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1. General Principles & Basic Science MCQs

Practice Set 588 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 11741

Topic: 1. General Principles & Basic Science
In the earliest stages of primary osteoarthritis, before macro-fissuring or severe loss of articular cartilage height occurs, which of the following biochemical changes is the earliest to be observed in the extracellular matrix?
. Increase in aggrecan content
. Decrease in water content
. Increase in water content
. Upregulation of Type X collagen synthesis
. Decrease in degradative matrix metalloproteinase (MMP) activity

Correct Answer & Explanation

. Increase in water content

Explanation

The earliest biochemical change in osteoarthritis is the disruption and breakdown of the superficial Type II collagen network. This loss of structural constraint allows the hydrophilic aggrecan molecules to swell excessively, leading to an absolute increase in the water content of the cartilage, making it softer and less stiff.

Question 11742

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is widely utilized for implant fixation. Which of the following statements regarding the physical and handling properties of PMMA is true?

. It is strongest in tension and weakest in compression.
. The polymerization reaction is highly endothermic.
. Increasing the ambient operating room temperature will increase the setting time.
. Antibiotics added in low doses (e.g., 1g per 40g) dramatically reduce compressive strength below mechanical failure limits.
. Barium sulfate or zirconium dioxide is added to the powder component to render the cement radiopaque.

Correct Answer & Explanation

. Barium sulfate or zirconium dioxide is added to the powder component to render the cement radiopaque.

Explanation

Barium sulfate or zirconium dioxide is added to PMMA to provide radiopacity. PMMA is strongest in compression and weak in tension/shear. The polymerization is an exothermic reaction. Increasing ambient temperature or humidity decreases the setting time (cures faster). Low doses of antibiotics do not clinically compromise compressive strength.

Question 11743

Topic: Infection, Pharmacology & VTE

Periprosthetic joint infections are notoriously difficult to eradicate due to the formation of a protective bacterial biofilm on the implant surface. During the development of a Staphylococcus aureus biofilm, what is the primary structural component of the extracellular polymeric substance (EPS) that protects the bacteria?

. Peptidoglycan
. Teichoic acid
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Lipopolysaccharide (LPS)

Correct Answer & Explanation

. Peptidoglycan

Explanation

In Staphylococcus aureus and Staphylococcus epidermidis biofilms, the major structural component of the extracellular polymeric matrix is Polysaccharide Intercellular Adhesin (PIA), which is synthesized by the products of the icaADBC operon. This matrix shields the bacteria from host immunity and antibiotics.

Question 11744

Topic: Biology, Genetics & Bone Healing

Which molecule acts as a decoy receptor to inhibit osteoclastogenesis by binding to Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL)?

. Osteoprotegerin (OPG)
. Sclerostin
. Cathepsin K
. Calcitonin
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This prevents downstream signaling and thereby inhibits osteoclast differentiation and bone resorption.

Question 11745

Topic: Biology, Genetics & Bone Healing

A genetic mutation causing a loss of function in sclerostin is most likely to result in which of the following bone phenotypes?

. Decreased bone mass due to increased osteoclast activity
. Increased bone mass due to uninhibited Wnt signaling
. Defective mineralization of osteoid leading to rickets
. Impaired endochondral ossification leading to short stature
. Fibrous dysplasia of the diaphyses

Correct Answer & Explanation

. Decreased bone mass due to increased osteoclast activity

Explanation

Sclerostin, produced by osteocytes, normally inhibits the Wnt/beta-catenin pathway. Loss of sclerostin function (as seen in sclerosteosis) leads to uninhibited Wnt signaling, resulting in profound osteoblast hyperactivity and massive bone overgrowth.

Question 11746

Topic: 1. General Principles & Basic Science

In comparing normal aging articular cartilage to early osteoarthritic cartilage, which of the following changes is uniquely characteristic of aging rather than early osteoarthritis?

. Increased overall water content
. Increased matrix metalloproteinase activity
. Increased keratin sulfate concentration
. Decreased collagen fibril diameter
. Increased chondrocyte proliferation

Correct Answer & Explanation

. Increased overall water content

Explanation

Normal aging cartilage is characterized by decreased water content, decreased chondroitin sulfate, and increased keratin sulfate. Conversely, early osteoarthritis is characterized by increased water content and a decrease in total proteoglycans.

