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Biology, Genetics & Bone Healing MCQs

Practice Set 14 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 261

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the mechanism of action of denosumab in the treatment of a giant cell tumor of bone?

. Binds to the RANK receptor on osteoclasts
. Binds to RANKL, preventing interaction with RANK
. Inhibits the formation of the osteoclast ruffled border
. Binds directly to osteoprotegerin (OPG)
. Inhibits cathepsin K activity

Correct Answer & Explanation

. Binds to RANKL, preventing interaction with RANK

Explanation

Denosumab is a monoclonal antibody that directly binds to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclasts and their precursors, thereby inhibiting bone resorption and tumor progression.

Question 262

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a comminuted tibia shaft fracture. Which of the following phases of secondary fracture healing is characterized by the initial formation of a soft callus, comprising predominantly fibrous tissue and cartilage?

. Inflammatory phase
. Granulation phase
. Soft callus phase
. Hard callus phase
. Remodeling phase

Correct Answer & Explanation

. Soft callus phase

Explanation

Correct Answer: CThe soft callus phase, or reparative phase, is indeed characterized by the proliferation of fibroblasts and chondroblasts that produce a fibrous matrix and fibrocartilage, forming the soft callus. The inflammatory phase involves hematoma formation and inflammatory cell influx. The granulation phase is early angiogenesis and fibrous tissue formation but not yet the mature soft callus. The hard callus phase involves calcification of the soft callus, and the remodeling phase is the conversion of woven to lamellar bone.

Question 263

Topic: Biology, Genetics & Bone Healing

Which growth factor is considered the most potent osteoinductive agent and plays a crucial role in initiating mesenchymal stem cell differentiation into osteoblasts during fracture healing?

. Platelet-Derived Growth Factor (PDGF)
. Transforming Growth Factor-beta (TGF-beta)
. Fibroblast Growth Factor (FGF)
. Insulin-like Growth Factor (IGF)
. Bone Morphogenetic Proteins (BMPs)

Correct Answer & Explanation

. Bone Morphogenetic Proteins (BMPs)

Explanation

Correct Answer: EBone Morphogenetic Proteins (BMPs), particularly BMP-2 and BMP-7, are well-known for their potent osteoinductive properties, capable of inducing mesenchymal stem cell differentiation into osteoblasts and initiating endochondral and intramembranous bone formation. TGF-beta is also involved but primarily regulates cell proliferation, differentiation, and extracellular matrix production. PDGF and FGF are mitogenic and angiogenic, while IGF promotes cell proliferation and matrix synthesis.

Question 264

Topic: Biology, Genetics & Bone Healing

Primary (direct) bone healing, as seen with rigid internal fixation, typically occurs under conditions of minimal interfragmentary strain. What is the characteristic cellular event that allows direct bone remodeling across the fracture gap without significant callus formation?

. Enchondral ossification
. Intramembranous ossification with extensive callus
. Formation of a fibrocartilaginous bridge
. Direct osteon remodeling by cutting cones
. Increased vascularity leading to hematoma resolution

Correct Answer & Explanation

. Direct osteon remodeling by cutting cones

Explanation

Correct Answer: DPrimary bone healing, occurring with rigid fixation and minimal gap (<0.1 mm) and strain (<2%), involves direct remodeling of the fracture site by cutting cones (Haversian systems). These cutting cones cross the fracture line, laying down new lamellar bone directly without an intermediate cartilaginous callus, a process akin to physiological bone remodeling. Enchondral ossification is characteristic of secondary healing, and extensive callus is also secondary healing.

Question 265

Topic: Biology, Genetics & Bone Healing

A 70-year-old patient with a history of chronic glucocorticoid use for rheumatoid arthritis sustains a distal radius fracture. What is the primary mechanism by which chronic glucocorticoid use impairs fracture healing?

