Menu

Infection, Pharmacology & VTE MCQs

Practice Set 51 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 1001

Topic: Infection, Pharmacology & VTE
According to the Kocher criteria, what is the probability of septic arthritis in a pediatric hip if a patient presents with a fever >38.5 C, non-weight-bearing status, ESR >40 mm/hr, and a serum WBC >12,000/mm3?
. <10%
. 30%
. 59%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria use four independent predictors to differentiate septic arthritis from transient synovitis: fever > 38.5 C, non-weight-bearing, ESR > 40, and WBC > 12,000. The probability of septic arthritis is approximately 3% for 1 predictor, 40% for 2, 93% for 3, and 99% when all 4 predictors are present.

Question 1002

Topic: Infection, Pharmacology & VTE
A 4-year-old boy is brought to the ED with right hip pain. He is refusing to bear weight on the right leg. His temperature is 38.6°C (101.5°F). Labs reveal an ESR of 45 mm/hr and a serum WBC of 10,000 cells/mm³. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include: 1) Non-weight-bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, and 4) Serum WBC > 12,000 cells/mm³. This patient meets 3 criteria (NWB, Temp > 38.5, ESR > 40). According to Kocher's original study, the probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 1003

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, fever (38.8 C), and inability to bear weight. His ESR is 55 mm/hr, CRP is 35 mg/L, and WBC count is 14,000/mm3. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?

. Less than 10%
. Approximately 40%
. Approximately 70%
. Greater than 90%
. 100% diagnostic certainty

Correct Answer & Explanation

. Less than 10%

Explanation

The patient meets all four Kocher criteria: non-weight bearing, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000/mm3. The presence of four criteria yields a 93-99% predictive probability for septic arthritis.

Question 1004

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with an acute onset of a right-sided limp. He has a temperature of 38.6 C (101.5 F), an ESR of 45 mm/hr, a WBC count of 13,000/mm3, and refuses to bear weight. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?

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

Correct Answer & Explanation

. 3%

Explanation

The Kocher criteria for septic arthritis 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.

Question 1005

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, Staphylococcus epidermidis utilizes a specific structural component to adhere to the biomedical implant and form a biofilm. Which of the following mediates this initial adherence and biofilm maturation?

. Protein A
. M protein
. Polysaccharide intercellular adhesin (PIA)
. Tetrodotoxin
. Alpha toxin

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis forms a biofilm by producing a polysaccharide intercellular adhesin (PIA), which is synthesized by the ica operon. This glycocalyx allows adherence to implants and protects against host defenses and antibiotics.

Question 1006

Topic: Infection, Pharmacology & VTE
A patient is prescribed enoxaparin for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary mechanism of action of this medication?
. Direct thrombin inhibition
. Inhibition of vitamin K epoxide reductase
. Binding to antithrombin III, primarily inhibiting Factor Xa
. Binding to plasminogen to prevent fibrinolysis
. Irreversible inhibition of cyclooxygenase

Correct Answer & Explanation

. Binding to antithrombin III, primarily inhibiting Factor Xa

Explanation

Enoxaparin is a low-molecular-weight heparin (LMWH). It binds to antithrombin III, potentiating its activity, but has a much higher ratio of anti-Factor Xa to anti-Factor IIa (thrombin) activity compared to unfractionated heparin.

Question 1007

Topic: Infection, Pharmacology & VTE
A patient is prescribed Enoxaparin for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Potentiation of antithrombin III to preferentially inhibit Factor Xa
. Irreversible inhibition of platelet cyclooxygenase
. Direct inhibition of Factor Xa without binding antithrombin III

Correct Answer & Explanation

. Potentiation of antithrombin III to preferentially inhibit Factor Xa

Explanation

Enoxaparin is a Low Molecular Weight Heparin (LMWH). It exerts its anticoagulant effect by binding to antithrombin III, which then preferentially inactivates Factor Xa over Factor IIa (thrombin).

Question 1008

Topic: Infection, Pharmacology & VTE

In the pathogenesis of implant-associated osteomyelitis, Staphylococcus aureus establishes a dense biofilm. What is the primary constituent of the extracellular polymeric substance (EPS) that protects the bacteria from host immunity?

. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Lipopolysaccharide (LPS)
. Fibronectin-binding protein
. Protein A

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix in Staphylococcus aureus infections is primarily composed of Polysaccharide Intercellular Adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG). This slime layer anchors the biofilm and shields bacteria from phagocytosis and systemic antibiotics.

