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1. General Principles & Basic Science MCQs

Practice Set 490 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 9781

Topic: 1. General Principles & Basic Science
A 60-year-old woman with a long-standing history of systemic sclerosis presents with severe, fixed flexion contractures of her proximal interphalangeal (PIP) joints bilaterally. At the cellular level, this joint deformity is primarily driven by the overproduction of which substance by hyperactive fibroblasts?
. Elastin
. Collagen types I and III
. Hyaluronic acid
. Fibrillin-1
. Keratan sulfate

Correct Answer & Explanation

. Collagen types I and III

Explanation

Systemic sclerosis is characterized by widespread microvascular damage and excessive fibrosis. The fibrosis and resulting joint contractures are driven by hyperactive fibroblasts overproducing extracellular matrix proteins, predominantly collagen types I and III.

Question 9782

Topic: 1. General Principles & Basic Science

A 50-year-old woman presents with calcinosis cutis, esophageal dysmotility, sclerodactyly, and telangiectasia.

Laboratory testing reveals the presence of anti-centromere antibodies. This patient is at the highest risk for developing which of the following life-threatening complications?

. Rapidly progressive interstitial lung disease
. Scleroderma renal crisis
. Pulmonary arterial hypertension
. Hepatic cirrhosis
. Constrictive pericarditis

Correct Answer & Explanation

. Pulmonary arterial hypertension

Explanation

The patient has CREST syndrome (limited cutaneous systemic sclerosis), marked by anti-centromere antibodies. These patients are at a particularly high risk for developing isolated pulmonary arterial hypertension, a leading cause of mortality in this subset.

Question 9783

Topic: Infection, Pharmacology & VTE

Which of the following is an absolute contraindication to performing a Debridement, Antibiotics, and Implant Retention (DAIR) procedure for a periprosthetic joint infection?

. Symptom duration of 2 weeks
. Infection with a fluoroquinolone-sensitive organism
. A radiographically loose femoral component
. Patient age greater than 80 years
. Serum CRP of 150 mg/L

Correct Answer & Explanation

. A radiographically loose femoral component

Explanation

A loose prosthesis is an absolute contraindication for a DAIR procedure, as biofilm cannot be adequately eradicated and the implant requires revision for mechanical stability. DAIR is best reserved for acute infections (<3-4 weeks) with well-fixed implants.

Question 9784

Topic: Biology, Genetics & Bone Healing

A patient with systemic sclerosis presents with progressive shortening of her distal digits. Radiographs reveal resorption of the terminal phalangeal tufts. Which pathophysiology primarily drives this specific musculoskeletal manifestation?

. Secondary hyperparathyroidism
. Microvascular ischemia and intimal proliferation
. Direct autoimmune destruction of osteoclasts
. Osteoblast apoptosis induced by anti-Scl-70 antibodies
. Synovial pannus invasion of the distal interphalangeal joints

Correct Answer & Explanation

. Microvascular ischemia and intimal proliferation

Explanation

Acro-osteolysis in systemic sclerosis is primarily driven by chronic microvascular ischemia resulting from intimal proliferation and endothelial injury (Raynaud phenomenon). This chronic ischemia leads to atrophy and resorption of the distal phalangeal tufts.

Question 9785

Topic: Biomechanics & Biomaterials

When formulating polymethyl methacrylate (PMMA) antibiotic-loaded bone cement for a spacer in a two-stage exchange for PJI, which characteristic is an absolute requirement for the admixed antibiotics?

. They must be strictly bacteriostatic
. They must be heat-stable
. They must be highly protein-bound
. They must have a low molecular weight to prevent elution
. They must be exclusively effective against Gram-negative organisms

Correct Answer & Explanation

. They must be heat-stable

Explanation

Antibiotics added to PMMA must be heat-stable because the exothermic polymerization reaction of bone cement reaches high temperatures. Vancomycin, tobramycin, and gentamicin are heat-stable and commonly used for this purpose.

Question 9786

Topic: Infection, Pharmacology & VTE

A 42-year-old woman presents with diffuse skin thickening extending proximal to her elbows and knees. She complains of progressive dyspnea on exertion. Serologic testing is positive for Anti-Scl-70 antibodies. What is the most likely pulmonary complication associated with this specific autoantibody profile?

. Pulmonary arterial hypertension without parenchymal disease
. Spontaneous pneumothorax
. Interstitial lung disease (pulmonary fibrosis)
. Asthma
. Pulmonary embolism

Correct Answer & Explanation

. Interstitial lung disease (pulmonary fibrosis)

Explanation

Anti-Scl-70 (anti-topoisomerase I) antibodies are associated with diffuse cutaneous systemic sclerosis, which carries a high risk of interstitial lung disease (pulmonary fibrosis). In contrast, anti-centromere antibodies (CREST) are more associated with isolated pulmonary arterial hypertension.

Question 9787

Topic: Infection, Pharmacology & VTE

Biofilm formation plays a critical role in the pathogenesis of periprosthetic joint infections. Within a mature biofilm, which characteristic best explains the extreme resistance of the embedded bacteria to systemic antibiotic therapy?

