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Infection, Pharmacology & VTE MCQs

Practice Set 25 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 481

Topic: Infection, Pharmacology & VTE

A patient is scheduled for an elective total knee arthroplasty. He is currently taking Rivaroxaban for atrial fibrillation. What is the mechanism of action of this medication?

. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Low molecular weight heparin
. COX-1 inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban (Xarelto) is a direct oral anticoagulant (DOAC) that functions as a direct and reversible inhibitor of Factor Xa, interrupting the intrinsic and extrinsic pathway of the blood coagulation cascade. Dabigatran, conversely, is a direct thrombin (Factor IIa) inhibitor.

Question 482

Topic: Infection, Pharmacology & VTE

A 45-year-old male is scheduled for open reduction and internal fixation of a closed tibial shaft fracture. He has a documented history of MRSA colonization and a severe anaphylactic allergy to penicillin (hives and shock). Which of the following is the most appropriate preoperative prophylactic antibiotic?

. Cefazolin
. Vancomycin
. Clindamycin
. Gentamicin
. Ceftriaxone

Correct Answer & Explanation

. Vancomycin

Explanation

For patients with a severe, IgE-mediated (anaphylactic) penicillin allergy, cephalosporins (like cefazolin and ceftriaxone) are generally avoided due to the small risk of cross-reactivity. Given the patient's documented history of MRSA colonization, Vancomycin is the definitive choice for preoperative prophylaxis to provide adequate coverage while avoiding an anaphylactic reaction.

Question 483

Topic: Infection, Pharmacology & VTE

Which of the following bacteria is most classically associated with the production of a dense glycocalyx (biofilm) that facilitates adhesion to orthopedic implants and resistance to antibiotics?

. Staphylococcus aureus
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Streptococcus pyogenes
. Cutibacterium acnes

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis (a coagulase-negative staphylococcus) is notorious for producing a thick exopolysaccharide layer known as a glycocalyx or biofilm. This slime layer allows it to adhere strongly to foreign bodies (such as arthroplasty components) and protects the bacteria from host immune responses and systemic antibiotics.

Question 484

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in the pathogenesis of periprosthetic joint infections, rendering bacteria highly resistant to systemic antibiotics. In Staphylococcus epidermidis infections, what is the primary extracellular polymeric substance responsible for intercellular adhesion and structural integrity of the biofilm?

. Hyaluronic acid
. Teichoic acid
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Alpha-toxin

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Biofilm formation by Staphylococcus epidermidis largely depends on the production of Polysaccharide Intercellular Adhesin (PIA), which is synthesized by products of the icaADBC operon. PIA acts as the primary extracellular matrix component, facilitating intercellular adhesion and shielding the bacteria from the host immune response and antibiotics.

Question 485

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with an acute monoarticular septic arthritis of the knee. Standard synovial fluid cultures are negative at 48 hours, but the ESR and CRP are significantly elevated. Which of the following organisms is most likely responsible and optimally requires inoculation into BACTEC blood culture bottles or PCR for detection?
. Staphylococcus aureus
. Haemophilus influenzae
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a gram-negative bacillus that has become recognized as the most common cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It is notoriously fastidious and difficult to isolate on standard solid media; the diagnostic yield is significantly increased by inoculating joint fluid directly into BACTEC blood culture bottles or using specific PCR assays.

Question 486

Topic: Infection, Pharmacology & VTE

A 20-year-old man presents with nocturnal thigh pain that is completely relieved by ibuprofen. Imaging shows a 1 cm radiolucent nidus with surrounding sclerosis in the femoral diaphysis. What is the primary biochemical mechanism underlying the effectiveness of NSAIDs for this specific lesion?

. Reduction of interleukin-6 production
. Inhibition of excessive cyclooxygenase-2 (COX-2) expression by the nidus
. Direct suppression of osteoclast activity
. Inhibition of vascular endothelial growth factor (VEGF)
. Blockade of substance P release in the periosteum

Correct Answer & Explanation

. Inhibition of excessive cyclooxygenase-2 (COX-2) expression by the nidus

Explanation

Osteoid osteomas characteristically cause severe nocturnal pain that is relieved by NSAIDs. This is because the nidus cells produce high levels of prostaglandins (specifically PGE2) due to marked expression of cyclooxygenase-2 (COX-2) enzymes. NSAIDs inhibit this COX-2 activity, directly eliminating the source of the pain.

