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1. General Principles & Basic Science MCQs

Practice Set 714 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 14261

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the physiological effect of continuous high-dose administration of Parathyroid Hormone (PTH) on bone remodeling?

. Net increase in bone formation via direct stimulation of osteoblasts
. Net increase in bone resorption via direct stimulation of osteoclasts
. Net increase in bone resorption via osteoblast-mediated activation of osteoclasts
. Net decrease in bone turnover by inhibiting both osteoblasts and osteoclasts
. Induction of osteocyte apoptosis leading to woven bone formation

Correct Answer & Explanation

. Net increase in bone resorption via osteoblast-mediated activation of osteoclasts

Explanation

Continuous high-dose PTH leads to a net increase in bone resorption. PTH receptors are located on osteoblasts (not osteoclasts). The osteoblasts respond to continuous PTH by upregulating RANKL and downregulating OPG, which in turn activates osteoclasts. Intermittent low-dose PTH (e.g., teriparatide), conversely, favors bone formation.

Question 14262

Topic: Biomechanics & Biomaterials
Increasing the radiation dose to highly cross-link ultra-high molecular weight polyethylene (UHMWPE) in total joint arthroplasty primarily improves wear resistance at the expense of which of the following mechanical properties?
. Yield strength
. Fatigue crack propagation resistance
. Ultimate tensile strength
. Modulus of elasticity
. Compressive strength

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE significantly reduces abrasive wear but diminishes its mechanical properties, particularly fatigue crack propagation resistance and fracture toughness. This increases the risk of component fracture, especially in thin liners.

Question 14263

Topic: Biology, Genetics & Bone Healing

A child presents with recurrent fractures, anemia, and cranial nerve palsies. Radiographs reveal generalized osteosclerosis with a "bone-within-bone" appearance. The primary cellular defect in this condition involves a failure of which mechanism?

. Defective collagen type I synthesis
. Inability to acidify the resorption pit via carbonic anhydrase II
. Overactive osteoblast function due to Wnt signaling
. Defective mineralization of osteoid
. Fibroblast growth factor receptor 3 (FGFR3) mutation

Correct Answer & Explanation

. Inability to acidify the resorption pit via carbonic anhydrase II

Explanation

This presentation is characteristic of osteopetrosis, a disease of osteoclast dysfunction. The most common underlying defect is a mutation in carbonic anhydrase II, which prevents osteoclasts from creating the acidic environment necessary for bone resorption.

Question 14264

Topic: 1. General Principles & Basic Science

In orthopedic screw design, which of the following geometric alterations will most significantly increase the pullout strength of a cortical screw in bone?

. Increasing the core diameter
. Decreasing the outer thread diameter
. Increasing the outer thread diameter
. Increasing the pitch
. Decreasing the thread depth

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

The pullout strength of a screw is most directly proportional to the outer (thread) diameter of the screw. Decreasing the pitch or increasing the thread depth also improves pullout strength.

Question 14265

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic, eccentrically located lesion in the distal femur epiphysis. Biopsy confirms Giant Cell Tumor (GCT) of bone. Denosumab is considered for neoadjuvant therapy. What is the specific target of this medication?

. Osteoprotegerin (OPG)
. RANK receptor on osteoclasts
. RANK Ligand (RANKL) on stromal cells
. Vascular Endothelial Growth Factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. RANK Ligand (RANKL) on stromal cells

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANK Ligand (RANKL), which is secreted by the neoplastic stromal cells in a GCT. This prevents RANKL from activating the RANK receptor on normal osteoclast precursors, stopping bone destruction.

Question 14266

Topic: 1. General Principles & Basic Science

When evaluating the ultrastructure of normal articular cartilage, which zone is characterized by having the highest water content, lowest proteoglycan content, and collagen fibers oriented parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone provides the gliding surface of the joint and resists shear forces. It has the highest water content, the lowest proteoglycan concentration, and type II collagen aligned parallel to the articular surface.

