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1. General Principles & Basic Science MCQs

Practice Set 402 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 8021

Topic: Biomechanics & Biomaterials

A surgeon performs an open reduction and internal fixation of a diaphyseal fracture using a titanium alloy (Ti-6Al-4V) plate and secures it with 316L stainless steel screws. The physiologic environment surrounding this mixed-metal construct will most likely predispose it to which of the following phenomena?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Intergranular corrosion
. Passivation

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive electrolytic solution (like bodily fluids). The less noble metal (anode) will corrode more rapidly, while the more noble metal (cathode) remains protected. In a titanium-stainless steel construct, stainless steel acts as the anode and corrodes, while titanium acts as the cathode. Thus, mixing these specific metals is generally avoided in orthopedic surgery.

Question 8022

Topic: Surgical Anatomy & Approaches

Following a traumatic transection of the radial nerve, the distal nerve segment undergoes Wallerian degeneration. Which of the following cells are primarily responsible for the rapid phagocytosis and clearance of myelin debris in the peripheral nervous system, thereby creating a permissible environment for axonal regeneration?

. Astrocytes and microglia
. Oligodendrocytes and neutrophils
. Schwann cells and macrophages
. Ependymal cells and fibroblasts
. Perineurial cells and lymphocytes

Correct Answer & Explanation

. Schwann cells and macrophages

Explanation

In the peripheral nervous system (PNS), Wallerian degeneration involves the breakdown of the axon and its myelin sheath distal to the injury. Schwann cells dedifferentiate, proliferate, and work alongside recruited blood-borne macrophages to rapidly phagocytose and clear the myelin debris. This clearance is crucial because myelin debris contains inhibitory factors for axon growth. In the central nervous system (CNS), oligodendrocytes and microglia clear debris much more slowly, which contributes to the poor regenerative capacity of the CNS.

Question 8023

Topic: Biomechanics & Biomaterials

Biomechanical compatibility between orthopedic implants and native bone is essential to prevent stress shielding. Which of the following lists correctly orders orthopedic materials from the lowest modulus of elasticity (most flexible) to the highest modulus of elasticity (stiffest)?

. Cortical bone, Titanium alloy, Stainless steel, Cobalt-chromium alloy
. Titanium alloy, Cortical bone, Stainless steel, Cobalt-chromium alloy
. Cortical bone, Stainless steel, Titanium alloy, Cobalt-chromium alloy
. Cancellous bone, Cobalt-chromium alloy, Titanium alloy, Cortical bone
. Titanium alloy, Cortical bone, Cobalt-chromium alloy, Stainless steel

Correct Answer & Explanation

. Cortical bone, Stainless steel, Titanium alloy, Cobalt-chromium alloy

Explanation

The modulus of elasticity (Young's modulus) represents the stiffness of a material. To minimize stress shielding, implant materials ideally should have a modulus closer to that of bone. Cortical bone has a modulus of approximately 15-20 GPa. Titanium alloy (Ti-6Al-4V) is approximately 110 GPa. Stainless steel (316L) is approximately 200 GPa. Cobalt-chromium alloys are the stiffest, with a modulus around 220-240 GPa. Thus, the correct order from lowest to highest stiffness is Cortical bone < Titanium alloy < Stainless steel < Cobalt-chromium alloy.

Question 8024

Topic: 1. General Principles & Basic Science

During the active phase of bone remodeling, an osteoclast attaches to the bone surface and creates an isolated, acidic microenvironment known as Howship's lacuna. While the acidic pH dissolves the inorganic mineral, which of the following enzymes is primarily secreted to degrade the organic Type I collagen matrix?

. Alkaline phosphatase
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase (TRAP)
. Cathepsin K
. Matrix metalloproteinase-13 (MMP-13)

Correct Answer & Explanation

. Cathepsin K

Explanation

Bone resorption by osteoclasts is a biphasic process. First, the inorganic hydroxyapatite is dissolved by hydrochloric acid, which is produced intracellularly by carbonic anhydrase II and actively pumped into the ruffled border cleft via a vacuolar H+-ATPase. Following demineralization, the organic matrix (predominantly Type I collagen) is degraded by proteolytic enzymes. Cathepsin K, a highly specific lysosomal cysteine protease secreted by the osteoclast, is the primary enzyme responsible for this organic matrix degradation. TRAP is a marker of osteoclast activity but not the primary collagenase.

Question 8025

Topic: Physiology & Rehabilitation

The excitation-contraction coupling of skeletal muscle relies heavily on calcium handling. Upon an action potential traveling down the T-tubule, calcium is released from the sarcoplasmic reticulum. What is the immediate direct effect of this intracellular calcium release?

