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1. General Principles & Basic Science MCQs

Practice Set 198 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 3941

Topic: 1. General Principles & Basic Science
Residual end-organ hypoperfusion in a polytraumatized patient is shown by which of the following?
. Urine output of 0.8 mL/kg/hr
. SpO2 < 90%
. Platelet count < 80
. Base excess of +3.0 mEq/L
. Serum lactate of 4.5 mmol/L

Correct Answer & Explanation

. Serum lactate of 4.5 mmol/L

Explanation

Traditional endpoints for shock, including blood pressure, heart rate, and urine output, are good endpoints for uncompensated shock, but most trauma patients are in a state of compensated shock where these endpoints have normalized. New endpoints for adequate resuscitation include serum lactate (normal < 2 mmol/L) and base deficit (normal -2 to +2, anything less than -2 indicates hypoperfusion). A serum lactate of 4.5 mmol/L indicates residual tissue hypoperfusion.

Question 3942

Topic: 1. General Principles & Basic Science

Which of the following is true regarding changes in the vascularity of the adult intervertebral disc with age? Review Topic

. Neovascularization occurs from the nucleus pulposus
. Neovascularization occurs from the outer annulus
. Neovascularization occurs from the endplates
. There is no change in vascularity
. There is a decrease in vascularity

Correct Answer & Explanation

. Neovascularization occurs from the nucleus pulposus

Explanation

As a person ages through adulthood, neovascularization of the intervertebral disc originates from the outer annulus.The intervertebral disc is composed of an outer structure called the annulus fibrosis and an inner structure called the nucleus pulposus. The annulus fibrosis is composedof type 1 collagen, water, and proteoglycans. The inner nucleus pulposus is composed of type 2 collagen, water, and proteoglycans. Intervertebral discs are avascular with capillaries terminating at the end plates. The nucleus pulposus receives nutrition primarily through diffusion through blood vessels within the endplate.Roberts et al. review the histology and pathology of the intervertebral disc. They note that at birth, the cartilagenous end plates have large vascular channels through them as well as vascular channels through the annulus. Soon after birth, these vascular channels close with none remaining at the end of the first decade of life. However, with age, more blood vessels grow into the disc from the outer annulus fibrosis in response to degenerative changes.Illustration A is a diagram of the vascular supply in an adult intervertebral disc. Incorrect Answers:

Question 3943

Topic: Biology, Genetics & Bone Healing
A 17-year-old cross country athlete runs 7 miles per day, 6 days per week. She has new-onset right groin pain. Passive flexion of her hip is normal, but internal rotation of the hip, resisted hip flexion, and knee extension reproduce the pain. Hip radiograph findings are normal. What is the best next step?
. Recommend decreasing her training regimen
. Obtain a bone scan
. Obtain an MRI
. Obtain a dual-energy x-ray absorptiometry (DEXA) scan

Correct Answer & Explanation

. Obtain an MRI

Explanation

A stress fracture of the femoral neck or pelvis should be ruled out in this patient. MRI is more accurate, more specific, and is superior to radionuclide bone scanning for the diagnosis of stress fracture in young endurance athletes. MRI detects early changes in osseous stress injury and allows precise definition of the anatomy and extent of injury.

Question 3944

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 3945

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 3946

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 3947

Topic: 1. General Principles & Basic Science

A 30-year-old construction worker sustains a deep, contaminated puncture wound to his boot from a rusty nail. His medical records confirm he received a full 5-dose childhood tetanus vaccination series, and his last Tdap booster was exactly 8 years ago. According to current guidelines, what is the appropriate tetanus prophylaxis for this patient today?

