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1. General Principles & Basic Science MCQs

Practice Set 381 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 7601

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties, meaning their mechanical behavior is highly dependent on the rate of loading. Which of the following correctly describes the viscoelastic phenomenon of 'creep'?

. Progressive decrease in stress when the tissue is held at a constant length
. Progressive increase in length when the tissue is subjected to a constant force
. Higher tissue stiffness and ultimate load with faster rates of loading
. Energy lost as heat during a single loading and unloading cycle
. Ultimate failure of the tissue after repeated cyclical sub-maximal loading

Correct Answer & Explanation

. Progressive decrease in stress when the tissue is held at a constant length

Explanation

Creep is defined as the progressive deformation (increase in length or strain) of a viscoelastic material when it is subjected to a constant load (force or stress) over time. Stress relaxation is the progressive decrease in stress when held at a constant length. Hysteresis represents the energy lost during a loading-unloading cycle.

Question 7602

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., alendronate) are commonly prescribed for osteoporosis. They primarily inhibit osteoclast function and induce apoptosis by interfering with which of the following intracellular pathways?

. RANK-RANKL binding interaction
. Mevalonate pathway via inhibition of farnesyl pyrophosphate (FPP) synthase
. Wnt/beta-catenin signaling pathway
. Sclerostin production by osteocytes
. Osteoprotegerin (OPG) secretion by osteoblasts

Correct Answer & Explanation

. RANK-RANKL binding interaction

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents the prenylation (lipid modification) of small GTP-binding proteins (like Ras, Rho, and Rab) that are essential for osteoclast ruffled border formation, function, and survival, ultimately leading to osteoclast apoptosis. Denosumab inhibits RANK-RANKL binding.

Question 7603

Topic: 1. General Principles & Basic Science

According to the Seddon classification of peripheral nerve injuries, which of the following best describes an axonotmesis?

. Interruption of the myelin sheath with structurally intact axons and epineurium
. Disruption of the axon with structurally intact endoneurial tubes
. Disruption of both the axon and the endoneurium, with intact perineurium
. Complete physical transection of the nerve including the epineurium
. Transient physiologic conduction block without any structural damage

Correct Answer & Explanation

. Interruption of the myelin sheath with structurally intact axons and epineurium

Explanation

Seddon classified nerve injuries into three main categories: Neurapraxia (focal conduction block, myelin injury, intact axons), Axonotmesis (disruption of axons with intact supporting structures like the endoneurium, allowing for predictable Wallerian degeneration and subsequent regeneration), and Neurotmesis (complete structural disruption). Options C and D refer to degrees of neurotmesis (Sunderland III-V).

Question 7604

Topic: Infection, Pharmacology & VTE

A patient undergoing total knee arthroplasty receives rivaroxaban for deep vein thrombosis (DVT) prophylaxis. Rivaroxaban exerts its anticoagulant effect by directly inhibiting which of the following coagulation factors?

. Thrombin (Factor IIa)
. Factor Xa
. Antithrombin III
. Vitamin K epoxide reductase
. Plasminogen

Correct Answer & Explanation

. Thrombin (Factor IIa)

Explanation

Rivaroxaban, apixaban, and fondaparinux are Factor Xa inhibitors. Dabigatran directly inhibits thrombin (Factor IIa). Warfarin acts by inhibiting vitamin K epoxide reductase, affecting factors II, VII, IX, and X. Heparin acts by potentiating antithrombin III.

Question 7605

Topic: Biology, Genetics & Bone Healing

Primary (direct) bone healing relies on absolute stability and occurs without radiographically visible callus formation. Which of the following histologic features is characteristic of primary bone healing?

. Formation of a soft fibrocartilaginous callus
. Chondrocyte hypertrophy and apoptosis
. Formation of cutting cones crossing the fracture gap
. Endochondral ossification
. Deposition of woven bone in a high-strain environment

Correct Answer & Explanation

. Formation of a soft fibrocartilaginous callus

Explanation

Primary (direct) bone healing occurs via Haversian remodeling. This requires absolute stability and direct bone-to-bone contact. Osteoclasts at the leading edge of a 'cutting cone' tunnel across the fracture line, followed immediately by osteoblasts that lay down new lamellar bone, directly bridging the gap. There is no intermediate cartilaginous phase or visible callus.