. It binds to tropomyosin, detaching it from the myosin head.
. It binds to troponin C, causing a conformational change that moves tropomyosin to expose the actin binding sites.
. It binds to the myosin head, providing the energy required for the power stroke.
. It alters the helical structure of actin directly, allowing it to accept ATP.
. It binds to troponin I, inhibiting the ATPase activity of myosin.

Correct Answer & Explanation

. It binds to troponin C, causing a conformational change that moves tropomyosin to expose the actin binding sites.

Explanation

According to the sliding filament theory, an action potential triggers calcium release from the sarcoplasmic reticulum. This calcium binds to troponin C, which undergoes a conformational change. This movement pulls tropomyosin away from the myosin-binding sites on the actin filament. Once these sites are exposed, the energized myosin heads can bind to actin to form cross-bridges, leading to the power stroke and muscle contraction.

Question 8026

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue responsible for minimizing friction and distributing loads across joints. Which of the following zones of articular cartilage contains the highest concentration of water and the lowest concentration of proteoglycans?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage is the thinnest layer but contains the highest water content (approximately 80%) and the lowest concentration of proteoglycans. The collagen fibers (primarily Type II) are aligned parallel to the joint surface to resist shear forces. The deep zone, in contrast, has the lowest water content, highest proteoglycan content, and collagen fibers aligned perpendicular to the joint surface to resist compressive loads.

Question 8027

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of an orthopedic implant, the stress-strain curve provides essential data.

Which of the following points on the curve represents the maximum stress a material can withstand before it begins to neck and ultimately fail?

. Yield point
. Proportional limit
. Ultimate tensile strength
. Failure point
. Endurance limit

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The Ultimate Tensile Strength (UTS) is the peak point on the stress-strain curve and represents the maximum stress a material can withstand before failure. After this point, the material begins to 'neck' (in ductile materials) and stress decreases until the failure point is reached. The yield point is the point at which elastic deformation transitions to plastic (irreversible) deformation.

Question 8028

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, various growth factors are expressed to orchestrate cellular differentiation and matrix synthesis. Which of the following growth factors is powerfully osteoinductive, signals predominantly through serine/threonine kinase receptors, and activates intracellular Smad proteins?

. Bone morphogenetic protein 2 (BMP-2)
. Platelet-derived growth factor (PDGF)
. Insulin-like growth factor 1 (IGF-1)
. Vascular endothelial growth factor (VEGF)
. Fibroblast growth factor 2 (FGF-2)

Correct Answer & Explanation

. Bone morphogenetic protein 2 (BMP-2)

Explanation

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, are potent osteoinductive growth factors of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate and activate intracellular Smad proteins (e.g., Smad 1, 5, 8). These activated Smads form a complex with Smad 4, translocate to the nucleus, and upregulate the transcription of osteogenic genes such as Runx2.

Question 8029

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological agent used in the management of osteoporosis and giant cell tumor of bone. Which of the following describes the exact mechanism of action of this medication?

. It binds directly to the RANK receptor on osteoclasts to induce apoptosis.
. It is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor.
. It acts as a synthetic analog of osteoprotegerin (OPG) by binding to the osteoclast ruffled border.
. It inhibits cathepsin K, preventing the degradation of Type I collagen.
. It inhibits the Wnt signaling pathway by antagonizing sclerostin.

Correct Answer & Explanation

. It is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor.

Explanation

Denosumab is a fully human monoclonal antibody (IgG2) that targets and binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). RANKL is typically expressed by osteoblasts and stromal cells. By binding to RANKL, denosumab prevents the interaction between RANKL and the RANK receptor on the surface of osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival, thereby reducing bone resorption. It effectively mimics the physiological role of osteoprotegerin (OPG).

Question 8030

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the wear properties of ultra-high-molecular-weight polyethylene (UHMWPE) are critical to long-term implant survival. Which of the following processing techniques optimizes wear resistance while minimizing the risk of oxidative degradation?
. Gamma irradiation in an oxygen-rich environment
. Ethylene oxide sterilization followed by natural aging
. Gamma irradiation in an inert gas environment followed by remelting
. Non-irradiated UHMWPE sterilized with hydrogen peroxide plasma
. Autoclave sterilization at 120°C

Correct Answer & Explanation

. Gamma irradiation in an inert gas environment followed by remelting

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by subjecting UHMWPE to gamma or electron beam irradiation, which creates free radicals that form cross-links between polymer chains. This significantly improves wear resistance. However, residual free radicals can react with oxygen over time, leading to oxidative degradation and embrittlement. To prevent this, the irradiated polyethylene undergoes a thermal treatment—either remelting (heating above the melting point) or annealing (heating just below the melting point)—often in an inert gas environment or vacuum, to quench the residual free radicals.