. Tetanus toxoid-containing vaccine only
. Tetanus immune globulin (TIG) only
. Both tetanus toxoid-containing vaccine and TIG
. Neither vaccine nor TIG is indicated
. Intravenous penicillin and local wound care only

Correct Answer & Explanation

. Tetanus toxoid-containing vaccine only

Explanation

For a 'dirty' or severe wound, a tetanus toxoid booster (Td or Tdap) is indicated if the patient has had a complete primary series but the last booster was more than 5 years ago. Tetanus immune globulin (TIG) is only indicated for dirty wounds if the patient has had fewer than 3 previous doses of tetanus toxoid or if the vaccination history is unknown.

Question 3948

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 3949

Topic: 1. General Principles & Basic Science

Polymethylmethacrylate (PMMA) impregnated with antibiotics is commonly utilized for local treatment of dead space in chronic osteomyelitis. Which of the following statements accurately describes the release kinetics and properties of antibiotic-loaded PMMA?

. It provides a constant, zero-order release of antibiotics over a period of 6 to 8 weeks.
. The polymerization reaction is endothermic, allowing heat-labile antibiotics to be safely added.
. The addition of high concentrations of antibiotics (e.g., >10% by weight) significantly increases the compressive strength of the cement.
. Antibiotic elution is primarily a surface phenomenon, characterized by an initial burst followed by a rapid exponential decline.
. Erythromycin and tetracycline are the antibiotics of choice for PMMA due to their broad spectrum and heat stability.

Correct Answer & Explanation

. It provides a constant, zero-order release of antibiotics over a period of 6 to 8 weeks.

Explanation

Antibiotic release from PMMA is a surface phenomenon. It is characterized by an initial 'burst' effect with high local concentrations within the first 24-48 hours, followed by a rapid exponential decline. PMMA polymerization is highly exothermic (which requires heat-stable antibiotics like vancomycin and aminoglycosides). Adding high doses of antibiotics negatively impacts the mechanical properties of the cement.

Question 3950

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 3951

Topic: 1. General Principles & Basic Science

A 6-year-old boy from Connecticut presents with an acute, painless, massive effusion of his right knee.

Aspiration reveals a WBC count of 45,000 cells/µL with a neutrophil predominance. Serology for Borrelia burgdorferi is positive. What is the most appropriate first-line treatment?

. Immediate arthroscopic irrigation and debridement
. 28-day course of oral doxycycline
. 28-day course of oral amoxicillin
. Intravenous ceftriaxone for 14 days
. Serial intra-articular corticosteroid injections

Correct Answer & Explanation

. Immediate arthroscopic irrigation and debridement

Explanation

This patient has Lyme arthritis. The first-line treatment for Lyme arthritis without neurologic involvement is a 28-day course of oral antibiotics. In children under 8 years of age, amoxicillin is the drug of choice because doxycycline can cause permanent tooth discoloration and enamel hypoplasia. Surgery is not the first-line treatment for Lyme arthritis.

Question 3952

Topic: Surgical Anatomy & Approaches

The 'MESS' (Mangled Extremity Severity Score) is a historical clinical tool designed to help predict the necessity of primary amputation versus limb salvage in severe lower extremity trauma. Which of the following variables is NOT formally included in the calculation of the MESS?

. Patient age
. Limb ischemia time and severity
. Presence of shock (hypotension)
. Skeletal and soft-tissue injury energy mechanism
. Presence of a neurological motor deficit

Correct Answer & Explanation

. Patient age

Explanation

The MESS evaluates 4 parameters: Skeletal/soft-tissue injury mechanism (1-4 points), Limb ischemia (1-3 points, doubled if ischemia >6 hours), Shock (0-2 points), and Patient Age (0-2 points). While an absent plantar sensation or sciatic nerve deficit is highly clinically relevant in decision-making, neurological deficit is NOT a mathematically scored variable in the MESS.

Question 3953

Topic: 1. General Principles & Basic Science

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) cement for the treatment of chronic osteomyelitis, which of the following properties is characteristic of an ideal antibiotic additive?

