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Infection, Pharmacology & VTE MCQs

Practice Set 58 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 1141

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct factor Xa inhibitor
. Indirect factor Xa inhibitor via antithrombin III
. Cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by selectively inhibiting Factor Xa. Unlike low-molecular-weight heparins, they directly inhibit the target without requiring antithrombin III.

Question 1142

Topic: Infection, Pharmacology & VTE
Following total hip arthroplasty, a patient is started on rivaroxaban for deep vein thrombosis prophylaxis. This medication exerts its anticoagulant effect by directly inhibiting which of the following?
. Thrombin (Factor IIa)
. Vitamin K epoxide reductase
. Antithrombin III
. Factor Xa
. Plasminogen

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban is an oral direct Factor Xa inhibitor that disrupts the coagulation cascade by preventing the conversion of prothrombin to thrombin. Dabigatran, in contrast, is a direct thrombin inhibitor.

Question 1143

Topic: Infection, Pharmacology & VTE

A 40-year-old patient presents with a swollen, painful knee. Synovial fluid analysis reveals a WBC count of 85,000 cells/mcL with 92% polymorphonuclear leukocytes. Glucose level in the fluid is markedly lower than serum levels. What is the most likely diagnosis?

. Rheumatoid arthritis
. Osteoarthritis
. Septic arthritis
. Tuberculous arthritis
. Lyme arthritis

Correct Answer & Explanation

. Septic arthritis

Explanation

A synovial fluid WBC count greater than 50,000 cells/mcL with a high PMN percentage (>90%) and low glucose is highly suspicious for bacterial septic arthritis until proven otherwise.

Question 1144

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with a limp, fever, and refusal to bear weight on his right leg. According to the Kocher criteria, which combination of clinical and laboratory findings yields the highest probability of septic arthritis of the hip?

. Non-weight bearing, ESR > 20 mm/hr, WBC > 10,000/mm3, Temperature > 38.0°C
. Non-weight bearing, ESR > 40 mm/hr, WBC > 12,000/mm3, Temperature > 38.5°C
. Limping, ESR > 30 mm/hr, WBC > 15,000/mm3, Temperature > 37.5°C
. Inability to flex hip, CRP > 10 mg/L, WBC > 12,000/mm3, Temperature > 39.0°C
. Non-weight bearing, CRP > 20 mg/L, WBC > 10,000/mm3, Temperature > 38.0°C

Correct Answer & Explanation

. Non-weight bearing, ESR > 40 mm/hr, WBC > 12,000/mm3, Temperature > 38.5°C

Explanation

The classic Kocher criteria include non-weight bearing, ESR > 40 mm/hr, WBC > 12,000/mm3, and Temperature > 38.5°C. When all four criteria are met, the probability of septic arthritis in a pediatric hip is estimated to be 99%.

Question 1145

Topic: Infection, Pharmacology & VTE

A 4-year-old girl refuses to bear weight on her left leg. She has a temperature of 38.6°C (101.5°F), an ESR of 45 mm/hr, a serum WBC count of 14,000/mm3, and refuses to move the hip. According to the Kocher criteria, what is the probability that she has septic arthritis?

. < 10%
. Approx 40%
. Approx 71%
. Approx 93%
. > 99%

Correct Answer & Explanation

. > 99%

Explanation

The Kocher criteria include non-weight-bearing, temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm3. The presence of all four criteria indicates a 99% probability of septic arthritis, warranting urgent joint aspiration.

Question 1146

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in prosthetic joint infections. Which phase of biofilm development involves the downregulation of planktonic genes and the secretion of an extracellular polymeric substance (EPS) matrix?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic proliferation

Correct Answer & Explanation

. Maturation

Explanation

Biofilm formation occurs in stages: 1) Reversible attachment of planktonic bacteria, 2) Irreversible attachment, 3) Maturation (microcolony formation, robust EPS production, downregulation of planktonic genes, and quorum sensing), and 4) Dispersion/detachment. The EPS matrix is heavily secreted during the maturation phase.

Question 1147

Topic: Infection, Pharmacology & VTE
A 35-year-old farmer sustains a highly contaminated Type IIIA open tibia fracture while working in a barn. In addition to standard broad-spectrum Gram-positive and Gram-negative antibiotic coverage, which of the following organisms must be specifically targeted with additional antibiotic prophylaxis?
. Methicillin-resistant Staphylococcus aureus (MRSA)
. Pseudomonas aeruginosa
. Clostridium perfringens
. Enterococcus faecalis
. Acinetobacter baumannii

Correct Answer & Explanation

. Clostridium perfringens

Explanation

Farm injuries and highly contaminated wounds carry a high risk of anaerobic infection, specifically Clostridium perfringens (gas gangrene). High-dose penicillin (or metronidazole/clindamycin for allergic patients) should be added to the antibiotic regimen.

