and strain) experienced by the adjacent bone. According to Wolff's Law, bone adapts to the loads placed upon it. When bone is 'shielded' from normal physiological stresses, osteocytes (the mechanosensors) detect reduced strain. This leads to reduced signaling for bone formation by osteoblasts and/or increased signaling for bone resorption by osteoclasts, resulting in a net loss of bone mass (osteopenia) in the shielded regions. It's a biological adaptation to altered mechanical environment, not direct trauma, foreign body reaction, or a direct increase in osteoblast proliferation.

Question 2324

Topic: Biology, Genetics & Bone Healing

A 7-year-old child with Osteogenesis Imperfecta Type IV has been on intravenous pamidronate therapy for 3 years. Which of the following radiographic findings is a direct consequence of this pharmacological treatment?

. Multiple radiolucent bone cysts
. Transverse sclerotic metaphyseal bands
. Cortical thickening and sclerosis
. Periosteal elevation
. Loss of the provisional zone of calcification

Correct Answer & Explanation

. Transverse sclerotic metaphyseal bands

Explanation

Intravenous bisphosphonates (like pamidronate) are commonly used in OI to increase bone mineral density and reduce fracture rates. Because bisphosphonates transiently inhibit osteoclast-mediated bone resorption, they lead to the formation of transverse dense sclerotic bands (often called 'zebra lines') in the metaphyses of growing bones. Each line represents a cycle of IV administration.

Question 2325

Topic: Biology, Genetics & Bone Healing

A 15-year-old girl with Osteogenesis Imperfecta Type I presents with progressive hearing loss. What is the most common etiology of hearing impairment in patients with OI?

. Sensorineural hearing loss due to primary cochlear nerve degeneration
. Conductive hearing loss due to ossicular dislocation or fixation
. Tympanic membrane rupture from minor trauma
. Chronic otitis media secondary to immunodeficiency
. Ototoxicity from long-term bisphosphonate use

Correct Answer & Explanation

. Conductive hearing loss due to ossicular dislocation or fixation

Explanation

Hearing loss in OI typically begins in the second or third decade of life and is most commonly conductive (though sensorineural and mixed forms also occur). Conductive hearing loss is usually due to otosclerosis-like fixation of the stapes footplate, stapedial crural fracture, or ossicular discontinuity. There is no known direct ototoxicity from bisphosphonates, nor is OI associated with immunodeficiency.

Question 2326

Topic: Biology, Genetics & Bone Healing

In Osteogenesis Imperfecta, treatment with bisphosphonates reduces fracture frequency and increases bone mineral density. However, long-term use has been associated with which of the following orthopedic complications?

. Avascular necrosis of the femoral head
. Delayed healing of osteotomies
. Increased rate of telescoping rod failure
. Premature physeal closure
. Development of secondary osteosarcoma

Correct Answer & Explanation

. Delayed healing of osteotomies

Explanation

Bisphosphonates inhibit osteoclast function, which impairs bone remodeling. While this increases bone density and decreases fracture rates, it can lead to delayed union or nonunion at osteotomy sites (e.g., following Fassier-Duval rodding). Surgeons often temporarily withhold bisphosphonate therapy around the time of surgery to minimize this risk. AVN of the jaw (ONJ) is a known but rare complication, mostly in adults.

Question 2327

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy presents with forearm deformity and restricted pronosupination. Radiographs reveal calcification of the interosseous membrane and a history of hyperplastic callus formation following a previous femur fracture. Which genetic mutation is most likely responsible for this specific phenotype?

. COL1A1
. IFITM5
. CRTAP
. SERPINF1
. LEPRE1

Correct Answer & Explanation

. IFITM5

Explanation

The patient exhibits classic signs of Osteogenesis Imperfecta (OI) Type V, which is uniquely characterized by hyperplastic callus formation, calcification of the interosseous membrane of the forearm (leading to radioulnar synostosis and restricted rotation), and radial head dislocation. Unlike the majority of OI types caused by type I collagen defects, Type V is caused by a dominant mutation in the IFITM5 gene, which encodes the BRIL protein.