Question 14267

Topic: 1. General Principles & Basic Science

A patient sustains a severe stretch injury to the brachial plexus. EMG suggests a Sunderland third-degree peripheral nerve injury. Histologically, this grade of injury is defined by disruption of the axon and which of the following structures?

. Myelin sheath only
. Endoneurium
. Perineurium
. Epineurium
. Both perineurium and epineurium

Correct Answer & Explanation

. Endoneurium

Explanation

A Sunderland third-degree injury involves disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Because the endoneurial tubes are disrupted, scarring can occur, making spontaneous recovery unpredictable and often incomplete.

Question 14268

Topic: Biology, Genetics & Bone Healing

A 55-year-old female immigrant presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). What is the most likely diagnosis?

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

Correct Answer & Explanation

. Osteomalacia

Explanation

This laboratory profile (low Ca, low PO4, high ALP, and secondary hyperparathyroidism) is the hallmark of osteomalacia, typically caused by severe Vitamin D deficiency. Paget's and osteoporosis generally feature normal calcium and phosphorus levels.

Question 14269

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is increasingly used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its mechanism of action?

. Irreversibly inhibits cyclooxygenase to prevent platelet aggregation
. Competitively inhibits the activation of plasminogen to plasmin
. Directly activates the extrinsic coagulation cascade
. Increases the synthesis of von Willebrand factor
. Inhibits factor Xa directly

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine-binding sites on plasminogen, competitively inhibiting its activation to plasmin, thereby preventing the degradation of fibrin clots.

Question 14270

Topic: 1. General Principles & Basic Science

During an extended orthopedic procedure requiring prolonged tourniquet use, ischemic injury to skeletal muscle occurs. Which type of muscle fibers are most susceptible to this ischemic damage, and what is their primary metabolic pathway?

. Type I fibers, glycolytic pathway
. Type I fibers, oxidative pathway
. Type IIb fibers, glycolytic pathway
. Type IIa fibers, oxidative pathway
. Type IIb fibers, oxidative pathway

Correct Answer & Explanation

. Type I fibers, oxidative pathway

Explanation

Type I (slow-twitch) muscle fibers rely heavily on oxidative metabolism and have high mitochondrial content. Consequently, they are much more susceptible to ischemic injury during prolonged tourniquet ischemia compared to Type II (fast-twitch, glycolytic) fibers.

Question 14271

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a given orthopaedic implant material, what term describes the specific point where plastic deformation begins and the material will no longer return to its original shape upon load removal?

. Ultimate tensile strength
. Yield point
. Failure point
. Elastic modulus
. Fatigue limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from the elastic region to the plastic region on a stress-strain curve. Beyond this point, the material sustains permanent, irreversible deformation.

Question 14272

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a history of malabsorption presents with diffuse bone pain. Radiographs show bilateral Looser zones in the femoral necks. Labs reveal low calcium, low phosphate, and elevated alkaline phosphatase. Which histologic finding is diagnostic of this metabolic bone disease?

. Decreased osteoclast activity and retained primary spongiosa
. Increased thickness and volume of unmineralized osteoid seams
. Thinning of normal trabeculae with normal mineralization ratios
. Extensive formation of disorganized woven bone
. Increased multinucleated giant cells within brown tumors

Correct Answer & Explanation

. Increased thickness and volume of unmineralized osteoid seams

Explanation

The patient has osteomalacia (adult rickets) caused by vitamin D deficiency or malabsorption. Histologically, it is characterized by defective mineralization of newly formed bone matrix, resulting in thick, unmineralized osteoid seams.

Question 14273

Topic: Infection, Pharmacology & VTE

A 6-year-old boy presents with high fever and refusal to bear weight on his right leg. MRI confirms acute hematogenous osteomyelitis of the proximal tibia. What is the primary anatomical location for the initial bacterial seeding in this age group?

. Diaphysis
. Metaphysis
. Epiphysis
. Physis
. Periosteum

Correct Answer & Explanation

. Metaphysis

Explanation

In children, acute hematogenous osteomyelitis most commonly begins in the metaphysis of long bones. Sluggish blood flow in the venous sinusoids adjacent to the physis provides an ideal environment for bacterial deposition and proliferation.

