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1. General Principles & Basic Science MCQs

Practice Set 600 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 11981

Topic: 1. General Principles & Basic Science

During the initiation of motion from a static standing position, which type of lubrication mechanism predominates in the articular cartilage of the human knee?

. Elastohydrodynamic lubrication
. Weeping lubrication
. Boundary lubrication
. Hydrodynamic lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Elastohydrodynamic lubrication

Explanation

Boundary lubrication predominates under high-load, low-speed conditions (e.g., initiating motion from a standing stop). It relies on molecules like lubricin (PRG4) attached to the articular surfaces to reduce friction. Elastohydrodynamic lubrication is a fluid-film mechanism that dominates during steady dynamic motion.

Question 11982

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) administration given as a continuous, high-dose infusion has which of the following primary cellular effects on bone?

. Direct binding to osteoclasts leading to increased resorption
. Binding to osteoblasts, leading to increased RANKL expression and subsequent osteoclast activation
. Direct inhibition of osteoblast apoptosis, leading to net bone formation
. Inhibition of 1-alpha-hydroxylase in the kidney, decreasing calcium absorption
. Binding to osteocytes, resulting in immediate down-regulation of sclerostin

Correct Answer & Explanation

. Direct binding to osteoclasts leading to increased resorption

Explanation

Continuous exposure to PTH results in a net catabolic effect on bone. PTH does not have receptors directly on osteoclasts. Instead, it binds to osteoblasts (and osteocytes), upregulating the expression of RANKL and downregulating Osteoprotegerin (OPG). The increased RANKL binds to RANK on osteoclast precursors, stimulating osteoclast differentiation and bone resorption.

Question 11983

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, which biochemical change is most characteristic of the maturing scar tissue?
. Replacement of Type I collagen with Type III collagen
. Replacement of Type III collagen with Type I collagen
. A profound increase in total glycosaminoglycan content
. Decreased cross-linking of collagen fibrils
. Conversion of predominantly Sharpey's fibers to pure elastin

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

During the early phases of ligament (and tendon) healing (inflammation and proliferation), fibroblasts produce a large amount of Type III collagen, which is disorganized and mechanically weak. During the remodeling phase, Type III collagen is gradually replaced by Type I collagen, and the collagen fibers align along lines of stress with increased cross-linking, resulting in increased tensile strength.

Question 11984

Topic: Infection, Pharmacology & VTE
Which of the following best describes the primary mechanism of action of rivaroxaban used for VTE prophylaxis following total joint arthroplasty?
. Direct, reversible inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III activation
. Direct, selective inhibition of Factor Xa
. Irreversible inhibition of ADP-induced platelet aggregation
. Inhibition of vitamin K epoxide reductase

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that act as direct, highly selective, reversible inhibitors of Factor Xa. Dabigatran is a direct thrombin (IIa) inhibitor. Low-molecular-weight heparin (LMWH) indirectly inhibits Factor Xa by binding to antithrombin III. Warfarin inhibits vitamin K epoxide reductase.

Question 11985

Topic: Infection, Pharmacology & VTE

Which phase of bacterial biofilm formation is characterized by the production of a dense extracellular polymeric substance (EPS) matrix and active quorum sensing?

. Initial reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic proliferation

Correct Answer & Explanation

. Initial reversible attachment

Explanation

Biofilm formation occurs in stages: 1) Initial reversible attachment. 2) Irreversible attachment (via adhesins). 3) Maturation, where bacteria multiply, produce a dense extracellular polymeric substance (EPS - 'glycocalyx'), and engage in cell-to-cell communication known as quorum sensing. 4) Dispersion/Detachment, where bacteria release planktonic cells to spread infection.

Question 11986

Topic: Biomechanics & Biomaterials

Which element is added to 316L stainless steel orthopedic implants to specifically reduce its susceptibility to pitting corrosion and crevice corrosion?

