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1. General Principles & Basic Science MCQs

Practice Set 578 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 11541

Topic: Biomechanics & Biomaterials

A surgeon elects to use a stainless steel screw to secure a commercially pure titanium plate to the diaphysis of a femur. Which type of corrosion is most likely to occur at the screw-plate interface due to the difference in electrochemical potential?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic medium (such as body fluids). The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 11542

Topic: Physiology & Rehabilitation

In skeletal muscle physiology, which type of muscle contraction is capable of generating the maximum peak force?

. Concentric contraction
. Isometric contraction
. Eccentric contraction
. Isokinetic contraction
. Isotonic contraction

Correct Answer & Explanation

. Concentric contraction

Explanation

Eccentric contractions (muscle lengthening under tension) can generate the highest forces, followed by isometric contractions, and finally concentric contractions (muscle shortening). This principle is depicted in the force-velocity curve of skeletal muscle.

Question 11543

Topic: 1. General Principles & Basic Science

Following a primary flexor tendon repair in Zone II, at which time point is the repair construct typically at its lowest tensile strength?

. Day 1
. Day 7
. Day 21
. Day 42
. Day 84

Correct Answer & Explanation

. Day 1

Explanation

The strength of a tendon repair initially drops due to the inflammatory response and collagen degradation exceeding new collagen synthesis. The repair is typically at its weakest between days 5 and 10 (Day 7) before the proliferative phase leads to a net increase in collagen and mechanical strength.

Question 11544

Topic: Biomechanics & Biomaterials

A researcher applies a constant strain (fixed length deformation) to a harvested anterior cruciate ligament specimen in a mechanical testing apparatus. Over a period of 60 seconds, the load required to maintain this specific strain gradually decreases. This viscoelastic property is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the decrease in stress (force/load) over time when a viscoelastic material is held at a constant strain. Creep, in contrast, is the gradual increase in strain (deformation) over time when subjected to a constant stress (load).

Question 11545

Topic: 1. General Principles & Basic Science

A 65-year-old man presents with acute knee swelling. Aneurysmal synovial fluid analysis reveals rhomboid-shaped crystals. What is the expected birefringence under polarized light microscopy, and what is the composition of the crystals?

. Strongly negative birefringence; monosodium urate
. Strongly positive birefringence; monosodium urate
. Weakly positive birefringence; calcium pyrophosphate dihydrate
. Weakly negative birefringence; calcium pyrophosphate dihydrate
. Non-birefringent; calcium hydroxyapatite

Correct Answer & Explanation

. Strongly negative birefringence; monosodium urate

Explanation

Pseudogout is caused by calcium pyrophosphate dihydrate (CPPD) crystals, which appear rhomboid-shaped and exhibit weakly positive birefringence under polarized light microscopy. Gout features monosodium urate crystals, which are needle-shaped and strongly negatively birefringent.

Question 11546

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, lamellar bone formation cannot occur if the mechanical strain at the fracture gap exceeds what threshold?

. 1%
. 2%
. 10%
. 30%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory dictates that lamellar bone can only form in environments with < 2% strain. Woven bone can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain without rupturing.

Question 11547

Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant frequently used for VTE prophylaxis following total joint arthroplasty. What is its primary molecular target?
. Direct inhibition of Thrombin (Factor IIa)
. Activation of Antithrombin III
. Direct inhibition of Factor Xa
. Inhibition of Vitamin K epoxide reductase
. Irreversible inhibition of cyclooxygenase-1 (COX-1)

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Heparin/LMWH works by activating Antithrombin III.

Question 11548

Topic: 1. General Principles & Basic Science

Which of the following local anesthetics is classified as an ester, and what is its primary mechanism of degradation?

. Lidocaine; hepatic metabolism
. Bupivacaine; hepatic metabolism
. Ropivacaine; plasma pseudocholinesterase
. Tetracaine; plasma pseudocholinesterase
. Prilocaine; plasma pseudocholinesterase

Correct Answer & Explanation

. Lidocaine; hepatic metabolism

Explanation

Tetracaine, procaine, and chloroprocaine are ester local anesthetics, which are metabolized in the bloodstream by plasma pseudocholinesterase. Lidocaine, bupivacaine, ropivacaine, and prilocaine are amides, which undergo hepatic metabolism. The mnemonic is that amides have two 'i's in their generic name.