. High protein binding capacity
. Heat lability
. Low water solubility
. Powder form formulation
. Narrow bactericidal spectrum

Correct Answer & Explanation

. High protein binding capacity

Explanation

Ideal antibiotics for PMMA inclusion must be heat stable, available in powder form to avoid altering cement mechanical properties, water-soluble for elution, and have a broad spectrum. Liquid antibiotics severely degrade the structural integrity of the cement.

Question 3954

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 3955

Topic: 1. General Principles & Basic Science

A 28-year-old male presents with a clenched-fist injury after striking another individual in the mouth, resulting in a laceration over the 3rd metacarpophalangeal joint. In addition to Staphylococcus and Streptococcus, which of the following organisms dictates the specific empiric antibiotic choice?

. Pasteurella multocida
. Capnocytophaga canimorsus
. Eikenella corrodens
. Bartonella henselae
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Pasteurella multocida

Explanation

Human bite wounds, particularly clenched-fist injuries, carry a high risk of Eikenella corrodens infection. Empiric treatment typically involves amoxicillin-clavulanate to cover this along with common skin and oral flora.

Question 3956

Topic: Biology, Genetics & Bone Healing

During the second stage of the Masquelet technique for an infected tibial nonunion, a surgeon plans to remove the antibiotic cement spacer and place bone graft. What is the optimal timing for this second stage to maximize the osteogenic potential of the induced membrane?

. 2 to 4 weeks
. 6 to 8 weeks
. 12 to 16 weeks
. 6 months
. 1 year

Correct Answer & Explanation

. 2 to 4 weeks

Explanation

The second stage of the Masquelet technique is ideally performed 6 to 8 weeks after spacer placement. At this time, the induced membrane has optimal vascularity and peak expression of osteogenic growth factors like VEGF and BMP-2.

Question 3957

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 3958

Topic: 1. General Principles & Basic Science

A soldier sustains severe bilateral lower extremity blast injuries from an IED. Several days after initial debridement, the wounds develop a progressive, necrotic appearance with a grayish mold. Histology reveals broad, non-septate hyphae branching at right angles. What is the most appropriate systemic pharmacological treatment?

. Fluconazole
. Liposomal amphotericin B
. Caspofungin
. Terbinafine
. Voriconazole

Correct Answer & Explanation

. Fluconazole

Explanation

The clinical presentation and histology (broad, non-septate hyphae with right-angle branching) are classic for mucormycosis. Treatment requires extensive surgical debridement and systemic liposomal amphotericin B.

Question 3959

Topic: 1. General Principles & Basic Science

A 25-year-old male presents with profound toxemia, tachycardia, and a bronze discoloration of the skin over his thigh 48 hours after sustaining a penetrating dirt-contaminated injury. Crepitus is palpable. Gram stain of the wound exudate shows large Gram-positive rods and an absence of polymorphonuclear leukocytes. Which of the following pathogens is the most likely cause?

. Streptococcus pyogenes
. Staphylococcus aureus
. Clostridium perfringens
. Pseudomonas aeruginosa
. Bacteroides fragilis

Correct Answer & Explanation

. Streptococcus pyogenes

Explanation

Clostridium perfringens causes gas gangrene (clostridial myonecrosis), characterized by rapid onset, bronze skin discoloration, crepitus, and systemic toxicity. The absence of PMNs on Gram stain is due to the elaboration of alpha and theta toxins that lyse leukocytes.

Question 3960

Topic: 1. General Principles & Basic Science
A 55-year-old diabetic male presents with severe lower extremity pain out of proportion to exam and swelling. A necrotizing soft tissue infection is suspected. According to the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score, which of the following laboratory parameters is most heavily weighted, yielding the maximum possible points for a single variable if highly elevated?
. C-reactive protein (CRP)
. White blood cell (WBC) count
. Hemoglobin
. Serum sodium
. Serum creatinine

Correct Answer & Explanation

. C-reactive protein (CRP)

Explanation

The LRINEC score utilizes CRP, WBC, hemoglobin, sodium, creatinine, and glucose. A CRP > 150 mg/L yields the highest individual point value (4 points) in this scoring system.

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