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Infection, Pharmacology & VTE MCQs

Practice Set 24 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 461

Topic: Infection, Pharmacology & VTE

A collegiate football player sustains a valgus injury to the knee, resulting in a complete tear of the medial collateral ligament (MCL). During surgical reconstruction, accurate identification of the superficial MCL footprints is critical. The distal insertion of the superficial MCL is correctly located:

. Immediately deep to the medial meniscus
. Approximately 1.5 cm distal to the joint line on the anteromedial tibia
. Approximately 4 to 5 cm distal to the joint line, deep to the pes anserinus
. Directly on the adductor tubercle of the distal femur
. On the medial aspect of the patellar tendon insertion

Correct Answer & Explanation

. Approximately 4 to 5 cm distal to the joint line, deep to the pes anserinus

Explanation

The superficial medial collateral ligament (sMCL) has its proximal footprint on the posterior aspect of the medial femoral epicondyle. Its distal footprint is located on the medial aspect of the proximal tibia, approximately 4.5 cm (range 4 to 5 cm) distal to the joint line, and lies deep to the pes anserinus. It is the primary restraint to valgus stress at 30 degrees of knee flexion.

Question 462

Topic: Infection, Pharmacology & VTE

When executing a posteromedial approach to the knee for open reduction and internal fixation of a posteromedial tibial plateau fracture, the surgeon must develop a plane. The optimal inter-nervous/inter-muscular interval is primarily developed by retracting the medial head of the gastrocnemius laterally and which structure medially?

. Semimembranosus
. Popliteus
. Soleus
. Tibialis posterior
. Pes anserinus

Correct Answer & Explanation

. Pes anserinus

Explanation

The posteromedial approach to the tibial plateau typically utilizes the interval between the medial head of the gastrocnemius (which is retracted laterally, protecting the neurovascular bundle in the popliteal fossa) and the pes anserinus (sartorius, gracilis, semitendinosus), which is retracted medially/anteriorly. The semimembranosus can also be retracted medially. The pes anserinus forms the medial boundary of this superficial dissection window.

Question 463

Topic: Infection, Pharmacology & VTE

In orthopedic surgery, preoperative antibiotics are routinely administered. Which of the following prophylactic antibiotics functions primarily by inhibiting bacterial cell wall synthesis via binding to the D-alanyl-D-alanine termini of the peptidoglycan precursor?

. Cefazolin
. Gentamicin
. Vancomycin
. Clindamycin
. Ciprofloxacin

Correct Answer & Explanation

. Vancomycin

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of the cell wall precursor units, preventing peptidoglycan polymerization. Cefazolin (a cephalosporin) also inhibits cell wall synthesis but does so by binding to penicillin-binding proteins (PBPs).

Question 464

Topic: Infection, Pharmacology & VTE

A 2-week-old infant has been referred for evaluation of nonmovement of the left hip. History reveals that the patient was delivered 6 weeks premature by cesarean section. Examination reveals no fever, and there is mild swelling of the thigh. Passive movement of the hip appears to elicit tenderness and very limited hip motion. A radiograph of the pelvis shows mild subluxation of the left hip. The next step in evaluation should consist of

. aspiration of the left hip.
. application of a Pavlik harness.
. a gallium scan.
. an MRI scan of the spine.
. modified Bryant traction.

Correct Answer & Explanation

. aspiration of the left hip.

Explanation

The diagnosis of bone and joint sepsis in a newborn is difficult because of the relative lack of obvious signs and symptoms. Fever is usually absent. A study of 34 newborns with osteomyelitis identified prematurity and delivery by cesarean section as predisposing factors. In that study, the most common clinical findings were pseudoparalysis, local swelling, and pain on passive movement. Because early diagnosis is so important, any infant who exhibits these findings should be suspected as having bone or joint sepsis. Once the area of involvement is identified, aspiration is mandatory. In newborns who have an infection about the hip, radiographs may reveal subluxation. In this patient, septic arthritis must be ruled out by aspiration of the hip. Developmental dysplasia of the hip is not painful and is not accompanied by localized swelling. If no purulent material is obtained at the time of hip aspiration, an arthrogram should be obtained to rule out epiphysiolysis of the proximal femur. Because the area of involvement has been identified by clinical examination, a gallium scan or MRI scan of the spine is not indicated. Knudsen CJ, Hoffman EB: Neonatal osteomyelitis. J Bone Joint Surg Br 1990;72:846-851.

Question 465

Topic: Infection, Pharmacology & VTE

During the posteromedial approach for fixation of a split-depression medial tibial plateau fracture, the optimal surgical interval to expose the posterior aspect of the medial tibial condyle is between the medial head of the gastrocnemius and which anterior structure?

