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1. General Principles & Basic Science MCQs

Practice Set 315 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 6281

Topic: Biology, Genetics & Bone Healing

Which of the following cellular mechanisms correctly describes the action of denosumab in the treatment of osteoporosis?

. Direct inhibition of the ruffled border of osteoclasts
. Binding to and inhibiting the RANK receptor directly on osteoclasts
. Monoclonal antibody binding to RANKL, preventing its interaction with RANK
. Stimulation of osteoprotegerin (OPG) secretion by osteoblasts
. Downregulation of sclerostin leading to increased Wnt signaling

Correct Answer & Explanation

. Direct inhibition of the ruffled border of osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL in the extracellular space. This prevents RANKL from engaging the RANK receptor on osteoclast precursors, thereby halting osteoclast differentiation and activity.

Question 6282

Topic: Biomechanics & Biomaterials

During cyclic loading of a tendon, a steady increase in deformation over time while the applied load remains strictly constant is best described by which viscoelastic property?

. Stress relaxation
. Creep
. Hysteresis
. Isotropic deformation
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the time-dependent deformation of a viscoelastic material under a constant load. In contrast, stress relaxation is the progressive decrease in stress over time when the material is held at a constant deformation.

Question 6283

Topic: Biomechanics & Biomaterials

Which of the following best describes the inherent mechanical behavior of cortical bone?

. Stronger in tension than in compression
. Stronger in shear than in compression
. Exhibits identical strength in all directions of loading
. Stronger in compression than in tension and shear
. Highly isotropic due to its crystalline hydroxyapatite structure

Correct Answer & Explanation

. Stronger in tension than in compression

Explanation

Cortical bone is highly anisotropic, meaning its mechanical properties vary depending on the direction of the applied load. It is strongest in compression, significantly weaker in tension, and weakest in shear.

Question 6284

Topic: 1. General Principles & Basic Science

In mature articular cartilage, which zone is characterized by the highest concentration of water and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage contains the highest water content and the lowest proteoglycan concentration. Its collagen fibrils are aligned parallel to the articular surface to optimize resistance to shear forces.

Question 6285

Topic: Biology, Genetics & Bone Healing

Which intracellular signaling pathway is directly activated by Bone Morphogenetic Proteins (BMPs) to stimulate osteoblast differentiation?

. Wnt/beta-catenin pathway
. Serine/threonine kinase to SMAD pathway
. RANKL/RANK pathway
. Notch signaling pathway
. MAPK/ERK pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

BMPs bind to cell surface serine/threonine kinase receptors, which subsequently phosphorylate intracellular SMAD proteins (SMAD 1, 5, and 8). The resulting SMAD complex translocates to the nucleus to directly regulate osteogenic gene transcription.

Question 6286

Topic: Biomechanics & Biomaterials

Which of the following physical properties accurately describes polymethylmethacrylate (PMMA) bone cement when utilized in arthroplasty?

. It acts as a biologic adhesive binding directly to hydroxyapatite
. It is notably stronger in tension than in compression
. It cures via an endothermic reaction allowing for immediate cooling
. It relies exclusively on mechanical interlock for implant stability
. Its modulus of elasticity is significantly greater than that of cortical bone

Correct Answer & Explanation

. It acts as a biologic adhesive binding directly to hydroxyapatite

Explanation

PMMA functions strictly as a grout, relying purely on macro- and micro-mechanical interlock with the surrounding cancellous bone and the implant, not as a chemical adhesive. It is strongest in compression, weakest in tension, and undergoes a highly exothermic curing process.

Question 6287

Topic: Biomechanics & Biomaterials

On a classic stress-strain curve for a typical metallic implant, the exact point at which the material ceases to deform elastically and begins to deform permanently is known as the:

. Ultimate tensile strength
. Proportional limit
. Yield point
. Modulus of elasticity
. Failure point

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The yield point marks the critical transition from elastic (fully reversible) deformation to plastic (irreversible) deformation on a stress-strain curve. The linear portion leading up to this point represents the material's modulus of elasticity.

