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Biology, Genetics & Bone Healing MCQs

Practice Set 10 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 181

Topic: Biology, Genetics & Bone Healing

Which of the following Bone Morphogenetic Proteins (BMPs) is an FDA-approved osteoinductive agent currently utilized as an alternative to autologous bone graft in single-level anterior lumbar interbody fusion (ALIF)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is utilized in spine surgery as a potent osteoinductive agent and is FDA-approved for specific fusions like ALIF. BMP-3 actually inhibits osteogenesis, and BMP-7 (OP-1) was previously used for nonunions but has less commercial utilization today.

Question 182

Topic: Biology, Genetics & Bone Healing

During open reduction and internal fixation of a transverse diaphyseal fracture, a surgeon applies a dynamic compression plate to achieve absolute stability and rigid fixation. Which mode of bone healing is primarily expected under these biomechanical conditions?

. Secondary bone healing via cartilaginous callus formation
. Primary bone healing via direct Haversian remodeling
. Endochondral ossification
. Intramembranous ossification with exuberant periosteal callus
. Fibrous nonunion progression

Correct Answer & Explanation

. Primary bone healing via direct Haversian remodeling

Explanation

Absolute stability (e.g., via compression plating) eliminates interfragmentary motion, leading to primary bone healing. This process occurs via cutting cones and direct Haversian remodeling without the formation of a visible fracture callus.

Question 183

Topic: Biology, Genetics & Bone Healing

In aseptic loosening of a total hip arthroplasty, particulate wear debris initiates a macrophage-mediated inflammatory response. What is the critical final common pathway mediator directly responsible for osteoclast activation in this process?

. Tumor necrosis factor-alpha (TNF-alpha)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Interleukin-1 (IL-1)
. Transforming growth factor-beta (TGF-beta)
. Platelet-derived growth factor (PDGF)

Correct Answer & Explanation

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

Explanation

While macrophages release inflammatory cytokines like TNF-alpha and IL-1 in response to wear debris, RANKL is the essential final common pathway mediator. RANKL binds to RANK on osteoclast precursors, stimulating their differentiation and leading to osteolysis.

Question 184

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what is the maximum tissue strain tolerated by lamellar bone formation?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Lamellar bone can only form in a low-strain environment of less than 2%. Cartilage tolerates up to 10% strain, while granulation tissue can tolerate up to 100% strain during secondary bone healing.

Question 185

Topic: Biology, Genetics & Bone Healing

Which endogenous molecule functions by binding to RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand) to inhibit osteoclast differentiation and prevent excessive bone resorption?

. Osteoprotegerin (OPG)
. Sclerostin
. Calcitonin
. Parathyroid Hormone (PTH)
. Bone Morphogenetic Protein 2 (BMP-2)

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) acts as a critical decoy receptor. By binding to RANKL, it prevents RANKL from interacting with its receptor (RANK) on osteoclast precursors, thereby halting osteoclastogenesis and reducing bone resorption.

Question 186

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are osteoinductive factors belonging to the TGF-beta superfamily. Which BMP is most heavily implicated in the standard FDA-approved formulation for open tibial shaft fractures (rhBMP-2)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail. BMP-7 (OP-1) was previously approved for recalcitrant tibial nonunions under a humanitarian device exemption.

Question 187

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with increasing leg bowing and deep bone pain. Radiographs reveal cortical thickening and coarsened trabeculae of the tibia. Serum alkaline phosphatase is markedly elevated, but calcium and phosphate are normal. Which medication is considered the first-line treatment for his symptomatic disease?

. Teriparatide
. Denosumab
. Oral bisphosphonates
. Intravenous zoledronic acid
. Calcitonin

Correct Answer & Explanation

. Intravenous zoledronic acid

Explanation

Intravenous nitrogen-containing bisphosphonates (like zoledronic acid) are the treatment of choice for symptomatic Paget's disease of bone due to their high efficacy and prolonged remission rates compared to older therapies.

Question 188

Topic: Biology, Genetics & Bone Healing

A 31-year-old male with a severe traumatic brain injury undergoes open reduction and internal fixation of an acetabular fracture. To prevent heterotopic ossification (HO), indomethacin is prescribed. What is the primary mechanism of action by which indomethacin prevents HO?

