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1. General Principles & Basic Science MCQs

Practice Set 278 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 5541

Topic: 1. General Principles & Basic Science

When analyzing an orthopedic implant's S-N (Stress-Number of cycles) curve, the "endurance limit" refers to the:

. Maximum stress an implant can withstand before plastic deformation
. Stress level below which the material can endure an infinite number of cyclic loads without failure
. Number of cycles required to cause catastrophic failure at yield strength
. Point of ultimate tensile strength before structural collapse
. Rate of microscopic crack propagation under constant physiological stress

Correct Answer & Explanation

. Stress level below which the material can endure an infinite number of cyclic loads without failure

Explanation

The endurance limit (fatigue limit) is the maximum stress amplitude below which a material can theoretically endure an infinite number of cyclic loading cycles without failing.

Question 5542

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) stimulates bone resorption primarily by binding to receptors on which of the following cell types?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

PTH binds to receptors on osteoblasts, stimulating them to express RANKL. RANKL then binds to RANK on osteoclast precursors to induce differentiation into active bone-resorbing osteoclasts.

Question 5543

Topic: Biology, Genetics & Bone Healing
The outer annulus fibrosus of the intervertebral disc is specialized to resist tensile hoop stresses. Which type of collagen predominantly provides this mechanical property?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The outer annulus fibrosus is composed predominantly of Type I collagen, which provides the high tensile strength needed to resist hoop stresses generated by axial loading of the disc.

Question 5544

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, which biochemical transition characterizes the maturation of the scar tissue?
. Replacement of Type I collagen with Type II collagen
. Replacement of Type III collagen with Type I collagen
. Upregulation of aggrecan synthesis
. Apoptosis of fibroblasts and replacement by chondrocytes
. Increasing content of loosely organized glycosaminoglycans (GAGs)

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

In the proliferative phase, fibroblasts synthesize weak Type III collagen. During remodeling, this is gradually replaced by stronger, highly cross-linked Type I collagen, improving tensile strength.

Question 5545

Topic: Biology, Genetics & Bone Healing

In the metabolic pathway of Vitamin D, the final hydroxylation step to produce the active form, 1,25-dihydroxyvitamin D3, occurs primarily in the:

. Liver
. Skin
. Intestine
. Kidney
. Bone marrow

Correct Answer & Explanation

. Kidney

Explanation

25-hydroxyvitamin D3 is converted by the enzyme 1-alpha-hydroxylase in the proximal tubules of the kidney to form the biologically active 1,25-dihydroxyvitamin D3 (calcitriol).

Question 5546

Topic: Physiology & Rehabilitation

During a normal human gait cycle, maximum muscle activity of the tibialis anterior occurs at which specific phase to prevent foot drop?

. Mid-stance
. Terminal stance
. Heel strike (Initial contact)
. Toe-off (Pre-swing)
. Mid-swing

Correct Answer & Explanation

. Heel strike (Initial contact)

Explanation

The tibialis anterior peaks in activity just after heel strike (initial contact). It fires eccentrically to control plantarflexion of the foot, preventing it from slapping against the ground.

Question 5547

Topic: 1. General Principles & Basic Science

Which of the following characteristics is true regarding Type I (slow-twitch) skeletal muscle fibers compared to Type IIb fibers?

. Higher glycolytic enzyme activity
. Lower mitochondrial density
. Higher myoglobin content
. Faster rate of fatigue
. Larger cross-sectional area

Correct Answer & Explanation

. Lower mitochondrial density

Explanation

Type I (slow-twitch) fibers are specialized for endurance. They rely on oxidative metabolism and have high mitochondrial density, low fatigue rates, and high myoglobin content, giving them a red appearance.

Question 5548

Topic: 1. General Principles & Basic Science

Which mechanism of joint lubrication is most critical for reducing friction between articular cartilage surfaces during high-load, low-speed activities, such as initiating standing from a chair?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Squeeze-film lubrication
. Weeping lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication relies on surface-bound molecules like lubricin to reduce friction under high-load, low-speed conditions where fluid films cannot be physically maintained.

Question 5549

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which of the following best describes the structural composition and mechanical function of the superficial zone?

. Highest proteoglycan content, primarily resists compressive loads
. Highest water content, primarily resists shear stresses
. Highest concentration of type I collagen, primarily resists tension
. Lowest cell density, primarily resists shear stresses
. Radially oriented collagen fibers, primarily resists compressive loads

Correct Answer & Explanation

. Highest water content, primarily resists shear stresses

Explanation

The superficial zone of articular cartilage has the highest water and lowest proteoglycan content. Its collagen fibers are oriented parallel to the joint surface to primarily resist shear stresses.

Question 5550

Topic: Biology, Genetics & Bone Healing

Which of the following biomechanical conditions is required for primary (strain-free) bone healing to occur, and what is the predominant mechanism of osteogenesis?

. Interfragmentary strain less than 2%, endochondral ossification
. Interfragmentary strain between 2% and 10%, intramembranous ossification
. Interfragmentary strain less than 2%, cutting cone remodeling
. Interfragmentary strain between 2% and 10%, cutting cone remodeling
. Interfragmentary strain greater than 10%, endochondral ossification

Correct Answer & Explanation

. Interfragmentary strain less than 2%, cutting cone remodeling

Explanation

Primary bone healing requires absolute stability with interfragmentary strain less than 2%. It occurs via direct Haversian remodeling (cutting cones) without intermediate callus formation.

Question 5551

Topic: Physiology & Rehabilitation

Which type of muscle contraction generates the highest maximum force, and what is its associated physiological energy characteristic?

