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Biology, Genetics & Bone Healing MCQs

Practice Set 12 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 221

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia without a sclerotic margin. Histology shows multinucleated giant cells. Which of the following is the standard medical treatment targeting the underlying pathophysiology?

. Methotrexate
. Denosumab
. Imatinib
. Doxorubicin
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone express high levels of RANKL, which drives the formation of osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is specifically used for unresectable or recurrent cases.

Question 222

Topic: Biology, Genetics & Bone Healing

Multiple Epiphyseal Dysplasia (MED) is characterized by delayed and irregular ossification of the epiphyses. Which of the following genes is NOT typically associated with MED?

. COMP
. MATN3
. COL9A1
. COL2A1
. RUNX2

Correct Answer & Explanation

. RUNX2

Explanation

RUNX2 mutations are associated with Cleidocranial Dysplasia, not MED. MED is typically caused by mutations in the genes encoding COMP, matrilin-3 (MATN3), or type IX collagen (COL9A1, COL9A2, COL9A3).

Question 223

Topic: Biology, Genetics & Bone Healing

A 10-year-old child presents with delayed closure of the cranial sutures, dental anomalies, and absent clavicles allowing extreme shoulder protraction. This condition is caused by a mutation in which of the following transcription factors?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. SHH
. HOXD13

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a mutation in the RUNX2 (CBFA1) gene, which is an essential transcription factor for osteoblast differentiation. Patients characteristically present with absent or hypoplastic clavicles and delayed fontanelle closure.

Question 224

Topic: Biology, Genetics & Bone Healing

Osteogenesis imperfecta (OI) is caused by defects in:

. Calcitonin
. Type I collagen
. Type II collagen
. Type X collagen
. Osteoclasts

Correct Answer & Explanation

. Type I collagen

Explanation

Both quantitative and qualitative defects in type I collagen lead to the various types of osteogenesis imperfecta (OI). Several hundred different collagen I mutations have been found in patients with OI. The less severe forms of OI are caused by mutations in which the defective gene product is not incorporated into collagen, so that formation of cells using the unimpaired strands can continue.

Question 225

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the histologic process of primary bone healing?

. It requires a robust cartilaginous intermediate before ossification.
. It occurs exclusively under conditions of absolute stability via direct Haversian remodeling.
. It depends heavily on the formation of a bridging external soft tissue callus.
. It is primarily mediated by osteoclasts without subsequent osteoblast activity.
. It is the typical mechanism of healing following closed reduction and casting.

Correct Answer & Explanation

. It occurs exclusively under conditions of absolute stability via direct Haversian remodeling.

Explanation

Primary bone healing (intramembranous ossification without callus formation) occurs only under conditions of absolute stability, such as with rigid internal compression plating. It proceeds via direct Haversian remodeling across the fracture gap.

Question 226

Topic: Biology, Genetics & Bone Healing

A 40-year-old patient sustains a transverse femur fracture treated with a rigid reamed intramedullary nail. Which type of bone healing is predominantly expected in this biomechanical environment?

. Primary bone healing via cutting cones
. Secondary bone healing via callus formation
. Endochondral ossification solely without intramembranous ossification
. Appositional bone growth exclusively
. Creeping substitution

Correct Answer & Explanation

. Secondary bone healing via callus formation

Explanation

Intramedullary nailing provides relative stability, which allows for micromotion at the fracture site. This mechanical environment promotes secondary bone healing characterized by the formation of a soft and hard callus.

Question 227

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the cartilaginous soft callus is eventually replaced by hard woven bone. Which of the following transcription factors is most essential for the initial differentiation of multipotent mesenchymal stem cells into the osteoblastic lineage?

. Sox9
. Runx2 (Cbfa1)
. HIF-1 alpha
. RANKL
. Osteoprotegerin (OPG)

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (Cbfa1) is the master transcription factor responsible for committing mesenchymal stem cells to the osteoblast lineage. In contrast, Sox9 is the primary transcription factor driving chondrogenic differentiation during soft callus formation.