. Inhibition of osteoclast activity via RANKL suppression
. Direct inhibition of osteoblast differentiation from mesenchymal stem cells
. Inhibition of cyclooxygenase-mediated prostaglandin E2 (PGE2) synthesis
. Suppression of bone morphogenetic protein 2 (BMP-2) expression
. Upregulation of osteoprotegerin (OPG) in the fracture hematoma

Correct Answer & Explanation

. Inhibition of cyclooxygenase-mediated prostaglandin E2 (PGE2) synthesis

Explanation

Indomethacin is an NSAID that prevents heterotopic ossification by inhibiting the cyclooxygenase (COX) enzymes, thereby decreasing the synthesis of prostaglandins (specifically PGE2). PGE2 is a crucial mediator in the differentiation of mesenchymal stem cells into osteoblasts.

Question 189

Topic: Biology, Genetics & Bone Healing

Which of the following correctly pairs the receptor and its specific cellular location during the physiological process of osteoclast activation?

. RANKL on the osteoclast surface
. RANK on the osteoclast surface
. Osteoprotegerin (OPG) on the osteoclast surface
. Macrophage colony-stimulating factor (M-CSF) on the osteoblast
. RANK on the osteoblast surface

Correct Answer & Explanation

. RANK on the osteoclast surface

Explanation

Receptor Activator of Nuclear factor Kappa-B (RANK) is located on the surface of osteoclasts and their precursors. Its ligand, RANKL, is expressed on the surface of osteoblasts and stromal cells.

Question 190

Topic: Biology, Genetics & Bone Healing

A 55-year-old woman with a history of celiac disease presents with diffuse bone pain. Radiographs demonstrate bilateral symmetrical pseudofractures (Looser zones) in the femoral neck. Laboratory tests reveal hypocalcemia, hypophosphatemia, and elevated alkaline phosphatase. What is the most likely diagnosis?

. Osteoporosis
. Paget's disease
. Osteomalacia
. Primary hyperparathyroidism
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

The presence of Looser zones (pseudofractures) combined with hypocalcemia, hypophosphatemia, and elevated alkaline phosphatase is the classic biochemical and radiographic profile of osteomalacia, often driven by severe Vitamin D deficiency.

Question 191

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a multifragmentary diaphyseal femur fracture. The surgeon opts for a bridge plating technique to provide relative stability. According to Perren's strain theory, what range of gap strain is optimal for promoting secondary bone healing (callus formation)?

. Less than 2%
. Between 2% and 10%
. Between 11% and 30%
. Between 31% and 50%
. Greater than 50%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

According to Perren's strain theory, gap strain between 2% and 10% stimulates the formation of granulation tissue and cartilage, leading to secondary bone healing via endochondral ossification.

Question 192

Topic: Biology, Genetics & Bone Healing

Denosumab is a monoclonal antibody utilized in the treatment of osteoporosis and giant cell tumor of bone. It exerts its clinical effect by binding directly to which of the following molecular targets?

. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

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

Explanation

Denosumab binds directly to RANKL, preventing it from interacting with RANK on the surface of osteoclasts and their precursors. This mechanism effectively mimics the natural inhibitory action of Osteoprotegerin (OPG).

Question 193

Topic: Biology, Genetics & Bone Healing

During primary bone healing following rigid plate fixation (absolute stability), healing occurs primarily without cartilaginous callus formation via Haversian remodeling. Which of the following best describes the cellular arrangement of the 'cutting cone' mechanism?

. Osteoblasts at the leading edge and osteoclasts at the trailing edge
. Osteoclasts at the leading edge and osteoblasts at the trailing edge
. Chondrocytes at the leading edge and osteoblasts at the trailing edge
. Macrophages at the leading edge and fibroblasts at the trailing edge
. Osteocytes at the leading edge and osteoclasts at the trailing edge

Correct Answer & Explanation

. Osteoclasts at the leading edge and osteoblasts at the trailing edge

Explanation

In the cutting cone of primary cortical bone healing, osteoclasts are situated at the front (leading edge) to resorb dead bone, followed closely by osteoblasts at the rear (trailing edge) which lay down new osteoid to form Haversian systems.

