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4. Pediatrics MCQs

Practice Set 282 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 5621

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic mutation primarily affects which process of bone formation?

. Intramembranous ossification in the skull vault
. Endochondral ossification in the proliferative zone of the physis
. Osteoclast-mediated bone resorption
. Type I collagen triple helix formation
. Lysosomal enzyme degradation of glycosaminoglycans

Correct Answer & Explanation

. Endochondral ossification in the proliferative zone of the physis

Explanation

Achondroplasia is caused by an activating mutation in FGFR3, which inhibits chondrocyte proliferation in the proliferative zone of the physis, thereby stunting endochondral ossification. Intramembranous ossification is relatively unaffected, leading to a normal-sized or enlarged calvaria.

Question 5622

Topic: Pediatric Hip

A 6-week-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the infant shows absent active knee extension. What is the most likely cause?

. Obturator nerve palsy due to excessive abduction
. Sciatic nerve palsy due to excessive extension
. Femoral nerve palsy due to excessive hyperflexion
. Tibial nerve palsy due to strap compression
. Peroneal nerve palsy due to tight stirrups

Correct Answer & Explanation

. Femoral nerve palsy due to excessive hyperflexion

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness caused by hyperflexion of the hips. Management involves loosening the anterior straps or temporarily discontinuing the harness until function returns.

Question 5623

Topic: 4. Pediatrics
In the evaluation of Legg-Calvé-Perthes disease, the Herring Lateral Pillar Classification is widely used to determine prognosis. This classification is based on the radiolucency and height of which specific anatomic region on an AP pelvis radiograph?
. The medial third of the capital femoral epiphysis
. The central third of the capital femoral epiphysis
. The lateral third of the capital femoral epiphysis
. The lateral physis of the proximal femur
. The acetabular sourcil

Correct Answer & Explanation

. The lateral third of the capital femoral epiphysis

Explanation

The Herring classification assesses the height of the lateral third of the capital femoral epiphysis during the fragmentation stage. A lateral pillar maintaining >50% of its original height (Group B) generally has a better prognosis than one with <50% height (Group C).

Question 5624

Topic: Pediatric Hip

A 4-month-old female is diagnosed with developmental dysplasia of the hip (DDH) and placed in a Pavlik harness. Which of the following limb positions is most highly associated with an iatrogenic femoral nerve palsy?

. Excessive hip flexion
. Excessive hip extension
. Excessive hip adduction
. Excessive hip abduction
. Forced knee extension

Correct Answer & Explanation

. Excessive hip flexion

Explanation

Hyperflexion of the hip in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to transient femoral nerve palsy. Excessive abduction, conversely, places the vascular supply to the femoral head at risk, leading to avascular necrosis.

Question 5625

Topic: Pediatric Hip
A 6-year-old boy presents with a painless limp and restricted hip internal rotation. Radiographs reveal fragmentation of the proximal femoral epiphysis. According to the Herring Lateral Pillar Classification for Legg-Calvé-Perthes disease, which of the following defines a Group B classification?
. No involvement of the lateral pillar
. Greater than 50% maintained lateral pillar height
. Less than 50% maintained lateral pillar height
. Complete collapse of the lateral pillar
. Medial pillar collapse only

Correct Answer & Explanation

. Greater than 50% maintained lateral pillar height

Explanation

The Herring Lateral Pillar classification predicts the outcome of Legg-Calvé-Perthes disease. Group B indicates that >50% of the lateral pillar height is maintained, while Group C involves >50% collapse of the lateral pillar.

Question 5626

Topic: 4. Pediatrics

When treating a newborn with idiopathic congenital talipes equinovarus using the Ponseti method, what is the correct sequence of deformity correction?

. Equinus, Varus, Adductus, Cavus
. Cavus, Adductus, Varus, Equinus
. Adductus, Varus, Cavus, Equinus
. Varus, Cavus, Adductus, Equinus
. Cavus, Equinus, Varus, Adductus

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method follows the CAVE sequence: Cavus, Adductus, Varus, and finally Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot.

Question 5627

Topic: Pediatric Hip

A 3-month-old female is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). At her follow-up, she exhibits an inability to actively extend her knee. This complication is most likely due to which improper positioning in the harness?

