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4. Pediatrics MCQs

Practice Set 20 of 334

This practice set contains high-yield board review questions covering key concepts in 4. Pediatrics. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 381

Topic: Pediatric Upper Extremity & Spine

A 14-year-old boy presents with a progressive thoracic kyphosis of 65 degrees. The apex of the curve is at T8, and his Risser sign is 1. He complains of mild aching back pain after sports. What is the most appropriate management?

. Observation with radiographs every 12 months
. Physical therapy focusing on core and hamstring stretching alone
. Extension bracing with a Thoracolumbosacral Orthosis (TLSO)
. Cervicothoracolumbosacral Orthosis (Milwaukee brace)
. Posterior spinal fusion with Ponte osteotomies

Correct Answer & Explanation

. Extension bracing with a Thoracolumbosacral Orthosis (TLSO)

Explanation

For a skeletally immature patient (Risser 0-2) with a flexible curve between 50 and 75 degrees, bracing is indicated. Because the apex is at T8 (T7 or below), a TLSO is effective; an apex above T7 would require a Milwaukee brace.

Question 382

Topic: 4. Pediatrics
A patient with myelomeningocele has good quadriceps function, fair hamstring motion, and no active ankle movement. He has bilateral clubfoot. His motor level is:
. L2
. L3
. L4
. L5
. S1

Correct Answer & Explanation

. L4

Explanation

The hamstrings are innervated at a level just proximal to the anterior tibialis muscle (with the highest innervated ankle motor at L5). Therefore, the patient's motor level is best estimated at L4.

Question 383

Topic: 4. Pediatrics
All of the following may be signs and symptoms of a tethered cord except:
. Back pain
. Leg pain
. Meryon's sign
. Increasing contracture
. Increasing motor weakness

Correct Answer & Explanation

. Increasing motor weakness

Explanation

A tethered cord is common in patients with myelomeningocele. A tethered cord occurs due to adhesion of the dysplastic distal cord to its surrounding structures. The onset of a tethered cord may be exacerbated by closure of the open cord. Signs and symptoms of a tethered cord may include back pain, leg pain, increasing motor weakness, and increasing contracture. Alternate explanations for some of these signs and symptoms exist as well. An adult with Meryon's sign may drop a child he or she is holding due to weakness of the pectorals and latissimus muscles. Meryon's sign is also common in patients with myelomeningocele who have a Chiari malformation. In this case, the patient with myelomeningocele does not experience weakness of the pectorals and latissimus muscles due to a tethered cord. Meryon's sign also occurs in some myopathies.

Question 384

Topic: 4. Pediatrics
CRISPR/Cas9 technology is being investigated for correcting mutations in osteogenesis imperfecta. What is the primary function of the Cas9 enzyme in this system?
. Synthesizing new DNA strands
. Acting as an RNA polymerase
. Functioning as a targeted endonuclease to create double-strand breaks
. Facilitating the integration of viral DNA into the host genome
. Ligating broken DNA ends together

Correct Answer & Explanation

. Functioning as a targeted endonuclease to create double-strand breaks

Explanation

In the CRISPR system, Cas9 acts as an endonuclease that creates site-specific double-strand breaks in DNA, guided by a specific RNA sequence. The cell's repair mechanisms are then exploited to correct the mutation.

Question 385

Topic: 4. Pediatrics

A patient with Osteogenesis Imperfecta Type I has a mutation causing a premature stop codon in the COL1A1 gene. This primarily results in which of the following?

. Production of structurally abnormal type I collagen
. Decreased quantity of structurally normal type I collagen
. Complete absence of type II collagen
. Substitution of glycine with a bulkier amino acid
. Overproduction of structurally normal type I collagen

Correct Answer & Explanation

. Decreased quantity of structurally normal type I collagen

Explanation

OI Type I is typically caused by a null allele mutation resulting in haploinsufficiency, meaning a decreased amount of structurally normal collagen is produced. Missense mutations usually cause more severe types via dominant-negative effects.

Question 386

Topic: 4. Pediatrics

Fibroblast Growth Factor Receptor 3 (FGFR3) mutations are the cause of achondroplasia. In a normal growth plate, what is the physiologic effect of FGFR3 activation?

. Stimulates chondrocyte proliferation
. Inhibits chondrocyte proliferation and hypertrophy
. Promotes rapid osteoblast differentiation
. Stimulates matrix metalloproteinase production
. Increases vascular endothelial growth factor (VEGF) secretion

Correct Answer & Explanation

. Inhibits chondrocyte proliferation and hypertrophy

Explanation

FGFR3 is a negative regulator of bone growth. In a normal growth plate, its activation inhibits chondrocyte proliferation and hypertrophy. In achondroplasia, a gain-of-function mutation causes constitutive activation.

