Menu

1. General Principles & Basic Science MCQs

Practice Set 468 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 9341

Topic: Infection, Pharmacology & VTE

When treating a periprosthetic joint infection caused by Staphylococcus aureus with retention of the hardware, rifampin is often added to the antibiotic regimen. What is the primary mechanism of action of rifampin?

. Inhibition of bacterial cell wall peptidoglycan synthesis
. Binding to the 30S ribosomal subunit to halt translation
. Inhibition of DNA-dependent RNA polymerase
. Direct disruption of the bacterial exopolysaccharide matrix

Correct Answer & Explanation

. Inhibition of DNA-dependent RNA polymerase

Explanation

Rifampin is highly effective against biofilm-associated Staphylococci in periprosthetic joint infections due to its ability to penetrate biofilms and target stationary-phase bacteria. It works by inhibiting DNA-dependent RNA polymerase.

Question 9342

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy with X-linked hypophosphatemia (XLH) continues to have progressive lower extremity bowing despite standard oral phosphate and calcitriol therapy. Which of the following targeted therapies directly addresses the underlying pathophysiology?

. High-dose intravenous Vitamin D3
. Teriparatide
. Denosumab
. Burosumab

Correct Answer & Explanation

. Burosumab

Explanation

Burosumab is an FDA-approved monoclonal antibody that binds to and inhibits FGF-23. It is a highly effective targeted therapy for X-linked hypophosphatemia (XLH), addressing the root cause of the renal phosphate wasting.

Question 9343

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain. Radiographs demonstrate bilateral pseudofractures of the medial femoral neck.

If an iliac crest bone biopsy with double tetracycline labeling is performed, what is the expected histologic finding?

. A mosaic pattern of woven and lamellar bone
. Increased osteoid seam width and a prolonged mineralization lag time
. Extensive subperiosteal bone resorption with brown tumors
. Empty osteocyte lacunae with signs of creeping substitution

Correct Answer & Explanation

. Increased osteoid seam width and a prolonged mineralization lag time

Explanation

The classic histologic finding in osteomalacia is an excess of unmineralized osteoid (increased osteoid seam width) and a prolonged mineralization lag time on tetracycline labeling. Radiographically, Looser zones (pseudofractures) are a hallmark sign.

Question 9344

Topic: Infection, Pharmacology & VTE

In children, acute hematogenous osteomyelitis most frequently affects which specific anatomic region of the long bone?

. Diaphysis
. Epiphysis
. Metaphysis
. Apophysis

Correct Answer & Explanation

. Metaphysis

Explanation

Pediatric acute hematogenous osteomyelitis typically begins in the metaphysis. The sluggish blood flow in the looping venous sinusoids adjacent to the physis creates an ideal low-oxygen environment for bacterial seeding.

Question 9345

Topic: 1. General Principles & Basic Science

A patient with CREST syndrome is referred for orthopedic evaluation of painful subcutaneous nodules in the digits that occasionally extrude a chalky white material. Which specific autoantibody is most closely associated with this patient's systemic disease?

. Anti-Jo-1
. Anti-centromere
. Anti-Scl-70 (Anti-topoisomerase I)
. Anti-double-stranded DNA

Correct Answer & Explanation

. Anti-centromere

Explanation

CREST syndrome (a limited cutaneous form of scleroderma) is strongly associated with Anti-centromere antibodies. The chalky white extrusions describe calcinosis cutis, the 'C' in CREST.

Question 9346

Topic: Biology, Genetics & Bone Healing

Which of the following statements most accurately distinguishes the underlying pathophysiology of osteomalacia from that of osteoporosis?

. Osteoporosis represents a defect in bone mineralization, resulting in a decreased mineral-to-matrix ratio.
. Osteomalacia is characterized by a normal bone mineral-to-matrix ratio but decreased overall bone mass.
. Osteomalacia features a decreased bone mineral-to-matrix ratio due to defective mineralization.
. Both conditions exhibit a decreased mineral-to-matrix ratio, but osteoporosis occurs exclusively in trabecular bone.

Correct Answer & Explanation

. Osteomalacia features a decreased bone mineral-to-matrix ratio due to defective mineralization.

Explanation

Osteomalacia is fundamentally a defect in bone mineralization, resulting in unmineralized osteoid and a decreased mineral-to-matrix ratio. Osteoporosis involves a loss of total bone mass, but the remaining bone has a normal mineral-to-matrix ratio.

Question 9347

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, what is the primary function of the bacterial glycocalyx?

. Facilitating rapid, exponential bacterial replication
. Acting as a mechanical barrier against host immunity and antibiotic penetration
. Promoting immediate planktonic dissemination to distant organs
. Increasing bacterial susceptibility to macrophage phagocytosis

Correct Answer & Explanation

. Acting as a mechanical barrier against host immunity and antibiotic penetration

Explanation

The glycocalyx (exopolysaccharide matrix) is a defining feature of bacterial biofilms in orthopedic implant infections. It acts as a mechanical and biochemical barrier that protects stationary-phase bacteria from both antibiotics and host immune clearance.

