Menu

4. Pediatrics MCQs

Practice Set 246 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 4901

Topic: Pediatric Hip
A 7-year-old boy is diagnosed with Legg-Calvé-Perthes disease. According to the Herring lateral pillar classification, which radiographic feature defines a Group C hip?
. >50% preserved height of the lateral pillar
. >50% loss of height of the lateral pillar
. 100% involvement of the medial pillar
. Subchondral fracture line (crescent sign)
. Extrusion of the femoral head >20%

Correct Answer & Explanation

. >50% loss of height of the lateral pillar

Explanation

In the Herring lateral pillar classification, Group C is defined by greater than 50% loss of height of the lateral pillar of the femoral head. This classification carries a poor prognosis for spherical head remodeling.

Question 4902

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The characteristic physical features, including rhizomelic shortening of the limbs, frontal bossing, and a trident hand, are caused by an activating mutation in the gene encoding for which of the following?

. Type 1 collagen (COL1A1)
. Fibroblast growth factor receptor 3 (FGFR3)
. Runx2/Cbfa1 transcription factor
. Cartilage oligomeric matrix protein (COMP)
. Parathyroid hormone-related protein (PTHrP)

Correct Answer & Explanation

. Type 1 collagen (COL1A1)

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function (activating) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation abnormally suppresses chondrocyte proliferation and hypertrophy in the growth plate, severely impairing endochondral ossification and leading to rhizomelic dwarfism.

Question 4903

Topic: 4. Pediatrics

A 13-year-old overweight boy presents with progressive knee pain and an obligatory external rotation of the hip with passive hip flexion. Slippage of the capital femoral epiphysis typically occurs through which histological zone of the physis?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Slipped Capital Femoral Epiphysis (SCFE) involves mechanical failure through the physis. Histologically, this failure occurs almost exclusively through the zone of hypertrophy, which is the weakest zone due to the large size of the chondrocytes and relatively less extracellular matrix.

Question 4904

Topic: Pediatric Hip

When evaluating an anteroposterior pelvic radiograph of a 4-month-old infant for Developmental Dysplasia of the Hip (DDH), Hilgenreiner's line is drawn as a horizontal line through which of the following landmarks?

. The lateral margin of the acetabular roof
. The superolateral edge of the ossified femoral head
. The triradiate cartilages of the acetabulum
. The inferior margin of the superior pubic ramus
. The greater sciatic notch

Correct Answer & Explanation

. The lateral margin of the acetabular roof

Explanation

Hilgenreiner's line is a horizontal reference line drawn through the right and left triradiate cartilages on an AP pelvis radiograph. Perkin's line is drawn perpendicularly to Hilgenreiner's line at the lateral edge of the acetabulum. The femoral head should normally reside in the inferomedial quadrant formed by these lines.

Question 4905

Topic: 4. Pediatrics

Achondroplasia is the most common form of skeletal dysplasia and is caused by a dominant mutation in the FGFR3 gene. What is the functional consequence of this specific gene mutation on bone development?

. Constitutive activation of FGFR3 leading to inhibition of endochondral ossification
. Loss of function of FGFR3 leading to inhibition of intramembranous ossification
. Constitutive activation of FGFR3 accelerating intramembranous ossification
. Loss of function of FGFR3 accelerating endochondral ossification
. Dominant-negative inhibition of Type II collagen synthesis

Correct Answer & Explanation

. Constitutive activation of FGFR3 leading to inhibition of endochondral ossification

Explanation

Achondroplasia 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 chondrocyte proliferation. Its constitutive activation leads to marked suppression of proliferation in the proliferative zone of the physis, severely inhibiting endochondral ossification.

Question 4906

Topic: Pediatric Hip

An 8-year-old boy presents with an acute on chronic slipped capital femoral epiphysis (SCFE). Because of the patient's atypical age at presentation, an underlying endocrine disorder must be strongly suspected. Which of the following is the most common endocrine etiology associated with atypical SCFE?

. Hyperthyroidism
. Hypothyroidism
. Cushing's disease
. Addison's disease
. Precocious puberty

Correct Answer & Explanation

. Hyperthyroidism

Explanation

Atypical SCFE includes presentations in children younger than 10 or older than 16, children whose weight is less than the 50th percentile, or bilateral sequential slips. Hypothyroidism is the most common endocrine disorder associated with SCFE. Other associated conditions include growth hormone deficiency and renal osteodystrophy.

Question 4907

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism. It is caused by a mutation in the FGFR3 gene that results in which of the following cellular effects?

