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1. General Principles & Basic Science MCQs

Practice Set 635 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 12681

Topic: Biomechanics & Biomaterials

During a complex flexor tendon reconstruction in Zone II, the surgeon must prioritize preserving or reconstructing specific pulleys to prevent bowstringing and maintain digital kinematics. Which two pulleys are the most critical biomechanically?

. A1 and A3
. A2 and A4
. A3 and A5
. A1 and A5
. C1 and C2

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the most crucial annular pulleys for preventing bowstringing and maintaining the functional excursion of the flexor tendons. They have broad osseous insertions onto the proximal and middle phalanges, respectively.

Question 12682

Topic: 1. General Principles & Basic Science
A 22-year-old rugby player felt a "pop" in his ring finger while grabbing an opponent's jersey and cannot actively flex the distal interphalangeal (DIP) joint. Radiographs show a small bony avulsion fragment localized at the level of the proximal interphalangeal (PIP) joint. According to the Leddy and Packer classification, what type of injury is this?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

A Leddy and Packer Type II injury involves retraction of the flexor digitorum profundus (FDP) tendon to the level of the PIP joint, often associated with a small avulsed bony fragment. The long vincula remain intact, preserving some blood supply and preventing retraction into the palm.

Question 12683

Topic: 1. General Principles & Basic Science

A 62-year-old female with severe rheumatoid arthritis presents with an inability to actively extend her ring and small fingers at the metacarpophalangeal joints. She has full passive extension and the tenodesis effect is absent. Radiographs show a distally prominent, subluxated ulnar head. What is the most likely diagnosis?

. Mannerfelt-Norman syndrome
. Vaughan-Jackson syndrome
. Posterior interosseous nerve entrapment at the Arcade of Frohse
. Sagittal band rupture
. Extensor digitorum communis subluxation

Correct Answer & Explanation

. Vaughan-Jackson syndrome

Explanation

Vaughan-Jackson syndrome describes the sequential attrition and rupture of the extensor tendons, typically starting ulnarly with the extensor digiti minimi (EDM). This is caused by friction against a prominent, arthritic distal ulna (caput ulnae syndrome).

Question 12684

Topic: Biomechanics & Biomaterials

Regarding polymethylmethacrylate (PMMA) bone cement, which of the following statements is FALSE?

. It functions as a mechanical interlock rather than an adhesive bond.
. It undergoes an exothermic reaction during polymerization.
. Antibiotics can be safely mixed into the cement for local delivery.
. Its strength significantly increases with the addition of barium sulfate.
. The monomer is a known allergen and tissue irritant.

Correct Answer & Explanation

. The monomer is a known allergen and tissue irritant.

Explanation

The addition of barium sulfate (or zirconium dioxide) to PMMA bone cement is for radiopacity, allowing the cement to be visible on X-ray. It does not significantly increase thestrengthof the cement; in fact, it can slightly decrease mechanical properties. PMMA functions via mechanical interlock (macro- and micro-interlock) with trabecular bone. Its polymerization is an exothermic reaction. Antibiotics are commonly mixed in for prophylaxis or treatment of infection. The monomer (methyl methacrylate) is a known irritant and allergen.

Question 12685

Topic: Biomechanics & Biomaterials

The 'creep' phenomenon in viscoelastic materials like articular cartilage refers to:

. The rapid deformation under immediate load.
. The time-dependent increase in deformation under a constant load.
. The ability to recover original shape after load removal.
. The constant deformation regardless of applied load.
. The decrease in stress over time under constant deformation.

Correct Answer & Explanation

. The time-dependent increase in deformation under a constant load.

Explanation

Creep is the time-dependent increase in deformation (strain) of a material under a constant applied load (stress). In articular cartilage, this is due to the slow exudation of fluid from the matrix under sustained compression. Viscoelastic materials also exhibit stress relaxation (decrease in stress under constant strain) and hysteresis. The rapid deformation is instantaneous elastic response, recovery is elasticity/viscoelasticity, and constant deformation regardless of load is incorrect. Decrease in stress over time under constant deformation is stress relaxation.

Question 12686

Topic: Biomechanics & Biomaterials
Which type of collagen is the most abundant in mature, healthy bone and provides its primary tensile strength?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen is the most abundant protein in the human body and constitutes approximately 90% of the organic matrix of bone. Its fibrous structure provides the bone's primary tensile strength and flexibility, complementing the compressive strength provided by the mineralized hydroxyapatite crystals. Type II collagen is found predominantly in cartilage, Type III in highly extensible tissues like skin and blood vessels (and early wound healing), and Types IX and X are associated with cartilage and the growth plate, respectively.