Question 7606

Topic: 1. General Principles & Basic Science

Articular cartilage is highly specialized for load-bearing and friction reduction in synovial joints. Which of the following is the predominant collagen type found in the extracellular matrix of normal hyaline articular cartilage?

. Type I
. Type II
. Type III
. Type X
. Type XI

Correct Answer & Explanation

. Type I

Explanation

Type II collagen accounts for 90-95% of the collagen in normal articular cartilage, providing the tissue with its tensile strength. Type I collagen is the predominant structural collagen in bone, tendon, meniscus, and fibrocartilage. Type X collagen is uniquely found in hypertrophic cartilage and the calcified zone of articular cartilage.

Question 7607

Topic: Biomechanics & Biomaterials

In modern total hip arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is frequently utilized. The process of cross-linking is performed primarily to achieve which of the following mechanical outcomes?

. Increase oxidative resistance over time
. Increase the yield strength and fracture toughness
. Decrease adhesive and abrasive wear rates
. Decrease the elastic modulus to match cortical bone
. Enhance osteointegration and biological fixation

Correct Answer & Explanation

. Increase oxidative resistance over time

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured via gamma or electron beam irradiation to create cross-links between polymer chains. This significantly decreases adhesive and abrasive wear rates, thus reducing the risk of osteolysis. However, cross-linking generates free radicals, which can lead to oxidation if not mitigated (via remelting or adding antioxidants like Vitamin E). Cross-linking also slightly reduces yield strength and fatigue resistance.

Question 7608

Topic: Biology, Genetics & Bone Healing

Which of the following genetic mutations is most likely to cause infantile malignant osteopetrosis due to the inability of osteoclasts to acidify the Howship lacuna?

. TCIRG1
. COL1A1
. FGFR3
. RUNX2
. SOX9

Correct Answer & Explanation

. TCIRG1

Explanation

Osteopetrosis is caused by defective osteoclast function resulting in failure of bone resorption. The most common autosomal recessive form (infantile malignant) is primarily due to a mutation in the TCIRG1 gene, which encodes the a3 subunit of the vacuolar H+-ATPase (V-ATPase) pump. This pump is essential for secreting hydrogen ions to acidify the resorption pit (Howship lacuna). COL1A1 mutations cause osteogenesis imperfecta. FGFR3 mutations lead to achondroplasia. RUNX2 mutations are associated with cleidocranial dysplasia. SOX9 mutations result in campomelic dysplasia.

Question 7609

Topic: Biomechanics & Biomaterials

When coupling a titanium alloy femoral stem with a cobalt-chromium modular head in a total hip arthroplasty, which of the following best describes the predominant type of corrosion that occurs at the head-neck trunnion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

The predominant form of corrosion at the modular head-neck junction (trunnion) of a total hip arthroplasty is mechanically assisted crevice corrosion, commonly referred to as fretting corrosion. Although galvanic corrosion is theoretically possible due to the mixed-metal couple (titanium and cobalt-chromium), the stable passivating oxide layers on both metals largely prevent it. Micro-motion at the interface leads to mechanical disruption of this protective oxide layer (fretting), exposing the underlying metal to the fluid environment and initiating the localized corrosive process.

Question 7610

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the joint surface?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface. It is also characterized by the highest concentration of proteoglycans and the lowest water content, allowing it to provide the greatest resistance to compressive loads. The superficial zone has collagen parallel to the joint surface, the highest water content, and the lowest proteoglycan concentration.

Question 7611

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) effectively reduces perioperative blood loss in total joint arthroplasty. What is the primary molecular mechanism of action of this agent?

. Directly inhibiting thrombin activity
. Activating Factor Xa
. Binding to plasminogen to inhibit fibrinolysis
. Stimulating von Willebrand factor release from endothelial cells
. Enhancing platelet aggregation and degranulation

Correct Answer & Explanation

. Directly inhibiting thrombin activity

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It acts as a competitive antagonist of plasminogen. By reversibly binding to the lysine receptor sites on plasminogen molecules, TXA prevents plasminogen from binding to fibrin, thereby inhibiting its activation to plasmin. This effectively halts the degradation of fibrin clots (fibrinolysis), stabilizing the clot and reducing blood loss.

Question 7612

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key regulatory glycoprotein produced primarily by mature osteocytes. It reduces bone formation by antagonizing which of the following intracellular signaling pathways?

