Menu

4. Pediatrics MCQs

Practice Set 163 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 3241

Topic: Pediatric Upper Extremity & Spine
A 5-year-old boy sustains a Gartland type III extension supracondylar humerus fracture. On initial presentation, his hand is pale, pulseless, and cool. Urgent closed reduction and percutaneous pinning are performed. Post-operatively, the hand becomes pink with brisk capillary refill, but the radial pulse remains non-palpable. What is the most appropriate next step in management?
. Immediate surgical exploration of the brachial artery
. Arteriography of the upper extremity
. Administration of systemic tissue plasminogen activator (tPA)
. Close observation and continuous pulse oximetry monitoring
. Immediate removal of the pins and conversion to open reduction

Correct Answer & Explanation

. Close observation and continuous pulse oximetry monitoring

Explanation

A pulseless, pink hand following reduction of a pediatric supracondylar humerus fracture indicates adequate collateral circulation. Close observation with continuous pulse oximetry is the standard of care. Surgical exploration is only indicated if the hand remains pale, pulseless, and poorly perfused after anatomical reduction.

Question 3242

Topic: Pediatric Hip

A 4-year-old girl presents with a painless limp and a positive Trendelenburg sign on the right. Radiographs reveal a high developmental dislocation of the right hip (DDH) with a false acetabulum and an acetabular index of 42 degrees. What is the most appropriate surgical management for this patient?

. Closed reduction and spica casting
. Open reduction and capsulorrhaphy alone
. Open reduction with a proximal femoral varus derotational osteotomy
. Open reduction, femoral shortening osteotomy, and pelvic osteotomy
. Shelf acetabuloplasty alone

Correct Answer & Explanation

. Open reduction, femoral shortening osteotomy, and pelvic osteotomy

Explanation

In children older than 3 years with neglected DDH, the soft tissues are contracted and the acetabulum is highly dysplastic. Open reduction combined with a femoral shortening osteotomy is required to safely decompress the joint and reduce the risk of avascular necrosis. A concomitant pelvic osteotomy is necessary to adequately cover the femoral head and correct the dysplasia.

Question 3243

Topic: Pediatric Hip

When performing a total hip arthroplasty on a 45-year-old female with a Crowe Type IV (high dislocation) developmental dysplasia of the hip (DDH), which of the following intraoperative strategies is most commonly required?

. Placement of the acetabular component in the false acetabulum to ensure bone coverage
. Use of a standard-offset femoral stem due to increased femoral canal width
. A subtrochanteric shortening osteotomy to safely bring the hip center to the true acetabulum
. Prophylactic release of the sciatic nerve at the sciatic notch to prevent impingement
. Use of an oversized acetabular reamer to medialise the true acetabulum

Correct Answer & Explanation

. A subtrochanteric shortening osteotomy to safely bring the hip center to the true acetabulum

Explanation

In Crowe Type IV DDH, the hip is completely dislocated. Reconstructing the hip at the true anatomic center of rotation is biomechanically superior. However, bringing the femur down risks severe traction injury to the sciatic nerve. Therefore, a subtrochanteric shortening osteotomy is frequently required to place the cup in the true acetabulum while safely reducing the hip without excessive nerve tension. The femoral canal in DDH is typically narrow (stovepipe), requiring specialized stems.

Question 3244

Topic: Pediatric Hip

Which of the following patient profiles represents an absolute contraindication to metal-on-metal hip resurfacing?

. A 45-year-old male with primary osteoarthritis
. A 50-year-old male with a history of slipped capital femoral epiphysis
. A 35-year-old female with developmental dysplasia of the hip and impaired renal function
. A 60-year-old male with a BMI of 30
. A 40-year-old male with early avascular necrosis (<30% head involvement)

Correct Answer & Explanation

. A 35-year-old female with developmental dysplasia of the hip and impaired renal function

Explanation

Impaired renal function is an absolute contraindication to metal-on-metal bearings due to the inability to clear circulating cobalt and chromium ions. Furthermore, females of childbearing age and those with DDH are generally considered poor candidates.

Question 3245

Topic: 4. Pediatrics

A 5-year-old boy presents with disproportionate short stature, a very short trunk, and a barrel chest. Radiographs reveal flattened vertebral bodies (platyspondyly) and delayed ossification of the epiphyses. His limbs are relatively proportional to his trunk, unlike classic dwarfism. A mutation in which of the following genes is most likely responsible for this condition?

