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4. Pediatrics MCQs

Practice Set 190 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 3781

Topic: 4. Pediatrics

A 4-year-old child presents with disproportionate short stature, normal facial features, and marked joint laxity. Radiographs demonstrate delayed epiphyseal ossification and irregular, fragmented metaphyses. The underlying genetic defect involves which of the following?

. FGFR3
. COMP
. COL1A1
. RUNX2
. PHEX

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike true achondroplasia, these patients have normal facial features and head circumference at birth, developing short stature and joint laxity later in childhood.

Question 3782

Topic: 4. Pediatrics
An infant is born with a profoundly soft skull, severe long bone deformities, and multiple acute fractures. Radiographs reveal "crumpled" long bones and beaded ribs. The infant succumbs to respiratory failure shortly after birth. Which type of Osteogenesis Imperfecta does this represent?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Osteogenesis Imperfecta Type II is the perinatal lethal form. It is characterized by severe in utero bone fragility, beaded ribs, crumpled long bones, and death secondary to respiratory failure.

Question 3783

Topic: Pediatric Hip

A 12-year-old girl with end-stage renal disease presents with bilateral hip pain. Radiographs demonstrate a "rugger jersey" spine and a slipped capital femoral epiphysis. Her PTH is markedly elevated. What is the primary mechanism driving her skeletal disease?

. Decreased renal excretion of calcium
. Increased 1-alpha-hydroxylase activity
. Phosphate retention and decreased calcitriol production
. Primary hyperparathyroidism
. Increased renal excretion of phosphate

Correct Answer & Explanation

. Phosphate retention and decreased calcitriol production

Explanation

In renal osteodystrophy, failing kidneys retain phosphate and lose 1-alpha-hydroxylase activity, decreasing active Vitamin D (calcitriol) production. This leads to hypocalcemia, secondary hyperparathyroidism, and resultant skeletal lesions like SCFE and osteitis fibrosa cystica.

Question 3784

Topic: Pediatric Hip

A 10-year-old girl with cleidocranial dysplasia presents with a progressively waddling gait.

Based on the typical pelvic pathology of this condition, what is the most likely diagnosis?

. Developmental dysplasia of the hip (DDH)
. Slipped capital femoral epiphysis (SCFE)
. Coxa vara
. Coxa valga
. Avascular necrosis of the femoral head

Correct Answer & Explanation

. Coxa vara

Explanation

Cleidocranial dysplasia is frequently associated with developmental coxa vara due to a primary ossification defect in the femoral neck. Progressive coxa vara results in a waddling gait and positive Trendelenburg sign.

Question 3785

Topic: 4. Pediatrics

A 6-year-old child with achondroplasia presents with progressive, symptomatic genu varum. Examination reveals fibular overgrowth relative to the tibia. What is the primary cause of this angular deformity?

. Premature closure of the medial proximal tibial physis
. Overgrowth of the proximal fibula relative to the tibia
. Concurrent Vitamin D deficiency
. Ligamentous laxity of the lateral collateral ligament
. Infantile Blount's disease

Correct Answer & Explanation

. Overgrowth of the proximal fibula relative to the tibia

Explanation

In achondroplasia, asymmetrical growth occurs between the tibia and fibula. The fibula outgrows the tibia, exerting a mechanical tethering effect that drives the classic development of genu varum.

Question 3786

Topic: 4. Pediatrics
A neonate is evaluated for short-limbed dwarfism, ichthyosis, and early-onset cataracts. Radiographs demonstrate striking, stippled calcifications around the epiphyses and within the extra-articular cartilage. Which of the following conditions is classically associated with these radiographic findings?
. Achondroplasia
. Conradi-Hünermann syndrome
. Osteogenesis Imperfecta
. Morquio syndrome
. Cleidocranial dysplasia

Correct Answer & Explanation

. Conradi-Hünermann syndrome

Explanation

Stippled epiphyses (chondrodysplasia punctata) are the classic hallmark of Conradi-Hünermann syndrome. The punctate calcifications occur within the cartilaginous skeleton and are often accompanied by asymmetric limb shortening, ichthyosis, and cataracts.

Question 3787

Topic: 4. Pediatrics

A 12-year-old boy with Osteogenesis Imperfecta has been receiving long-term intravenous bisphosphonate therapy.

Radiographs demonstrate multiple transverse metaphyseal bands. Which of the following is a known potential complication of prolonged bisphosphonate use in this population?

. Atypical subtrochanteric femur fractures
. Chronic hypercalcemia
. Slipped capital femoral epiphysis
. Rapid loss of diaphyseal bone mass
. Premature physeal closure

Correct Answer & Explanation

. Atypical subtrochanteric femur fractures

Explanation

Prolonged bisphosphonate therapy aggressively suppresses bone turnover and remodeling. Over time, this leads to the accumulation of microdamage, resulting in hard but brittle bones that are susceptible to atypical fractures in the subtrochanteric or diaphyseal femur.

