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Infection, Pharmacology & VTE MCQs

Practice Set 29 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 561

Topic: Infection, Pharmacology & VTE

The most important factor in preventing surgical site infections (SSIs) in orthopedic surgery is:

. Strict perioperative glycemic control in diabetic patients.
. Administration of broad-spectrum antibiotics for at least 7 days post-op.
. Maintaining normothermia during surgery.
. Appropriate timing and selection of prophylactic antibiotics.
. Aggressive deep vein thrombosis prophylaxis.

Correct Answer & Explanation

. Strict perioperative glycemic control in diabetic patients.

Explanation

While all options except for prolonged broad-spectrum antibiotics play a role in SSI prevention, the appropriate timing and selection of prophylactic antibiotics is widely considered the single most important intervention. Antibiotics should be administered within 60 minutes prior to incision and cover anticipated pathogens. Prolonged post-operative antibiotics are generally not recommended due to resistance concerns. Glycemic control, normothermia, and DVT prophylaxis are important adjuncts.

Question 562

Topic: Infection, Pharmacology & VTE

A patient with a history of intravenous drug use presents with acute pain and swelling in the knee. Arthrocentesis reveals purulent fluid. Which organism is a common cause of septic arthritis in this population, besides Staphylococcus aureus?

. Neisseria gonorrhoeae
. Streptococcus pneumoniae
. Pseudomonas aeruginosa
. Borrelia burgdorferi
. Salmonella spp.

Correct Answer & Explanation

. Neisseria gonorrhoeae

Explanation

In intravenous drug users (IVDUs), Pseudomonas aeruginosa is a common cause of septic arthritis, particularly affecting large joints like the knee or sternoclavicular joint, in addition to Staphylococcus aureus. Neisseria gonorrhoeae is common in sexually active young adults. Streptococcus pneumoniae is less common. Borrelia burgdorferi causes Lyme arthritis. Salmonella spp. can cause osteomyelitis in sickle cell patients but is less common for septic arthritis in IVDUs.

Question 563

Topic: Infection, Pharmacology & VTE

Which of the following is a recognized complication of using indomethacin for prophylactic ossification after total hip arthroplasty?

. Increased risk of deep vein thrombosis
. Delayed fracture healing
. Hypertension crisis
. Elevated liver enzymes
. Auditory disturbances

Correct Answer & Explanation

. Increased risk of deep vein thrombosis

Explanation

Indomethacin, a non-selective NSAID, can inhibit prostaglandin synthesis, which is crucial for early stages of fracture healing and bone formation. Therefore, a recognized complication of its use (e.g., for heterotopic ossification prophylaxis) is delayed fracture healing, especially in fresh fractures. It is not typically associated with increased DVT risk (aspirin is used for DVT prophylaxis), hypertension crisis, or auditory disturbances as its main adverse effects.

Question 564

Topic: Infection, Pharmacology & VTE

Which imaging feature on plain radiographs is most indicative of chronic osteomyelitis?

. Soft tissue swelling and periarticular effusion
. Periosteal elevation and lucent metaphyseal lesions
. Sequestrum (dead bone) and involucrum (new bone formation around infected segment)
. Normal findings in early stages
. Displaced fracture fragment

Correct Answer & Explanation

. Soft tissue swelling and periarticular effusion

Explanation

The presence of a sequestrum (a fragment of necrotic bone that has separated from the healthy bone) and an involucrum (a sheath of new bone laid down by the periosteum around the infected, dead bone) are classic radiographic signs of chronic osteomyelitis. Soft tissue swelling and periarticular effusion are nonspecific. Periosteal elevation and lucent lesions can be seen in acute osteomyelitis but are less specific for chronicity. Early stages can be normal.

Question 565

Topic: Infection, Pharmacology & VTE

A patient develops a prosthetic joint infection 6 months after a total knee arthroplasty. Which characteristic of the bacterial biofilm is the primary reason why systemic, culture-directed antibiotics alone frequently fail to eradicate the infection without surgical debridement?

. Increased overall bacterial metabolic rate within the biofilm matrix
. Lack of a protective polymeric glycocalyx layer
. Transition of bacteria into a highly active planktonic state
. Presence of dormant persister cells with low metabolic activity
. Enhanced intracellular penetration into host macrophages

Correct Answer & Explanation

. Increased overall bacterial metabolic rate within the biofilm matrix

Explanation

Biofilms protect bacteria via a polymeric glycocalyx matrix. Deep within the biofilm, a lack of oxygen and nutrients induces bacteria to become dormant 'persister' cells. Because most antibiotics target actively dividing cells, these metabolically inactive bacteria are highly tolerant to antimicrobial therapy, necessitating surgical removal of the biofilm.

