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1. General Principles & Basic Science MCQs

Practice Set 579 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 11561

Topic: 1. General Principles & Basic Science

During the proliferative phase of flexor tendon healing, intrinsic healing relies primarily on the migration and proliferation of fibroblasts originating from which of the following structures?

. Epitenon and endotenon
. Paratenon
. Synovial sheath
. Adjacent muscle belly
. Bone-tendon junction

Correct Answer & Explanation

. Epitenon and endotenon

Explanation

Tendon healing occurs via intrinsic and extrinsic pathways. Intrinsic healing is mediated by cells residing within the tendon itself, specifically fibroblasts originating from the epitenon and endotenon. Extrinsic healing relies on inflammatory cells and fibroblasts migrating from the surrounding paratenon or synovial sheath, which often leads to restrictive adhesions.

Question 11562

Topic: Biomechanics & Biomaterials

Cortical bone is a viscoelastic material. When loaded at a very high strain rate, such as during a high-speed motor vehicle accident, how do the mechanical properties of the bone change compared to a low strain rate?

. Decreased stiffness and decreased ultimate strength
. Increased stiffness and increased ultimate strength
. No change in stiffness but increased ductility
. Decreased stiffness and increased energy to failure
. Increased ductility and decreased ultimate strength

Correct Answer & Explanation

. Decreased stiffness and decreased ultimate strength

Explanation

Because bone is viscoelastic, its mechanical behavior is highly dependent on the rate of loading. At high strain rates, bone becomes both stiffer (higher modulus of elasticity) and stronger (higher ultimate strength), allowing it to absorb more energy before failure. When it does fail, this high energy release often results in comminution.

Question 11563

Topic: Biology, Genetics & Bone Healing
Secondary fracture healing proceeds through predictable stages, including a cartilaginous intermediate. Which type of collagen is the predominant structural protein synthesized during the soft callus phase of fracture healing?
. Type I
. Type II
. Type III
. Type X
. Type XI

Correct Answer & Explanation

. Type II

Explanation

During the soft callus phase of secondary fracture healing, the predominant cell type is the proliferating chondrocyte, which synthesizes a cartilaginous matrix rich in Type II collagen. As the callus matures into hard callus, hypertrophic chondrocytes produce Type X collagen, followed by osteoblasts depositing Type I collagen.

Question 11564

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, which of the following anatomical descriptions defines a third-degree nerve injury?

. Axonal disruption with intact endoneurium
. Axonal disruption with loss of endoneurial continuity but intact perineurium
. Complete disruption of the axon, endoneurium, and perineurium with intact epineurium
. Complete transection of the entire nerve trunk
. Focal demyelination without axonal discontinuity

Correct Answer & Explanation

. Axonal disruption with intact endoneurium

Explanation

In the Sunderland classification: 1st degree is neuropraxia (demyelination); 2nd degree is axonotmesis (axon disrupted, endoneurium intact); 3rd degree involves disruption of the axon and endoneurium, but the perineurium remains intact; 4th degree involves disruption of the perineurium with an intact epineurium; 5th degree is a complete neurotmesis.

Question 11565

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman is prescribed denosumab for the treatment of osteoporosis. By what precise mechanism does this medication alter bone metabolism?

. Binding directly to the RANK receptor on osteoclasts
. Binding to RANKL and preventing it from activating RANK
. Inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway
. Mimicking osteoprotegerin (OPG) binding to osteoblasts
. Direct inhibition of the osteoclast ruffled border proton pumps

Correct Answer & Explanation

. Binding directly to the RANK receptor on osteoclasts

Explanation

Denosumab is a human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By sequestering RANKL, it prevents the ligand from binding to and activating the RANK receptor on osteoclast precursors and mature osteoclasts, thereby potently inhibiting bone resorption.

