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1. General Principles & Basic Science MCQs

Practice Set 510 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 10181

Topic: 1. General Principles & Basic Science

During the cycle of skeletal muscle contraction, an action potential leads to the release of calcium ions from the sarcoplasmic reticulum. To which specific molecule does calcium directly bind to expose the myosin-binding sites on the actin filament?

. Myosin heavy chain
. Actin monomer
. Tropomyosin
. Troponin C
. Troponin I

Correct Answer & Explanation

. Troponin C

Explanation

In skeletal muscle, calcium released from the sarcoplasmic reticulum binds directly to Troponin C. This binding induces a conformational change in the troponin complex, which pulls tropomyosin away from the myosin-binding sites on the actin filament, allowing the myosin heads to bind and initiate the power stroke. Troponin I inhibits actin-myosin interaction, and Troponin T binds to tropomyosin.

Question 10182

Topic: Infection, Pharmacology & VTE

A 70-year-old male is diagnosed with a chronic periprosthetic joint infection of the hip caused by Staphylococcus epidermidis. The bacteria have formed a robust glycocalyx (biofilm) on the implant surface. Which of the following systemic antibiotics has the highest efficacy in penetrating the staphylococcal biofilm?

. Cefazolin
. Vancomycin
. Rifampin
. Gentamicin
. Daptomycin

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin has unique chemical properties that allow it to penetrate staphylococcal biofilms effectively and kill sessile bacteria in the stationary phase. However, it should never be used as monotherapy due to the rapid development of resistance; it is typically used as an adjunct (e.g., with a fluoroquinolone or beta-lactam) after the bacterial burden has been reduced.

Question 10183

Topic: Infection, Pharmacology & VTE

A patient undergoes a surgical procedure with a peripheral nerve block using bupivacaine. During the injection, the patient inadvertently receives an intravascular dose and suddenly develops perioral numbness, tinnitus, metallic taste, and subsequently ventricular tachycardia. What is the most appropriate initial specific pharmacologic antidote?

. Intravenous flumazenil
. Intravenous naloxone
. 20% lipid emulsion therapy
. Intravenous calcium gluconate
. Intravenous amiodarone

Correct Answer & Explanation

. 20% lipid emulsion therapy

Explanation

The patient is experiencing Local Anesthetic Systemic Toxicity (LAST), characteristic of bupivacaine given its high lipid solubility and cardiac toxicity (blocks voltage-gated sodium channels in the myocardium). The specific, life-saving antidote is 20% intravenous lipid emulsion (Intralipid), which creates a 'lipid sink' to draw the lipophilic anesthetic out of the tissue/plasma and also provides a direct metabolic benefit to the myocardium.

Question 10184

Topic: 1. General Principles & Basic Science

A structural cortical bone autograft is utilized in reconstructive surgery for a massive bone defect. Regarding its incorporation compared to cancellous autograft, which of the following statements accurately characterizes the biological behavior of the cortical graft?

. It incorporates faster due to higher initial osteoinductive potential
. It exhibits a steady increase in mechanical strength during the first 6 months due to appositional new bone growth
. It remodels via creeping substitution, experiencing a significant temporary decrease in mechanical strength
. It is completely resorbed by osteoclasts before any new osteoid is deposited
. It relies solely on surviving transplanted osteocytes for graft incorporation

Correct Answer & Explanation

. It remodels via creeping substitution, experiencing a significant temporary decrease in mechanical strength

Explanation

Cortical bone grafts undergo incorporation via creeping substitution, characterized by an initial phase of osteoclastic resorption (cutting cones) followed by osteoblastic bone deposition. Because resorption initially outpaces formation, cortical grafts become significantly weaker (increased porosity) between 6 weeks and 6 months before regaining strength. Cancellous grafts incorporate faster and tend to increase in strength initially.

Question 10185

Topic: Infection, Pharmacology & VTE

A postoperative orthopedic patient receiving unfractionated heparin for DVT prophylaxis experiences a 50% drop in platelet count on postoperative day 6, complicated by a new symptomatic deep vein thrombosis. What is the underlying mechanism of this paradoxical thrombotic state?