Question 487

Topic: Infection, Pharmacology & VTE

During a total knee arthroplasty for a patient with a severe, fixed varus deformity, the surgeon must perform a sequential medial release to achieve a balanced extension and flexion gap. Which of the following represents the most accepted sequence of release after osteophyte removal?

. Superficial MCL, Deep MCL, Pes anserinus, Posteromedial capsule
. Pes anserinus, Deep MCL, Superficial MCL, Posteromedial capsule
. Deep MCL, Posteromedial capsule, Superficial MCL, Pes anserinus
. Posteromedial capsule, Pes anserinus, Deep MCL, Superficial MCL
. Deep MCL, Pes anserinus, Posteromedial capsule, Superficial MCL

Correct Answer & Explanation

. Deep MCL, Posteromedial capsule, Superficial MCL, Pes anserinus

Explanation

In a severe varus knee, sequential release of the tight medial structures is necessary. Following the removal of medial osteophytes, the classic stepwise release begins with the deep MCL, followed by the posteromedial corner/capsule, then the superficial MCL (often subperiosteally off the tibia), and finally the pes anserinus tendons if further correction is required.

Question 488

Topic: Infection, Pharmacology & VTE

Vancomycin is frequently administered in orthopedic surgery for both prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. What is the precise mechanism of action by which vancomycin exerts its bactericidal effect?

. Inhibits protein synthesis by reversibly binding to the 50S ribosomal subunit
. Inhibits protein synthesis by irreversibly binding to the 30S ribosomal subunit
. Inhibits DNA gyrase and topoisomerase IV, preventing DNA replication
. Inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of peptidoglycan precursors
. Inhibits folic acid synthesis by competitively inhibiting dihydropteroate synthase

Correct Answer & Explanation

. Inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of peptidoglycan precursors

Explanation

Vancomycin is a glycopeptide antibiotic that bactericidally inhibits cell wall synthesis. It works by binding non-covalently but very tightly to the D-alanyl-D-alanine terminal dipeptide of the peptidoglycan precursors, preventing their cross-linking by transpeptidases. This differs from beta-lactam antibiotics (like penicillins and cephalosporins), which bind directly to the penicillin-binding proteins (transpeptidases) themselves.

Question 489

Topic: Infection, Pharmacology & VTE

A 65-year-old man is diagnosed with an acute staphylococcal periprosthetic joint infection (PJI) of his total hip arthroplasty. He is treated with irrigation, debridement, and modular exchange. His post-operative antibiotic regimen includes Rifampin. What is the primary reason for including Rifampin, and what is its mechanism of action?

. High penetration into bone; inhibits bacterial cell wall synthesis by binding PBPs
. Synergistic effect with vancomycin on planktonic bacteria; inhibits protein synthesis at the 30S ribosomal subunit
. Prevention of deep vein thrombosis; inhibits folate synthesis
. Ability to penetrate bacterial biofilms; inhibits DNA-dependent RNA polymerase
. Promotes osteoblast differentiation; inhibits DNA gyrase

Correct Answer & Explanation

. Ability to penetrate bacterial biofilms; inhibits DNA-dependent RNA polymerase

Explanation

Rifampin is utilized in the treatment of staphylococcal periprosthetic joint infections due to its exceptional ability to penetrate established bacterial biofilms and eradicate sessile organisms. Its mechanism of action is the inhibition of DNA-dependent RNA polymerase, which disrupts bacterial RNA transcription.

Question 490

Topic: Infection, Pharmacology & VTE
A patient is admitted for an elective primary total hip arthroplasty. He is currently taking Rivaroxaban, which needs to be managed perioperatively. What is the specific mechanism of action by which Rivaroxaban exerts its anticoagulant effect?
. Direct, competitive inhibition of Factor IIa (Thrombin)
. Direct, selective inhibition of Factor Xa
. Enhancement of Antithrombin III activity
. Inhibition of Vitamin K epoxide reductase
. Direct activation of Plasminogen

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa, preventing the conversion of prothrombin to thrombin. Dabigatran directly inhibits Factor IIa (Thrombin). Warfarin inhibits Vitamin K epoxide reductase. Heparins work by enhancing Antithrombin III.

Question 491

Topic: Infection, Pharmacology & VTE

In a 2-year-old child, why does acute hematogenous osteomyelitis of the proximal femur carry a high risk of rapidly developing into septic arthritis of the hip?

