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4. Pediatrics MCQs

Practice Set 195 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 3881

Topic: 4. Pediatrics

A child with short stature, frontal bossing, and rhizomelic limb shortening is evaluated. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Which of the following describes the underlying molecular defect?

. Defect in type I collagen synthesis
. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in RUNX2
. Defect in sulfate transport (SLC26A2)
. Mutation in the EXT1 gene

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This leads to profound inhibition of chondrocyte proliferation in the proliferative zone of the physis, resulting in rhizomelic dwarfism and spinal stenosis.

Question 3882

Topic: 4. Pediatrics

A 3-year-old child presents with a painless waddling gait.

AP pelvis radiograph demonstrates a decreased femoral neck-shaft angle, a vertically oriented physis, and a distinct triangular bone fragment in the inferior femoral neck. What radiographic measurement is the primary determinant for surgical intervention in this condition?

. Reimer's migration index > 33%
. Hilgenreiner's epiphyseal angle > 60 degrees
. Center-edge angle < 20 degrees
. Alpha angle > 55 degrees
. Neck-shaft angle < 120 degrees

Correct Answer & Explanation

. Hilgenreiner's epiphyseal angle > 60 degrees

Explanation

In infantile coxa vara, a Hilgenreiner's epiphyseal angle (HEA) greater than 60 degrees is a strong indication for surgical correction via a valgus-producing osteotomy. Angles less than 45 degrees typically resolve spontaneously.

Question 3883

Topic: Pediatric Hip



A 3-week-old neonate presents with pseudoparalysis of the right leg and crying with diaper changes. There is no fever, but CRP is significantly elevated. Ultrasound reveals a hip effusion. If this neonatal septic arthritis (coxitis) is diagnosed late and untreated, what is the most severe classical long-term orthopedic complication?

. Slipped capital femoral epiphysis
. Resorption of the femoral head and neck (Tom Smith arthritis)
. Legg-Calve-Perthes disease
. Development of an aneurysmal bone cyst
. Progressive tibia vara

Correct Answer & Explanation

. Resorption of the femoral head and neck (Tom Smith arthritis)

Explanation

Neonatal septic arthritis of the hip often lacks classic systemic signs like high fever. Delayed diagnosis and treatment lead to rapid cartilaginous destruction and complete resorption of the proximal femur, a devastating sequela known as Tom Smith arthritis.

Question 3884

Topic: 4. Pediatrics

A 6-year-old boy is evaluated for short stature, a waddling gait, and a barrel chest. Radiographs demonstrate delayed ossification of the capital femoral epiphyses, coxa vara, and platyspondyly. Ophthalmic examination reveals high myopia. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COMP
. COL1A1
. COL2A1
. RUNX2

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) affects the spine and epiphyses, and is associated with coxa vara, high myopia, and retinal detachment. It is caused by an autosomal dominant mutation in the COL2A1 gene affecting Type II collagen.

Question 3885

Topic: 4. Pediatrics

A 4-year-old girl with frontal bossing, midface hypoplasia, and rhizomelic shortening of the upper and lower extremities is being evaluated in the clinic. Her parents are of normal stature. Which of the following describes the pathophysiologic mechanism of the genetic mutation in this patient?

. Gain of function mutation in FGFR3 inhibiting chondrocyte proliferation
. Loss of function mutation in FGFR3 stimulating chondrocyte proliferation
. Defect in cartilage oligomeric matrix protein leading to apoptosis
. Impaired sulfate transport in chondrocytes
. Mutation in the diastrophic dysplasia sulfate transporter (DTDST) gene

Correct Answer & Explanation

. Gain of function mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This overactivity continuously inhibits normal chondrocyte proliferation in the proliferative zone of the physis, leading to restricted endochondral ossification.

Question 3886

Topic: 4. Pediatrics

A 4-year-old child with rhizomelic short stature, frontal bossing, and trident hands is diagnosed with achondroplasia. Which of the following best describes the underlying genetic defect?

. Mutation in the COL1A1 gene causing defective type 1 collagen
. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation
. Loss-of-function mutation in the COMP gene
. Mutation in the RUNX2 gene
. Defect in the diastrophic dysplasia sulfate transporter (DTDST)

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This overactivity continuously inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 3887

Topic: 4. Pediatrics

An infant is placed in a Pavlik harness for developmental dysplasia of the hip. At the 2-week follow-up, the parents report the infant is no longer actively kicking the right leg. Physical examination reveals absent active knee extension on the affected side. What is the most likely cause?