Question 566

Topic: Infection, Pharmacology & VTE

A 19-year-old man reports persistent thigh pain that is significantly worse at night and reliably relieved within 30 minutes of taking ibuprofen. Computed tomography (CT) of the femur demonstrates a 1.2 cm radiolucent nidus surrounded by dense reactive sclerotic bone in the femoral diaphysis. What is the primary molecular mechanism responsible for the severe pain and its relief by nonsteroidal anti-inflammatory drugs (NSAIDs) in this condition?

. Inhibition of leukotriene synthesis within the reactive zone
. Direct suppression of osteoclast activity within the nidus
. Reduction of intramedullary pressure via sympathetic blockade
. Inhibition of cyclooxygenase-2 (COX-2), decreasing high levels of prostaglandin E2 (PGE2)
. Inhibition of substance P release from unmyelinated C-fibers

Correct Answer & Explanation

. Inhibition of leukotriene synthesis within the reactive zone

Explanation

The patient's clinical and radiographic presentation is classic for an osteoid osteoma. The central nidus of an osteoid osteoma produces extraordinarily high levels of prostaglandins, particularly prostaglandin E2 (PGE2), due to up-regulation of the cyclooxygenase-2 (COX-2) enzyme. This local overproduction of prostaglandins stimulates adjacent nerve endings causing severe, characteristic nocturnal pain. NSAIDs provide dramatic relief by inhibiting COX-2, thereby halting the production of PGE2.

Question 567

Topic: Infection, Pharmacology & VTE

A 68-year-old man is prescribed rivaroxaban for venous thromboembolism prophylaxis following an elective total knee arthroplasty. What is the precise mechanism of action of this pharmacological agent?

. Indirect inhibition of Factor Xa via antithrombin III binding
. Direct, reversible inhibition of free and clot-bound Factor Xa
. Direct inhibition of thrombin (Factor IIa)
. Irreversible inhibition of the adenosine diphosphate (ADP) P2Y12 receptor
. Competitive antagonism of vitamin K epoxide reductase

Correct Answer & Explanation

. Indirect inhibition of Factor Xa via antithrombin III binding

Explanation

Rivaroxaban is an oral anticoagulant that functions as a direct, reversible, and highly selective inhibitor of Factor Xa (both free and clot-bound forms). By inhibiting Factor Xa, it interrupts the intrinsic and extrinsic pathways of the blood coagulation cascade, inhibiting both thrombin generation and thrombus development. Indirect inhibition of Factor Xa via antithrombin III is the mechanism of fondaparinux and low-molecular-weight heparins. Direct inhibition of thrombin is the mechanism of dabigatran.

Question 568

Topic: Infection, Pharmacology & VTE

A 65-year-old man undergoes a primary total knee arthroplasty. Four weeks later, he presents with acute knee pain, swelling, and a draining sinus tract. Aspiration reveals purulent fluid, and cultures grow Staphylococcus epidermidis. The pathogenesis of this periprosthetic joint infection involves bacterial adherence and biofilm formation on the implant surface. Which of the following phases of biofilm formation is characterized by intercellular signaling and phenotypic changes within the bacterial population?

. Reversible attachment
. Irreversible attachment
. Quorum sensing
. Planktonic dispersal
. Glycocalyx degradation

Correct Answer & Explanation

. Reversible attachment

Explanation

Quorum sensing is a complex cell-to-cell communication mechanism used by bacteria within a biofilm to coordinate gene expression based on their population density. Once a critical mass of bacteria is reached, these signaling molecules trigger phenotypic changes, increasing virulence, structural maturation of the biofilm, and enhanced resistance to host immune responses and systemic antibiotics. Reversible and irreversible attachments are earlier phases, while planktonic dispersal is a late phase where bacteria detach to colonize new sites.

Question 569

Topic: Infection, Pharmacology & VTE

A 55-year-old woman presents with severe pain and swelling of her left knee that began spontaneously 2 days ago. She has a history of plaque psoriasis. On examination, the knee is erythematous, warm, and holds a moderate effusion. She is afebrile. Arthrocentesis yields 35 mL of cloudy fluid. Synovial fluid analysis reports a white blood cell (WBC) count of 42,000 cells/mm³ with 60% polymorphonuclear leukocytes (PMNs). Gram stain is negative, and no crystals are observed under polarized light. What is the most likely diagnosis?