Question 11566

Topic: Physiology & Rehabilitation

Skeletal muscle fibers are classified based on their metabolic and contractile properties. Which of the following biochemical and functional profiles is characteristic of Type I (slow-twitch) muscle fibers?

. High glycogen content, anaerobic metabolism, large diameter
. High myoglobin content, high oxidative capacity, low glycolytic capacity
. Low mitochondria density, fast contraction velocity, easily fatigued
. High ATP consumption, reliance on phosphocreatine, few capillaries
. Low myoglobin content, high oxidative capacity, fast fatigue

Correct Answer & Explanation

. High glycogen content, anaerobic metabolism, large diameter

Explanation

Type I muscle fibers are 'slow-twitch oxidative' fibers designed for endurance. They have a high density of capillaries, mitochondria, and myoglobin (giving them a red appearance), allowing them to rely on aerobic oxidative phosphorylation. They have a low glycolytic capacity and are highly resistant to fatigue.

Question 11567

Topic: Biomechanics & Biomaterials

Mixing dissimilar metals in orthopedic implants (e.g., using a stainless steel screw in a titanium plate) can potentially lead to galvanic corrosion. In such a mixed-metal construct, which classic electrochemical process occurs?

. The less noble (more anodic) metal undergoes accelerated corrosion
. The more noble (more cathodic) metal undergoes accelerated corrosion
. Both metals corrode equally due to fluid electrolyte mediation
. Titanium acts as the anode and corrodes rapidly
. Passivation prevents any electron transfer regardless of the metal types

Correct Answer & Explanation

. The less noble (more anodic) metal undergoes accelerated corrosion

Explanation

In a galvanic couple formed by two dissimilar metals in an electrolyte (body fluid), the metal with the lower electrode potential (the less noble or more anodic metal, such as stainless steel) will lose electrons and undergo accelerated corrosion. The more noble metal (cathodic, such as titanium) is protected.

Question 11568

Topic: 1. General Principles & Basic Science




The multinucleated cell responsible for the resorptive pit (Howship's lacuna) utilizes which of the following enzymes as its primary means to dissolve the organic matrix of bone?

. Alkaline phosphatase
. Cathepsin K
. Matrix metalloproteinase-3
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Alkaline phosphatase

Explanation

Osteoclasts initially resorb bone by creating an acidic microenvironment (via proton pumps and carbonic anhydrase II) to dissolve the inorganic hydroxyapatite. Following demineralization, the organic matrix (predominantly Type I collagen) is enzymatically degraded primarily by Cathepsin K.

Question 11569

Topic: Biology, Genetics & Bone Healing

A patient with end-stage chronic kidney disease presents with severe renal osteodystrophy. Which of the following enzymatic conversions is most directly impaired in this condition, driving the development of secondary hyperparathyroidism?

. 25-hydroxylation of cholecalciferol in the liver
. 1-alpha-hydroxylation of 25-hydroxyvitamin D3
. Conversion of 7-dehydrocholesterol to pre-vitamin D3 in the skin
. 24-hydroxylation of 1,25-dihydroxyvitamin D3
. Cleavage of intact PTH by the parathyroid gland

Correct Answer & Explanation

. 25-hydroxylation of cholecalciferol in the liver

Explanation

The kidneys are responsible for the production of 1-alpha-hydroxylase, the enzyme that converts 25-hydroxyvitamin D3 into 1,25-dihydroxyvitamin D3 (calcitriol), the most active form of vitamin D. In chronic kidney disease, this enzyme is deficient, leading to low calcitriol levels, decreased intestinal calcium absorption, hypocalcemia, and subsequent secondary hyperparathyroidism.

Question 11570

Topic: 1. General Principles & Basic Science

With advancing age, the intervertebral disc undergoes progressive degeneration. Which of the following biochemical changes most accurately describes the normal aging process of the nucleus pulposus?