Question 3788

Topic: 4. Pediatrics
A 2-year-old child presents with multiple fractures, blue sclerae, and dentinogenesis imperfecta. Genetic testing reveals a quantitative defect in type I collagen. Which of the following classifications best describes this patient's condition?
. Type I Osteogenesis Imperfecta
. Type II Osteogenesis Imperfecta
. Type III Osteogenesis Imperfecta
. Type IV Osteogenesis Imperfecta
. Type V Osteogenesis Imperfecta

Correct Answer & Explanation

. Type I Osteogenesis Imperfecta

Explanation

Type I OI is characterized by a quantitative defect in type I collagen (decreased amount of structurally normal collagen) and typically presents with mild to moderate fragility and blue sclerae. Types II, III, and IV involve qualitative structural defects in the collagen chain.

Question 3789

Topic: 4. Pediatrics

A child with recurrent femur fractures is diagnosed with Osteogenesis Imperfecta and started on intravenous pamidronate. Radiographs after 2 years of treatment will most likely demonstrate which of the following findings?

. Widened physes with cupping and fraying
. Sclerotic metaphyseal bands parallel to the physis
. Progressive bowing with increased cortical thickness
. Lucent metaphyseal bands (leukemic lines)
. Erlenmeyer flask deformity of the distal femur

Correct Answer & Explanation

. Sclerotic metaphyseal bands parallel to the physis

Explanation

Bisphosphonates inhibit osteoclast-mediated bone resorption, leading to transient retained primary spongiosa during periods of drug administration. This creates dense, sclerotic metaphyseal bands known as "zebra lines" that run parallel to the physis.

Question 3790

Topic: 4. Pediatrics

Achondroplasia is caused by an activating mutation in the FGFR3 gene. Which specific zone of the physis is primarily inhibited by this mutation?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

The FGFR3 gain-of-function mutation in achondroplasia primarily inhibits the proliferation of chondrocytes. Consequently, the proliferative zone of the physis is narrowed, leading to defective endochondral ossification and rhizomelic dwarfism.

Question 3791

Topic: 4. Pediatrics
A 5-year-old boy with Type III Osteogenesis Imperfecta presents with a highly deformed, frequently fracturing right femur. The optimal surgical management to correct the deformity and prevent further fractures in this growing child involves which of the following?
. Application of a multi-planar external fixator
. Open reduction and rigid plating of the diaphysis
. Multiple corrective osteotomies and telescoping intramedullary nail fixation
. Epiphysiodesis of the distal femur
. Resection of the diaphysis and massive allograft reconstruction

Correct Answer & Explanation

. Multiple corrective osteotomies and telescoping intramedullary nail fixation

Explanation

In severe Osteogenesis Imperfecta, long bone deformities are best managed with "Sofield-Millar" multiple osteotomies to straighten the bone, stabilized with telescoping intramedullary nails (e.g., Fassier-Duval). This construct accommodates remaining longitudinal growth while protecting the entire bone from fractures.

Question 3792

Topic: 4. Pediatrics

A 4-year-old child is evaluated for short stature. Examination reveals short-trunk dwarfism. Radiographs show delayed ossification of the capital femoral epiphyses and coxa vara. Ophthalmologic exam reveals high myopia. The defect in this condition primarily involves which of the following?

. Type I collagen
. Type II collagen
. Type X collagen
. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3

Correct Answer & Explanation

. Type II collagen

Explanation

Spondyloepiphyseal dysplasia (SED) congenita is an autosomal dominant disorder caused by mutations in the COL2A1 gene, resulting in abnormal Type II collagen. It heavily affects tissues rich in Type II collagen, such as articular cartilage, the spine, and the vitreous humor, explaining the associated myopia.

Question 3793

Topic: Pediatric Hip

A 9-year-old girl with cleidocranial dysplasia presents for follow-up.

She has bilateral coxa vara with a neck-shaft angle of 95 degrees and a Hilgenreiner epiphyseal angle (HEA) of 65 degrees. What is the most appropriate management for her hips?

. Observation and annual radiographs
. Bilateral spica casting
. Valgus-producing proximal femoral osteotomies
. In situ single screw pinning of the hips
. Bilateral pelvic support osteotomies

Correct Answer & Explanation

. Valgus-producing proximal femoral osteotomies

Explanation

Coxa vara is a common orthopedic issue in cleidocranial dysplasia. Surgical correction via valgus proximal femoral osteotomy is indicated when the neck-shaft angle is less than 110-120 degrees or the HEA is greater than 60 degrees, due to a high risk of progression and pseudoarthrosis.

