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1. General Principles & Basic Science MCQs

Practice Set 199 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 3961

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 3962

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 3963

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 3964

Topic: 1. General Principles & Basic Science

During the first stage of the Masquelet technique for an infected 6 cm tibial diaphyseal defect, a polymethylmethacrylate (PMMA) spacer is inserted. When performing the second stage 6 to 8 weeks later, what is the primary biological function of the induced pseudosynovial membrane?

. It acts strictly as a mechanical barrier against surrounding muscle intrusion.
. It serves as a permanent reservoir for continued local antibiotic elution.
. It secretes vascular endothelial growth factor (VEGF) and osteoinductive cytokines.
. It provides rigid structural support allowing immediate weight-bearing.
. It converts allogenic bone graft into autologous bone via creeping substitution.

Correct Answer & Explanation

. It acts strictly as a mechanical barrier against surrounding muscle intrusion.

Explanation

The PMMA spacer induces the formation of a highly vascularized, fibrous "pseudo-membrane" over 6 to 8 weeks. This membrane secretes critical growth factors like VEGF, TGF-beta, and BMP-2, creating a favorable biological environment for the subsequent bone graft.

Question 3965

Topic: 1. General Principles & Basic Science

In the Masquelet technique for managing infected bone defects, a PMMA cement spacer is placed to induce a biological membrane. At what time point does this induced membrane typically exhibit its peak concentration of vascular endothelial growth factor (VEGF) and osteoinductive factors (e.g., BMP-2)?

. 3 to 5 days
. 2 to 4 weeks
. 6 to 8 weeks
. 10 to 12 weeks
. 16 to 20 weeks

Correct Answer & Explanation

. 3 to 5 days

Explanation

The biological activity of the induced membrane, including peak vascularity and concentrations of VEGF and BMP-2, is highest at 2 to 4 weeks post-implantation. While the second stage (bone grafting) is often practically performed at 6 to 8 weeks, the physiological peak occurs earlier.

Question 3966

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 3967

Topic: 1. General Principles & Basic Science
A 60-year-old male presents with severe leg pain, swelling, and tense erythema out of proportion to physical findings. You calculate a Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score. Which of the following laboratory values contributes the highest possible point value (4 points) to this scoring system?
. White blood cell count > 25,000/mm3
. Serum sodium < 135 mmol/L
. C-reactive protein (CRP) > 150 mg/L
. Hemoglobin < 11 g/dL
. Serum creatinine > 1.6 mg/dL

Correct Answer & Explanation

. C-reactive protein (CRP) > 150 mg/L

Explanation

In the LRINEC score, a C-reactive protein (CRP) level greater than 150 mg/L contributes the highest single weight of 4 points. The other variables (WBC, Hb, Sodium, Creatinine, Glucose) contribute 1 to 2 points when abnormal.

Question 3968

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 3969

Topic: 1. General Principles & Basic Science

A 30-year-old construction worker sustains a deep, heavily contaminated crush injury to his thigh. 48 hours later, he develops severe pain, tachycardia, and palpable crepitus in the thigh. Gram stain of the wound exudate reveals large Gram-positive rods without spores. Which of the following is the primary virulence factor responsible for tissue destruction in this infection?

. Toxic shock syndrome toxin-1 (TSST-1)
. Alpha-toxin (lecithinase/phospholipase C)
. Panton-Valentine leukocidin (PVL)
. Streptolysin O
. Tetanospasmin

Correct Answer & Explanation

. Toxic shock syndrome toxin-1 (TSST-1)

Explanation

The clinical picture and Gram stain (large Gram-positive, boxcar-shaped rods without spores) are classic for Clostridium perfringens gas gangrene. Its major virulence factor is alpha-toxin, a lecithinase (phospholipase C) that destroys cell membranes.

Question 3970

Topic: 1. General Principles & Basic Science

When utilizing local antibiotic delivery vehicles for the treatment of chronic osteomyelitis, synthetic calcium sulfate has gained popularity as an alternative to polymethylmethacrylate (PMMA). Which of the following is a recognized disadvantage or complication specifically associated with calcium sulfate beads?

. Requirement for a secondary surgery for removal
. Inability to elute vancomycin or tobramycin
. Exothermic reaction leading to local tissue necrosis
. Prolonged retention of the beads indefinitely
. Significant sterile serous wound drainage

Correct Answer & Explanation

. Requirement for a secondary surgery for removal

Explanation

Calcium sulfate is fully bioabsorbable and does not require a second surgery for removal (unlike non-absorbable PMMA). However, its rapid degradation often leads to significant sterile serous wound drainage, which can mimic persistent infection.