Question 1148

Topic: Infection, Pharmacology & VTE

During a total knee arthroplasty for a severe varus deformity, the knee is found to be tight medially in both flexion and extension. After releasing the deep medial collateral ligament (MCL), what is the next appropriate step in the medial soft tissue release sequence?

. Superficial MCL release off the tibia
. Posteromedial corner and capsule release
. Pes anserinus release
. Medial head of the gastrocnemius release
. Semimembranosus release

Correct Answer & Explanation

. Posteromedial corner and capsule release

Explanation

In a varus knee, the standard sequential medial release to balance both the flexion and extension gaps starts with osteophyte removal and deep MCL release. If the knee remains tight in both flexion and extension, the next structure released is the posteromedial corner and capsule, followed by the superficial MCL, and finally the pes anserinus if further balancing is required.

Question 1149

Topic: Infection, Pharmacology & VTE
A 2-year-old boy presents with a 2-day history of refusal to bear weight on his right leg, a fever of 38.5°C, and an ESR of 55 mm/hr. Joint aspiration yields purulent fluid. Culturing the fluid on traditional solid agar fails to grow organisms, but growth is observed in liquid BACTEC blood culture bottles. What is the most likely pathogen?
. Staphylococcus aureus
. Streptococcus pyogenes
. Kingella kingae
. Haemophilus influenzae type B
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is increasingly recognized as a leading cause of septic arthritis in children aged 6 months to 4 years. It is difficult to grow on standard solid media and requires inoculation into liquid blood culture vials (e.g., BACTEC) for optimal detection.

Question 1150

Topic: Infection, Pharmacology & VTE

During a primary total knee arthroplasty for severe varus osteoarthritis, the knee remains tight medially in both flexion and extension after initial bony cuts. Which sequence of soft tissue release is most appropriate to balance the knee?

. Deep MCL, then posteromedial corner, then superficial MCL
. Superficial MCL, then pes anserinus, then PCL
. Posteromedial corner, then semimembranosus, then deep MCL
. Popliteus, then lateral collateral ligament, then iliotibial band
. PCL, then medial head of gastrocnemius, then superficial MCL

Correct Answer & Explanation

. Deep MCL, then posteromedial corner, then superficial MCL

Explanation

To correct a fixed varus deformity, step-wise medial release is performed starting with osteophytes, followed by the deep medial collateral ligament (MCL). If it remains tight, the release progresses to the posteromedial corner/capsule, and finally the superficial MCL and pes anserinus if necessary.

Question 1151

Topic: Infection, Pharmacology & VTE
Following a total hip arthroplasty, a patient is prescribed Rivaroxaban for deep vein thrombosis (DVT) prophylaxis. What is the precise pharmacological mechanism of action of this medication?
. Reversible, competitive inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Direct, selective inhibition of Factor Xa
. Vitamin K epoxide reductase inhibition
. Activation of antithrombin III to inhibit both Factor Xa and Thrombin

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are novel oral anticoagulants (NOACs) that work as direct, highly selective inhibitors of Factor Xa. This blocks the convergence point of the intrinsic and extrinsic coagulation pathways, preventing the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. LMWH works via antithrombin III.

Question 1152

Topic: Infection, Pharmacology & VTE

A 65-year-old male presents with acute knee pain. Synovial fluid analysis reveals weakly positively birefringent rhomboid-shaped crystals under polarized light microscopy. Which of the following conditions is most strongly associated with these findings?

. Hemochromatosis
. Psoriatic arthritis
. Chronic renal failure
. Lesch-Nyhan syndrome
. Rheumatoid arthritis

Correct Answer & Explanation

. Hemochromatosis

Explanation

The crystals described are calcium pyrophosphate dihydrate (CPPD), which are characteristic of pseudogout. Pseudogout is strongly associated with the '3 Hs': Hyperparathyroidism, Hemochromatosis, and Hypothyroidism, as well as hypomagnesemia and hypophosphatasia. Lesch-Nyhan and chronic renal failure are more typically associated with gout (negatively birefringent needle-shaped monosodium urate crystals).

Question 1153

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent cause of periprosthetic joint infection primarily due to its ability to form a biofilm. Which of the following describes the critical first step in biofilm formation on a metal orthopedic implant?

. Bacterial quorum sensing activation
. Synthesis of bacterial exopolysaccharide glycocalyx
. Adsorption of host proteins (fibronectin/fibrinogen) onto the implant surface
. Shedding of planktonic bacteria into the joint fluid
. Intracellular bacterial invasion into host macrophages

Correct Answer & Explanation

. Adsorption of host proteins (fibronectin/fibrinogen) onto the implant surface

Explanation

The sequence of biofilm formation begins instantly upon implantation with the rapid adsorption of host proteins (such as fibronectin, fibrinogen, and vitronectin) onto the foreign body surface. This forms a conditioning layer that facilitates the subsequent initial adhesion of bacteria, which then proliferate and secrete an exopolysaccharide matrix.