Question 3794

Topic: 4. Pediatrics
A 4-year-old child with a history of multiple fractures following minimal trauma presents for evaluation. Sclerae are distinctly blue. The patient is diagnosed with Osteogenesis Imperfecta (OI). Which of the following is the most common underlying genetic mechanism for Sillence Type I OI?
. Qualitative defect in Type I collagen due to a missense mutation
. Quantitative defect resulting in decreased production of structurally normal Type I collagen
. Defect in Type II collagen production
. Mutation in the COMP gene
. Mutation in the tissue-nonspecific alkaline phosphatase gene

Correct Answer & Explanation

. Quantitative defect resulting in decreased production of structurally normal Type I collagen

Explanation

Sillence Type I OI, the mildest and most common form, is typically caused by a null allele mutation resulting in a quantitative defect (decreased amount) of structurally normal Type I collagen. Types II, III, and IV generally involve qualitative defects (structurally abnormal collagen) due to glycine substitutions.

Question 3795

Topic: 4. Pediatrics

Which zone of the physis is primarily affected by the genetic mutation responsible for Achondroplasia?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation inhibits chondrocyte proliferation, primarily affecting the proliferative zone of the physis and leading to impaired endochondral bone formation.

Question 3796

Topic: 4. Pediatrics

A 3-year-old child presents with short trunk dwarfism, a barrel chest, and a waddling gait. Radiographs show severe coxa vara, flattened vertebral bodies, and delayed ossification of the femoral heads. Genetic analysis reveals a mutation in the COL2A1 gene. Which condition does this child most likely have?

. Achondroplasia
. Spondyloepiphyseal Dysplasia Congenita
. Multiple Epiphyseal Dysplasia
. Pseudoachondroplasia
. Diastrophic Dysplasia

Correct Answer & Explanation

. Spondyloepiphyseal Dysplasia Congenita

Explanation

Spondyloepiphyseal Dysplasia Congenita (SEDC) is caused by mutations in the COL2A1 gene, affecting Type II collagen. It presents with short trunk disproportionate dwarfism, severe coxa vara, and epiphyseal/spinal involvement, with relative sparing of the metaphyses.

Question 3797

Topic: 4. Pediatrics

Which of the following conditions is characterized by disproportionate short stature, normal craniofacial appearance, joint laxity, and is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene?

. Achondroplasia
. Diastrophic Dysplasia
. Pseudoachondroplasia
. Osteogenesis Imperfecta
. Mucopolysaccharidosis Type IV (Morquio)

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia is caused by a mutation in the COMP gene. Unlike true achondroplasia, patients have normal craniofacial features and intelligence at birth, with growth retardation and joint laxity becoming apparent in early childhood.

Question 3798

Topic: 4. Pediatrics

A newborn presents with a 'hitchhiker's thumb', cystic swelling of the external ear, severe clubfeet, and shortened limbs. Radiographs show a shortened first metacarpal. What is the underlying genetic defect?

. SLC26A2 gene mutation affecting sulfate transport
. FGFR3 gene mutation affecting chondrocyte proliferation
. CBFA1 gene mutation affecting osteoblast differentiation
. COMP gene mutation affecting cartilage matrix
. COL1A1 gene mutation affecting Type I collagen

Correct Answer & Explanation

. SLC26A2 gene mutation affecting sulfate transport

Explanation

The clinical description is pathognomonic for diastrophic dysplasia. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene, leading to defective intracellular sulfate transport and undersulfation of cartilage proteoglycans.

Question 3799

Topic: 4. Pediatrics

A 9-year-old child presents with short stature, waddling gait, and prominent joints. Radiographs demonstrate normal vertebrae, but the patellae appear to have a 'double-layer' on the lateral view. Which of the following is the most likely diagnosis?

. Achondroplasia
. Spondyloepiphyseal Dysplasia
. Multiple Epiphyseal Dysplasia
. Cleidocranial Dysplasia
. Osteopetrosis

Correct Answer & Explanation

. Multiple Epiphyseal Dysplasia

Explanation

Multiple Epiphyseal Dysplasia (MED) primarily affects the epiphyses, sparing the spine (unlike SED). A classic radiographic hallmark for MED is the 'double-layer' patella, which occurs due to delayed or irregular ossification centers in the patella.

Question 3800

Topic: 4. Pediatrics

A child with Osteogenesis Imperfecta presents with progressive bowing of the femurs and a history of three femoral shaft fractures in the past year.

What is the gold standard surgical management for correcting long bone deformities in this growing child?

. Repeated closed reduction and spica casting
. External fixation with gradual spatial correction
. Multiple osteotomies and fixation with a telescoping intramedullary rod
. Plate and screw osteosynthesis after single-level osteotomy
. Soft tissue release and bracing

Correct Answer & Explanation

. Multiple osteotomies and fixation with a telescoping intramedullary rod

Explanation

The gold standard surgical treatment for severe long bone bowing and recurrent fractures in growing children with OI is 'Sofield-Millar' multiple osteotomies stabilized with a telescoping intramedullary rod (e.g., Fassier-Duval rod). This allows the implant to lengthen as the child grows, protecting the entire bone.

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