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1. General Principles & Basic Science MCQs

Practice Set 645 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 12881

Topic: Biology, Genetics & Bone Healing

A patient on long-term alendronate therapy sustains an atypical subtrochanteric femur fracture. Bisphosphonates such as alendronate reduce bone resorption primarily by inhibiting which of the following enzymes in the mevalonate pathway?

. HMG-CoA reductase
. Farnesyl pyrophosphate (FPP) synthase
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase (TRAP)
. Matrix metalloproteinase-9 (MMP-9)

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins essential for osteoclast ruffled border formation and function, leading to osteoclast apoptosis.

Question 12882

Topic: 1. General Principles & Basic Science

A 45-year-old malnourished patient presents with impaired wound healing and spontaneous bleeding gums. A deficiency in vitamin C is diagnosed. This deficiency directly impairs collagen synthesis by limiting the function of which of the following?

. Lysyl oxidase
. Prolyl hydroxylase
. Matrix metalloproteinases
. Elastase
. Chondroitin sulfate

Correct Answer & Explanation

. Prolyl hydroxylase

Explanation

Vitamin C (ascorbic acid) is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase. These enzymes are responsible for the hydroxylation of proline and lysine residues, which is required for the stable triple-helix formation of collagen.

Question 12883

Topic: 1. General Principles & Basic Science
During a bilateral total knee arthroplasty, the surgeon administers intravenous tranexamic acid (TXA) to reduce perioperative blood loss. What is the mechanism of action of this agent?
. Inhibition of cyclooxygenase
. Activation of tissue plasminogen activator (tPA)
. Competitive inhibition of plasminogen activation
. Direct stimulation of the extrinsic coagulation cascade
. Irreversible binding to platelet GP IIb/IIIa receptors

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby preventing the breakdown of fibrin clots (fibrinolysis).

Question 12884

Topic: Biomechanics & Biomaterials
To reduce wear rates in total joint arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) undergoes highly cross-linking. To prevent in vivo oxidation and premature degradation, the cross-linked UHMWPE must be subjected to which of the following processes?
. Gamma irradiation in ambient air
. Ethylene oxide sterilization
. Remelting or annealing to eliminate free radicals
. Addition of polymethylmethacrylate (PMMA)
. Cold drawing of the polymer chains

Correct Answer & Explanation

. Remelting or annealing to eliminate free radicals

Explanation

Gamma irradiation creates cross-links but also leaves behind free radicals. Remelting or annealing the polyethylene after irradiation eliminates these free radicals, preventing subsequent oxidation and degradation.

Question 12885

Topic: Biomechanics & Biomaterials

A surgeon applies a stainless steel plate to a femur fracture and secures it using titanium alloy screws. This mixing of dissimilar metals primarily increases the risk of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Mixing dissimilar metals in an electrolytic environment (like the human body) creates an electrochemical cell, leading to galvanic corrosion. The less noble metal becomes the anode and corrodes faster.

Question 12886

Topic: 1. General Principles & Basic Science

A new rapid diagnostic test for periprosthetic joint infection is evaluated in a specialized tertiary orthopedic center with a high infection rate and a community hospital with a very low infection rate. Which of the following statistical values for the test will be significantly higher at the tertiary center?

. Sensitivity
. Specificity
. Positive predictive value
. Negative predictive value
. Likelihood ratio

Correct Answer & Explanation

. Positive predictive value

Explanation

Positive predictive value (PPV) is highly dependent on the prevalence of the disease in the tested population. A higher disease prevalence (as seen in the tertiary center) will result in a higher PPV.

Question 12887

Topic: Infection, Pharmacology & VTE

In the pathogenesis of orthopedic implant infections, bacteria form a mature biofilm that makes them highly resistant to systemic antibiotics and host immune defenses. The structural integrity and protective barrier of this biofilm are primarily provided by which of the following?

. Peptidoglycan cell wall
. Extracellular polymeric substance (glycocalyx)
. Bacterial flagella
. Lipopolysaccharide (LPS) layer
. Planktonic dissemination factors

Correct Answer & Explanation

. Extracellular polymeric substance (glycocalyx)

Explanation

Once bacteria adhere to an implant, they secrete an extracellular polymeric substance (glycocalyx) to form a mature biofilm. This matrix acts as a physical barrier and alters the metabolic state of the bacteria (sessile state), making them highly resistant to antibiotics.

