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1. General Principles & Basic Science MCQs

Practice Set 597 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 11921

Topic: 1. General Principles & Basic Science

Normal synovial fluid serves as an excellent joint lubricant due to its unique rheological properties, which adapt to different loading rates. How does the viscosity of healthy synovial fluid change as the shear rate (e.g., speed of joint movement) increases?

. Viscosity increases (shear-thickening behavior)
. Viscosity decreases (shear-thinning behavior)
. Viscosity remains constant (Newtonian fluid behavior)
. Viscosity initially increases then abruptly drops to zero
. Viscosity behaves purely elastically with no measureable viscous component

Correct Answer & Explanation

. Viscosity increases (shear-thickening behavior)

Explanation

Synovial fluid is a non-Newtonian, thixotropic (shear-thinning) fluid. This means its viscosity is inversely proportional to the shear rate. At rest or during slow movement (low shear rate), the hyaluronic acid molecules entangle, making the fluid highly viscous. During rapid joint movement (high shear rate), the molecules align in the direction of flow, significantly decreasing the fluid's viscosity to reduce joint friction.

Question 11922

Topic: Infection, Pharmacology & VTE
Direct oral anticoagulants (DOACs) such as apixaban and rivaroxaban are frequently utilized for deep vein thrombosis prophylaxis following total joint arthroplasty. What is their specific target in the coagulation cascade?
. Direct inhibition of Thrombin (Factor IIa)
. Direct, reversible inhibition of Factor Xa
. Irreversible binding to Antithrombin III
. Inhibition of the Vitamin K epoxide reductase complex
. Inhibition of the platelet ADP receptor (P2Y12)

Correct Answer & Explanation

. Direct, reversible inhibition of Factor Xa

Explanation

Apixaban and rivaroxaban are highly selective, direct, and reversible inhibitors of Factor Xa, halting the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Heparin works by binding and activating Antithrombin III. Clopidogrel acts on the P2Y12 ADP receptor on platelets.

Question 11923

Topic: 1. General Principles & Basic Science
When evaluating the biomechanical holding power of a cortical bone screw, the pull-out strength is directly and linearly proportional to which of the following screw parameters?
. Core diameter of the screw
. Outer (thread) diameter of the screw
. Pitch of the threads
. Length of the screw head
. Distance between the threads

Correct Answer & Explanation

. Outer (thread) diameter of the screw

Explanation

The pull-out strength of a bone screw is directly proportional to the outer (thread) diameter, the length of engagement in the bone, and the shear strength of the bone material itself (Pullout strength ~ Outer Diameter × Length of engagement × Shear strength of bone). The core diameter primarily determines the screw's resistance to breaking (bending and torsional strength), not its pull-out strength.

Question 11924

Topic: 1. General Principles & Basic Science

Which specific modification to a cortical screw's design most significantly increases its pullout strength from bone?

. Increasing the inner (core) diameter
. Increasing the outer (thread) diameter
. Decreasing the thread pitch
. Decreasing the insertion torque
. Adding a cannulation to the screw

Correct Answer & Explanation

. Increasing the inner (core) diameter

Explanation

Pullout strength is most heavily influenced by the outer diameter of the screw. Increasing the outer diameter increases the volume of bone caught between the threads, thereby maximizing purchase.

Question 11925

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the management of osteoporosis and giant cell tumors of bone. What is its exact cellular mechanism of action?

. Binds directly to the RANK receptor on osteoclasts
. Binds to RANKL, preventing its interaction with the RANK receptor
. Directly inhibits the proton pumps on the osteoclast ruffled border
. Stimulates Osteoprotegerin (OPG) production by mature osteoblasts
. Inhibits the Wnt/beta-catenin signaling pathway in osteoprogenitors

Correct Answer & Explanation

. Binds directly to the RANK receptor on osteoclasts

Explanation

Denosumab is a monoclonal antibody that acts as a decoy receptor, binding directly to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclasts, thus inhibiting their activation and survival.