. Avascular necrosis of the femoral head
. Hyperflexion of the hip causing femoral nerve palsy
. Excessive abduction causing obturator nerve palsy
. Ischemic contracture of the quadriceps
. Improper posterior strap placement causing sciatic nerve entrapment

Correct Answer & Explanation

. Hyperflexion of the hip causing femoral nerve palsy

Explanation

Femoral nerve palsy in a Pavlik harness is typically caused by excessive hip flexion resulting from overtightened anterior straps. Management involves loosening the anterior straps or discontinuing the harness temporarily.

Question 3888

Topic: 4. Pediatrics

A 5-year-old boy presents with disproportionate short stature, normal facies, and joint laxity. Radiographs demonstrate delayed epiphyseal ossification and platyspondyly with anterior tongue-like projections. What is the most likely diagnosis?

. Achondroplasia
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Spondyloepiphyseal dysplasia congenita
. Diastrophic dysplasia

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia presents with short-limb dwarfism, severe joint laxity, and normal facial features (unlike achondroplasia). It is caused by a mutation in the COMP gene.

Question 3889

Topic: Pediatric Hip

A 12-year-old obese boy presents with a left slipped capital femoral epiphysis (SCFE). Which of the following is an absolute indication for prophylactic in situ pinning of the contralateral, asymptomatic hip?

. Age greater than 14 years
. Presence of an underlying endocrine disorder
. Presence of a large effusion on the symptomatic side
. Male gender
. Mild slip angle (less than 30 degrees)

Correct Answer & Explanation

. Presence of an underlying endocrine disorder

Explanation

Prophylactic pinning of the contralateral hip in SCFE is strongly recommended in patients with endocrine disorders (e.g., hypothyroidism, renal osteodystrophy) due to the very high risk of bilateral involvement.

Question 3890

Topic: Pediatric Lower Extremity

During the Ponseti method for treating idiopathic clubfoot, the very first step in casting manipulation addresses which component of the deformity?

. Hindfoot equinus
. Forefoot adduction
. Midfoot cavus
. Hindfoot varus
. Tibial internal torsion

Correct Answer & Explanation

. Midfoot cavus

Explanation

The first step in the Ponseti method is to correct the cavus deformity. This is achieved by elevating the first ray and supinating the forefoot to align it with the hindfoot.

Question 3891

Topic: Pediatric Hip
In Legg-Calvรฉ-Perthes disease, the Herring Lateral Pillar classification is most reliably applied at what stage of the disease to predict the ultimate deformity?
. Initial (ischemic) stage
. Early fragmentation stage
. Reossification stage
. Residual stage
. Pre-ischemic stage

Correct Answer & Explanation

. Early fragmentation stage

Explanation

The Herring Lateral Pillar classification assesses the structural height of the lateral pillar of the femoral head. It is most accurately determined during the early to mid fragmentation stage before reossification begins.

Question 3892

Topic: 4. Pediatrics



A 6-year-old child is evaluated for a severe limp and limb length discrepancy. History is significant for a prolonged neonatal intensive care unit stay for sepsis. Radiographs demonstrate complete absence of the femoral head and neck, as seen in the provided late-stage example. What is this specific sequela of neonatal septic arthritis called?

. Legg-Calve-Perthes disease
. Tom Smith arthritis
. Blount disease
. Sever's disease
. Kohler disease

Correct Answer & Explanation

. Tom Smith arthritis

Explanation

Tom Smith arthritis refers to the complete resorption or destruction of the femoral head and neck following severe infantile septic arthritis. This results in a chronically dislocated, unstable hip with a profound limb length discrepancy.

Question 3893

Topic: 4. Pediatrics

A 4-year-old child with disproportionate short stature, frontal bossing, and rhizomelic shortening of the limbs is diagnosed with achondroplasia. Which of the following accurately describes the molecular pathogenesis of this condition?

. Loss-of-function mutation in the FGFR3 gene
. Gain-of-function mutation in the FGFR3 gene
. Mutation in the COMP gene
. Mutation in the COL2A1 gene
. Defect in the SLC26A2 sulfate transporter

Correct Answer & Explanation

. Gain-of-function mutation in the FGFR3 gene

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. This constitutively active receptor inhibits normal chondrocyte proliferation at the growth plate, leading to rhizomelic dwarfism.

