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Biology, Genetics & Bone Healing MCQs

Practice Set 13 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 241

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone healing via osteoinduction. Which of the following BMPs is an FDA-approved recombinant agent commonly used to enhance anterior lumbar interbody fusion (ALIF)?

. BMP-1
. BMP-2
. BMP-4
. BMP-6
. BMP-12

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is heavily utilized and FDA-approved for specific applications, including anterior lumbar interbody fusion (ALIF) and acute open tibial shaft fractures, due to its potent osteoinductive capabilities.

Question 242

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) promotes osteoblast differentiation and bone formation primarily by binding to cell membrane receptors and activating which of the following intracellular signaling pathways?

. Wnt/beta-catenin
. RANK/RANKL
. Smad 1/5/8
. JAK/STAT
. Notch signaling

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell membrane, which subsequently phosphorylate and activate the intracellular Smad 1/5/8 pathway to upregulate osteogenic transcription factors like Runx2.

Question 243

Topic: Biology, Genetics & Bone Healing
During the remodeling phase of fracture healing, woven bone is replaced by lamellar bone. Which type of collagen is the predominant organic component of the extracellular matrix in mature lamellar bone?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen makes up roughly 90% of the organic matrix of mature bone. It provides tensile strength and serves as the primary scaffolding for mineralization.

Question 244

Topic: Biology, Genetics & Bone Healing
Which type of collagen is predominantly synthesized by chondrocytes during the soft callus phase of secondary fracture healing?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

During the soft callus phase of secondary fracture healing, endochondral ossification occurs where chondrocytes primarily synthesize Type II collagen. As the callus calcifies, hypertrophic chondrocytes express Type X collagen before bone (Type I) is deposited.

Question 245

Topic: Biology, Genetics & Bone Healing

A 35-year-old female is diagnosed with a giant cell tumor of the distal femur. If medical therapy is considered for an unresectable lesion, denosumab may be used. What is the mechanism of action of denosumab?

. Monoclonal antibody against the RANK receptor on osteoclasts
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Direct inhibition of osteoblast apoptosis
. Stimulation of osteoclast differentiation and apoptosis
. Binding directly to osteoprotegerin to increase bone mass

Correct Answer & Explanation

. Monoclonal antibody against RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing it from activating RANK on the surface of osteoclasts, thereby inhibiting bone resorption.

Question 246

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on long-term bisphosphonate therapy presents with a non-traumatic thigh ache. Radiographs reveal an incomplete atypical femoral fracture. Where does the cortical thickening and fracture initiation typically occur in these injuries?

. Medial cortex with a spiral pattern
. Medial cortex as a tension failure
. Lateral cortex as a tension failure with a transverse or short oblique pattern
. Anterior cortex of the femoral neck
. Posterior cortex of the intertrochanteric line

Correct Answer & Explanation

. Lateral cortex as a tension failure with a transverse or short oblique pattern

Explanation

Atypical femur fractures associated with prolonged bisphosphonate use characteristically originate at the lateral cortex (the tension side) with localized periosteal thickening and a transverse or short oblique fracture pattern.

Question 247

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) and BMP-7 promote bone healing primarily through which of the following molecular intracellular pathways?

. Inhibition of osteoclastogenesis via RANKL blockade
. Direct stimulation of angiogenesis via VEGF upregulation
. Activation of the SMAD signaling pathway
. Enhancement of Wnt/beta-catenin signaling
. Suppression of sclerostin production

Correct Answer & Explanation

. Activation of the SMAD signaling pathway

Explanation

BMPs bind to serine/threonine kinase receptors on mesenchymal stem cells, phosphorylating intracellular SMAD proteins (SMAD 1/5/8). These proteins then translocate to the nucleus to induce osteogenic gene transcription.

Question 248

Topic: Biology, Genetics & Bone Healing

A closed tibia fracture is treated with a long leg cast. The fracture heals primarily through callus formation. This type of bone healing relies fundamentally on which cellular process?