. Excessive hip flexion
. Excessive hip abduction
. Inadequate hip flexion
. Excessive hip internal rotation
. Inadequate hip abduction

Correct Answer & Explanation

. Excessive hip flexion

Explanation

Excessive hip flexion in a Pavlik harness can cause femoral nerve compression against the inguinal ligament, leading to transient femoral nerve palsy (manifesting as an inability to extend the knee). Excessive abduction is associated with avascular necrosis of the femoral head.

Question 5628

Topic: Pediatric Hip

A 13-year-old obese boy presents with left knee pain, a limp, and obligate external rotation of the left hip with passive flexion. Radiographs confirm a moderate slipped capital femoral epiphysis (SCFE). Which of the following is the most significant risk factor for the subsequent development of a contralateral SCFE?

. Age < 10 years at initial presentation
. Male gender
. Obesity > 95th percentile
. Presentation with an acute-on-chronic slip
. Slip angle > 50 degrees

Correct Answer & Explanation

. Age < 10 years at initial presentation

Explanation

Age less than 10 years at initial presentation (or generally <11 in boys, <10 in girls), open triradiate cartilage, and underlying endocrine disorders are strong predictors for the development of a contralateral SCFE. Prophylactic pinning of the contralateral hip is often recommended in patients meeting these criteria.

Question 5629

Topic: Pediatric Hip

A 4-month-old infant with developmental dysplasia of the hip (DDH) has failed 6 weeks of compliant Pavlik harness treatment, and the affected hip remains completely dislocated and irreducible on ultrasound. What is the most appropriate next step in management?

. Continue Pavlik harness treatment for an additional 4 to 6 weeks
. Switch immediately to a rigid abduction orthosis (e.g., Ilfeld splint)
. Proceed with closed reduction and spica casting under general anesthesia
. Proceed directly to open reduction and capsulorrhaphy
. Perform a proximal femoral varus derotation osteotomy

Correct Answer & Explanation

. Proceed with closed reduction and spica casting under general anesthesia

Explanation

If an infant with DDH fails Pavlik harness treatment (usually defined by 3-4 weeks of complete irreducibility or up to 6 weeks of failure to progress), continued use is contraindicated due to the risk of 'Pavlik harness disease' (erosion of the posterior acetabulum). The standard next step is an examination under anesthesia, arthrogram, and attempted closed reduction with spica casting.

Question 5630

Topic: 4. Pediatrics

A 4-year-old boy presents with multiple recurrent fractures and blue sclerae. Genetic testing reveals a mutation in the COL1A1 gene. The defective protein normally follows which structural configuration in the extracellular matrix?

. Double helix
. Right-handed triple helix
. Beta-pleated sheet
. Globular tetramer
. Alpha-helical monomer

Correct Answer & Explanation

. Right-handed triple helix

Explanation

Osteogenesis imperfecta is caused by structural defects in Type I collagen. Normal Type I collagen is composed of two alpha-1 chains and one alpha-2 chain that wind together to form a highly stable, right-handed triple helix.

Question 5631

Topic: Pediatric Hip

Which of the following factors is most strongly associated with the development of avascular necrosis (AVN) following surgical pinning of a slipped capital femoral epiphysis (SCFE)?

. Male gender
. Patient obesity
. Unstable slip classification
. Concomitant hyperparathyroidism
. Use of a single cannulated screw

Correct Answer & Explanation

. Unstable slip classification

Explanation

An unstable SCFE, defined clinically by the inability to bear weight even with crutches, carries a high risk of AVN (up to 50%). Other iatrogenic risks include forceful reduction and hardware placed in the superoanterior quadrant.

Question 5632

Topic: 4. Pediatrics
A 4-year-old child presents with frequent fractures, blue sclerae, and dentinogenesis imperfecta. Genetic testing is most likely to reveal a defect in which of the following collagens?
. Type I
. Type II
. Type III
. Type IV
. Type IX

Correct Answer & Explanation

. Type I

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, leading to defective Type I collagen. Type I collagen is the predominant structural protein in bone, sclera, and dentin.

Question 5633

Topic: Pediatric Hip

A 13-year-old obese male presents with a slipped capital femoral epiphysis (SCFE). If the slip is determined to be unstable, the patient is at highest risk for which of the following complications?

. Chondrolysis
. Osteonecrosis of the femoral head
. Premature osteoarthritis
. Limb length discrepancy
. Femoroacetabular impingement

Correct Answer & Explanation

. Osteonecrosis of the femoral head

Explanation

An unstable SCFE is defined clinically as the inability to bear weight even with crutches. It carries a significantly higher risk of osteonecrosis (avascular necrosis) of the femoral head, reportedly as high as 47%, compared to stable slips.

