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4. Pediatrics MCQs

Practice Set 308 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 6141

Topic: Pediatric Hip
In the evaluation of a 7-year-old boy with Legg-Calvé-Perthes disease, the Herring Lateral Pillar classification is used to determine prognosis. This classification is based on the radiolucency and height of the lateral pillar of the femoral head during which stage of the disease?
. Initial (necrosis) stage
. Fragmentation stage
. Reossification stage
. Residual stage
. Pre-collapse stage

Correct Answer & Explanation

. Fragmentation stage

Explanation

The Herring Lateral Pillar classification is the most widely used prognostic classification for Legg-Calvé-Perthes disease. It evaluates the height of the lateral pillar of the capital femoral epiphysis on an AP pelvic radiograph during the fragmentation stage of the disease, as this is when the maximum extent of epiphyseal collapse is evident.

Question 6142

Topic: Pediatric Hip

A 13-year-old obese boy presents with groin pain and an obligate external rotation of the hip during flexion. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following best describes the anatomical displacement of the femoral neck relative to the capital epiphysis in this condition?

. The neck displaces posteriorly and inferiorly.
. The neck displaces anteriorly and superiorly.
. The neck displaces anteriorly and inferiorly.
. The neck displaces posteriorly and superiorly.
. The neck displaces medially and inferiorly.

Correct Answer & Explanation

. The neck displaces anteriorly and superiorly.

Explanation

Correct Answer: The neck displaces anteriorly and superiorly.In Slipped Capital Femoral Epiphysis (SCFE), the capital femoral epiphysis remains relatively fixed in the acetabulum while the femoral neck displaces anteriorly and superiorly. This biomechanical shift leads to the classic clinical presentation of obligate external rotation when the hip is flexed.

Question 6143

Topic: 4. Pediatrics

A newborn is diagnosed with achondroplasia. Which of the following best describes the underlying genetic mutation and its effect on bone growth?

. A mutation in the COL1A1 gene leading to defective type I collagen synthesis.
. An activating mutation in the FGFR3 gene leading to inhibition of chondrocyte proliferation in the proliferative zone.
. A mutation in the COMP gene affecting the hypertrophic zone of the physis.
. A defect in the CBFA1 (RUNX2) transcription factor affecting membranous ossification.
. A mutation in the diastrophic dysplasia sulfate transporter (DTDST) gene.

Correct Answer & Explanation

. An activating mutation in the FGFR3 gene leading to inhibition of chondrocyte proliferation in the proliferative zone.

Explanation

Correct Answer: An activating mutation in the FGFR3 gene leading to inhibition of chondrocyte proliferation in the proliferative zone.Achondroplasia is the most common form of short-limb dwarfism. It is caused by an autosomal dominant, gain-of-function (activating) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation leads to a paradoxical inhibition of chondrocyte proliferation in the proliferative zone of the physis, resulting in impaired endochondral ossification and rhizomelic shortening of the limbs.

Question 6144

Topic: Pediatric Hip

During open reduction of Developmental Dysplasia of the Hip (DDH) via an anterior approach, several anatomical structures must be addressed to allow concentric reduction. Which of the following is NOT typically considered an anatomical block to reduction in DDH?

. Inverted limbus
. Hypertrophied ligamentum teres
. Fibrofatty pulvinar
. Tight iliopsoas tendon
. Shortened piriformis tendon

Correct Answer & Explanation

. Shortened piriformis tendon

Explanation

Obstacles to reduction in DDH include the inverted limbus, hypertrophied ligamentum teres, pulvinar, tight iliopsoas tendon, and transverse acetabular ligament. The piriformis is located posteriorly and is not typically a block to reduction.

Question 6145

Topic: Pediatric Hip

An 11-year-old obese male presents to the emergency department unable to bear weight on his left leg after a minor slip. Radiographs confirm a severe left slipped capital femoral epiphysis (SCFE). Which of the following factors is most predictive of developing avascular necrosis (AVN) of the femoral head in this patient?

