Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 134 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 2661

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with increasing skull size, hearing loss, and a bowing deformity of his left tibia. Serum calcium and phosphorus are normal, but alkaline phosphatase is markedly elevated. The primary cellular defect in this disease is characterized by:

. A primary defect in osteoblast bone formation due to RUNX2 mutation
. A deficiency of tissue-nonspecific alkaline phosphatase
. A primary defect causing hyperactive, large multinucleated osteoclasts
. Autoimmune destruction of the organic bone matrix
. A mutation in the COL1A1 gene leading to brittle bone matrix

Correct Answer & Explanation

. A primary defect in osteoblast bone formation due to RUNX2 mutation

Explanation

The clinical presentation is classic for Paget's disease of bone (osteitis deformans). The primary cellular abnormality is found in the osteoclast, which is hyper-responsive to RANKL, excessively large, and highly multinucleated (up to 100 nuclei). This initiates a phase of aggressive osteolysis, followed by disorganized, woven bone formation by osteoblasts. Paget's has been linked to SQSTM1 mutations and paramyxovirus inclusions.

Question 2662

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs), such as BMP-2 and BMP-7, are utilized clinically to enhance bone formation. They initiate osteoblastic differentiation primarily through binding cell surface receptors that subsequently activate which of the following intracellular signaling pathways?

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

Correct Answer & Explanation

. Wnt / beta-catenin pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which phosphorylate receptor-regulated Smads (specifically Smad 1, 5, and 8). These phosphorylated Smads form a complex with the co-Smad (Smad 4), translocate to the nucleus, and induce the transcription of osteogenic genes (e.g., Runx2). The Wnt pathway (Option A) is regulated by LRP5/6 and sclerostin, independent of BMP primary signaling.

Question 2663

Topic: Biology, Genetics & Bone Healing
A patient with osteopetrosis presents with multiple fractures and a 'rugger jersey' spine appearance on radiographs. The disease is caused by an inability of osteoclasts to resorb bone. A known genetic defect underlying the most common autosomal recessive form of this condition affects which of the following?
. Type I collagen (COL1A1/COL1A2)
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II (CAII)
. Tissue-nonspecific alkaline phosphatase (TNSALP)
. Fibrillin-1 (FBN1)

Correct Answer & Explanation

. Carbonic anhydrase II (CAII)

Explanation

Osteopetrosis is fundamentally a failure of osteoclast-mediated bone resorption. Osteoclasts require a highly acidic environment in the Howship lacuna to dissolve mineralized bone matrix. Mutations in Carbonic Anhydrase II (CAII), as well as the TCIRG1 gene (vacuolar proton pump), prevent the osteoclast from generating and pumping protons (H+), thereby nullifying bone resorption and resulting in abnormally dense, brittle bone.

Question 2664

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain and muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH) levels. What is the most likely diagnosis?

. Osteoporosis
. Osteomalacia
. Paget disease
. Primary hyperparathyroidism
. Multiple myeloma

Correct Answer & Explanation

. Osteoporosis

Explanation

The patient's laboratory profile (low calcium, low phosphate, high alkaline phosphatase, high PTH) is characteristic of osteomalacia, most commonly caused by profound Vitamin D deficiency. This leads to impaired intestinal calcium absorption, triggering secondary hyperparathyroidism which increases phosphate excretion. Osteoporosis typically presents with normal lab values. Primary hyperparathyroidism would feature elevated serum calcium. Paget disease typically presents with an isolated elevation in alkaline phosphatase with normal calcium and phosphate.

Question 2665

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the process of 'creeping substitution' seen during the incorporation of a cortical bone allograft?

. Simultaneous resorption of the graft by osteoclasts and formation of new bone by osteoblasts
. Induction of undifferentiated mesenchymal stem cells into osteoblasts by BMPs
. Scaffold-mediated direct primary bone healing without any intermediate callus
. Rapid revascularization followed by immediate structural strengthening of the graft
. Complete dissolution of the graft by osteoclasts before any osteoblast activity begins

Correct Answer & Explanation

. Simultaneous resorption of the graft by osteoclasts and formation of new bone by osteoblasts

Explanation

Creeping substitution is the classical histological process by which a structural bone graft (such as a cortical allograft) is incorporated. It involves the simultaneous, coupled process of graft resorption by osteoclasts and the deposition of new host bone by osteoblasts. During this slow process, cortical allografts often become temporarily weaker before full incorporation is achieved.

Question 2666

Topic: Biology, Genetics & Bone Healing

A pediatric patient presents with gingival bleeding, petechiae, and metaphyseal radiolucent bands on radiographs. This condition is caused by a nutritional deficiency that directly impairs which specific step of collagen synthesis?