. Increase in chondroitin sulfate relative to keratin sulfate
. Decrease in overall proteoglycan content and water content
. Shift from Type I collagen synthesis to Type II collagen synthesis
. Increase in absolute water content with decreased viscosity
. Increased cellularity and proliferation of notochordal cells

Correct Answer & Explanation

. Increase in chondroitin sulfate relative to keratin sulfate

Explanation

As the intervertebral disc ages, the nucleus pulposus undergoes a significant decrease in total proteoglycan content. There is also a specific decrease in the ratio of chondroitin sulfate to keratin sulfate. These changes reduce the osmotic pressure within the disc, leading to a marked decrease in water content (dehydration) and a loss of disc height and mechanical resilience.

Question 11571

Topic: Biomechanics & Biomaterials

When a stainless steel screw is used in conjunction with a titanium plate, galvanic corrosion may occur. Which of the following best describes the electrochemical roles of the two metals in this scenario?

. Stainless steel acts as the anode and corrodes
. Stainless steel acts as the cathode and corrodes
. Titanium acts as the anode and corrodes
. Titanium acts as the cathode and corrodes
. Both metals act as anodes and corrode equally

Correct Answer & Explanation

. Stainless steel acts as the anode and corrodes

Explanation

In galvanic corrosion, the less noble metal acts as the anode and undergoes active corrosion. Stainless steel is less noble than titanium, so it acts as the anode and corrodes when the two are coupled in an electrolytic environment.

Question 11572

Topic: 1. General Principles & Basic Science

Which of the following biochemical changes accurately differentiates normal aging of articular cartilage from early osteoarthritis?

. Aging cartilage has increased water content, whereas osteoarthritis has decreased water content
. Aging cartilage has decreased water content, whereas osteoarthritis has increased water content
. Aging cartilage has an increased ratio of chondroitin sulfate to keratin sulfate
. Osteoarthritis is characterized by a decrease in degradative matrix metalloproteinases
. Both aging and osteoarthritis exhibit increased total proteoglycan content

Correct Answer & Explanation

. Aging cartilage has increased water content, whereas osteoarthritis has decreased water content

Explanation

Normal aging of cartilage is characterized by decreased water content, decreased total proteoglycans, and an increased keratin sulfate to chondroitin sulfate ratio. In contrast, early osteoarthritis features an initial increase in water content and swollen collagen networks.

Question 11573

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain threshold that allows for primary (lamellar) bone healing without the formation of a callus?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing via endochondral ossification (callus formation).

Question 11574

Topic: Biology, Genetics & Bone Healing

Osteoclasts utilize specialized enzymes to degrade the organic and inorganic components of bone in Howship's lacunae. Which combination correctly matches the component with its primary degradation mechanism?

. Inorganic mineral by Cathepsin K; Organic matrix by Carbonic Anhydrase II
. Inorganic mineral by Tartrate-Resistant Acid Phosphatase; Organic matrix by Vacuolar H+-ATPase
. Inorganic mineral by Vacuolar H+-ATPase (HCl); Organic matrix by Cathepsin K
. Inorganic mineral by Alkaline Phosphatase; Organic matrix by Matrix Metalloproteinases
. Inorganic mineral by Cathepsin K; Organic matrix by Vacuolar H+-ATPase

Correct Answer & Explanation

. Inorganic mineral by Cathepsin K; Organic matrix by Carbonic Anhydrase II

Explanation

Osteoclasts dissolve inorganic bone mineral by creating an acidic environment via vacuolar H+-ATPase and carbonic anhydrase II. The organic matrix (predominantly Type I collagen) is then degraded by the protease Cathepsin K.

Question 11575

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates serum calcium levels by stimulating bone resorption. Which of the following describes the direct cellular target and initial mechanism of PTH in bone tissue?

