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1. General Principles & Basic Science MCQs

Practice Set 758 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 15141

Topic: 1. General Principles & Basic Science
A 55-year-old poorly controlled diabetic presents with rapid-onset, severe right leg swelling, erythema, hemorrhagic bullae, and excruciating pain out of proportion to physical findings. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score is 9. What is the single most critical intervention?
. STAT MRI of the lower extremity with gadolinium contrast
. Administration of broad-spectrum IV antibiotics and ICU observation
. Immediate emergent surgical debridement
. Initiation of hyperbaric oxygen therapy
. Application of a negative pressure wound therapy device

Correct Answer & Explanation

. Immediate emergent surgical debridement

Explanation

Necrotizing fasciitis is a life-threatening surgical emergency. While broad-spectrum antibiotics are necessary, immediate radical surgical debridement of all necrotic tissue is the absolute most critical intervention to improve survival.

Question 15142

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents to the emergency department with a 2-day history of right hip pain and a limp. He currently refuses to bear weight on the right leg. His oral temperature is 38.6°C (101.5°F). Laboratory studies reveal a white blood cell (WBC) count of 10,500/mm³, an erythrocyte sedimentation rate (ESR) of 45 mm/hr, and a C-reactive protein (CRP) of 2.5 mg/dL. According to the classic Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 71%

Explanation

The Kocher criteria are used to differentiate septic arthritis from transient synovitis in the pediatric hip. The four classic criteria are: 1) Non-weight-bearing on the affected side, 2) Temperature > 38.5°C (101.3°F), 3) ESR > 40 mm/hr, and 4) WBC count > 12,000/mm³. This patient meets three of the four criteria (non-weight-bearing, fever > 38.5°C, and ESR > 40 mm/hr). His WBC count is normal (< 12,000). According to Kocher's original study, the probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2 criteria, 93% for 3 criteria, and 99% for all 4 criteria. Therefore, with 3 criteria met, the probability is 93%.

Question 15143

Topic: Infection, Pharmacology & VTE

A 2-year-old girl presents with a fever of 39 C, refusal to bear weight, an ESR of 55 mm/hr, and a WBC count of 14,000. Hip aspiration yields purulent fluid with a negative Gram stain. What is the most sensitive method to identify the most common atypical bacterial pathogen in this age group?

. Routine blood agar culture for 48 hours
. Acid-fast bacillus smear
. Polymerase chain reaction (PCR) assay of synovial fluid
. Fungal culture
. Synovial fluid glucose and protein levels

Correct Answer & Explanation

. Polymerase chain reaction (PCR) assay of synovial fluid

Explanation

Kingella kingae is a frequent cause of pediatric septic arthritis in children under 4 years old and is notoriously difficult to culture. PCR of synovial fluid is highly sensitive and the diagnostic test of choice.

Question 15144

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy with a history of multiple low-energy fractures, blue sclerae, and dentinogenesis imperfecta is being evaluated. He has bowing of both femurs. A genetic panel confirms a mutation in the COL1A1 gene. Which of the following describes the mechanism of action of the first-line medical therapy used to decrease fracture burden in this condition?

. Stimulation of osteoblast proliferation and differentiation
. Inhibition of osteoclast-mediated bone resorption via farnesyl pyrophosphate synthase
. Exogenous replacement of type I collagen molecules
. Activation of the calcium-sensing receptor on the parathyroid gland
. Selective modulation of estrogen receptors on bone trabeculae

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption via farnesyl pyrophosphate synthase

Explanation

Osteogenesis imperfecta is typically managed medically with bisphosphonates (e.g., pamidronate). Nitrogen-containing bisphosphonates inhibit osteoclast-mediated bone resorption by blocking the enzyme farnesyl pyrophosphate synthase, which decreases fracture incidence and increases bone mineral density.

Question 15145

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen, red, and painful knee. Aspiration yields turbid fluid. Synovial fluid analysis confirms the diagnosis of gout. Which of the following describes the characteristic microscopic findings under polarized light?

. Positively birefringent rhomboid-shaped crystals
. Negatively birefringent needle-shaped crystals
. Non-birefringent envelope-shaped crystals
. Positively birefringent rod-shaped crystals
. Negatively birefringent rhomboid-shaped crystals

Correct Answer & Explanation

. Negatively birefringent needle-shaped crystals

Explanation

Gout is caused by the deposition of monosodium urate crystals in the joint. Under polarized light microscopy, these crystals classically appear negatively birefringent and needle-shaped.

