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1. General Principles & Basic Science MCQs

Practice Set 443 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 8841

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which type of tissue is capable of tolerating the highest amount of interfragmentary strain before rupturing?

. Woven bone
. Lamellar bone
. Cartilage
. Granulation tissue
. Fibrous tissue

Correct Answer & Explanation

. Granulation tissue

Explanation

Granulation tissue can tolerate up to 100% strain without rupturing, bridging the initial highly mobile fracture gap. As stability increases and strain decreases, the tissue differentiates into cartilage (tolerates ~10% strain) and eventually bone (tolerates ~2% strain).

Question 8842

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, the release of calcium ions from the sarcoplasmic reticulum initiates cross-bridge cycling. Calcium directly binds to which of the following proteins to expose the myosin-binding sites on actin?

. Tropomyosin
. Troponin C
. Troponin I
. Troponin T
. Calmodulin

Correct Answer & Explanation

. Troponin C

Explanation

In skeletal muscle, calcium released from the sarcoplasmic reticulum binds specifically to Troponin C. This interaction induces a conformational change that pulls tropomyosin away, exposing the myosin-binding sites on the actin filament.

Question 8843

Topic: 1. General Principles & Basic Science

What factor has the greatest influence on the pullout strength of a cortical screw in diaphyseal bone?

. Outer diameter
. Inner (root) diameter
. Pitch
. Thread depth
. Core diameter

Correct Answer & Explanation

. Outer diameter

Explanation

The outer diameter of the screw is the most significant factor determining screw pullout strength. This is followed closely by the length of thread engagement in the bone.

Question 8844

Topic: 1. General Principles & Basic Science

In which specific zone of normal articular cartilage are the collagen fibers oriented perpendicular to the joint surface and the chondrocytes arranged in vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone of articular cartilage, collagen fibers are oriented perpendicularly to the articular surface. Chondrocytes are also arranged in vertical columns to effectively resist compressive forces.

Question 8845

Topic: Biomechanics & Biomaterials

When analyzing the stress-strain curve of an orthopedic implant material, the area under the curve strictly within the elastic region represents which mechanical property?

. Toughness
. Yield strength
. Resilience
. Ultimate tensile strength
. Ductility

Correct Answer & Explanation

. Resilience

Explanation

Resilience is defined as the area under the stress-strain curve in the elastic region, representing the material's ability to absorb energy without permanent deformation. Toughness is the total area under the entire curve.

Question 8846

Topic: Infection, Pharmacology & VTE

Which of the following bacterial organisms is most highly associated with early implant-related infections mediated by excessive glycocalyx (biofilm) production?

. Streptococcus pyogenes
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Cutibacterium acnes
. Enterococcus faecalis

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis is a coagulase-negative staphylococcus renowned for its ability to produce a robust exopolysaccharide glycocalyx. This biofilm allows it to aggressively adhere to metallic orthopedic implants and evade both host immunity and antibiotics.

Question 8847

Topic: Biology, Genetics & Bone Healing

Denosumab is used in the treatment of postmenopausal osteoporosis and giant cell tumor of bone. What is its precise mechanism of action?

. Binds directly to the ruffled border of active osteoclasts
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Acts as a human monoclonal antibody against RANKL
. Competitively blocks the RANK receptor on osteoblasts
. Stimulates endogenous osteoprotegerin (OPG) production

Correct Answer & Explanation

. Acts as a human monoclonal antibody against RANKL

Explanation

Denosumab is a human monoclonal antibody that specifically binds to RANKL. By doing so, it prevents RANKL from interacting with the RANK receptor on osteoclasts, profoundly inhibiting osteoclast formation, function, and survival.

Question 8848

Topic: 1. General Principles & Basic Science

Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cells are primarily responsible for clearing myelin debris in the peripheral nervous system to facilitate eventual axonal regeneration?

