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1. General Principles & Basic Science MCQs

Practice Set 337 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 6721

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, inhibit osteoclastic bone resorption primarily by targeting which of the following enzymes in the mevalonate pathway?

. HMG-CoA reductase
. Farnesyl pyrophosphate synthase
. Cathepsin K
. Tartrate-resistant acid phosphatase
. Carbonic anhydrase II

Correct Answer & Explanation

. HMG-CoA reductase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents the prenylation of small GTPases (such as Rho, Rac, and Rab) which are essential for osteoclast ruffled border formation and cell survival, leading to osteoclast apoptosis.

Question 6722

Topic: Biomechanics & Biomaterials

The torsional rigidity of a solid cylindrical intramedullary nail is mathematically proportional to its radius raised to which of the following powers?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. First power

Explanation

The torsional rigidity of a solid cylinder is determined by its polar moment of inertia, which is proportional to the radius to the fourth power (r^4). Therefore, even small increases in the nail's radius will significantly increase its torsional stiffness.

Question 6723

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum local tissue strain environment that allows for the formation of lamellar bone?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 100%
. Greater than 100%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory postulates that lamellar bone can only form and survive in very low-strain environments of less than 2%. Moderate strain (2% to 10%) allows for woven bone or cartilage formation, while higher strain (10% to 30%) promotes granulation tissue.

Question 6724

Topic: 1. General Principles & Basic Science

During the initial phase of acute, high-rate loading of articular cartilage, which component is primarily responsible for resisting the applied compressive force?

. Type II collagen tension
. Proteoglycan electrostatic expansion
. Interstitial fluid pressurization
. Hyaluronic acid backbone deformation
. Chondrocyte cytoskeletal resistance

Correct Answer & Explanation

. Type II collagen tension

Explanation

When articular cartilage is acutely loaded, the immediate resistance to compression is primarily due to interstitial fluid pressurization, as the fluid cannot easily escape the extracellular matrix. Over time, as fluid is extruded, the load transfers to the solid matrix (proteoglycans and collagen).

Question 6725

Topic: Biology, Genetics & Bone Healing

Which process accurately describes the incorporation of a massive cortical structural allograft, characterized by simultaneous osteoclastic resorption and osteoblastic bone formation that gradually replaces the dead graft?

. Osteoinduction
. Osteoconduction
. Creeping substitution
. Endochondral ossification
. Intramembranous ossification

Correct Answer & Explanation

. Osteoinduction

Explanation

Creeping substitution is the process by which a bone graft is slowly resorbed by osteoclasts and sequentially replaced by host bone from osteoblasts. Cortical allografts incorporate primarily by this mechanism, though the process is much slower and less complete than in cancellous autografts.

Question 6726

Topic: Biomechanics & Biomaterials

A surgeon utilizes a stainless steel plate and secures it with titanium alloy screws. Which specific type of corrosion is most likely to occur at the plate-screw interface?

. Pitting corrosion
. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Pitting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in physical contact within an electrolytic medium like body fluid. The less noble metal becomes the anode and undergoes accelerated corrosion, making the mixing of stainless steel and titanium implants contraindicated.

Question 6727

Topic: Biology, Genetics & Bone Healing

A patient with chronic severe vitamin C deficiency presents with joint effusions, gingival bleeding, and poor wound healing. The underlying pathophysiologic mechanism directly impairs which step of collagen synthesis?

. Cleavage of procollagen C-terminal propeptides
. Glycosylation of hydroxylysine residues
. Hydroxylation of proline and lysine residues
. Cross-linking by lysyl oxidase
. Transcription of alpha chains in the nucleus

Correct Answer & Explanation

. Cleavage of procollagen C-terminal propeptides

Explanation

Vitamin C (ascorbic acid) is an essential cofactor for prolyl and lysyl hydroxylases in the rough endoplasmic reticulum. Without it, hydroxylation of proline and lysine residues fails, preventing the formation of stable collagen triple helices, leading to scurvy.

Question 6728

Topic: 1. General Principles & Basic Science

Parathyroid hormone (PTH) acts directly on the kidney to increase serum calcium levels through which of the following mechanisms?

. Increasing calcium reabsorption in the proximal convoluted tubule
. Increasing calcium reabsorption in the distal convoluted tubule
. Decreasing phosphate excretion in the proximal tubule
. Inhibiting 1-alpha-hydroxylase activity
. Stimulating 24-hydroxylase activity

Correct Answer & Explanation

. Increasing calcium reabsorption in the proximal convoluted tubule

Explanation

PTH directly increases calcium reabsorption in the distal convoluted tubule of the kidney. It also decreases phosphate reabsorption in the proximal tubule and stimulates 1-alpha-hydroxylase to produce active 1,25-dihydroxyvitamin D.

Question 6729

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials possesses a Young's modulus (elastic modulus) that is closest to that of human cortical bone?

. Cobalt-chromium alloy
. Stainless steel 316L
. Titanium alloy (Ti-6Al-4V)
. Polyetheretherketone (PEEK)
. Ceramic (Alumina)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

PEEK has an elastic modulus of approximately 3-4 GPa, making it much closer to cortical bone (15-20 GPa) than metallic alloys. This minimizes stress shielding compared to titanium (~110 GPa), stainless steel (~200 GPa), or cobalt-chromium (~240 GPa).