Question 12888

Topic: Biology, Genetics & Bone Healing

During a spinal fusion, a surgeon decides to use demineralized bone matrix (DBM) to supplement local autograft. Which of the following best describes the bone healing properties inherent to commercially available DBM?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteoconductive, osteoinductive, and osteogenic
. Osteogenic only

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

Demineralized bone matrix (DBM) provides a structural scaffold (osteoconductive) and contains inherent growth factors like BMPs (osteoinductive). However, it lacks live cells and is therefore not osteogenic.

Question 12889

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, an action potential triggers the release of calcium ions from the sarcoplasmic reticulum. The direct binding of these calcium ions to which of the following proteins initiates the cross-bridge cycle?

. Actin
. Myosin heavy chain
. Troponin C
. Tropomyosin
. Titin

Correct Answer & Explanation

. Troponin C

Explanation

Calcium released from the sarcoplasmic reticulum binds directly to Troponin C. This causes a conformational change that moves tropomyosin away from the myosin-binding sites on the actin filament, allowing cross-bridge cycling to occur.

Question 12890

Topic: 1. General Principles & Basic Science

The alpha chains of Type I collagen form a rigid triple helix. This structural conformation is exclusively possible because every third amino acid in the primary sequence is universally which of the following?

. Proline
. Hydroxyproline
. Lysine
. Glycine
. Glutamine

Correct Answer & Explanation

. Glycine

Explanation

Glycine is the smallest amino acid and is present at every third position in the collagen alpha chain (Gly-X-Y repeating sequence). Its small size allows the three chains to pack tightly into the central core of the triple helix.

Question 12891

Topic: 1. General Principles & Basic Science

Following a severe traction injury to the brachial plexus, a patient undergoes evaluation for nerve continuity. In an axonotmesis injury, distal axonal degeneration occurs over several days. Which cell type is primarily responsible for clearing the myelin debris in the peripheral nervous system during this process?

. Astrocytes
. Oligodendrocytes
. Schwann cells
. Microglia
. Fibroblasts

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Wallerian degeneration involves the breakdown of the axon distal to the injury. Schwann cells and recruited macrophages are responsible for phagocytosing and clearing the myelin and axonal debris to prepare for regeneration.

Question 12892

Topic: Biology, Genetics & Bone Healing

Which of the following cellular markers or transcription factors is considered the master regulator required for mesenchymal stem cells to differentiate into the osteoblast lineage?

. SOX9
. Runx2 (Cbfa1)
. PPAR-gamma
. MyoD
. Sclerostin

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor essential for osteoblast differentiation from mesenchymal stem cells. A deficiency in Runx2 results in cleidocranial dysplasia and a complete lack of mature osteoblasts.

Question 12893

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical screw is a critical factor in achieving stable internal fixation. Based on the standard mathematical formula for screw pullout strength, which of the following design parameters is directly proportional to the pullout resistance?

. Inner (core) diameter
. Pitch of the threads
. Outer (major) diameter
. Screw head size
. Distance between threads

Correct Answer & Explanation

. Outer (major) diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter of the screw, the length of thread engagement, and the shear strength of the bone material.

Question 12894

Topic: Biomechanics & Biomaterials

A surgeon is revising a nonunion and plans to use a combination of implants. To minimize the risk of clinically significant galvanic corrosion, which of the following combinations of metals should be strictly avoided in direct contact?

. Cobalt-chromium and Titanium
. Stainless steel and Titanium
. Titanium and Tantalum
. Cobalt-chromium and Zirconium
. Commercially pure Titanium and Titanium alloy (Ti-6Al-4V)

Correct Answer & Explanation

. Stainless steel and Titanium

Explanation

Mixing stainless steel and titanium implants can lead to severe galvanic corrosion of the less noble metal (stainless steel), causing implant failure and adverse local tissue reactions.

Question 12895

Topic: 1. General Principles & Basic Science

Following the placement of a massive cortical structural allograft for a segmental bone defect, what is the primary mechanism of graft incorporation and its initial mechanical consequence?