Question 11747

Topic: Biology, Genetics & Bone Healing
A newborn is diagnosed with an autosomal dominant disorder characterized by multiple fractures, blue sclerae, and hearing loss. This condition is primarily due to a quantitative or qualitative defect in which of the following?
. Type I collagen
. Type II collagen
. Type III collagen
. Fibroblast growth factor receptor 3
. Fibrillin-1

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is most commonly caused by mutations in the COL1A1 or COL1A2 genes, leading to defective Type I collagen. Type I collagen constitutes approximately 90% of the organic matrix of bone.

Question 11748

Topic: Biomechanics & Biomaterials

On a stress-strain curve representing a typical orthopaedic implant material, the total area under the elastic portion of the curve represents which mechanical property?

. Ultimate tensile strength
. Yield strength
. Modulus of resilience
. Toughness
. Ductility

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The area under the elastic (linear) portion of the stress-strain curve represents the modulus of resilience, which is the energy a material can absorb without undergoing permanent deformation. Toughness is the total area under the entire curve until failure.

Question 11749

Topic: Biomechanics & Biomaterials

The primary mechanism of wear in a properly functioning metal-on-highly cross-linked polyethylene total hip arthroplasty is best described as:

. Abrasive wear
. Adhesive wear
. Third-body wear
. Fretting wear
. Galvanic corrosion

Correct Answer & Explanation

. Abrasive wear

Explanation

Adhesive wear is the predominant mode of wear in a well-functioning metal-on-polyethylene articulation. It occurs when microscopic asperities on the two bearing surfaces bond together and then tear away, generating polyethylene debris.

Question 11750

Topic: 1. General Principles & Basic Science

A ligament inserts into bone via a direct (fibrocartilaginous) enthesis. What is the correct histologic sequence of the four transition zones from ligament to bone?

. Ligament, uncalcified fibrocartilage, calcified fibrocartilage, bone
. Ligament, calcified fibrocartilage, uncalcified fibrocartilage, bone
. Ligament, loose areolar tissue, calcified fibrocartilage, bone
. Ligament, Sharpey's fibers, uncalcified fibrocartilage, bone
. Ligament, uncalcified fibrocartilage, Sharpey's fibers, bone

Correct Answer & Explanation

. Ligament, uncalcified fibrocartilage, calcified fibrocartilage, bone

Explanation

Direct insertions minimize stress concentrations by transitioning through four distinct zones: ligament/tendon, uncalcified fibrocartilage, calcified fibrocartilage, and bone. A tidemark separates the uncalcified and calcified fibrocartilage zones.

Question 11751

Topic: Biology, Genetics & Bone Healing

Which enzyme is responsible for the final conversion of 25-hydroxyvitamin D to the active 1,25-dihydroxyvitamin D, and where is it primarily located?

. 25-hydroxylase in the liver
. 1-alpha-hydroxylase in the kidney
. 24-hydroxylase in the kidney
. 1-alpha-hydroxylase in the liver
. 25-hydroxylase in the skin

Correct Answer & Explanation

. 25-hydroxylase in the liver

Explanation

The active form of Vitamin D (1,25-dihydroxyvitamin D) is synthesized in the kidney by the enzyme 1-alpha-hydroxylase. This conversion is up-regulated by parathyroid hormone (PTH) and hypophosphatemia.

Question 11752

Topic: Biology, Genetics & Bone Healing

During the incorporation of a massive, non-vascularized cortical bone allograft, what is the initial cellular process that immediately follows vascular invasion?

. Appositional bone formation
. Osteoclastic resorption
. Woven bone deposition
. Chondrocyte hypertrophy
. Fibroblast proliferation

Correct Answer & Explanation

. Appositional bone formation

Explanation

Non-vascularized cortical grafts incorporate via creeping substitution, where vascular invasion is immediately followed by osteoclastic resorption via cutting cones. This initial resorptive phase temporarily weakens the graft before osteoblasts lay down new bone.

Question 11753

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of nerve injuries, a third-degree nerve injury involves the disruption of which specific anatomical structures?

. Myelin sheath only
. Axon and myelin sheath only
. Axon, myelin, and endoneurium
. Axon, myelin, endoneurium, and perineurium
. Entire nerve trunk including epineurium

Correct Answer & Explanation

. Myelin sheath only

Explanation

A Sunderland 3rd-degree injury involves complete disruption of the axon, myelin, and endoneurium, but the perineurium remains intact. Recovery is unpredictable due to intrafascicular scarring blocking regenerating axons.

Question 11754

Topic: 1. General Principles & Basic Science

In comparing normal skeletal muscle fibers, Type 1 (slow-twitch) fibers are uniquely characterized by which of the following physiological profiles?

