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1. General Principles & Basic Science MCQs

Practice Set 587 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 11721

Topic: 1. General Principles & Basic Science
Following a complete peripheral nerve transection (neurotmesis) with immediate primary epineurial repair, an organized cascade of events occurs in the distal stump to clear debris. Which process is responsible for the degradation of the axon and myelin sheath distal to the injury site?
. Chromatolysis
. Wallerian degeneration
. Segmental demyelination
. Neuroma-in-continuity formation
. Axonal sprouting

Correct Answer & Explanation

. Wallerian degeneration

Explanation

Wallerian degeneration is the physiological process of breakdown and clearance of the axon and surrounding myelin sheath distal to the site of nerve transection. It is orchestrated by macrophages and Schwann cells, which phagocytose the debris. The remaining Schwann cells then proliferate to form endoneurial tubes (Bands of Büngner) that provide a supportive pathway for regenerating axons growing from the proximal stump.

Question 11722

Topic: Infection, Pharmacology & VTE
A patient with a history of recurrent pulmonary emboli requires total knee arthroplasty and is currently managed therapeutically with dabigatran. What is the specific biochemical mechanism of action of this medication?
. Direct inhibition of Factor Xa
. Indirect inhibition of Factor Xa via antithrombin III activation
. Direct and reversible inhibition of thrombin (Factor IIa)
. Inhibition of the Vitamin K epoxide reductase complex
. Irreversible blockade of the P2Y12 ADP receptor on platelets

Correct Answer & Explanation

. Direct and reversible inhibition of thrombin (Factor IIa)

Explanation

Dabigatran is a direct oral anticoagulant (DOAC) that functions by directly and reversibly binding to and inhibiting thrombin (Factor IIa). In contrast, rivaroxaban and apixaban are direct Factor Xa inhibitors. Enoxaparin (a LMWH) predominantly acts by indirectly inhibiting Factor Xa through antithrombin III. Warfarin inhibits Vitamin K epoxide reductase.

Question 11723

Topic: Biomechanics & Biomaterials

During revision trauma surgery, a 316L stainless steel screw is inadvertently used to lag a fracture fragment through a Titanium alloy (Ti-6Al-4V) plate. Which electrochemical process explains why this combination is contraindicated?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with differing anodic/cathodic potentials are placed in direct physical contact within an electrolytic solution, such as human extracellular fluid. The less noble metal acts as an anode and undergoes accelerated oxidative corrosion, which can lead to rapid implant failure, adverse tissue reactions, and metallosis.

Question 11724

Topic: Biology, Genetics & Bone Healing

A surgeon intends to fill a contained metaphyseal defect with a synthetic bone graft substitute that possesses purely osteoconductive properties, lacking any inherent osteoinductive or osteogenic potential. Which of the following materials fits this description?

. Iliac crest autograft
. Demineralized bone matrix (DBM)
. Calcium phosphate ceramic
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Fresh frozen structural allograft

Correct Answer & Explanation

. Iliac crest autograft

Explanation

Calcium phosphate ceramics are synthetic, biologically inert materials that provide only a three-dimensional porous scaffold for vascular and cellular ingrowth. Therefore, they are purely osteoconductive. Autograft is osteogenic, osteoinductive, and osteoconductive. DBM is osteoconductive and retains some osteoinductive properties due to surviving BMPs. rhBMP-2 is highly osteoinductive.

Question 11725

Topic: Biology, Genetics & Bone Healing
During the progression of secondary bone healing following a fracture, which specific type of collagen is predominantly synthesized and deposited by chondrocytes during the soft callus phase?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Secondary fracture healing relies on endochondral ossification, progressing through hematoma, soft callus, hard callus, and remodeling. During the soft callus phase, a cartilaginous template bridges the fracture gap. The chondrocytes in this phase predominantly synthesize Type II collagen, which is standard for hyaline-like cartilage, before transitioning to Type X during hypertrophy, and eventually being replaced by Type I collagen from osteoblasts.

Question 11726

Topic: Physiology & Rehabilitation

During the normal human gait cycle, which muscle undergoes a critical eccentric contraction at initial contact (heel strike) to decelerate the foot and prevent it from slapping against the ground?