. Semimembranosus
. Popliteus
. Pes anserinus
. Medial collateral ligament (MCL)
. Soleus

Correct Answer & Explanation

. Pes anserinus

Explanation

The posteromedial approach to the proximal tibia utilizes the interval between the medial head of the gastrocnemius (retracted posteriorly) and the pes anserinus tendons (retracted anteriorly) to safely place a buttress plate.

Question 466

Topic: Infection, Pharmacology & VTE

Intravenous Vancomycin is frequently used as prophylaxis or treatment in orthopedic surgery for MRSA infections. What is the specific cellular mechanism of action of this antibiotic?

. Inhibiting DNA gyrase to prevent bacterial replication
. Binding to the 30S ribosomal subunit to inhibit protein synthesis
. Binding to the D-alanyl-D-alanine terminus of cell wall precursor peptides
. Inhibiting beta-lactamase enzymes directly
. Disrupting the bacterial cell membrane by binding to phospholipids

Correct Answer & Explanation

. Binding to the D-alanyl-D-alanine terminus of cell wall precursor peptides

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine portion of the peptidoglycan precursor, preventing cross-linking.

Question 467

Topic: Infection, Pharmacology & VTE

A 50-year-old female presents with acute pain and swelling in her right shoulder. She is febrile and reports a history of intravenous drug use. On examination, the shoulder is exquisitely tender, erythematous, and warm. She resists all attempts at passive range of motion. Joint aspiration yields purulent fluid. Which of the following is the MOST critical initial step in management, after obtaining cultures?

. Initiate oral antibiotics immediately
. Perform a CT scan to assess bone involvement
. Refer for urgent surgical irrigation and debridement
. Apply ice and immobilize the shoulder
. Start NSAIDs for pain and inflammation

Correct Answer & Explanation

. Refer for urgent surgical irrigation and debridement

Explanation

This clinical picture is highly suggestive of septic arthritis of the shoulder. After obtaining Gram stain and cultures from the aspirated fluid, urgent surgical irrigation and debridement is paramount to remove pus and necrotic tissue, reduce bacterial load, and prevent cartilage destruction. This should be combined with appropriate intravenous antibiotics. Oral antibiotics alone are insufficient for septic arthritis. A CT scan may be useful later for osteomyelitis assessment but is not the immediate priority for acute septic arthritis. Ice and immobilization are palliative and do not address the infection. NSAIDs will mask symptoms and do not treat the underlying pathology.

Question 468

Topic: Infection, Pharmacology & VTE

A patient sustains an open fracture of the proximal phalanx of the small finger. Following debridement and fixation, prophylactic antibiotics are typically administered. Which of the following is the most appropriate empirical antibiotic choice for an open hand fracture?

. Vancomycin
. Ciprofloxacin
. Cephalexin
. Cefazolin
. Metronidazole

Correct Answer & Explanation

. Cefazolin

Explanation

Cefazolin (a first-generation cephalosporin) is the most appropriate empirical antibiotic for open fractures, including those of the hand. It provides excellent coverage against Gram-positive organisms, particularly Staphylococcus aureus, which is the most common pathogen in open fractures. Vancomycin is reserved for MRSA. Ciprofloxacin and Metronidazole have different spectrums and are not first-line for this indication.

Question 469

Topic: Infection, Pharmacology & VTE

A patient presents with persistent pain, redness, and swelling in the DIP joint of the small finger, accompanied by a 'sausage digit' appearance. He has a history of psoriasis. What is the most likely diagnosis?

. Osteoarthritis
. Gout
. Rheumatoid arthritis
. Psoriatic arthritis
. Septic arthritis

Correct Answer & Explanation

. Psoriatic arthritis

Explanation

The combination of dactylitis ('sausage digit' swelling of an entire finger) affecting the DIP joints, especially in a patient with psoriasis, is highly characteristic of Psoriatic Arthritis. While gout can cause acute inflammation, it's typically monoarticular. RA rarely affects DIP joints primarily and typically causes symmetrical polyarthritis. Septic arthritis would be more acute and have systemic signs. Osteoarthritis involves cartilage degeneration without such inflammatory signs.

Question 470

Topic: Infection, Pharmacology & VTE

A 70-year-old male with a prosthetic aortic valve on warfarin therapy sustains a displaced intertrochanteric hip fracture. His INR is 3.5. Which of the following is the most appropriate perioperative anticoagulant management?