Question 228

Topic: Biology, Genetics & Bone Healing

Orthopedic sequelae of frostbite injury include all of the following except:

. Joint contractures
. Localized osteoporosis
. Decreased risk of future frostbite injury
. Punched-out subchondral bony lesions
. C old intolerance

Correct Answer & Explanation

. Decreased risk of future frostbite injury

Explanation

People who have had previous frostbite injuries are at increased risk of thermal injury, whether cold or heat related. Joint contractures, localized osteoporosis, punched-out subchondral bony lesions, and cold intolerance are often present after frostbite injury.

Question 229

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, absolute stability and primary bone healing require the interfragmentary strain at the fracture gap to be maintained below what critical threshold?

. 2%
. 10%
. 15%
. 20%
. 25%

Correct Answer & Explanation

. 2%

Explanation

Primary bone healing requires absolute stability with interfragmentary strain maintained below 2%. This low-strain environment allows for direct osteonal remodeling (cutting cones) without intermediate callus formation.

Question 230

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are used to enhance bone healing. Which of the following BMPs is an FDA-approved osteoinductive agent commonly used in anterior lumbar interbody fusion?

. BMP-1
. BMP-2
. BMP-3
. BMP-4
. BMP-12

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is heavily utilized and FDA-approved for specific spinal fusions, including ALIF with a specific cage. BMP-2 and BMP-7 are the primary osteoinductive BMPs used clinically.

Question 231

Topic: Biology, Genetics & Bone Healing

In the process of secondary bone healing, which physiological phase is characterized by the replacement of the cartilaginous soft callus with woven bone through endochondral ossification?

. Inflammatory phase
. Soft callus phase
. Hard callus phase
. Remodeling phase
. Hematoma phase

Correct Answer & Explanation

. Hard callus phase

Explanation

The hard callus phase of secondary fracture healing involves the mineralization of the fibrocartilaginous soft callus, converting it into woven bone. This is primarily achieved via endochondral ossification.

Question 232

Topic: Biology, Genetics & Bone Healing

Denosumab is often utilized in the management of unresectable Giant Cell Tumor of bone. What is the specific mechanism of action of this medication?

. It binds to the RANK receptor on osteoclasts, inducing apoptosis.
. It binds directly to RANKL, preventing its interaction with the RANK receptor.
. It inhibits macrophage colony-stimulating factor (M-CSF) production.
. It binds to osteoprotegerin (OPG), increasing its circulating half-life.

Correct Answer & Explanation

. It binds directly to RANKL, preventing its interaction with the RANK receptor.

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from activating the RANK receptor on osteoclasts and giant cells, thereby inhibiting their function and bone resorption.

Question 233

Topic: Biology, Genetics & Bone Healing

Which of the following transcription factors is considered the essential "master regulator" for the differentiation of mesenchymal stem cells into osteoblasts?

. SOX9
. RUNX2 (Cbfa1)
. PPAR-gamma
. MyoD

Correct Answer & Explanation

. RUNX2 (Cbfa1)

Explanation

RUNX2 (also known as Core-binding factor subunit alpha-1 or Cbfa1) is the master transcription factor for osteoblast differentiation. SOX9 regulates chondrogenesis, and PPAR-gamma drives adipogenesis.

Question 234

Topic: Biology, Genetics & Bone Healing

During fracture healing via endochondral ossification, the production of Type X collagen in the fracture callus is primarily mediated by which of the following cell types?

. Proliferating chondrocytes
. Hypertrophic chondrocytes
. Osteoblasts
. Multinucleated osteoclasts
. Mesenchymal stem cells

Correct Answer & Explanation

. Hypertrophic chondrocytes

Explanation

Hypertrophic chondrocytes in the callus specifically express and produce Type X collagen. This structural protein facilitates the calcification of the cartilage matrix, a crucial step before invasion by blood vessels and osteoprogenitor cells.