Question 12687

Topic: Biology, Genetics & Bone Healing

The 'zone of Ranvier' in the growth plate is primarily responsible for:

. Longitudinal bone growth.
. Appositional bone growth (width).
. Vascular invasion and mineralization.
. Maintaining chondrocyte stem cell population.
. Repair of articular cartilage defects.

Correct Answer & Explanation

. Appositional bone growth (width).

Explanation

The zone of Ranvier is a periosteal ring located circumferentially around the periphery of the growth plate. It contains chondrocytes and osteoblasts and is primarily responsible for appositional bone growth, contributing to the increase in the width of the bone metaphysis. Longitudinal growth occurs through the proliferation and hypertrophy of chondrocytes within the growth plate itself. Vascular invasion and mineralization occur in the zone of calcification/ossification. The zone of Ranvier is distinct from articular cartilage repair.

Question 12688

Topic: 1. General Principles & Basic Science
Which statement regarding peripheral nerve regeneration is most accurate?
. Schwann cells primarily inhibit axonal regrowth after injury.
. Regeneration is faster in the central nervous system than in the peripheral nervous system.
. The basal lamina tubes formed by Schwann cells guide regenerating axons.
. Myelin sheath remnants actively promote regeneration.
. Regenerating axons typically grow at a rate of 10 mm/day.

Correct Answer & Explanation

. The basal lamina tubes formed by Schwann cells guide regenerating axons.

Explanation

After peripheral nerve injury and Wallerian degeneration, Schwann cells dedifferentiate, proliferate, and form 'Büngner bands' or basal lamina tubes. These tubes provide a scaffold and release neurotrophic factors (e.g., NGF, BDNF) that guide the regenerating axonal sprouts from the proximal stump toward the target. Schwann cells promote regeneration. Regeneration is much slower and less successful in the CNS. Myelin debris contains inhibitory factors. Axonal growth rate is typically 1-3 mm/day, not 10 mm/day.

Question 12689

Topic: 1. General Principles & Basic Science

In the context of bone grafts, which property describes the ability of the graft to provide a scaffold for new bone formation?

. Osteoinduction
. Osteoconduction
. Osteogenesis
. Osteointegration
. Osteopromotion

Correct Answer & Explanation

. Osteoconduction

Explanation

Osteoconduction refers to the ability of a bone graft material to serve as a scaffold for the ingrowth of new bone-forming cells and capillaries from the host bone. This allows for creeping substitution, where new bone is laid down on the graft surface. Osteoinduction is the ability to stimulate undifferentiated mesenchymal cells to differentiate into osteoblasts and form bone. Osteogenesis is the formation of new bone by cells within the graft (e.g., autograft). Osteointegration describes direct structural and functional connection between living bone and the surface of a load-bearing implant.

Question 12690

Topic: Biomechanics & Biomaterials

The mechanical behavior of articular cartilage is highly dependent on the interactions between collagen, proteoglycans, and water. What is the primary role of water in enabling cartilage's load-bearing function?

. Provides direct tensile strength.
. Acts as a lubricating agent only.
. Creates an osmotic pressure that resists compression.
. Initiates collagen synthesis.
. Maintains chondrocyte viability through oxygen transport.

Correct Answer & Explanation

. Creates an osmotic pressure that resists compression.

Explanation

Water, held within the aggrecan-hyaluronic acid complexes, creates a significant osmotic (swelling) pressure within the cartilage matrix. When compressive loads are applied, water is exuded, but the trapped proteoglycans resist this outflow, creating a fluid-pressurization effect that supports the load. This fluid-solid interaction is fundamental to cartilage's ability to resist compression and allows for its viscoelastic properties. While water aids lubrication and nutrient transport, its primary load-bearing role is via osmotic pressure.

Question 12691

Topic: Biomechanics & Biomaterials

Regarding implant materials, what is the primary advantage of titanium alloys (e.g., Ti-6Al-4V) over stainless steel (e.g., 316L) for orthopedic implants?

. Higher modulus of elasticity, reducing stress shielding.
. Superior corrosion resistance and biocompatibility.
. Greater ultimate tensile strength.
. Lower manufacturing cost.
. Significantly higher wear resistance.

Correct Answer & Explanation

. Superior corrosion resistance and biocompatibility.