. Carbon
. Chromium
. Nickel
. Molybdenum
. Titanium

Correct Answer & Explanation

. Carbon

Explanation

The 'L' in 316L stainless steel stands for low carbon, preventing intergranular corrosion. Chromium provides the passivation (oxide) layer. Nickel stabilizes the austenitic crystal structure. Molybdenum (2-3%) is added specifically to significantly improve resistance to pitting and crevice corrosion in chloride-rich environments like the human body.

Question 11987

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) primarily relies on which of the following mechanisms to aid in bone formation?

. Osteogenesis
. Osteoconduction
. Osteoinduction
. Osteointegration
. Osteopromotion

Correct Answer & Explanation

. Osteogenesis

Explanation

Demineralized bone matrix (DBM) is created by acid-extracting the mineral phase of allograft bone, which exposes osteoinductive proteins, specifically Bone Morphogenetic Proteins (BMPs). Therefore, its primary mechanism is osteoinduction (stimulating host mesenchymal cells to differentiate into osteoblasts). It contains no living cells (not osteogenic) and lacks structural integrity (limited osteoconduction compared to cancellous bone).

Question 11988

Topic: 1. General Principles & Basic Science
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is routinely used in total hip arthroplasty to reduce wear. Which of the following material property changes occurs as a direct result of the high-dose irradiation used to create highly cross-linked UHMWPE?
. Increased yield strength
. Decreased ultimate tensile strength and fatigue resistance
. Increased ductility and elongation at break
. Decreased resistance to adhesive wear
. Increased resistance to third-body abrasive wear without altering fatigue limits

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue resistance

Explanation

Highly cross-linked PE is produced by exposing UHMWPE to high doses of gamma or electron-beam radiation (usually 50-100 kGy), which creates free radicals that recombine to form cross-links. While this profoundly increases wear resistance, it comes at a mechanical cost: it decreases ductility, yield strength, ultimate tensile strength, and fatigue crack propagation resistance.

Question 11989

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the microarchitectural orientation of collagen fibers varies by zone. Which zone is responsible for the majority of the tissue's resistance to shear forces, and what is its dominant collagen orientation?

. Superficial zone; parallel to the joint surface
. Transitional zone; random oblique orientation
. Deep zone; perpendicular to the subchondral bone
. Calcified zone; parallel to the subchondral bone
. Tidemark zone; perpendicular to the joint surface

Correct Answer & Explanation

. Superficial zone; parallel to the joint surface

Explanation

The superficial (tangential) zone makes up 10-20% of articular cartilage thickness. The Type II collagen fibers here are tightly packed and aligned parallel to the articular surface, which optimally resists the high shear stresses generated during joint motion.

Question 11990

Topic: 1. General Principles & Basic Science

A surgeon is evaluating screw designs to maximize pullout strength in osteoporotic cancellous bone. According to standard biomechanical principles, which of the following alterations to a cortical screw design will most significantly increase its pullout strength?

. Increasing the inner (core) diameter
. Decreasing the outer (thread) diameter
. Increasing the thread pitch
. Decreasing the thread pitch
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the inner (core) diameter

Explanation

Pullout strength is directly proportional to the outer thread diameter, the length of engagement, and the shear strength of the bone, while it is inversely proportional to thread pitch. Decreasing the thread pitch increases the number of threads engaged per unit length, thereby increasing the pullout strength. Increasing the inner core diameter increases bending strength but decreases thread depth, lowering pullout strength.

Question 11991

Topic: Physiology & Rehabilitation

A 28-year-old elite marathon runner undergoes a muscle biopsy for a physiology study. Compared to a sedentary individual, her lower extremity muscles are expected to show an increased proportion of Type I fibers. Which of the following best characterizes Type I skeletal muscle fibers?