. Body Mass Index (BMI) greater than 35
. Degree of posterior epiphyseal slip greater than 50%
. Inability to bear weight with or without crutches
. Delay in surgical pinning beyond 24 hours
. Prophylactic pinning of the contralateral hip

Correct Answer & Explanation

. Inability to bear weight with or without crutches

Explanation

The inability to bear weight defines an unstable SCFE according to the Loder classification. Unstable SCFE has a significantly higher risk of developing AVN (up to 50%) compared to stable SCFE, regardless of slip severity.

Question 6146

Topic: 4. Pediatrics

A 5-year-old boy presents with waddling gait and delayed motor milestones. Radiographs show flattened, irregular epiphyses in the hips and knees, but the spine radiographs show normal vertebral bodies. What is the most likely genetic mutation responsible for his condition?

. COL2A1
. COMP
. FGFR3
. RUNX2
. CBFA1

Correct Answer & Explanation

. COMP

Explanation

The patient has Multiple Epiphyseal Dysplasia (MED), which spares the spine (unlike Spondyloepiphyseal Dysplasia, linked to COL2A1). MED is most commonly caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 6147

Topic: Pediatric Hip

A 6-week-old female is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). During follow-up, she exhibits decreased active extension of the knee on the affected side. What is the most appropriate next step in management?

. Immediate closed reduction and spica casting
. Adjust the harness to increase hip flexion
. Discontinue the harness temporarily or adjust it to decrease hip flexion
. Continue current harness settings and re-evaluate in 2 weeks
. Perform an ultrasound-guided intra-articular steroid injection

Correct Answer & Explanation

. Discontinue the harness temporarily or adjust it to decrease hip flexion

Explanation

Decreased active knee extension indicates a femoral nerve palsy, a known complication of excessive hip flexion in a Pavlik harness. The harness should be adjusted to decrease flexion or temporarily removed until nerve function recovers.

Question 6148

Topic: Pediatric Hip

A 10-year-old boy with chronic renal failure presents with a limp and obligate external rotation of the hip during flexion. Radiographs confirm a moderate stable slipped capital femoral epiphysis (SCFE). In addition to pinning the affected hip, what is the primary indication for prophylactic pinning of the contralateral hip?

. Age older than 12 years
. Male gender
. Presence of an underlying endocrine or metabolic disorder
. Severity of the initial slip angle
. Body mass index > 95th percentile

Correct Answer & Explanation

. Presence of an underlying endocrine or metabolic disorder

Explanation

Patients with SCFE associated with endocrinopathies or metabolic disorders (like renal failure, hypothyroidism) have a very high risk of bilateral involvement. Prophylactic pinning of the contralateral hip is highly recommended in these specific populations.

Question 6149

Topic: Pediatric Upper Extremity & Spine
A 6-year-old boy sustains an extension-type Gartland III supracondylar humerus fracture. On examination, he cannot flex his thumb interphalangeal joint or the distal interphalangeal joint of his index finger. Which structure is most likely injured?
. Anterior interosseous nerve
. Median nerve proper
. Radial nerve
. Posterior interosseous nerve
. Ulnar nerve

Correct Answer & Explanation

. Median nerve proper

Explanation

The inability to make an 'OK sign' (flexion of thumb IP and index DIP joints) indicates an injury to the anterior interosseous nerve (AIN). AIN palsy is the most common neurologic deficit associated with extension-type supracondylar humerus fractures.

Question 6150

Topic: Pediatric Hip

A 7-year-old boy is diagnosed with Legg-Calve-Perthes disease. According to the lateral pillar (Herring) classification, which radiographic feature in the fragmentation stage portends the worst prognosis?