Question 8031

Topic: Biomechanics & Biomaterials

During the clinical examination of a patient with a chronic knee flexion contracture, dynamic splinting is applied to provide a constant, low-load stretch to the posterior soft tissues. Over time, the contracted ligaments and capsule gradually elongate. Which of the following viscoelastic properties does this process demonstrate?

. Stress relaxation
. Creep
. Hysteresis
. Isotropic deformation
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant, sustained load over time. This principle is applied clinically in dynamic splinting and serial casting. In contrast, stress relaxation refers to the decrease in stress (force) within a material over time when it is held at a constant deformation (length). Hysteresis is the energy lost as heat during the loading and unloading cycle of a viscoelastic material.

Question 8032

Topic: Infection, Pharmacology & VTE
A 65-year-old female is prescribed fondaparinux for deep vein thrombosis (DVT) prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this pharmacological agent?
. Direct, competitive inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Indirect inhibition of Factor Xa via antithrombin III
. Direct, reversible inhibition of Factor Xa
. Inhibition of vitamin K epoxide reductase

Correct Answer & Explanation

. Indirect inhibition of Factor Xa via antithrombin III

Explanation

Fondaparinux is a synthetic pentasaccharide that exerts its anticoagulant effect by binding specifically to antithrombin III (ATIII). This binding induces a conformational change in ATIII, accelerating its ability to irreversibly inactivate Factor Xa by a factor of 300. Because it is an indirect inhibitor of Factor Xa and does not directly bind the factor itself, it differs from agents like rivaroxaban and apixaban (direct Factor Xa inhibitors). Dabigatran is a direct thrombin inhibitor, aspirin inhibits COX-1, and warfarin inhibits vitamin K epoxide reductase.

Question 8033

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which of the following best describes the structural and biochemical properties of the deep zone compared to the superficial zone?

. Highest water content, parallel collagen fibers, low proteoglycan content
. Lowest water content, perpendicular collagen fibers, highest proteoglycan content
. Highest water content, perpendicular collagen fibers, highest proteoglycan content
. Lowest water content, random collagen fibers, lowest proteoglycan content
. Highest water content, parallel collagen fibers, highest proteoglycan content

Correct Answer & Explanation

. Highest water content, perpendicular collagen fibers, highest proteoglycan content

Explanation

The deep zone of articular cartilage has the lowest water content, highest proteoglycan content, and collagen fibers (primarily type II) arranged perpendicularly to the subchondral bone to best resist compressive forces. The superficial zone has the highest water content, lowest proteoglycan content, and collagen fibers arranged parallel to the joint surface to resist shear forces.

Question 8034

Topic: Biology, Genetics & Bone Healing

Which of the following factors is directly secreted by osteoblasts to inhibit osteoclastogenesis and limit bone resorption?

. RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. M-CSF (Macrophage Colony-Stimulating Factor)
. Osteoprotegerin (OPG)
. Cathepsin K
. Sclerostin

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is a decoy receptor produced by osteoblasts that binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This prevents osteoclast differentiation and activation, thereby limiting bone resorption. RANKL and M-CSF promote osteoclastogenesis. Sclerostin is produced by osteocytes to inhibit bone formation via the Wnt pathway, and Cathepsin K is an enzyme secreted by osteoclasts to degrade collagen.

Question 8035

Topic: Physiology & Rehabilitation

During a marathon, an endurance runner predominantly utilizes a specific type of skeletal muscle fiber. Which of the following best characterizes this muscle fiber type?

. High glycogen content, high anaerobic capacity, fast twitch
. High mitochondrial density, high myoglobin content, fatigue-resistant
. Low oxidative capacity, fast twitch, large motor unit size
. High myosin ATPase activity, rapid fatigue, low capillary density
. Low triglyceride content, high glycolytic enzyme activity, fast contraction

Correct Answer & Explanation

. High mitochondrial density, high myoglobin content, fatigue-resistant

Explanation

Type I muscle fibers (slow-twitch) are highly utilized during endurance activities like marathons. They are characterized by high oxidative capacity, high mitochondrial density, high myoglobin content (giving them a red color), and strong resistance to fatigue. Type II fibers (fast-twitch) are utilized for short, explosive movements and have higher glycolytic capacity and fatigue more rapidly.

