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Biology, Genetics & Bone Healing MCQs

Practice Set 140 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 2781

Topic: Biology, Genetics & Bone Healing

During the proliferative phase of fracture healing, mesenchymal stem cells differentiate into osteoblasts. Which of the following intracellular signaling pathways is most essential for committing these mesenchymal precursors exclusively to the osteoblast lineage?

. Notch signaling pathway
. Wnt/beta-catenin pathway
. Hedgehog signaling pathway
. Smad1/5/8 pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Notch signaling pathway

Explanation

The Wnt/beta-catenin signaling pathway is critical for promoting osteoblast differentiation from mesenchymal stem cells while simultaneously inhibiting chondrogenic and adipogenic lineages. LRP5/6 are key co-receptors in this pathway.

Question 2782

Topic: Biology, Genetics & Bone Healing

Fibroblast Growth Factor 23 (FGF-23) plays a critical role in phosphate homeostasis. Which of the following actions is a direct physiological effect of elevated circulating FGF-23 levels?

. Increased intestinal absorption of calcium
. Increased synthesis of 1,25-dihydroxyvitamin D
. Decreased renal reabsorption of phosphate
. Decreased secretion of parathyroid hormone
. Increased osteoblastic bone formation

Correct Answer & Explanation

. Increased intestinal absorption of calcium

Explanation

FGF-23 is a hormone primarily secreted by osteocytes in response to hyperphosphatemia. It acts on the kidneys to decrease phosphate reabsorption (by downregulating NaPi-IIa and NaPi-IIc cotransporters) and decreases the synthesis of active 1,25-dihydroxyvitamin D by inhibiting 1-alpha-hydroxylase.

Question 2783

Topic: Biology, Genetics & Bone Healing

An orthopaedic surgeon utilizes a massive structural cortical allograft for a segmental defect reconstruction following tumor resection. Which of the following best describes the classical sequence of events during the creeping substitution of this cortical bone graft?

. Osteoclastic resorption followed immediately by osteoblastic new bone formation within Haversian canals
. Initial osteoblastic apposition on dead trabeculae followed by osteoclastic resorption
. Rapid revascularization followed by widespread chondrogenesis and endochondral ossification
. Immediate vascular ingrowth without an intermediate resorptive phase
. Initial fibrous encapsulation followed by intramembranous ossification

Correct Answer & Explanation

. Osteoclastic resorption followed immediately by osteoblastic new bone formation within Haversian canals

Explanation

Creeping substitution in cortical bone grafts involves osteoclastic resorption cutting cones that bore through the dead cortical bone, closely followed by osteoblasts that lay down new lamellar bone. This process temporarily weakens the graft mechanically before it incorporates and regains strength.

Question 2784

Topic: Biology, Genetics & Bone Healing
While reviewing the histological properties of dense regular connective tissue, it is noted that ligaments and tendons have slightly different ultrastructural compositions. Compared to a typical tendon, a typical ligament contains a higher proportion of which of the following?
. Type I collagen
. Type II collagen
. Proteoglycans and elastin
. Fibroblasts in parallel rows
. Water content

Correct Answer & Explanation

. Proteoglycans and elastin

Explanation

Tendons and ligaments are both primarily composed of Type I collagen. However, ligaments generally have slightly less Type I collagen and a higher proportion of proteoglycans, elastin, and Type III collagen compared to tendons, giving them slightly more extensibility.

Question 2785

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with multiple unexplained fractures and a radiograph showing a 'bone-within-bone' appearance.

Genetic testing reveals a mutation in the gene encoding Carbonic Anhydrase II. Which of the following best describes the resulting cellular dysfunction?

. Inability of osteoblasts to synthesize type I collagen
. Failure of osteoclasts to generate hydrogen ions for ruffled border secretion
. Defective mineralization of osteoid leading to rickets
. Overproduction of osteoprotegerin (OPG) blocking RANKL
. Inhibition of chondrocyte proliferation in the resting zone

Correct Answer & Explanation

. Inability of osteoblasts to synthesize type I collagen

Explanation

Carbonic Anhydrase II mutation causes an autosomal recessive form of osteopetrosis. This enzyme is essential for osteoclasts to produce protons, which are pumped into Howship's lacuna to dissolve bone mineral.

Question 2786

Topic: Biology, Genetics & Bone Healing

A patient undergoes spinal fusion using a massive structural cortical bone allograft. Compared to a cancellous autograft, which of the following accurately describes the incorporation process of the cortical allograft?

