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1. General Principles & Basic Science MCQs

Practice Set 573 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 11441

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, combining a titanium femoral stem with a stainless steel cerclage wire increases the risk of which specific type of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive fluid environment. The more anodic metal in the galvanic series (stainless steel) will preferentially corrode.

Question 11442

Topic: Biomechanics & Biomaterials

A surgeon decides to use a titanium locking plate with stainless steel cortical screws to treat a femoral shaft fracture. Which type of material degradation is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electronegativities are placed in contact within an electrolytic solution (like bodily fluids). This sets up a battery effect where the less noble metal corrodes. Mixing titanium and stainless steel implants greatly increases this risk.

Question 11443

Topic: 1. General Principles & Basic Science

A new point-of-care synovial fluid test for periprosthetic joint infection has 95% sensitivity and 90% specificity. If this test is utilized in a patient population where the true prevalence of periprosthetic joint infection is progressively decreasing, what is the effect on the predictive values of the test?

. Positive Predictive Value (PPV) increases and Negative Predictive Value (NPV) decreases
. Positive Predictive Value (PPV) decreases and Negative Predictive Value (NPV) increases
. Both PPV and NPV decrease
. Both PPV and NPV increase
. PPV and NPV remain unchanged because sensitivity and specificity are constant

Correct Answer & Explanation

. Positive Predictive Value (PPV) increases and Negative Predictive Value (NPV) decreases

Explanation

While sensitivity and specificity are intrinsic properties of a diagnostic test, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) are heavily dependent on disease prevalence. As the prevalence of a disease decreases in a population, the proportion of false positives to true positives increases, leading to a decreased PPV. Conversely, the NPV increases.

Question 11444

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with multiple unexplained fractures and hepatosplenomegaly. Radiographs reveal a classic 'bone-in-bone' appearance and generalized diffuse osteosclerosis. The underlying genetic and cellular defect in this condition primarily affects which of the following?

. Defective osteoblast differentiation via Runx2 mutation
. Premature apoptosis of osteocytes
. Defective Type I collagen triple helix formation
. Carbonic anhydrase II deficiency impairing osteoclast ruffled border function
. Hyperactive osteoclasts due to RANKL over-expression

Correct Answer & Explanation

. Defective osteoblast differentiation via Runx2 mutation

Explanation

The clinical scenario and radiographic findings are classic for malignant infantile osteopetrosis. This disease is characterized by defective osteoclastic bone resorption. A common genetic defect involves mutations in Carbonic anhydrase II or the TCIRG1 gene, which impairs the osteoclast's ability to acidify Howship's lacuna at the ruffled border, preventing bone resorption.

Question 11445

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. What is its exact mechanism of action within the coagulation cascade?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase complex 1 (VKORC1) antagonist
. Potentiates antithrombin III to inhibit factors IIa and Xa
. Irreversibly inhibits platelet P2Y12 ADP receptors

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are oral anticoagulants that selectively and directly inhibit Factor Xa, interrupting the intrinsic and extrinsic pathways of the blood coagulation cascade. Dabigatran is a direct thrombin inhibitor. Warfarin is a Vitamin K antagonist. Low molecular weight heparins potentiate antithrombin III.

Question 11446

Topic: 1. General Principles & Basic Science

Normal adult articular cartilage is composed of multiple distinct zones. Which zone possesses the highest concentration of water and collagen, the lowest concentration of proteoglycans, and chondrocytes that are oriented parallel to the joint surface?

. 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 represents the gliding surface of the joint. It contains the highest water content (up to 80%), highest collagen content (mostly parallel to the surface to resist shear forces), the lowest proteoglycan content, and flattened chondrocytes aligned parallel to the surface.

Question 11447

Topic: Infection, Pharmacology & VTE

In the pathogenesis of orthopedic implant-related infections, Staphylococcus aureus forms a complex biofilm. Which phase of biofilm development is specifically characterized by quorum sensing and the robust production of an extracellular polymeric substance (EPS) matrix?

. Reversible attachment
. Irreversible attachment
. Maturation phase
. Dispersion phase
. Planktonic phase

Correct Answer & Explanation

. Reversible attachment

Explanation

Biofilm formation occurs in stages: reversible attachment, irreversible attachment, maturation, and dispersion. The maturation phase is characterized by the robust synthesis of the extracellular polymeric substance (EPS) matrix, complex three-dimensional architectural growth, and active bacterial communication known as quorum sensing.

Question 11448

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture resulting in a radial nerve palsy. According to the Sunderland classification of peripheral nerve injuries, a third-degree injury is characterized by the disruption of the axon and which other structural element(s)?

