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1. General Principles & Basic Science MCQs

Practice Set 241 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 4801

Topic: Infection, Pharmacology & VTE

A patient sustaining an open tibia fracture is placed on a course of systemic antibiotics. Which antibiotic class achieves high concentrations in bone tissue due to its hydrophilic nature and good penetration into the bone matrix?

. Macrolides
. Fluoroquinolones
. Aminoglycosides
. Tetracyclines
. Lincosamides

Correct Answer & Explanation

. Fluoroquinolones

Explanation

Fluoroquinolones, such as ciprofloxacin and levofloxacin, are known for their excellent tissue penetration, including into bone and cartilage, due to their relatively small molecular size and favorable lipophilicity, despite being often described as hydrophilic (they have a good balance). This property makes them highly effective in treating osteomyelitis and other bone and joint infections. Lincosamides (e.g., clindamycin) also have good bone penetration but a narrower spectrum (primarily gram-positive and anaerobes). Aminoglycosides (e.g., gentamicin) are potent but have limited bone penetration and require higher doses or local delivery for significant bone levels. Macrolides and tetracyclines generally have less reliable or lower bone concentrations compared to fluoroquinolones for treating established osteomyelitis.

Question 4802

Topic: 1. General Principles & Basic Science

Type I collagen is the most abundant collagen in the body, primarily found in bone, skin, and tendons. A key structural feature of Type I collagen is its triple-helical coiled-coil domain formed by which specific amino acid repeating sequence?

. Gly-Ala-Pro
. Pro-Hyp-Gly
. Gly-X-Y
. Ala-Gly-Pro
. Hyp-Pro-Gly

Correct Answer & Explanation

. Gly-X-Y

Explanation

The triple helical structure of collagen is fundamental to its tensile strength and structural integrity. This structure is formed by three alpha chains coiling around each other. A critical requirement for this coiling is the repeating amino acid sequence Glycine-X-Y, where Glycine (Gly) occupies every third position. The small side chain of Glycine allows for the tight packing of the three alpha chains. X and Y positions are frequently occupied by Proline (Pro) and Hydroxyproline (Hyp), which contribute to the stability of the helix through hydrogen bonding.

Question 4803

Topic: 1. General Principles & Basic Science

During muscle contraction, calcium ions play a pivotal role. What is the primary target protein that calcium binds to in skeletal muscle, initiating the contraction cycle?

. Myosin
. Actin
. Tropomyosin
. Troponin
. Titin

Correct Answer & Explanation

. Troponin

Explanation

In skeletal muscle, the process of excitation-contraction coupling begins with the release of calcium ions (Ca2+) from the sarcoplasmic reticulum. These calcium ions then bind to the Troponin C subunit of the troponin complex. This binding induces a conformational change in the troponin complex, which in turn moves tropomyosin away from the myosin-binding sites on the actin filaments. This uncovers the binding sites, allowing myosin heads to attach to actin and initiate the cross-bridge cycle, leading to muscle contraction. Myosin is the motor protein, Actin is the filament, Tropomyosin covers the binding sites, and Titin provides elasticity.

Question 4804

Topic: Biomechanics & Biomaterials

Synovial fluid provides lubrication and nutrient supply to articular cartilage. Which component of synovial fluid is primarily responsible for its non-Newtonian, viscoelastic properties, and boundary lubrication?

. Hyaluronic acid
. Lubricin
. Albumin
. IgG
. Fibrinogen

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Hyaluronic acid (HA), a very large, unsulfated glycosaminoglycan, is the key component responsible for the unique rheological properties of synovial fluid, including its non-Newtonian viscosity and viscoelasticity. Its long, entangled molecular chains create a viscous solution that acts as a lubricant and shock absorber, particularly important for boundary lubrication where surfaces are in direct contact under high load. Lubricin (proteoglycan 4) is also critical for boundary lubrication, but HA is primarily responsible for the bulk fluid's viscoelasticity. Albumin, IgG, and Fibrinogen are plasma proteins that contribute to osmotic pressure but not the primary viscoelastic properties.