Question 8036

Topic: Biology, Genetics & Bone Healing

A 45-year-old man sustains a closed midshaft femur fracture treated with a reamed, statically locked intramedullary nail. Fracture healing in this construct is predominantly expected to occur via:

. Direct osteonal remodeling without a cartilaginous intermediate
. Endochondral ossification forming a fracture callus
. Intramembranous ossification without callus formation
. Appositional bone growth exclusively
. Haversian canal widening and primary bone formation

Correct Answer & Explanation

. Endochondral ossification forming a fracture callus

Explanation

Intramedullary nailing provides relative mechanical stability rather than absolute stability. This strain environment stimulates secondary bone healing, which primarily occurs via endochondral ossification. This process progresses through stages of inflammation, soft callus (cartilaginous), hard callus, and remodeling. Primary bone healing (direct osteonal remodeling without callus) requires absolute stability and direct cortical contact, typically achieved with rigid compression plating.

Question 8037

Topic: 1. General Principles & Basic Science

According to the Seddon classification of nerve injuries, which of the following best describes an injury characterized by disruption of the axon and myelin sheath, but with preservation of the endoneurium, perineurium, and epineurium?

. Neurapraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade IV
. Sunderland Grade V

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis (which corresponds to Sunderland Grade II) involves disruption of the axon and its myelin sheath, while the surrounding connective tissue frameworks (endoneurium, perineurium, and epineurium) remain intact. This allows for Wallerian degeneration distally but provides an intact anatomical path for axonal regeneration, typically resulting in favorable functional recovery. Neurapraxia is a temporary conduction block, while neurotmesis involves complete nerve transection.

Question 8038

Topic: 1. General Principles & Basic Science
During the remodeling phase of normal tendon healing, the biochemical composition of the extracellular matrix shifts to restore tensile strength. Which of the following changes is most characteristic of this phase?
. Substitution of Type I collagen with Type III collagen
. Increase in overall cellularity and inflammatory cytokines
. Substitution of Type III collagen with Type I collagen
. Rapid and sustained increase in glycosaminoglycan content
. Transformation of resident tenocytes into chondrocytes

Correct Answer & Explanation

. Substitution of Type III collagen with Type I collagen

Explanation

Tendon healing occurs in three overlapping phases: inflammatory, proliferative (reparative), and remodeling. During the early proliferative phase, fibroblasts rapidly synthesize Type III collagen, which is disorganized and weaker. In the remodeling phase, cellularity decreases, and Type III collagen is gradually replaced by Type I collagen. These Type I fibers align along the axis of mechanical stress, restoring the tendon's mature architecture and tensile strength.

Question 8039

Topic: Infection, Pharmacology & VTE
Which of the following best describes the specific mechanism of action of rivaroxaban, an oral anticoagulant frequently used for deep vein thrombosis prophylaxis following total joint arthroplasty?
. Direct and reversible inhibition of thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Activation of antithrombin III to indirectly inhibit Factor Xa
. Direct competitive inhibition of active Factor Xa
. Irreversible inhibition of ADP binding to P2Y12 platelet receptors

Correct Answer & Explanation

. Direct competitive inhibition of active Factor Xa

Explanation

Rivaroxaban is a Direct Oral Anticoagulant (DOAC) that exerts its effect by directly and competitively inhibiting active Factor Xa. This interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade, preventing thrombin generation and subsequent thrombus formation. Dabigatran directly inhibits thrombin (Factor IIa). Warfarin is a vitamin K antagonist. Low-molecular-weight heparins activate antithrombin III. Clopidogrel targets ADP receptors on platelets.

Question 8040

Topic: Biomechanics & Biomaterials

A 45-year-old man undergoes revision internal fixation of a femoral nonunion. The surgeon plans to use a titanium alloy plate for stabilization. Which of the following screw materials, if used in combination with this titanium plate, would be most likely to result in significant galvanic corrosion, and which material would preferentially undergo corrosive degradation?

. Stainless steel screws; the stainless steel will preferentially corrode.
. Stainless steel screws; the titanium will preferentially corrode.
. Cobalt-chromium screws; the cobalt-chromium will preferentially corrode.
. Cobalt-chromium screws; the titanium will preferentially corrode.
. Titanium alloy screws; the titanium will preferentially corrode.

Correct Answer & Explanation

. Stainless steel screws; the stainless steel will preferentially corrode.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (like bodily fluids), causing the less noble (more anodic) metal to corrode. In the galvanic series, titanium and cobalt-chromium are more noble (cathodic) compared to 316L stainless steel (anodic). If stainless steel screws are used with a titanium plate, the stainless steel acts as the anode and will preferentially corrode. Mixing stainless steel with titanium or cobalt-chromium implants is generally contraindicated in orthopedics for this reason.

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