Question 9348

Topic: Infection, Pharmacology & VTE
Which of the following correctly describes Kingella kingae, an increasingly recognized cause of pediatric osteoarticular infections?
. It is a fastidious Gram-negative organism that is best isolated using BACTEC blood culture vials or PCR.
. It is a Gram-positive coccus that typically affects adolescents and young adults.
. It is easily cultured on standard MacConkey agar without special growth factors.
. It primarily causes chronic contiguous osteomyelitis in diabetic patients.

Correct Answer & Explanation

. It is a fastidious Gram-negative organism that is best isolated using BACTEC blood culture vials or PCR.

Explanation

Kingella kingae is a fastidious Gram-negative bacillus and is a leading cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. Because it is difficult to culture on standard solid media, it is best isolated by inoculating synovial fluid directly into blood culture vials or using PCR.

Question 9349

Topic: Biology, Genetics & Bone Healing
A 2-year-old child presents with rickets-like skeletal deformities and early loss of deciduous teeth. Laboratory analysis shows marked osteomalacia with a notably low serum alkaline phosphatase level. What is the primary underlying defect?
. Mutation in the PHEX gene leading to FGF-23 excess
. Deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) due to an ALPL mutation
. Dietary deficiency of cholecalciferol
. Impaired 1-alpha-hydroxylase activity in the kidneys

Correct Answer & Explanation

. Deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) due to an ALPL mutation

Explanation

Hypophosphatasia is an inborn error of metabolism caused by mutations in the ALPL gene, leading to deficient tissue-nonspecific alkaline phosphatase (TNSALP) activity. It mimics rickets or osteomalacia radiographically but is distinctly characterized by low serum alkaline phosphatase.

Question 9350

Topic: Infection, Pharmacology & VTE

In the lifecycle of a bacterial biofilm associated with orthopedic implants, what is the final stage that facilitates the spread of infection to new sites?

. Irreversible planktonic attachment
. Quorum sensing and matrix production
. Detachment and dispersal
. Intracellular invasion and host cell lysis

Correct Answer & Explanation

. Detachment and dispersal

Explanation

The biofilm lifecycle consists of initial attachment, irreversible adherence, matrix maturation, and finally, detachment or dispersal. During dispersal, clumps of bacteria or planktonic cells are released to seed new areas, propagating the infection.

Question 9351

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with progressive bowing of the lower extremities. Labs show normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the primary mechanism of this disease?

. Decreased intestinal calcium absorption
. Excessive production of FGF23 leading to renal phosphate wasting
. Mutation in the Type I collagen gene
. Deficiency of 1 alpha-hydroxylase
. Inadequate dietary intake of Vitamin D

Correct Answer & Explanation

. Excessive production of FGF23 leading to renal phosphate wasting

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation, resulting in excessive FGF23. Elevated FGF23 causes renal phosphate wasting and impairs 1-alpha-hydroxylase, leading to defective bone mineralization.

Question 9352

Topic: Biology, Genetics & Bone Healing

A 45-year-old female with a history of systemic sclerosis presents with progressive shortening of her distal fingers and painful, chalky subcutaneous nodules on her fingertips. Radiographs reveal resorption of the terminal phalangeal tufts. What is the most appropriate initial management for the subcutaneous nodules if they become acutely inflamed but lack signs of systemic infection?

. Immediate surgical excision
. Empiric intravenous antibiotics
. Intralesional corticosteroid injections or systemic calcium channel blockers
. Amputation of the affected digits
. Bisphosphonate therapy

Correct Answer & Explanation

. Intralesional corticosteroid injections or systemic calcium channel blockers

Explanation

The patient has calcinosis cutis and acro-osteolysis secondary to scleroderma. Initial treatment is medical with calcium channel blockers or intralesional steroids, as surgical excision is fraught with poor wound healing and infection risk.

Question 9353

Topic: Infection, Pharmacology & VTE

A 14-month-old girl presents with a limp and refusal to bear weight on the right leg. She has a low-grade fever and a recent upper respiratory infection. Inflammatory markers are mildly elevated. Blood cultures are negative, but a joint aspiration of the knee grows a fastidious Gram-negative coccobacillus on blood agar. What is the most likely causative organism?

. Staphylococcus aureus
. Haemophilus influenzae type B
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria meningitidis

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a common cause of pediatric septic arthritis and osteomyelitis in children under 4 years old. It is a fastidious Gram-negative organism that often follows upper respiratory infections.

Question 9354

Topic: Infection, Pharmacology & VTE

A 72-year-old male with an infected total hip arthroplasty undergoes a two-stage revision. During the extraction of the components, thick biofilm is noted on the prosthesis. Which of the following describes the primary characteristic of the bacteria within the deeper layers of this biofilm?

. High metabolic activity and rapid replication
. Exclusively Gram-negative organisms
. Decreased metabolic rate and resistance to standard antibiotics
. Planktonic state with high susceptibility to beta-lactams
. Lack of an extracellular polymeric substance (EPS) matrix

Correct Answer & Explanation

. Decreased metabolic rate and resistance to standard antibiotics

Explanation

Bacteria embedded deep within a biofilm enter a stationary phase with a lowered metabolic rate (persister cells). This makes them highly recalcitrant to traditional antibiotics that target actively dividing cells.