Question 3894

Topic: 4. Pediatrics

A 5-year-old child presents with waddling gait and disproportionate short stature. Unlike patients with achondroplasia, this child has normal craniofacial features. Radiographs show delayed epiphyseal ossification and irregular, fragmented metaphyses. A mutation in which gene is most likely responsible?

. FGFR3
. COMP
. COL1A2
. GNAS
. FBN1

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia presents with severe disproportionate short stature but is distinguished from achondroplasia by completely normal craniofacial features. It is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 3895

Topic: 4. Pediatrics

Spondyloepiphyseal Dysplasia Congenita (SEDC) is a disproportionate short-trunk dwarfism. Patients frequently present with severe coxa vara. Which genetic mutation is primarily responsible for SEDC?

. COL1A1
. COL2A1
. COMP
. SLC26A2
. FGFR3

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal Dysplasia Congenita (SEDC) is caused by autosomal dominant mutations in the COL2A1 gene, which encodes type II collagen. This leads to defective endochondral ossification, prominent spinal involvement (platyspondyly), and coxa vara.

Question 3896

Topic: 4. Pediatrics

A 2-year-old boy presents with anterolateral bowing of the left tibia. Radiographs reveal sclerosis and a narrowing of the medullary canal at the apex of the bow. Which of the following systemic conditions is most strongly associated with this finding?

. Neurofibromatosis type 1
. McCune-Albright syndrome
. Osteogenesis Imperfecta
. Marfan syndrome
. Achondroplasia

Correct Answer & Explanation

. Neurofibromatosis type 1

Explanation

Anterolateral bowing of the tibia is the hallmark precursor to congenital pseudarthrosis of the tibia (CPT). It is highly associated with Neurofibromatosis Type 1 (NF-1), occurring in up to 50% of CPT patients.

Question 3897

Topic: 4. Pediatrics

A 2-year-old boy presents with disproportionate short stature, rhizomelic shortening, and frontal bossing. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Which of the following gene mutations is the primary cause of this condition?

. COL1A1
. COMP
. FGFR3
. RUNX2
. SOX9

Correct Answer & Explanation

. FGFR3

Explanation

Achondroplasia is the most common form of short-limbed dwarfism, caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This mutation inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to defective endochondral ossification.

Question 3898

Topic: 4. Pediatrics

A 6-year-old child presents with a femoral shaft fracture after a minor mechanical fall. Physical examination reveals blue sclerae and mild hearing loss. Radiographs show generalized osteopenia and thin cortices. Which of the following represents the underlying molecular defect in this patient's condition?

. Defective mineralization of osteoid matrix
. Quantitative or qualitative defect in type I collagen
. Abnormal osteoclast function leading to failed bone resorption
. Mutation in the cartilage oligomeric matrix protein (COMP)
. Deficient production of alkaline phosphatase

Correct Answer & Explanation

. Quantitative or qualitative defect in type I collagen

Explanation

Osteogenesis imperfecta is typically caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, leading to defective type I collagen synthesis or structure. This results in brittle bones, multiple fractures, blue sclerae, and early-onset hearing loss.

Question 3899

Topic: 4. Pediatrics

A 3-week-old infant is brought to the emergency department for pseudoparalysis of the right leg. Ultrasound confirms a large hip effusion.

Diagnostic aspiration yields frankly purulent fluid. In addition to Staphylococcus aureus, which pathogen is uniquely highly prevalent in this specific age group?

. Kingella kingae
. Group B Streptococcus
. Streptococcus pneumoniae
. Salmonella enteritidis
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Group B Streptococcus

Explanation

While Staphylococcus aureus is the most common cause of septic arthritis across all pediatric age groups, Group B Streptococcus (S. agalactiae) is the second most common pathogen uniquely seen in neonates. Kingella kingae is more frequently seen in older infants and toddlers (6 months to 4 years).

Question 3900

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, midface hypoplasia, and trident hands. Which genetic mutation is responsible for his condition?

. GNAS
. EXT1
. FGFR3
. COMP
. COL1A1

Correct Answer & Explanation

. FGFR3

Explanation

Achondroplasia is the most common form of short-limb dwarfism and is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This mutation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis.

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