Question 6288

Topic: Biology, Genetics & Bone Healing

What is the primary cellular mechanism of action of parathyroid hormone (PTH) when administered intermittently at low doses (e.g., Teriparatide) for fracture healing or osteoporosis?

. It directly inhibits osteoclast ruffled border formation
. It directly stimulates osteoclast apoptosis
. It stimulates osteoblast activity leading to net bone formation
. It decreases renal tubular reabsorption of calcium
. It acts exclusively to increase secretion of osteoprotegerin (OPG)

Correct Answer & Explanation

. It directly inhibits osteoclast ruffled border formation

Explanation

While continuous endogenous PTH exposure typically leads to net bone resorption, intermittent administration of low-dose PTH (Teriparatide) exerts a powerful anabolic effect. It directly stimulates osteoblasts, leading to net bone formation.

Question 6289

Topic: Biomechanics & Biomaterials

Regarding the modulus of elasticity (Young's modulus), which of the following sequences correctly orders common orthopedic materials from most stiff to least stiff?

. Cobalt-chromium > Stainless steel > Titanium > Cortical bone
. Stainless steel > Cobalt-chromium > Titanium > Cortical bone
. Titanium > Cobalt-chromium > Stainless steel > Cortical bone
. Cortical bone > Titanium > Stainless steel > Cobalt-chromium
. Cobalt-chromium > Titanium > Stainless steel > Cortical bone

Correct Answer & Explanation

. Cobalt-chromium > Stainless steel > Titanium > Cortical bone

Explanation

The modulus of elasticity is a measure of material stiffness. Cobalt-chromium is the stiffest (approx. 220 GPa), followed by stainless steel (200 GPa), titanium alloy (110 GPa), and finally cortical bone (15-20 GPa).

Question 6290

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants is most highly accelerated and likely to occur under which of the following specific conditions?

. A single titanium implant placed in a highly oxygenated tissue environment
. Mixed implantation of stainless steel and cobalt-chromium in a saline environment
. Implantation of ultra-high-molecular-weight polyethylene articulating with a ceramic head
. Implantation of two identical stainless steel plates side by side
. A well-fixed PMMA cemented cobalt-chromium stem

Correct Answer & Explanation

. A single titanium implant placed in a highly oxygenated tissue environment

Explanation

Galvanic corrosion requires two dissimilar metals with different anodic indices (such as stainless steel and cobalt-chromium) placed in electrical contact within an electrolytic solution (like physiologic saline). This electrochemical cell leads to accelerated corrosion of the less noble metal.

Question 6291

Topic: Biology, Genetics & Bone Healing
Which specific collagen type is predominantly expressed by cells during the soft callus (chondrogenic) phase of secondary fracture healing?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

During the soft callus phase of secondary fracture healing, local chondrocytes proliferate and synthesize a cartilage matrix that is highly rich in Type II collagen. This matrix is later calcified and replaced by Type I collagen as the soft callus converts to hard woven bone.

Question 6292

Topic: Biology, Genetics & Bone Healing

Increasing the working length of a locked plate construct has which of the following biomechanical effects?

. Decreases axial stiffness
. Increases torsional stiffness
. Increases stress shielding
. Decreases interfragmentary strain
. Increases pullout strength

Correct Answer & Explanation

. Decreases axial stiffness

Explanation

Increasing the working length of a locked plate construct decreases its axial and torsional stiffness. This allows for greater interfragmentary motion, which promotes secondary bone healing through robust callus formation.

Question 6293

Topic: 1. General Principles & Basic Science

Which of the following signaling pathways is most directly inhibited by the administration of nonsteroidal anti-inflammatory drugs (NSAIDs) during fracture healing?