Question 3971

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 3972

Topic: 1. General Principles & Basic Science

A healthy 30-year-old male sustains a minor laceration to his forearm that rapidly progresses over 24 hours to severe pain, bullae formation, and skin necrosis. Surgical exploration reveals classic Type II (monomicrobial) necrotizing fasciitis. Which of the following is the most common causative organism for this specific classification?

. Staphylococcus aureus
. Clostridium perfringens
. Group A Streptococcus (Streptococcus pyogenes)
. Bacteroides fragilis
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Type II necrotizing fasciitis is monomicrobial and classically caused by Group A Streptococcus (Streptococcus pyogenes). Type I is polymicrobial and typically occurs in immunocompromised or diabetic hosts.

Question 3973

Topic: 1. General Principles & Basic Science

In the evaluation of a mangled lower extremity, the Mangled Extremity Severity Score (MESS) is historically utilized to assist in the decision between salvage and amputation. Which of the following parameters in the MESS scoring system has its point value doubled if the delay to treatment exceeds 6 hours?

. Patient age
. Shock status
. Skeletal and soft tissue injury energy
. Limb ischemia
. Neurological deficit

Correct Answer & Explanation

. Patient age

Explanation

In the MESS criteria, the score for Limb Ischemia (which ranges from 1 to 3 points based on pulse and capillary refill) is doubled if the duration of ischemia exceeds 6 hours. A total MESS score of 7 or higher historically predicted amputation.

Question 3974

Topic: 1. General Principles & Basic Science
When formulating antibiotic-loaded polymethylmethacrylate (PMMA) cement for an articulating spacer in a two-stage revision, certain antibiotics are preferred due to their heat stability and elution properties. Which of the following antibiotics is generally contraindicated for mixing into PMMA due to significant disruption of the polymerization process?
. Vancomycin
. Tobramycin
. Gentamicin
. Rifampin
. Cefazolin

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin is generally contraindicated for mixing into PMMA cement because it acts as a radical scavenger, severely inhibiting the exothermic polymerization reaction and preventing the cement from curing properly.

Question 3975

Topic: 1. General Principles & Basic Science

A 40-year-old male is undergoing the induced membrane (Masquelet) technique for an infected 8 cm tibial bone defect. Following placement of the PMMA spacer, what is the peak timeframe for maximal vascularity and expression of osteoinductive factors (e.g., VEGF) within the newly formed pseudomembrane?

. 1 week
. 4 weeks
. 8 weeks
. 12 weeks
. 16 weeks

Correct Answer & Explanation

. 1 week

Explanation

Studies demonstrate that the induced membrane in the Masquelet technique reaches its peak vascularity and maximal expression of growth factors (such as VEGF and BMP-2) at approximately 4 weeks post-implantation. Waiting excessively long (e.g., >8 weeks) results in a thicker, less vascular, and fibrotic membrane.

Question 3976

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 3977

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 3978

Topic: 1. General Principles & Basic Science

A 24-year-old male sustains a clenched-fist bite wound over the third metacarpophalangeal joint. Cultures subsequently grow Eikenella corrodens. Which of the following antibiotics is this organism characteristically resistant to?

. Amoxicillin-clavulanate
. Penicillin G
. Ceftriaxone
. Clindamycin
. Ciprofloxacin

Correct Answer & Explanation

. Amoxicillin-clavulanate

Explanation

Eikenella corrodens is a Gram-negative bacillus frequently found in human bite wounds. It is characteristically resistant to clindamycin, first-generation cephalosporins, and macrolides, making amoxicillin-clavulanate the first-line treatment of choice.

Question 3979

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.

Question 3980

Topic: Biomechanics & Biomaterials

When formulating antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for the treatment of an infected tibial nonunion, which of the following physical properties is absolutely essential for the admixed antibiotic?

. High lipid solubility
. Thermostability
. Bacteriostatic action
. High molecular weight
. Rapid systemic absorption

Correct Answer & Explanation

. High lipid solubility

Explanation

The curing of PMMA is an exothermic reaction that can generate temperatures high enough to denature many drugs. Therefore, any antibiotic mixed into bone cement must be highly thermostable (e.g., vancomycin, tobramycin, gentamicin).

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