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Biology, Genetics & Bone Healing MCQs

Practice Set 172 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 3421

Topic: Biology, Genetics & Bone Healing

A 72-year-old female treated with alendronate for 8 years presents with a 3-month history of progressive left thigh pain. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the left femur. What is the most appropriate management?

. Discontinue alendronate, begin teriparatide, and restrict weight bearing
. Discontinue alendronate and perform prophylactic cephalomedullary nailing
. Continue alendronate and perform prophylactic cephalomedullary nailing
. Switch to denosumab and observe with serial radiographs
. Discontinue alendronate and perform open reduction internal fixation with a lateral plate

Correct Answer & Explanation

. Discontinue alendronate and perform prophylactic cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use, characterized by lateral cortical beaking, transverse radiolucency, and thigh pain. Because she has a symptomatic impending fracture with radiographic changes, prophylactic intramedullary nailing (cephalomedullary preferred in the subtrochanteric region) is indicated. Bisphosphonates must be discontinued immediately. Plating is biomechanically inferior for AFFs.

Question 3422

Topic: Biology, Genetics & Bone Healing

A 45-year-old male undergoes a posterolateral lumbar fusion using recombinant human bone morphogenetic protein-2 (rhBMP-2). Through which specific intracellular signaling pathway does this biologic agent primarily promote osteoblast differentiation?

. Wnt/beta-catenin pathway
. RANK/RANKL signaling
. SMAD 1/5/8 phosphorylation
. Notch signaling pathway
. Hedgehog pathway

Correct Answer & Explanation

. SMAD 1/5/8 phosphorylation

Explanation

rhBMP-2 binds to serine/threonine kinase receptors, causing phosphorylation of SMAD 1, 5, and 8. These molecules then complex with SMAD 4 to enter the nucleus and upregulate osteogenic genes like Runx2.

Question 3423

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with a destructive, expansile lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy with denosumab is initiated, what is its primary mechanism of action?

. Inhibition of vascular endothelial growth factor (VEGF)
. Monoclonal antibody targeting RANK ligand (RANKL)
. Bisphosphonate-mediated induction of osteoclast apoptosis
. Direct stimulation of osteoprotegerin (OPG) production
. Inhibition of tissue matrix metalloproteinases (MMPs)

Correct Answer & Explanation

. Monoclonal antibody targeting RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL, preventing it from activating RANK on osteoclasts and their precursors. This effectively inhibits osteoclast-mediated bone destruction characteristic of giant cell tumors.

Question 3424

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that permits primary bone healing?

. Less than 2%
. Between 2% and 10%
. Between 10% and 15%
. Greater than 15%
. Primary bone healing is independent of strain

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing occurs without callus formation and requires absolute stability. According to Perren's strain theory, the interfragmentary strain must be less than 2% to allow osteoclasts to form cutting cones across the fracture site.

Question 3425

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with bone pain, anemia, and hypercalcemia. Radiographs show multiple 'punched-out' lytic lesions in the skull and pelvis. The primary mechanism of bone destruction in this disease is driven by the upregulation of which of the following?

. RANK ligand (RANKL)
. Osteoprotegerin (OPG)
. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-beta (TGF-b)
. Fibroblast Growth Factor Receptor 3 (FGFR3)

Correct Answer & Explanation

. RANK ligand (RANKL)

Explanation

The patient has Multiple Myeloma. The myeloma cells secrete factors (like MIP-1 alpha) that upregulate RANKL and downregulate OPG, leading to massive osteoclast activation and the characteristic lytic bone lesions.

Question 3426

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is considered to have osteo-inhibitory effects rather than osteoinductive effects?

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

Correct Answer & Explanation

. BMP-3

Explanation

While most BMPs (such as BMP-2 and BMP-7) are strongly osteoinductive and promote bone formation, BMP-3 is unique as it acts as an antagonist to osteogenic BMPs, thereby inhibiting bone formation.

Question 3427

Topic: Biology, Genetics & Bone Healing

A 72-year-old female presents with a 3-month history of dull, aching pain in her left thigh, exacerbated by weight-bearing. She has been on alendronate for osteoporosis for 8 years. Physical examination is unremarkable. Initial X-rays of the femur are normal. What is the most appropriate next step in her diagnostic workup?

. Order a bone scan to evaluate for stress reaction.
. Prescribe NSAIDs and advise activity modification.
. Obtain an MRI of the left femur.
. Refer for a consultation with a pain management specialist.
. Discontinue alendronate immediately and observe.

Correct Answer & Explanation

. Obtain an MRI of the left femur.