. Rapid exponential replication of the bacteria
. High metabolic rate demanding constant nutrient influx
. The bacteria enter a dormant, stationary growth phase
. The complete absence of an exopolysaccharide matrix
. Increased cell-wall permeability to large molecules

Correct Answer & Explanation

. The bacteria enter a dormant, stationary growth phase

Explanation

Bacteria within a mature biofilm exhibit a markedly altered phenotype, entering a dormant, stationary growth phase. Because most antibiotics target active cell division and metabolic processes, these dormant bacteria are highly resistant to standard antimicrobial therapy.

Question 9788

Topic: Infection, Pharmacology & VTE

A 68-year-old man undergoes DAIR for an acute hematogenous periprosthetic joint infection of his knee. Intraoperative cultures grow methicillin-sensitive Staphylococcus aureus (MSSA). Which of the following oral antibiotic regimens is best supported by evidence for long-term suppression after initial IV therapy?

. Cephalexin alone
. Ciprofloxacin alone
. Amoxicillin alone
. Dicloxacillin and rifampin
. Ciprofloxacin and rifampin

Correct Answer & Explanation

. Ciprofloxacin and rifampin

Explanation

Rifampin has excellent biofilm penetration and is highly effective against staphylococcal species in PJI. It must be combined with a companion drug (such as a fluoroquinolone like ciprofloxacin) to prevent the rapid emergence of resistance.

Question 9789

Topic: 1. General Principles & Basic Science

During a 2-stage revision for a chronic periprosthetic knee infection, an articulating antibiotic spacer is placed.

Compared to static spacers, articulating spacers in the knee have been shown to provide which of the following benefits?

. Lower overall re-infection rates
. Improved extensor mechanism mobilization and ease of second-stage reimplantation
. Higher rates of local antibiotic elution
. Decreased systemic antibiotic toxicity
. Increased stability allowing return to high-impact activities between stages

Correct Answer & Explanation

. Improved extensor mechanism mobilization and ease of second-stage reimplantation

Explanation

Articulating spacers maintain joint mobility, preventing severe capsular contracture and preserving the length of the extensor mechanism. This significantly facilitates surgical exposure during the second stage, yielding comparable infection eradication rates to static spacers.

Question 9790

Topic: 1. General Principles & Basic Science

A 50-year-old female presents with severe Raynaud's phenomenon, esophageal dysmotility, and the findings shown in the clinical image.

Which autoantibody is most specifically associated with her likely diagnosis?

. Anti-Scl-70
. Anti-centromere
. Anti-dsDNA
. Rheumatoid factor
. Anti-Jo-1

Correct Answer & Explanation

. Anti-centromere

Explanation

The image and clinical presentation describe CREST syndrome (limited cutaneous systemic sclerosis). Anti-centromere antibodies are highly specific for CREST syndrome.

Question 9791

Topic: Infection, Pharmacology & VTE

Which of the following antibiotics is most critical to include in the treatment regimen for a retained total joint arthroplasty infected with methicillin-sensitive Staphylococcus aureus, owing to its efficacy against biofilm-associated bacteria?

. Vancomycin
. Linezolid
. Rifampin
. Ciprofloxacin
. Daptomycin

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin has unique activity against staphylococcal species residing within a mature biofilm. It is universally recommended as an adjunct in the medical management of staphylococcal PJI treated with debridement and implant retention.

Question 9792

Topic: Biomechanics & Biomaterials

The optimal initial and sustained elution of antibiotics from a polymethylmethacrylate (PMMA) cement spacer is best achieved by which of the following preparation techniques?

. Increasing the vacuum mixing time to minimize air bubbles
. Using a low-viscosity cement with a high ratio of liquid monomer to powder
. Hand mixing the cement to increase porosity and surface area
. Adding antibiotics strictly in a liquid formulation
. Using pure crystalline antibiotics instead of powdered formulations

Correct Answer & Explanation

. Hand mixing the cement to increase porosity and surface area

Explanation

Antibiotic elution from PMMA is highly dependent on the surface area and porosity of the cement. Hand mixing (avoiding vacuum mixing) increases porosity, thereby enhancing the release of the admixed antibiotics.

Question 9793

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with limited cutaneous systemic sclerosis presents with painful, firm subcutaneous nodules on her fingertips that occasionally extrude a chalky white material.

What is the initial recommended medical therapy to manage these symptomatic lesions?

. Intravenous cyclophosphamide
. Oral calcium channel blockers
. Surgical amputation of the affected digits
. Intralesional corticosteroid injections
. High-dose oral vitamin D supplementation

Correct Answer & Explanation

. Oral calcium channel blockers

Explanation

Calcinosis cutis in systemic sclerosis is notoriously difficult to treat. Calcium channel blockers, such as diltiazem, are often considered first-line medical therapy to reduce calcium influx into cells, though surgical excision may be required for recalcitrant lesions.

Question 9794

Topic: 1. General Principles & Basic Science

Flexion contractures of the fingers in patients with systemic sclerosis are primarily driven by which of the following pathologic processes?