Question 4805

Topic: Infection, Pharmacology & VTE

The formation of a bacterial biofilm on orthopedic implants is a major challenge in treating periprosthetic joint infections. Which of the following is a primary characteristic of bacteria within a biofilm that contributes to their increased resistance to antibiotics?

. Increased metabolic rate
. Enhanced nutrient uptake
. Downregulation of efflux pumps
. Formation of an extracellular polymeric substance (EPS) matrix
. Reduced cell-to-cell communication

Correct Answer & Explanation

. Formation of an extracellular polymeric substance (EPS) matrix

Explanation

Bacterial biofilms are communities of microorganisms encased in an extracellular polymeric substance (EPS) matrix that they produce and attach to surfaces, such as orthopedic implants. This EPS matrix provides a protective barrier against host immune defenses and significantly impedes the penetration and efficacy of antibiotics. Bacteria within the biofilm often exhibit a reduced metabolic rate and altered gene expression, further contributing to their tolerance and resistance to conventional antibiotic therapy. While changes in efflux pumps can occur, the physical barrier and altered microenvironment provided by the EPS matrix are considered the primary mechanisms for increased antibiotic resistance in biofilms.

Question 4806

Topic: Biology, Genetics & Bone Healing

Mesenchymal Stem Cells (MSCs) are often investigated for orthopedic regenerative applications due0 to their multipotent differentiation capacity. Which of the following is a key cell surface marker commonly used to identify human MSCs?

. CD34
. CD45
. CD90
. CD14
. CD19

Correct Answer & Explanation

. CD90

Explanation

Mesenchymal Stem Cells (MSCs) are characterized by their adherence to plastic, multipotent differentiation capacity (into osteoblasts, chondrocytes, adipocytes), and a specific immunophenotype. The International Society for Cellular Therapy (ISCT) defines minimal criteria for MSCs, which include expressing CD73, CD90, and CD105, and lacking the expression of hematopoietic markers such as CD34, CD45, CD14, CD11b, CD79a, or CD19, and HLA-DR. Therefore, CD90 is a commonly used positive marker to identify human MSCs. CD34 and CD45 are markers for hematopoietic stem cells and leukocytes, respectively.

Question 4807

Topic: 1. General Principles & Basic Science

When obtaining an X-ray image, increasing the kilovoltage (kVp) primarily affects which aspect of the radiographic image?

. Image sharpness
. Geometric distortion
. Magnification
. Penetration and contrast
. Receptor exposure

Correct Answer & Explanation

. Penetration and contrast

Explanation

Kilovoltage peak (kVp) is a primary factor in X-ray imaging that controls the energy and penetrating power of the X-ray beam. Increasing kVp means the X-ray photons have higher energy, allowing them to penetrate denser tissues more effectively. This leads to a wider range of tissue densities being represented on the image (more shades of gray), which generally decreases the overall image contrast (the difference in density between adjacent tissues). However, it increases the overall penetration and exposure of the image receptor. MAs (milliampere-seconds) primarily controls receptor exposure/density. Image sharpness, geometric distortion, and magnification are more influenced by focal spot size, object-to-film distance, and source-to-film distance, respectively.

Question 4808

Topic: Biology, Genetics & Bone Healing

Which of the following cells is directly responsible for sensing mechanical stress and initiating the bone remodeling cascade in response to altered loading?

. Osteoblasts
. Osteoclasts
. Osteocytes
. Chondrocytes
. Fibroblasts

Correct Answer & Explanation

. Osteocytes

Explanation

Osteocytes, which are mature osteoblasts embedded within the mineralized bone matrix, are considered the primary mechanosensors of bone. They form an intricate network through their dendritic processes, which connect via gap junctions within canaliculi. When mechanical stresses are applied to bone, the fluid flow through these canaliculi is altered, stimulating osteocytes. In response, osteocytes release signaling molecules (e.g., sclerostin, RANKL) that can influence the activity and recruitment of osteoblasts and osteoclasts, thereby initiating the bone remodeling process to adapt bone structure to mechanical demands.

