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1. General Principles & Basic Science MCQs

Practice Set 689 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 13761

Topic: 1. General Principles & Basic Science
What is the primary pharmacological mechanism by which low-molecular-weight heparin (LMWH) provides deep vein thrombosis prophylaxis in postoperative orthopedic patients?
. Direct inhibition of thrombin (Factor IIa) active sites
. Irreversible binding to ADP receptors on platelet membranes
. Competitive Vitamin K antagonism in the liver
. Potentiation of antithrombin III to predominantly inhibit Factor Xa
. Direct activation of circulating plasminogen to plasmin

Correct Answer & Explanation

. Potentiation of antithrombin III to predominantly inhibit Factor Xa

Explanation

LMWH binds to and induces a conformational change in antithrombin III. Unlike unfractionated heparin, its smaller molecular size causes it to predominantly accelerate the inhibition of Factor Xa rather than thrombin (Factor IIa).

Question 13762

Topic: Biology, Genetics & Bone Healing

A 65-year-old male undergoes a total hip arthroplasty for severe secondary osteoarthritis. Preoperative radiographs reveal extensive cortical thickening and a "cotton wool" appearance of the hemipelvis. Histological examination of this bone would most likely demonstrate:

. A classic mosaic pattern of lamellar bone with prominent, haphazard cement lines
. Extensive osteoid seams with completely absent mineralization
. A high density of empty lacunae indicating avascular necrosis
. Malignant spindle cells producing primitive tumor osteoid
. Monoclonal sheets of plasma cells with clock-face nuclei

Correct Answer & Explanation

. A classic mosaic pattern of lamellar bone with prominent, haphazard cement lines

Explanation

The radiographic findings suggest Paget's disease of bone. The pathognomonic histologic feature is a mosaic pattern of lamellar bone characterized by prominent, haphazardly arranged cement lines due to erratic, coupled bone resorption and formation.

Question 13763

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) poses a severe challenge in periprosthetic joint infections. Its specific resistance to beta-lactam antibiotics is primarily mediated by which of the following mechanisms?

. Production of extended-spectrum beta-lactamases (ESBL)
. Upregulation and over-expression of membrane efflux pumps
. Alteration of penicillin-binding protein (PBP2a) encoded by the mecA gene
. Ribosomal methylation encoded by the erm gene
. Hyperproduction of biofilm exopolysaccharide matrix

Correct Answer & Explanation

. Alteration of penicillin-binding protein (PBP2a) encoded by the mecA gene

Explanation

MRSA resistance is directly conferred by the mecA gene, which encodes for an altered penicillin-binding protein, PBP2a. This mutant protein has an extremely low affinity for beta-lactam antibiotics, allowing cell wall cross-linking to continue even in their presence.

Question 13764

Topic: 1. General Principles & Basic Science
Which type of collagen forms the predominant structural tensile framework in the annulus fibrosus of the intervertebral disc?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

The annulus fibrosus consists predominantly of Type I collagen, which provides the necessary tensile strength to contain the inner structures. Conversely, the central nucleus pulposus is rich in Type II collagen and water-binding proteoglycans.

Question 13765

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial osteoinductive role in fracture healing. Which intracellular signaling molecules are phosphorylated by BMP receptors to translocate to the nucleus and regulate osteogenic gene expression?

. JAK/STAT proteins
. Smad proteins
. Beta-catenin
. c-AMP dependent protein kinases
. MAP kinases

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs are part of the TGF-beta superfamily and signal through serine/threonine kinase receptors. Upon activation, these receptors phosphorylate receptor-regulated Smad proteins (such as Smad1/5/8), which then bind Smad4 and translocate to the nucleus.

Question 13766

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, the pullout strength of a standard cortical bone screw is most significantly increased by maximizing which of the following design parameters?

. Inner (core) diameter
. Outer (thread) diameter
. Thread pitch
. Screw shaft length
. Screw head diameter

Correct Answer & Explanation

. Outer (thread) diameter

Explanation

The pullout strength of a screw is most strongly related to the outer (thread) diameter because it dictates the volume of bone engaged between the threads. Increasing the inner core diameter increases bending strength but does not primarily maximize pullout resistance.

Question 13767

Topic: 1. General Principles & Basic Science

According to the inverse square law of radiation physics, if an orthopedic surgeon steps back from 1 meter to 2 meters away from the C-arm during intraoperative fluoroscopy, the radiation exposure is reduced to what fraction of the original dose?