. Septic arthritis
. Psoriatic arthritis
. Gouty arthritis
. Osteoarthritis
. Hemorrhagic arthritis

Correct Answer & Explanation

. Septic arthritis

Explanation

The clinical picture and synovial fluid analysis strongly support an inflammatory arthropathy, such as psoriatic arthritis. Inflammatory synovial fluid is defined by a WBC count typically ranging from 2,000 to 50,000 cells/mm³ with a PMN predominance (usually 50-75%). Septic arthritis typically presents with a much higher WBC count (often >50,000 to >100,000 cells/mm³) and a higher PMN percentage (>75-90%), although there can be overlap. Gout is ruled out by the absence of negatively birefringent crystals. Osteoarthritis fluid is non-inflammatory (<2,000 WBCs/mm³).

Question 570

Topic: Infection, Pharmacology & VTE

Orthopedic implant-associated infections are notoriously difficult to eradicate. Pathogenic bacteria, such as Staphylococcus aureus, form biofilms on the surface of foreign materials. Once a mature biofilm is established, the bacteria become highly resistant to both systemic antibiotics and host immune clearance. Which of the following components is primarily responsible for conferring this structural integrity and profound antibiotic tolerance to the mature biofilm?

. The rigid peptidoglycan cell wall
. Teichoic acid and lipoteichoic acid
. The extracellular polymeric substance (EPS)
. Surface-bound Protein A
. Intracellular fibronectin-binding proteins

Correct Answer & Explanation

. The rigid peptidoglycan cell wall

Explanation

A critical feature of orthopedic device-related infections is the ability of bacteria like S. aureus and S. epidermidis to form a mature biofilm. The defining characteristic of a mature biofilm is the production of an extracellular polymeric substance (EPS), also known as the glycocalyx. The EPS is a complex, self-produced matrix consisting of polysaccharides (such as PIA/PNAG), structural proteins, and extracellular DNA. This thick matrix encases the bacteria, providing a formidable physical and chemical barrier that prevents the penetration of host immune cells (e.g., macrophages, neutrophils) and drastically reduces the diffusion and efficacy of antimicrobial agents. While peptidoglycan, teichoic acid, and Protein A are important virulence factors for S. aureus, it is the EPS matrix that specifically defines the mature biofilm phenotype and its characteristic recalcitrance to medical therapy.

Question 571

Topic: Infection, Pharmacology & VTE

A 62-year-old woman is scheduled for an elective total knee arthroplasty. She has a history of atrial fibrillation and is currently taking apixaban. When considering her perioperative deep vein thrombosis (DVT) prophylaxis and bleeding risk, the mechanism of action of apixaban must be accounted for. Apixaban exerts its anticoagulant effect by directly inhibiting which of the following?

. Thrombin (Factor IIa)
. Factor Xa
. Vitamin K epoxide reductase
. Antithrombin III
. Platelet ADP receptor (P2Y12)

Correct Answer & Explanation

. Thrombin (Factor IIa)

Explanation

Apixaban and rivaroxaban are direct oral anticoagulants (DOACs) that function as direct, reversible inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K epoxide reductase, affecting factors II, VII, IX, and X. Heparins function by potentiating Antithrombin III. Clopidogrel and ticagrelor are platelet P2Y12 ADP receptor inhibitors.

Question 572

Topic: Infection, Pharmacology & VTE

A 65-year-old man undergoes a two-stage revision for a periprosthetic joint infection of the hip. Operative tissue cultures grow Staphylococcus epidermidis. Which of the following virulence factors is primarily responsible for allowing this organism to persistently adhere to the orthopedic implant and evade host immune responses?

. Endotoxin production
. Spore formation
. Intracellular replication within macrophages
. Polysaccharide glycocalyx (biofilm) production
. Release of hyaluronidase

Correct Answer & Explanation

. Endotoxin production

Explanation

Staphylococcus epidermidis is a leading cause of implant-associated periprosthetic joint infections. Its primary virulence mechanism is the ability to form a dense biofilm on the surface of foreign biomaterials. This biofilm consists of an extracellular polymeric substance, primarily a polysaccharide glycocalyx, which physically shields the bacteria from systemic antibiotics and host immune cells (such as macrophages and neutrophils).

Question 573

Topic: Infection, Pharmacology & VTE

Staphylococcus aureus is the most common organism associated with periprosthetic joint infections. Which of the following phases of biofilm formation is characterized by the production of extracellular polymeric substances (EPS) and decreased metabolic activity of bacteria deep within the structure?