. Myelin sheath only (axon remains intact)
. Axon only (endoneurium remains intact)
. Axon and endoneurium (perineurium remains intact)
. Axon, endoneurium, and perineurium (epineurium remains intact)
. Complete transection of the nerve including the epineurium

Correct Answer & Explanation

. Myelin sheath only (axon remains intact)

Explanation

Sunderland classification: 1st degree: myelin disruption (Neuropraxia). 2nd degree: axon disrupted, endoneurium intact (Axonotmesis). 3rd degree: axon and endoneurium disrupted, perineurium intact. 4th degree: axon, endoneurium, and perineurium disrupted, epineurium intact. 5th degree: complete nerve transection (Neurotmesis).

Question 11449

Topic: 1. General Principles & Basic Science

Low-Intensity Pulsed Ultrasound (LIPUS) is an adjunctive therapy used to accelerate fracture healing and treat nonunions. At the cellular and molecular level, how does LIPUS primarily stimulate osteogenesis?

. By increasing osteoclast apoptosis and shifting balance to bone formation
. By stimulating the integrin/cyclooxygenase-2 (COX-2) signaling pathway
. By downregulating BMP-2 expression to reduce excessive callus
. By inducing controlled thermal necrosis of the periosteum to trigger remodeling
. By inhibiting angiogenesis to allow cartilage consolidation

Correct Answer & Explanation

. By increasing osteoclast apoptosis and shifting balance to bone formation

Explanation

LIPUS imparts a mechanical acoustic wave that produces micromotion at the fracture site. At the cellular level, this mechanical signal is transduced through integrins on the cell membrane, which leads to the upregulation of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2) synthesis, and increased expression of various osteoinductive factors like BMPs.

Question 11450

Topic: Physiology & Rehabilitation

Which type of muscle contraction generates the greatest force per unit of muscle cross-sectional area, but is also most strongly associated with the highest risk of delayed onset muscle soreness (DOMS) and musculotendinous injury?

. Isometric contraction
. Concentric contraction
. Eccentric contraction
. Isokinetic contraction
. Auxotonic contraction

Correct Answer & Explanation

. Isometric contraction

Explanation

An eccentric contraction occurs when a muscle lengthens while under tension. Eccentric contractions generate the highest maximum force compared to isometric or concentric contractions. Because of the high tension and mechanical stress during lengthening, eccentric contractions result in the most microtrauma to muscle fibers, leading to DOMS and an increased risk of injury.

Question 11451

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical bone screw is an essential biomechanical property for construct stability. Which of the following alterations to the geometry of the screw most significantly increases its pullout strength?

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

Correct Answer & Explanation

. Increasing the core (inner) diameter

Explanation

The pullout strength of a bone screw is directly proportional to the length of thread engagement, the outer diameter (major diameter) of the threads, and the shear strength of the surrounding bone. It is inversely proportional to the thread pitch. Therefore, increasing the outer diameter is the most powerful screw design modification to increase pullout strength.

Question 11452

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely utilized as a bone graft substitute in orthopedics. By definition, DBM primarily provides which of the following biological properties to facilitate bone healing?

. Osteogenesis and osteoconduction
. Osteoconduction and structural stability
. Osteoinduction only
. Osteoinduction and osteoconduction
. Osteogenesis only

Correct Answer & Explanation

. Osteogenesis and osteoconduction

Explanation

Demineralized bone matrix (DBM) is allograft bone that has had its inorganic mineral content removed. This exposes osteoinductive proteins, primarily Bone Morphogenetic Proteins (BMPs). DBM also retains its collagen scaffold, making it osteoconductive. However, because it contains no living cells, it is not osteogenic. It also provides virtually no structural stability.

Question 11453

Topic: 1. General Principles & Basic Science

Following an acute traumatic peripheral nerve transection (neurotmesis), electromyography (EMG) is often utilized to confirm the diagnosis and establish a baseline. What is the minimum time required post-injury for fibrillation potentials to reliably manifest on an EMG in the denervated distal muscles?

. 1 to 2 days
. 4 to 6 days
. 2 to 3 weeks
. 6 to 8 weeks
. 3 months

Correct Answer & Explanation

. 1 to 2 days

Explanation

Following a complete nerve transection, the distal axon undergoes Wallerian degeneration. The muscle fibers lose their innervation and develop denervation hypersensitivity. The classic EMG findings of denervation, such as fibrillation potentials and positive sharp waves, typically take 2 to 3 weeks (often cited as 10 to 21 days) to develop and become detectable.

