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Infection, Pharmacology & VTE MCQs

Practice Set 20 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 381

Topic: Infection, Pharmacology & VTE
Hip pain of 1-month duration has developed in a 72-year-old man with a previous total hip arthroplasty. He underwent dental work 6 weeks ago. Aspiration shows a white blood cell count of more than 6,000 cells/μL (reference range 4,500 to 11,000 cells/μL) and the presence of gram-positive cocci in clusters on Gram stain. The orthopaedic surgeon recommends urgent debridement and irrigation. Fixation of the components is judged to be stable, and the surgeon elects to retain the implants. The patient has a final culture that reveals methicillin-resistant Staphylococcus aureus (MRSA). If the attending physician recommends the two-stage protocol, including the use of an antibiotic-cement spacer, what is the most likely prognosis for this patient?
. Better functional outcome than that associated with infections from sensitive organisms
. Same functional outcome as that associated with infections from sensitive organisms
. Same prognosis for eradication of infection as that associated with infections from sensitive organisms
. Poorer prognosis for eradication of infection than that associated with infection from sensitive organisms

Correct Answer & Explanation

. Poorer prognosis for eradication of infection than that associated with infection from sensitive organisms

Explanation

DISCUSSION: The patient has a late infection of at least 4 weeks symptomatic duration that most likely is hematogenous in etiology. This infection is not an acute hematogenous infection that can successfully be treated with irrigation and debridement. Retention of the implants with debridement and irrigation alone has been associated with a poor prognosis. In a recent study, the success rate was only 44% in a series of 104 patients at a mean 5.7-year follow-up. In one study of 50 infections attributable to MRSA or methicillin-resistant Staphylococcus epidermidis organisms treated with a two-stage protocol, the failure rate was 21%. Patients who experienced successful infection treatment had lower functional outcome measures using the Western Ontario and McMaster Universities Osteoarthritis Index, the University of California Los Angeles Activity Score, and the 12-item Oxford Knee Score, however.

Question 382

Topic: Infection, Pharmacology & VTE
The figure below shows the abdominal radiograph obtained from a 70-year-old woman who experiences nausea and abdominal tightness 48 hours following left total knee arthroplasty performed under general anesthesia. She received 24 hours of cefazolin antibiotic prophylaxis and a patient-controlled analgesia narcotic pump for pain management. She has been receiving warfarin for thromboembolic prophylaxis. Her severe abdominal distension and markedly decreased bowel sounds are most likely secondary to the administration of
. general anesthesia.
. antibiotics.
. warfarin.
. narcotics.

Correct Answer & Explanation

. narcotics.

Explanation

DISCUSSION: The radiograph reveals severe intestinal dilatation, which has occurred as the result of acute colonic pseudo-obstruction and is associated with excessive narcotic administration following total joint arthroplasty. Anesthetic type, antibiotic administration, and warfarin have not been associated with this obstruction. Electrolyte imbalances such as hypokalemia have been associated with postsurgical acute colonic pseudo-obstruction.

Question 383

Topic: Infection, Pharmacology & VTE

A 22-year-old sustains an acute ACL tear and a complete distal avulsion of the MCL from its tibial insertion. MRI reveals the distal end of the MCL is displaced superficial to the pes anserinus tendons. What is the most appropriate management for the MCL injury?

. Brace the knee for 6 weeks, followed by ACL reconstruction
. Acute surgical repair of the MCL, with delayed ACL reconstruction
. Corticosteroid injection into the pes bursa to prevent scarring
. Immediate ACL reconstruction leaving the MCL to heal secondarily
. Excision of the torn MCL to prevent symptomatic painful neuroma

Correct Answer & Explanation

. Brace the knee for 6 weeks, followed by ACL reconstruction

Explanation

A distal tibial avulsion of the MCL displaced superficial to the pes anserinus is termed a 'Stener-like lesion of the knee.' Because the pes tendons physically block anatomic reduction, this injury cannot heal nonoperatively with bracing. Acute surgical repair of the MCL is indicated.

Question 384

Topic: Infection, Pharmacology & VTE
The mother of a 26-month-old boy reports that he has been unwilling to bear weight on his left lower extremity since he awoke this morning. She denies any history of trauma. He has a temperature of 99.4°F (37.4°C), and examination reveals that abduction of the left hip is limited to 30°. Laboratory studies show a WBC of 11,000/mm³ and an erythrocyte sedimentation rate of 22 mm/h. A radiograph of the pelvis is shown in Figure 13. Management should consist of
. aspiration of the hip.
. a bone scan.
. an MRI scan.
. bed rest, frequent temperature checks, and reevaluation in 24 to 48 hours.
. hospital admission and placement in traction.

