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1. General Principles & Basic Science MCQs

Practice Set 336 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 6701

Topic: Biomechanics & Biomaterials

If the inner diameter of a hollow intramedullary nail is kept constant while the outer diameter is doubled, how does the torsional rigidity of the nail change?

. Increases by a factor of 2
. Increases by a factor of 4
. Increases by a factor of 8
. Increases by a factor of 16
. Increases by a factor of greater than 15 but less than 16

Correct Answer & Explanation

. Increases by a factor of 2

Explanation

Torsional rigidity of a cylinder is proportional to its polar moment of inertia, which relates to the outer radius to the fourth power minus the inner radius to the fourth power. Doubling the outer diameter dramatically increases rigidity by slightly less than 16 due to the hollow core.

Question 6702

Topic: Biomechanics & Biomaterials

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

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the property of a viscoelastic material where it continues to deform progressively over time under a constant applied load. Stress relaxation is the decrease in stress over time under a constant deformation.

Question 6703

Topic: Biology, Genetics & Bone Healing

Sclerostin, an important regulator of bone mass, primarily functions by inhibiting which of the following signaling pathways?

. RANKL/RANK
. Wnt/beta-catenin
. TGF-beta/Smad
. BMP/Smad
. Notch

Correct Answer & Explanation

. RANKL/RANK

Explanation

Sclerostin is secreted by osteocytes and inhibits bone formation by antagonizing the Wnt/beta-catenin signaling pathway in osteoblasts. Monoclonal antibodies targeting sclerostin are used to treat osteoporosis.

Question 6704

Topic: Biology, Genetics & Bone Healing

Which of the following bones undergoes formation primarily via intramembranous ossification?

. Femur
. Clavicle
. Vertebral body
. Phalanges
. Tibia

Correct Answer & Explanation

. Femur

Explanation

The clavicle, flat bones of the skull, and portions of the mandible form via intramembranous ossification. In this process, mesenchymal cells differentiate directly into osteoblasts without a cartilaginous model.

Question 6705

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical bone allograft, the process of simultaneous bone resorption and formation by osteoclasts and osteoblasts cutting cones is termed:

. Osteoinduction
. Osteoconduction
. Creeping substitution
. Distraction osteogenesis
. Endochondral ossification

Correct Answer & Explanation

. Osteoinduction

Explanation

Creeping substitution is the process by which cortical bone grafts are slowly resorbed by osteoclasts and replaced by new bone from host osteoblasts. This progressive remodeling process can take years to complete.

Question 6706

Topic: Biology, Genetics & Bone Healing

In the metabolism of Vitamin D, the conversion of 25-hydroxyvitamin D to its most active form, 1,25-dihydroxyvitamin D, occurs primarily in which organ?

. Skin
. Liver
. Kidney
. Bone
. Intestine

Correct Answer & Explanation

. Skin

Explanation

The kidney enzyme 1-alpha-hydroxylase is responsible for converting 25-hydroxyvitamin D into the active 1,25-dihydroxyvitamin D. This step is strongly stimulated by parathyroid hormone (PTH).

Question 6707

Topic: 1. General Principles & Basic Science

According to the piezoelectric properties of bone, compression of a long bone results in which of the following electrical charges and cellular responses at the compressed surface?

. Electronegative charge with osteoblastic bone formation
. Electropositive charge with osteoclastic bone resorption
. Electronegative charge with osteoclastic bone resorption
. Electropositive charge with osteoblastic bone formation
. Neutral charge with balanced remodeling

Correct Answer & Explanation

. Electronegative charge with osteoblastic bone formation

Explanation

Under mechanical load, the compressed side of bone becomes electronegative, stimulating osteoblastic bone formation. The tension side becomes electropositive, stimulating osteoclastic resorption.

Question 6708

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., alendronate) inhibit bone resorption primarily by inhibiting which of the following enzymes?

. Cathepsin K
. Carbonic anhydrase II
. Farnesyl pyrophosphate synthase
. Alkaline phosphatase
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. Cathepsin K

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents prenylation of small GTPases essential for osteoclast function and survival.

Question 6709

Topic: Biomechanics & Biomaterials

Which of the following scenarios is most likely to result in galvanic corrosion?

. Implantation of a titanium alloy screw into a titanium alloy plate
. Implantation of a stainless steel screw into a cobalt-chrome plate
. Use of a highly cross-linked polyethylene liner with a cobalt-chrome head
. Fretting of a single titanium plate against an adjacent bone
. A ceramic head articulating with a ceramic liner

Correct Answer & Explanation

. Implantation of a titanium alloy screw into a titanium alloy plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct physical contact within a conductive fluid environment. It leads to accelerated degradation of the less noble metal.

Question 6710

Topic: 1. General Principles & Basic Science

The resistance of a rectangular plate to bending depends on its area moment of inertia. If the thickness of the plate in the plane of bending is doubled, how does its bending rigidity change?