. One-half
. One-third
. One-fourth
. One-eighth
. One-sixteenth

Correct Answer & Explanation

. One-fourth

Explanation

The inverse square law dictates that radiation intensity is inversely proportional to the square of the distance from the source. Doubling the distance (from 1m to 2m) reduces the exposure by a factor of 2 squared, leaving the surgeon exposed to only one-fourth (25%) of the original dose.

Question 13768

Topic: 1. General Principles & Basic Science

When administering local anesthetics for an intra-articular block, the clinical duration of action of the agent is primarily determined by its:

. pKa (ionization constant)
. Lipid solubility
. Degree of protein binding
. Molecular weight
. Volume of distribution

Correct Answer & Explanation

. Degree of protein binding

Explanation

The duration of action of a local anesthetic is primarily determined by its affinity for plasma and tissue proteins. Agents with high protein binding, such as bupivacaine, remain attached to the sodium channel receptor site longer, providing prolonged clinical anesthesia.

Question 13769

Topic: Biology, Genetics & Bone Healing

During the incorporation of a massive cortical bone allograft, the process of "creeping substitution" is accurately defined by which initial sequence of events?

. Immediate revascularization through existing intact Haversian canals
. Osteoclastic resorption at the host-graft junction followed by osteoblastic bone formation
. Direct differentiation of donor graft osteocytes into active osteoblasts
. Formation of an endochondral hematoma that differentiates into cartilage
. Inflammatory giant cell degradation of the entire graft core

Correct Answer & Explanation

. Osteoclastic resorption at the host-graft junction followed by osteoblastic bone formation

Explanation

Cortical allografts incorporate via creeping substitution, wherein host osteoclasts first resorb the necrotic graft matrix to create cutting cones. This resorptive phase temporarily weakens the graft before host osteoblasts trail behind to deposit new, living bone.

Question 13770

Topic: 1. General Principles & Basic Science

In the structural organization of normal articular cartilage, the deep (basal) zone is characterized by which specific biomechanical arrangement of its collagen fibers?

. Randomly oriented to resist multi-directional shear forces
. Parallel to the articular surface to reduce friction
. Perpendicular to the articular surface, anchoring to the subchondral bone
. Oblique, crossing at 45-degree angles to absorb peak loads
. Arranged in concentric whorls surrounding individual chondrocytes

Correct Answer & Explanation

. Perpendicular to the articular surface, anchoring to the subchondral bone

Explanation

In the deep zone of articular cartilage, Type II collagen fibers are arranged perpendicularly to the articular surface. This vertical orientation allows them to firmly anchor the cartilage across the tidemark into the underlying subchondral bone, effectively resisting compressive forces.

Question 13771

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is now routinely utilized in major orthopedic procedures like arthroplasty to minimize perioperative blood loss. Which of the following accurately describes its molecular mechanism of action?

. It activates the extrinsic coagulation cascade via Tissue Factor upregulation
. It binds to plasminogen and competitively inhibits its activation to plasmin
. It directly cross-links fibrin polymers by activating Factor XIII
. It acts as a direct, irreversible thrombin inhibitor
. It rapidly consumes circulating antithrombin III

Correct Answer & Explanation

. It binds to plasminogen and competitively inhibits its activation to plasmin

Explanation

Tranexamic acid is a synthetic lysine analog that reversibly binds to the lysine-binding sites on plasminogen. This competitively inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of established fibrin clots (a potent antifibrinolytic effect).

Question 13772

Topic: 1. General Principles & Basic Science

Which of the following best describes the primary mechanism by which a cancellous bone autograft incorporates into the host site, as compared to a cortical bone autograft?

. Cancellous bone incorporates exclusively via osteoinduction without structural bridging.
. Cancellous bone undergoes initial osteoclastic resorption (creeping substitution) before new bone apposition.
. Cancellous bone relies solely on the diffusion of systemic growth factors for structural integration.
. Cancellous bone incorporates via initial osteoblastic apposition on the existing trabecular framework.
. Cancellous bone fails to revascularize, acting only as an inert space filler.

Correct Answer & Explanation

. Cancellous bone incorporates via initial osteoblastic apposition on the existing trabecular framework.

Explanation

Cancellous bone incorporates by initial osteoblastic apposition directly onto the existing trabecular framework (osteoconduction). In contrast, cortical bone must undergo initial osteoclastic resorption (creeping substitution) before new bone can be formed.

Question 13773

Topic: Biomechanics & Biomaterials

During the biomechanical testing of an articular cartilage explant, a constant strain is applied and maintained over time. The gradual decrease in the force required to maintain this constant strain is biomechanically defined as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Yield point

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the time-dependent decrease in stress (force) under a constant state of strain. Creep, conversely, is the progressive deformation (strain) of a material under a constant stress (load).