Question 15146

Topic: Infection, Pharmacology & VTE

A 4-year-old boy refuses to bear weight on his right leg. His temperature is 38.8°C, WBC is 13,500/mm3, and ESR is 45 mm/hr. An ultrasound of the right hip demonstrates a significant joint effusion. What is the most appropriate next step in management?

. Intravenous antibiotics and serial clinical observation
. MRI of the pelvis with and without contrast
. Urgent aspiration and surgical drainage of the hip joint
. CT scan of the hip to rule out osteomyelitis
. Bone scintigraphy (bone scan)

Correct Answer & Explanation

. Urgent aspiration and surgical drainage of the hip joint

Explanation

This child meets all four Kocher criteria (fever, inability to bear weight, ESR >40, WBC >12,000) for a septic hip, predicting a >99% probability of the disease. The standard of care is emergent aspiration and surgical washout to prevent devastating cartilage destruction and osteonecrosis.

Question 15147

Topic: Biology, Genetics & Bone Healing

A patient with symptomatic Paget's disease of the tibia is prescribed the first-line pharmacologic treatment to reduce bone pain and turnover. What is the primary cellular mechanism of action of this medication class?

. Osteoblast inhibition via sclerostin binding
. Osteoclast apoptosis via inhibition of farnesyl pyrophosphate synthase
. RANKL inhibition preventing osteoclast maturation
. Parathyroid hormone receptor agonism
. Direct inhibition of matrix metalloproteinases

Correct Answer & Explanation

. Osteoclast apoptosis via inhibition of farnesyl pyrophosphate synthase

Explanation

Bisphosphonates are the first-line treatment for symptomatic Paget's disease. Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase, which disrupts the mevalonate pathway and ultimately causes osteoclast apoptosis.

Question 15148

Topic: 1. General Principles & Basic Science

A neonate in the NICU develops irritability, fever, and pseudoparalysis of the left lower extremity. Physical examination reveals the left hip is held in a specific resting posture to minimize intracapsular pressure. Which position is most characteristic of a hip joint effusion in septic coxitis?

. Flexion, adduction, and internal rotation
. Extension, abduction, and external rotation
. Flexion, abduction, and external rotation
. Extension, adduction, and internal rotation
. Neutral flexion with maximum internal rotation

Correct Answer & Explanation

. Flexion, abduction, and external rotation

Explanation

A septic hip effusion increases intracapsular pressure, leading to severe pain. The joint capsule accommodates the maximum volume of fluid when the hip is placed in flexion, abduction, and external rotation (FABER), which is the classic position of comfort.

Question 15149

Topic: Biology, Genetics & Bone Healing

Routine laboratory testing in an asymptomatic 65-year-old male reveals an isolated, marked elevation of serum alkaline phosphatase. Calcium, phosphorus, and GGT levels are completely normal. Radiographs of the pelvis show coarse trabeculations and cortical thickening. What phase of Paget's disease does this presentation most likely represent?

. Early pure lytic phase
. Mixed lytic and sclerotic phase
. Late sclerotic phase
. Burned-out phase
. Malignant transformation phase

Correct Answer & Explanation

. Mixed lytic and sclerotic phase

Explanation

Paget's disease progresses through lytic, mixed, and sclerotic phases. The mixed lytic and sclerotic phase is characterized by markedly elevated alkaline phosphatase due to exuberant osteoblastic activity attempting to keep pace with chaotic osteoclastic resorption.

Question 15150

Topic: Biology, Genetics & Bone Healing

A 60-year-old male on long-term hemodialysis presents with diffuse bone pain. Radiographs demonstrate a 'rugger jersey' appearance of the spine. His labs show elevated PTH, low calcium, and high phosphorus. What is the primary pathophysiologic trigger for his skeletal disease?

. Autonomous parathyroid adenoma secreting excess PTH
. Deficient 1-alpha-hydroxylase activity and phosphate retention
. Excessive intestinal calcium absorption
. A primary gain-of-function mutation in the SQSTM1 gene
. Defective mineralization of osteoid leading to osteomalacia

Correct Answer & Explanation

. Deficient 1-alpha-hydroxylase activity and phosphate retention

Explanation

Secondary hyperparathyroidism in chronic kidney disease is primarily driven by phosphate retention and decreased renal 1-alpha-hydroxylase activity, which reduces active Vitamin D. This leads to chronic hypocalcemia, stimulating compensatory PTH hypersecretion.