Question 11926

Topic: 1. General Principles & Basic Science

In articular cartilage, which structural zone contains the highest concentration of water and has collagen fibers oriented parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. The tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial tangential zone has the highest water content (about 80%) and a high concentration of collagen fibers oriented parallel to the joint surface to resist shear forces. The deep zone has the lowest water content and perpendicular fibers.

Question 11927

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, intracellular calcium release from the sarcoplasmic reticulum binds to which specific molecule to initiate the exposure of myosin-binding sites on actin?

. Tropomyosin
. Troponin C
. Troponin I
. Troponin T
. Calmodulin

Correct Answer & Explanation

. Tropomyosin

Explanation

Calcium ions bind to Troponin C on the thin actin filaments. This causes a conformational change that moves tropomyosin out of the way, exposing the binding sites for the myosin heads.

Question 11928

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is heavily utilized in anterior lumbar interbody fusions. BMPs belong to which larger superfamily of growth factors?

. Insulin-like growth factors (IGF)
. Transforming growth factor-beta (TGF-beta) superfamily
. Fibroblast growth factors (FGF)
. Platelet-derived growth factors (PDGF)
. Vascular endothelial growth factors (VEGF)

Correct Answer & Explanation

. Insulin-like growth factors (IGF)

Explanation

Bone Morphogenetic Proteins (BMPs) are part of the TGF-beta superfamily of signaling molecules. They induce osteoblastic differentiation from mesenchymal stem cells through the Smad intracellular signaling pathway.

Question 11929

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which of the following tissues can tolerate the highest amount of interfragmentary strain before mechanical failure?

. Primary lamellar bone
. Woven bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Primary lamellar bone

Explanation

Granulation tissue can tolerate up to 100% strain before tearing. As the fracture stabilizes and strain decreases, the tissue transitions to fibrocartilage (tolerates 10-15% strain), woven bone (tolerates up to 2% strain), and finally lamellar bone.

Question 11930

Topic: Biomechanics & Biomaterials

Which of the following clinical scenarios poses the highest theoretical risk for galvanic corrosion in orthopedic implants?

. Implanting a stainless steel screw through a titanium plate
. Using a highly cross-linked polyethylene liner with a cobalt-chrome head
. Fretting of a titanium screw in a titanium locking plate
. Implanting an alumina ceramic head on a titanium trunnion
. Utilizing two stainless steel components of the exact same alloy

Correct Answer & Explanation

. Implanting a stainless steel screw through a titanium plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic fluid medium. Mixing stainless steel and titanium implants generates an electrochemical potential difference, leading to accelerated corrosion of the less noble metal.

Question 11931

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely used to reduce perioperative blood loss in orthopedic surgery. Which of the following accurately describes its pharmacological mechanism?

. Direct inhibition of activated Factor X (Factor Xa)
. Competitive inhibition of plasminogen activation
. Direct activation of the extrinsic coagulation cascade
. Increasing von Willebrand factor release from the endothelium
. Irreversible inhibition of cyclooxygenase-1 (COX-1)

Correct Answer & Explanation

. Direct inhibition of activated Factor X (Factor Xa)

Explanation

Tranexamic acid is a synthetic lysine analog. It binds competitively to the lysine-binding sites on plasminogen, preventing its activation into plasmin and thereby stabilizing the fibrin clot against fibrinolysis.

Question 11932

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a third-degree nerve injury involves complete disruption of the axon and which other neural structure?

. Epineurium
. Endoneurium
. Myelin sheath exclusively
. Perineurium
. Schwann cell basement membrane only

Correct Answer & Explanation

. Epineurium

Explanation

A Sunderland third-degree injury involves disruption of both the axon and the surrounding endoneurium, but the perineurium and epineurium remain intact. This injury creates internal scarring that impairs spontaneous axonal regeneration, often requiring surgical intervention.

Question 11933

Topic: Biology, Genetics & Bone Healing

In the microscopic anatomy of mature cortical bone, what is the primary structural function of the Volkmann canals?