Correct Answer & Explanation

. bed rest, frequent temperature checks, and reevaluation in 24 to 48 hours.

Explanation

The most likely diagnosis is transient synovitis. Initial management should consist of bed rest and serial observation to rule out atypical septic arthritis of the hip. In an unreliable family situation, hospitalization for bed rest and observation may be indicated. Transient synovitis of the hip in children is a diagnosis of exclusion; other possibilities should be explored if the patient’s symptoms do not follow a typical course and resolve in 4 to 21 days.

Question 385

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with a draining sinus tract over his tibial shaft fracture, which was treated with an intramedullary nail 6 months ago. Cultures grow Staphylococcus epidermidis. During the process of biofilm formation on the hardware, which specific mechanism regulates the transition from initial bacterial attachment to mature biofilm architecture through complex cell-to-cell communication?

. Quorum sensing
. Chemotaxis
. Opsonization
. Phagocytosis
. Transduction

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is the mechanism of cell-to-cell communication used by bacteria (such as S. aureus and S. epidermidis) to coordinate gene expression in response to population density. Once a critical threshold is reached, quorum sensing triggers the production of the extracellular polymeric substance (EPS) matrix and leads to biofilm maturation.

Question 386

Topic: Infection, Pharmacology & VTE
A 55-year-old diabetic patient presents with severe pain out of proportion to physical exam findings in his lower leg, 3 days after sustaining a minor abrasion. Radiographs demonstrate tracking of subcutaneous gas. Laboratory workup reveals a WBC of 22,000/µL, CRP 250 mg/L, and Sodium 128 mEq/L. What is the most critical next step in management?
. Intravenous administration of vancomycin and piperacillin-tazobactam followed by close observation
. MRI of the lower extremity with and without contrast to define the extent of involvement
. Immediate surgical exploration and radical debridement in the operating room
. Transfer for hyperbaric oxygen therapy
. Bedside incision and drainage of the superficial abrasion

Correct Answer & Explanation

. Immediate surgical exploration and radical debridement in the operating room

Explanation

This clinical picture, including pain out of proportion, subcutaneous gas, and laboratory derangements, is highly indicative of necrotizing fasciitis. This is a surgical emergency. Immediate aggressive surgical debridement is life-saving and takes precedence over imaging or waiting for antibiotic efficacy.

Question 387

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents to the emergency department with a 2-day history of right hip pain and complete refusal to bear weight. His temperature is 38.6°C (101.5°F), WBC count is 13.5 x 10^9/L, ESR is 45 mm/hr, and CRP is 25 mg/L. According to the classic Kocher criteria, what is the approximate statistical probability that this child has a septic joint?

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

Correct Answer & Explanation

. 3%

Explanation

The Kocher criteria for pediatric septic arthritis of the hip include: Non-weight-bearing, Temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12.0 x 10^9/L. This patient meets all 4 criteria. The probability of septic arthritis is approximately: 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 93%, 4 criteria = 99%.

Question 388

Topic: Infection, Pharmacology & VTE

A 10-year-old African American girl with sickle cell disease develops osteomyelitis of the diaphysis of her right femur. While S. aureus is a common pathogen, she is at uniquely elevated risk for Salmonella osteomyelitis. Which of the following pathophysiological mechanisms most directly explains the source of the Salmonella bacteremia in this patient population?

. Direct bacterial inoculation from chronic vaso-occlusive leg ulcers
. Microinfarction of the intestinal mucosa permitting bacterial translocation
. Defective humoral immunity leading to inability to opsonize encapsulated organisms
. Increased affinity of Salmonella for abnormal Hemoglobin S
. Impaired complement activation specifically targeting Gram-negative rods

Correct Answer & Explanation

. Direct bacterial inoculation from chronic vaso-occlusive leg ulcers

Explanation

In patients with sickle cell disease, vaso-occlusion within the microvasculature of the gastrointestinal tract leads to localized bowel ischemia and microinfarcts. This compromises the mucosal barrier, allowing for the translocation of Salmonella species (which colonize the gut) into the systemic circulation. Additionally, infarcted bone marrow provides a favorable nidus for these bacteria to settle and proliferate.

Question 389

Topic: Infection, Pharmacology & VTE
A 60-year-old patient with chronic osteomyelitis of the tibia is evaluated for surgical management. The infection is classified as Cierny-Mader Type III-B. What does this classification specifically indicate about the disease pattern and the host?
. Medullary osteomyelitis in a healthy host
. Superficial osteomyelitis in a host with systemic compromise
. Localized (cortical) osteomyelitis in a host with systemic or local immune compromise
. Diffuse (mechanically unstable) osteomyelitis in a healthy host
. Medullary osteomyelitis requiring a local tissue flap

Correct Answer & Explanation

. Localized (cortical) osteomyelitis in a host with systemic or local immune compromise

Explanation

The Cierny-Mader classification evaluates both the anatomic extent of the infection and the physiologic status of the host. Type III indicates localized (cortical) osteomyelitis, and Type B indicates a compromised host (local or systemic).