. Increased osteoclast activity leading to bone resorption
. Enhanced inflammatory response at the fracture site
. Inhibition of osteoblast proliferation and differentiation
. Reduced vascularization of the fracture hematoma
. Accelerated bone turnover leading to premature callus maturation

Correct Answer & Explanation

. Inhibition of osteoblast proliferation and differentiation

Explanation

Correct Answer: CChronic glucocorticoid use significantly impairs fracture healing primarily by inhibiting osteoblast proliferation and differentiation, reducing collagen synthesis, and promoting osteoblast apoptosis. They also interfere with local growth factor production and angiogenesis. While they can affect bone metabolism, their direct impact on osteoblast function is key to impaired healing.

Question 266

Topic: Biology, Genetics & Bone Healing

Secondary fracture healing predominantly involves which of the following processes?

. Direct Haversian remodeling
. Intramembranous ossification only
. Endochondral ossification
. Creeping substitution without callus
. Fibrous union followed by direct bone formation

Correct Answer & Explanation

. Endochondral ossification

Explanation

Correct Answer: CSecondary fracture healing, characterized by the formation of a callus, primarily involves endochondral ossification, where cartilage is formed first and then replaced by bone, similar to long bone development. Intramembranous ossification also contributes at the periosteal surface, but enchondral ossification is central to the soft and hard callus phases. Direct Haversian remodeling is primary healing. Creeping substitution is seen in bone graft incorporation. Fibrous union is often a step towards nonunion if not ossified.

Question 267

Topic: Biology, Genetics & Bone Healing

Wolff's Law describes the principle by which bone remodels in response to mechanical stresses. In the context of fracture healing, during which phase is Wolff's Law most actively demonstrated?

. Inflammatory phase
. Soft callus phase
. Hard callus phase
. Remodeling phase
. Consolidation phase

Correct Answer & Explanation

. Remodeling phase

Explanation

Correct Answer: DWolff's Law is most evident during the remodeling phase. After the hard callus has bridged the fracture and been mineralized, the woven bone of the callus is gradually replaced by stronger, more organized lamellar bone, and the medullary cavity is re-established, all in response to the functional loads and stresses placed upon it. The consolidation phase is part of the hard callus to early remodeling phase, but remodeling is the specific phase where the bone's architecture is refined according to stress.

Question 268

Topic: Biology, Genetics & Bone Healing

Which cell type is primarily responsible for the resorption of both the initial fracture hematoma and any necrotic bone fragments during the early stages of fracture healing?

. Osteoblasts
. Chondrocytes
. Fibroblasts
. Osteoclasts
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteoclasts

Explanation

Correct Answer: DOsteoclasts are multinucleated cells derived from hematopoietic stem cells that are responsible for bone resorption. During fracture healing, they are crucial for removing necrotic bone fragments and remodeling the bone at the fracture site. Macrophages also play a role in clearing the hematoma and debris, but osteoclasts are specific to bone resorption. Osteoblasts form bone, chondrocytes form cartilage, fibroblasts form fibrous tissue, and mesenchymal stem cells differentiate into these cell types.

Question 269

Topic: Biology, Genetics & Bone Healing

During fracture healing after intramedullary nailing, the soft callus primarily consists of which of the following tissues, and how is it subsequently replaced?

. Woven bone, replaced by lamellar bone through primary healing
. Cartilage, replaced by bone through endochondral ossification
. Fibrous tissue, replaced by bone through intramembranous ossification
. Lamellar bone, replaced by Haversian systems through cutting cones
. Hyaline cartilage, replaced by fibrocartilage through creeping substitution

Correct Answer & Explanation

. Cartilage, replaced by bone through endochondral ossification

Explanation

Intramedullary nailing provides relative stability, initiating secondary fracture healing. The initial soft callus is composed primarily of cartilage, which is subsequently mineralized and replaced by woven bone via endochondral ossification.

Question 270

Topic: Biology, Genetics & Bone Healing

Intramedullary nailing of a diaphyseal femur fracture predominantly promotes which type of bone healing, and through what stabilization mechanism?