Question 11549

Topic: 1. General Principles & Basic Science
A patient sustains a peripheral nerve injury that results in complete disruption of the axon and myelin sheath, but the endoneurium, perineurium, and epineurium remain intact. This injury corresponds to which classification?
. Seddon Neuropraxia / Sunderland Grade I
. Seddon Axonotmesis / Sunderland Grade II
. Seddon Axonotmesis / Sunderland Grade III
. Seddon Neurotmesis / Sunderland Grade IV
. Seddon Neurotmesis / Sunderland Grade V

Correct Answer & Explanation

. Seddon Axonotmesis / Sunderland Grade II

Explanation

Sunderland Grade II corresponds to Seddon's Axonotmesis where the axon is disrupted but the endoneurium (and all other outer layers) is intact. Sunderland III involves disruption of the endoneurium but intact perineurium. Sunderland IV is disruption up to the perineurium (intact epineurium). Sunderland V is complete nerve transection.

Question 11550

Topic: Biomechanics & Biomaterials

When mixing polymethylmethacrylate (PMMA) bone cement, which of the following statements regarding the addition of prophylactic antibiotics is true?

. Adding antibiotics in a liquid form increases the ultimate compressive strength of the cement.
. Thermal necrosis of surrounding bone is prevented due to a massive decrease in the exothermic reaction temperature.
. Adding more than 2 grams of antibiotic powder per 40-gram bag of cement substantially decreases the mechanical strength of the cement.
. Aminoglycosides are contraindicated because they are inactivated by the exothermic polymerization reaction.
. The porosity of the cement is decreased, preventing long-term antibiotic elution.

Correct Answer & Explanation

. Adding antibiotics in a liquid form increases the ultimate compressive strength of the cement.

Explanation

For prophylaxis, usually < 2g of antibiotic per 40g bag of PMMA is used to preserve structural integrity. Using more than 2g (as in a spacer) significantly weakens the mechanical properties of the cement. Antibiotics must be added in powder form; liquid antibiotics severely degrade cement strength. Aminoglycosides and vancomycin are heat-stable and survive the exothermic reaction. Adding powder increases porosity.

Question 11551

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacologic therapy for osteoporosis and giant cell tumor of bone. It exerts its primary biological effect by directly binding to which of the following targets?

. RANK receptor
. RANK Ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Calcitonin receptor

Correct Answer & Explanation

. RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that directly binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

Question 11552

Topic: 1. General Principles & Basic Science

In native articular cartilage, the primary lubrication mechanism functioning under conditions of high physiological load and low sliding speed is:

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

Correct Answer & Explanation

. Hydrodynamic fluid film lubrication

Explanation

Boundary lubrication is the primary mechanism under high loads and low speeds. It is mediated by molecules like lubricin (PRG4) attached to the articular surface. Fluid film lubrication (hydrodynamic, squeeze-film) operates primarily under high speed and lower loads.

Question 11553

Topic: 1. General Principles & Basic Science

Stress shielding around a femoral prosthesis relies on the principle of load-sharing between the implant and host bone. Stress shielding is most exacerbated by an implant made of a material with which of the following properties relative to cortical bone?

. Higher porosity
. Higher ductility
. Higher elastic (Young's) modulus
. Lower yield strength
. Lower ultimate tensile strength

Correct Answer & Explanation

. Higher porosity

Explanation

According to Wolff's law, bone models according to the stress applied. If an implant has a much higher elastic (Young's) modulus (i.e., is much stiffer) than cortical bone, the implant will absorb the majority of the mechanical load. The 'shielded' bone experiences reduced mechanical stress, leading to disuse osteopenia (stress shielding).

Question 11554

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are essential for osteoinduction. Upon binding to their respective cell surface receptors, which intracellular signaling pathway is primarily responsible for transmitting the osteogenic signal to the nucleus?

. JAK-STAT pathway
. Wnt/beta-catenin pathway
. cAMP/PKA pathway
. Smad 1/5/8 pathway
. MAP kinase pathway

Correct Answer & Explanation

. JAK-STAT pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which then phosphorylate specific intracellular Smad proteins (typically Smad 1, 5, and 8). These form a complex with Smad 4, translocate to the nucleus, and regulate the transcription of osteogenic genes.