Question 390

Topic: Infection, Pharmacology & VTE
A 42-year-old female presents with chronic osteomyelitis of the femur. The infection is characterized as a diffuse osteomyelitis involving the entire circumference of the segment, necessitating an intercalary resection. She has a history of smoking and poorly controlled diabetes. According to the Cierny-Mader classification, what is her clinical stage?
. Stage I C
. Stage II B
. Stage III A
. Stage IV B
. Stage IV A

Correct Answer & Explanation

. Stage IV B

Explanation

The Cierny-Mader system classifies osteomyelitis by anatomy (I: medullary, II: superficial, III: localized, IV: diffuse) and host status (A: normal, B: compromised, C: treatment worse than disease). Diffuse involvement causing instability or requiring segmental resection in a diabetic host is Type IV B.

Question 391

Topic: Infection, Pharmacology & VTE

A 65-year-old male is undergoing treatment for a retained orthopedic implant infection caused by methicillin-susceptible Staphylococcus aureus. Which of the following antibiotics is uniquely effective against the stationary-phase bacteria residing deep within the established biofilm?

. Cefazolin
. Vancomycin
. Rifampin
. Daptomycin
. Linezolid

Correct Answer & Explanation

. Cefazolin

Explanation

Rifampin has high penetrability into biofilms and unique bactericidal activity against stationary-phase staphylococci. It should never be used as monotherapy due to rapid resistance, but is a critical adjunct in retained hardware infections.

Question 392

Topic: Infection, Pharmacology & VTE

A 32-year-old male is treated for an acute periprosthetic infection of a tibia intramedullary nail with debridement, antibiotics, and implant retention (DAIR). Cultures return positive for methicillin-resistant Staphylococcus aureus (MRSA). Which of the following adjunctive oral antibiotics is most critical for penetrating the established bacterial biofilm on the retained hardware?

. Linezolid
. Clindamycin
. Rifampin
. Ciprofloxacin
. Trimethoprim-sulfamethoxazole

Correct Answer & Explanation

. Linezolid

Explanation

Rifampin has high activity against staphylococcal species residing in the stationary phase within biofilms. It should never be used as monotherapy due to rapid resistance development, but is an essential adjunct in implant-retained staphylococcal infections.

Question 393

Topic: Infection, Pharmacology & VTE

A 24-year-old male sustains an open distal tibia fracture after crashing his ATV into a freshwater lake. He is started on broad-spectrum antibiotics and taken for urgent debridement. To adequately cover the most characteristic virulent pathogen associated with freshwater contamination, which of the following antibiotics is typically recommended?

. Penicillin G
. Vancomycin
. Fluoroquinolone or Third-generation Cephalosporin
. Clindamycin
. Doxycycline

Correct Answer & Explanation

. Penicillin G

Explanation

Aeromonas hydrophila is the classic pathogen associated with freshwater injuries. It is typically susceptible to fluoroquinolones, third-generation cephalosporins, and aminoglycosides, making them crucial additions to the antibiotic regimen.

Question 394

Topic: Infection, Pharmacology & VTE

A 12-year-old girl is evaluated for a deep cat bite to her index finger over the MCP joint. Which of the following is the most appropriate prophylactic antibiotic regimen to prevent the most likely infectious complication?

. Oral cephalexin
. Oral clindamycin
. Oral amoxicillin-clavulanate
. Oral ciprofloxacin
. Intravenous vancomycin

Correct Answer & Explanation

. Oral cephalexin

Explanation

Pasteurella multocida is the most common and clinically significant pathogen in cat bite wounds. Amoxicillin-clavulanate provides excellent coverage for Pasteurella, as well as other potential oral flora anaerobes and Staphylococcus species.

Question 395

Topic: Infection, Pharmacology & VTE
A 55-year-old poorly controlled diabetic male with peripheral neuropathy presents with a chronic draining sinus tract over his anterior tibia. Imaging shows a cortical sequestrum with a distinct reactive involucrum, but the medullary canal is entirely spared and the bone is biomechanically stable. According to the Cierny-Mader classification, what is the correct designation for this patient's osteomyelitis?
. Type I A
. Type II B
. Type III B
. Type IV B
. Type IV C

Correct Answer & Explanation

. Type III B

Explanation

This is a Type III (Localized) osteomyelitis because it involves full-thickness cortical sequestration that is mechanically stable, without diffuse medullary involvement (Type IV) or mere superficial involvement (Type II). The patient is a Type B host due to systemic compromise (diabetes, neuropathy).