. Cleavage of procollagen C-terminal propeptides
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Transcription of the COL1A1 gene
. Intracellular assembly of the triple helix

Correct Answer & Explanation

. Cleavage of procollagen C-terminal propeptides

Explanation

The clinical presentation describes scurvy, which is caused by a deficiency of Vitamin C (ascorbic acid). Vitamin C is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes are responsible for the hydroxylation of proline and lysine residues on the nascent procollagen chains, a step absolutely critical for the stable formation of the collagen triple helix.

Question 2667

Topic: Biology, Genetics & Bone Healing

What is the primary biomechanical function of the proteoglycan aggrecan in the extracellular matrix of normal articular cartilage?

. Providing tensile strength to the tissue
. Anchoring chondrocytes to the subchondral bone
. Drawing water into the matrix to provide compressive stiffness
. Directly inhibiting osteoclast activity
. Mediating the cross-linking of Type II collagen

Correct Answer & Explanation

. Providing tensile strength to the tissue

Explanation

Aggrecan is a massive proteoglycan densely populated with negatively charged glycosaminoglycans (chondroitin sulfate and keratan sulfate). These fixed negative charges repel each other and create a strong Donnan osmotic effect, drawing water into the cartilage matrix. This swelling pressure, constrained by the Type II collagen network, provides articular cartilage with its exceptional compressive stiffness.

Question 2668

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary (direct) bone healing without the formation of an intermediate callus requires the absolute interfragmentary strain to be kept below what threshold?

. 2%
. 10%
. 15%
. 25%
. 50%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory postulates that the type of tissue that can form in a fracture gap is dictated by the level of interfragmentary strain. Granulation tissue can form at high strain (up to 100%), cartilage up to 10%, and woven/lamellar bone can only form if the strain is less than 2%. Therefore, for primary (direct) bone healing (which bypasses the cartilaginous callus phase), absolute stability must be achieved to keep strain below 2%.

Question 2669

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) primarily induces bone formation and osteoblast differentiation through which intracellular signaling pathway?

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

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

BMP-2 binds to cell surface receptors to activate the intracellular Smad 1/5/8 pathway. These activated Smad proteins complex with Smad 4 and translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 2670

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is FDA approved for use in acute open tibial shaft fractures?

. BMP-2
. BMP-4
. BMP-7
. BMP-9
. BMP-14

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for acute open tibial shaft fractures stabilized with intramedullary nailing. BMP-7 (rhBMP-7/OP-1) was previously approved for recalcitrant tibial nonunions under a humanitarian device exemption.

Question 2671

Topic: Biology, Genetics & Bone Healing

A 55-year-old male with end-stage renal disease presents with bilateral spontaneous quadriceps tendon ruptures. Which of the following underlying physiological mechanisms most directly contributes to this condition?

. Vitamin D toxicity
. Secondary hyperparathyroidism
. Primary hypoparathyroidism
. Excessive calcitonin secretion
. Osteopetrosis

Correct Answer & Explanation

. Vitamin D toxicity

Explanation

Patients with end-stage renal disease frequently develop secondary hyperparathyroidism due to hyperphosphatemia and decreased active vitamin D. The resulting excess PTH causes bone resorption and weakens the osteotendinous junction, predisposing to spontaneous tendon ruptures.

Question 2672

Topic: Biology, Genetics & Bone Healing

A 5-year-old girl with a history of multiple fractures, blue sclerae, and dentinogenesis imperfecta presents with a new diaphyseal femur fracture. She is currently treated with intravenous pamidronate. What is the primary mechanism of action of this medication in her condition?

. Stimulation of osteoblast differentiation and bone formation
. Inhibition of osteoclast-mediated bone resorption
. Direct binding to and inhibition of RANK-ligand
. Enhancement of collagen type I synthesis
. Direct inhibition of sclerostin

Correct Answer & Explanation

. Stimulation of osteoblast differentiation and bone formation

Explanation

The patient has Osteogenesis Imperfecta (OI), caused by mutations in COL1A1 or COL1A2. Bisphosphonates, such as pamidronate, are the medical treatment of choice. They act by binding to hydroxyapatite crystals in bone and inhibiting osteoclast-mediated bone resorption. This increases bone mineral density and decreases fracture incidence, though it does not correct the underlying collagen defect.

Question 2673

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl is evaluated for multiple recurrent fractures with minimal trauma. She has blue sclerae and mild bowing of her femurs. Genetic testing confirms a mutation affecting type I collagen. Which of the following medical treatments is most commonly used to decrease fracture frequency in this condition?

. Subcutaneous Denosumab injections
. Daily Teriparatide therapy
. Intravenous bisphosphonates
. High-dose Vitamin D and Calcium supplementation
. Recombinant growth hormone therapy

Correct Answer & Explanation

. Subcutaneous Denosumab injections

Explanation

Intravenous bisphosphonates (e.g., pamidronate) are the standard of care in moderate to severe Osteogenesis Imperfecta. They inhibit osteoclast activity, increase bone mineral density, and significantly reduce fracture rates.

Question 2674

Topic: Biology, Genetics & Bone Healing

Secondary bone healing occurs via enchondral ossification.