Question 387

Topic: 4. Pediatrics

A research team is attempting to detect the presence of a specific DNA mutation in a patient with Osteogenesis Imperfecta. Which of the following laboratory techniques is primarily used to detect specific DNA sequences?

. Northern blotting
. Southern blotting
. Western blotting
. Eastern blotting
. Enzyme-Linked Immunosorbent Assay (ELISA)

Correct Answer & Explanation

. Southern blotting

Explanation

Southern blotting is used to detect specific DNA sequences. The mnemonic SNoW DRoP helps differentiate the techniques: Southern=DNA, Northern=RNA, Western=Protein.

Question 388

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. It is caused by a mutation in the FGFR3 gene. Which best describes the molecular consequence of this specific mutation?

. Gain of function mutation leading to constitutive activation of the receptor
. Loss of function mutation resulting in defective receptor trafficking
. Dominant negative mutation disrupting heterotrimer formation
. Haploinsufficiency leading to inadequate receptor density
. Frameshift mutation resulting in a truncated, inactive protein

Correct Answer & Explanation

. Gain of function mutation leading to constitutive activation of the receptor

Explanation

Achondroplasia results from a gain-of-function mutation in the FGFR3 gene. This constitutively activates the receptor, which normally functions to inhibit chondrocyte proliferation, thus prematurely arresting endochondral ossification.

Question 389

Topic: 4. Pediatrics
Which of the following mutations results in a classic 'dominant negative' effect, as frequently observed in severe, lethal forms of Osteogenesis Imperfecta (Type II)?
. A missense mutation substituting glycine with a bulkier amino acid in the collagen triple helix
. A nonsense mutation causing a premature stop codon and early mRNA degradation
. A complete deletion of one allele of the COL1A1 gene
. A promoter mutation decreasing the transcription rate of the wild-type allele
. A frameshift mutation leading to an absent protein product

Correct Answer & Explanation

. A missense mutation substituting glycine with a bulkier amino acid in the collagen triple helix

Explanation

In dominant negative mutations, the defective gene product structurally interferes with the function of the normal protein from the wild-type allele. A missense mutation substituting glycine prevents proper folding of the entire type I collagen triple helix, leading to severe qualitative defects (Type II, III, IV OI).

Question 390

Topic: 4. Pediatrics

Achondroplasia is the most common form of disproportionate short stature and is caused by a specific mutation in the FGFR3 gene. At the molecular level, this mutation typically results in which of the following?

. Haploinsufficiency of the receptor
. Constitutive activation (gain-of-function) of the receptor
. Loss-of-function mutation preventing ligand binding
. Complete deletion of the associated gene segment
. Frameshift mutation leading to an early stop codon

Correct Answer & Explanation

. Constitutive activation (gain-of-function) of the receptor

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, leading to its constitutive activation. This abnormal continuous signaling powerfully inhibits chondrocyte proliferation in the growth plate.

Question 391

Topic: 4. Pediatrics
Osteogenesis imperfecta (OI) type II is typically lethal in the perinatal period. This extreme severity is most commonly explained by which genetic mechanism affecting the assembly of the type I collagen triple helix?
. Dominant negative effect
. Haploinsufficiency
. Nonsense mediated decay
. Recessive loss of function
. X-linked recessive inheritance

Correct Answer & Explanation

. Dominant negative effect

Explanation

Severe forms of OI (Types II, III, IV) are usually caused by missense mutations (often substituting glycine) that produce abnormal collagen chains. These mutant chains disrupt the entire triple helix, exhibiting a dominant negative effect.

Question 392

Topic: 4. Pediatrics

This infant was born with an anomaly of the left lower extremity (Slides). What is the most likely diagnosis:

. Clubfoot
. Proximal focal femoral deficiency
. Fibular hemimelia
. Tibial hemimelia
. C ongenital pseudarthrosis of the tibia

Correct Answer & Explanation

. Tibial hemimelia

Explanation

This infant has tibial hemimelia, which is a complete absence of the tibia with resultant inversion of the foot. The presence of an intact fibula causing focal lateral prominence, a shortened but complete femur, and absence of a visible tibia rule out a diagnosis of clubfoot, proximal focal femoral deficiency, fibular hemimelia, and congenital pseudarthrosis of the tibia.

Question 393

Topic: 4. Pediatrics

This child with tibial hemimelia does not have a proximal tibial remnant (Slides). The preferred treatment is:

. Knee disarticulation
. Femoral-fibular fusion with Syme disarticulation
. Centralization of the fibula at the knee and ankle
. Syme disarticulation
. Rotationplasty

Correct Answer & Explanation

. Knee disarticulation

Explanation

If the proximal tibial remnant is absent, the prospect of a functionally useful extension at the knee is nil. Disarticulation at the knee is the best option for this patient.