Question 9355

Topic: 1. General Principles & Basic Science

A 60-year-old female with end-stage renal disease on hemodialysis presents with bilateral hip pain. Radiographs reveal pseudofractures in the femoral neck. Lab values show elevated PTH, hyperphosphatemia, and hypocalcemia. What is the primary cause of her impaired bone mineralization?

. Overproduction of 1,25-dihydroxyvitamin D
. Inability of the kidneys to convert 25-hydroxyvitamin D to its active form
. Primary hyperparathyroidism
. Intestinal malabsorption of phosphorus
. Excessive production of calcitonin

Correct Answer & Explanation

. Inability of the kidneys to convert 25-hydroxyvitamin D to its active form

Explanation

In chronic kidney disease, the failing kidneys cannot properly convert 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D. This leads to hypocalcemia, secondary hyperparathyroidism, and renal osteodystrophy (osteomalacia).

Question 9356

Topic: Infection, Pharmacology & VTE

A 12-year-old boy is diagnosed with acute hematogenous osteomyelitis of the proximal tibia. Cultures grow Methicillin-resistant Staphylococcus aureus (MRSA). The patient has a known severe anaphylactic allergy to vancomycin. Which of the following intravenous antibiotics is the most appropriate alternative for targeting the MRSA?

. Cefazolin
. Clindamycin
. Daptomycin
. Ceftriaxone
. Ampicillin-sulbactam

Correct Answer & Explanation

. Daptomycin

Explanation

Daptomycin is an excellent bactericidal alternative for MRSA in patients with vancomycin allergies or intolerance. Clindamycin resistance in MRSA is increasing and depends on local antibiograms, making daptomycin a more reliable empiric IV choice.

Question 9357

Topic: Infection, Pharmacology & VTE

A 22-year-old sexually active female presents with acute onset of right knee pain, swelling, and fever. She also reports migrating polyarthralgia over the past three days and a few painless pustular skin lesions on her hands. Synovial fluid aspiration shows 45,000 WBC/uL. What is the most likely pathogen?

. Staphylococcus aureus
. Neisseria gonorrhoeae
. Streptococcus pyogenes
. Borrelia burgdorferi
. Treponema pallidum

Correct Answer & Explanation

. Neisseria gonorrhoeae

Explanation

Disseminated gonococcal infection classically presents in young, sexually active patients with migratory polyarthritis, tenosynovitis, and painless pustular dermatitis. Synovial WBC counts may be lower than those seen in staphylococcal septic arthritis.

Question 9358

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy presents with progressive bowing of the legs and short stature. Labs show normal serum calcium, markedly low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following best explains the pathophysiology of his condition?

. Defective osteoclast carbonic anhydrase II
. Overproduction of FGF23 leading to renal phosphate wasting
. Defective type 1 collagen synthesis
. Autoimmune destruction of osteoblasts
. Inadequate dietary intake of Vitamin D

Correct Answer & Explanation

. Overproduction of FGF23 leading to renal phosphate wasting

Explanation

X-linked hypophosphatemia is caused by a PHEX gene mutation, leading to decreased degradation and overproduction of FGF23. High FGF23 levels cause decreased renal reabsorption of phosphate, leading to profound hypophosphatemia and defective bone mineralization.

Question 9359

Topic: Biology, Genetics & Bone Healing



A 45-year-old strict vegan presents with generalized bone pain and a waddling gait. Radiographs show transverse radiolucent bands in the femoral neck and pubic rami. If a bone biopsy were performed following double tetracycline labeling, what would be the expected finding?

. Increased osteoclastic tunneling with normal mineralization
. Decreased distance between tetracycline labels with widened unmineralized osteoid seams
. Woven bone lacking Haversian systems with mosaic cement lines
. Empty lacunae indicating osteonecrosis
. Thickened trabeculae with narrow osteoid seams

Correct Answer & Explanation

. Decreased distance between tetracycline labels with widened unmineralized osteoid seams

Explanation

The patient has nutritional osteomalacia characterized by Looser zones (pseudofractures). Histomorphometry with double tetracycline labeling would show a decreased distance between labels (low mineralization rate) and widened unmineralized osteoid seams.

Question 9360

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a limp, low-grade fever, and refusal to bear weight on the right leg. Hip aspiration yields synovial fluid with a WBC count of 45,000 cells/uL. Standard Gram stain and routine cultures are negative at 48 hours. What is the most appropriate method to identify the most likely causative organism?
. Acid-fast bacilli smear
. Darkfield microscopy
. Inoculation of synovial fluid directly into BACTEC blood culture vials or PCR testing
. Fungal cultures on Sabouraud dextrose agar
. Enzyme-linked immunosorbent assay (ELISA) for Lyme disease

Correct Answer & Explanation

. Inoculation of synovial fluid directly into BACTEC blood culture vials or PCR testing

Explanation

Kingella kingae is the most common cause of septic arthritis in children under 4 years old. It is a fastidious organism that is notoriously difficult to grow on solid media; inoculation into blood culture vials or PCR significantly increases detection.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page