. FGFR3
. COMP
. COL1A1
. COL2A1
. RUNX2

Correct Answer & Explanation

. COL2A1

Explanation

The patient's presentation of disproportionate short stature with a short trunk, barrel chest, and platyspondyly is classic for Spondyloepiphyseal Dysplasia Congenita (SEDC). SEDC is caused by an autosomal dominant mutation in the COL2A1 gene, which encodes type II collagen (crucial for normal cartilage formation). FGFR3 mutations cause achondroplasia (characteristically short limbs, relatively normal trunk). COMP mutations cause Multiple Epiphyseal Dysplasia or Pseudoachondroplasia. COL1A1 causes Osteogenesis Imperfecta. RUNX2 causes Cleidocranial Dysplasia.

Question 3246

Topic: 4. Pediatrics

A 4-year-old boy presents with disproportionate short stature, rhizomelic shortening of the limbs, and frontal bossing. A mutation in the fibroblast growth factor receptor 3 (FGFR3) gene is identified. What is the molecular consequence of this mutation?

. Loss of function resulting in decreased cartilage matrix synthesis
. Gain of function leading to accelerated endochondral ossification
. Gain of function resulting in constitutive inhibition of chondrocyte proliferation
. Dominant negative effect disrupting Type 1 collagen triple helix formation
. Haploinsufficiency leading to premature osteoblast apoptosis

Correct Answer & Explanation

. Gain of function leading to accelerated endochondral ossification

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. Normally, FGFR3 negatively regulates bone growth by inhibiting chondrocyte proliferation and differentiation in the growth plate. The mutation causes constitutive activation of this receptor, leading to profound inhibition of endochondral ossification and resulting in disproportionate dwarfism.

Question 3247

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism in humans. Which of the following best describes the underlying genetic mutation and its cellular consequence at the level of the physis?

. Defect in COL1A1 leading to abnormal type I collagen triple helix formation
. Activating mutation in FGFR3 leading to excessive inhibition of chondrocyte proliferation
. Inactivating mutation in FGFR3 leading to uncontrolled chondrocyte hypertrophy
. Defect in COMP gene leading to retained mutated cartilage oligomeric matrix protein in the rough ER
. Mutation in CBFA1 (RUNX2) causing failed membranous ossification

Correct Answer & Explanation

. Activating mutation in FGFR3 leading to excessive inhibition of chondrocyte proliferation

Explanation

Achondroplasia is an autosomal dominant condition caused by an activating mutation (gain of function) in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts to inhibit endochondral ossification by suppressing chondrocyte proliferation in the proliferative zone of the physis. The activating mutation causes over-inhibition, leading to arrested long bone growth. Defective COMP is seen in pseudoachondroplasia and multiple epiphyseal dysplasia. CBFA1 mutations cause cleidocranial dysplasia.

Question 3248

Topic: 4. Pediatrics

A 4-year-old boy presents with short stature, frontal bossing, and rhizomelic shortening of the limbs. The genetic mutation responsible for this condition results in which of the following cellular level abnormalities?

. Decreased production of type I collagen
. Gain-of-function mutation leading to inhibition of chondrocyte proliferation
. Loss-of-function mutation in a voltage-gated chloride channel
. Defective mineralization of osteoid
. Abnormal accumulation of mucopolysaccharides in lysosomes

Correct Answer & Explanation

. Gain-of-function mutation leading to inhibition of chondrocyte proliferation

Explanation

The clinical presentation is classic for achondroplasia, the most common form of short-limb dwarfism. It is caused by an autosomal dominant gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts as a negative regulator of bone growth. The mutation leads to constitutive activation of the receptor, which severely inhibits chondrocyte proliferation and hypertrophy in the proliferative zone of the physis.

Question 3249

Topic: 4. Pediatrics

A pediatric patient with a diagnosis of achondroplasia presents for evaluation. At the cellular and molecular level within the physis, the gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene primarily leads to:

. Hyperactivation of chondrocyte proliferation in the resting zone
. Inhibition of chondrocyte proliferation in the proliferative zone
. Accelerated apoptosis in the hypertrophic zone
. Defective type I collagen triple helix formation
. Impaired mineralization of the primary spongiosa

Correct Answer & Explanation

. Inhibition of chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the FGFR3 gene. Normally, FGFR3 acts as a negative regulator of endochondral ossification. The mutation results in constitutive activation of the receptor, which severely inhibits chondrocyte proliferation and differentiation in the proliferative zone of the physis, resulting in short-limbed dwarfism.

Question 3250

Topic: 4. Pediatrics

A 4-year-old child presents with disproportionate short stature, frontal bossing, and rhizomelic shortening of the limbs. Radiographs reveal narrowing of the interpedicular distances in the lumbar spine. This condition is caused by a mutation resulting in the altered function of a specific receptor. What is the molecular consequence of this mutation?