Explanation

This patient's symptoms and history (long-term bisphosphonate use, thigh pain, normal initial X-rays) are highly suggestive of a prodromal or incomplete atypical femoral fracture (AFF). While a bone scan might show increased uptake, MRI is the most sensitive and specific imaging modality to detect cortical thickening, periosteal reaction, or a transverse lucency, which are characteristic findings of an impending or incomplete AFF. Early diagnosis is crucial to prevent a complete fracture. Discontinuing bisphosphonates might be part of the management but not the immediate next diagnostic step without confirming the pathology. NSAIDs and observation are inappropriate given the high suspicion for an AFF.

Question 3428

Topic: Biology, Genetics & Bone Healing

A 35-year-old man undergoes rigid plate fixation for a transverse radius shaft fracture. During the healing process, no fracture callus is visualized on radiographs. Which biological process dictates primary bone healing in this scenario?

. Endochondral ossification
. Cutting cone remodeling
. Fibrocartilage template formation
. Intramembranous ossification with abundant callus
. Mesenchymal cell condensation

Correct Answer & Explanation

. Cutting cone remodeling

Explanation

Primary bone healing occurs under absolute stability and relies on osteoclastic cutting cones crossing the fracture site, followed by osteoblasts depositing new lamellar bone. This process entirely bypasses the formation of a fibrocartilaginous callus.

Question 3429

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman, who has been treated with alendronate for 10 years, presents with a transverse fracture of the subtrochanteric femur after simply rising from a chair. Radiographs reveal focal lateral cortical thickening and a 'beaking' appearance. What is the underlying pathophysiologic mechanism caused by her prolonged medication use?

. Inhibition of osteoclast function leading to severe suppression of bone remodeling
. Direct cytotoxic effect on mature osteoblasts preventing osteoid formation
. Overstimulation of parathyroid hormone resulting in cortical thinning
. Inhibition of lysyl oxidase causing defective collagen cross-linking
. Increased osteocyte apoptosis leading to avascular necrosis of the diaphysis

Correct Answer & Explanation

. Inhibition of osteoclast function leading to severe suppression of bone remodeling

Explanation

Prolonged bisphosphonate therapy inhibits osteoclast activity and induces their apoptosis, heavily suppressing normal bone remodeling. This failure to clear normal microdamage over time reduces bone toughness, leading to atypical subtrochanteric or diaphyseal femur fractures.

Question 3430

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a destructive, lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, what is the primary mechanism of action of the most commonly utilized pharmacological agent?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of multinucleated giant cells
. Inhibition of RANK ligand (RANKL)
. Modulation of estrogen receptors
. Cross-linking of DNA strands

Correct Answer & Explanation

. Inhibition of RANK ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody frequently used in the treatment of Giant Cell Tumor of bone. It works by binding to and inhibiting RANKL, which prevents the maturation and activation of the osteoclast-like multinucleated giant cells.

Question 3431

Topic: Biology, Genetics & Bone Healing

A 70-year-old male complains of increasing hat size and dull, deep bone pain in his pelvis and thighs. Laboratory tests show normal serum calcium, normal serum phosphorus, and significantly elevated alkaline phosphatase. Radiographs of the skull show a characteristic "cotton wool" appearance. Which cell type is primarily responsible for the initial phase of this disease process?

. Osteoblast
. Osteoclast
. Osteocyte
. Chondrocyte
. Macrophage

Correct Answer & Explanation

. Osteoclast

Explanation

The patient's presentation and labs are diagnostic of Paget's disease of bone. The disease process is characterized by an initial phase of excessive osteoclastic bone resorption, followed by chaotic osteoblastic bone formation resulting in structurally weak woven bone.

Question 3432

Topic: Biology, Genetics & Bone Healing

During the remodeling phase of secondary fracture healing, woven bone is gradually replaced by highly organized lamellar bone. According to Wolff's Law, this physiological process is primarily driven and directed by which of the following mechanisms?

. Hormonal regulation via parathyroid hormone
. Systemic inflammatory cytokines (IL-1, IL-6)
. Mechanical stress and piezoelectric forces
. Angiogenesis factors like VEGF
. Transforming growth factor-beta (TGF-b) concentration gradient

Correct Answer & Explanation

. Mechanical stress and piezoelectric forces

Explanation

Wolff's law dictates that bone models and remodels in response to the mechanical stresses placed upon it. Mechanical loading generates piezoelectric forces that stimulate osteoclasts and osteoblasts to align trabeculae along lines of stress.

Question 3433

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, the soft callus transitions to a hard callus. Which type of collagen is predominantly synthesized during the cartilaginous phase of soft callus formation?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type II

Explanation

During secondary (indirect) fracture healing, the soft callus primarily consists of cartilage, which is rich in Type II collagen produced by proliferating chondrocytes. As the cartilage becomes hypertrophic and calcifies, Type X collagen is produced, before finally being replaced by Type I collagen in the hard bony callus.

Question 3434

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowed legs, a waddling gait, and prominent costochondral junctions. Laboratory results show low serum calcium, low serum phosphate, and elevated parathyroid hormone (PTH). What is the most likely primary diagnosis?