. Schwann cells and macrophages
. Oligodendrocytes and microglia
. Astrocytes and neutrophils
. Ependymal cells and lymphocytes
. Fibroblasts and plasma cells

Correct Answer & Explanation

. Schwann cells and macrophages

Explanation

In the peripheral nervous system, Schwann cells and recruited blood-derived macrophages phagocytose myelin and axonal debris during Wallerian degeneration. This clearing process is essential to create a permissible environment for axonal regrowth.

Question 8849

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely utilized in major orthopedic procedures to reduce perioperative blood loss. What is the specific molecular mechanism of action of TXA?

. Irreversibly inhibits factor Xa
. Directly binds and inhibits thrombin
. Blocks the conversion of plasminogen to active plasmin
. Stimulates the immediate release of von Willebrand factor
. Irreversibly inhibits cyclooxygenase-1 (COX-1) in platelets

Correct Answer & Explanation

. Blocks the conversion of plasminogen to active plasmin

Explanation

Tranexamic acid is a synthetic lysine analog and antifibrinolytic agent. It competitively inhibits the activation of plasminogen to plasmin, thereby stabilizing existing fibrin clots and preventing their premature degradation.

Question 8850

Topic: Biology, Genetics & Bone Healing

During normal secondary fracture healing, which phase is distinctly characterized by the highest peak of cellular proliferation and the critical transition of soft cartilaginous callus to hard woven bone callus?

. Hematoma formation phase
. Acute inflammation phase
. Reparative phase
. Remodeling phase
. Direct ossification phase

Correct Answer & Explanation

. Reparative phase

Explanation

The reparative phase features intense cellular proliferation, initially forming a soft cartilaginous callus. This soft callus subsequently undergoes endochondral ossification to form a mechanically stable hard bony callus.

Question 8851

Topic: 1. General Principles & Basic Science

When comparing different skeletal muscle fiber types, which of the following physiological characteristics is accurately associated with Type I (slow-twitch) fibers compared to Type II (fast-twitch) fibers?

. Higher concentration of glycolytic enzymes
. Lower capillary density
. Higher mitochondrial density
. Faster rate of clinical fatigue
. Significantly larger overall fiber diameter

Correct Answer & Explanation

. Higher mitochondrial density

Explanation

Type I fibers are designed for aerobic endurance and sustained postural control. Consequently, they possess high mitochondrial density, rich capillary networks, and high myoglobin content, rendering them highly resistant to fatigue.

Question 8852

Topic: Biomechanics & Biomaterials

A 60-year-old man presents with an acutely swollen knee. Aspiration yields cloudy synovial fluid that demonstrates positively birefringent, rhomboid-shaped crystals under compensated polarized light microscopy. What specific material constitutes these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Calcium pyrophosphate dihydrate (CPPD) crystals are the hallmark of pseudogout. They classically appear as rhomboid-shaped crystals with weak positive birefringence under polarized light.

Question 8853

Topic: Biomechanics & Biomaterials
Which of the following modern manufacturing modifications to ultra-high-molecular-weight polyethylene (UHMWPE) most significantly decreases its adhesive and abrasive wear rates in total joint arthroplasty?
. Standard gamma irradiation strictly in an air environment
. Highly cross-linking via irradiation followed by melting or annealing
. Significantly decreasing the overall molecular weight
. Addition of polymethylmethacrylate (PMMA) to the resin matrix
. Increasing the crystalline-to-amorphous phase ratio without cross-linking

Correct Answer & Explanation

. Highly cross-linking via irradiation followed by melting or annealing

Explanation

Highly cross-linking UHMWPE with elevated doses of irradiation drastically improves its wear resistance. Subsequent thermal treatment (melting or annealing) is required to extinguish residual free radicals and prevent in vivo oxidative degradation.

Question 8854

Topic: Biology, Genetics & Bone Healing

Which of the following signaling molecules, produced primarily by mature osteocytes, acts as a potent negative regulator of bone formation by inhibiting the Wnt/beta-catenin pathway in osteoblasts?