Question 194

Topic: Biology, Genetics & Bone Healing
Which of the following structures enables the growth plate to grow in diameter as the skeleton gets larger?
. The chondroepiphysis
. The apophysis
. The groove of Ranvier
. The ring of Lacroix
. The secondary spongiosa

Correct Answer & Explanation

. The groove of Ranvier

Explanation

The ossification groove of Ranvier contains chondrocytes that provide latitudinal growth of the growth plate. The groove of Ranvier may be thought of as the growth ring of the growth plate. The chondroepiphysis is the cartilage precursor of the epiphysis. The apophysis is a nonarticular growth region. The ring of Lacroix is a peripheral structure that reinforces the growth plate. The secondary spongiosa is mature lamellar bone after it has been remodeled.

Question 195

Topic: Biology, Genetics & Bone Healing
An African-American mother brings her 18-month-old baby in for examination because he has bowing of the legs. The child's past medical history is normal including height and weight. The child is still breast-fed. Radiographs reveal mild widening and irregularity of the physes. Which of the following conditions is likely to be found on laboratory examination?
. Elevated phosphorus
. Decreased alkaline phosphatase
. Normal 1,25 dihydroxyvitamin D
. Elevated creatinine
. Elevated parathyroid hormone

Correct Answer & Explanation

. Elevated parathyroid hormone

Explanation

This patient has nutritional rickets because of a combination of decreased vitamin D intake and increased need for sunlight due to dark skin. The laboratory findings should include a low-normal calcium phosphate, elevated alkaline phosphatase and parathyroid hormone, and low vitamin D levels and precursors. Vitamin D supplementation without bracing is adequate treatment.

Question 196

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological treatment for Giant Cell Tumor of bone. What is its specific mechanism of action?

. Inhibits matrix metalloproteinases in the tumor microenvironment
. Binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors
. Directly induces apoptosis of the neoplastic stromal cells
. Acts as a synthetic analog of osteoprotegerin to stimulate osteoblast activity
. Inhibits the SMAD intracellular signaling pathway

Correct Answer & Explanation

. Binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors

Explanation

Denosumab is a monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor, thereby inhibiting the recruitment and activation of osteoclast-like giant cells in the tumor.

Question 197

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) enhances spinal fusion through which of the following cellular mechanisms?

. Direct osteogenesis via transplantation of viable osteoprogenitor cells
. Osteoconduction by providing a porous structural scaffold
. Osteoinduction via activation of the intracellular SMAD signaling cascade
. Inhibition of osteoclastic bone resorption via RANKL blockade
. Stimulation of primarily endochondral ossification without an inflammatory phase

Correct Answer & Explanation

. Osteoinduction via activation of the intracellular SMAD signaling cascade

Explanation

BMP-2 is a potent osteoinductive protein that binds to cell surface serine/threonine kinase receptors on mesenchymal stem cells. This binding activates the intracellular SMAD signaling pathway, driving the differentiation of these cells into functioning osteoblasts.

Question 198

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate intracellular signaling leading to osteoblast differentiation primarily through which of the following pathways?

. Wnt/beta-catenin pathway
. JAK-STAT pathway
. Smad 1/5/8 pathway
. MAPK/ERK pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which phosphorylate Smad 1, 5, and 8. These receptor-regulated Smads then form a complex with Smad 4 to enter the nucleus and regulate the transcription of osteogenic genes.

Question 199

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft or bone graft substitute materials simultaneously possesses osteoinductive, osteoconductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Autologous iliac crest bone graft
. Calcium phosphate cement
. Recombinant human BMP-2

Correct Answer & Explanation

. Autologous iliac crest bone graft

Explanation

Autologous bone graft, such as from the iliac crest, is considered the gold standard because it provides all three properties necessary for bone healing. It supplies an osteoconductive scaffold, osteoinductive growth factors, and live osteogenic progenitor cells.

Question 200

Topic: Biology, Genetics & Bone Healing

Core binding factor alpha 1 (C bfa1) is a transcription factor having which of the following effects:

. Cbfa1 induces cells to differentiate into osteoblasts.
. Cbfa1 induces cells to differentiate into osteoclasts.
. Cbfa1 inhibits endochondral ossification.
. Cbfa1 impairs sulfation of proteoglycans.
. Cbfa1 causes premature cell death.

Correct Answer & Explanation

. Cbfa1 induces cells to differentiate into osteoblasts.

Explanation

Cbfa1 is a transcription factor that causes cells to differentiate into osteoblasts. An abnormality in its gene causes cleidocranial dysplasia.

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