. Hypophosphatemic rickets
. Vitamin D-dependent rickets
. Nutritional rickets
. Renal osteodystrophy
. Osteogenesis imperfecta

Correct Answer & Explanation

. Nutritional rickets

Explanation

Nutritional rickets is caused by Vitamin D deficiency, leading to decreased intestinal calcium and phosphate absorption. The resulting hypocalcemia triggers secondary hyperparathyroidism (elevated PTH), which normalizes calcium slightly at the expense of severe urinary phosphate wasting, leading to the classic low Ca, low P, high PTH laboratory profile.

Question 3435

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery to augment spinal fusion masses. What is the primary biologic property of DBM that facilitates bone healing?

. Osteogenesis
. Osteoconduction
. Osteoinduction
. Angiogenesis
. Mechanical structural support

Correct Answer & Explanation

. Osteoinduction

Explanation

Demineralized bone matrix (DBM) is produced by acid extraction of allograft bone, removing the mineralized component but preserving collagen and growth factors, including bone morphogenetic proteins (BMPs). Its primary utility is osteoinduction—the ability to stimulate undifferentiated mesenchymal stem cells to differentiate into osteoblasts.

Question 3436

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with gingival bleeding, petechiae, and metaphyseal radiolucent bands on radiographs. The underlying condition is caused by a deficiency that impairs which of the following steps in collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Glycosylation of hydroxylysine residues
. Hydroxylation of proline and lysine residues
. Formation of cross-links by lysyl oxidase
. Transcription of alpha-1 collagen genes

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy (Vitamin C deficiency). Vitamin C is a necessary cofactor for prolyl hydroxylase and lysyl hydroxylase, the enzymes responsible for the hydroxylation of proline and lysine residues in procollagen. Without this step, the collagen triple helix cannot form properly, leading to fragile connective tissue.

Question 3437

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with an unresectable giant cell tumor of the sacrum. She is started on denosumab therapy. What is the mechanism of action of this medication?

. Monoclonal antibody against RANK
. Monoclonal antibody against RANKL
. Inhibitor of farnesyl pyrophosphate synthase
. Recombinant human parathyroid hormone
. Selective estrogen receptor modulator

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), preventing it from interacting with the RANK receptor on osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival, which is highly effective in treating Giant Cell Tumor of bone.

Question 3438

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with bone pain and increasing hat size. Radiographs show cortical thickening and coarse trabeculae in the skull and pelvis. Laboratory testing reveals elevated alkaline phosphatase with normal calcium and phosphorus. Mutations in which of the following genes are most strongly associated with this condition?

. COL1A1
. FGFR3
. SQSTM1
. PHEX
. RUNX2

Correct Answer & Explanation

. SQSTM1

Explanation

The patient's presentation is classic for Paget's disease of bone. Up to 40-50% of familial cases and 5-10% of sporadic cases are associated with mutations in the SQSTM1 gene, which encodes the p62 protein. This mutation leads to increased osteoclastogenesis and hyperactive osteoclasts. COL1A1 is associated with osteogenesis imperfecta; FGFR3 with achondroplasia; PHEX with X-linked hypophosphatemic rickets; and RUNX2 with cleidocranial dysplasia.

Question 3439

Topic: Biology, Genetics & Bone Healing

During the process of secondary bone healing, which phase is characterized by the highest level of osteoclastic activity to restore the medullary canal and original bone contours?

. Inflammation phase
. Soft callus formation
. Hard callus formation
. Remodeling phase
. Hematoma phase

Correct Answer & Explanation

. Remodeling phase

Explanation

Secondary bone healing occurs in overlapping stages: hematoma/inflammation, soft callus (chondrogenesis), hard callus (endochondral ossification), and remodeling. The remodeling phase is driven by osteoclastic resorption and osteoblastic deposition (coupled remodeling) according to Wolff's law, eventually restoring the medullary canal and bone contour over months to years.

Question 3440

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) plays a key role in calcium homeostasis. By which of the following mechanisms does continuous high-level exposure to PTH induce bone resorption?

. Direct binding to PTH receptors on osteoclasts
. Stimulating osteoblasts to release RANKL
. Inhibiting osteoprotegerin (OPG) synthesis by osteocytes
. Direct activation of bone-resorbing macrophages
. Decreasing renal tubular reabsorption of calcium

Correct Answer & Explanation

. Stimulating osteoblasts to release RANKL

Explanation

Osteoclasts do not possess PTH receptors. Continuous PTH binds to PTH receptors on osteoblasts (and stromal cells), stimulating them to upregulate the expression of RANKL (and downregulate OPG). RANKL then binds to RANK on osteoclast precursors, promoting their differentiation and activation into mature, bone-resorbing osteoclasts.

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