. Proceed directly to surgery; continue warfarin.
. Stop warfarin; proceed to surgery immediately.
. Reverse warfarin with Vitamin K and FFP; proceed to surgery when INR is normal.
. Bridge with unfractionated heparin until INR is therapeutic, then proceed to surgery.
. Reverse warfarin with PCC and Vitamin K; aim for an INR <1.5 and proceed to surgery within 24 hours.

Correct Answer & Explanation

. Reverse warfarin with PCC and Vitamin K; aim for an INR <1.5 and proceed to surgery within 24 hours.

Explanation

For a patient with a displaced intertrochanteric hip fracture on warfarin, timely surgery is crucial to reduce morbidity and mortality. Reversing warfarin with Prothrombin Complex Concentrate (PCC) provides rapid correction of INR within hours, and Vitamin K provides sustained effect. The goal is typically to achieve an INR <1.5 to safely proceed with surgery, ideally within 24-48 hours. Stopping warfarin alone will take days to normalize INR, increasing DVT risk and delaying surgery. Bridging with unfractionated heparin is too slow and not indicated for emergent INR reversal. Continuing warfarin with an INR of 3.5 carries a significant bleeding risk. Immediate surgery without reversal is highly dangerous. Balancing the risk of bleeding with the need for prompt surgery is critical, and PCC combined with Vitamin K offers the quickest and safest pathway.

Question 471

Topic: Infection, Pharmacology & VTE

A patient sustaining an open tibia fracture is placed on a course of systemic antibiotics. Which antibiotic class achieves high concentrations in bone tissue due to its hydrophilic nature and good penetration into the bone matrix?

. Macrolides
. Fluoroquinolones
. Aminoglycosides
. Tetracyclines
. Lincosamides

Correct Answer & Explanation

. Fluoroquinolones

Explanation

Fluoroquinolones, such as ciprofloxacin and levofloxacin, are known for their excellent tissue penetration, including into bone and cartilage, due to their relatively small molecular size and favorable lipophilicity, despite being often described as hydrophilic (they have a good balance). This property makes them highly effective in treating osteomyelitis and other bone and joint infections. Lincosamides (e.g., clindamycin) also have good bone penetration but a narrower spectrum (primarily gram-positive and anaerobes). Aminoglycosides (e.g., gentamicin) are potent but have limited bone penetration and require higher doses or local delivery for significant bone levels. Macrolides and tetracyclines generally have less reliable or lower bone concentrations compared to fluoroquinolones for treating established osteomyelitis.

Question 472

Topic: Infection, Pharmacology & VTE

The formation of a bacterial biofilm on orthopedic implants is a major challenge in treating periprosthetic joint infections. Which of the following is a primary characteristic of bacteria within a biofilm that contributes to their increased resistance to antibiotics?

. Increased metabolic rate
. Enhanced nutrient uptake
. Downregulation of efflux pumps
. Formation of an extracellular polymeric substance (EPS) matrix
. Reduced cell-to-cell communication

Correct Answer & Explanation

. Formation of an extracellular polymeric substance (EPS) matrix

Explanation

Bacterial biofilms are communities of microorganisms encased in an extracellular polymeric substance (EPS) matrix that they produce and attach to surfaces, such as orthopedic implants. This EPS matrix provides a protective barrier against host immune defenses and significantly impedes the penetration and efficacy of antibiotics. Bacteria within the biofilm often exhibit a reduced metabolic rate and altered gene expression, further contributing to their tolerance and resistance to conventional antibiotic therapy. While changes in efflux pumps can occur, the physical barrier and altered microenvironment provided by the EPS matrix are considered the primary mechanisms for increased antibiotic resistance in biofilms.

Question 473

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, Staphylococcus epidermidis frequently forms a protective biofilm. What is the primary constituent of the extracellular polymeric substance (slime layer) that mediates adherence and provides resistance to host immune cells and antibiotics?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide intercellular adhesin (PIA)
. Teichoic acid
. Hyaluronic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix in Staphylococcal infections is primarily composed of Polysaccharide Intercellular Adhesin (PIA), synthesized by the products of the icaADBC operon. This layer protects the bacteria from phagocytosis and antibiotic penetration.

Question 474

Topic: Infection, Pharmacology & VTE

A patient develops a deep periprosthetic joint infection due to Staphylococcus epidermidis. The chronicity of this infection is primarily mediated by a protective biofilm. Which bacterial communication mechanism is most critical for coordinating the formation and maturation of this biofilm?

. Phagocytosis evasion
. Quorum sensing
. Chemotaxis
. Opsonization
. Plasmid conjugation

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is a cell-to-cell communication system based on bacterial population density. It regulates gene expression essential for biofilm maturation, allowing bacteria to adapt and survive against host defenses and antibiotics.