. BMP / Smad pathway
. Wnt / β-catenin pathway
. RANK / RANKL pathway
. Notch / Hes pathway
. Hedgehog / Gli pathway

Correct Answer & Explanation

. BMP / Smad pathway

Explanation

Sclerostin, encoded by the SOST gene, is a potent inhibitor of bone formation. It functions by binding to the LRP5/6 coreceptors on the surface of osteoblasts, which competitively inhibits the binding of Wnt ligands. This prevents the activation of the canonical Wnt/β-catenin signaling pathway, leading to decreased osteoblast proliferation and function. Monoclonal antibodies targeting sclerostin, such as romosozumab, are utilized to treat severe osteoporosis.

Question 7613

Topic: 1. General Principles & Basic Science

A patient sustained a severe traction injury to the brachial plexus. Electrodiagnostic studies suggest a 4th-degree nerve injury according to the Sunderland classification. This implies complete structural disruption of the axon and which of the following combinations of connective tissue sheaths?

. Myelin sheath only (axon remains intact)
. Myelin sheath and endoneurium only
. Myelin sheath, endoneurium, and epineurium only
. Myelin sheath, endoneurium, and perineurium (epineurium intact)
. Myelin sheath, endoneurium, perineurium, and epineurium

Correct Answer & Explanation

. Myelin sheath only (axon remains intact)

Explanation

The Sunderland classification describes 5 degrees of nerve injury. A 1st-degree injury (neuropraxia) involves local myelin disruption but intact axons. A 2nd-degree injury (axonotmesis) involves axonal disruption with intact endoneurium. A 3rd-degree injury involves disruption of the axon and endoneurium, with an intact perineurium. A 4th-degree injury involves disruption of the axon, endoneurium, and perineurium, leaving only the epineurium intact. A 5th-degree injury (neurotmesis) is a complete nerve transection.

Question 7614

Topic: Infection, Pharmacology & VTE

Rifampin is frequently included in combination antibiotic regimens for periprosthetic joint infections due to its exceptional ability to penetrate bacterial biofilms. What is the precise mechanism of action of rifampin?

. Inhibition of DNA gyrase and topoisomerase IV
. Inhibition of peptidoglycan chain cross-linking
. Binding to the 30S ribosomal subunit to disrupt mRNA translation
. Binding to the 50S ribosomal subunit to prevent peptide bond formation
. Inhibition of DNA-dependent RNA polymerase

Correct Answer & Explanation

. Inhibition of DNA gyrase and topoisomerase IV

Explanation

Rifampin is a bactericidal antibiotic that binds strongly to the β-subunit of bacterial DNA-dependent RNA polymerase. This prevents the initiation of RNA synthesis (transcription), leading to cell death. It is highly effective against slow-growing and stationary-phase staphylococci residing within biofilms, making it an essential adjunctive therapy for retained infected orthopedic hardware.

Question 7615

Topic: Physiology & Rehabilitation

Skeletal muscle fibers are broadly classified based on their metabolic properties and contractile speeds. Compared to Type IIb fibers, Type I muscle fibers are characterized by which of the following?

. Higher concentration of glycogen stores
. Faster rate of contraction and relaxation
. Higher susceptibility to fatigue
. Metabolism is predominantly oxidative
. Rely primarily on anaerobic glycolysis

Correct Answer & Explanation

. Higher concentration of glycogen stores

Explanation

Type I muscle fibers (slow-twitch) are specialized for endurance and continuous, low-intensity contraction. They have a rich capillary supply, high myoglobin content, and a high density of mitochondria, allowing them to rely predominantly on oxidative (aerobic) metabolism. They are highly fatigue-resistant. In contrast, Type IIb fibers (fast-twitch) are optimized for short, powerful bursts. They have high glycogen content, fewer mitochondria, rely heavily on anaerobic glycolysis, and fatigue rapidly.

Question 7616

Topic: 1. General Principles & Basic Science

A researcher evaluates a histological section of normal human articular cartilage under a polarized light microscope. In the superficial (tangential) zone, which of the following best describes the orientation of the collagen fibers and the primary type of collagen present?