. Maintenance of 100% of lateral pillar height
. Lateral pillar height >50% but <100%
. Lateral pillar height <50% of original height
. Central pillar collapse with an intact lateral pillar
. Involvement of the medial pillar only

Correct Answer & Explanation

. Lateral pillar height <50% of original height

Explanation

The Herring Lateral Pillar classification predicts the outcome of Legg-Calve-Perthes disease based on the height of the lateral pillar during the fragmentation stage. Group C (<50% lateral pillar height maintained) indicates severe collapse and carries the worst prognosis.

Question 6151

Topic: Pediatric Hip

A 3-month-old female with developmental dysplasia of the hip (DDH) has been treated in a Pavlik harness for two weeks. Her mother reports that the baby is no longer kicking her right leg. Examination reveals absent active knee extension on the right, but ankle and toe movements are normal. What is the most likely cause of this finding?

. Avascular necrosis of the femoral head
. Obturator nerve palsy due to extreme abduction
. Femoral nerve palsy due to hyperflexion
. Sciatic nerve palsy due to extreme abduction
. Tibial nerve palsy due to posterior strap tightness

Correct Answer & Explanation

. Femoral nerve palsy due to hyperflexion

Explanation

Femoral nerve palsy is the most common neurologic complication associated with the Pavlik harness, typically resulting from hyperflexion of the hip. Management consists of adjusting the harness to decrease flexion, which usually allows the palsy to resolve completely.

Question 6152

Topic: 4. Pediatrics

A neonate presents with severe rhizomelic limb shortening, rigid clubfeet, 'hitchhiker' thumbs, and cystic swelling of the external ears (cauliflower ears). Which of the following gene mutations is the underlying cause of this skeletal dysplasia?

. COMP
. SLC26A2
. FGFR3
. RUNX2
. COL2A1

Correct Answer & Explanation

. SLC26A2

Explanation

Diastrophic dysplasia is caused by an autosomal recessive mutation in the SLC26A2 (DTDST) gene, which encodes a sulfate transporter. Classic clinical features include hitchhiker thumbs, severe rigid clubfeet, and cauliflower ears.

Question 6153

Topic: Pediatric Hip

A 12-year-old boy with a BMI of 35 is diagnosed with a severe left slipped capital femoral epiphysis (SCFE) and undergoes in situ pinning. In which of the following scenarios is prophylactic pinning of the contralateral asymptomatic hip most strongly indicated?

. Male gender
. Age older than 14 years
. Underlying hypothyroidism
. Idiopathic presentation
. Unilateral severe slippage

Correct Answer & Explanation

. Underlying hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly recommended for patients with endocrine disorders (such as hypothyroidism) due to a very high risk of bilateral involvement. Patients who present at an atypically young age (less than 10 years) are also strong candidates for prophylaxis.

Question 6154

Topic: 4. Pediatrics

A 3-year-old obese girl presents with progressive bilateral tibia vara. Radiographs demonstrate prominent metaphyseal beaking of the medial proximal tibias with a metaphyseal-diaphyseal angle of 20 degrees. Based on her age and radiographic findings, what is the most appropriate initial management?

. Reassurance and clinical observation
. High-dose Vitamin D supplementation
. Knee-ankle-foot orthosis (KAFO) bracing
. Proximal tibial valgus osteotomy
. Guided growth (hemiepiphysiodesis) of the lateral proximal tibia

Correct Answer & Explanation

. Knee-ankle-foot orthosis (KAFO) bracing

Explanation

Infantile Blount disease (age under 4 years) with Langenskiold stage I or II and an elevated metaphyseal-diaphyseal angle should initially be treated conservatively. KAFO bracing is the first-line treatment to unload the medial compartment and guide normal growth.

Question 6155

Topic: Pediatric Hip

A 12-year-old obese boy presents with a 4-week history of right groin pain and a limp. He denies trauma. During the physical examination of the right hip, what is the most characteristic finding indicating a slipped capital femoral epiphysis (SCFE)?

