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1. General Principles & Basic Science MCQs

Practice Set 298 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 5941

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate intracellular signaling through transmembrane serine/threonine kinase receptors. Which of the following downstream intracellular mediators are primarily activated by BMPs?

. Smad 1, 5, and 8
. Smad 2 and 3
. Smad 4
. Beta-catenin
. NF-kappa B

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs signal primarily through the phosphorylation of Smad 1, 5, and 8. These phosphorylated Smads then form a complex with Smad 4 to translocate to the nucleus and regulate gene transcription for osteoblastogenesis.

Question 5942

Topic: 1. General Principles & Basic Science
In total joint arthroplasty, the generation of ultra-high molecular weight polyethylene (UHMWPE) wear debris typically incites an inflammatory response that leads to osteolysis. Which of the following cell types is the primary effector responsible for phagocytosing this debris and releasing pro-inflammatory cytokines?
. Osteoblasts
. Fibroblasts
. Macrophages
. T lymphocytes
. Neutrophils

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose UHMWPE wear particles and release pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-6. This inflammatory cascade subsequently stimulates osteoclast-mediated bone resorption, leading to osteolysis.

Question 5943

Topic: Biology, Genetics & Bone Healing

Which of the following cells produces osteoprotegerin (OPG), acting as a decoy receptor to prevent bone resorption?

. Osteoclasts
. Osteoblasts
. Macrophages
. T-lymphocytes
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteoblasts and osteocytes secrete OPG, which binds to RANKL and prevents it from interacting with RANK on osteoclast precursors. This inhibits osteoclast differentiation and activation, thereby decreasing bone resorption.

Question 5944

Topic: Biomechanics & Biomaterials

Galvanic corrosion is most likely to occur in an orthopaedic implant under which of the following conditions?

. Using a titanium screw in a stainless steel plate
. Using a cobalt-chrome femoral head on a cobalt-chrome stem
. Using a stainless steel screw in a stainless steel plate
. Scratching the passivation layer of an isolated titanium implant
. Cyclic loading of a polyethylene liner

Correct Answer & Explanation

. Using a titanium screw in a stainless steel plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in electrical contact within a conductive fluid medium, such as body fluid. The less noble metal serves as the anode and undergoes accelerated corrosion.

Question 5945

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed teriparatide for severe osteoporosis. What is the primary mechanism of action of this medication?

. Inhibition of osteoclast ruffled border formation
. Stimulation of intermittent parathyroid hormone receptors to increase osteoblast activity
. Binding to hydroxyapatite to inhibit farnesyl pyrophosphate synthase
. Neutralization of sclerostin
. Antagonism of the RANK ligand

Correct Answer & Explanation

. Stimulation of intermittent parathyroid hormone receptors to increase osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it strongly stimulates osteoblastic bone formation, unlike continuous PTH exposure which promotes bone resorption.

Question 5946

Topic: Biomechanics & Biomaterials

Stress shielding around a femoral stem is most strongly influenced by which of the following material properties of the implant?

. Yield strength
. Ultimate tensile strength
. Modulus of elasticity
. Fatigue limit
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Modulus of elasticity relates to a material's stiffness. Implants with a high modulus of elasticity bear most of the load when placed in bone, causing stress shielding and subsequent resorption of the unloaded surrounding bone.

Question 5947

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used to reduce blood loss in total joint arthroplasty. What is its mechanism of action?
. Direct inhibition of Factor Xa
. Competitive inhibition of plasminogen activation
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase
. Direct inhibition of thrombin

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

TXA is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine receptor sites on plasminogen, preventing its activation to plasmin and thus effectively inhibiting fibrinolysis.

Question 5948

Topic: Biology, Genetics & Bone Healing
During secondary bone healing, which type of collagen is predominantly synthesized during the soft callus phase?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

The soft callus phase of endochondral ossification is characterized by the production of fibrocartilage and hyaline cartilage, which are predominantly composed of Type II collagen. This is later replaced by Type I collagen during the hard callus phase.

Question 5949

Topic: Biomechanics & Biomaterials

The progressive deformation of a polyethylene tibial insert over time under a constant static load is an example of which biomechanical principle?

. Stress relaxation
. Fatigue failure
. Creep
. Hysteresis
. Strain rate dependency

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material when subjected to a constant, continuous stress over time. Stress relaxation, conversely, is the decrease in stress over time when a material is held at a constant strain.

Question 5950

Topic: Biomechanics & Biomaterials

When adding antibiotics to polymethylmethacrylate (PMMA) bone cement, which of the following characteristics is essential for the antibiotic to be effective?

. High molecular weight
. Heat stability
. Hydrophobic nature
. Bacteriostatic mechanism
. Narrow spectrum of activity

Correct Answer & Explanation

. Heat stability

Explanation

PMMA polymerization is an exothermic reaction that can reach temperatures exceeding 80 degrees Celsius. Therefore, any antibiotic mixed into the cement (such as tobramycin or vancomycin) must be heat stable to maintain its antimicrobial efficacy.

Question 5951

Topic: Biology, Genetics & Bone Healing

A patient presents with hypocalcemia following a total thyroidectomy. How does the body naturally attempt to correct this via parathyroid hormone (PTH) release?

