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 941
Topic: Infection, Pharmacology & VTE
A 7-year-old child presents with an acute inability to bear weight on the right leg. Kocher's criteria are used to differentiate septic arthritis from transient synovitis. Which of the following is NOT one of the original four Kocher criteria?
Correct Answer & Explanation
. C-reactive protein (CRP) > 2.0 mg/dL
Explanation
The original Kocher criteria include non-weight-bearing, fever > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm³. Although CRP is a highly sensitive modern marker, it was not included in Kocher's original 1999 study.
Question 942
Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain, a limp, and a fever of 38.6°C. He absolutely refuses to bear weight on the right leg. Blood work reveals a WBC count of 14,000/mm³ and an ESR of 45 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
Correct Answer & Explanation
. 99%
Explanation
The Kocher criteria are used to differentiate septic arthritis from transient synovitis of the pediatric hip. The four criteria are: (1) Non-weight-bearing on affected side, (2) ESR > 40 mm/hr, (3) Fever > 38.5°C, and (4) WBC count > 12,000/mm³. This patient meets all 4 criteria. The probability of septic arthritis is 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.
Question 943
Topic: Infection, Pharmacology & VTE
A 65-year-old female develops a delayed prosthetic joint infection 14 months after a total knee arthroplasty. Cultures yield Staphylococcus epidermidis. The pathogenesis of this infection relies heavily on the bacteria's ability to form a biofilm. Which bacterial surface component is most critical for the accumulation phase of biofilm formation in this organism?
Correct Answer & Explanation
. Protein A
Explanation
Biofilm formation in coagulase-negative staphylococci (like S. epidermidis) occurs in two main phases: primary attachment and accumulation. The accumulation phase is primarily mediated by the production of polysaccharide intercellular adhesin (PIA), which is encoded by the ica operon.
Question 944
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?
Correct Answer & Explanation
. Poorer prognosis for eradication of infection than that associated with infection from sensitive organisms
Explanation
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 945
Topic: Infection, Pharmacology & VTE
An 80-year-old African American woman who lives in a large city is scheduled for total hip arthroplasty
to address primary osteoarthritis. Part of the presurgical protocol includes nasal swab screening to assess for methicillin-resistant Staphylococcus aureus (MRSA) colonization. Which demographic factor places this patient at highest risk for a positive result?
Correct Answer & Explanation
. Gender
Explanation
Demographic factors are associated with increased risk for MRSA colonization, so it is important to identify vulnerable patients. Female gender and advanced age reduce the risk for colonization, whereas African American race increases this risk. Urban environments do not influence MRSA colonization.
Question 946
Topic: Infection, Pharmacology & VTE
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
Correct Answer & Explanation
. general anesthesia.
Explanation
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 947
Topic: Infection, Pharmacology & VTE
During the formation of a bacterial biofilm on a metallic orthopedic implant, which component is primarily responsible for forming the structural framework of the mature biofilm and conferring profound resistance to host immune cells and systemic antibiotics?
Correct Answer & Explanation
. Peptidoglycan wall
Explanation
Once planktonic bacteria adhere to an implant surface, they undergo phenotypic changes and secrete an extracellular polymeric substance known as the exopolysaccharide matrix or glycocalyx. This slime layer forms the structural backbone of the biofilm, encasing the bacteria in a protective environment that prevents penetration by antibodies, phagocytes, and antibiotics.
Question 948
Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. What is its exact mechanism of action within the coagulation cascade?
Correct Answer & Explanation
. Direct Factor Xa inhibitor
Explanation
Rivaroxaban and apixaban are oral anticoagulants that selectively and directly inhibit Factor Xa, interrupting the intrinsic and extrinsic pathways of the blood coagulation cascade. Dabigatran is a direct thrombin inhibitor. Warfarin is a Vitamin K antagonist. Low molecular weight heparins potentiate antithrombin III.
Question 949
Topic: Infection, Pharmacology & VTE
In the pathogenesis of orthopedic implant-related infections, Staphylococcus aureus forms a complex biofilm. Which phase of biofilm development is specifically characterized by quorum sensing and the robust production of an extracellular polymeric substance (EPS) matrix?
Correct Answer & Explanation
. Reversible attachment
Explanation
Biofilm formation occurs in stages: reversible attachment, irreversible attachment, maturation, and dispersion. The maturation phase is characterized by the robust synthesis of the extracellular polymeric substance (EPS) matrix, complex three-dimensional architectural growth, and active bacterial communication known as quorum sensing.
Question 950
Topic: Infection, Pharmacology & VTE
A 65-year-old patient develops sudden onset dyspnea, tachycardia, and pleuritic chest pain 3 days after undergoing an elective total hip arthroplasty. A 12-lead electrocardiogram (ECG) is obtained to evaluate for an acute pulmonary embolism (PE). What is the most common electrocardiographic finding in patients with a PE?
Correct Answer & Explanation
. Sinus tachycardia
Explanation
While the S1Q3T3 pattern (prominent S wave in lead I, Q wave and inverted T wave in lead III) is the classic 'textbook' finding associated with acute right heart strain from a pulmonary embolism, it is relatively insensitive. The single most common ECG abnormality seen in patients with an acute pulmonary embolism is sinus tachycardia.
