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4. Pediatrics MCQs

Practice Set 227 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 4521

Topic: Pediatric Hip

Prophylactic in situ pinning of the contralateral asymptomatic hip is most strongly indicated in a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE) and which of the following concurrent conditions?

. Morbid obesity
. Hypothyroidism
. Attention-deficit/hyperactivity disorder
. Type 1 diabetes mellitus
. Down syndrome

Correct Answer & Explanation

. Hypothyroidism

Explanation

Patients with SCFE secondary to endocrine disorders (e.g., hypothyroidism, panhypopituitarism) or renal osteodystrophy have an exceptionally high risk of bilateral involvement. Prophylactic pinning of the contralateral hip is strongly recommended in these cases.

Question 4522

Topic: Pediatric Lower Extremity

According to the Ponseti method for the treatment of idiopathic clubfoot, what is the correct sequence of deformity correction?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method follows the CAVE sequence for correcting clubfoot deformities: Cavus, Adductus, Varus, and finally Equinus. The cavus is corrected first by supinating the forefoot to align it with the hindfoot.

Question 4523

Topic: Pediatric Hip

A 6-week-old female infant is undergoing ultrasound evaluation for developmental dysplasia of the hip (DDH). The Graf alpha angle is measured at 52 degrees. What does this measurement indicate?

. A normal, mature hip
. A physiologically immature hip expected to normalize without intervention
. A dysplastic hip requiring treatment
. A completely dislocated hip resting outside the labrum
. An artifact of incorrect probe positioning

Correct Answer & Explanation

. A dysplastic hip requiring treatment

Explanation

An alpha angle less than 60 degrees indicates a shallow bony acetabular roof and is considered abnormal. An angle of 52 degrees falls into the dysplastic category (Graf type IIc or worse) and generally warrants treatment with a Pavlik harness.

Question 4524

Topic: Pediatric Hip

In Legg-Calve-Perthes disease, the lateral pillar classification is highly prognostic of long-term head shape outcomes. According to Herring's lateral pillar classification, a Type B hip is characterized radiographically by which of the following?

. No radiolucency or collapse of the lateral pillar
. >50% maintenance of the lateral pillar height
. <50% maintenance of the lateral pillar height
. Complete collapse of the lateral pillar with lateral extrusion
. Central pillar collapse with structurally intact medial and lateral pillars

Correct Answer & Explanation

. <50% maintenance of the lateral pillar height

Explanation

Herring's lateral pillar classification assesses the height of the lateral portion of the capital femoral epiphysis on an AP pelvis radiograph during the fragmentation phase. Type A involves no lateral pillar involvement. Type B involves >50% maintenance of lateral pillar height. Type C involves <50% maintenance of lateral pillar height. Type B/C border cases have a specific prognostic significance.

Question 4525

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying pathophysiology involves a specific genetic mutation that leads to which of the following cellular effects at the physeal growth plate?

. Defective synthesis of Type II collagen in the proliferative zone
. Gain-of-function mutation resulting in constitutive inhibition of chondrocyte proliferation
. Loss-of-function mutation leading to uncontrolled chondrocyte hypertrophy
. Defective conversion of cartilage to woven bone in the primary spongiosa
. Failure of osteoclast-mediated resorption of the secondary spongiosa

Correct Answer & Explanation

. Gain-of-function mutation resulting in constitutive inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a dominantly inherited, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 signaling negatively regulates chondrocyte proliferation and hypertrophy in the growth plate. The gain-of-function mutation leads to constitutive activation of the receptor, causing profound, continuous inhibition of normal physeal growth and resulting in short-limb dwarfism.

Question 4526

Topic: 4. Pediatrics

A 13-year-old obese boy presents with an acute-on-chronic slipped capital femoral epiphysis (SCFE). He is unable to bear weight. The biomechanical failure through the proximal femoral physis in a SCFE primarily occurs within which specific histologic zone of the growth plate?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of hypertrophy
. Zone of provisional calcification

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

A Slipped Capital Femoral Epiphysis (SCFE) is characterized by a biomechanical failure (shear) primarily through the zone of hypertrophy of the physis. The hypertrophic zone in these patients is abnormally widened due to complex endocrine and mechanical factors, creating a structurally weak plane. In contrast, typical Salter-Harris fractures classically fail through the zone of provisional calcification or the junction of the hypertrophic/calcification zones.