Question 1009

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

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and Apixaban are highly selective, direct oral inhibitors of Factor Xa. By inhibiting Factor Xa, they halt the coagulation cascade at the crucial intersection of the intrinsic and extrinsic pathways, preventing the conversion of prothrombin to thrombin.

Question 1010

Topic: Infection, Pharmacology & VTE

A 68-year-old male is undergoing treatment for a prosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis of this organism's persistence on the implant surface is most dependent on the production of:

. Alpha-toxin
. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin
. Toxic shock syndrome toxin-1

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis forms robust biofilms on inert implant surfaces. The extracellular polymeric substance of the biofilm is largely composed of poly-N-acetylglucosamine, which is synthesized by Polysaccharide Intercellular Adhesin (PIA) encoded by the ica operon.

Question 1011

Topic: Infection, Pharmacology & VTE

A 72-year-old female presents with acute knee pain. Aspiration reveals negatively birefringent, needle-shaped crystals under polarized light microscopy. The inflammatory response triggered by these crystals is primarily mediated by the activation of which complex?

. Toll-like receptor 4 (TLR4)
. NF-kappaB pathway
. NLRP3 inflammasome
. Janus kinase (JAK) STAT pathway
. Cyclooxygenase-2 (COX-2)

Correct Answer & Explanation

. NLRP3 inflammasome

Explanation

Gout is caused by monosodium urate crystals, which are phagocytosed by macrophages. This triggers the NLRP3 inflammasome, leading to the cleavage of pro-IL-1beta into active IL-1beta by caspase-1, thereby initiating an intense local inflammatory response.

Question 1012

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent causative organism in chronic periprosthetic joint infections due to its robust ability to adhere to inert implant surfaces. This adherence and subsequent resistance to host immune clearance and systemic antibiotics is primarily mediated by the pathogen's production of which of the following?

. Coagulase
. Protein A
. Alpha-toxin
. A polysaccharide glycocalyx
. Panton-Valentine leukocidin

Correct Answer & Explanation

. A polysaccharide glycocalyx

Explanation

Staphylococcus epidermidis (a coagulase-negative staphylococcus) is an opportunistic pathogen known for its ability to form a dense biofilm on foreign materials, such as orthopedic implants. This biofilm formation relies on the secretion of an extracellular polymeric substance, predominantly a polysaccharide glycocalyx (often referred to as 'slime'), which mediates firm adhesion and shields the bacteria from antibiotics and phagocytosis.

Question 1013

Topic: Infection, Pharmacology & VTE

To minimize surgical site infections during clean orthopedic operations, prophylactic intravenous antibiotics must be maintained at therapeutic tissue concentrations throughout the case. For an adult patient receiving standard cefazolin prophylaxis, which intraoperative redosing protocol is recommended by the AAOS and CDC guidelines?

. Every 2 hours or after 500 mL of intraoperative blood loss
. Every 3 hours or after 1000 mL of intraoperative blood loss
. Every 4 hours or after 1500 mL of intraoperative blood loss
. Every 6 hours or after 2000 mL of intraoperative blood loss
. Every 8 hours regardless of intraoperative blood loss

Correct Answer & Explanation

. Every 4 hours or after 1500 mL of intraoperative blood loss

Explanation

Cefazolin is a first-generation cephalosporin with a half-life of approximately 1.8 to 2 hours. Current clinical practice guidelines from the AAOS, CDC, and WHO recommend redosing cefazolin every 4 hours during prolonged surgical procedures (measured from the time of the initial preoperative dose) or if major intraoperative blood loss (> 1,500 mL) occurs, to ensure tissue concentrations remain above the minimum inhibitory concentration (MIC) for target pathogens.

Question 1014

Topic: Infection, Pharmacology & VTE

A patient undergoing total hip arthroplasty has a history of heparin-induced thrombocytopenia (HIT). The surgeon elects to use a direct thrombin inhibitor for postoperative DVT prophylaxis. Which of the following medications fits this description?

. Rivaroxaban
. Fondaparinux
. Dabigatran
. Apixaban
. Warfarin

Correct Answer & Explanation

. Dabigatran

Explanation

Dabigatran is an oral direct thrombin (Factor IIa) inhibitor. Rivaroxaban and Apixaban are direct Factor Xa inhibitors, while Fondaparinux is an indirect Factor Xa inhibitor.

Question 1015

Topic: Infection, Pharmacology & VTE

In implant-related orthopedic infections, bacteria such as Staphylococcus epidermidis evade host immune responses and antibiotic penetration by producing a biofilm. What is the primary structural component of this biofilm matrix?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide intercellular adhesin (glycocalyx)
. Teichoic acid
. Fibronectin-binding proteins

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (glycocalyx)

Explanation

The biofilm matrix is predominantly composed of an exopolysaccharide known as polysaccharide intercellular adhesin (PIA) or glycocalyx. This slimy matrix encases the bacteria, protecting them from immune cells and restricting antimicrobial penetration.