. Osteocalcin
. Osteopontin
. Sclerostin
. Bone morphogenetic protein-2 (BMP-2)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Correct Answer & Explanation

. Sclerostin

Explanation

Sclerostin is a glycoprotein selectively secreted by osteocytes that binds to LRP5/6 receptors on osteoblasts. This binding directly inhibits the Wnt/beta-catenin signaling pathway, thereby reducing bone formation.

Question 8855

Topic: 1. General Principles & Basic Science

Bupivacaine is an amide local anesthetic known for its relatively long duration of action. What is the primary mechanism by which it halts nerve action potential conduction?

. Opening of voltage-gated potassium channels
. Blockade of voltage-gated sodium channels from the intracellular side
. Inhibition of calcium influx at the presynaptic terminal
. Direct activation of inhibitory GABA receptors
. Irreversible inhibition of presynaptic acetylcholine release

Correct Answer & Explanation

. Blockade of voltage-gated sodium channels from the intracellular side

Explanation

Local anesthetics enter the nerve cell membrane in their uncharged, lipophilic state and then bind to the intracellular portion of voltage-gated sodium channels. This blockade prevents the sodium influx required for action potential propagation.

Question 8856

Topic: Biomechanics & Biomaterials
Which of the following modifications to ultra-high-molecular-weight polyethylene (UHMWPE) most effectively reduces adhesive and abrasive wear in total joint arthroplasty?
. Gamma irradiation in air
. Highly cross-linking and remelting
. Adding calcium hydroxyapatite
. Decreasing the molecular weight
. Sterilization with ethylene oxide

Correct Answer & Explanation

. Highly cross-linking and remelting

Explanation

Highly cross-linking UHMWPE significantly improves wear resistance by reducing polymer chain mobility. Subsequent remelting or annealing eliminates free radicals, reducing oxidative degradation.

Question 8857

Topic: Biology, Genetics & Bone Healing

A novel therapeutic agent targets the RANK receptor to inhibit osteoclastogenesis. Which of the following cells primarily expresses the RANK receptor?

. Osteoblasts
. Osteocytes
. Osteoclast precursors
. Mesenchymal stem cells
. Chondrocytes

Correct Answer & Explanation

. Osteoclast precursors

Explanation

The RANK receptor is expressed on the surface of osteoclast precursors and mature osteoclasts. Binding of RANKL (produced by osteoblasts) to RANK stimulates osteoclast differentiation and activation.

Question 8858

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman with chronic kidney disease presents with diffuse bone pain. Laboratory studies reveal hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH). What is the primary underlying pathophysiology of her bone disease?

. Deficiency of 25-hydroxyvitamin D
. Inability to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
. Primary hyperparathyroidism
. Defective Type I collagen synthesis
. Overproduction of osteoprotegerin (OPG)

Correct Answer & Explanation

. Inability to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

Explanation

Renal osteodystrophy is driven by the failing kidneys' inability to synthesize 1-alpha-hydroxylase, preventing the conversion of 25(OH)D to active 1,25(OH)2D. This leads to hypocalcemia, triggering secondary hyperparathyroidism.

Question 8859

Topic: 1. General Principles & Basic Science

Articular cartilage relies on its structural organization for biomechanical competence. Which zone of articular cartilage contains the highest concentration of water and collagen, but the lowest concentration of proteoglycans?

. Superficial zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content and collagen concentration, with collagen fibers oriented parallel to the joint surface to resist shear stress. It has the lowest concentration of proteoglycans.

Question 8860

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibition
. Direct Factor Xa inhibition
. Vitamin K antagonism
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase-1 (COX-1)

Correct Answer & Explanation

. Direct Factor Xa inhibition

Explanation

Rivaroxaban is a highly selective direct Factor Xa inhibitor. Unlike low-molecular-weight heparins, it does not require antithrombin III to exert its anticoagulant effect.

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