. They contain the primary ossification center during development
. They connect adjacent Haversian systems perpendicularly to the long axis of the bone
. They house resting osteoprogenitor cells exclusively in the endosteum
. They provide the central longitudinal axis for the osteon
. They store large aggregations of unmineralized osteoid

Correct Answer & Explanation

. They contain the primary ossification center during development

Explanation

Volkmann canals transmit blood vessels laterally from the periosteum into the bone, connecting the longitudinally oriented Haversian canals. This creates an interconnected vascular network throughout the dense cortical bone.

Question 11934

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic behavior. The biomechanical phenomenon where tissue deformation steadily increases over time while subjected to a constant, continuous load is defined as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic elasticity

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the time-dependent continuous deformation of a viscoelastic material under a constant load. Conversely, stress relaxation is the decrease in required stress over time to maintain a constant deformation.

Question 11935

Topic: 1. General Principles & Basic Science

Boundary lubrication in articular cartilage is most critical at high loads and low sliding speeds. Which molecule is the primary mediator of this boundary lubrication mechanism?

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

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Lubricin, also known as Proteoglycan 4 (PRG4), is a glycoprotein secreted by superficial zone chondrocytes and synoviocytes. It binds to the articular surface, preventing direct cartilage-to-cartilage contact and mediating boundary lubrication.

Question 11936

Topic: 1. General Principles & Basic Science

A 65-year-old female presents with diffuse skeletal pain. Radiographs reveal bilateral Looser zones (pseudofractures) in the femoral necks. Labs show hypocalcemia, hypophosphatemia, and elevated alkaline phosphatase. What is the defining histological feature of this condition?

. Defective mineralization of newly formed osteoid
. Excessive uncoupled osteoclastic bone resorption
. Deficient Type I collagen synthesis by osteoblasts
. A missense mutation in the COL1A1 gene
. Premature closure of the physes due to impaired endochondral ossification

Correct Answer & Explanation

. Defective mineralization of newly formed osteoid

Explanation

The patient has osteomalacia, commonly caused by severe Vitamin D deficiency. The hallmark histological finding in osteomalacia is an accumulation of widened, unmineralized osteoid seams due to a failure to precipitate calcium hydroxyapatite.

Question 11937

Topic: Biomechanics & Biomaterials

To minimize stress shielding around a diaphysis, an orthopedic implant should have a modulus of elasticity closely matching that of cortical bone. Among standard solid metals, which of the following is closest?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Zirconium oxide (Ceramic)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Titanium alloy has a modulus of elasticity around 110 GPa, which is roughly half that of CoCr (210 GPa) or stainless steel (190 GPa). Although still stiffer than cortical bone (15-20 GPa), titanium is the closest among standard solid metallic structural implants, reducing stress shielding.

Question 11938

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, Staphylococcus epidermidis evades the host immune system and antibiotic therapy by forming a robust biofilm. Which specific substance constitutes the primary structural backbone of this biofilm?

. Polysaccharide intercellular adhesin (PIA)
. Peptidoglycan
. Lipopolysaccharide (LPS)
. Teichoic acid
. Hyaluronic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), is the main exopolysaccharide secreted by S. epidermidis. It forms the slimy extracellular polymeric matrix that cements the biofilm to the implant surface.

Question 11939

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. What is its precise mechanism of action in the coagulation cascade?
. Direct thrombin (Factor IIa) inhibitor
. Indirect Factor Xa inhibitor via potentiation of antithrombin III
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase inhibitor
. Adenosine diphosphate (ADP) receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and Apixaban are Direct Oral Anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. Unlike low-molecular-weight heparins, they do not require antithrombin III to exert their effect.

Question 11940

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed denosumab for osteoporosis. This medication primarily acts by binding to which of the following, thereby mimicking the natural function of osteoprotegerin (OPG)?

. RANK
. RANKL
. M-CSF
. Cathepsin K
. Alpha-v beta-3 integrin

Correct Answer & Explanation

. RANK

Explanation

Denosumab is a monoclonal antibody that binds directly to RANKL, preventing it from interacting with RANK on osteoclasts. This mimics the action of OPG, thereby inhibiting osteoclast activation and bone resorption.

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