. Isometric contraction; lowest energy expenditure
. Concentric contraction; greatest muscle hypertrophy potential
. Eccentric contraction; lowest energy expenditure for a given force
. Isokinetic contraction; variable velocity throughout the arc of motion
. Concentric contraction; highest energy expenditure for a given force

Correct Answer & Explanation

. Eccentric contraction; lowest energy expenditure for a given force

Explanation

Eccentric contractions generate the highest maximum force while consuming less ATP compared to concentric contractions. However, they are more frequently associated with delayed-onset muscle soreness.

Question 5552

Topic: Biomechanics & Biomaterials

A continuous, constant compressive load is applied to an intervertebral disc over several hours, resulting in progressive deformation over time. This specific viscoelastic property is defined as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material when subjected to a constant load over time. Conversely, stress relaxation is the decrease in stress over time under a constant deformation.

Question 5553

Topic: Physiology & Rehabilitation

During the normal human gait cycle, which muscle group demonstrates peak activity during the initial contact (heel strike) to loading response phase to safely lower the foot?

. Plantar flexors (gastrocnemius-soleus) eccentrically
. Plantar flexors (gastrocnemius-soleus) concentrically
. Dorsiflexors (tibialis anterior) eccentrically
. Dorsiflexors (tibialis anterior) concentrically
. Quadriceps eccentrically

Correct Answer & Explanation

. Dorsiflexors (tibialis anterior) eccentrically

Explanation

At initial contact to loading response, the tibialis anterior contracts eccentrically to smoothly lower the foot to the ground. This prevents the rapid plantar flexion known as "foot slap".

Question 5554

Topic: 1. General Principles & Basic Science

Following a severe traction injury to the brachial plexus resulting in axonotmesis, Wallerian degeneration begins. Which of the following best describes this physiological process?

. Demyelination of the nerve proximal to the injury site
. Degeneration of the axon and myelin sheath distal to the injury site
. Proliferation of Schwann cells proximal to the injury site
. Scarring of the epineurium preventing axonal sprouting
. Retrograde degeneration to the anterior horn cell leading to cell death

Correct Answer & Explanation

. Degeneration of the axon and myelin sheath distal to the injury site

Explanation

Wallerian degeneration involves the clearance of the axon and myelin sheath distal to the site of injury. It is mediated by macrophages and Schwann cells to prepare the environment for axonal regeneration.

Question 5555

Topic: Biomechanics & Biomaterials

On the stress-strain curve of a normal tendon, the initial "toe region" represents which of the following structural events?

. Rupture of microscopic cross-links
. Plastic deformation of collagen fibrils
. Uncrimping of type I collagen fibers
. Yield point of the tendon
. Complete macroscopic failure

Correct Answer & Explanation

. Uncrimping of type I collagen fibers

Explanation

The "toe region" of a tendon's stress-strain curve represents the initial elastic stretch. During this phase, the normal wavy, crimped pattern of the resting collagen fibers straightens out.

Question 5556

Topic: 1. General Principles & Basic Science

Under high-load, low-velocity conditions (such as standing from a seated position), which type of lubrication mechanism predominantly protects the articular cartilage surfaces?

. Hydrodynamic fluid-film lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Squeeze-film lubrication
. Weeping lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication is the primary protective mechanism under high-load, low-velocity conditions when fluid-film cannot be maintained. It is mediated by lubricin (PRG4) binding directly to the articular surface.

Question 5557

Topic: Biology, Genetics & Bone Healing

Denosumab, a biological therapy used in the treatment of osteoporosis, exerts its effect by directly targeting which of the following molecular mechanisms?

. Binding to the RANK receptor on osteoclasts
. Mimicking the action of osteoprotegerin (OPG) by binding RANKL
. Inhibiting the wnt/beta-catenin pathway
. Stimulating sclerostin production
. Directly inhibiting cathepsin K

Correct Answer & Explanation

. Mimicking the action of osteoprotegerin (OPG) by binding RANKL

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, effectively mimicking the inhibitory effect of OPG. This prevents RANKL from activating the RANK receptor on osteoclasts, thereby halting osteoclastogenesis.

Question 5558

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the incorporation of highly cross-linked polyethylene primarily improves wear resistance by mitigating which specific mechanism of wear?

. Third-body wear
. Adhesive wear
. Abrasive wear
. Fatigue wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Highly cross-linked polyethylene significantly reduces adhesive wear at the bearing surface, which decreases osteolytic particulate debris. However, the cross-linking process may make the material more susceptible to fatigue wear or fracture.

Question 5559

Topic: 1. General Principles & Basic Science

Which of the following screw design alterations will most significantly increase the pullout strength of a cortical bone screw in diaphyseal bone?

. Decreasing the outer (major) diameter
. Increasing the inner (minor) diameter
. Decreasing the thread pitch
. Decreasing the length of screw engagement
. Changing from a self-tapping to a non-self-tapping design

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer diameter and length of engagement, and inversely proportional to thread pitch. Decreasing the thread pitch increases the number of threads per unit length, thus increasing pullout strength.

Question 5560

Topic: 1. General Principles & Basic Science

The blood supply to the adult medial meniscus is primarily derived from the medial inferior genicular artery. Approximately what portion of the meniscus receives a direct vascular supply?

. The entire meniscus is vascularized
. The peripheral 10% to 30%
. The central 50%
. The inner (free) 10% to 30%
. The meniscus is entirely avascular

Correct Answer & Explanation

. The peripheral 10% to 30%

Explanation

In adults, only the peripheral 10% to 30% of the medial meniscus (the red-red zone) is vascularized by branches of the genicular arteries. This vascularity is critical for the healing potential of peripheral meniscal tears.

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