Question 4809

Topic: Biology, Genetics & Bone Healing
The natural healing process of a ruptured Achilles tendon often results in tissue with inferior mechanical properties compared to the native tendon. This is primarily due to:
. Excessive collagen Type II deposition
. Persistent inflammatory response
. Formation of disorganized Type III collagen
. Reduced vascularization
. Lack of neural innervation

Correct Answer & Explanation

. Formation of disorganized Type III collagen

Explanation

Tendon healing, particularly after a rupture, is a complex process that often leads to scar tissue formation. The reparative tissue initially consists of granulation tissue rich in fibroblasts, macrophages, and new capillaries. During the remodeling phase, there is an increase in collagen synthesis. However, a significant portion of the newly synthesized collagen is Type III collagen, which is mechanically weaker and has smaller, less organized fibrils compared to the predominantly Type I collagen found in healthy, mature tendons. Over time, there is some conversion to Type I collagen and better organization, but the healed tendon rarely retains the full strength and elasticity of the original tissue due to the persistent presence of more disorganized Type III collagen and altered collagen cross-linking.

Question 4810

Topic: Physiology & Rehabilitation

Local anesthetics primarily exert their action by blocking which specific ion channel in nerve cell membranes?

. Voltage-gated potassium channels
. Ligand-gated chloride channels
. Voltage-gated sodium channels
. Voltage-gated calcium channels
. ATP-sensitive potassium channels

Correct Answer & Explanation

. Voltage-gated sodium channels

Explanation

Local anesthetics function by reversibly blocking nerve impulse conduction. Their primary mechanism of action involves binding to and inactivating voltage-gated sodium channels located on the inner surface of the neuronal cell membrane. By doing so, they prevent the rapid influx of sodium ions necessary for the depolarization phase of an action potential. This blockade inhibits the generation and propagation of nerve impulses, leading to a temporary loss of sensation in the region innervated by the affected nerves.

Question 4811

Topic: Biomechanics & Biomaterials

Hydroxyapatite is the primary mineral component of bone, providing its hardness and rigidity. What is the approximate percentage by weight that hydroxyapatite constitutes in mature cortical bone?

. 10-20%
. 30-40%
. 60-70%
. 80-90%
. >95%

Correct Answer & Explanation

. 60-70%

Explanation

Mature cortical bone is composed of both organic and inorganic components. The inorganic component, primarily hydroxyapatite crystals (calcium phosphate), accounts for approximately 60-70% of the dry weight of bone, providing its compressive strength and rigidity. The organic matrix, predominantly Type I collagen, constitutes about 20-30% and provides tensile strength and flexibility. The remaining percentage is water and other non-collagenous proteins.

Question 4812

Topic: Physiology & Rehabilitation

The primary type of nerve fiber responsible for transmitting the acute, sharp pain signals associated with an acute fracture or injury to the periosteum is:

. Unmyelinated C fibers
. Large myelinated A-alpha fibers
. Medium myelinated A-beta fibers
. Small myelinated A-delta fibers
. Autonomic efferent fibers

Correct Answer & Explanation

. Small myelinated A-delta fibers

Explanation

Nociceptive (pain-sensing) nerve fibers are broadly classified into A-delta fibers and C fibers. A-delta fibers are small, thinly myelinated fibers that conduct impulses faster than C fibers. They are responsible for transmitting the "first pain" sensation – sharp, well-localized, and acute pain, such as that experienced immediately after a fracture or periosteal injury. C fibers are unmyelinated, conduct impulses more slowly, and are responsible for the "second pain" – dull, aching, burning, and poorly localized pain. A-alpha and A-beta fibers are large, heavily myelinated fibers associated with proprioception, motor control, and touch/pressure, respectively, not primary pain transmission.