Question 15151

Topic: Infection, Pharmacology & VTE

A 55-year-old male presents with an acute gout flare in his first metatarsophalangeal joint. He has a history of a recent severe upper gastrointestinal bleed and end-stage renal disease on dialysis. Which of the following is the most appropriate acute pharmacologic treatment?

. Indomethacin
. Naproxen
. Colchicine
. Intra-articular or systemic corticosteroids
. Allopurinol

Correct Answer & Explanation

. Intra-articular or systemic corticosteroids

Explanation

NSAIDs (indomethacin, naproxen) are contraindicated due to his recent GI bleed and ESRD. Colchicine must be dose-adjusted or avoided in severe renal failure due to toxicity. Corticosteroids are the safest and most effective acute treatment in this patient.

Question 15152

Topic: Infection, Pharmacology & VTE

A 2-year-old, fully immunized child is brought to the emergency department with a 2-day history of fever, refusal to walk, and left hip pain. Joint aspiration yields purulent fluid with a WBC count of 85,000/mm3. What is the most common causative organism overall for this condition?

. Kingella kingae
. Staphylococcus aureus
. Haemophilus influenzae type b
. Streptococcus agalactiae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus remains the most common overall cause of septic arthritis in children. While Kingella kingae is increasingly recognized as a common pathogen in children aged 6 months to 4 years, S. aureus is still universally considered the most prevalent pathogen.

Question 15153

Topic: Biology, Genetics & Bone Healing

Which of the following laboratory profiles most accurately differentiates primary hyperparathyroidism from secondary hyperparathyroidism?

. Elevated PTH in primary; decreased PTH in secondary
. Hypercalcemia in primary; hypocalcemia or low-normal calcium in secondary
. Hypophosphatemia in primary; hypophosphatemia in secondary
. Elevated alkaline phosphatase in primary; normal alkaline phosphatase in secondary
. Elevated 1,25-dihydroxyvitamin D in primary; elevated in secondary

Correct Answer & Explanation

. Hypercalcemia in primary; hypocalcemia or low-normal calcium in secondary

Explanation

Primary hyperparathyroidism involves autonomous overproduction of PTH, leading to hypercalcemia. Secondary hyperparathyroidism is a normal physiologic response to chronic hypocalcemia (often from renal failure or vitamin D deficiency), resulting in elevated PTH but low or normal serum calcium.

Question 15154

Topic: Biology, Genetics & Bone Healing

A bone biopsy from the thickened, bowed tibia of a patient with Paget's disease demonstrates a characteristic mosaic pattern of lamellar bone with prominent, disorganized cement lines. What is the underlying primary cellular abnormality driving this disease process?

. Excessive osteoblastic bone formation secondary to a genetic mutation
. Hyperactive, enlarged, and excessively multinucleated osteoclasts
. Defective mineralization of osteoid by impaired osteoblasts
. Autoimmune destruction of articular cartilage leading to subchondral changes
. Malignant proliferation of plasma cells stimulating osteoclast activating factor

Correct Answer & Explanation

. Hyperactive, enlarged, and excessively multinucleated osteoclasts

Explanation

The primary pathophysiologic defect in Paget's disease is the presence of hyperactive, massively enlarged osteoclasts with an excessive number of nuclei (often up to 100). The pathognomonic mosaic pattern of cement lines results from the subsequent chaotic, rapid bone formation by osteoblasts.

Question 15155

Topic: Surgical Anatomy & Approaches



A 65-year-old male presents with massive, ulcerated, chalky white tophaceous deposits over his olecranon and PIP joints, causing severe mechanical restriction and recurrent secondary infections. Initial surgical management of these symptomatic lesions primarily involves:

. Amputation of the affected digits to prevent systemic sepsis
. Total joint arthroplasty of the involved joints
. Careful surgical debulking and excision of tophi to preserve viable tissue
. Primary arthrodesis of the involved joints
. Intralesional injection of pegloticase to dissolve the masses

Correct Answer & Explanation

. Careful surgical debulking and excision of tophi to preserve viable tissue

Explanation

Surgical indications for gouty tophi include infection, intractable pain, ulceration, severe nerve compression, and mechanical block to motion. The primary surgical approach is careful debulking and excision of the tophi while rigorously preserving adjacent functional tendons, nerves, and skin.

