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Infection, Pharmacology & VTE MCQs

Practice Set 33 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 641

Topic: Infection, Pharmacology & VTE

During the pathogenesis of periprosthetic joint infection, Staphylococcus aureus produces a robust biofilm. What is the primary structural component of the extracellular polymeric substance in this biofilm?

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

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix of S. aureus is primarily composed of polysaccharide intercellular adhesin (PIA), which is synthesized by products of the icaADBC operon. This matrix protects the bacteria from antibiotics and host immune cells.

Question 642

Topic: Infection, Pharmacology & VTE

A 45-year-old man develops a chronic prosthetic joint infection one year after a total knee arthroplasty. Intraoperative cultures yield Staphylococcus epidermidis. The organism's ability to persistently colonize the implant surface and evade the host immune system is primarily mediated by the production of which of the following?

. Panton-Valentine leukocidin
. Biofilm
. Protein A
. Alpha-toxin
. Endotoxin

Correct Answer & Explanation

. Biofilm

Explanation

Staphylococcus epidermidis forms a robust polysaccharide glycocalyx, or biofilm, that facilitates adherence to inert implant surfaces. This biofilm acts as a physical barrier, protecting the bacteria from both host cellular immunity and systemic antimicrobial therapy.

Question 643

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain, fever of 38.8°C (101.8°F), and refusal to bear weight. His WBC count is 14,000/mm3 and ESR is 55 mm/hr. According to Kocher's criteria, what is the approximate probability that this child has septic arthritis?

. 10%
. 40%
. 70%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The patient has 4 of 4 Kocher criteria (fever >38.5°C, non-weight-bearing, WBC >12,000, ESR >40). This correlates with a 99% probability of septic arthritis.

Question 644

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with an atraumatic limp and refuses to bear weight on his right leg. His temperature is 38.0°C (100.4°F), WBC count is 13,000/mm³, and ESR is 45 mm/hr. 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

. 93%

Explanation

This patient meets three of the four Kocher criteria: non-weight-bearing, WBC >12,000/mm³, and ESR >40 mm/hr (his temperature is below the 38.5°C threshold). Having three criteria yields a 93% probability of septic arthritis.

Question 645

Topic: Infection, Pharmacology & VTE
A 5-year-old girl presents with a 2-day history of right hip pain, a limp, and a fever of 38.6°C (101.5°F). She is refusing to bear weight. Her serum WBC count is 13,000/mm³, and ESR is 45 mm/hr. According to the Kocher criteria, what is the probability of septic arthritis?
. Less than 10%
. 30%
. 50%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The patient meets 4 out of 4 Kocher criteria (fever >38.5°C, non-weight-bearing, WBC >12,000, ESR >40). The probability of septic arthritis with 4 criteria is approximately 93-99%, mandating immediate hip aspiration.

Question 646

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with an inability to bear weight on his right leg. His oral temperature is 38.6°C (101.5°F), ESR is 45 mm/hr, and peripheral WBC is 13,500/mm³. Radiographs of the hip are normal. According to the Kocher criteria, what is the most appropriate next step in management?
. Prescribe oral NSAIDs and observe at home
. Initiate empiric oral antibiotics
. Perform an MRI of the right hip with contrast
. Perform an ultrasound-guided aspiration of the right hip joint
. Apply a Pavlik harness for pain relief

Correct Answer & Explanation

. Perform an ultrasound-guided aspiration of the right hip joint

Explanation

This patient meets all four Kocher criteria (fever, inability to bear weight, ESR >40, WBC >12,000), giving him a 99% probability of septic arthritis. The essential next step is an urgent joint aspiration to confirm the diagnosis and obtain cultures before surgical debridement.

Question 647

Topic: Infection, Pharmacology & VTE
A 3-year-old girl is brought to the emergency department for a limp. She has a temperature of 38.8°C, an ESR of 45 mm/hr, and a WBC count of 13,000/mm³. She refuses to bear weight on her right leg. According to the Kocher criteria, what is the approximate probability that she has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

This patient has all four Kocher predictors: fever >38.5°C, non-weight bearing, ESR >40, and WBC >12,000. The presence of all four criteria yields a 93% to 99% probability of septic arthritis.

Question 648

Topic: Infection, Pharmacology & VTE

A 2-year-old boy presents with a 3-day history of fever, irritability, and refusal to bear weight on his right leg. MRI reveals a subperiosteal abscess of the proximal femoral metaphysis with extension into the hip joint. What is the most likely mechanism of joint involvement?