. Synovial hypertrophy and inflammatory pannus formation
. Primary enzymatic destruction of the articular cartilage
. Extensive fibrosis of the skin, subcutaneous tissues, and joint capsules
. Spontaneous rupture of the extensor tendons
. Ischemic necrosis of the intrinsic lumbrical muscles

Correct Answer & Explanation

. Extensive fibrosis of the skin, subcutaneous tissues, and joint capsules

Explanation

In systemic sclerosis, the overproduction and accumulation of collagen result in extensive fibrosis of the skin and deeper connective tissues. This fibrotic process leads to severe, progressive tethering and flexion contractures of the digits without primary articular destruction.

Question 9795

Topic: 1. General Principles & Basic Science

A patient with scleroderma-associated Raynaud's phenomenon presents with an acute, extremely painful ischemic digital ulcer. Conservative measures and oral therapies have failed. Which of the following is the most appropriate next step in management to prevent autoamputation?

. Immediate proximal ray amputation
. Intravenous epoprostenol (prostacyclin analogue)
. Oral methotrexate
. Local injection of epinephrine
. Initiation of high-dose oral corticosteroids

Correct Answer & Explanation

. Intravenous epoprostenol (prostacyclin analogue)

Explanation

For severe, limb-threatening Raynaud's phenomenon with ischemic digital ulcers in systemic sclerosis, intravenous prostacyclin analogues (e.g., epoprostenol or iloprost) are indicated. They promote intense vasodilation and inhibit platelet aggregation to salvage the digit.

Question 9796

Topic: 1. General Principles & Basic Science

Which of the following somatic genetic mutations is found in approximately 50-60% of patients with Langerhans cell histiocytosis, supporting its modern classification as a myeloid neoplastic disorder?

. t(11;22) translocation
. BRAF V600E mutation
. p53 deletion
. GNAS mutation
. EXT1 mutation

Correct Answer & Explanation

. BRAF V600E mutation

Explanation

The BRAF V600E somatic mutation is identified in more than half of patients with Langerhans cell histiocytosis. This discovery has led to its reclassification as a neoplastic disorder rather than a reactive process, and it offers a target for specific inhibitor therapies.

Question 9797

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a common pathogen in periprosthetic joint infections. Which of the following components is primarily responsible for the structural integrity of the biofilm produced by this organism?

. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Alpha-toxin
. Panton-Valentine leukocidin
. Lipoteichoic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm of S. epidermidis is primarily composed of polysaccharide intercellular adhesin (PIA), which is synthesized by the icaADBC operon. This extracellular polymeric substance protects the bacteria from host immune responses and antibiotics.

Question 9798

Topic: 1. General Principles & Basic Science

Recent molecular advancements have classified Langerhans cell histiocytosis (LCH) as an inflammatory myeloid neoplasm. Which of the following genetic mutations is present in over 50% of LCH cases and serves as a potential target for molecular therapy?

. FLT3-ITD
. BCR-ABL1
. BRAF V600E
. JAK2 V617F
. IDH1 R132H

Correct Answer & Explanation

. BRAF V600E

Explanation

The BRAF V600E somatic mutation is found in 50-60% of LCH cases, leading to constitutive activation of the MAPK/ERK pathway. Targeted therapies, such as the BRAF inhibitor vemurafenib, are utilized for severe, refractory multisystem cases.

Question 9799

Topic: Infection, Pharmacology & VTE

In a patient undergoing Debridement, Antibiotics, and Implant Retention (DAIR) for a periprosthetic joint infection, which of the following factors is considered an absolute contraindication to the procedure?

. Age greater than 65 years
. Infection with Streptococcus species
. Duration of symptoms less than 7 days
. Presence of a draining sinus tract
. Exchange of modular components

Correct Answer & Explanation

. Presence of a draining sinus tract

Explanation

The presence of a sinus tract indicates a chronic infection with an established, mature biofilm. This is an absolute contraindication to a DAIR procedure, as eradication cannot be achieved without complete implant removal.

Question 9800

Topic: 1. General Principles & Basic Science

A 68-year-old female undergoes first-stage explantation and placement of an articulating antibiotic cement spacer for a chronic PJI of the knee. The cement is loaded with high doses of vancomycin and tobramycin. Postoperatively, she develops rising serum creatinine and oliguria. Which of the following is the most likely cause?

. Systemic toxicity strictly from postoperative IV antibiotics
. Anaphylactic reaction to the polymethylmethacrylate (PMMA)
. Acute kidney injury from local elution of high-dose aminoglycosides and glycopeptides
. Deep vein thrombosis
. Unrecognized intraoperative ureteral injury

Correct Answer & Explanation

. Acute kidney injury from local elution of high-dose aminoglycosides and glycopeptides

Explanation

Antibiotics locally eluted from PMMA spacers can reach high systemic concentrations. When large amounts of cement and high doses of nephrotoxic antibiotics (like vancomycin and tobramycin) are used, patients are at significant risk for acute kidney injury.

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