Question 15156

Topic: 1. General Principles & Basic Science

A 58-year-old male with a history of prolonged hemodialysis followed by a successful renal transplant 3 years ago presents to the clinic. Routine labs show persistent, severe hypercalcemia and markedly elevated PTH levels despite normal renal graft function. What is the most likely diagnosis?

. Primary hyperparathyroidism
. Secondary hyperparathyroidism
. Tertiary hyperparathyroidism
. Pseudohypoparathyroidism
. Familial hypocalciuric hypercalcemia

Correct Answer & Explanation

. Tertiary hyperparathyroidism

Explanation

Tertiary hyperparathyroidism occurs when the parathyroid glands become completely autonomous and secrete excessive PTH irrespective of serum calcium levels. This typically occurs after a long period of secondary hyperparathyroidism, such as in a dialysis patient who subsequently receives a kidney transplant.

Question 15157

Topic: 1. General Principles & Basic Science

A 55-year-old man presents with a swollen, erythematous first metatarsophalangeal joint. Joint aspiration is performed to confirm the diagnosis of acute gout.

Which of the following describes the characteristic crystal findings under polarized light microscopy?

. Positively birefringent, rhomboid-shaped crystals
. Negatively birefringent, needle-shaped crystals
. Positively birefringent, envelope-shaped crystals
. Negatively birefringent, rhomboid-shaped crystals
. Non-birefringent, needle-shaped crystals

Correct Answer & Explanation

. Negatively birefringent, needle-shaped crystals

Explanation

Gout is characterized by monosodium urate crystals that appear needle-shaped and strongly negatively birefringent under polarized light. Under parallel polarized light, they appear yellow. Calcium pyrophosphate crystals (pseudogout) are positively birefringent and rhomboid-shaped.

Question 15158

Topic: Biology, Genetics & Bone Healing

What is the primary cellular defect that initiates the pathogenesis of Paget's disease of bone?

. Defective osteoblast mineralization
. Overactive, large multinucleated osteoclasts
. Decreased osteocyte apoptosis
. Proliferation of malignant mesenchymal spindle cells
. Impaired collagen type I cross-linking

Correct Answer & Explanation

. Overactive, large multinucleated osteoclasts

Explanation

Paget's disease begins with an initial osteolytic phase driven by overactive, massive multinucleated osteoclasts, often linked to SQSTM1 gene mutations. This is followed by a compensatory but disorganized mixed osteoblastic/osteoclastic phase, leading to weak, woven bone formation.

Question 15159

Topic: Biology, Genetics & Bone Healing

A 62-year-old woman with chronic kidney disease presents with diffuse bone pain. Radiographs of her hands show subperiosteal bone resorption on the radial aspect of the middle phalanges.

What is the most likely primary driving mechanism for these osseous changes?

. Deposition of monosodium urate crystals
. Mutation in the SQSTM1 gene
. Sustained elevation of parathyroid hormone (PTH)
. Chronic vitamin C deficiency
. Loss of functioning osteoclasts

Correct Answer & Explanation

. Sustained elevation of parathyroid hormone (PTH)

Explanation

Subperiosteal bone resorption on the radial aspect of the middle phalanges is the pathognomonic radiographic sign of hyperparathyroidism. In the context of chronic kidney disease, secondary hyperparathyroidism results in sustained PTH elevation leading to osteitis fibrosa cystica.

Question 15160

Topic: 1. General Principles & Basic Science

A 10-day-old neonate presents with irritability, fever, and asymmetric active leg movement. The affected hip is held in flexion, abduction, and external rotation.

What is the physiologic reason for this classic posture?

. It maximizes the resting tension of the iliopsoas muscle.
. It isolates the articular cartilage from purulent enzymatic degradation.
. It maximizes the intra-articular capsular volume to accommodate an effusion.
. It prevents secondary subluxation of the femoral head.
. It minimizes capsular volume to increase stability.

Correct Answer & Explanation

. It maximizes the intra-articular capsular volume to accommodate an effusion.

Explanation

In septic coxitis, the hip joint is typically held in flexion, abduction, and external rotation (FABER). This specific position maximizes the intra-articular capsular volume, which minimizes pain and prevents ischemia from the high-pressure distension caused by a purulent effusion.

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