Question 13774

Topic: Biomechanics & Biomaterials

A surgeon revises a nonunion treated previously with a stainless steel plate by placing a new titanium plate over the existing retained stainless steel screws. Which type of corrosion is most likely to rapidly degrade the implant interface?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conducting fluid medium (like body fluids). This creates an electrochemical cell, leading to accelerated corrosion of the less noble metal.

Question 13775

Topic: Biology, Genetics & Bone Healing

The compressive strength and stiffness of normal articular cartilage are primarily provided by the interaction between interstitial fluid and which of the following extracellular matrix components?

. Type I collagen
. Type II collagen
. Aggrecan
. Hyaluronic acid
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a large proteoglycan, is highly negatively charged and draws water into the cartilage matrix via Donnan osmotic pressure. This swelling pressure is constrained by the Type II collagen network, providing cartilage with its vital compressive strength.

Question 13776

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy sustains a transverse subtrochanteric fracture. Radiographs reveal generalized, symmetric increased bone density with an absent medullary canal (Erlenmeyer flask deformity). The underlying pathophysiology of this condition is a defect in which of the following?

. Osteoblast proliferation
. Osteoid mineralization
. Type I collagen synthesis
. Osteoclast function
. Fibroblast growth factor receptor 3 (FGFR3) signaling

Correct Answer & Explanation

. Osteoclast function

Explanation

This clinical picture describes osteopetrosis, a genetic disorder characterized by excessively dense, brittle bones. It is caused by defective osteoclast function, preventing normal bone resorption and remodeling.

Question 13777

Topic: Infection, Pharmacology & VTE

A 45-year-old man presents with an acutely swollen, erythematous knee. Joint aspiration yields opaque synovial fluid. Which of the following synovial fluid analysis profiles is most diagnostic for acute bacterial septic arthritis?

. WBC 35,000 cells/mcL, 60% PMNs, normal glucose
. WBC 65,000 cells/mcL, 90% PMNs, negatively birefringent crystals
. WBC 85,000 cells/mcL, 95% PMNs, synovial glucose level < 50% of serum glucose
. WBC 40,000 cells/mcL, 80% PMNs, positively birefringent crystals
. WBC 15,000 cells/mcL, 50% PMNs, normal lactic acid

Correct Answer & Explanation

. WBC 85,000 cells/mcL, 95% PMNs, synovial glucose level < 50% of serum glucose

Explanation

Septic arthritis typically presents with a synovial fluid WBC count > 50,000 cells/mcL, > 90% polymorphonuclear leukocytes (PMNs), and decreased glucose compared to serum. While definitive diagnosis requires culture, these parameters dictate immediate empiric treatment.

Question 13778

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently used in major orthopedic arthroplasty and trauma to reduce perioperative blood loss. Which of the following best describes its primary mechanism of action?
. Irreversible inhibition of cyclooxygenase
. Direct inhibition of Factor Xa
. Reversible blockade of lysine binding sites on plasminogen
. Activation of antithrombin III
. Competitive inhibition of vitamin K epoxide reductase

Correct Answer & Explanation

. Reversible blockade of lysine binding sites on plasminogen

Explanation

TXA is a synthetic analog of the amino acid lysine. It competitively and reversibly binds to the lysine receptor sites on plasminogen, preventing its activation to plasmin and thereby inhibiting fibrinolysis.

Question 13779

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) enhances bone healing by inducing the differentiation of mesenchymal stem cells into osteoblasts. This osteoinductive effect is mediated by activating which of the following intracellular signaling pathways?

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

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs exert their effects by binding to serine/threonine kinase transmembrane receptors. This binding phosphorylates and activates the intracellular Smad 1/5/8 pathway, which translocates to the nucleus to regulate osteogenic gene transcription.

Question 13780

Topic: Infection, Pharmacology & VTE
Following a total hip arthroplasty, a patient is prescribed rivaroxaban for routine venous thromboembolism prophylaxis. Which of the following best describes the precise molecular target of this medication?
. Direct thrombin (Factor IIa) inhibition
. Direct competitive inhibition of Factor Xa
. Potentiation of antithrombin III
. Vitamin K epoxide reductase antagonism
. Inhibition of platelet ADP (P2Y12) receptors

Correct Answer & Explanation

. Direct competitive inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. This interrupts the intrinsic and extrinsic pathways of the blood coagulation cascade.

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