. Decreased activity of the Runx2 transcription factor
. Gain of function of Fibroblast Growth Factor Receptor 3 (FGFR3)
. Loss of function of the COL1A1 gene
. Inability to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
. Defect in the chloride channel CLCN7

Correct Answer & Explanation

. Gain of function of Fibroblast Growth Factor Receptor 3 (FGFR3)

Explanation

Achondroplasia is the most common form of disproportionate dwarfism and is inherited in an autosomal dominant pattern. It is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Paradoxically, the overactive FGFR3 receptor inhibits normal chondrocyte proliferation and differentiation in the proliferative zone of the physis, leading to impaired endochondral ossification.

Question 3251

Topic: 4. Pediatrics

A 4-year-old boy presents with disproportionate short stature, rhizomelic shortening of the limbs, frontal bossing, and midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Figure 2 demonstrates the characteristic appearance of his long bones. The genetic mutation responsible for this condition primarily affects which histologic zone of the physis?

. Reserve (resting) zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

The patient has achondroplasia, the most common form of short-limbed dwarfism. It is caused by an autosomal dominant gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts as a negative regulator of bone growth. Its overactivity primarily suppresses chondrocyte proliferation, leading to profound defects in the proliferative zone of the growth plate and resulting in impaired endochondral ossification.

Question 3252

Topic: 4. Pediatrics

A 4-year-old boy presents with disproportionate short stature, frontal bossing, and rhizomelic shortening of the limbs. Genetic testing confirms a mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. What is the precise molecular effect of this mutation on the physeal growth plate?

. Loss of function leading to accelerated chondrocyte proliferation in the resting zone
. Gain of function resulting in decreased inhibition of chondrocyte hypertrophy
. Gain of function leading to increased inhibition of chondrocyte proliferation in the proliferative zone
. Loss of function causing premature apoptosis of osteoblasts in the primary spongiosa
. Impaired synthesis of type X collagen in the hypertrophic zone

Correct Answer & Explanation

. Gain of function resulting in decreased inhibition of chondrocyte hypertrophy

Explanation

Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in the FGFR3 gene. In normal physiology, FGFR3 signaling functions to inhibit chondrocyte proliferation and differentiation at the growth plate. The gain-of-function mutation constitutively activates this pathway, leading to excessive inhibition of chondrocyte proliferation in the proliferative zone of the physis, resulting in characteristic dwarfism.

Question 3253

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lumbar spine. The genetic mutation responsible for this condition primarily disrupts endochondral ossification in which of the following zones of the physis?

. Reserve zone via impaired Type II collagen synthesis
. Proliferative zone via a gain-of-function mutation in FGFR3
. Hypertrophic zone via impaired mineralization
. Primary spongiosa via decreased osteoclast activity
. Secondary spongiosa via abnormal osteoblast differentiation

Correct Answer & Explanation

. Proliferative zone via a gain-of-function mutation in FGFR3

Explanation

Achondroplasia is an autosomal dominant skeletal dysplasia caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts as a negative regulator of bone growth. The constitutively active mutated receptor inappropriately inhibits chondrocyte proliferation, thereby profoundly affecting the proliferative zone of the physis and resulting in impaired endochondral ossification and rhizomelic dwarfism.

Question 3254

Topic: 4. Pediatrics

A 6-month-old infant is evaluated for short-limbed dwarfism, frontal bossing, and midface hypoplasia. Genetic testing confirms a mutation in the FGFR3 gene. Which of the following best describes the pathophysiologic consequence of this specific genetic alteration?

. Loss of function leading to excessive chondrocyte proliferation
. Gain of function leading to constitutive inhibition of chondrocyte proliferation
. Defect in type 1 collagen synthesis causing brittle bones
. Failure of osteoclast differentiation due to RANKL deficiency
. Impaired mineralization of the osteoid matrix

Correct Answer & Explanation

. Gain of function leading to constitutive inhibition of chondrocyte proliferation

Explanation

Achondroplasia is the most common form of short-limbed dwarfism and is caused by an autosomal dominant mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 functions as a negative regulator of linear bone growth. The mutation (most commonly a G380R substitution) causes a 'gain of function', meaning the receptor is constitutively active even without its ligand. This leads to profound, continuous inhibition of chondrocyte proliferation and hypertrophy in the proliferative zone of the physis, ultimately resulting in stunted endochondral ossification.

Question 3255

Topic: 4. Pediatrics

A 4-year-old child presents with short stature, frontal bossing, and rhizomelic shortening of the upper and lower extremities. Radiographs demonstrate narrowing of the interpedicular distances in the lumbar spine. The pathogenesis of this child's condition is primarily driven by which of the following genetic mechanisms?

