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1. General Principles & Basic Science MCQs

Practice Set 358 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 7141

Topic: Biology, Genetics & Bone Healing

Following a displaced, severely comminuted midshaft tibia fracture, the endosteal blood supply is entirely disrupted. Which vascular system provides the initial compensatory blood supply to the healing fracture callus?

. Nutrient artery system
. Metaphyseal vessels
. Epiphyseal vessels
. Periosteal vessels
. Haversian canals

Correct Answer & Explanation

. Nutrient artery system

Explanation

When the primary endosteal (nutrient artery) blood supply is disrupted by a fracture or intramedullary reaming, the periosteal blood supply undergoes transient hypertrophy. This reversed flow provides the major blood supply to the early healing callus.

Question 7142

Topic: 1. General Principles & Basic Science

The piezoelectric effect in bone is characterized by which of the following phenomena during mechanical loading?

. The compression side becomes electronegative and stimulates osteoblastic activity
. The tension side becomes electronegative and stimulates osteoclastic activity
. The compression side becomes electropositive and stimulates osteoblastic activity
. The tension side becomes electropositive and stimulates osteoclastic activity
. Both sides become neutral to promote creeping substitution

Correct Answer & Explanation

. The compression side becomes electronegative and stimulates osteoblastic activity

Explanation

According to the piezoelectric effect, mechanical compression of bone generates an electronegative potential that stimulates osteoblastic bone formation. Conversely, tension generates an electropositive potential favoring osteoclastic resorption.

Question 7143

Topic: Biomechanics & Biomaterials

Ligaments exhibit viscoelastic properties, meaning their mechanical behavior is highly dependent on the rate of loading. How does a ligament respond to a rapid, high-velocity load compared to a slow load?

. It becomes less stiff and fails at a lower load
. It becomes stiffer and absorbs more energy before failure
. Its modulus of elasticity decreases significantly
. It elongates further before reaching the yield point
. It demonstrates increased stress relaxation

Correct Answer & Explanation

. It becomes less stiff and fails at a lower load

Explanation

Viscoelastic materials like ligaments and bone become stiffer (increased modulus of elasticity) and can absorb more energy before failure when subjected to high loading rates compared to slow loading rates.

Question 7144

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a given orthopaedic material, what does the area under the curve in the elastic region represent?

. Toughness
. Resilience
. Yield strength
. Ultimate tensile strength
. Plastic deformation

Correct Answer & Explanation

. Toughness

Explanation

The area under the stress-strain curve in the elastic region represents the resilience of the material. The total area under the entire curve (elastic and plastic regions combined) represents the material's toughness.

Question 7145

Topic: Biomechanics & Biomaterials

When increasing the outer diameter of a solid intramedullary nail by a factor of 2, the torsional rigidity increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

For a solid cylinder, torsional rigidity is proportional to the polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, doubling the diameter increases the torsional rigidity by a factor of 16.

Question 7146

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain compatible with the formation of lamellar bone?

. 1%
. 2%
. 10%
. 20%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory states that lamellar bone can only form under conditions of low strain, typically less than 2%. Granulation tissue tolerates up to 100% strain, while fibrocartilage tolerates up to 10% strain before tearing.

Question 7147

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing, which growth factor is primarily responsible for inducing the differentiation of mesenchymal stem cells into chondrocytes?

. BMP-2
. TGF-beta
. PDGF
. VEGF
. FGF

Correct Answer & Explanation

. BMP-2

Explanation

Bone morphogenetic proteins (such as BMP-2) are osteoinductive and strongly induce mesenchymal stem cell differentiation into chondrogenic and osteogenic lineages. TGF-beta stimulates matrix synthesis, and VEGF is essential for angiogenesis.

Question 7148

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant load demonstrates a progressive increase in deformation over time. This phenomenon is known as:

. Hysteresis
. Fatigue
. Creep
. Stress relaxation
. Anisotropy

Correct Answer & Explanation

. Hysteresis

Explanation

Creep is the time-dependent increase in deformation (strain) under a constant load (stress). In contrast, stress relaxation is the decrease in stress over time under a constant state of deformation.

Question 7149

Topic: Biology, Genetics & Bone Healing

Following a displaced diaphyseal fracture of the adult tibia, what is the primary source of blood supply to the healing callus during the early stages of secondary bone healing?

. Nutrient artery
. Periosteal vessels
. Metaphyseal arteries
. Epiphyseal arteries
. Haversian canals

Correct Answer & Explanation

. Nutrient artery

Explanation

Following a fracture, the medullary nutrient artery is often disrupted. The extraosseous periosteal blood supply temporarily becomes the dominant source of blood flow to the healing fracture callus early in the reparative process.

Question 7150

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopaedic implant materials is most likely to result in severe galvanic corrosion when placed in direct contact in vivo?

. Titanium and Titanium alloy
. Stainless steel and Cobalt-chrome
. Titanium alloy and Cobalt-chrome
. 316L Stainless steel and Titanium
. Ceramic and Titanium

Correct Answer & Explanation

. Titanium and Titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact in an electrolytic environment. The combination of stainless steel and titanium creates a significant difference in electrochemical potential, leading to severe galvanic corrosion of the less noble metal (stainless steel).