. Intramembranous ossification
. Endochondral ossification
. Haversian remodeling
. Primary bone healing
. Creeping substitution

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary bone healing (callus formation), typically seen with cast immobilization or relative stability, occurs mainly via endochondral ossification. In this process, a cartilage model is initially formed and subsequently replaced by bone.

Question 249

Topic: Biology, Genetics & Bone Healing

A 45-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate providing absolute stability. Which of the following histologic processes predominantly characterizes the bone healing in this scenario?

. Endochondral ossification
. Intramembranous ossification with bridging callus
. Primary bone healing via cutting cones
. Fibrous tissue interposition followed by calcification
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Rigid internal fixation providing absolute stability and anatomic reduction bypasses callus formation. It relies on primary (direct) bone healing via osteoclast cutting cones that cross the fracture gap, followed directly by osteoblastic bone deposition.

Question 250

Topic: Biology, Genetics & Bone Healing

A basic science researcher is studying the mechanics of fracture healing.

Under conditions of absolute stability, such as rigid compression plating where the fracture site experiences less than 2% interfragmentary strain, which biological process predominantly dictates bone healing?

. Endochondral ossification
. Primary bone healing via cutting cones
. Secondary bone healing with robust callus formation
. Fibrocartilaginous callus maturation
. Intramembranous ossification alone

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Absolute stability yielding less than 2% strain suppresses callus formation and permits primary bone healing. This process occurs directly via osteoclastic cutting cones crossing the fracture gap, closely followed by osteoblasts laying down new lamellar bone.

Question 251

Topic: Biology, Genetics & Bone Healing

A diaphyseal tibial fracture is treated with a rigid locked intramedullary nail. Which type of bone healing predominantly occurs in this scenario?

. Primary bone healing via cutting cones
. Secondary bone healing with callus formation
. Intramembranous ossification exclusively
. Endochondral ossification exclusively
. Creeping substitution

Correct Answer & Explanation

. Secondary bone healing with callus formation

Explanation

Intramedullary nailing provides relative stability rather than absolute stability. This biomechanical environment promotes secondary bone healing through the formation of a soft and hard fracture callus.

Question 252

Topic: Biology, Genetics & Bone Healing

During the process of secondary bone healing, which of the following mechanical and biological environments most strongly promotes the differentiation of mesenchymal stem cells into chondrocytes, leading to endochondral ossification?

. Absolute rigid stability with high oxygen tension
. High oxygen tension with low mechanical strain
. Moderate cyclic mechanical strain and low oxygen tension
. Extremely high shear stress and high oxygen tension
. Complete absence of vascularity and strain

Correct Answer & Explanation

. Moderate cyclic mechanical strain and low oxygen tension

Explanation

Secondary bone healing involves callus formation via endochondral ossification. A relatively low oxygen (hypoxic) environment combined with moderate cyclic mechanical strain promotes the differentiation of mesenchymal stem cells into chondrocytes to form a cartilaginous callus.

Question 253

Topic: Biology, Genetics & Bone Healing

Which of the following molecules causes the expression of matrix metalloproteinases that can degrade the articular cartilage extracellular matrix:

. Insulin-dependent growth factor I
. Transforming growth factor beta
. Interleukin I
. Bone morphogenetic protein 2
. Bone morphogenetic protein 7

Correct Answer & Explanation

. Interleukin I

Explanation

Interleukin I has the potential to increase expression of matrix metalloproteinases that can dissolve the extracellular matrix. The other responses are anabolic factors: Insulin-dependent growth factor I Transforming growth factor beta Bone morphogenetic protein 2 Bone morphogenetic protein 7

Question 254

Topic: Biology, Genetics & Bone Healing
Which of the following cytokines is considered the major stimulator of osteoclast differentiation, activation, and bone resorption?
. Osteoprotegerin (OPG)
. Interleukin-10 (IL-10)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Transforming growth factor-beta (TGF-β)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

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

Explanation

RANKL binds to the RANK receptor on osteoclast precursors, stimulating their differentiation and survival. Osteoprotegerin (OPG) acts as a decoy receptor for RANKL, competitively inhibiting this bone-resorbing cascade.