Question 396

Topic: Infection, Pharmacology & VTE

Systemic antibiotic therapy often fails to eradicate fracture-related infections due to biofilm formation on the orthopedic implants. Which of the following accurately describes the relationship between the minimum inhibitory concentration (MIC) for planktonic bacteria and the minimum biofilm eradication concentration (MBEC)?

. MBEC is generally 10 to 50 times lower than the MIC
. MBEC is identical to the MIC for gram-positive organisms
. MBEC is generally 100 to 1000 times higher than the MIC
. MBEC cannot be measured for staphylococcal species
. MBEC decreases as the extracellular polymeric substance matures

Correct Answer & Explanation

. MBEC is generally 10 to 50 times lower than the MIC

Explanation

Bacteria within a mature biofilm enter a stationary metabolic phase and are protected by an extracellular polymeric substance. This makes them highly resistant to antimicrobials, resulting in an MBEC that is 100 to 1000 times higher than the MIC of free-floating (planktonic) bacteria.

Question 397

Topic: Infection, Pharmacology & VTE

A 25-year-old male sustains a low-velocity handgun gunshot wound to the right knee. Radiographs reveal a retained bullet lodged within the medial femoral condyle, and a CT scan confirms the bullet trajectory crossed the articular cavity. Which of the following is the most appropriate initial orthopedic management?

. Local wound care and observation
. Intravenous antibiotics for 48 hours without surgical intervention
. Arthroscopic or open formal joint debridement and bullet removal
. Application of a bridging external fixator without joint penetration
. Immediate intra-articular injection of broad-spectrum antibiotics

Correct Answer & Explanation

. Local wound care and observation

Explanation

While extra-articular low-velocity gunshot wounds can often be managed with local wound care, an intra-articular bullet or trajectory transversing the joint requires prompt arthroscopic or open joint debridement, irrigation, and removal of the bullet to prevent septic arthritis and lead arthropathy.

Question 398

Topic: Infection, Pharmacology & VTE

A 72-year-old female presents with an acute hematogenous periprosthetic joint infection of her total hip arthroplasty caused by a susceptible strain of Staphylococcus aureus. She undergoes debridement, antibiotics, and implant retention (DAIR). Following initial IV therapy, which oral antibiotic is highly recommended as part of a combination regimen due to its potent anti-biofilm properties?

. Cephalexin
. Amoxicillin-clavulanate
. Rifampin
. Linezolid
. Trimethoprim-sulfamethoxazole

Correct Answer & Explanation

. Cephalexin

Explanation

Rifampin has unique efficacy against staphylococcal species residing within biofilms on orthopedic hardware. It should never be used as monotherapy due to rapid resistance emergence, but it is standardly combined with agents like fluoroquinolones for suppressive or step-down therapy following DAIR.

Question 399

Topic: Infection, Pharmacology & VTE
According to the Cierny-Mader classification of osteomyelitis, how is a Type III (localized) osteomyelitis best described anatomically?
. Confined strictly to the medullary cavity without cortical involvement
. Superficial cortical infection without marrow involvement
. A full-thickness cortical sequestration that can be excised without compromising mechanical stability
. A diffuse infection involving the entire circumference of the bone requiring segmental resection
. An infection involving a prosthetic joint with severe osteolysis

Correct Answer & Explanation

. A full-thickness cortical sequestration that can be excised without compromising mechanical stability

Explanation

In the Cierny-Mader system, Type III (localized) osteomyelitis involves a full-thickness cortical sequestration. Excision of the lesion does not typically compromise the mechanical stability of the bone, unlike Type IV (diffuse) osteomyelitis, which requires segmental resection.

Question 400

Topic: Infection, Pharmacology & VTE

A patient with an open tibial fracture develops a methicillin-resistant Staphylococcus aureus (MRSA) infection. Intravenous vancomycin is initiated. What is the precise mechanism of action of this antibiotic?

. Inhibition of bacterial protein synthesis by binding the 30S ribosomal subunit
. Inhibition of DNA gyrase and topoisomerase IV
. Binding to the D-alanyl-D-alanine termini of peptidoglycan precursors
. Irreversible binding to penicillin-binding proteins (PBPs)
. Disruption of the bacterial cell membrane via lipopeptide insertion

Correct Answer & Explanation

. Inhibition of bacterial protein synthesis by binding the 30S ribosomal subunit

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis by binding tightly to the D-alanyl-D-alanine portion of cell wall precursors. This prevents the cross-linking of peptidoglycan matrices.

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