Question 4527

Topic: Pediatric Hip

A 13-year-old obese male presents with right groin pain and a limp for 3 weeks. On physical examination, as his right hip is passively flexed, it falls into obligatory external rotation. He is unable to bear weight on the right leg, even with the use of crutches. Which of the following is the most accurate statement regarding his condition?

. This is a stable slipped capital femoral epiphysis (SCFE) and carries a low risk of avascular necrosis.
. The definition of an unstable SCFE is based entirely on the radiographic slip angle being greater than 50 degrees.
. Prophylactic pinning of the contralateral hip is universally required regardless of age or endocrine status.
. This is an unstable SCFE, which carries an increased risk of avascular necrosis (up to 50%).
. The primary blood supply at risk during closed reduction of this condition is the artery of the ligamentum teres.

Correct Answer & Explanation

. This is an unstable SCFE, which carries an increased risk of avascular necrosis (up to 50%).

Explanation

The patient's presentation of obligatory external rotation with hip flexion is classic for Slipped Capital Femoral Epiphysis (SCFE). The inability to bear weight, even with crutches, defines an unstable SCFE according to Loder's classification. Unstable SCFE carries a significantly higher risk of avascular necrosis (AVN), historically ranging from 20% to 50%, compared to nearly 0% in stable SCFE.

Question 4528

Topic: 4. Pediatrics

A 6-month-old infant is brought to the emergency department for irritability. Radiographs demonstrate a 'bucket-handle' fracture of the distal femur. Which of the following statements regarding this type of fracture is most accurate?

. It is a normal variant of ossification in premature infants.
. It occurs almost exclusively from a direct, high-energy impact.
. It represents a classic metaphyseal lesion (CML) and is highly specific for non-accidental trauma.
. It is a hallmark sign of underlying osteogenesis imperfecta.
. It primarily involves failure of the diaphysis under torsional loads.

Correct Answer & Explanation

. It represents a classic metaphyseal lesion (CML) and is highly specific for non-accidental trauma.

Explanation

The 'bucket-handle' or 'corner' fracture is a classic metaphyseal lesion (CML) resulting from planar microfractures through the immature primary spongiosa. It is typically caused by pulling, twisting, or shaking of the infant's limb. These fractures are considered pathognomonic (highly specific) for non-accidental trauma (child abuse) in infants.

Question 4529

Topic: 4. Pediatrics

A 6-year-old child presents with frequent fractures, blue sclerae, and conductive hearing loss. Genetic analysis reveals a mutation in the COL1A1 gene. At the molecular level, this condition is most commonly characterized by which of the following?

. Defective cross-linking of collagen fibrils outside the cell
. Substitution of bulkier amino acids for glycine in the triple helix
. Impaired hydroxylation of proline residues by vitamin C deficiency
. Defective cleavage of propeptides from procollagen
. Absence of type II collagen in the epiphyseal plate

Correct Answer & Explanation

. Substitution of bulkier amino acids for glycine in the triple helix

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in COL1A1 or COL1A2. The most common molecular defect is the substitution of a bulky amino acid for glycine, which disrupts the tight coiling of the collagen triple helix.

Question 4530

Topic: 4. Pediatrics

A newborn is evaluated for short-limbed dwarfism, frontal bossing, and midface hypoplasia. Radiographs show rhizomelic shortening of the long bones. This condition is caused by a gain-of-function mutation in FGFR3, which leads to which of the following abnormalities at the physis?

. Increased proliferation of chondrocytes in the hypertrophic zone
. Decreased proliferation of chondrocytes in the proliferative zone
. Defective mineralization in the zone of provisional calcification
. Accelerated apoptosis of osteoblasts in the metaphysis
. Overactivity of osteoclasts in the primary spongiosa

Correct Answer & Explanation

. Decreased proliferation of chondrocytes in the proliferative zone

Explanation

Achondroplasia is due to a gain-of-function mutation in FGFR3, which constitutively suppresses chondrocyte proliferation. This leads to early closure of the physis and a narrowed zone of proliferative chondrocytes.