. It undergoes initial osteoblastic bone formation followed by resorption
. It incorporates via creeping substitution with osteoclasts leading the cutting cones
. It provides superior osteoinduction compared to cancellous autografts
. It achieves maximum mechanical strength 6 weeks after implantation
. It relies entirely on woven bone formation without remodeling

Correct Answer & Explanation

. It undergoes initial osteoblastic bone formation followed by resorption

Explanation

Structural cortical grafts incorporate via creeping substitution, where osteoclasts first resorb the dead bone (cutting cones) before osteoblasts lay down new bone. This causes the graft to become temporarily weaker before full incorporation.

Question 2787

Topic: Biology, Genetics & Bone Healing

Romosozumab is an anabolic agent used for the treatment of severe osteoporosis. Which of the following best describes its mechanism of action at the cellular level?

. Binds and inhibits RANKL, preventing osteoclast activation
. Inhibits cathepsin K, disrupting osteoclast function
. Binds and inhibits sclerostin, increasing Wnt/beta-catenin signaling
. Directly stimulates parathyroid hormone (PTH) receptors
. Acts as a decoy receptor for osteoprotegerin (OPG)

Correct Answer & Explanation

. Binds and inhibits RANKL, preventing osteoclast activation

Explanation

Romosozumab is a monoclonal antibody that binds and inhibits sclerostin. Because sclerostin is a natural inhibitor of the Wnt/beta-catenin pathway, its inhibition leads to increased osteoblastogenesis and enhanced bone formation.

Question 2788

Topic: Biology, Genetics & Bone Healing

Aggrecan is the most abundant proteoglycan in articular cartilage. Its ability to draw water into the extracellular matrix and resist compressive loads is primarily due to which of the following glycosaminoglycan side chains?

. Hyaluronan and lubricin
. Chondroitin sulfate and keratan sulfate
. Heparan sulfate and dermatan sulfate
. Collagen type II and IX
. Fibronectin and tenascin

Correct Answer & Explanation

. Hyaluronan and lubricin

Explanation

Aggrecan contains numerous chondroitin sulfate and keratan sulfate glycosaminoglycan (GAG) chains. The high density of negative charges on these sulfated GAGs creates a large osmotic swelling pressure that draws water into the tissue.

Question 2789

Topic: Biology, Genetics & Bone Healing

Recombinant human BMP-2 (rhBMP-2) is frequently utilized in spine surgery to enhance bone fusion. Through which intracellular signaling cascade do bone morphogenetic proteins primarily exert their osteoinductive effects?

. JAK/STAT pathway
. Smad pathway
. cAMP/PKA pathway
. Notch signaling pathway
. MAPK/ERK pathway

Correct Answer & Explanation

. JAK/STAT pathway

Explanation

Bone morphogenetic proteins (BMPs) bind to cell surface serine/threonine kinase receptors, which phosphorylate intracellular Smad proteins. The activated Smad complex translocates to the nucleus to regulate target gene transcription for osteoblast differentiation.

Question 2790

Topic: Biology, Genetics & Bone Healing

Which of the following biomechanical conditions is an absolute prerequisite for primary (direct) bone healing to occur without the formation of an intermediate cartilaginous callus?

. Interfragmentary strain less than 2%
. Interfragmentary strain between 2% and 10%
. Absolute gap size greater than 1 mm
. High oxygen tension combined with high construct compliance
. Controlled micromotion at the fracture site

Correct Answer & Explanation

. Interfragmentary strain less than 2%

Explanation

Primary bone healing relies on direct Haversian remodeling across the fracture gap. This requires absolute stability with an interfragmentary strain of less than 2% and a minimal gap distance (less than 0.1 mm).

Question 2791

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a graft substitute in orthopedic surgery. Which of the following biologic properties does DBM possess that synthetic calcium phosphate ceramics lack?

. Osteoinductivity
. Osteoconductivity
. Osteogenicity
. Immediate rigid structural support
. Inherent vascularization potential

Correct Answer & Explanation

. Osteoinductivity

Explanation

DBM is produced by removing the mineral content of allograft bone, exposing the underlying native bone morphogenetic proteins (BMPs). This provides DBM with osteoinductive properties, whereas synthetic ceramics are purely osteoconductive.

Question 2792

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with osteoporosis is started on a new treatment regimen. Normal bone homeostasis relies on the balance between osteoblastic and osteoclastic activity. Osteoprotegerin (OPG) functions to inhibit bone resorption by directly binding to which of the following molecules?

. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Macrophage colony-stimulating factor (M-CSF)
. Integrin alpha-v beta-3
. Cathepsin K

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B (RANK)

Explanation

Osteoprotegerin (OPG) is a decoy receptor produced by osteoblasts that binds to RANKL. This prevents RANKL from interacting with RANK on osteoclast precursors, thereby inhibiting osteoclast differentiation and bone resorption.

Question 2793

Topic: Biology, Genetics & Bone Healing

In articular cartilage, compressive resilience and the ability to withstand physiological loads are primarily provided by the interaction between interstitial fluid and which of the following extracellular matrix components?