. Gastrocnemius
. Quadriceps femoris
. Tibialis anterior
. Gluteus maximus
. Hamstrings

Correct Answer & Explanation

. Gastrocnemius

Explanation

At initial contact (heel strike), the ankle is in a neutral or slightly dorsiflexed position. As the body progresses over the foot toward the 'foot flat' phase, the ankle rapidly plantarflexes. The tibialis anterior and other anterior compartment muscles undergo an eccentric contraction (lengthening under active tension) to control this descent and smoothly absorb the shock, preventing 'foot slap.'

Question 11727

Topic: Biology, Genetics & Bone Healing

The spatial and temporal regulation of limb development along the proximal-to-distal axis is governed by interactions between the apical ectodermal ridge (AER) and underlying mesenchyme. Which specific family of genes is responsible for dictating the regional identity and segmentation of these developing elements (e.g., specifying humerus vs. radius vs. phalanges)?

. Wnt genes
. Fibroblast growth factors (FGFs)
. Sonic hedgehog (SHH)
. Hox (Homeobox) genes
. Bone morphogenetic proteins (BMPs)

Correct Answer & Explanation

. Wnt genes

Explanation

Hox (Homeobox) genes encode critical transcription factors that determine the specific positional identity of segments along the proximal-distal axis of the developing limb. For instance, Hox9-10 dictate stylopod (humerus/femur) formation, Hox11 regulates the zeugopod (radius-ulna/tibia-fibula), and Hox12-13 govern the autopod (hand/foot). FGFs maintain overall limb outgrowth.

Question 11728

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe post-menopausal osteoporosis, characterized by multiple vertebral fragility fractures, is started on daily subcutaneous teriparatide therapy. What is the fundamental mechanism of action by which this medication increases bone mineral density?

. Monoclonal antibody directly targeting and neutralizing RANKL
. Induction of osteoclast apoptosis by inhibiting farnesyl pyrophosphate synthase
. Intermittent administration of recombinant PTH strongly stimulating osteoblast activity
. Selective estrogen receptor modulation to downregulate osteoclastogenesis
. Inhibition of sclerostin to promote Wnt signaling

Correct Answer & Explanation

. Monoclonal antibody directly targeting and neutralizing RANKL

Explanation

Teriparatide is a synthetic, recombinant polypeptide representing the active 1-34 amino acid sequence of human parathyroid hormone (PTH). While continuous, elevated levels of endogenous PTH lead to net bone resorption, the intermittent (daily bolus) administration of exogenous PTH has a paradoxical profound anabolic effect, primarily stimulating osteoblast proliferation and bone formation over osteoclast activity.

Question 11729

Topic: Biomechanics & Biomaterials

A patient with a modular metal-on-polyethylene total hip arthroplasty presents with groin pain and a palpable mass. Revision surgery reveals blackened debris and local tissue necrosis at the head-neck junction (trunnion), but no significant wear at the bearing surface.

Which of the following wear mechanisms is primarily responsible for the failure at the modular junction?

. Galvanic corrosion
. Fretting corrosion
. Pitting corrosion
. Adhesive wear
. Abrasive wear

Correct Answer & Explanation

. Galvanic corrosion

Explanation

The scenario describes mechanically assisted crevice corrosion (MACC), commonly referred to as fretting corrosion, occurring at the modular head-neck junction (taperosis/trunnionosis). Fretting involves micromotion between two loaded surfaces that destroys the passivation layer, allowing crevice corrosion to rapidly degrade the metal, producing metallic debris and adverse local tissue reactions (ALTR).

Question 11730

Topic: Biomechanics & Biomaterials

During cyclic compressive loading of articular cartilage, the tissue initially deforms rapidly, followed by a slow, time-dependent deformation until an equilibrium is reached. Which of the following tissue components and physical mechanisms primarily dictate this time-dependent viscoelastic response (creep)?

. Intrinsic stiffness of Type II collagen
. Fluid exudation out of the extracellular matrix
. Superficial zone chondrocyte density
. Covalent cross-linking of Type IX collagen
. Molecular weight of the hyaluronan backbone

Correct Answer & Explanation

. Intrinsic stiffness of Type II collagen

Explanation

The viscoelastic behavior of articular cartilage in compression is primarily governed by fluid flow. The highly negatively charged glycosaminoglycans (GAGs) on aggrecan create high osmotic pressure that draws water in. When compressed, fluid is forced out of the extracellular matrix. The frictional drag of fluid moving through the porous solid matrix causes the time-dependent creep response.