Question 4813

Topic: Biomechanics & Biomaterials

A bone specimen is subjected to increasing tensile load. It deforms elastically until it reaches its yield point, after which it deforms plastically. What happens to the specimen if the load is removed before the yield point is reached?

. It fractures immediately
. It retains its deformed shape permanently
. It returns to its original length
. It undergoes work hardening
. It experiences creep

Correct Answer & Explanation

. It returns to its original length

Explanation

The stress-strain curve of a material illustrates its mechanical properties under load. The elastic region is the initial phase where stress is proportional to strain (Hooke's Law). In this region, deformation is entirely reversible; if the load is removed, the material returns to its original dimensions. The yield point marks the transition from elastic to plastic deformation. Beyond the yield point, permanent deformation occurs, meaning the material will not fully recover its original shape even after the load is removed. Fracture occurs at the ultimate tensile strength or fracture point, which is typically well beyond the yield point.

Question 4814

Topic: Biology, Genetics & Bone Healing

Endochondral ossification is the primary process by which long bones are formed. What is the initial template for bone formation in endochondral ossification?

. Fibrous connective tissue
. Cartilaginous model
. Dermal condensation
. Mesenchymal membrane
. Woven bone scaffold

Correct Answer & Explanation

. Cartilaginous model

Explanation

Endochondral ossification is one of the two main processes of bone formation (osteogenesis). In this process, bone develops from a pre-existing hyaline cartilage model. Mesenchymal cells first differentiate into chondrocytes, which form a cartilage template that largely mimics the future bone shape. This cartilage model then undergoes calcification, hypertrophy, and ultimately apoptosis, and is gradually replaced by bone tissue laid down by osteoblasts. This mechanism is responsible for the formation of most bones in the appendicular skeleton and many in the axial skeleton (e.g., vertebrae). Intramembranous ossification, in contrast, forms bone directly from mesenchymal tissue without a cartilage intermediate.

Question 4815

Topic: 1. General Principles & Basic Science

Elastin is a key component of ligaments and tendons that provides elasticity. Which amino acid is primarily responsible for forming the unique cross-links (desmosine and isodesmosine) that give elastin its rubber-like properties?

. Glycine
. Proline
. Hydroxyproline
. Lysine
. Alanine

Correct Answer & Explanation

. Lysine

Explanation

Elastin is a highly elastic protein found in various connective tissues, including ligaments, skin, and blood vessel walls, enabling them to stretch and recoil. Its unique rubber-like properties are largely due to specialized covalent cross-links called desmosine and isodesmosine. These cross-links are formed from four lysine residues by the action of lysyl oxidase. The initial step involves the oxidative deamination of lysine side chains to allysine residues, which then condense to form the characteristic pyridinium ring structures of desmosine and isodesmosine, tethering multiple elastin monomers together into a resilient network.

Question 4816

Topic: Biomechanics & Biomaterials
Ultra-high molecular weight polyethylene (UHMWPE) is widely used in total joint arthroplasty as the bearing surface. What is the primary long-term failure mechanism associated with conventional UHMWPE?
. Creep deformation
. Stress shielding
. Osteolysis due to wear particles
. Bulk fracture
. Corrosion

Correct Answer & Explanation

. Osteolysis due to wear particles

Explanation

While UHMWPE is an excellent bearing material, the primary long-term failure mechanism of conventional UHMWPE in total joint arthroplasty is aseptic loosening, which is largely driven by osteolysis induced by wear particles. Over time, microscopic UHMWPE particles are generated from the bearing surface due to friction and abrasion. These particles are phagocytosed by macrophages and other immune cells, triggering a chronic inflammatory response that leads to local bone resorption (osteolysis) around the implant, ultimately causing the implant to loosen. Cross-linking UHMWPE is a strategy to reduce wear particle generation. Creep can occur but is less of a primary failure mechanism than osteolysis. Stress shielding relates to bone adaptation to implant stiffness. Bulk fracture and corrosion are typically associated with metallic components, though fatigue fracture of UHMWPE can occur.