Question 951
Topic: Infection, Pharmacology & VTE
A patient develops a deep surgical site infection following an open tibia fracture. Cultures grow Methicillin-resistant Staphylococcus aureus (MRSA). Which of the following antibiotics is a lipopeptide that is effective for osteomyelitis but inactivated by pulmonary surfactant, making it unsuitable for MRSA pneumonia?
Correct Answer & Explanation
. Vancomycin
Explanation
Daptomycin is a cyclic lipopeptide active against Gram-positive organisms, including MRSA. It is highly effective for skin/soft tissue infections and osteomyelitis but is notoriously inactivated by pulmonary surfactant, rendering it useless for the treatment of pneumonia.
Question 952
Topic: Infection, Pharmacology & VTE
A patient is prescribed Rivaroxaban for DVT prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this medication?
Correct Answer & Explanation
. Direct Factor Xa inhibitor
Explanation
Rivaroxaban and Apixaban are oral direct Factor Xa inhibitors (indicated by the 'xa' in their names). Dabigatran is a direct thrombin inhibitor. Warfarin is a Vitamin K antagonist. Heparin and LMWH exert their effect by binding to and activating antithrombin III.
Question 953
Topic: Infection, Pharmacology & VTE
A 65-year-old patient undergoing a total knee arthroplasty is prescribed oral Rivaroxaban for deep vein thrombosis prophylaxis. What is the specific mechanism of action of this medication?
Correct Answer & Explanation
. Direct Factor Xa inhibitor
Explanation
Rivaroxaban and Apixaban are direct, competitive inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Low molecular weight heparins (like enoxaparin) act by enhancing antithrombin III.
Question 954
Topic: Infection, Pharmacology & VTE
Orthopedic implant-associated infections are notoriously difficult to eradicate with systemic antibiotics alone. This resistance is primarily attributed to which structural or physiological characteristic of bacterial biofilms?
Correct Answer & Explanation
. Rapid and unchecked exponential division of bacteria within the biofilm
Explanation
Biofilms confer extreme resistance to antibiotics and the host immune system because the bacteria encase themselves in a protective extracellular polymeric substance (EPS) matrix (glycocalyx). Within this matrix, deep layers of bacteria exist in a sessile, metabolically dormant state, rendering cell-wall-active antibiotics largely ineffective.
Question 955
Topic: Infection, Pharmacology & VTE
During the formation of a bacterial biofilm on an orthopedic implant, at what stage do the bacteria begin to use "quorum sensing" to coordinate gene expression and produce the extracellular polymeric substance (EPS) matrix?
Correct Answer & Explanation
. Initial reversible attachment
Explanation
Quorum sensing typically begins during irreversible attachment and early maturation. It allows bacteria to communicate based on population density, leading to the coordinated secretion of the protective EPS matrix.
Question 956
Topic: Infection, Pharmacology & VTE
A patient requires deep vein thrombosis (DVT) prophylaxis following total knee arthroplasty. The surgeon prescribes rivaroxaban. What is the specific target of this medication in the coagulation cascade?
Correct Answer & Explanation
. It inhibits Factor Xa directly.
Explanation
Rivaroxaban is a direct oral anticoagulant (DOAC) that selectively and reversibly inhibits free and clot-bound Factor Xa. Dabigatran, in contrast, is a direct thrombin (Factor IIa) inhibitor.
Question 957
Topic: Infection, Pharmacology & VTE
Which of the following prophylactic antibiotics used in orthopedic surgery functions by binding to the 50S ribosomal subunit, thereby inhibiting bacterial protein synthesis?
Correct Answer & Explanation
. Cefazolin
Explanation
Clindamycin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. Cefazolin and vancomycin inhibit cell wall synthesis, while gentamicin binds to the 30S ribosomal subunit.
Question 958
Topic: Infection, Pharmacology & VTE
A patient develops heparin-induced thrombocytopenia (HIT) after receiving unfractionated heparin for deep vein thrombosis prophylaxis. Which of the following is the most appropriate alternative anticoagulant?
Correct Answer & Explanation
. Enoxaparin
Explanation
Argatroban is a direct thrombin inhibitor and is the treatment of choice for patients who develop HIT. Low molecular weight heparins like enoxaparin cross-react with HIT antibodies and are contraindicated.
Question 959
Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant frequently used for VTE prophylaxis following total joint arthroplasty. What is its primary molecular target?
Correct Answer & Explanation
. Direct inhibition of Factor Xa
Explanation
Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Heparin/LMWH works by activating Antithrombin III.
Question 960
Topic: Infection, Pharmacology & VTE
During the formation of a biofilm by Staphylococcus epidermidis on a prosthetic joint, which of the following is the key structural component of the extracellular polymeric substance (EPS) that shields the bacteria from host immunity and antibiotics?
Correct Answer & Explanation
. Teichoic acid
Explanation
Staphylococcus epidermidis produces a robust biofilm whose primary structural component is polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC operon. This glycocalyx matrix is critical for bacterial aggregation and evasion of host defenses.
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