Question 11731

Topic: 1. General Principles & Basic Science

Following a sharp transection injury to a peripheral nerve, Wallerian degeneration begins distal to the injury site. Which cell type is initially responsible for the earliest breakdown of the myelin sheath in the first 48 hours of this process?

. Hematogenous macrophages
. Schwann cells
. Resident microglia
. Fibroblasts
. Endothelial cells

Correct Answer & Explanation

. Hematogenous macrophages

Explanation

In the initial phase of Wallerian degeneration (within the first 24-48 hours), Schwann cells dedifferentiate, cease producing myelin, and actively begin to degrade their own myelin sheaths via autophagy and phagocytosis. Subsequently, they secrete chemokines (like MCP-1) to recruit hematogenous macrophages, which arrive later to clear the majority of the myelin debris.

Question 11732

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with recurrent fractures, anemia, and hepatosplenomegaly. Radiographs reveal diffuse, uniform sclerosis of all bones.

Genetic testing identifies a mutation in the TCIRG1 gene. This mutation primarily disrupts which of the following cellular processes?

. Formation of the osteoclast ruffled border
. Carbonic anhydrase II synthesis
. Chloride channel function in the osteoclast membrane
. V-ATPase dependent proton pumping into the resorption pit
. RANKL-mediated osteoclast differentiation

Correct Answer & Explanation

. V-ATPase dependent proton pumping into the resorption pit

Explanation

The patient has autosomal recessive malignant osteopetrosis. The most common genetic cause is a mutation in the TCIRG1 gene, which encodes the a3 subunit of the vacuolar proton pump (V-ATPase). This impairs the osteoclast's ability to pump protons (acidify) into the sealed resorption pit, rendering them unable to resorb bone, despite being present in normal or increased numbers.

Question 11733

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely administered perioperatively in total joint arthroplasty to reduce blood loss. By which of the following molecular mechanisms does TXA exert its primary antifibrinolytic effect?
. Irreversible inhibition of cyclooxygenase-1
. Competitive inhibition of plasminogen activation
. Direct cross-linking of fibrin strands
. Enhancement of antithrombin III activity
. Direct inhibition of factor Xa

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine receptor sites on plasminogen, thereby preventing plasminogen from binding to fibrin. This competitively inhibits the activation of plasminogen to plasmin, effectively blocking fibrinolysis.

Question 11734

Topic: Biology, Genetics & Bone Healing

During tibial lengthening utilizing an Ilizarov circular external fixator (distraction osteogenesis), the latency period is followed by a distraction phase at a rate of 1 mm/day. What type of bone formation primarily occurs in the distraction gap during this steady process?

. Endochondral ossification
. Intramembranous ossification
. Creeping substitution
. Appositional enchondral ossification
. Primary cortical healing via cutting cones

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis, when performed with stable fixation and appropriate distraction rates (e.g., 1 mm/day), primarily proceeds via intramembranous ossification. The mechanical tension stimulates osteoblasts to lay down osteoid directly in the gap along the lines of tension without a cartilaginous intermediate.

Question 11735

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) reduces volumetric wear in total hip arthroplasty. However, the gamma irradiation used to induce cross-linking generates free radicals. What is the primary biomechanical trade-off of "remelting" the UHMWPE above its melting temperature to completely eliminate these free radicals?
. Decreased wear resistance
. Decreased yield strength and fatigue resistance
. Increased rate of in vivo oxidation
. Increased generation of third-body debris
. Loss of radiolucency on plain radiographs

Correct Answer & Explanation

. Decreased yield strength and fatigue resistance

Explanation

Irradiation causes cross-linking but leaves free radicals that can cause long-term oxidation and degradation. Remelting (heating above 150°C) completely eliminates the free radicals but alters the crystalline structure of the polymer, resulting in decreased yield strength, ultimate tensile strength, and fatigue resistance. Annealing (heating below the melting point) preserves mechanical properties better but leaves residual free radicals.