Question 235

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femoral epiphysis extending to the subchondral bone without a sclerotic margin. Biopsy reveals multinucleated giant cells. Which medication acts by binding to RANKL to treat this condition?

. Zoledronic acid
. Denosumab
. Methotrexate
. Doxorubicin
. Imatinib

Correct Answer & Explanation

. Denosumab

Explanation

The clinical and histologic findings describe a giant cell tumor (GCT) of bone. Denosumab is a monoclonal antibody that binds to RANKL, inhibiting osteoclast-like giant cells, and is used for advanced or recurrent GCTs.

Question 236

Topic: Biology, Genetics & Bone Healing

Which of the following is the true neoplastic cell population in a Giant Cell Tumor (GCT) of bone?

. Multinucleated giant cells
. Osteoclasts
. Spindle-shaped mononuclear cells
. Chondroblasts
. Histiocytes

Correct Answer & Explanation

. Spindle-shaped mononuclear cells

Explanation

The neoplastic cells in GCT are the spindle-shaped mononuclear cells of osteoblastic lineage. The hallmark multinucleated giant cells are actually reactive osteoclast-like cells recruited by RANKL expression from the mononuclear cells.

Question 237

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman on long-term bisphosphonate therapy presents with prodromal thigh pain. Radiographs show cortical thickening and a transverse radiolucent line on the lateral aspect of the femoral diaphysis. What is the recommended management?

. Discontinue bisphosphonate and prescribe crutches for non-weight bearing
. Switch to teriparatide and repeat radiographs in 6 weeks
. Prophylactic intramedullary nailing of the femur
. Application of a hip spica cast
. Observation with serial dual-energy X-ray absorptiometry (DEXA) scans

Correct Answer & Explanation

. Prophylactic intramedullary nailing of the femur

Explanation

The presence of prodromal thigh pain combined with a radiographic "beaking" or a radiolucent line on the lateral femoral cortex indicates an impending atypical femoral fracture. The standard of care is prophylactic intramedullary nailing to prevent complete displacement.

Question 238

Topic: Biology, Genetics & Bone Healing

In normal development, the differentiation of the interdigital web space is influenced by which of the following factors:

. Bone morphogenetic protein (BMP)
. Fibroblast growth factor-3 (FGF-3)
. Interleukin-1 (IL-1)
. Apical ectodermal ridge maintenance factor (AERMF)
. Thalidomide

Correct Answer & Explanation

. Apical ectodermal ridge maintenance factor (AERMF)

Explanation

The distal phalanges are composed of two germ cell layers. Ectodermal cells produce the tuft of the distal phalanx and the nail elements, while mesodermal cells form the epiphysis, physis, and metaphysis. Apical ectodermal ridge maintenance factor (AERMF) is a substance elaborated by the mesenchymal condensations between digits. When AERMF ceases to be produced, the apical ectodermal ridge begins to break apart. This in turn triggers the release of lysosomes which dissolve the mesenchymal connections between the developing digits, completing web space formation.

Question 239

Topic: Biology, Genetics & Bone Healing
Which type of collagen is the predominant structural protein synthesized by hypertrophic chondrocytes during the endochondral ossification phase of fracture healing?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type X collagen

Explanation

Hypertrophic chondrocytes specifically synthesize Type X collagen during endochondral ossification. This marks the transition from cartilage matrix production to calcification and subsequent bone formation.

Question 240

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with an expansile lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor of bone. She is prescribed denosumab prior to surgery. What is the mechanism of action of this medication?

. Inhibits VEGF to decrease tumor vascularity
. Binds to RANKL to inhibit osteoclast-like giant cell formation
. Directly induces apoptosis of mononuclear neoplastic cells
. Inhibits matrix metalloproteinases to prevent local invasion
. Stimulates osteoblast differentiation via BMP-2 pathways

Correct Answer & Explanation

. Binds to RANKL to inhibit osteoclast-like giant cell formation

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL, preventing its interaction with the RANK receptor on osteoclasts and giant cells. This effectively halts the severe osteolysis characteristic of Giant Cell Tumors.

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