. Decreasing renal reabsorption of calcium
. Increasing renal excretion of phosphate
. Decreasing 1-alpha-hydroxylase activity
. Inhibiting osteoclast activity
. Decreasing intestinal calcium absorption

Correct Answer & Explanation

. Increasing renal excretion of phosphate

Explanation

PTH responds to hypocalcemia by increasing bone resorption, increasing renal reabsorption of calcium, and increasing renal excretion of phosphate. It also stimulates 1-alpha-hydroxylase in the kidney to boost active vitamin D synthesis.

Question 5952

Topic: Biology, Genetics & Bone Healing

Denosumab is a targeted biological therapy used to treat severe osteoporosis. What is its specific molecular target?

. RANK
. RANKL
. Sclerostin
. Cathepsin K
. Osteoprotegerin

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a monoclonal antibody that binds directly to RANKL. By neutralizing RANKL, it prevents interaction with the RANK receptor on osteoclasts, severely inhibiting osteoclast formation, function, and survival.

Question 5953

Topic: 1. General Principles & Basic Science

The pullout strength of a standard cortical screw is most heavily dependent on which of the following thread parameters?

. Inner root diameter
. Pitch
. Outer thread diameter
. Thread angle
. Lead

Correct Answer & Explanation

. Outer thread diameter

Explanation

Pullout strength is directly proportional to the outer thread diameter, the length of thread engagement, and the shear strength of the host bone. Increases in the outer thread diameter significantly enhance the screw's resistance to pullout.

Question 5954

Topic: Biology, Genetics & Bone Healing

Compared to mature lamellar bone, woven bone is characterized by which of the following properties?

. Higher mineral content
. Highly organized collagen alignment
. Slower rate of deposition
. Greater number of osteocytes per unit volume
. Increased biomechanical stiffness

Correct Answer & Explanation

. Greater number of osteocytes per unit volume

Explanation

Woven bone is immature, rapidly formed bone with a random, disorganized collagen fiber orientation. It contains a greater number of osteocytes per unit volume, higher water content, and lower mineral content compared to mature lamellar bone.

Question 5955

Topic: 1. General Principles & Basic Science

When a long bone is subjected to pure bending forces, where do the maximum tensile and compressive stresses occur?

. Along the neutral axis
. At the metaphyseal-diaphyseal junction
. At the outer surfaces furthest from the neutral axis
. In the center of the medullary canal
. Uniformly across the entire cross-section

Correct Answer & Explanation

. At the outer surfaces furthest from the neutral axis

Explanation

In bending, normal stresses are zero at the neutral axis and increase linearly with distance from it. Therefore, the maximum tensile and compressive stresses are located at the outermost surfaces of the bone.

Question 5956

Topic: Infection, Pharmacology & VTE
Rivaroxaban is commonly prescribed for deep vein thrombosis prophylaxis following total joint arthroplasty. Which of the following best describes its mechanism of action?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Antithrombin III activator
. Plasminogen activator

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that directly inhibits free and clot-bound Factor Xa. This interrupts the intrinsic and extrinsic pathway of the blood coagulation cascade, preventing thrombin generation.

Question 5957

Topic: 1. General Principles & Basic Science

Which enzyme is primarily responsible for generating the acidic environment within the sealing zone of the osteoclast ruffled border?

. Matrix metalloproteinase
. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K
. Alkaline phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II generates protons from carbon dioxide and water inside the osteoclast. These protons are then actively pumped across the ruffled border via an H+-ATPase pump, creating the acidic environment necessary for dissolving hydroxyapatite.

Question 5958

Topic: 1. General Principles & Basic Science

The "toe region" of a typical load-elongation curve for a normal ligament corresponds to which of the following physiological phenomena?

. Microscopic failure of collagen fibers
. Uncrimping of collagen fibers
. Plastic deformation of the ligament matrix
. Ultimate failure of the ligament
. Strain hardening of elastin

Correct Answer & Explanation

. Uncrimping of collagen fibers

Explanation

The initial non-linear toe region of a ligament's load-elongation curve represents the straightening out, or uncrimping, of the normally wavy collagen fibers. Once uncrimped, the ligament enters the linear elastic region where stiffness increases.

Question 5959

Topic: 1. General Principles & Basic Science

Which of the following best describes the mechanism by which non-steroidal anti-inflammatory drugs (NSAIDs) may impair fracture healing?

. Decreased expression of bone morphogenetic proteins
. Direct cellular toxicity to osteoblasts
. Inhibition of cyclooxygenase-2 (COX-2) mediated prostaglandin synthesis
. Increased osteoclast activation via RANKL over-expression
. Inhibition of 1-alpha-hydroxylase

Correct Answer & Explanation

. Inhibition of cyclooxygenase-2 (COX-2) mediated prostaglandin synthesis

Explanation

Fracture healing relies on a coordinated inflammatory response. NSAIDs inhibit COX-2, which drastically decreases the production of prostaglandins (like PGE2) that are critical for normal osteoblast differentiation and early endochondral ossification.

Question 5960

Topic: Biology, Genetics & Bone Healing

Sclerostin, a glycoprotein produced primarily by osteocytes, regulates bone formation by directly inhibiting which of the following intracellular signaling pathways?

. Wnt/beta-catenin
. RANK/RANKL
. TGF-beta/Smad
. Notch signaling
. Hedgehog signaling

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

Sclerostin binds to LRP5/6 receptors on osteoblasts, effectively antagonizing the canonical Wnt/beta-catenin signaling pathway. This inhibition halts osteoblast differentiation and fundamentally decreases bone formation.

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