. BMP-2 receptor binding
. Wnt/beta-catenin signaling
. Cyclooxygenase-2 (COX-2) mediated prostaglandin E2 synthesis
. Osteoclast RANKL receptor activation
. Runx2 transcription factor expression

Correct Answer & Explanation

. BMP-2 receptor binding

Explanation

NSAIDs inhibit both COX-1 and COX-2 enzymes. COX-2 is highly upregulated during fracture healing, and its inhibition impairs endochondral ossification and callus formation by reducing prostaglandin E2 synthesis.

Question 6294

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopedic biomaterial, the slope of the curve strictly within its linear elastic region represents which of the following material properties?

. Yield strength
. Ultimate tensile strength
. Toughness
. Young's modulus
. Ductility

Correct Answer & Explanation

. Yield strength

Explanation

Young's modulus, a direct measure of a material's intrinsic stiffness, is defined as the slope of the stress-strain curve within its linear elastic region. Toughness, in contrast, represents the total energy absorbed before failure (total area under the curve).

Question 6295

Topic: Biomechanics & Biomaterials
Increasing the radiation dose during the cross-linking process of ultra-high molecular weight polyethylene (UHMWPE) for total joint arthroplasty has what primary effect on its material properties?
. Increases volumetric wear
. Increases fatigue strength
. Decreases ductility
. Decreases oxidation resistance
. Increases yield strength

Correct Answer & Explanation

. Decreases ductility

Explanation

Increasing the radiation dose increases the density of cross-links, which significantly reduces the volumetric wear of the polyethylene. However, this process sacrifices mechanical properties, notably decreasing the material's ductility, fatigue strength, and fracture toughness.

Question 6296

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) promote osteoinduction primarily through the activation of which of the following intracellular signaling pathways?

. Wnt/beta-catenin pathway
. SMAD 1/5/8 pathway
. JAK/STAT pathway
. Notch/Hes pathway
. cAMP/PKA pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

BMPs bind to cell-surface serine-threonine kinase receptors on mesenchymal stem cells, leading to the phosphorylation of intracellular SMAD 1/5/8 proteins. This complex then translocates to the nucleus to upregulate osteogenic transcription factors like Runx2.

Question 6297

Topic: 1. General Principles & Basic Science

In the biphasic model of articular cartilage, which structural component is primarily responsible for generating the internal swelling pressure that resists compressive loads?

. Type II collagen
. Hyaluronic acid
. Chondroitin sulfate
. Type IX collagen
. Elastin

Correct Answer & Explanation

. Type II collagen

Explanation

Chondroitin sulfate and keratin sulfate are glycosaminoglycans on aggrecan molecules that possess fixed negative charges. These charges repel each other and draw in water via Donnan osmosis, creating the inherent swelling pressure that provides compressive stiffness.

Question 6298

Topic: Biomechanics & Biomaterials

A patient undergoes an ACL reconstruction. When the graft is tensioned and secured at a constant fixed length, the tension within the graft is observed to gradually decrease over time. What is this specific viscoelastic property called?

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the viscoelastic property where a tissue or material experiences a decrease in stress (tension) over time when held at a constant strain (length). In contrast, creep refers to continued deformation over time under a constant load.

Question 6299

Topic: 1. General Principles & Basic Science

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

. Core (inner) diameter
. Thread pitch
. Outer (major) diameter
. Screw head diameter
. Insertion torque

Correct Answer & Explanation

. Core (inner) diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, length of thread engagement, and the shear strength of the host bone. It is inversely proportional to the thread pitch.

Question 6300

Topic: Biology, Genetics & Bone Healing

Primary bone healing is characterized by direct Haversian remodeling without the formation of a visible fracture callus. What is the maximum interfragmentary strain threshold compatible with primary bone healing?

. Less than 2 percent
. Between 2 and 10 percent
. Between 10 and 15 percent
. Between 15 and 20 percent
. Greater than 30 percent

Correct Answer & Explanation

. Less than 2 percent

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2 percent. At this low strain, osteoclastic cutting cones can cross the fracture site without being disrupted by mechanical motion.

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