Question 11555

Topic: 1. General Principles & Basic Science

Which of the following best describes the structural composition and matrix orientation of the superficial (tangential) zone of normal articular cartilage?

. Highest proteoglycan content with perpendicularly aligned collagen fibers
. Highest water content with collagen fibers aligned parallel to the articular surface
. Lowest cellularity with randomly oriented collagen fibers
. Highest concentration of Type X collagen with a calcified matrix
. Lowest water content with perpendicularly aligned collagen fibers

Correct Answer & Explanation

. Highest proteoglycan content with perpendicularly aligned collagen fibers

Explanation

The superficial (tangential) zone of articular cartilage contains the highest water content and the highest concentration of collagen, with the collagen fibers oriented parallel to the joint surface to effectively resist shear stresses. It has the lowest concentration of proteoglycans.

Question 11556

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is commonly used in total hip arthroplasty to reduce volumetric wear. What is the primary mechanical trade-off associated with increasing the degree of cross-linking in UHMWPE?
. Increased oxidation resistance but decreased stiffness
. Decreased abrasive wear but increased adhesive wear
. Increased wear resistance but decreased fatigue strength and fracture toughness
. Increased fracture toughness but decreased wear resistance
. Decreased elastic modulus but increased yield strength

Correct Answer & Explanation

. Increased wear resistance but decreased fatigue strength and fracture toughness

Explanation

Cross-linking UHMWPE significantly improves its wear resistance, particularly against adhesive and abrasive wear. However, the cross-linking process reduces the material's ductility, ultimate tensile strength, fatigue strength, and fracture toughness, making it more prone to rim cracking in certain applications like thin acetabular liners.

Question 11557

Topic: 1. General Principles & Basic Science

Which of the following synovial fluid or cartilage matrix constituents is primarily responsible for boundary lubrication, reducing friction during load-bearing at the articular surface?

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

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Lubricin (proteoglycan 4 or PRG4) is a glycoprotein synthesized by superficial zone chondrocytes and synovial fibroblasts. It adheres to the articular surface and is the primary molecule responsible for boundary lubrication. Hyaluronic acid is mainly responsible for fluid-film lubrication and the viscosity of synovial fluid.

Question 11558

Topic: Biology, Genetics & Bone Healing

A child presents with irritability, bleeding gums, and subperiosteal hemorrhages on radiographs. The suspected dietary deficiency primarily impairs which step of collagen synthesis?

. Cleavage of propeptides from procollagen
. Assembly of three alpha chains into a triple helix
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Glycosylation of hydroxylysine residues

Correct Answer & Explanation

. Cleavage of propeptides from procollagen

Explanation

The clinical picture describes scurvy, caused by Vitamin C deficiency. Vitamin C (ascorbic acid) is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase, the enzymes responsible for the intracellular hydroxylation of proline and lysine residues in procollagen. Without this, the collagen triple helix cannot form stably.

Question 11559

Topic: Biology, Genetics & Bone Healing

Romosozumab is an anabolic agent approved for the treatment of severe osteoporosis. What is its specific molecular target?

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Parathyroid hormone 1 (PTH1) receptor
. Sclerostin
. Cathepsin K
. Farnesyl pyrophosphate synthase

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Sclerostin, secreted by osteocytes, normally inhibits the Wnt/beta-catenin signaling pathway in osteoblasts. Inhibiting sclerostin results in a dual effect: it significantly increases bone formation and moderately decreases bone resorption.

Question 11560

Topic: Infection, Pharmacology & VTE

During the formation of a biofilm by Staphylococcus epidermidis on a prosthetic joint, which of the following is the key structural component of the extracellular polymeric substance (EPS) that shields the bacteria from host immunity and antibiotics?

. Teichoic acid
. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Lipopolysaccharide

Correct Answer & Explanation

. Teichoic acid

Explanation

Staphylococcus epidermidis produces a robust biofilm whose primary structural component is polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC operon. This glycocalyx matrix is critical for bacterial aggregation and evasion of host defenses.

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