. Creeping substitution resulting in early increased mechanical strength
. Creeping substitution resulting in early decreased mechanical strength
. Osteoinduction leading to rapid callous formation and stability
. Direct intramembranous ossification with no initial mechanical alteration
. Endochondral ossification leading to permanently delayed strength

Correct Answer & Explanation

. Creeping substitution resulting in early decreased mechanical strength

Explanation

Cortical allografts incorporate via creeping substitution, where early osteoclastic resorption initially decreases the structural strength of the graft before osteoblasts deposit new bone.

Question 12896

Topic: 1. General Principles & Basic Science

In adult articular cartilage, which of the following statements best describes the specific biochemical and structural characteristics of the superficial (tangential) zone?

. Highest proteoglycan content with perpendicularly aligned collagen
. Lowest water content with randomly oriented collagen fibers
. Highest concentration of collagen with fibers oriented parallel to the articular surface
. Highest concentration of spherical chondrocytes with vertically aligned collagen
. Lowest collagen content with maximal proteoglycan concentration

Correct Answer & Explanation

. Highest concentration of collagen with fibers oriented parallel to the articular surface

Explanation

The superficial zone of articular cartilage has the highest collagen content, lowest proteoglycan content, and collagen fibers oriented parallel to the joint surface to resist shear forces.

Question 12897

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) plays a key role in systemic calcium homeostasis. PTH stimulates osteoclastic bone resorption primarily through which of the following cellular mechanisms?

. Direct binding to PTH receptors on the osteoclast surface
. Upregulation of RANKL expression on osteoblasts
. Downregulation of Osteoprotegerin (OPG) expression directly by osteoclasts
. Direct stimulation of macrophage colony-stimulating factor (M-CSF) within osteoclasts
. Upregulation of RANK receptor expression directly on osteoblasts

Correct Answer & Explanation

. Upregulation of RANKL expression on osteoblasts

Explanation

Osteoclasts lack PTH receptors; PTH binds to osteoblasts, upregulating RANKL expression which then binds to RANK on osteoclast precursors to stimulate their differentiation and activation.

Question 12898

Topic: Biomechanics & Biomaterials

When applying a bridging plate to a highly comminuted diaphyseal fracture, how does decreasing the working length of the plate (placing the innermost screws closer to the fracture site) alter the biomechanics of the construct?

. It significantly increases the axial stiffness of the construct
. It decreases the torsional stiffness of the construct
. It increases the overall flexibility of the fixation
. It decreases the stress concentration at the innermost screw holes
. It promotes greater micromotion to stimulate secondary healing

Correct Answer & Explanation

. It significantly increases the axial stiffness of the construct

Explanation

Decreasing the working length of a plate concentrates stress over a shorter segment of the implant, substantially increasing the overall stiffness of the construct and reducing interfragmentary motion.

Question 12899

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection, biofilm formation is a critical factor in antibiotic resistance. Which of the following best describes the function of "quorum sensing" in this process?

. Initial adherence of planktonic bacteria to the host proteins on the implant
. Irreversible bacterial attachment mediated by fibronectin-binding proteins
. Intercellular bacterial communication regulating gene expression and biofilm maturation
. Active dispersion of individual bacteria from a mature biofilm into the bloodstream
. Evasion of host phagocytosis strictly through capsular polysaccharide production

Correct Answer & Explanation

. Intercellular bacterial communication regulating gene expression and biofilm maturation

Explanation

Quorum sensing is a chemical communication system used by bacteria to monitor population density, allowing them to coordinate gene expression essential for mature biofilm formation and virulence.

Question 12900

Topic: 1. General Principles & Basic Science
According to the Sunderland classification of peripheral nerve injuries, a Grade III injury is anatomically characterized by the specific disruption of which of the following structures?
. Myelin sheath only, with intact axons
. Axon only, with intact endoneurium
. Axon and endoneurium, with intact perineurium
. Axon, endoneurium, and perineurium, with intact epineurium
. Complete transection of all nerve components including epineurium

Correct Answer & Explanation

. Axon and endoneurium, with intact perineurium

Explanation

A Sunderland Grade III injury corresponds to a lesion that disrupts the axon and the endoneurium, while the perineurium and epineurium remain intact. Recovery is unpredictable.

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