. Gain of function leading to inhibition of chondrocyte proliferation
. Loss of function leading to uncontrolled chondrocyte hypertrophy
. Defective synthesis of Type I collagen
. Impaired osteoclast function and thick bone formation
. Absence of the primary spongiosa in the physis

Correct Answer & Explanation

. Gain of function leading to inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. In the normal growth plate, FGFR3 acts as a negative regulator of bone growth; the mutation constitutively activates this inhibition, resulting in decreased chondrocyte proliferation.

Question 4908

Topic: Pediatric Hip
A 21-year-old hockey player presents with chronic groin pain exacerbated by deep flexion. Examination reveals a positive anterior impingement (FADIR) test. AP pelvis and Dunn lateral radiographs are obtained. The radiograph shows an alpha angle of 68 degrees. This finding is most characteristic of which pathomorphology?
. Pincer impingement due to acetabular retroversion
. Cam impingement due to asphericity of the anterolateral femoral head-neck junction
. Dysplastic hip with insufficient lateral center edge angle
. Slipped capital femoral epiphysis
. Legg-Calvé-Perthes disease

Correct Answer & Explanation

. Cam impingement due to asphericity of the anterolateral femoral head-neck junction

Explanation

An alpha angle greater than 50-55 degrees on a lateral or Dunn view of the hip indicates Cam morphology, characterized by asphericity (a "bump") at the anterolateral femoral head-neck junction. This bony prominence impacts the anterosuperior acetabular rim during flexion and internal rotation, causing labral and chondral damage.

Question 4909

Topic: 4. Pediatrics

A 13-year-old elite baseball pitcher presents with insidious onset of shoulder pain in his throwing arm. Radiographs reveal widening and lateral fragmentation of the proximal humeral physis. What is the fundamental pathophysiology of this condition (Little League Shoulder)?

. Avascular necrosis of the humeral head
. Salter-Harris type I stress fracture of the proximal humeral physis
. Traction apophysitis of the coracoid process
. Partial articular-sided supraspinatus tendon avulsion
. Glenohumeral internal rotation deficit (GIRD) causing labral shear

Correct Answer & Explanation

. Avascular necrosis of the humeral head

Explanation

Little League Shoulder is an overuse injury seen in skeletally immature overhead throwing athletes. The repetitive rotational torque stresses the open physis, causing a fatigue failure that manifests as a Salter-Harris type I stress fracture (epiphysiolysis) of the proximal humeral physis.

Question 4910

Topic: 4. Pediatrics

A 12-year-old elite baseball pitcher presents with poorly localized shoulder pain that worsens strictly with throwing. Radiographs reveal widening and lateral fragmentation of the proximal humeral physis compared to the contralateral side. What is the most appropriate initial management for this condition?

. Arthroscopic labral repair
. Immobilization in a rigid shoulder spica cast for 6 weeks
. Corticosteroid injection into the subacromial space
. Complete rest from throwing for 3 months followed by a structured return-to-throw program
. Physical therapy focused strictly on aggressive stretching of the posterior capsule

Correct Answer & Explanation

. Arthroscopic labral repair

Explanation

Little League Shoulder is an overuse injury causing proximal humeral epiphysiolysis (stress fracture of the physis). The definitive initial treatment is complete cessation of throwing (usually for 3 months) until the patient is asymptomatic and radiographs show healing, followed by a gradual return-to-throwing program.

Question 4911

Topic: 4. Pediatrics
A 12-year-old boy presents with a history of recurrent long bone fractures after minimal trauma, blue sclerae, and early-onset hearing loss. A genetic mutation in the gene encoding which of the following collagen types is most likely responsible?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type I

Explanation

The clinical presentation is classic for Osteogenesis Imperfecta (OI), which is predominantly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. These genes encode the alpha chains of Type I collagen, the principal structural protein in bone, sclera, ligaments, and dentin. Defective Type I collagen leads to brittle bones, blue sclerae, and dentinogenesis imperfecta.

Question 4912

Topic: 4. Pediatrics

Achondroplasia is an autosomal dominant condition and the most common cause of short-limb dwarfism. It is caused by an activating mutation in the FGFR3 gene. This mutation exerts its primary pathological effect on which zone of the physis?

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

Correct Answer & Explanation

. Resting zone

Explanation

Fibroblast Growth Factor Receptor 3 (FGFR3) normally acts to inhibit chondrocyte proliferation in the physis. An activating (gain-of-function) mutation in FGFR3 results in excessive inhibition of chondrocyte replication. This defect primarily manifests in the proliferative zone of the growth plate, leading to decreased longitudinal bone growth via endochondral ossification.

Question 4913

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism and is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. What is the primary cellular effect of this mutation on the growth plate?