. Hematogenous spread directly to the synovium
. Direct trauma introducing environmental bacteria
. Transphyseal spread through vascular channels
. Spread through the intra-articular metaphysis
. Lymphatic spread from a pelvic focus

Correct Answer & Explanation

. Spread through the intra-articular metaphysis

Explanation

In the proximal femur, the metaphysis is intracapsular. Therefore, metaphyseal osteomyelitis can easily break through the cortex directly into the joint space, causing a concurrent septic arthritis.

Question 649

Topic: Infection, Pharmacology & VTE

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

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

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria include non-weight-bearing status, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000/mm3. Having all 4 positive criteria correlates with a 99% probability of septic arthritis.

Question 650

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, a temperature of 38.8°C (101.8°F), inability to bear weight, and a WBC count of 14,000/mm3. ESR is 55 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis rather than transient synovitis?

. 3%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The patient meets all four Kocher criteria (fever >38.5°C, inability to bear weight, WBC >12,000, ESR >40). The probability of septic arthritis with 4 positive predictors is approximately 99%.

Question 651

Topic: Infection, Pharmacology & VTE

A 14-month-old girl presents with refusal to bear weight on her right leg. She is afebrile with normal inflammatory markers. MRI shows early osteomyelitis in the distal tibial metaphysis. Given her age, what fastidious organism should be highly suspected, and how can its culture yield be optimized?

. Staphylococcus aureus; culture on MacConkey agar
. Kingella kingae; inoculate directly into aerobic blood culture vials
. Group B Streptococcus; inoculate into anaerobic vials
. Salmonella enteritidis; culture on Thayer-Martin agar
. Pseudomonas aeruginosa; culture on chocolate agar

Correct Answer & Explanation

. Kingella kingae; inoculate directly into aerobic blood culture vials

Explanation

Kingella kingae is a leading cause of pediatric osteoarticular infections in children aged 6 to 36 months, often presenting with mild systemic symptoms. Culturing aspirates directly into aerobic blood culture vials significantly improves detection.

Question 652

Topic: Infection, Pharmacology & VTE

A 3-year-old girl refuses to bear weight on her right leg for 2 days. Her temperature is 38.8 C, ESR is 50 mm/hr, and peripheral WBC is 14,000. Ultrasound confirms a hip effusion. According to the Kocher criteria, what is the probability of septic arthritis?

. Less than 10 percent
. Approximately 30 percent
. Approximately 50 percent
. Greater than 90 percent
. Exactly 100 percent

Correct Answer & Explanation

. Greater than 90 percent

Explanation

The patient meets all four Kocher criteria: non-weight bearing, temperature >38.5 C, ESR >40, and WBC >12,000. The presence of four criteria is associated with a 93 to 99 percent probability of septic arthritis.

Question 653

Topic: Infection, Pharmacology & VTE

When attempting to differentiate transient synovitis from septic arthritis of the pediatric hip, which laboratory value has been shown to be the strongest independent multivariate predictor for septic arthritis?

. Erythrocyte sedimentation rate (ESR)
. Peripheral white blood cell count
. C-reactive protein (CRP) level greater than 2.0 mg/dL
. Serum procalcitonin
. Interleukin-6 (IL-6)

Correct Answer & Explanation

. C-reactive protein (CRP) level greater than 2.0 mg/dL

Explanation

C-reactive protein (CRP) greater than 2.0 mg/dL has been validated as the single strongest independent predictor for septic arthritis, and it is frequently added to modified Kocher criteria to increase diagnostic accuracy.

Question 654

Topic: Infection, Pharmacology & VTE

According to the latest guidelines from the American Academy of Orthopaedic Surgeons (AAOS) and the American Association of Hip and Knee Surgeons (AAHKS), what is the recommended pharmacological strategy for routine venous thromboembolism (VTE) prophylaxis in a standard-risk patient undergoing primary THA?

. Warfarin with an INR target of 2.0-3.0 for 4 weeks
. Aspirin 81 mg twice daily for 2 to 6 weeks
. Therapeutic enoxaparin bridging
. Intravenous unfractionated heparin
. Mechanical prophylaxis alone (SCDs)

Correct Answer & Explanation

. Aspirin 81 mg twice daily for 2 to 6 weeks

Explanation

Recent AAOS/AAHKS guidelines strongly support the use of aspirin for VTE prophylaxis in standard-risk patients undergoing primary total joint arthroplasty, owing to its efficacy and lower risk of major bleeding compared to potent anticoagulants.