Question 255

Topic: Biology, Genetics & Bone Healing

Perren's strain theory postulates specific mechanical environments for different types of bone healing. According to this theory, primary bone healing occurs without callus formation when the interfragmentary strain is maintained at:

. Less than 2%
. Between 2% and 10%
. Between 10% and 20%
. Between 20% and 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory states that absolute stability with an interfragmentary strain of less than 2% is required for primary bone healing. Strains between 2% and 10% promote secondary bone healing via endochondral ossification and callus formation.

Question 256

Topic: Biology, Genetics & Bone Healing

During the process of secondary bone healing following a diaphyseal fracture, which of the following signaling molecules is most directly responsible for stimulating the differentiation of multipotent mesenchymal stem cells into osteoblasts?

. Interleukin-1 (IL-1)
. Transforming growth factor-beta (TGF-beta)
. Bone morphogenetic protein-2 (BMP-2)
. Tumor necrosis factor-alpha (TNF-alpha)
. Platelet-derived growth factor (PDGF)

Correct Answer & Explanation

. Bone morphogenetic protein-2 (BMP-2)

Explanation

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, are potent osteoinductive growth factors. They play a critical role in the bone healing cascade by stimulating mesenchymal stem cell differentiation into osteoblastic lineages.

Question 257

Topic: Biology, Genetics & Bone Healing

A 55-year-old male smoker presents with persistent pain 8 months after a midshaft humerus fracture treated nonoperatively. Radiographs show an atrophic nonunion with minimal callus. What is the most reliable definitive treatment?

. Bone morphogenetic protein (BMP) injection
. Extracorporeal shockwave therapy
. Intramedullary nailing without bone graft
. ORIF with compression plating and autogenous bone graft
. Functional bracing for an additional 6 months

Correct Answer & Explanation

. ORIF with compression plating and autogenous bone graft

Explanation

Atrophic nonunions lack adequate biology and stability. ORIF with rigid compression plating combined with autologous bone grafting (to stimulate osteogenesis) is the gold standard for treating atrophic humeral shaft nonunions.

Question 258

Topic: Biology, Genetics & Bone Healing

A 58-year-old woman presents with severe hand pain. Radiographs demonstrate central erosions of the PIP and DIP joints with a characteristic 'gull-wing' appearance. Rheumatoid factor and anti-CCP antibodies are negative. What cytokine is most strongly implicated in the pathogenesis of the cartilage destruction in this condition?

. Interleukin-10 (IL-10)
. Transforming growth factor-beta (TGF-beta)
. Interleukin-1 (IL-1)
. Interferon-gamma (IFN-gamma)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Interleukin-1 (IL-1)

Explanation

Erosive osteoarthritis is characterized by 'gull-wing' central erosions. Inflammatory cytokines, particularly Interleukin-1 (IL-1) and TNF-alpha, drive the production of matrix metalloproteinases, leading to aggressive cartilage degradation.

Question 259

Topic: Biology, Genetics & Bone Healing

During fracture healing, endochondral ossification requires an intermediate cartilage template. Which of the following transcription factors is essential for driving the differentiation of mesenchymal stem cells into chondrocytes?

. Runx2
. Sox9
. Osterix
. Beta-catenin
. MyoD

Correct Answer & Explanation

. Sox9

Explanation

Sox9 is the master transcription factor for chondrogenesis, directing mesenchymal stem cells to differentiate into chondrocytes. In contrast, Runx2 and Osterix are the key transcription factors required for osteoblast differentiation.

Question 260

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, primary bone healing occurs without callous formation under conditions of absolute stability. For primary bone healing to occur, the interfragmentary strain must be maintained below what percentage?

. 2%
. 10%
. 20%
. 30%
. 50%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory states that primary bone healing (via cutting cones) requires absolute stability, defined as interfragmentary strain less than 2%. Strain between 2% and 10% promotes secondary bone healing with callus formation.

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