Question 475

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III activation
. Direct, reversible inhibition of Factor Xa
. Inhibition of vitamin K epoxide reductase
. Irreversible inhibition of cyclooxygenase-1 (COX-1)

Correct Answer & Explanation

. Direct, reversible inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. This interrupts the intrinsic and extrinsic pathway cascade, preventing thrombin generation.

Question 476

Topic: Infection, Pharmacology & VTE
The FRCS (Tr & Orth) examination assesses a candidate's ability to manage complex cases. When discussing a case of chronic osteomyelitis, the examiner asks about the most critical component of successful treatment. What is it?
. High-dose intravenous antibiotics for a prolonged period.
. Surgical debridement and removal of necrotic/infected bone.
. Placement of antibiotic-impregnated beads.
. Hyperbaric oxygen therapy.
. Systemic antifungal therapy.

Correct Answer & Explanation

. Surgical debridement and removal of necrotic/infected bone.

Explanation

Surgical debridement and removal of all necrotic and infected bone (sequestra) is the single most critical component in the treatment of chronic osteomyelitis. Without adequate debridement, antibiotics alone cannot penetrate the avascular tissue or eradicate biofilms effectively. While prolonged antibiotics, antibiotic-impregnated beads, and sometimes hyperbaric oxygen are important adjuncts, surgical debridement is paramount for source control. Antifungal therapy would only be relevant if a fungal infection were identified.

Question 477

Topic: Infection, Pharmacology & VTE
In the assessment of a patient with a suspected deep vein thrombosis (DVT) in the leg, which clinical assessment tool is commonly used to estimate the pre-test probability?
. Glasgow Coma Scale (GCS).
. Wells' Score.
. Modified Rankin Scale (MRS).
. APACHE II Score.
. VAS Score.

Correct Answer & Explanation

. Wells' Score.

Explanation

The Wells' Score for DVT is a widely used clinical prediction rule to estimate the pre-test probability of a DVT, guiding further diagnostic investigations such as D-dimer testing and ultrasound. GCS is for neurological impairment, MRS for disability following stroke, APACHE II for severity of illness in ICU, and VAS (Visual Analogue Scale) for pain.

Question 478

Topic: Infection, Pharmacology & VTE

Which characteristic of Staphylococcus aureus makes it particularly challenging to treat in orthopedic infections?

. Its obligate anaerobic nature.
. Its slow growth rate, making detection difficult.
. Its ability to form biofilms on implanted materials.
. Its universal susceptibility to common antibiotics.
. Its exclusive presence in the hospital environment.

Correct Answer & Explanation

. Its ability to form biofilms on implanted materials.

Explanation

Staphylococcus aureus is a major pathogen in orthopedic infections, and its ability to form biofilms on implanted materials (like prostheses or plates) is a critical factor contributing to chronicity and difficulty in treatment. Biofilms protect bacteria from antibiotics and the host immune system. S. aureus is a facultative anaerobe, grows relatively quickly, is often resistant to common antibiotics (e.g., MRSA), and is widely present in both hospital and community settings.

Question 479

Topic: Infection, Pharmacology & VTE
Low-molecular-weight heparin (LMWH) is frequently used for DVT prophylaxis following orthopedic surgery. Which of the following best describes the primary mechanism of action of LMWH compared to unfractionated heparin?
. Directly inhibits thrombin (Factor IIa) independently of antithrombin III
. Binds to antithrombin III, with a stronger preferential inhibition of Factor Xa than Factor IIa
. Binds to antithrombin III, with equal inhibition of Factor Xa and Factor IIa
. Inhibits the vitamin K epoxide reductase complex
. Directly and reversibly inhibits Factor Xa at the active site

Correct Answer & Explanation

. Binds to antithrombin III, with a stronger preferential inhibition of Factor Xa than Factor IIa

Explanation

LMWH binds to antithrombin III (ATIII). Because of its shorter polysaccharide chain length compared to unfractionated heparin, it cannot efficiently form a ternary complex with ATIII and thrombin (Factor IIa). Thus, it has a high ratio of anti-Factor Xa to anti-Factor IIa activity, typically between 2:1 and 4:1.

Question 480

Topic: Infection, Pharmacology & VTE
Apixaban is frequently used for venous thromboembolism (VTE) prophylaxis following total joint arthroplasty. What is its specific mechanism of action?
. Direct inhibition of thrombin (Factor IIa)
. Competitive inhibition of Vitamin K epoxide reductase
. Direct, reversible inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase-1

Correct Answer & Explanation

. Direct, reversible inhibition of Factor Xa

Explanation

Apixaban and rivaroxaban are direct, reversible inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Heparins activate antithrombin III.

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