. Primary bone healing via absolute stability
. Secondary bone healing via relative stability
. Primary bone healing via relative stability
. Secondary bone healing via absolute stability
. Membranous ossification via rigid compression

Correct Answer & Explanation

. Secondary bone healing via relative stability

Explanation

Intramedullary nails act as internal, load-sharing splints that provide relative stability. This permits controlled micromotion at the fracture site, which biologically stimulates secondary bone healing through enchondral ossification and callus formation.

Question 271

Topic: Biology, Genetics & Bone Healing

A diaphyseal tibia fracture is treated with a statically locked intramedullary nail. According to Perren's strain theory, what range of interfragmentary strain is expected to promote the predominant mode of bone healing in this scenario?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 100%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Intramedullary nailing provides relative stability, resulting in interfragmentary strain typically between 2% and 10%. This strain environment promotes secondary bone healing through enchondral ossification and robust callus formation.

Question 272

Topic: Biology, Genetics & Bone Healing

According to the principles of fracture healing, which tissue is the first to bridge a fracture gap undergoing secondary healing following stabilization with an intramedullary nail, due to its exceptionally high strain tolerance?

. Woven bone
. Lamellar bone
. Hyaline cartilage
. Granulation tissue
. Fibrocartilage

Correct Answer & Explanation

. Granulation tissue

Explanation

Granulation tissue is the first reparative tissue to form in a fracture gap. It can tolerate up to 100% strain without rupturing, effectively stabilizing the gap enough for stiffer tissues with lower strain tolerances to eventually form.

Question 273

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a high-energy midshaft tibia fracture treated with reamed intramedullary nailing is 8 weeks post-operative. Radiographs show early callus formation, and she has good pain control. According to the post-operative rehabilitation protocols, what is the most appropriate progression for her weight-bearing status at this stage?

. Continue strict non-weight bearing (NWB) until full cortical bridging is evident.
. Initiate full weight bearing as tolerated (FWBAT) immediately to promote bone healing.
. Progress from non-weight bearing (NWB) or touch-down weight bearing (TDWB) to protected weight bearing (PWB) or weight bearing as tolerated (WBAT).
. Begin plyometric exercises to strengthen the quadriceps and calf muscles.
. Remove all assistive devices and encourage independent ambulation.

Correct Answer & Explanation

. Progress from non-weight bearing (NWB) or touch-down weight bearing (TDWB) to protected weight bearing (PWB) or weight bearing as tolerated (WBAT).

Explanation

Correct Answer: CExplanation:The case's 'Phase 2 Early Mobilization & Progressive Loading (Weeks 6-12)' section states, 'Weight Bearing: Progress from NWB/TDWB to PWB/WBAT as radiological signs of healing (early callus formation) become evident and pain allows. Regular follow-up radiographs (every 4-6 weeks) guide progression.' The patient is 8 weeks post-op with early callus, fitting this phase.Option A is incorrect:Continuing strict NWB until full cortical bridging is too conservative for this stage, especially with early callus formation and good pain control.Option B is incorrect:Initiating FWBAT immediately is too aggressive. FWBAT is typically achieved later, once clinical and radiographic union are confirmed (Phase 3).Option D is incorrect:Plyometric exercises are part of 'Phase 3 Advanced Strengthening & Return to Activity (Weeks 12+)' and are too aggressive for 8 weeks post-op.Option E is incorrect:Removing all assistive devices and encouraging independent ambulation is part of later stages of rehabilitation (Phase 3), after significant progression in strength and confidence.

Question 274

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Imaging reveals an eccentric, purely lytic epiphyseal lesion extending to the subchondral bone of the distal femur. A core needle biopsy shows mononuclear cells interspersed with multinucleated giant cells. Which targeted medical therapy is most appropriate for a surgically unresectable recurrence of this tumor?

. Imatinib
. Denosumab
. Rituximab
. Methotrexate
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

The diagnosis is Giant Cell Tumor of bone, driven by the overexpression of RANKL by the neoplastic mononuclear cells. Denosumab is a monoclonal antibody against RANKL and is highly effective for unresectable or recurrent disease.