Question 4817

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) plays a vital role in regulating bone resorption. What is its primary mechanism of action?

. Directly inhibiting osteoclast activity
. Stimulating osteoblast differentiation
. Sequestration of RANKL
. Promoting osteoclast apoptosis
. Enhancing calcium reabsorption in the kidney

Correct Answer & Explanation

. Sequestration of RANKL

Explanation

Osteoprotegerin (OPG) is a soluble decoy receptor for Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). RANKL is a transmembrane protein primarily expressed by osteoblasts and stromal cells that binds to its receptor, RANK, on osteoclast precursors and mature osteoclasts, leading to their differentiation, activation, and survival, thus promoting bone resorption. OPG competes with RANK for RANKL binding. By binding to and sequestering RANKL, OPG prevents RANKL from interacting with RANK, thereby inhibiting osteoclast formation and activity and effectively reducing bone resorption.

Question 4818

Topic: Biology, Genetics & Bone Healing

Which of the following systemic factors is most detrimental to fracture healing by inhibiting angiogenesis and collagen synthesis, and promoting catabolism?

. Vitamin D deficiency
. Growth hormone excess
. Uncontrolled diabetes mellitus
. Estrogen deficiency
. Glucocorticoid excess

Correct Answer & Explanation

. Glucocorticoid excess

Explanation

Glucocorticoids, particularly in excessive or chronic doses, are well-known inhibitors of fracture healing. They exert multiple detrimental effects, including: suppressing osteoblast proliferation and differentiation, inhibiting collagen synthesis, decreasing local growth factor production, reducing vascularization (angiogenesis), and promoting osteoclastogenesis and bone resorption. This overall effect shifts the balance towards delayed healing, non-union, and increased risk of complications. While other factors like Vitamin D deficiency and uncontrolled diabetes can also impair healing, glucocorticoid excess is a particularly potent inhibitor of the entire repair process. Growth hormone is generally anabolic, and estrogen deficiency can lead to osteoporosis but its direct acute effect on fracture healing is less profound than glucocorticoid excess.

Question 4819

Topic: 1. General Principles & Basic Science

In Magnetic Resonance Imaging (MRI), a T1-weighted sequence is primarily used to visualize anatomical detail. Which of the following tissues typically appears brightest (high signal intensity) on a T1-weighted image?

. Cortical bone
. Cerebrospinal fluid
. Muscle
. Fat
. Edema

Correct Answer & Explanation

. Fat

Explanation

T1-weighted MRI sequences are designed to maximize contrast based on T1 relaxation times. Tissues with short T1 relaxation times appear bright (high signal intensity), while those with long T1 times appear dark (low signal intensity). Fat has a characteristically short T1 relaxation time and thus appears bright on T1-weighted images. Water-rich tissues, such as cerebrospinal fluid (CSF) and edema, have long T1 times and appear dark. Cortical bone produces very little signal on MRI due to its low water content, and muscle appears intermediate.

Question 4820

Topic: Biomechanics & Biomaterials

Ligaments exhibit viscoelastic properties, meaning their mechanical response depends on the rate of loading. Which of the following phenomena is a direct manifestation of viscoelasticity in a ligament when subjected to a constant load over time?

. Increased stiffness
. Creep
. Hysteresis
. Fatigue
. Ultimate tensile strength

Correct Answer & Explanation

. Creep

Explanation

Viscoelastic materials, such as ligaments and tendons, exhibit both viscous and elastic characteristics. Creep is a key manifestation of viscoelasticity, referring to the tendency of a material to deform (e.g., elongate) permanently under the influence of persistent mechanical stress (constant load) over time. This is distinct from elastic deformation, which is instantaneous and reversible. Other viscoelastic phenomena include stress relaxation (decrease in stress over time under constant strain) and hysteresis (energy loss during loading-unloading cycles). Stiffness, fatigue, and ultimate tensile strength are general mechanical properties, not exclusively tied to creep.

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