Question 2328

Topic: Biology, Genetics & Bone Healing

A 3-year-old child with severe Osteogenesis Imperfecta is started on cyclical intravenous Pamidronate. Which of the following best describes the cellular mechanism of action of this medication?

. Stimulates osteoblast proliferation and matrix synthesis
. Inhibits osteoclast activity by disrupting the mevalonate pathway
. Directly cross-links abnormal type I collagen fibers to increase tensile strength
. Increases intestinal calcium absorption via vitamin D receptor agonism
. Enhances the secretion of osteoprotegerin (OPG) from osteocytes

Correct Answer & Explanation

. Inhibits osteoclast activity by disrupting the mevalonate pathway

Explanation

Pamidronate is a nitrogen-containing bisphosphonate. These drugs localize to sites of bone resorption and are ingested by osteoclasts. Inside the osteoclast, they inhibit the enzyme farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (like Ras, Rho, Rac) essential for osteoclast function and survival, ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 2329

Topic: Biology, Genetics & Bone Healing
A histomorphometric analysis of an iliac crest bone biopsy from a patient with severe osteogenesis imperfecta (Type III) would most likely demonstrate which of the following findings compared to a healthy, age-matched control?
. Increased cortical thickness and lamellar bone formation
. Decreased number of osteoblasts and osteoclasts (hypocellularity)
. Increased trabecular bone volume with thickened trabeculae
. Decreased cortical thickness, decreased trabecular volume, and hypercellularity
. Absent osteoid seams and severe mineralization defects

Correct Answer & Explanation

. Decreased cortical thickness, decreased trabecular volume, and hypercellularity

Explanation

Bone biopsies in osteogenesis imperfecta reveal an uncoupling of bone turnover favoring resorption. Histomorphometry typically shows severe osteopenia with decreased cortical thickness and reduced trabecular bone volume. Because the bone attempts to repair itself rapidly but with defective collagen, the tissue is hypercellular (increased numbers of both osteoblasts and osteoclasts) and features a persistence of disorganized woven bone rather than mature lamellar bone.

Question 2330

Topic: Biology, Genetics & Bone Healing

A patient diagnosed with Osteogenesis Imperfecta Type VI is noted to have a paradoxically poor response to bisphosphonate therapy and exhibits an isolated mineralization defect on bone histology that mimics osteomalacia. Which gene is most likely mutated in this patient?

. COL1A1
. CRTAP
. LEPRE1
. SERPINF1
. IFITM5

Correct Answer & Explanation

. SERPINF1

Explanation

Osteogenesis Imperfecta Type VI is a rare, autosomal recessive form of the disease caused by loss-of-function mutations in the SERPINF1 gene. This gene encodes pigment epithelium-derived factor (PEDF). The hallmark of OI Type VI is an osteomalacia-like mineralization defect on bone biopsy (increased unmineralized osteoid) despite normal calcium and phosphate levels, and these patients notoriously respond poorly to standard bisphosphonate therapy.

Question 2331

Topic: Biology, Genetics & Bone Healing

The Sofield-Millar operation remains a foundational concept in the surgical management of severe long bone deformities in Osteogenesis Imperfecta. What does this classic procedure fundamentally entail?

. Single-level closing wedge osteotomy stabilized by dynamic compression plating
. Multiple sequential osteotomies of the diaphysis, realignment, and intramedullary rod fixation
. Guided growth via temporary hemiepiphysiodesis using tension band plates
. Gradual distraction osteogenesis using a circular external fixator
. Percutaneous drilling and injection of bone morphogenetic protein (BMP) to stimulate hypertrophy

Correct Answer & Explanation

. Multiple sequential osteotomies of the diaphysis, realignment, and intramedullary rod fixation

Explanation

First described in 1959, the Sofield-Millar procedure is the classic 'shish kebab' operation used to treat severe bowing in OI. It involves subperiosteal exposure of the long bone, performing multiple diaphyseal osteotomies to correct the bowing, threading the bone fragments onto a straight intramedullary rod to realign them, and allowing them to heal in a straight configuration.