Question 275

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs demonstrate an eccentric, lytic, epiphyseal lesion in the proximal tibia. Histology shows multinucleated giant cells. Which medication can be used as a targeted neoadjuvant therapy?

. Imatinib
. Denosumab
. Methotrexate
. Doxorubicin
. Bisphosphonates

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL used for Giant Cell Tumors of bone. It inhibits osteoclast-like giant cells, leading to tumor consolidation and facilitating subsequent surgical curettage.

Question 276

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a painful lytic epiphyseal lesion in the distal femur. Biopsy reveals mononuclear cells and multinucleated giant cells. Which of the following best describes the mechanism of action of the targeted pharmacological therapy often utilized for this tumor?

. Inhibition of vascular endothelial growth factor (VEGF)
. Inhibition of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Restoration of wild-type TP53 function
. Direct tyrosine kinase inhibition
. Inhibition of the mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Inhibition of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Denosumab is highly effective for Giant Cell Tumor of bone and acts as a monoclonal antibody that inhibits RANKL. This prevents osteoclast-like giant cell formation, thereby reducing tumor-associated bone resorption.

Question 277

Topic: Biology, Genetics & Bone Healing
A 70-year-old female with severe osteoporosis is prescribed denosumab. What is the primary mechanism of action of this medication in treating osteoporosis?
. Increases osteoblast activity and bone formation
. Stimulates parathyroid hormone release to increase calcium levels
. Binds directly to hydroxyapatite crystals on the bone surface
. Monoclonal antibody that targets and inhibits RANKL
. Increases intestinal absorption of calcium and phosphate

Correct Answer & Explanation

. Monoclonal antibody that targets and inhibits RANKL

Explanation

Denosumab is a human monoclonal antibody that specifically targets and inhibits Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL). RANKL is a key mediator of osteoclast formation, function, and survival. By binding to RANKL, denosumab prevents it from activating its receptor (RANK) on pre-osteoclasts and mature osteoclasts. This inhibition leads to a decrease in osteoclast numbers and activity, thereby reducing bone resorption and increasing bone mineral density.

Question 278

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is primarily achieved when a fracture is stabilized with absolute stability, such as with a dynamic compression plate?

. Endochondral ossification
. Primary bone healing via cutting cones
. Secondary bone healing with callus formation
. Intramembranous ossification
. Chondrogenesis

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Absolute stability limits interfragmentary strain to <2%, allowing for primary bone healing via osteoclastic cutting cones and direct osteoblastic bone formation. Secondary bone healing involves cartilaginous callus formation and occurs with relative stability.

Question 279

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a painful lytic lesion in the distal radius epiphysis. Biopsy reveals mononuclear stromal cells interspersed with multinucleated giant cells. Which of the following correctly identifies the neoplastic cell in this lesion and its characteristic marker?

. Multinucleated giant cell; RANKL
. Multinucleated giant cell; RANK
. Mononuclear stromal cell; RANKL
. Mononuclear stromal cell; RANK
. Osteoblast; Runx2

Correct Answer & Explanation

. Mononuclear stromal cell; RANKL

Explanation

In giant cell tumors of bone, the mononuclear stromal cells are the actual neoplastic cells, and they express RANKL. The multinucleated giant cells are reactive osteoclast-like cells recruited by the RANKL expression.

Question 280

Topic: Biology, Genetics & Bone Healing

A 55-year-old female undergoes a DEXA scan revealing a T-score of -2.8 in the lumbar spine. She is prescribed a bisphosphonate. What is the primary cellular mechanism of action for this medication?

. Inhibition of RANKL
. Inhibition of osteoclast farnesyl pyrophosphate synthase
. Stimulation of osteoblast Wnt signaling
. Inhibition of sclerostin
. Binding to the parathyroid hormone receptor

Correct Answer & Explanation

. Inhibition of osteoclast farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates work by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway, leading to osteoclast apoptosis. Denosumab inhibits RANKL, and Romosozumab inhibits sclerostin.

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