. Fast twitch, anaerobic metabolism, rich in glycogen
. Slow twitch, oxidative metabolism, high mitochondrial density
. Fast twitch, oxidative metabolism, rapid fatigue rate
. Slow twitch, anaerobic metabolism, low myoglobin content
. Fast twitch, glycolytic metabolism, low capillary density

Correct Answer & Explanation

. Fast twitch, anaerobic metabolism, rich in glycogen

Explanation

Type I muscle fibers are 'slow-twitch' fibers. They rely on oxidative (aerobic) metabolism, have high mitochondrial density, high myoglobin content (giving them a red appearance), and are highly resistant to fatigue, making them essential for endurance activities like marathon running.

Question 11992

Topic: Biomechanics & Biomaterials

During tensile testing of a normal anterior cruciate ligament, a stress-strain curve is generated. The initial non-linear 'toe region' of the curve represents which of the following microstructural events?

. Yielding of collagen intermolecular cross-links
. Plastic deformation of the ligament substance
. Uncrimping of the resting Type I collagen fibrils
. Failure of intrafibrillar hydrogen bonds
. Macroscopic tearing of individual collagen bundles

Correct Answer & Explanation

. Yielding of collagen intermolecular cross-links

Explanation

Ligaments and tendons possess a crimped (wavy) collagen structure at rest. When tensile force is first applied, the 'toe region' of the stress-strain curve reflects the uncrimping of these Type I collagen fibrils. Once uncrimped, the curve enters the linear (elastic) region.

Question 11993

Topic: Biomechanics & Biomaterials

A surgeon incorrectly utilizes a 316L stainless steel plate with titanium alloy screws for internal fixation of a femur fracture. Which specific type of corrosion is most likely to be accelerated at the interface between these two distinct implant materials?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in physical contact within an electrolytic medium (like body fluid). The less noble metal acts as an anode and corrodes at an accelerated rate, while the more noble metal acts as a cathode.

Question 11994

Topic: Biomechanics & Biomaterials

Titanium alloys demonstrate excellent biocompatibility and high resistance to physiological corrosion. This characteristic is primarily dependent upon which of the following surface phenomena?

. High carbon content preventing sub-surface oxidation
. Spontaneous formation of a highly stable passivation layer of titanium dioxide
. Addition of nickel to stabilize the austenitic crystalline phase
. Complete absence of grain boundaries within the alpha-beta lattice
. Inherent antimicrobial properties of the titanium metal ions

Correct Answer & Explanation

. High carbon content preventing sub-surface oxidation

Explanation

Titanium and its alloys spontaneously form a thin, tenacious, and self-healing oxide layer (primarily TiO2) immediately upon exposure to oxygen or bodily fluids. This passivation layer protects the underlying bulk metal from chemical attack and provides excellent corrosion resistance and biocompatibility.

Question 11995

Topic: 1. General Principles & Basic Science

Under conditions of high physiological load and low relative surface speed, such as standing from a seated position, articular cartilage relies heavily on a specific lubrication mechanism governed by lubricin (PRG4). Which type of lubrication does this describe?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication
. Boosted lubrication

Correct Answer & Explanation

. Hydrodynamic lubrication

Explanation

Boundary lubrication is the dominant mechanism at high loads and low speeds, where a fluid film cannot be maintained and the cartilage surfaces come extremely close together. Lubricin (PRG4), a glycoprotein, binds to the articular surface to reduce friction and wear under these boundary conditions.

Question 11996

Topic: 1. General Principles & Basic Science

Aggrecan is the most abundant large aggregating proteoglycan in the extracellular matrix of articular cartilage. Its primary biomechanical function is best described by which of the following mechanisms?

. Providing immense tensile strength via covalent cross-linking
. Anchoring the superficial chondrocytes to the Type II collagen network
. Providing fixed negative charges that attract water to resist compressive loads
. Facilitating elastohydrodynamic lubrication at the fluid-cartilage interface
. Inhibiting the catabolic activity of matrix metalloproteinases

Correct Answer & Explanation

. Providing immense tensile strength via covalent cross-linking

Explanation

Aggrecan consists of a core protein with numerous covalently attached glycosaminoglycans (chondroitin sulfate and keratan sulfate). The sulfate groups provide a massive fixed negative charge density, which draws cations and water into the tissue (Donnan osmotic effect), creating swelling pressure that enables cartilage to resist compressive loads.