. Obligatory internal rotation during passive hip flexion
. Obligatory external rotation during passive hip flexion
. Severe pain primarily during hip extension
. A palpable click during passive hip abduction
. Inability to actively extend the knee

Correct Answer & Explanation

. Obligatory external rotation during passive hip flexion

Explanation

The Drehmann sign is the classic physical exam finding in SCFE. As the hip is passively flexed, the thigh obligatorily abducts and externally rotates due to the altered geometry of the proximal femur.

Question 6156

Topic: Pediatric Hip

A 4-month-old infant with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. During a follow-up visit, the parents report the infant is not kicking the affected leg. Examination reveals decreased active knee extension on that side. This complication is most likely due to which of the following mechanical issues?

. Excessive hip abduction
. Excessive hip flexion
. Inadequate hip flexion
. Inadequate hip abduction
. Excessive hip extension

Correct Answer & Explanation

. Excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by hyperflexion of the hip. Excessive hip abduction, on the other hand, increases the risk of avascular necrosis (AVN) of the femoral head.

Question 6157

Topic: Pediatric Hip

A 6-year-old boy is diagnosed with Legg-Calve-Perthes disease. According to the Herring lateral pillar classification, which of the following radiographic parameters best determines his prognosis and likelihood of developing femoral head deformity?

. The degree of subchondral fracture (Crescent sign)
. The extent of metaphyseal cyst formation
. The height of the lateral pillar of the epiphysis during the fragmentation phase
. The amount of lateral subluxation of the femoral head
. The rate of re-ossification of the medial pillar

Correct Answer & Explanation

. The height of the lateral pillar of the epiphysis during the fragmentation phase

Explanation

The Herring classification focuses on the height of the lateral third (lateral pillar) of the capital femoral epiphysis during the fragmentation phase. A maintained lateral pillar height (>50%) correlates with a more spherical femoral head outcome.

Question 6158

Topic: Pediatric Lower Extremity

A newborn is diagnosed with idiopathic clubfoot (talipes equinovarus) and treatment is initiated using the Ponseti method. What is the correct initial step in manipulating the foot prior to applying the first cast?

. Forced dorsiflexion of the ankle to correct the equinus
. Abduction of the forefoot with counter-pressure on the cuboid
. Pronation of the forefoot to align it with the hindfoot
. Elevation of the first ray to correct the cavus deformity
. Eversion of the calcaneus to correct the varus deformity

Correct Answer & Explanation

. Elevation of the first ray to correct the cavus deformity

Explanation

The Ponseti method requires a specific sequence of correction (CAVE: Cavus, Adductus, Varus, Equinus). The first step is to supinate the forefoot and elevate the first ray to align the forefoot with the hindfoot, correcting the cavus.

Question 6159

Topic: 4. Pediatrics

A 5-year-old girl is evaluated for disproportionate short stature. Physical exam reveals a barrel chest, severe myopia, and normal intelligence. Radiographs show delayed ossification of the pubic bones, coxa vara, and platyspondyly. Which of the following genes is most likely mutated?

. COL1A1
. COL2A1
. FGFR3
. COMP
. GNAS

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) is caused by mutations in the COL2A1 gene, affecting type II collagen. It classically presents with disproportionate short trunk dwarfism, myopia, and atlantoaxial instability.

Question 6160

Topic: 4. Pediatrics

A 3-year-old severely obese girl presents with bilateral bowing of her legs and a lateral thrust during the stance phase of gait. Standing radiographs show significant tibia vara. Which radiographic parameter definitively distinguishes infantile Blount disease from physiologic bowing?

. Metaphyseal-diaphyseal angle > 16 degrees
. Tibiofemoral angle > 15 degrees
. Medial physeal slope < 10 degrees
. Presence of a medial metaphyseal beak
. Lateral physeal widening

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle > 16 degrees

Explanation

A metaphyseal-diaphyseal angle (Drennan's angle) greater than 16 degrees strongly suggests infantile Blount disease rather than physiologic bowing, which typically has an angle of less than 10 degrees.

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