Explanation

Titanium alloys are generally preferred for long-term orthopedic implants due to their superior corrosion resistance and excellent biocompatibility compared to stainless steel. They form a stable, passive oxide layer (TiO2) that prevents ion release. Titanium also has a lower modulus of elasticity than stainless steel (closer to bone), which can reduce stress shielding, making 'A' a plausible distractor but 'B' is a more encompassing primary advantage. Stainless steel often has higher ultimate tensile strength but is less bioinert. Titanium wear resistance is not universally superior; for example, ceramic is superior.

Question 12692

Topic: Biology, Genetics & Bone Healing

Which of the following cellular events is characteristic of the 'soft callus' stage of fracture healing?

. Direct apposition of new bone on fracture ends.
. Differentiation of mesenchymal stem cells into chondroblasts.
. Vascularization and mineralization of cartilage.
. Remodeling of woven bone into lamellar bone.
. Activation of osteoclasts at the fracture site.

Correct Answer & Explanation

. Differentiation of mesenchymal stem cells into chondroblasts.

Explanation

The soft callus stage is characterized by the differentiation of mesenchymal stem cells from the periosteum and bone marrow into chondroblasts, which then produce cartilage. This cartilage forms a soft, flexible bridge across the fracture gap. Direct bone apposition is primary healing. Vascularization and mineralization of cartilage occur in the hard callus stage, and remodeling is a later stage. Osteoclasts are active throughout but are notcharacteristicof the soft callus itself.

Question 12693

Topic: Biology, Genetics & Bone Healing

Which physiological process is critically dependent on cyclic loading and fluid flow for maintaining bone health and stimulating remodeling?

. Hematopoiesis within the bone marrow.
. Osteocyte mechanotransduction.
. Parathyroid hormone (PTH) release from glands.
. Vitamin D synthesis in the skin.
. Formation of type I collagen by osteoblasts.

Correct Answer & Explanation

. Osteocyte mechanotransduction.

Explanation

Osteocytes, through their extensive lacunar-canalicular network, are exquisitely sensitive to mechanical stimuli, particularly fluid flow within the canaliculi induced by cyclic loading. This mechanotransduction is the primary mechanism by which bone senses its mechanical environment and initiates remodeling cascades (involving both osteoblasts and osteoclasts) to adapt its structure to applied loads, maintaining bone health. The other options are related to bone but not directly dependent on cyclic loading and fluid flow for their function in this context.

Question 12694

Topic: Biomechanics & Biomaterials

Which of the following statements about the mechanical properties of cancellous (trabecular) bone is MOST accurate?

. It is anisotropic, with strength varying significantly with load direction.
. It is typically stronger in tension than in compression.
. Its mechanical properties are largely independent of bone density.
. It has a lower modulus of elasticity and is more ductile than cortical bone.
. It is primarily designed to resist high torsional forces.

Correct Answer & Explanation

. It is anisotropic, with strength varying significantly with load direction.

Explanation

Cancellous bone, like cortical bone, is anisotropic. Its strength and stiffness vary significantly depending on the direction of loading, due to the orientation of its trabecular network along lines of stress. It is stronger in compression than tension. Its mechanical properties are highly dependent on bone density (volume fraction) and architecture. It is more compliant (lower modulus) and ductile than cortical bone, but this option isn't themostaccurate overall descriptor of its specific mechanical nature regarding anisotropy and density dependence. It is not primarily designed to resist high torsional forces, which are better handled by cortical bone.

Question 12695

Topic: Biology, Genetics & Bone Healing

Which growth factor plays a crucial role in initiating the cascade of endochondral ossification, particularly in chondrogenesis and osteogenesis?

. Epidermal Growth Factor (EGF)
. Fibroblast Growth Factor (FGF)
. Bone Morphogenetic Protein (BMP)
. Vascular Endothelial Growth Factor (VEGF)
. Insulin-like Growth Factor (IGF)

Correct Answer & Explanation

. Bone Morphogenetic Protein (BMP)

Explanation

Bone Morphogenetic Proteins (BMPs) are a family of growth factors that are potent osteoinductive agents. They play a critical role in bone and cartilage formation, differentiation of mesenchymal stem cells into chondroblasts and osteoblasts, and are essential for both embryonic development and fracture repair. VEGF is critical for angiogenesis, IGF for cell proliferation, EGF and FGF have broader mitogenic roles but are not as specific to initiating osteochondral differentiation as BMPs.

Question 12696

Topic: Biology, Genetics & Bone Healing

Which factor is LEAST likely to promote angiogenesis at a fracture site?