. Directly binds to osteoclasts to upregulate Cathepsin K
. Directly binds to osteoclasts to increase RANK expression
. Binds to osteoblasts to increase RANKL and decrease OPG expression
. Binds to osteocytes to upregulate sclerostin production
. Binds to macrophages to induce differentiation into active osteoclasts

Correct Answer & Explanation

. Directly binds to osteoclasts to upregulate Cathepsin K

Explanation

PTH does not bind directly to osteoclasts; instead, it binds to PTH receptors on osteoblasts. This stimulates osteoblasts to upregulate RANKL and downregulate osteoprotegerin (OPG), which subsequently activates osteoclasts.

Question 11576

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely used in total joint arthroplasty to reduce wear. What is the primary mechanical trade-off associated with the radiation-induced cross-linking of UHMWPE?
. Increased abrasive wear
. Decreased fatigue strength and fracture toughness
. Increased oxidation potential without remelting
. Decreased ultimate tensile strength but increased ductility
. Increased elastic modulus leading to stress shielding

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

While high-dose irradiation cross-linking significantly decreases adhesive and abrasive wear of UHMWPE, it reduces mechanical properties such as fatigue strength, fracture toughness, and ductility. Post-irradiation melting is often used to eliminate free radicals and prevent oxidation, though it further reduces crystallinity.

Question 11577

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of BMP to its transmembrane serine/threonine kinase receptor, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus?

. JAK and STAT
. Smad 1, 5, and 8
. Wnt and beta-catenin
. MAPK and ERK
. NF-kappaB

Correct Answer & Explanation

. JAK and STAT

Explanation

BMP signaling operates primarily through the canonical Smad pathway. Upon receptor activation, receptor-regulated Smads (Smad 1, 5, and 8) are phosphorylated, bind to Co-Smad (Smad 4), and translocate to the nucleus to regulate gene transcription.

Question 11578

Topic: Biology, Genetics & Bone Healing

During primary bone healing under conditions of absolute stability, cutting cones traverse the fracture site. Which of the following best describes the spatial organization of cells within a cutting cone?

. Osteoblasts at the leading edge, osteoclasts at the trailing edge
. Osteoclasts at the leading edge, osteoblasts at the trailing edge
. Chondrocytes at the leading edge, osteoblasts at the trailing edge
. Macrophages at the leading edge, fibroblasts at the trailing edge
. Osteocytes at the leading edge, osteoclasts at the trailing edge

Correct Answer & Explanation

. Osteoblasts at the leading edge, osteoclasts at the trailing edge

Explanation

Primary cortical bone healing relies on osteonal remodeling via cutting cones. Osteoclasts form the leading edge (cutting head) to resorb bone, while osteoblasts follow in the trailing edge to deposit new lamellar bone.

Question 11579

Topic: Biology, Genetics & Bone Healing

Nutritional rickets results from a deficiency in Vitamin D, leading to impaired mineralization of the physis. This pathological failure of mineralization causes characteristic widening and thickening of which specific physeal zone?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Reserve zone

Explanation

In rickets, the lack of calcium and phosphorus prevents normal mineralization in the zone of provisional calcification (within the hypertrophic zone). This causes a buildup of unmineralized cartilage, leading to physeal widening.

Question 11580

Topic: 1. General Principles & Basic Science
The intervertebral disc is composed of the annulus fibrosus and the nucleus pulposus. What is the predominant collagen type found in each of these structures, respectively?
. Annulus fibrosus: Type I; Nucleus pulposus: Type II
. Annulus fibrosus: Type II; Nucleus pulposus: Type I
. Annulus fibrosus: Type III; Nucleus pulposus: Type II
. Annulus fibrosus: Type I; Nucleus pulposus: Type III
. Annulus fibrosus: Type II; Nucleus pulposus: Type III

Correct Answer & Explanation

. Annulus fibrosus: Type I; Nucleus pulposus: Type II

Explanation

The annulus fibrosus is adapted to resist tensile forces and is predominantly composed of Type I collagen. The nucleus pulposus is adapted to resist compressive forces and is rich in Type II collagen and proteoglycans.

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