Question 2332

Topic: Biology, Genetics & Bone Healing
Dentinogenesis imperfecta (DI) is a common manifestation of certain types of osteogenesis imperfecta. Which of the following accurately describes the dental findings and its most common associated OI types?
. The teeth appear chalky white and are highly resistant to caries; commonly seen in OI Type I.
. The primary dentition has delayed eruption and macrognathia; associated exclusively with OI Type V.
. The primary and secondary dentition appear opalescent, yellow-brown, and wear rapidly; commonly associated with OI Types III and IV.
. It only affects the primary dentition and is reversed with cyclical bisphosphonate therapy.
. The teeth have a distinct blue discoloration but normal enamel integrity; commonly seen in OI Type VI.

Correct Answer & Explanation

. The primary and secondary dentition appear opalescent, yellow-brown, and wear rapidly; commonly associated with OI Types III and IV.

Explanation

Dentinogenesis imperfecta (DI) is characterized by teeth that are opalescent (bluish-gray or yellow-brown) due to defective dentin. The enamel is normal but tends to flake off because the underlying dentin is soft, leading to rapid wear and breakage. It affects both primary and secondary dentition and is most commonly associated with COL1A1/COL1A2 mutations, particularly in OI Types III and IV.

Question 2333

Topic: Biology, Genetics & Bone Healing

While bisphosphonates (antiresorptive agents) are the standard of care for severe Osteogenesis Imperfecta, recent research has explored anabolic agents to increase bone formation. Which of the following drugs represents an anabolic approach by acting as a monoclonal antibody against sclerostin?

. Denosumab
. Teriparatide
. Romosozumab
. Burosumab
. Asfotase alfa

Correct Answer & Explanation

. Romosozumab

Explanation

Romosozumab is a monoclonal antibody that targets and binds to sclerostin. Sclerostin is a glycoprotein secreted by osteocytes that normally inhibits the Wnt signaling pathway, thereby inhibiting osteoblast bone formation. By blocking sclerostin, Romosozumab has a dual effect: it strongly stimulates bone formation (anabolic) and moderately decreases bone resorption. It is currently being investigated as a bone-building therapy for OI.

Question 2334

Topic: Biology, Genetics & Bone Healing

A 14-year-old female with Osteogenesis Imperfecta has been treated with intravenous pamidronate for 10 years. Radiographs of her distal femur reveal multiple transverse radiodense lines.

What is the mechanism of action of this medication in producing these lines?

. Inhibition of osteoblast apoptosis
. Stimulation of calcium deposition in the physis
. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Direct binding to the COL1A1 promoter
. Neutralization of RANK ligand

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Nitrogen-containing bisphosphonates like pamidronate inhibit farnesyl pyrophosphate synthase, leading to osteoclast apoptosis. The transverse dense lines (zebra lines) correspond to the cycles of IV administration causing temporary failure of primary spongiosa resorption.

Question 2335

Topic: Biology, Genetics & Bone Healing
A 3-year-old child presents with frequent fractures, blue sclerae, and hyperplastic callus formation following a recent tibia fracture. Genetic analysis reveals a mutation in the IFITM5 gene. Which type of osteogenesis imperfecta does this patient have?
. Type I
. Type III
. Type IV
. Type V
. Type VI

Correct Answer & Explanation

. Type V

Explanation

OI Type V is uniquely characterized by hyperplastic callus formation, calcification of the interosseous membrane, and an autosomal dominant mutation in the IFITM5 gene. Sclerae can be variable but hyperplastic callus is the hallmark.

Question 2336

Topic: Biology, Genetics & Bone Healing

A 16-year-old male with Osteogenesis Imperfecta Type VI presents with a femur fracture. He has a known SERPINF1 mutation. How does the pathophysiology and medical management of Type VI differ from classical OI (Types I-IV)?