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

Correct Answer & Explanation

. Reversible attachment

Explanation

Biofilm formation occurs in several distinct phases: 1) Reversible attachment of planktonic bacteria to the surface, 2) Irreversible attachment mediated by adhesins, 3) Maturation, characterized by cell proliferation, intercellular communication (quorum sensing), and the production of a protective extracellular polymeric substance (EPS) matrix. In the maturation phase, bacteria deep within the biofilm enter a stationary, low-metabolic dormant state, making them highly resistant to both antibiotics and the host immune system, and 4) Dispersion, where bacteria detach to colonize new sites.

Question 574

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 575

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 576

Topic: Infection, Pharmacology & VTE

In the pathogenesis of prosthetic joint infections (PJI), biofilm formation protects bacteria from host immune clearance and antimicrobial therapy. During biofilm development, which of the following phases is characterized by cell proliferation and the extensive production of an extracellular polymeric substance (EPS) matrix?

. Planktonic phase
. Initial reversible attachment
. Maturation phase
. Dispersal phase
. Quorum sensing phase

Correct Answer & Explanation

. Planktonic phase

Explanation

Biofilm formation occurs in several distinct stages: (1) Reversible attachment of planktonic bacteria to a surface, (2) Irreversible attachment mediated by adhesins, (3) Maturation phase, which is characterized by bacterial proliferation, three-dimensional growth, and the production of a protective extracellular polymeric substance (EPS) matrix, and (4) Dispersal phase, where bacteria detach to colonize new sites. The EPS matrix is heavily responsible for antibiotic resistance.

Question 577

Topic: Infection, Pharmacology & VTE

During the harvesting of hamstring tendons for an anterior cruciate ligament (ACL) reconstruction, the surgeon dissects the superficial layer of the pes anserinus to locate the correct tendons. Which of the following tendons forms the most proximal and anterior/superficial layer of the pes anserinus insertion on the anteromedial tibia?

. Sartorius
. Gracilis
. Semitendinosus
. Semimembranosus
. Medial head of the gastrocnemius

Correct Answer & Explanation

. Sartorius

Explanation

The pes anserinus (goose foot) consists of the conjoined insertions of the sartorius, gracilis, and semitendinosus muscles on the proximal anteromedial tibia. The sartorius is the most superficial and proximal tendon, forming a fascial expansion that covers the underlying gracilis (middle) and semitendinosus (inferior and distal) tendons.

Question 578

Topic: Infection, Pharmacology & VTE

During the harvest of semitendinosus and gracilis tendons for an anterior cruciate ligament reconstruction, the surgeon inadvertently transects a nerve branch that crosses superficial to the gracilis tendon at the level of the pes anserinus. Which of the following clinical deficits will the patient most likely experience postoperatively?

. Numbness over the anteromedial aspect of the proximal leg
. Numbness over the lateral aspect of the distal leg
. Loss of sensation over the dorsum of the foot
. Burning pain over the plantar aspect of the heel
. Weakness in ankle dorsiflexion

Correct Answer & Explanation

. Numbness over the anteromedial aspect of the proximal leg

Explanation

The infrapatellar branch of the saphenous nerve emerges proximally and crosses superficial to the pes anserinus (often passing between or superficial to the gracilis and semitendinosus tendons). Injury to this branch during hamstring harvest leads to sensory loss, numbness, or a painful neuroma over the anteromedial aspect of the proximal leg.

Question 579

Topic: Infection, Pharmacology & VTE

When performing a posteromedial approach to the knee to repair the posterior horn of the medial meniscus, the sartorius fascia must be incised. Which of the following correctly identifies the anterior-to-posterior arrangement of the pes anserinus tendons?

. Sartorius, Gracilis, Semitendinosus
. Gracilis, Sartorius, Semitendinosus
. Semitendinosus, Gracilis, Sartorius
. Sartorius, Semitendinosus, Gracilis
. Gracilis, Semitendinosus, Sartorius

Correct Answer & Explanation

. Sartorius, Gracilis, Semitendinosus

Explanation

The anatomic arrangement of the pes anserinus tendons at their proximal tibial insertion from anterior to posterior (and superficial to deep) is Sartorius, Gracilis, and Semitendinosus.

Question 580

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, an acute limp, and refusal to bear weight for the past 24 hours. His oral temperature is 38.6°C (101.5°F). Laboratory tests show a WBC count of 13,500/mm3, an ESR of 45 mm/hr, and a CRP of 2.5 mg/dL. He has no history of recent trauma. Based on the Kocher criteria, what is the approximate predicted probability that this child has a septic arthritis of the hip?

. 3%
. 40%
. 75%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria differentiate septic arthritis from transient synovitis of the hip in children. The four classic criteria are: inability to bear weight, temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm3. This patient meets all four criteria. The predicted probability of septic arthritis based on the number of positive criteria is approximately: 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 93%, and 4 criteria = 99%.

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