Question 5634

Topic: Pediatric Hip

A 3-month-old female with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. Hyperflexion of the hips in the harness places the infant at highest risk for which of the following complications?

. Avascular necrosis of the femoral head
. Femoral nerve palsy
. Sciatic nerve palsy
. Inferior hip dislocation
. Acetabular dysplasia

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Hyperflexion of the hip in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to an iatrogenic femoral nerve palsy (manifesting as decreased active knee extension). Excessive abduction, on the other hand, increases the risk of avascular necrosis (AVN) of the femoral head.

Question 5635

Topic: 4. Pediatrics

A 4-year-old child presents with multiple fractures, blue sclerae, and dentinogenesis imperfecta. The underlying pathophysiology of this condition is primarily a defect in which of the following?

. Type I collagen synthesis
. Type II collagen synthesis
. Type X collagen synthesis
. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type I collagen synthesis

Explanation

Osteogenesis imperfecta is typically caused by mutations in the COL1A1 or COL1A2 genes, leading to defective Type I collagen. This widespread matrix defect results in brittle bones, blue sclerae, and hearing loss.

Question 5636

Topic: Pediatric Hip

In the management of Legg-Calve-Perthes disease, the Herring lateral pillar classification relies on radiographs taken during which stage of the disease?

. Initial (Necrosis) stage
. Fragmentation stage
. Reossification stage
. Healed stage
. Remodeling stage

Correct Answer & Explanation

. Fragmentation stage

Explanation

The Herring lateral pillar classification is assessed on an AP radiograph during the fragmentation stage of Legg-Calve-Perthes disease. It evaluates the height of the lateral pillar of the femoral head to determine prognosis and the need for intervention.

Question 5637

Topic: 4. Pediatrics

In the Ponseti method for correcting congenital talipes equinovarus (clubfoot), what is the first deformity that must be addressed during serial casting?

. Equinus
. Varus
. Adductus
. Cavus
. Internal rotation

Correct Answer & Explanation

. Cavus

Explanation

The sequence of correction in the Ponseti method follows the acronym CAVE: Cavus, Adductus, Varus, then Equinus. Cavus is corrected first by supinating the forefoot to align it with the hindfoot.

Question 5638

Topic: Pediatric Hip

In treating developmental dysplasia of the hip (DDH) with a Pavlik harness, hyperflexion of the hips beyond 120 degrees places the infant at highest risk for which of the following complications?

. Avascular necrosis of the femoral head
. Inferior dislocation of the hip
. Femoral nerve palsy
. Sciatic nerve palsy
. Acetabular dysplasia

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Hyperflexion of the hips in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to transient femoral nerve palsy. Conversely, excessive abduction is the primary risk factor for avascular necrosis.

Question 5639

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The pathogenesis of this condition involves a mutation in the FGFR3 gene. What is the specific effect of this mutation on the growth plate?

. Increased proliferation of chondrocytes in the reserve zone
. Gain-of-function mutation leading to decreased chondrocyte proliferation in the proliferative zone
. Loss-of-function mutation resulting in delayed ossification in the hypertrophic zone
. Defect in Type X collagen synthesis in the hypertrophic zone
. Defect in the production of matrix metalloproteinases leading to failed vascular invasion

Correct Answer & Explanation

. Gain-of-function mutation leading to decreased chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. In normal physiology, FGFR3 functions as a negative regulator of linear bone growth. The mutation causes constitutive activation of the receptor, which severely suppresses chondrocyte proliferation and differentiation in the proliferative zone of the physis.

Question 5640

Topic: 4. Pediatrics
A 10-year-old child sustains an ankle injury. Radiographs reveal a fracture line that traverses the distal tibial physis and extends vertically through the epiphysis into the tibiotalar articular surface, without involving the metaphysis. According to the Salter-Harris classification, what type of physeal fracture is this?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type III

Explanation

A Salter-Harris Type III fracture is characterized by a fracture line that extends through the physis and exits vertically through the epiphysis, thus intra-articularly. Type I traverses only the physis. Type II (most common) involves the physis and exits through the metaphysis (Thurston-Holland fragment). Type IV crosses the metaphysis, physis, and epiphysis. Type V is a compression/crush injury of the physis.

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