. Loss-of-function mutation in the COL1A1 gene
. Gain-of-function mutation in the FGFR3 gene
. Mutation in the COMP gene leading to endoplasmic reticulum stress
. Defect in the CBFA1 (RUNX2) transcription factor
. Mutation in the diastrophic dysplasia sulfate transporter (DTDST) gene

Correct Answer & Explanation

. Gain-of-function mutation in the FGFR3 gene

Explanation

The clinical and radiographic presentation is classic for achondroplasia, the most common form of short-limb dwarfism. It is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts as a negative regulator of bone growth. The mutation causes constitutive activation of the receptor, which severely inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to diminished enchondral ossification.

Question 3256

Topic: 4. Pediatrics

A 4-year-old child presents with frontal bossing, midface hypoplasia, and rhizomelic shortening of the upper and lower extremities. Genetic testing reveals an activating mutation in the FGFR3 gene. The pathogenesis of this child's condition is primarily localized to which region of the physis?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

The child has achondroplasia, the most common form of short-limbed dwarfism, caused by an autosomal dominant, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 negatively regulates chondrocyte proliferation. The activating mutation leads to profound inhibition of chondrocyte proliferation, thereby localizing the primary defect to the proliferative zone of the growth plate.

Question 3257

Topic: 4. Pediatrics

Mutations in the gene encoding for Type X collagen are most commonly associated with which of the following skeletal dysplasias?

. Osteogenesis imperfecta
. Achondroplasia
. Schmid metaphyseal chondrodysplasia
. Multiple epiphyseal dysplasia
. Cleidocranial dysplasia

Correct Answer & Explanation

. Schmid metaphyseal chondrodysplasia

Explanation

Type X collagen is a short-chain, network-forming collagen exclusively expressed by hypertrophic chondrocytes in the hypertrophic zone of the physis (growth plate) and in calcifying cartilage. Mutations in the COL10A1 gene, which encodes for Type X collagen, cause Schmid metaphyseal chondrodysplasia. Osteogenesis imperfecta is caused by mutations in Type I collagen (COL1A1 or COL1A2). Achondroplasia is due to a gain-of-function mutation in the FGFR3 gene. Cleidocranial dysplasia is caused by an alteration in the RUNX2/CBFA1 transcription factor. Multiple epiphyseal dysplasia is genetically heterogeneous, often involving COMP or Type IX collagen mutations.

Question 3258

Topic: 4. Pediatrics

A 4-year-old boy presents with a history of recurrent fractures following minimal trauma. On examination, he is noted to have blue sclerae and mild hearing loss. Which of the following describes the underlying molecular defect most likely responsible for his condition?

. Mutation in the FGFR3 gene
. Defective synthesis of Type X collagen
. Mutation in the COL1A1 or COL1A2 genes
. Mutation in the fibrillin-1 gene
. Defect in core binding factor alpha-1 (CBFA1) or RUNX2

Correct Answer & Explanation

. Mutation in the COL1A1 or COL1A2 genes

Explanation

The clinical presentation is classic for osteogenesis imperfecta (OI). OI is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen, leading to defective collagen synthesis. FGFR3 mutations cause achondroplasia. Fibrillin-1 mutations cause Marfan syndrome. CBFA1/RUNX2 mutations cause cleidocranial dysplasia.

Question 3259

Topic: 4. Pediatrics

A child presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. Genetic testing reveals a mutation in the FGFR3 gene. Which of the following describes the molecular consequence of this mutation?

. Loss-of-function leading to hyperproliferation of chondrocytes
. Gain-of-function resulting in constitutive activation and inhibition of chondrocyte proliferation
. Defective type I collagen synthesis
. Impaired production of parathyroid hormone-related peptide (PTHrP)
. Disruption of the Indian Hedgehog (IHH) signaling pathway

Correct Answer & Explanation

. Gain-of-function resulting in constitutive activation and inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally functions to negatively regulate endochondral bone growth. A gain-of-function mutation leads to its constitutive activation, which prematurely inhibits chondrocyte proliferation in the proliferative zone of the physis, resulting in dwarfism.

Question 3260

Topic: 4. Pediatrics

A 7-year-old boy sustains a closed Salter-Harris Type II fracture of the distal radius. The initial fracture plane traverses transversely through the physis before exiting vertically through the metaphysis. Biomechanically, this initial transverse failure across the growth plate characteristically occurs through which histological zone?

. Reserve (resting) zone
. Proliferative zone
. Hypertrophic zone
. Primary spongiosa
. Secondary spongiosa

Correct Answer & Explanation

. Hypertrophic zone

Explanation

Physeal fractures classically occur through the hypertrophic zone of the growth plate (specifically near the zone of provisional calcification). Biomechanically, this zone is the weakest layer of the physis due to the high volume of swollen, hypertrophic chondrocytes and the relatively sparse extracellular matrix separating them. The lack of robust structural matrix predisposes this specific zone to transverse shearing or tension failure, which is the pathognomonic starting point for Salter-Harris injuries.

Test Yourself

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

On this Page