According to Perren's strain theory, what is the maximum interfragmentary strain that allows for the formation of woven bone?

. 1%
. 2%
. 10%
. 30%
. 100%

Correct Answer & Explanation

. 1%

Explanation

According to Perren's strain theory, the type of tissue that can form in a fracture gap depends on the interfragmentary strain. Lamellar bone requires <2% strain (primary healing). Woven bone can form with up to 10% strain. Fibrocartilage can tolerate up to 10-30% strain, and granulation tissue can tolerate up to 100% strain. Thus, woven bone requires strain to be less than 10%.

Question 2675

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with knee pain. Radiographs show an eccentric, lytic, expansile lesion in the epiphysis of the proximal tibia extending to the subchondral bone.

Biopsy demonstrates multinucleated giant cells in a stroma of mononuclear cells. The neoplastic stromal cells in this tumor are characterized by the excessive expression of which of the following?

. RANK ligand
. CD99
. MUC4
. SATB2
. T (Brachyury)

Correct Answer & Explanation

. RANK ligand

Explanation

Giant cell tumor of bone is composed of neoplastic stromal cells that excessively express RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This expression recruits and activates osteoclast-like multinucleated giant cells, which are responsible for the aggressive osteolysis characteristic of the tumor. Denosumab, a monoclonal antibody against RANKL, is used in the treatment of advanced or unresectable cases.

Question 2676

Topic: Biology, Genetics & Bone Healing

Rigid internal fixation with an absolute stability construct (e.g., a lag screw and neutralization plate) for a transverse diaphyseal fracture promotes primary bone healing. Which of the following is the primary histological mechanism by which primary bone healing occurs?

. Endochondral ossification
. Intramembranous ossification
. Haversian remodeling via cutting cones
. Hematoma organization and woven bone formation
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Endochondral ossification

Explanation

Primary bone healing occurs without intermediate callus formation when there is absolute stability and compression across the fracture site. It is driven directly by Haversian remodeling, where osteoclasts create 'cutting cones' that cross the fracture line, followed immediately by osteoblasts laying down lamellar bone. Endochondral ossification is the hallmark of secondary bone healing (callus formation).

Question 2677

Topic: Biology, Genetics & Bone Healing

A 35-year-old male undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate, achieving absolute stability. Which of the following describes the primary mechanism of bone healing expected in this scenario?

. Endochondral ossification with robust soft callus formation
. Direct osteonal remodeling via cutting cones across the fracture site
. Intramembranous ossification starting from the periosteum
. Fibrocartilage bridging followed by woven bone substitution
. Distraction osteogenesis driven by mechanical strain

Correct Answer & Explanation

. Endochondral ossification with robust soft callus formation

Explanation

When absolute stability is achieved (e.g., rigid plate fixation with anatomic reduction), secondary fracture healing (callus formation) is suppressed. The bone heals via primary (direct) bone healing, characterized by osteoclast-led cutting cones crossing the fracture gap followed immediately by osteoblast-mediated osteonal formation.

Question 2678

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism by which denosumab affects bone metabolism?

. Directly induces apoptosis of osteoclasts
. Binds to RANK ligand (RANKL), preventing its interaction with RANK
. Inhibits the Wnt/beta-catenin signaling pathway
. Binds to the parathyroid hormone (PTH) receptor on osteoblasts
. Cross-links collagen fibrils in the extracellular matrix

Correct Answer & Explanation

. Directly induces apoptosis of osteoclasts

Explanation

Denosumab is a monoclonal antibody that targets RANKL. By binding to RANKL, it prevents it from activating the RANK receptor on osteoclast precursors, thus inhibiting their maturation, function, and survival.

Question 2679

Topic: Biology, Genetics & Bone Healing

Which phase of fracture healing is characterized by the peak activity of chondrocytes and the formation of a soft callus?

. Inflammation
. Hard callus formation
. Remodeling
. Reparative phase
. Hematoma organization

Correct Answer & Explanation

. Inflammation

Explanation

The reparative phase is characterized by the formation of a soft callus. During this phase, chondrocytes produce a cartilaginous matrix that bridges the fracture gap prior to endochondral ossification.

Question 2680

Topic: Biology, Genetics & Bone Healing

The "creeping substitution" process observed in the incorporation of a massive structural cortical bone allograft is primarily mediated by which of the following mechanisms?

. Direct differentiation of host mesenchymal stem cells into osteocytes
. Osteoclastic resorption followed by host osteoblastic bone deposition
. Rapid revascularization through pre-existing Haversian canals
. Enchondral ossification from a cartilaginous intermediate
. Inflammatory fibrous tissue replacing the graft

Correct Answer & Explanation

. Direct differentiation of host mesenchymal stem cells into osteocytes

Explanation

Creeping substitution is the process by which a bone graft is slowly resorbed by host osteoclasts and simultaneously replaced by host osteoblasts laying down new bone. Cortical allografts undergo this process much slower than cancellous autografts.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page