. High glycolytic capacity and low fatigue resistance
. High oxidative capacity and high myoglobin content
. Low mitochondrial density and large fiber diameter
. Rapid contraction speed and low capillary density
. High reliance on anaerobic metabolism

Correct Answer & Explanation

. High glycolytic capacity and low fatigue resistance

Explanation

Type 1 muscle fibers are adapted for endurance and postural maintenance. They have a high oxidative capacity, abundant mitochondria, and high myoglobin content, which imparts a characteristic red color.

Question 11755

Topic: Biology, Genetics & Bone Healing

Which transcription factor is recognized as the essential master regulator for the differentiation of mesenchymal stem cells into the osteoblast lineage?

. SOX9
. PPAR-gamma
. Runx2 (Cbfa1)
. Osterix
. MyoD

Correct Answer & Explanation

. SOX9

Explanation

Runx2, also known as Core-binding factor alpha 1 (Cbfa1), is the master transcription factor for osteoblast differentiation. Complete absence of Runx2 results in a total failure of bone formation, as seen in knock-out models.

Question 11756

Topic: Biomechanics & Biomaterials

Modular junctions in total joint arthroplasty, such as the head-neck taper interface in a total hip replacement, are most primarily susceptible to which type of corrosion?

. Galvanic corrosion
. Intergranular corrosion
. Fretting corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at loaded contact areas subjected to microscopic relative motion, such as a modular head-neck taper. This micromotion continually disrupts the protective passivation layer, accelerating local corrosion.

Question 11757

Topic: Biomechanics & Biomaterials

When mixing antibiotic powder into polymethylmethacrylate (PMMA) bone cement, which of the following characteristics is absolute necessary for the antibiotic to maintain clinical efficacy?

. Heat lability
. Bacteriostatic mechanism of action
. Liquid formulation compatibility
. Thermal stability
. High molecular weight

Correct Answer & Explanation

. Thermal stability

Explanation

The polymerization of PMMA is a highly exothermic chemical reaction. Antibiotics incorporated into the cement (such as vancomycin or tobramycin) must possess thermal stability to survive the high curing temperatures without degrading.

Question 11758

Topic: Biology, Genetics & Bone Healing

Intermittent administration of low-dose Parathyroid Hormone (PTH), such as teriparatide, effectively treats severe osteoporosis because its primary action in this specific dosing regimen is to:

. Directly inhibit osteoclast apoptosis
. Promote osteoblast differentiation and survival
. Neutralize RANKL directly in the bone marrow
. Stimulate continuous cortical resorption
. Decrease intestinal calcium absorption

Correct Answer & Explanation

. Promote osteoblast differentiation and survival

Explanation

While continuous endogenous hyperparathyroidism favors bone resorption, exogenous intermittent low-dose PTH administration has an anabolic effect. It strongly promotes osteoblast differentiation, inhibits osteoblast apoptosis, and increases bone mass.

Question 11759

Topic: Biology, Genetics & Bone Healing

Cleidocranial dysplasia is an autosomal dominant skeletal condition characterized by absent or hypoplastic clavicles and delayed closure of cranial sutures. It is most directly caused by a mutation in which gene?

. COL1A1
. FGFR3
. RUNX2 (CBFA1)
. COMP
. SOX9

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is caused by a heterozygous mutation in the RUNX2 (CBFA1) gene. Because RUNX2 is crucial for osteoblast differentiation and membranous bone formation, mutations manifest with severe clavicular and cranial defects.

Question 11760

Topic: Surgical Anatomy & Approaches

A 28-year-old male presents with a closed, mid-shaft transverse humerus fracture following an arm-wrestling injury. On initial examination, he has an isolated radial nerve palsy. What is the most appropriate initial management for his nerve injury?

. Immediate surgical exploration of the radial nerve and fracture fixation
. EMG/NCS testing at 1 week post-injury
. Observation and supportive wrist splinting alongside functional bracing or operative fracture care
. Ultrasound of the radial nerve to assess continuity
. Primary nerve grafting

Correct Answer & Explanation

. Observation and supportive wrist splinting alongside functional bracing or operative fracture care

Explanation

Primary radial nerve palsy in the setting of a closed humeral shaft fracture is typically a neurapraxia (Sunderland first or second degree) and recovers spontaneously in up to 90% of cases. Observation and supportive care (e.g., cock-up wrist splint) is the standard of care, regardless of whether the fracture is treated operatively or non-operatively.

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