Question 1154

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents refusing to bear weight on his right leg. He has a fever of 39 C, ESR of 55 mm/hr, WBC of 14,000/mm3, and resists all hip range of motion. According to Kocher's criteria, what is the predictive probability that this child has septic arthritis?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The patient meets all four of Kocher's criteria: non-weight-bearing, temperature > 38.5 C, ESR > 40, and WBC > 12,000. The presence of all four predictors yields a 99% probability of septic arthritis.

Question 1155

Topic: Infection, Pharmacology & VTE

A patient presents with an acutely swollen and painful knee. Joint aspiration yields synovial fluid with a WBC count of 85,000 cells/µL, 90% polymorphonuclear leukocytes, and a glucose level significantly lower than serum glucose. What is the most likely diagnosis?

. Osteoarthritis
. Rheumatoid arthritis
. Gouty arthritis
. Septic arthritis
. Traumatic hemarthrosis

Correct Answer & Explanation

. Septic arthritis

Explanation

A synovial fluid WBC count greater than 50,000 cells/µL (often >80,000 in reality) with >75-90% PMNs and low glucose is highly indicative of septic arthritis. Inflammatory arthritis (RA, gout) typically has WBC counts between 2,000 and 50,000 cells/µL.

Question 1156

Topic: Infection, Pharmacology & VTE

Cefazolin is widely used as a prophylactic antibiotic in orthopedic surgery. What is its primary mechanism of action?

. Inhibition of bacterial protein synthesis via the 30S ribosomal subunit
. Inhibition of DNA gyrase
. Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins
. Inhibition of folic acid synthesis
. Disruption of bacterial cell membrane permeability

Correct Answer & Explanation

. Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins

Explanation

Cefazolin is a first-generation cephalosporin (a beta-lactam). Beta-lactams exert their bactericidal effect by binding to penicillin-binding proteins (PBPs), thereby inhibiting the cross-linking of peptidoglycan during bacterial cell wall synthesis.

Question 1157

Topic: Infection, Pharmacology & VTE
An orthopedic surgeon prescribes rivaroxaban for venous thromboembolism prophylaxis following a total hip arthroplasty. What is the mechanism of action of this medication?
. Inhibition of vitamin K epoxide reductase
. Direct inhibition of thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase-1

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by specifically inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K epoxide reductase. Heparin/LMWH acts via antithrombin III.

Question 1158

Topic: Infection, Pharmacology & VTE

A 6-year-old child presents to the emergency department with hip pain and a limp. He refuses to bear weight. His temperature is 38.6°C (101.5°F). Labs show WBC 13,000/mm3, ESR 45 mm/hr, and CRP 2.5 mg/dL. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?

. Less than 5%
. Approximately 40%
. Approximately 71%
. Approximately 93%
. Approximately 99%

Correct Answer & Explanation

. Approximately 99%

Explanation

The Kocher criteria for pediatric septic arthritis of the hip are: 1) Non-weight bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, 4) WBC > 12,000/mm3. This patient meets all 4 criteria. The probability of septic arthritis is approximately 99% when all 4 criteria are present. (3 criteria = 93%, 2 criteria = 40%, 1 criterion = 3%).

Question 1159

Topic: Infection, Pharmacology & VTE
Following a total knee arthroplasty, a patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis. What is the specific mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase inhibitor
. Enhances antithrombin III activity
. Irreversible cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct Factor Xa inhibitors. Dabigatran is a direct thrombin (IIa) inhibitor. Warfarin inhibits vitamin K epoxide reductase. Heparin and LMWH enhance antithrombin III activity.

Question 1160

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in the pathogenesis of prosthetic joint infections. Which of the following phases of biofilm development or bacterial state is targeted most effectively by the adjunctive use of Rifampin?

. Initial reversible bacterial adherence to the implant
. Irreversible attachment via cell-surface adhesins
. Maturation and production of the exopolysaccharide matrix
. Stationary phase planktonic bacteria
. Sessile bacteria embedded within the established biofilm

Correct Answer & Explanation

. Sessile bacteria embedded within the established biofilm

Explanation

Rifampin has a unique molecular ability to penetrate the exopolysaccharide matrix (glycocalyx) of established biofilms and kill sessile (dormant or slow-growing) staphylococcal organisms. It is highly effective against these biofilm-embedded bacteria, which is why it is utilized as an adjunctive treatment in prosthetic joint infections, provided the implant is retained and the bacterial burden has been surgically minimized. Standard IV antibiotics primarily target planktonic (free-floating) bacteria.

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