. The femoral head lacks a blood supply in toddlers
. The physis is fully permeable to bacteria
. The metaphysis is intra-articular
. The joint capsule inserts on the greater trochanter
. Synovial fluid is highly acidic in children

Correct Answer & Explanation

. The metaphysis is intra-articular

Explanation

In the proximal femur (as well as the proximal humerus, lateral malleolus, and radial neck), the metaphysis is located within the joint capsule (intra-articular). Therefore, an infection starting in the metaphyseal bone can easily breach the thin cortex and directly enter the joint space, causing septic arthritis.

Question 492

Topic: Infection, Pharmacology & VTE

Periprosthetic joint infections are notoriously difficult to eradicate due to the formation of bacterial biofilms on the implant surface. While the exopolysaccharide matrix provides a physical barrier, what is considered the primary biological mechanism by which biofilms convey profound resistance to systemic bactericidal antibiotics?

. Rapid bacterial replication and hypermutation within the biofilm matrix
. Upregulated expression of efflux pumps by actively dividing surface bacteria
. The presence of metabolically dormant 'persister' cells deep within the matrix
. Direct enzymatic degradation of antibiotics by the extracellular polymeric substance
. Prevention of macrophage infiltration by a highly vascularized host envelope

Correct Answer & Explanation

. The presence of metabolically dormant 'persister' cells deep within the matrix

Explanation

The most significant mechanism of antibiotic tolerance in biofilms is the phenotypic shift of bacteria deep within the matrix into a metabolically inactive or dormant state, known as 'persister' cells. Because most bactericidal antibiotics (like beta-lactams) target cellular processes that occur during active replication (e.g., cell wall synthesis), these dormant cells are inherently immune to the drug's mechanism of action.

Question 493

Topic: Infection, Pharmacology & VTE

A 42-year-old patient sustains a high-energy bicondylar tibial plateau fracture. Computed tomography reveals a large, vertically oriented, displaced posteromedial shear fragment. The surgical plan includes anti-glide buttress plating of this specific fragment. Which surgical interval provides the most direct and appropriate access?

. Between the rectus femoris and vastus lateralis
. Between the semimembranosus and popliteal artery
. Between the medial head of the gastrocnemius and the pes anserinus
. Between the lateral head of the gastrocnemius and the soleus
. Through a direct medial approach splitting the medial collateral ligament

Correct Answer & Explanation

. Between the medial head of the gastrocnemius and the pes anserinus

Explanation

The posteromedial approach to the tibial plateau utilizes the interval between the medial head of the gastrocnemius and the pes anserinus tendons. Retracting the medial gastrocnemius laterally protects the neurovascular bundle in the popliteal fossa, while the pes anserinus is retracted medially or distally. This provides direct visualization of the posteromedial cortex, allowing for the application of an anti-glide buttress plate for posteromedial shear fragments.

Question 494

Topic: Infection, Pharmacology & VTE

Acetaminophen is an antipyretic medication. It exerts its pharmacologic effects by inhibiting which of the following enzymes?

. Cyclooxygenase-2 (COX-2)
. Interleukin-1 beta (IL-1 B)
. Tumor necrosis factor alpha (TNF-A)
. 5-Hydroxytryptamine (5-HT)
. Metalloproteinases (MMPs)

Correct Answer & Explanation

. Interleukin-1 beta (IL-1 B)

Explanation

Acetaminophen inhibits prostaglandin E2 production via IL-1 B, without affecting cyclooxygenase-2 enzymatic activity. The therapeutic concentrations of acetaminophen induce an inhibition of IL-1 B-dependent NF-kappa B nuclear translocation. The selectivity of this effect suggests the existence of an acetaminophen-specific activity at the transcriptional level that may be one of the mechanisms through which the drug exerts its pharmacologic effects. Acetaminophen does not affect any of the other enzymes named above.

Question 495

Topic: Infection, Pharmacology & VTE

An 82-year-old woman with a history of atrial fibrillation sustains an intertrochanteric femur fracture. She takes daily warfarin. Her initial INR in the emergency department is 3.5. Which of the following is the most appropriate method to rapidly reverse her coagulopathy for surgical fixation within 24 hours?