Question 655

Topic: Infection, Pharmacology & VTE

A 52-year-old female presents with persistent lateral hip pain exacerbated by prolonged walking and lying on the affected side. Physical examination reveals localized point tenderness directly over the greater trochanter. She has failed physical therapy and NSAIDs. When performing a corticosteroid injection, which anatomical space is the primary target?

. Intra-articular hip joint
. Subgluteus minimus bursa
. Subgluteus medius bursa
. Subgluteus maximus (trochanteric) bursa
. Ischial bursa

Correct Answer & Explanation

. Subgluteus maximus (trochanteric) bursa

Explanation

Greater trochanteric pain syndrome (GTPS) is most commonly related to pathology of the gluteus medius/minimus tendons or inflammation of the overlying bursa. Therapeutic corticosteroid injections for GTPS are targeted into the subgluteus maximus (trochanteric) bursa.

Question 656

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, refusal to bear weight, a temperature of 38.8 C (101.8 F), an ESR of 45 mm/hr, and a serum WBC count of 13,000/mm3. According to the Kocher criteria, what is the probability that he has septic arthritis?

. 2%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The four Kocher criteria are non-weight-bearing, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000. With all 4 criteria present, the probability of septic arthritis is approximately 99%.

Question 657

Topic: Infection, Pharmacology & VTE
A 40-year-old farmer sustains a Grade IIIb open tibia fracture heavily contaminated with soil and manure. Based on current trauma guidelines, which of the following prophylactic antibiotic regimens is most appropriate upon presentation?
. Cefazolin monotherapy for 24 hours
. Ceftriaxone and vancomycin for 7 days
. Cefazolin and clindamycin for 48 hours
. Ceftriaxone, vancomycin, and high-dose penicillin for 72 hours
. Ciprofloxacin monotherapy for 5 days

Correct Answer & Explanation

. Ceftriaxone, vancomycin, and high-dose penicillin for 72 hours

Explanation

High-energy Grade III open fractures require broad-spectrum coverage, typically a cephalosporin and vancomycin. When there is gross soil or farm contamination, adding high-dose penicillin is strongly recommended to cover for Clostridium species.

Question 658

Topic: Infection, Pharmacology & VTE

A 60-year-old diabetic male undergoes a lumbar microdiscectomy. Three weeks later, he presents with severe, unremitting back pain and elevated inflammatory markers. An MRI shows fluid in the disc space with endplate enhancement. What is the most likely causative organism?

. Pseudomonas aeruginosa
. Escherichia coli
. Staphylococcus aureus
. Streptococcus epidermidis
. Mycobacterium tuberculosis

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is the most common causative organism for both spontaneous and postoperative pyogenic discitis and vertebral osteomyelitis.

Question 659

Topic: Infection, Pharmacology & VTE

A diabetic patient presents with a chronic plantar ulcer under the first metatarsal head. There is no systemic toxicity. Which clinical finding has the highest positive predictive value for underlying osteomyelitis?

. Erythema extending 2 cm from the ulcer margins
. An elevated erythrocyte sedimentation rate (ESR) > 40 mm/hr
. A positive probe-to-bone test
. Periosteal reaction on plain radiographs
. An elevated C-reactive protein (CRP)

Correct Answer & Explanation

. A positive probe-to-bone test

Explanation

A positive probe-to-bone test (feeling a hard, gritty surface) in the presence of a chronic diabetic foot ulcer is highly predictive of underlying osteomyelitis, often confirming the diagnosis without the immediate need for an MRI.

Question 660

Topic: Infection, Pharmacology & VTE

A patient presents with acute monoarticular knee swelling. A joint aspiration is performed. The synovial fluid has a leukocyte count of 75,000 cells/mm^3 with 90% polymorphonuclear cells. Which of the following is the most appropriate next step in management?

. Intra-articular corticosteroid injection
. Observation and NSAIDs
. Uric acid level and polarized light microscopy
. Urgent surgical irrigation and debridement
. MRI of the knee

Correct Answer & Explanation

. Urgent surgical irrigation and debridement

Explanation

A synovial fluid leukocyte count >50,000 cells/mm^3 with a predominance of PMNs is highly suspicious for septic arthritis. The gold standard treatment is urgent surgical irrigation and debridement along with empiric intravenous antibiotics.

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