Question 11997

Topic: Surgical Anatomy & Approaches

A patient sustains a closed mid-shaft humerus fracture and subsequent radial nerve palsy. Electromyography at 4 weeks reveals fibrillation potentials in the extensor muscles. Theoretical microscopic evaluation shows Wallerian degeneration, but the endoneurial tubes remain intact. According to the Sunderland classification, what grade of nerve injury is this?

. First degree
. Second degree
. Third degree
. Fourth degree
. Fifth degree

Correct Answer & Explanation

. First degree

Explanation

Sunderland Second degree represents axonotmesis. The axon is disrupted (leading to Wallerian degeneration and EMG fibrillations), but the endoneurium is intact, providing an optimal tube for regeneration. First degree is neurapraxia (no Wallerian degeneration). Third degree involves endoneurium disruption; Fourth involves perineurium disruption; Fifth is complete nerve transection (neurotmesis).

Question 11998

Topic: 1. General Principles & Basic Science

Osteoclasts dissolve the inorganic mineral component of bone matrix by acidifying the isolated subosteoclastic microenvironment (Howship's lacuna). Which intracellular enzyme is primarily responsible for the generation of the hydrogen ions required for this process?

. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase-9 (MMP-9)
. Alkaline phosphatase

Correct Answer & Explanation

. Tartrate-resistant acid phosphatase (TRAP)

Explanation

Carbonic anhydrase II inside the osteoclast catalyzes the conversion of CO2 and H2O into carbonic acid, which dissociates into protons (H+) and bicarbonate. The H+ ions are then actively pumped into the ruffled border via V-ATPases to dissolve hydroxyapatite. TRAP and Cathepsin K are involved in degrading the organic matrix.

Question 11999

Topic: Biology, Genetics & Bone Healing

Sclerostin is a glycoprotein secreted primarily by osteocytes that acts as a potent negative regulator of bone formation. It achieves this effect primarily by binding to LRP5/6 coreceptors and inhibiting which of the following crucial intracellular signaling pathways?

. RANK/RANKL pathway
. TGF-beta signaling pathway
. Wnt/beta-catenin pathway
. Notch signaling pathway
. Hedgehog signaling pathway

Correct Answer & Explanation

. RANK/RANKL pathway

Explanation

Sclerostin antagonizes the canonical Wnt/beta-catenin signaling pathway by binding to LRP5/6 receptors on the osteoblast surface. This prevents Wnt ligands from binding, ultimately blocking beta-catenin translocation to the nucleus and leading to decreased osteoblast proliferation and bone formation. Romosozumab is a monoclonal antibody against sclerostin.

Question 12000

Topic: 1. General Principles & Basic Science

As the human intervertebral disc undergoes physiological aging and degeneration, distinct biochemical alterations occur within the nucleus pulposus. Which of the following profiles accurately describes the anticipated biochemical changes?

. Increase in total water content and a decrease in total proteoglycans
. Increase in the ratio of chondroitin sulfate to keratan sulfate
. Decrease in the ratio of chondroitin sulfate to keratan sulfate
. Decrease in the absolute concentration of Type I collagen
. Transformation of the inner anulus fibrosus to predominantly Type II collagen

Correct Answer & Explanation

. Increase in total water content and a decrease in total proteoglycans

Explanation

With aging, the nucleus pulposus undergoes a decrease in total water content and total proteoglycans. Furthermore, the ratio of chondroitin sulfate to keratan sulfate decreases (i.e., keratan sulfate increases relative to chondroitin sulfate). There is also a relative increase in Type I collagen as the disc becomes more fibrotic.

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