Question 11736

Topic: Biology, Genetics & Bone Healing
Romosozumab is a bone-building medication used in the treatment of severe osteoporosis. It exerts its anabolic effect by binding to and neutralizing sclerostin. Sclerostin normally inhibits bone formation by acting as an antagonist to which of the following signaling pathways?
. RANK/RANKL/OPG pathway
. TGF-beta/Smad pathway
. Wnt/β-catenin pathway
. Notch signaling pathway
. Hedgehog signaling pathway

Correct Answer & Explanation

. Wnt/β-catenin pathway

Explanation

Sclerostin, produced primarily by osteocytes, inhibits bone formation by binding to LRP5 and LRP6 receptors on osteoblasts. This action blocks the Wnt/β-catenin signaling pathway, which is essential for osteoblast differentiation and survival. Inhibiting sclerostin (e.g., with Romosozumab) thereby upregulates Wnt signaling and increases bone formation.

Question 11737

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently chosen over 316L stainless steel for the manufacturing of diaphyseal fracture plates. Compared to 316L stainless steel, titanium alloy is characterized by:

. A higher modulus of elasticity, resulting in increased stress shielding.
. A lower modulus of elasticity, resulting in decreased stress shielding.
. Higher ultimate tensile strength and increased ductility.
. Increased susceptibility to crevice corrosion.
. A higher density and higher modulus of elasticity.

Correct Answer & Explanation

. A lower modulus of elasticity, resulting in decreased stress shielding.

Explanation

Titanium alloy has a modulus of elasticity (Young's modulus) of approximately 110 GPa, which is about half that of 316L stainless steel (~200 GPa). Because it is closer to the modulus of cortical bone (~15-20 GPa), titanium plates distribute load more evenly, thereby decreasing the effect of stress shielding compared to stiffer stainless steel implants.

Question 11738

Topic: Biology, Genetics & Bone Healing

A 50-year-old patient with severe alcohol use disorder and poor dentition presents with perifollicular hemorrhages and poor incisional wound healing. The underlying nutritional deficiency directly impairs a critical intracellular step in collagen synthesis. Which specific enzyme and cellular location are affected?

. Procollagen peptidase in the extracellular space
. Lysyl oxidase in the extracellular matrix
. Prolyl hydroxylase in the rough endoplasmic reticulum
. Galactosyltransferase in the Golgi apparatus
. Protein disulfide isomerase in the cytoplasm

Correct Answer & Explanation

. Prolyl hydroxylase in the rough endoplasmic reticulum

Explanation

The patient has scurvy (Vitamin C deficiency). Vitamin C (ascorbic acid) acts as an essential cofactor for prolyl hydroxylase and lysyl hydroxylase, enzymes located within the rough endoplasmic reticulum that hydroxylate proline and lysine residues. This hydroxylation is critical for stabilizing the triple helix structure of procollagen.

Question 11739

Topic: Biology, Genetics & Bone Healing
A synthetic β-tricalcium phosphate (β-TCP) bone void filler is used to pack a defect following curettage of a benign bone cyst. Over time, the material is resorbed and replaced by host bone. Which of the following best describes the primary biological mechanism of this synthetic material?
. Osteoinduction
. Osteogenesis
. Osteoconduction
. Osteopromotion
. Osteoclastogenesis

Correct Answer & Explanation

. Osteoconduction

Explanation

Synthetic ceramics like β-TCP act purely as an inert 3D structural scaffold for host capillaries and osteoprogenitor cells to migrate across. This property is termed osteoconduction. Osteoinduction (e.g., BMPs) refers to stimulating the differentiation of mesenchymal stem cells into osteoblasts. Osteogenesis refers to living cells (e.g., autograft) synthesizing bone.

Question 11740

Topic: 1. General Principles & Basic Science
A randomized controlled trial compares a novel NSAID to standard ibuprofen for knee osteoarthritis pain. The study concludes there is no statistically significant difference in pain reduction (p = 0.15). However, a true clinical difference actually exists in the population, but the study failed to detect it because it only enrolled 20 patients. This scenario is a classic example of:
. Type I error
. Type II error
. Selection bias
. Confounding bias
. Recall bias

Correct Answer & Explanation

. Type II error

Explanation

A Type II error (false negative, represented by β) occurs when a study fails to reject a false null hypothesis—meaning it misses a true difference that actually exists. This is typically due to inadequate sample size and resulting low statistical power (Power = 1 - β).

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