. Direct chemical toxicity of heparin to bone marrow megakaryocytes
. IgG antibodies directed against the heparin-platelet factor 4 (PF4) complex
. Depletion of Vitamin K-dependent clotting factors II, VII, IX, and X
. Activation of plasminogen to plasmin causing uninhibited systemic fibrinolysis
. An unmasked genetic mutation in Factor V Leiden exacerbated by heparin

Correct Answer & Explanation

. IgG antibodies directed against the heparin-platelet factor 4 (PF4) complex

Explanation

The patient is presenting with Heparin-Induced Thrombocytopenia (HIT) Type II. The mechanism involves the formation of IgG antibodies against the complex of heparin and Platelet Factor 4 (PF4). These immune complexes bind to Fc receptors on platelets, causing massive platelet activation, consumption (thrombocytopenia), and a highly prothrombotic state leading to arterial or venous thromboses.

Question 10186

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) are utilized clinically to enhance spinal fusion and fracture healing. Recombinant human BMP-2 acts on mesenchymal stem cells primarily through which of the following intracellular signaling pathways to promote osteoblastic differentiation?

. Wnt / beta-catenin pathway
. Smad 1/5/8 pathway
. JAK / STAT pathway
. MAP kinase pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs are members of the TGF-beta superfamily. Upon binding to their serine/threonine kinase cell surface receptors, BMPs (including BMP-2 and BMP-7) induce phosphorylation of the intracellular Smad proteins, specifically Smad 1, 5, and 8. These phosphorylated Smads then form a complex with Smad 4, translocate to the nucleus, and upregulate the transcription of osteogenic genes like Runx2.

Question 10187

Topic: Biomechanics & Biomaterials

A ligament undergoes a constant load over a prolonged period. It is observed that the ligament continues to deform slowly over time despite the load remaining unchanged. Which of the following biomechanical properties best describes this phenomenon?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material under a constant load over time. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant deformation. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycles of a viscoelastic material.

Question 10188

Topic: 1. General Principles & Basic Science

Articular cartilage relies on its distinct zonal architecture for optimal biomechanical function. In which zone of articular cartilage do the collagen fibers predominantly orient themselves perpendicular to the joint surface to resist compressive forces, and which type of collagen is most abundant?

. Superficial zone; Type II collagen
. Transitional (middle) zone; Type I collagen
. Deep zone; Type II collagen
. Calcified zone; Type I collagen
. Tidemark; Type X collagen

Correct Answer & Explanation

. Deep zone; Type II collagen

Explanation

In the deep zone of articular cartilage, chondrocytes are arranged in columns, and the collagen fibers (predominantly Type II, which is the main collagen type throughout articular cartilage) are oriented perpendicularly to the subchondral bone to resist high compressive forces. The superficial zone has fibers oriented parallel to the joint surface to resist shear stress.

Question 10189

Topic: Biomechanics & Biomaterials

A patient with a stainless steel dynamic compression plate for a femur fracture undergoes revision surgery where a titanium screw is inadvertently used to secure a loose segment of the plate. Over time, localized corrosion is noted at the titanium-stainless steel interface. Which of the following statements regarding galvanic corrosion in this scenario is true?

. Titanium acts as the anode and corrodes
. Stainless steel acts as the anode and corrodes
. Titanium acts as the cathode and corrodes
. Stainless steel acts as the cathode and corrodes
. Galvanic corrosion cannot occur between titanium and stainless steel in vivo

Correct Answer & Explanation

. Stainless steel acts as the anode and corrodes

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (like bodily fluids). The less noble metal (anode) undergoes accelerated corrosion, while the more noble metal (cathode) is protected. Stainless steel is less noble than titanium; therefore, the stainless steel acts as the anode and corrodes.

Question 10190

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with multiple low-energy fractures and is found to have 'rugger jersey spine' and 'bone-in-bone' appearances on radiographs. A mutation affecting which of the following is most likely responsible for his condition?

. Type I collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II
. Cathepsin K
. Runx2

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

The patient has osteopetrosis, characterized by dense, brittle bones due to osteoclast dysfunction. A well-known cause of the autosomal recessive form (which can present with renal tubular acidosis and cerebral calcification) is a mutation in the carbonic anhydrase II gene. This enzyme is crucial for generating the acidic environment (via hydrogen ion secretion at the ruffled border) necessary to dissolve bone mineral.

Question 10191

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) are often withheld following acute fracture due to concerns regarding impaired bone healing. By what mechanism do NSAIDs primarily exert this inhibitory effect on fracture healing?