Question 1016

Topic: Infection, Pharmacology & VTE

A 60-year-old male with poorly controlled diabetes mellitus presents with a chronic, draining neuropathic ulcer under the 3rd metatarsal head. A probe easily contacts bone at the base of the ulcer. MRI demonstrates high T2 signal and low T1 signal replacing the marrow fat of the 3rd metatarsal head. What is the single most common causative organism for osteomyelitis in this clinical setting?

. Pseudomonas aeruginosa
. Staphylococcus aureus
. Streptococcus epidermidis
. Bacteroides fragilis
. Escherichia coli

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

A positive probe-to-bone test is highly predictive of osteomyelitis in the setting of a diabetic foot ulcer. While diabetic foot infections are frequently polymicrobial (especially chronic or ischemic wounds), Staphylococcus aureus is unequivocally the single most common causative pathogen isolated in diabetic pedal osteomyelitis.

Question 1017

Topic: Infection, Pharmacology & VTE

A 35-year-old landscaper accidentally steps on a nail that completely penetrates through the sole of his athletic rubber-soled sneaker into his foot. He presents two weeks later with signs of osteomyelitis. What is the most likely causative organism specific to this mechanism?

. Staphylococcus aureus
. Streptococcus pyogenes
. Pseudomonas aeruginosa
. Clostridium perfringens
. Pasteurella multocida

Correct Answer & Explanation

. Pseudomonas aeruginosa

Explanation

While Staphylococcus aureus is the most common cause of osteomyelitis overall, puncture wounds through the rubber sole of an athletic shoe carry a unique and highly classic risk for Pseudomonas aeruginosa osteomyelitis. The rubber sole creates an optimal environment for Pseudomonas colonization.

Question 1018

Topic: Infection, Pharmacology & VTE

A 58-year-old diabetic patient presents with a swollen, red, and warm foot.

Radiographs show no fractures but severe osteopenia. To differentiate clinically between an acute Charcot neuroarthropathy and cellulitis/osteomyelitis, the physician performs the leg elevation test. What is the expected result if the diagnosis is acute Charcot?

. The erythema and swelling worsen after 5 minutes of elevation.
. The erythema significantly diminishes or resolves after 5-10 minutes of elevation.
. The patient experiences severe, unrelenting pain upon elevation.
. Bounding pulses disappear after 5 minutes of elevation.
. The erythema remains completely unchanged regardless of position.

Correct Answer & Explanation

. The erythema significantly diminishes or resolves after 5-10 minutes of elevation.

Explanation

The elevation test takes advantage of dependent rubor seen in the autonomic neuropathy of Charcot. Elevating the limb for 5-10 minutes will cause the erythema to dissipate in acute Charcot, whereas erythema from infection will persist.

Question 1019

Topic: Infection, Pharmacology & VTE

During a primary TKA for a severe varus deformity, the medial compartment remains excessively tight in both flexion and extension after standard bone resections. Which of the following soft tissue structures should ideally be released first to correct this imbalance?

. Superficial medial collateral ligament
. Deep medial collateral ligament
. Pes anserinus
. Semimembranosus tendon
. Posterior cruciate ligament

Correct Answer & Explanation

. Deep medial collateral ligament

Explanation

In the stepwise soft tissue release for a severe varus knee, the deep medial collateral ligament is typically released first. If further balancing is needed, subsequent releases may include the posteromedial capsule and progressive fractional lengthening of the superficial MCL.

Question 1020

Topic: Infection, Pharmacology & VTE

A 66-year-old male with severe varus osteoarthritis is undergoing a primary TKA. During the procedure, the medial gap remains tight in both flexion and extension despite removal of peripheral osteophytes. What is the most appropriate sequential release to balance this varus deformity?

. Superficial MCL, deep MCL, pes anserinus
. Deep MCL, posteromedial corner, superficial MCL (pie-crusting)
. Pes anserinus, deep MCL, semimembranosus
. Posterior cruciate ligament, superficial MCL, lateral collateral ligament
. Popliteus, iliotibial band, lateral collateral ligament

Correct Answer & Explanation

. Deep MCL, posteromedial corner, superficial MCL (pie-crusting)

Explanation

For a tight medial compartment, sequential release begins with peripheral osteophytes and the deep MCL, followed by the posteromedial capsule. If still tight, pie-crusting or release of the superficial MCL is performed.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page