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

Correct Answer & Explanation

. Type I collagen

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage and possesses a high negative charge density due to its glycosaminoglycan chains. This creates a high osmotic pressure that draws water into the tissue, providing resistance to compressive forces.

Question 2794

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that can be tolerated to allow for primary bone healing (osteonal reconstruction) without the formation of a visible fracture callus?

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

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that primary bone healing (direct osteonal remodeling without callus formation) requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary bone healing via endochondral ossification.

Question 2795

Topic: Biology, Genetics & Bone Healing

A 68-year-old female presents with diffuse bone pain and proximal muscle weakness. Laboratory evaluation reveals hypocalcemia, hypophosphatemia, and elevated alkaline phosphatase. A transiliac bone biopsy with double tetracycline labeling would most likely demonstrate which of the following?

. Decreased osteoid seam width
. Increased osteoid seam width with delayed mineralization
. Normal bone turnover with microarchitectural deterioration
. Hyperactive osteoclasts with woven bone formation
. Empty lacunae with necrotic bone trabeculae

Correct Answer & Explanation

. Decreased osteoid seam width

Explanation

The patient's clinical and laboratory findings are consistent with osteomalacia. Histologically, osteomalacia is characterized by an increased width of unmineralized osteoid seams and an extended mineralization lag time, as evidenced by abnormal tetracycline labeling.

Question 2796

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are signaling molecules belonging to the TGF-beta superfamily that promote bone formation. Which of the following BMPs is an FDA-approved osteoinductive agent commonly used in acute open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-6
. BMP-7

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is an FDA-approved osteoinductive biologic used to enhance fracture healing, particularly in acute open tibial shaft fractures treated with an intramedullary nail. BMP-7 (osteogenic protein-1) has also been used for fracture nonunions.

Question 2797

Topic: Biology, Genetics & Bone Healing

The anterior cruciate ligament (ACL) of the knee is primarily composed of water and a highly organized extracellular matrix of collagen. Which of the following cell types is predominantly responsible for the synthesis, maintenance, and repair of this extracellular matrix?

. Chondrocytes
. Osteoblasts
. Fibroblasts
. Synoviocytes
. Macrophages

Correct Answer & Explanation

. Chondrocytes

Explanation

Fibroblasts are the primary cellular components of ligaments and tendons. They synthesize and secrete the extracellular matrix proteins, predominantly Type I collagen, and maintain the structural integrity of the tissue.

Question 2798

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a nonunion of the tibial shaft. A treatment plan involving demineralized bone matrix (DBM) is chosen. Which of the following best describes the osteogenic potential and primary mechanism of bone formation associated with DBM?

. It contains live marrow cells and works via osteogenesis
. It provides a scaffold only and works via osteoconduction
. It contains BMPs that stimulate mesenchymal stem cells and works via osteoinduction
. It possesses both osteoinductive and osteogenic properties
. It solely acts by inhibiting osteoclastic bone resorption

Correct Answer & Explanation

. It contains live marrow cells and works via osteogenesis

Explanation

DBM is osteoinductive and osteoconductive but completely lacks osteogenic properties as it contains no live cells. Its osteoinductive ability is derived from retained bone morphogenetic proteins (BMPs) that recruit and differentiate mesenchymal stem cells.

Question 2799

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with facial nerve palsy and hearing loss. Radiographs demonstrate marked cortical thickening and sclerosis of the skull and long bones. Genetic testing reveals a mutation in the SOST gene. The protein encoded by this gene normally regulates bone mass by antagonizing which of the following intracellular signaling pathways?

. RANKL/RANK
. Osteoprotegerin (OPG)
. Wnt/beta-catenin
. Notch
. TGF-beta

Correct Answer & Explanation

. RANKL/RANK

Explanation

The SOST gene encodes sclerostin, which is produced by osteocytes. Sclerostin binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway, which normally promotes bone formation. Mutations in SOST lead to sclerosteosis, characterized by massive bone overgrowth.

Question 2800

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, direct or primary bone healing can occasionally occur if there is rigid internal fixation with absolute stability. This involves bone remodeling via cutting cones. Which of the following best describes the cellular arrangement at the advancing leading edge of a cortical cutting cone?

. Osteoblasts depositing osteoid
. Osteocytes communicating via canaliculi
. Osteoclasts resorbing bone
. Chondrocytes undergoing hypertrophy
. Mesenchymal stem cells differentiating

Correct Answer & Explanation

. Osteoblasts depositing osteoid

Explanation

In primary bone healing, remodeling occurs via cutting cones. The leading edge (head) of the cutting cone is composed of osteoclasts that bore through the necrotic bone. They are followed by a capillary loop and osteoblasts (in the trailing edge or closing cone) that lay down new concentric lamellae of bone.

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