. Inhibition of COX-1 leading to reduced osteoblast proliferation
. Inhibition of COX-2 leading to decreased prostaglandin E2 (PGE2) production
. Direct toxicity to osteoclasts inhibiting bone remodeling
. Downregulation of BMP-2 expression in the fracture hematoma
. Inhibition of macrophage migration inhibitory factor (MIF)

Correct Answer & Explanation

. Inhibition of COX-2 leading to decreased prostaglandin E2 (PGE2) production

Explanation

NSAIDs inhibit cyclooxygenase (COX) enzymes. COX-2 is heavily upregulated during the early inflammatory phase of fracture healing, producing prostaglandins (especially PGE2). PGE2 is crucial for mediating mesenchymal stem cell differentiation into osteoblasts and promoting angiogenesis. Inhibition of COX-2 impairs this early phase of endochondral ossification.

Question 10192

Topic: Infection, Pharmacology & VTE

In the context of periprosthetic joint infection (PJI), staphylococcal species frequently form biofilms on orthopedic implants. Which of the following best describes the critical transition step in the formation of a mature, antibiotic-resistant biofilm?

. Planktonic attachment via fibronectin-binding proteins
. Secretion of an extracellular polymeric substance (EPS) matrix
. Quorum sensing mediated dispersion of individual bacteria
. Expression of the mecA gene
. Phagocytosis of bacteria by local macrophages

Correct Answer & Explanation

. Secretion of an extracellular polymeric substance (EPS) matrix

Explanation

Biofilm formation occurs in stages: reversible attachment, irreversible attachment (via adhesins), maturation, and dispersion. The hallmark of maturation and the primary reason for profound antibiotic resistance is the production of an extracellular polymeric substance (EPS) matrix, which creates a physical and metabolic barrier protecting the bacteria.

Question 10193

Topic: Biology, Genetics & Bone Healing

Cancellous autograft is often considered the 'gold standard' for bone grafting due to possessing osteogenic, osteoinductive, and osteoconductive properties. Which of the following components of the graft provides its osteoinductive capacity?

. The three-dimensional trabecular bone matrix
. Surviving mesenchymal stem cells
. Bone morphogenetic proteins (BMPs) in the matrix
. Live osteoblasts transferred with the graft
. High vascularity of the graft tissue

Correct Answer & Explanation

. Bone morphogenetic proteins (BMPs) in the matrix

Explanation

Osteoinduction is the ability of a graft to stimulate host stem cells to differentiate into osteoblasts. This is primarily mediated by growth factors, such as Bone Morphogenetic Proteins (BMPs), contained within the bone matrix. Osteoconduction is provided by the physical 3D trabecular matrix, and osteogenesis is provided by the surviving cellular elements (MSCs and osteoblasts).

Question 10194

Topic: 1. General Principles & Basic Science

During a prolonged lower extremity orthopedic procedure, a pneumatic tourniquet is utilized. Which of the following represents the earliest histopathologic cellular change occurring in the skeletal muscle distal to the tourniquet?

. Z-band disruption
. Myocyte necrosis
. Mitochondrial swelling
. Nuclear fragmentation
. Endothelial cell swelling

Correct Answer & Explanation

. Mitochondrial swelling

Explanation

Mitochondrial swelling is the first observable ultra-structural cellular change during ischemic periods from tourniquet use, typically occurring within 30-60 minutes. Extended use beyond 2-3 hours can lead to irreversible damage, progressing to Z-line disruption and eventually myocyte necrosis.

Question 10195

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowing of the lower extremities, widened physes, and costochondral junction enlargements. Laboratory evaluation reveals normal serum calcium, significantly low serum phosphate, and elevated alkaline phosphatase. Which of the following is the most likely underlying mechanism of this condition?

. Deficiency of dietary vitamin D
. Mutation in the PHEX gene leading to excess FGF23
. Mutation in the COL1A1 gene
. Deficiency of 1-alpha-hydroxylase
. Resistance to parathyroid hormone

Correct Answer & Explanation

. Mutation in the PHEX gene leading to excess FGF23

Explanation

The patient has X-linked hypophosphatemic rickets (XLH), characterized by low phosphate, normal calcium, and elevated alkaline phosphatase, along with clinical signs of rickets. XLH is caused by a mutation in the PHEX gene, leading to overproduction of FGF23. FGF23 decreases renal tubular reabsorption of phosphate, causing profound hypophosphatemia.