. Increases by a factor of 2
. Increases by a factor of 4
. Increases by a factor of 8
. Increases by a factor of 16
. Remains unchanged

Correct Answer & Explanation

. Increases by a factor of 2

Explanation

For a rectangular cross-section, the area moment of inertia is proportional to the base multiplied by the height cubed. Doubling the thickness (height in the direction of bending) increases the bending rigidity by a factor of 8.

Question 6711

Topic: Biology, Genetics & Bone Healing

Continuous, high-dose administration of Parathyroid Hormone (PTH) leads to which of the following net effects on bone?

. Net bone formation via direct stimulation of osteoblasts
. Net bone resorption via direct stimulation of osteoclasts
. Net bone resorption via osteoblast-mediated stimulation of osteoclasts
. Net bone formation via inhibition of osteoclasts
. No net change in bone mass

Correct Answer & Explanation

. Net bone formation via direct stimulation of osteoblasts

Explanation

Continuous exposure to PTH causes net bone resorption by binding to osteoblasts, which then upregulate RANKL to stimulate osteoclast activity. Conversely, intermittent, low-dose PTH promotes net bone formation.

Question 6712

Topic: Biology, Genetics & Bone Healing

Absolute stability of a fracture (e.g., rigid compression plating) leads to which type of bone healing?

. Primary (Haversian) bone healing
. Secondary bone healing with robust callus formation
. Endochondral ossification
. Intramembranous ossification with callus
. Fibrocartilaginous healing

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability minimizes interfragmentary strain, leading to primary bone healing through Haversian remodeling (cutting cones) without visible callus formation. Secondary healing occurs with relative stability.

Question 6713

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) transmit signals to the nucleus of osteoprogenitor cells primarily through which of the following intracellular mediators?

. beta-catenin
. cAMP
. Smad proteins
. JAK/STAT
. MAP kinase

Correct Answer & Explanation

. beta-catenin

Explanation

BMPs are part of the TGF-beta superfamily and signal primarily through the activation of intracellular Smad proteins. These Smads translocate to the nucleus to regulate gene transcription.

Question 6714

Topic: Biomechanics & Biomaterials

On a stress-strain curve, the area under the entire curve up to the point of failure represents which mechanical property of the material?

. Stiffness
. Yield strength
. Toughness
. Ductility
. Elastic limit

Correct Answer & Explanation

. Stiffness

Explanation

Toughness is defined as the total amount of energy a material can absorb before failure, represented by the total area under the stress-strain curve. Stiffness is represented by the slope of the linear elastic region.

Question 6715

Topic: Biology, Genetics & Bone Healing

Which of the following histologic findings is characteristic of osteomalacia?

. Decreased osteoid volume
. Increased woven bone
. Increased osteoid seam width
. Empty lacunae
. Increased osteoclast tunneling

Correct Answer & Explanation

. Decreased osteoid volume

Explanation

Osteomalacia is characterized by defective mineralization of newly formed osteoid, leading to an increased accumulation and width of the unmineralized osteoid seams. The absolute bone mass may be normal, but it is poorly mineralized.

Question 6716

Topic: 1. General Principles & Basic Science

Which type of collagen is the predominant organic component of normal mature cortical bone?

. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen makes up approximately 90% of the organic matrix of bone. Type II is predominantly found in hyaline cartilage.

Question 6717

Topic: Biomechanics & Biomaterials

In biomechanics, the S-N curve (stress vs. number of cycles) is used to evaluate a material's susceptibility to:

. Creep
. Galvanic corrosion
. Fatigue failure
. Stress shielding
. Viscoelasticity

Correct Answer & Explanation

. Creep

Explanation

The S-N curve graphically displays the relationship between the magnitude of a cyclic stress (S) and the number of cycles to failure (N). This is used to determine the fatigue endurance limit of a material.

Question 6718

Topic: Biomechanics & Biomaterials

Which of the following mechanical properties best describes a material whose mechanical behavior is dependent on the rate at which the load is applied?

. Anisotropy
. Viscoelasticity
. Plasticity
. Isotropy
. Ductility

Correct Answer & Explanation

. Anisotropy

Explanation

Viscoelastic materials exhibit a time- and rate-dependent mechanical response. Cortical bone is viscoelastic; it is stiffer and stronger when loaded rapidly compared to when loaded slowly.

Question 6719

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) functions to inhibit osteoclastogenesis by directly binding to which of the following molecular targets?

. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Macrophage colony-stimulating factor (M-CSF)
. Integrin alpha-v beta-3
. Carbonic anhydrase II

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B (RANK)

Explanation

OPG is a decoy receptor produced by osteoblasts that binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This prevents activation of the NF-kappa B pathway, thereby inhibiting osteoclast differentiation and bone resorption.

Question 6720

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for cortical bone, the slope of the curve within the linear elastic region represents which of the following mechanical properties?

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

Correct Answer & Explanation

. Toughness

Explanation

The slope of the linear elastic portion of the stress-strain curve represents Young's modulus (modulus of elasticity), indicating the material's stiffness. Toughness represents the total energy absorbed before failure and is the total area under the stress-strain curve.

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