. Hypoxia
. Vascular Endothelial Growth Factor (VEGF)
. Fibroblast Growth Factor (FGF)
. Interleukin-1 (IL-1)
. Sclerostin

Correct Answer & Explanation

. Sclerostin

Explanation

Sclerostin is a protein produced by osteocytes that inhibits bone formation by antagonizing Wnt signaling. It is not directly involved in promoting angiogenesis; in fact, its primary role is related to bone remodeling balance. Hypoxia is a potent stimulus for VEGF production, which is a key promoter of angiogenesis. VEGF and FGF are major pro-angiogenic growth factors. IL-1 is a pro-inflammatory cytokine that can indirectly contribute to angiogenesis in the context of tissue repair, although its primary role is not angiogenesis.

Question 12697

Topic: 1. General Principles & Basic Science

In muscle physiology, what is the primary role of tropomyosin?

. To bind calcium ions and initiate muscle contraction.
. To form the thick filaments of the sarcomere.
. To block myosin-binding sites on actin in a relaxed muscle.
. To generate the force for muscle contraction.
. To facilitate the release of acetylcholine at the neuromuscular junction.

Correct Answer & Explanation

. To block myosin-binding sites on actin in a relaxed muscle.

Explanation

Tropomyosin is a regulatory protein that, in a relaxed muscle, wraps around the actin filaments and covers the myosin-binding sites, preventing the myosin heads from binding to actin. When calcium ions (released from the sarcoplasmic reticulum) bind to troponin, troponin undergoes a conformational change that pulls tropomyosin away from the myosin-binding sites, allowing cross-bridge formation and muscle contraction. Troponin binds calcium, myosin forms thick filaments and generates force, and acetylcholine release is at the NMJ.

Question 12698

Topic: Biomechanics & Biomaterials

The 'fatigue life' of an orthopedic implant refers to its ability to:

. Resist corrosion over its expected lifespan.
. Undergo plastic deformation without fracture.
. Withstand repeated cycles of loading without catastrophic failure.
. Maintain its mechanical properties at elevated temperatures.
. Undergo substantial elastic deformation before permanent change.

Correct Answer & Explanation

. Withstand repeated cycles of loading without catastrophic failure.

Explanation

Fatigue life is a critical material property for orthopedic implants. It refers to the number of stress cycles an implant can withstand before fracturing. Implants in the body are subjected to millions of loading cycles (e.g., walking, running) at stresses below their ultimate tensile strength. Fatigue failure is a common mode of implant failure, making high fatigue life a crucial design consideration. Plastic deformation without fracture is ductility; elastic deformation is elasticity.

Question 12699

Topic: Biomechanics & Biomaterials

The 'creep' phenomenon in a cancellous bone graft, if significant, could lead to:

. Accelerated revascularization of the graft.
. Increased mechanical stability of the construct.
. Loss of initial reduction and graft collapse.
. Enhanced osteoinduction within the graft.
. Reduced risk of infection due to improved perfusion.

Correct Answer & Explanation

. Loss of initial reduction and graft collapse.

Explanation

Creep in a bone graft refers to its time-dependent deformation under sustained load. If a cancellous bone graft, which has viscoelastic properties, is subjected to significant sustained compressive forces, it can slowly deform and collapse over time. This 'creep' can lead to a loss of initial reduction, settling of the construct, and potential instability, especially in reconstructive surgery where structural integrity is paramount. It does not directly affect revascularization, stability, osteoinduction, or infection risk in this manner.

Question 12700

Topic: 1. General Principles & Basic Science

What is the primary mechanism by which non-steroidal anti-inflammatory drugs (NSAIDs) can potentially impair fracture healing?

. Direct inhibition of osteoblast differentiation.
. Interference with angiogenesis at the fracture site.
. Inhibition of prostaglandin synthesis, particularly COX-2 mediated.
. Increased osteoclast activity leading to excessive bone resorption.
. Disruption of the initial fracture hematoma formation.

Correct Answer & Explanation

. Inhibition of prostaglandin synthesis, particularly COX-2 mediated.

Explanation

NSAIDs exert their anti-inflammatory and analgesic effects by inhibiting cyclooxygenase (COX) enzymes, particularly COX-2. COX-2 is crucial for the synthesis of prostaglandins, which play a vital role in the early inflammatory phase of fracture healing, including callus formation, angiogenesis, and chondrogenesis. By inhibiting prostaglandin synthesis, NSAIDs can impair or delay fracture healing, especially in the early stages, though the clinical significance of this effect can vary.

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