. Excessive proliferation of chondrocytes in the proliferative zone
. Inhibition of chondrocyte proliferation and hypertrophy
. Premature apoptosis of osteoblasts in the primary spongiosa
. Defective mineralization of the cartilaginous matrix in the calcified zone
. Failure of osteoclast remodeling in the metaphysis

Correct Answer & Explanation

. Excessive proliferation of chondrocytes in the proliferative zone

Explanation

The normal function of the Fibroblast Growth Factor Receptor 3 (FGFR3) is to inhibit cartilage proliferation. A gain-of-function mutation in FGFR3 results in constitutive activation of this inhibitory pathway, leading to suppression of chondrocyte proliferation and hypertrophy in the growth plate, thus causing short-limbed dwarfism.

Question 4914

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic mutation primarily exerts its pathological effect by inhibiting chondrocyte activity in which specific zone of the growth plate (physis)?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Achondroplasia is caused by an activating mutation in the FGFR3 gene, which leads to abnormal inhibition of chondrocyte proliferation. This defect manifests directly in the proliferative zone of the physis, resulting in decreased longitudinal bone growth.

Question 4915

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic mutation primarily affects which specific zone of the physis?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This overactivity inhibits chondrocyte proliferation, primarily affecting the proliferative zone of the physis.

Question 4916

Topic: 4. Pediatrics

A 5-year-old boy presents with disproportionate short stature, rhizomelic shortening, and frontal bossing. This condition is caused by a gain-of-function mutation in the FGFR3 gene. What is the effect of this mutation on bone growth?

. Inhibition of chondrocyte proliferation in the proliferative zone
. Excessive hypertrophy in the hypertrophic zone
. Failure of osteoclast function in the primary spongiosa
. Overproduction of type I collagen by osteoblasts
. Defective mineralization of osteoid

Correct Answer & Explanation

. Inhibition of chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which constitutively inhibits chondrocyte proliferation in the proliferative zone of the physis. This ultimately leads to decreased and defective endochondral ossification.

Question 4917

Topic: 4. Pediatrics

Osteogenesis imperfecta is most commonly caused by an autosomal dominant mutation affecting the synthesis of which structural protein, leading to defective triple helix formation?

. Type I collagen
. Type II collagen
. Type IX collagen
. Type X collagen
. Fibrillin-1

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is typically caused by genetic mutations in the COL1A1 or COL1A2 genes. These mutations lead to quantitative or qualitative defects in Type I collagen, the predominant structural protein found in bone.

Question 4918

Topic: 4. Pediatrics

A 4-year-old boy presents with multiple fractures after minimal trauma, blue sclerae, and dentinogenesis imperfecta. Genetic testing reveals a mutation affecting the synthesis of Type I collagen. The pathogenesis of this condition most likely involves a substitution of which amino acid in the repeating triple helix sequence?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Glutamine

Correct Answer & Explanation

. Proline

Explanation

The clinical scenario describes osteogenesis imperfecta (OI), commonly caused by mutations in the COL1A1 or COL1A2 genes. The classic molecular defect is the substitution of a bulky amino acid for glycine in the repeating Gly-X-Y sequence of the collagen triple helix. Glycine is the smallest amino acid and is required at every third position to allow the tight coiling of the three alpha chains; its substitution disrupts the helix structure.

Question 4919

Topic: 4. Pediatrics

A newborn is evaluated for short-limbed dwarfism, frontal bossing, and midface hypoplasia. Radiographs show classic rhizomelic shortening of the long bones. This condition is caused by an activating mutation in which of the following receptors, and what is its normal physiological role in the growth plate?

. FGFR3; normally stimulates chondrocyte proliferation
. FGFR3; normally inhibits chondrocyte proliferation
. PTHrP; normally delays chondrocyte hypertrophy
. COMP; normally stabilizes the extracellular matrix
. COL2A1; normally provides tensile strength to cartilage

Correct Answer & Explanation

. FGFR3; normally stimulates chondrocyte proliferation

Explanation

Achondroplasia is the most common form of short-limbed dwarfism and is caused by an autosomal dominant gain-of-function (activating) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. In the normal physis, FGFR3 signaling acts as a negative regulator, inhibiting chondrocyte proliferation and hypertrophy. The activating mutation leads to exaggerated inhibition of endochondral ossification.

Question 4920

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. It is caused by an activating mutation in the FGFR3 gene. In which specific zone of the physis (growth plate) does this mutation primarily exert its inhibitory effect?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Achondroplasia results from a gain-of-function mutation in FGFR3, which constitutively inhibits chondrocyte proliferation. This directly disrupts the proliferative zone of the growth plate, leading to decreased longitudinal bone growth.

Test Yourself

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

On this Page