. Hold warfarin for 5 days prior to surgery
. Administer Intravenous Vitamin K and Prothrombin Complex Concentrate (PCC)
. Administer Fresh Frozen Plasma (FFP) alone
. Administer a prophylactic dose of Enoxaparin
. Transfuse one unit of pooled platelets

Correct Answer & Explanation

. Administer Intravenous Vitamin K and Prothrombin Complex Concentrate (PCC)

Explanation

The most rapid and reliable reversal of warfarin-induced coagulopathy for urgent orthopedic trauma surgery is achieved with Prothrombin Complex Concentrate (PCC) and Intravenous Vitamin K.

Question 496

Topic: Infection, Pharmacology & VTE

A 7-year-old girl presents with torticollis 1 week after a pharyngitis infection. CT scan shows C1 rotated on C2 with no anterior displacement. What is the initial treatment of choice for this Fielding Type I rotatory subluxation?

. Emergent posterior C1-C2 fusion
. Halter traction followed by a rigid collar
. Soft collar and NSAIDs with close observation
. Manipulation under anesthesia
. Halo vest immobilization

Correct Answer & Explanation

. Soft collar and NSAIDs with close observation

Explanation

For Grisel syndrome (atlantoaxial rotatory subluxation associated with head/neck infections) presenting acutely (less than 1 week) as Fielding Type I, initial management is a soft collar, NSAIDs, and treatment of the underlying infection.

Question 497

Topic: Infection, Pharmacology & VTE

A 55-year-old diabetic patient presents with a swollen, erythematous foot. Radiographs demonstrate bone destruction at the midfoot. MRI shows diffuse marrow edema in the cuboid and cuneiforms. T1-weighted images show complete loss of signal, but contrast-enhanced T2 images show distinct preserved margins of the cuboid and cuneiforms (the "ghost sign"). What is the most likely diagnosis?

. Acute osteomyelitis
. Acute Charcot neuroarthropathy
. Chronic osteomyelitis
. Bone infarction
. Gouty arthropathy

Correct Answer & Explanation

. Acute Charcot neuroarthropathy

Explanation

The "ghost sign" on MRI describes the loss of bony morphology on T1-weighted images that becomes distinctly demarcated again on T2 or post-contrast images. This finding is highly characteristic of acute Charcot neuroarthropathy rather than osteomyelitis, which typically lacks preserved bone margins.

Question 498

Topic: Infection, Pharmacology & VTE

A 60-year-old diabetic patient presents with a chronic, non-healing plantar foot ulcer beneath the first metatarsal head. Total contact casting (TCC) is being considered for offloading. Which of the following represents an absolute contraindication to the use of a total contact cast?

. Wagner Grade 1 ulcer
. Wagner Grade 2 ulcer
. Active deep infection or osteomyelitis
. History of Charcot neuroarthropathy
. Mild peripheral neuropathy

Correct Answer & Explanation

. Active deep infection or osteomyelitis

Explanation

Total contact casting is the gold standard for offloading non-infected, non-ischemic plantar diabetic foot ulcers. However, it is absolutely contraindicated in the presence of an active deep space infection, osteomyelitis, severe peripheral arterial disease, or highly exudative wounds.

Question 499

Topic: Infection, Pharmacology & VTE

During the early stages of osteoarthritis, which of the following enzymes is primarily responsible for the aggressive cleavage of Type II collagen in the extracellular matrix?

. Alkaline phosphatase
. Matrix metalloproteinase-13 (MMP-13)
. Cathepsin K
. Cyclooxygenase-2 (COX-2)
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Matrix metalloproteinase-13 (MMP-13)

Explanation

MMP-13 (collagenase 3) is significantly upregulated in osteoarthritis and is the primary enzyme responsible for degrading type II collagen in the articular cartilage matrix.

Question 500

Topic: Infection, Pharmacology & VTE

A 22-year-old athlete requires an anatomic repair of a completely avulsed superficial medial collateral ligament (sMCL). The femoral origin is on the medial epicondyle. Where is the normal anatomic insertion of the sMCL on the proximal tibia?

. Deep to the pes anserinus approximately 4-5 cm distal to the joint line
. Superficial to the pes anserinus approximately 2 cm distal to the joint line
. Directly onto the capsular reflection of the medial meniscus
. On the anterior crest of the tibia
. Just posterior to the semimembranosus insertion

Correct Answer & Explanation

. Deep to the pes anserinus approximately 4-5 cm distal to the joint line

Explanation

The superficial MCL has a broad tibial insertion located deep to the pes anserinus tendons, approximately 4.5 to 5 cm distal to the medial joint line of the knee. The deep MCL inserts much more proximally, near the joint margin.

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