Question 7151

Topic: Biology, Genetics & Bone Healing

The Wnt/beta-catenin signaling pathway plays a crucial role in bone homeostasis. Sclerostin (SOST) regulates bone mass by:

. Activating osteoclasts via RANKL
. Inhibiting the Wnt/beta-catenin pathway
. Stimulating osteoblast proliferation directly
. Enhancing BMP-2 expression
. Increasing VEGF secretion

Correct Answer & Explanation

. Activating osteoclasts via RANKL

Explanation

Sclerostin is produced by osteocytes and binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway. This inhibition leads to decreased osteoblastogenesis and a net reduction in bone formation.

Question 7152

Topic: Biomechanics & Biomaterials

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

. Core diameter
. Inner diameter
. Outer thread diameter
. Pitch
. Thread depth

Correct Answer & Explanation

. Core diameter

Explanation

The pullout strength of a screw is directly proportional to the outer (major) diameter of the thread, the length of thread engagement, and the shear strength of the bone. The core (inner) diameter determines the screw's tensile strength and resistance to fatigue failure.

Question 7153

Topic: Physiology & Rehabilitation

During normal gait, the peak joint reaction forces acting on the hip joint occur during which phase of the gait cycle?

. Initial contact (heel strike)
. Mid-stance
. Terminal stance (heel off)
. Pre-swing (toe off)
. Mid-swing

Correct Answer & Explanation

. Initial contact (heel strike)

Explanation

Peak joint reaction forces across the hip often reach 2.5 to 3 times body weight and occur primarily during the mid-stance phase of gait. This is driven largely by the strong contraction of the hip abductor muscles necessary to stabilize the pelvis.

Question 7154

Topic: 1. General Principles & Basic Science

As a fracture callus matures from woven to lamellar bone, what biomechanical change occurs?

. Yield point decreases
. Stiffness decreases
. Ultimate strength increases
. Brittleness decreases
. Elastic modulus decreases

Correct Answer & Explanation

. Yield point decreases

Explanation

As woven bone remodels into lamellar bone, the tissue becomes more organized, anisotropic, and highly mineralized. This remodeling phase results in a significant increase in stiffness, ultimate strength, and elastic modulus, while the material becomes relatively more brittle.

Question 7155

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage contains collagen fibers oriented perpendicularly to the subchondral bone. It also possesses the highest concentration of proteoglycans, providing maximal resistance to compressive forces.

Question 7156

Topic: 1. General Principles & Basic Science

Osteoclasts resorb bone by creating an acidic environment in the sealed zone. Which enzyme is responsible for the production of hydrogen ions required for this process?

. Alkaline phosphatase
. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase-9 (MMP-9)

Correct Answer & Explanation

. Alkaline phosphatase

Explanation

Carbonic anhydrase II catalyzes the conversion of CO2 and water into carbonic acid, which then dissociates into hydrogen ions and bicarbonate. The hydrogen ions are pumped into the resorption pit to dissolve the inorganic hydroxyapatite, while Cathepsin K degrades the organic matrix.

Question 7157

Topic: Biomechanics & Biomaterials

Cortical bone exhibits different mechanical properties depending on the direction of the applied load. This material property is defined as:

. Viscoelasticity
. Anisotropy
. Isotropic behavior
. Creep
. Hysteresis

Correct Answer & Explanation

. Viscoelasticity

Explanation

Anisotropy refers to a material exhibiting varying mechanical properties when loaded in different directions. Cortical bone is highly anisotropic, being strongest when resisting longitudinal compression and weakest under transverse tension.

Question 7158

Topic: Biology, Genetics & Bone Healing

The normal tendon-to-bone insertion (enthesis) consists of four zones. Following surgical repair, the regenerated insertion site typically heals by:

. Re-establishing the original four distinct zones exactly
. Formation of a fibrovascular scar tissue interface
. Direct intramembranous ossification
. Endochondral ossification
. Hyaline cartilage formation

Correct Answer & Explanation

. Re-establishing the original four distinct zones exactly

Explanation

The native enthesis consists of tendon, uncalcified fibrocartilage, calcified fibrocartilage, and bone. After surgical repair, this highly specialized transitional zone does not typically regenerate; instead, it heals via a biomechanically weaker fibrovascular scar tissue interface.

Question 7159

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) alters its mechanical properties by:

. Decreasing wear rate and increasing fatigue strength
. Decreasing wear rate and decreasing toughness
. Increasing wear rate and increasing ductility
. Increasing both wear rate and toughness
. Eliminating the potential for oxidation completely

Correct Answer & Explanation

. Decreasing wear rate and increasing fatigue strength

Explanation

Highly cross-linked UHMWPE demonstrates a significantly decreased wear rate, which effectively reduces particle-induced osteolysis. However, the cross-linking process negatively alters mechanical properties, leading to decreased toughness, reduced fatigue strength, and lower ductility.

Question 7160

Topic: 1. General Principles & Basic Science

According to the Sunderland classification, a third-degree nerve injury involves disruption of the axon and which of the following structures?

. Myelin sheath only
. Endoneurium
. Perineurium
. Epineurium
. Surrounding muscle fascia

Correct Answer & Explanation

. Myelin sheath only

Explanation

A Sunderland third-degree injury involves disruption of the axon, myelin sheath, and the endoneurium, while the perineurium and epineurium remain intact. Wallerian degeneration occurs, and clinical recovery can be unpredictable due to intrafascicular scarring.

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