Question 394

Topic: Pediatric Upper Extremity & Spine
Which of the following Risser signs most accurately describes the patient presented?
. Risser 1
. Risser 2
. Risser 3
. Risser 4
. Risser 5

Correct Answer & Explanation

. Risser 5

Explanation

Despite its biologic variability, the Risser sign is one of the most useful indicators of maturity used in the management of pediatric spine disorders. The Risser sign is a depiction of the progressive ossification and fusion of the iliac apophysis, which begins anterolaterally and finishes posteromedially. The initial ossification (Risser 1) begins just after the peak height velocity, after triradiate cartilage closure, and approximately at the time of menarche. The completion of ossification and fusion usually takes 1.5 to 2 years in girls and 2 to 3 years in boys. As the iliac apophysis matures and Risser 4 is reached, the Risser sign becomes a sclerotic line that is whiter than the adjacent ilium. Risser 0 and Risser 5 may be difficult to distinguish except that the cranial border of the ilium in Risser 0 is wavy or ruffled, while it is smooth and sclerotic in Risser 5.

Question 395

Topic: Pediatric Lower Extremity
Which of the following terms best describes the condition shown?
. Calcaneovalgus
. Equinovarus
. Posteromedial bow
. Fibular hemimelia
. Metatarsus adductus

Correct Answer & Explanation

. Calcaneovalgus

Explanation

This patient's foot is in calcaneovalgus. Treatment is not required because calcaneovalgus spontaneously resolves.

Question 396

Topic: Pediatric Hip

A 13-year-old obese boy presents with right knee pain and an obligate external rotation of the hip during passive flexion. Radiographs show a "trellis" sign and Klein's line not intersecting the lateral epiphysis. What is the most appropriate initial treatment?

. Spica casting
. In situ single screw fixation
. Closed reduction and internal fixation
. Proximal femoral osteotomy
. Observation with protected weight-bearing

Correct Answer & Explanation

. In situ single screw fixation

Explanation

The clinical presentation and radiographic findings are classic for Slipped Capital Femoral Epiphysis (SCFE). The standard initial treatment is in situ fixation with a single cannulated screw.

Question 397

Topic: Pediatric Hip

In a 7-year-old boy diagnosed with Legg-Calve-Perthes disease, which of the following radiographic findings represents a "head at risk" sign indicating a poorer prognosis?

. Medial subluxation of the femoral head
. Gage sign
. Decreased medial joint space
. Intact lateral pillar
. Metaphyseal sclerosis

Correct Answer & Explanation

. Gage sign

Explanation

Catterall's "head at risk" signs include lateral subluxation, Gage sign (V-shaped defect in the lateral epiphysis), calcification lateral to the epiphysis, and horizontal growth plate.

Question 398

Topic: Pediatric Hip

A 4-week-old female infant has a positive Ortolani test on the left side. Ultrasound shows an alpha angle of 40 degrees. What is the most appropriate next step in management?

. Triple pelvic osteotomy
. Closed reduction and spica casting
. Pavlik harness application
. Observation with repeat ultrasound in 4 weeks
. Open reduction

Correct Answer & Explanation

. Pavlik harness application

Explanation

A positive Ortolani test with an alpha angle < 60 degrees indicates a dislocated but reducible hip. The Pavlik harness is the gold standard initial treatment for DDH in infants under 6 months.

Question 399

Topic: 4. Pediatrics

A 3-year-old boy presents with progressive bilateral genu varum. Radiographs show a sharp varus angulation at the proximal tibial metaphysis with medial beaking. What is the most likely diagnosis?

. Physiologic bowing
. Infantile Blount's disease
. Rickets
. Achondroplasia
. Renal osteodystrophy

Correct Answer & Explanation

. Infantile Blount's disease

Explanation

Infantile Blount's disease involves a growth disturbance of the medial aspect of the proximal tibial physis. Radiographically, it is characterized by medial metaphyseal beaking and fragmentation.

Question 400

Topic: 4. Pediatrics
A 13-year-old boy sustains a Salter-Harris III fracture of the anterolateral aspect of the distal tibial epiphysis. What is the primary deforming force causing this specific fracture pattern?
. Avulsion by the anterior inferior tibiofibular ligament (AITFL)
. Axial loading in plantar flexion
. Avulsion by the posterior inferior tibiofibular ligament (PITFL)
. Direct blow to the lateral malleolus
. Medial collateral ligament avulsion

Correct Answer & Explanation

. Avulsion by the anterior inferior tibiofibular ligament (AITFL)

Explanation

A juvenile Tillaux fracture is an SH III fracture of the anterolateral distal tibial epiphysis. It is caused by an avulsion force from the AITFL during external rotation, occurring because the medial physis closes before the lateral physis.

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