Question 10196

Topic: 1. General Principles & Basic Science
In the process of ligament healing following an acute tear, there is a sequential progression through inflammatory, proliferative, and remodeling phases. During the remodeling phase, which specific biochemical change is most responsible for the increasing tensile strength of the healing ligament?
. Replacement of Type I collagen with Type II collagen
. Replacement of Type III collagen with Type I collagen
. Increased production of proteoglycans
. Elastin fiber hypertrophy
. Decreased cross-linking of collagen fibrils

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

During the early proliferative phase of ligament healing, fibroblasts primarily deposit Type III collagen, forming a disorganized and relatively weak matrix. During the remodeling phase, this Type III collagen is gradually replaced by Type I collagen, which is highly cross-linked and oriented along lines of stress, significantly increasing the tensile strength of the tissue.

Question 10197

Topic: Biomechanics & Biomaterials
To reduce wear rates in total joint arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) is often highly cross-linked via irradiation. However, irradiation creates free radicals that can lead to oxidation and embrittlement. Which of the following is the most definitive traditional method used to eliminate these free radicals post-irradiation?
. Cold sterilization using ethylene oxide
. Melting the polyethylene above its crystalline melting point
. Immersing the polyethylene in a saline bath
. Doping the polyethylene with cobalt-chromium particles
. Irradiating the polyethylene in an oxygen-rich environment

Correct Answer & Explanation

. Melting the polyethylene above its crystalline melting point

Explanation

Highly cross-linked polyethylene is produced by gamma or electron beam irradiation, which leaves free radicals. Heating the polymer above its crystalline melting point (remelting, ~150°C) provides enough molecular mobility for the free radicals to recombine, effectively eliminating them and reducing future oxidation (though it slightly reduces mechanical strength). Alternatively, annealing or doping with Vitamin E can be used.

Question 10198

Topic: Surgical Anatomy & Approaches

A surgeon is performing an anterior (Smith-Petersen) approach to the hip. The superficial surgical interval lies between two muscles innervated by different nerves. What are the respective nerve innervations of these two muscles?

. Femoral nerve and Superior gluteal nerve
. Femoral nerve and Obturator nerve
. Superior gluteal nerve and Inferior gluteal nerve
. Sciatic nerve and Superior gluteal nerve
. Femoral nerve and Sciatic nerve

Correct Answer & Explanation

. Femoral nerve and Superior gluteal nerve

Explanation

The anterior (Smith-Petersen) approach utilizes a superficial internervous plane between the Sartorius (innervated by the femoral nerve) and the Tensor Fasciae Latae (innervated by the superior gluteal nerve). The deep plane lies between the Rectus Femoris (femoral nerve) and Gluteus Medius (superior gluteal nerve).

Question 10199

Topic: Biology, Genetics & Bone Healing
Osteoclasts attach to the bone surface to form a sealed zone, allowing for localized bone resorption in an acidic environment. Which specific integrin is primarily responsible for mediating the attachment of osteoclasts to bone matrix proteins such as osteopontin?
. Alpha-5 beta-1
. Alpha-v beta-3
. Alpha-2 beta-1
. Alpha-M beta-2
. Alpha-L beta-2

Correct Answer & Explanation

. Alpha-v beta-3

Explanation

Osteoclasts utilize the Alpha-v beta-3 (αvβ3) integrin to bind to specific amino acid sequences (RGD - arginine-glycine-aspartic acid motifs) found on bone matrix proteins like osteopontin and bone sialoprotein. This integrin-mediated binding is critical for forming the sealing zone required for effective bone resorption.

Question 10200

Topic: 1. General Principles & Basic Science

In normal human synovial fluid, which molecule is primarily responsible for the boundary lubrication of articular cartilage, specifically functioning to reduce friction at the cartilage-cartilage interface under high loads?

. Hyaluronic acid
. Lubricin (PRG4)
. Aggrecan
. Chondroitin sulfate
. Type IX collagen

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Lubricin (Proteoglycan 4 or PRG4) is a glycoprotein secreted by synovial fibroblasts and superficial zone chondrocytes. It is the primary molecule responsible for boundary lubrication at the cartilage surface, which reduces friction and wear under high-load conditions. Hyaluronic acid contributes mostly to the overall viscosity and elastohydrodynamic lubrication of the joint fluid.

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