. Parallel to the joint surface; Type I collagen
. Parallel to the joint surface; Type II collagen
. Perpendicular to the joint surface; Type I collagen
. Perpendicular to the joint surface; Type II collagen
. Randomly oriented; Type II collagen

Correct Answer & Explanation

. Parallel to the joint surface; Type I collagen

Explanation

The superficial (tangential) zone of articular cartilage consists of flattened chondrocytes and collagen fibers that are oriented parallel to the joint surface to effectively resist shear forces. Hyaline articular cartilage is primarily composed of Type II collagen. In contrast, the deep zone contains collagen fibers that are oriented perpendicular to the subchondral bone to resist compressive loads.

Question 7617

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is selecting an intramedullary nail for a highly comminuted tibial shaft fracture. When reviewing the mechanical properties of the available titanium and stainless steel implants, which of the following material properties most closely defines the stiffness of the implant, represented by the slope of the elastic region on a stress-strain curve?

. Yield point
. Ultimate tensile strength
. Young's modulus
. Fatigue limit
. Toughness

Correct Answer & Explanation

. Yield point

Explanation

Young's modulus (modulus of elasticity) represents the intrinsic stiffness of a material. On a stress-strain curve, it is defined as the slope of the linear, elastic portion of the curve. The yield point is the point at which plastic (irreversible) deformation begins. Ultimate tensile strength is the maximum stress a material can withstand, and toughness is defined by the total area under the stress-strain curve, representing the energy absorbed before failure.

Question 7618

Topic: Biology, Genetics & Bone Healing

A 65-year-old postmenopausal woman with severe osteoporosis is treated with denosumab to reduce her fracture risk. Which of the following describes the precise mechanism of action of this medication in modulating bone metabolism?

. It binds directly to the RANK receptor on osteoclasts, inhibiting their activation.
. It acts as an endogenous decoy receptor for RANKL, similar in structure to osteoprotegerin.
. It binds to RANKL, preventing its subsequent interaction with the RANK receptor.
. It inhibits the enzyme cathepsin K, reducing the breakdown of type I collagen.
. It directly stimulates the Wnt/beta-catenin signaling pathway in osteoblasts.

Correct Answer & Explanation

. It binds directly to the RANK receptor on osteoclasts, inhibiting their activation.

Explanation

Denosumab is a fully human monoclonal antibody that specifically targets and binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding to RANKL, denosumab prevents it from interacting with the RANK receptor on the surface of osteoclasts and their precursors. This effectively inhibits osteoclast formation, function, and survival, leading to decreased bone resorption. Osteoprotegerin (OPG) is the body's natural decoy receptor for RANKL, but denosumab itself is an antibody, not a decoy receptor.

Question 7619

Topic: Biology, Genetics & Bone Healing

During embryonic development of the upper extremity, a genetic mutation results in dysfunction of the Zone of Polarizing Activity (ZPA). Which of the following developmental abnormalities is most likely to be observed in the developing fetus?

. Proximal-distal limb truncation (e.g., amelia)
. Anteroposterior axis defects (e.g., polydactyly)
. Dorsal-ventral axis defects (e.g., absent nails)
. Failure of normal joint cavitation
. Defective intramembranous ossification of the clavicle

Correct Answer & Explanation

. Proximal-distal limb truncation (e.g., amelia)

Explanation

The Zone of Polarizing Activity (ZPA) is a cluster of cells located at the posterior margin of the developing limb bud. It regulates the anteroposterior (radioulnar) patterning of the limb primarily via the expression of Sonic Hedgehog (SHH). Mutations affecting the ZPA or the SHH pathway typically result in radioulnar defects, such as preaxial or postaxial polydactyly, or mirror-image digits. Proximal-distal growth is regulated by the Apical Ectodermal Ridge (AER) via Fibroblast Growth Factors (FGFs), and dorsal-ventral patterning is regulated by the dorsal ectoderm via Wnt-7a.

Question 7620

Topic: Biomechanics & Biomaterials

A 45-year-old man undergoes a revision of a total hip arthroplasty due to an adverse local tissue reaction (ALTR). Intraoperative evaluation of the retrieved modular femoral head-neck taper junction reveals significant material degradation. This degradation is attributed to an electrochemical process exacerbated by repetitive mechanical micromotion. Which of the following best describes this phenomenon?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion (also known as mechanically assisted crevice corrosion) occurs at the contact interface of two modular components (such as a femoral head-neck taper) subjected to load. Repetitive micromotion mechanically disrupts the protective oxide (passivation) layer of the metal, allowing an accelerated electrochemical corrosion process to occur. Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic solution, but the primary driver of taper failure in modern modular hips is fretting corrosion.

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