Question 11454

Topic: Infection, Pharmacology & VTE
A 65-year-old patient develops sudden onset dyspnea, tachycardia, and pleuritic chest pain 3 days after undergoing an elective total hip arthroplasty. A 12-lead electrocardiogram (ECG) is obtained to evaluate for an acute pulmonary embolism (PE). What is the most common electrocardiographic finding in patients with a PE?
. S1Q3T3 pattern
. Right bundle branch block (RBBB)
. Sinus tachycardia
. Atrial fibrillation
. ST segment elevation in V1-V3

Correct Answer & Explanation

. Sinus tachycardia

Explanation

While the S1Q3T3 pattern (prominent S wave in lead I, Q wave and inverted T wave in lead III) is the classic 'textbook' finding associated with acute right heart strain from a pulmonary embolism, it is relatively insensitive. The single most common ECG abnormality seen in patients with an acute pulmonary embolism is sinus tachycardia.

Question 11455

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel screw with a titanium plate. What is the primary reason this combination of metals should be avoided in orthopedic implants?

. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Fretting corrosion secondary to modulus mismatch
. Crevice corrosion due to poor oxygen tension at the interface
. Pitting corrosion from chloride ion accumulation

Correct Answer & Explanation

. Galvanic corrosion with titanium acting as the anode

Explanation

Mixing different metals can lead to galvanic corrosion. In the case of stainless steel and titanium, stainless steel is less noble (more anodic) than titanium. Therefore, the stainless steel will act as the anode and undergo accelerated corrosion, while the titanium acts as the cathode.

Question 11456

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with a history of multiple fractures and a 'rugger jersey' spine noted on lateral radiographs. A defect in which of the following mechanisms or genes is most likely responsible?

. Type I collagen synthesis
. Carbonic anhydrase II deficiency
. Fibroblast growth factor receptor 3 mutation
. COMP gene mutation
. Defective mineralization of osteoid

Correct Answer & Explanation

. Type I collagen synthesis

Explanation

The clinical picture describes osteopetrosis, characterized by dense, brittle bones and a 'rugger jersey' spine (sclerosis at the vertebral endplates). A known genetic cause is a deficiency in Carbonic anhydrase II, which impairs the ability of osteoclasts to acidify Howship's lacunae, thus preventing normal bone resorption.

Question 11457

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene has significantly reduced wear rates. However, increasing the radiation dose to achieve higher cross-linking primarily compromises which of the following material properties?
. Elastic modulus
. Ultimate tensile strength
. Fatigue crack propagation resistance
. Wettability
. Melting point

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While high-dose gamma irradiation improves the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) by increasing cross-linking, it simultaneously decreases its ductility and fatigue crack propagation resistance, making the material more brittle and susceptible to fracture under cyclical loading.

Question 11458

Topic: 1. General Principles & Basic Science

Articular cartilage is avascular, relying on alternative methods for chondrocyte nutrition. How do chondrocytes in the deeper layers of adult articular cartilage primarily receive their nutrients?

. Capillary diffusion directly from the subchondral bone
. Direct vascular penetration through the tidemark
. Diffusion from the synovial fluid facilitated by mechanical loading
. Active transport via the perichondrium
. Lymphatic channels within the extracellular matrix

Correct Answer & Explanation

. Capillary diffusion directly from the subchondral bone

Explanation

Adult articular cartilage is avascular, aneural, and alymphatic. The tidemark acts as a barrier to diffusion from the subchondral bone in mature skeletons. Therefore, chondrocytes rely on diffusion from the synovial fluid, a process significantly enhanced by cyclical mechanical loading and unloading (the 'pump' mechanism).

Question 11459

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, calcium ions released from the sarcoplasmic reticulum bind directly to which of the following proteins to initiate the exposure of myosin-binding sites on actin?

. Tropomyosin
. Troponin C
. Troponin I
. Troponin T
. Calmodulin

Correct Answer & Explanation

. Tropomyosin

Explanation

In skeletal muscle, calcium binds to Troponin C. This binding causes a conformational change in the troponin complex (which includes Troponin I and Troponin T) that pulls tropomyosin away from the myosin-binding sites on the actin filament, allowing cross-bridge cycling to occur.

Question 11460

Topic: Infection, Pharmacology & VTE

A patient develops a deep surgical site infection following an open tibia fracture. Cultures grow Methicillin-resistant Staphylococcus aureus (MRSA). Which of the following antibiotics is a lipopeptide that is effective for osteomyelitis but inactivated by pulmonary surfactant, making it unsuitable for MRSA pneumonia?

. Vancomycin
. Linezolid
. Daptomycin
. Clindamycin
. Ceftaroline

Correct Answer & Explanation

. Vancomycin

Explanation

Daptomycin is a cyclic lipopeptide active against Gram-positive organisms, including MRSA. It is highly effective for skin/soft tissue infections and osteomyelitis but is notoriously inactivated by pulmonary surfactant, rendering it useless for the treatment of pneumonia.

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