Question 14274

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by having the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicularly to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It contains the highest proteoglycan content, the lowest water content, and has type II collagen fibers arranged vertically (perpendicular to the joint surface).

Question 14275

Topic: Biomechanics & Biomaterials

When comparing Titanium alloy (Ti-6Al-4V) to Stainless Steel (316L) for use in orthopedic fracture fixation plates, Titanium is characterized by which of the following mechanical properties?

. Higher modulus of elasticity
. Greater risk of galvanic corrosion when used alone
. Lower modulus of elasticity
. Higher rate of biofilm adherence
. Increased stiffness resulting in higher stress shielding

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloy has a lower modulus of elasticity compared to stainless steel or cobalt-chrome, making it mechanically closer to the elasticity of cortical bone. This property decreases stress shielding and promotes a more physiologic load transfer.

Question 14276

Topic: 1. General Principles & Basic Science
During the remodeling and maturation phase of tendon healing, the cellularity of the tissue decreases and the extracellular matrix becomes highly organized. Which type of collagen primarily replaces Type III collagen during this phase?
. Type I
. Type II
. Type IV
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

In the early phases of tendon and ligament healing, the initial scar tissue is predominantly composed of Type III collagen. During the remodeling phase, this is gradually replaced by stronger, more organized Type I collagen.

Question 14277

Topic: 1. General Principles & Basic Science

Bupivacaine is commonly used in orthopaedic regional nerve blocks but carries a known risk of severe cardiotoxicity if injected intravascularly. What is the primary molecular mechanism by which local anesthetics like bupivacaine exert their effect?

. Opening of presynaptic calcium channels
. Blockade of intracellular voltage-gated sodium channels
. Activation of inhibitory GABA receptors
. Competitive inhibition of NMDA receptors
. Blockade of delayed-rectifier potassium channels

Correct Answer & Explanation

. Blockade of intracellular voltage-gated sodium channels

Explanation

Local anesthetics work by crossing the nerve cell membrane and binding to the intracellular portion of voltage-gated sodium channels. This blockade prevents sodium influx, thereby halting action potential propagation.

Question 14278

Topic: Biology, Genetics & Bone Healing

Alendronate is prescribed to a patient for the treatment of postmenopausal osteoporosis. What is the primary cellular mechanism of action for this nitrogen-containing bisphosphonate?

. Inhibition of osteoblast apoptosis
. Direct binding and neutralization of RANKL
. Inhibition of farnesyl pyrophosphate (FPP) synthase
. Stimulation of the Wnt signaling pathway
. Direct inhibition of cathepsin K

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronic acid) act by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins in osteoclasts, leading to osteoclast apoptosis.

Question 14279

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, expansile lesion in the distal femoral epiphysis extending to the subchondral bone. Histology shows multinucleated giant cells in a background of mononuclear stromal cells. What targeted medical therapy has shown high efficacy for unresectable cases of this tumor?

. Imatinib
. Denosumab
. Methotrexate
. Rituximab
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

The patient has a Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear stromal cells overexpress RANKL, which recruits osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective targeted therapy to halt bone destruction.

Question 14280

Topic: Biology, Genetics & Bone Healing

A 14-year-old male sustains a subtrochanteric femur fracture. Radiographs show diffusely dense, 'chalk-like' bones with loss of the medullary canal. He has a history of multiple cranial nerve palsies. A defect in which of the following mechanisms is most likely responsible?

. Type I collagen synthesis
. Osteoclastic carbonic anhydrase II
. Fibroblast growth factor receptor 3
. Osteoblast differentiation
. Matrix metalloproteinase activity

Correct Answer & Explanation

. Osteoclastic carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, commonly due to a mutation in carbonic anhydrase II or TCIRG1. This leads to dense but brittle bones and narrowed neural foramina causing cranial nerve palsies.

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