Question 6730

Topic: Biomechanics & Biomaterials

In the context of the viscoelastic properties of ligaments and tendons, what is the biomechanical term for the progressive decrease in tension over time when the tissue is held at a constant length?

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is defined as the decrease in stress (tension) over time when a viscoelastic material is held at a constant strain (length). Conversely, creep refers to the progressive increase in strain (deformation) when a material is subjected to a constant stress (load).

Question 6731

Topic: Biomechanics & Biomaterials

A patient sustains a ligamentous injury. The viscoelastic property where the ligament lengthens continuously under a constant applied load over time is called:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic behavior

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the time-dependent permanent deformation of a viscoelastic material under a constant load. In contrast, stress relaxation is a decrease in stress over time under a constant deformation.

Question 6732

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum strain tolerated by lamellar bone before it fails?

. 2 percent
. 10 percent
. 30 percent
. 50 percent
. 100 percent

Correct Answer & Explanation

. 2 percent

Explanation

Perren's strain theory states that lamellar bone tolerates only up to 2 percent strain before failure. Woven bone tolerates up to 10 percent, and granulation tissue tolerates up to 100 percent strain.

Question 6733

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) primarily exert their osteoinductive effects by binding to cell surface receptors and directly activating which of the following intracellular signaling pathways?

. Smad proteins
. Wnt/beta-catenin
. RANK ligand
. MAP kinase
. Cyclooxygenase

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs bind to serine-threonine kinase receptors on the cell surface. This binding phosphorylates and activates intracellular Smad proteins, which translocate to the nucleus to regulate osteogenic gene transcription.

Question 6734

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical bone screw is most directly proportional to which of the following parameters?

. Inner root diameter
. Outer thread diameter
. Screw pitch
. Core diameter
. Insertion torque

Correct Answer & Explanation

. Inner root diameter

Explanation

Screw pullout strength is directly proportional to the outer (major) thread diameter, length of thread engagement, and thread depth. The inner root diameter primarily determines the screw's tensile and torsional strength, not pullout strength.

Question 6735

Topic: Biology, Genetics & Bone Healing

The compressive stiffness and elasticity of articular cartilage are primarily provided by which of its molecular components?

. Type I collagen
. Type II collagen
. Proteoglycans
. Chondrocytes
. Hyaluronic acid

Correct Answer & Explanation

. Type I collagen

Explanation

Proteoglycans, primarily aggrecan, are highly negatively charged and attract water, providing the osmotic swelling pressure that resists compression. Type II collagen forms the structural framework that resists tensile and shear forces.

Question 6736

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis, when performed under stable mechanical conditions, primarily results in new bone formation through which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional bone growth
. Creeping substitution
. Chondrolysis

Correct Answer & Explanation

. Endochondral ossification

Explanation

Under stable conditions, distraction osteogenesis stimulates bone formation via intramembranous ossification. The distraction gap fills with a fibrous, collagenous zone that mineralizes directly into bone without a cartilaginous intermediate phase.

Question 6737

Topic: Biomechanics & Biomaterials

The torsional rigidity of a solid cylindrical intramedullary nail is proportional to its radius raised to what power?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. First power

Explanation

The torsional rigidity of a solid cylinder is governed by its polar moment of inertia, which is proportional to the radius to the fourth power. Therefore, a small increase in the nail's diameter significantly increases its resistance to torsional deformation.

Question 6738

Topic: Biology, Genetics & Bone Healing

In the process of secondary fracture healing, the soft callus phase is characterized predominantly by the formation of:

. Lamellar bone
. Woven bone
. Cartilage
. Dense fibrous connective tissue
. Hematoma

Correct Answer & Explanation

. Lamellar bone

Explanation

Secondary fracture healing involves a soft callus phase composed primarily of cartilage formed by chondrocytes. This cartilaginous soft callus is later replaced by woven bone during the hard callus phase via endochondral ossification.

Question 6739

Topic: Infection, Pharmacology & VTE

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to delay fracture healing. This effect is primarily mediated through the inhibition of which enzyme crucial for early inflammatory signaling?

. Lipoxygenase
. Phospholipase A2
. Cyclooxygenase-2
. Matrix metalloproteinase-9
. Cathepsin K

Correct Answer & Explanation

. Lipoxygenase

Explanation

NSAIDs inhibit cyclooxygenase-2 (COX-2), an enzyme essential for synthesizing prostaglandins during the initial inflammatory phase of fracture healing. This inhibition impairs early angiogenesis, mesenchymal stem cell differentiation, and endochondral ossification.

Question 6740

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for cortical bone, the point at which the material begins to exhibit permanent plastic deformation and will not return to its original shape upon unloading is called the:

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

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The yield point marks the transition from elastic (reversible) deformation to plastic (irreversible) deformation. Beyond this point, microstructural damage occurs, and the material will not return to its original dimensions when the load is removed.

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