. It involves an isolated defect in osteoclast activity, treatable with Denosumab
. It features a mineralization defect resembling osteomalacia and responds poorly to bisphosphonates
. It is characterized by hyperplastic callus formation treated with NSAIDs
. It causes widespread soft tissue ossification requiring surgical excision
. It is an X-linked recessive condition requiring bone marrow transplant

Correct Answer & Explanation

. It features a mineralization defect resembling osteomalacia and responds poorly to bisphosphonates

Explanation

OI Type VI is caused by an autosomal recessive mutation in SERPINF1, resulting in a severe mineralization defect with increased unmineralized osteoid (similar to osteomalacia). Unlike classical OI, it typically has a poor response to bisphosphonate therapy.

Question 2337

Topic: Biology, Genetics & Bone Healing

A 15-year-old with severe OI has experienced multiple long bone fractures despite years of maximum-dose IV bisphosphonate therapy. The multidisciplinary team considers switching to Denosumab. What is the mechanism of action of Denosumab?

. Directly stimulates osteoblast differentiation via the Wnt pathway
. Binds and neutralizes RANK ligand (RANKL), preventing osteoclast activation
. Binds directly to the hydroxyapatite matrix, physically blocking osteoclasts
. Modulates the calcium-sensing receptor on the parathyroid gland
. Suppresses sclerostin, increasing bone formation

Correct Answer & Explanation

. Binds and neutralizes RANK ligand (RANKL), preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with RANK on osteoclasts. This effectively inhibits osteoclast formation, function, and survival, serving as an alternative treatment for severe OI.

Question 2338

Topic: Biology, Genetics & Bone Healing
A 5-year-old boy with osteogenesis imperfecta type III has been receiving cyclic intravenous pamidronate therapy. Radiographs demonstrate horizontal sclerotic bands in the metaphyses. What is the primary cellular mechanism of action of this medication?
. Stimulates osteoblast differentiation via the Wnt pathway
. Inhibits osteoclast farnesyl pyrophosphate synthase
. Binds directly to RANKL, preventing osteoclast activation
. Increases the renal reabsorption of calcium
. Inhibits matrix metalloproteinase cleavage of type I collagen

Correct Answer & Explanation

. Inhibits osteoclast farnesyl pyrophosphate synthase

Explanation

Pamidronate is a nitrogen-containing bisphosphonate that inhibits farnesyl pyrophosphate synthase in the mevalonate pathway. This leads to osteoclast apoptosis and produces the characteristic metaphyseal sclerotic 'zebra lines' on radiographs.

Question 2339

Topic: Biology, Genetics & Bone Healing
If a bone biopsy is taken from the iliac crest of a patient with severe osteogenesis imperfecta (type III), which of the following histologic findings is most expected?
. Thickened cortical bone with narrowed Haversian canals
. Presence of woven bone retaining primary trabeculae rather than mature lamellar bone
. Significant decrease in osteocyte density per unit of bone
. Complete absence of osteoclasts
. Accumulation of unmineralized osteoid resembling rickets

Correct Answer & Explanation

. Presence of woven bone retaining primary trabeculae rather than mature lamellar bone

Explanation

Histologically, bone in severe OI exhibits thin cortices and sparse trabeculae with hypercellularity (increased osteocyte density). The bone frequently fails to remodel into mature lamellar bone, remaining predominantly as disorganized woven bone.

Question 2340

Topic: Biology, Genetics & Bone Healing

A 9-year-old boy with a history of multiple fractures presents with a painless, limited range of motion in his right forearm. Radiographs reveal calcification of the interosseous membrane and a history of hyperplastic callus formation following previous fractures.

Genetic testing is most likely to show a mutation in which of the following genes?

. COL1A1
. COL1A2
. IFITM5
. SERPINF1
. CRTAP

Correct Answer & Explanation

. IFITM5

Explanation

This presentation is classic for Osteogenesis Imperfecta (OI) Type V, which is characterized by hyperplastic callus formation, radial head dislocation, and calcification of the interosseous membrane. It is caused by an autosomal dominant mutation in the IFITM5 gene.

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