Question 4531

Topic: 4. Pediatrics

A 10-year-old child presents with cavovarus feet, clumsy gait, and distal muscle weakness. Neurologic examination reveals decreased deep tendon reflexes. What is the most common genetic mutation associated with this condition?

. PMP22 duplication
. Dystrophin gene deletion
. SMN1 gene deletion
. Fibrillin-1 mutation
. FGFR3 mutation

Correct Answer & Explanation

. PMP22 duplication

Explanation

The patient has Charcot-Marie-Tooth (CMT) disease. CMT type 1A is the most common variant and is caused by a duplication of the PMP22 gene on chromosome 17.

Question 4532

Topic: 4. Pediatrics

An infant is being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. While examining the child, you notice the harness is adjusted in extreme hyperflexion. This positioning places the infant at highest risk for which complication?

. Avascular necrosis of the femoral head
. Femoral nerve palsy
. Inferior hip dislocation
. Acetabular dysplasia
. Knee flexion contracture

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Extreme hyperflexion in a Pavlik harness can compress the femoral nerve against the inguinal ligament, leading to femoral nerve palsy. Excessive abduction is the primary risk factor for avascular necrosis.

Question 4533

Topic: Pediatric Hip

A 13-year-old obese boy presents with severe, sudden hip pain and inability to bear weight after a minor fall, superimposed on months of mild groin pain. In an unstable slipped capital femoral epiphysis (SCFE), which vessel is at greatest risk of injury leading to osteonecrosis?

. Ligamentum teres artery
. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Inferior gluteal artery
. Obturator artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The medial femoral circumflex artery, specifically its posterosuperior retinacular branches, provides the primary blood supply to the femoral head. It is at the highest risk of disruption in an unstable SCFE.

Question 4534

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. What is the precise cellular mechanism of the genetic mutation responsible for this condition?

. Loss-of-function mutation leading to unregulated chondrocyte hypertrophy
. Gain-of-function mutation causing inhibition of chondrocyte proliferation
. Defect in the synthesis of type I collagen triple helix
. Impaired degradation of glycosaminoglycans in the lysosome
. Failure of osteoclasts to create an acidic microenvironment

Correct Answer & Explanation

. Gain-of-function mutation causing inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation aberrantly activates signaling pathways that inhibit chondrocyte proliferation in the proliferative zone of the physis.

Question 4535

Topic: 4. Pediatrics

A 6-year-old girl is evaluated for recurrent fractures following minor trauma. Examination reveals blue sclerae and mild dentinogenesis imperfecta. Genetic testing is most likely to show a mutation resulting in the substitution of which amino acid in the collagen triple helix?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Glutamine

Correct Answer & Explanation

. Glycine

Explanation

Osteogenesis imperfecta is most commonly caused by mutations in COL1A1 or COL1A2. This typically results in the substitution of bulkier amino acids for glycine, the smallest amino acid, disrupting the tight packing of the collagen triple helix.

Question 4536

Topic: Pediatric Hip

A 4-month-old female with Developmental Dysplasia of the Hip (DDH) is being treated in a Pavlik harness. During a follow-up visit, the parents note she has stopped kicking her leg on the affected side. On exam, she has an absent patellar reflex and cannot actively extend the knee. Which of the following positioning errors most likely caused this complication?

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

Correct Answer & Explanation

. Excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive hip flexion (hyperflexion), which compresses the femoral nerve against the inguinal ligament. It presents as an inability to actively extend the knee. Excessive abduction is associated with avascular necrosis of the femoral head.

Question 4537

Topic: Pediatric Hip

A 12-year-old boy presents with a unilateral slipped capital femoral epiphysis (SCFE) of the left hip. He is scheduled for in situ screw fixation. Which of the following factors is the strongest indication for prophylactic pinning of the contralateral, asymptomatic hip?

. Age at presentation less than 10 years
. Presence of an underlying endocrine disorder
. Initial slip angle greater than 50 degrees
. Body mass index greater than the 95th percentile
. African American ethnicity

Correct Answer & Explanation

. Presence of an underlying endocrine disorder

Explanation

Patients with underlying endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy) have a significantly higher risk of developing bilateral SCFE, approaching 100% in some series. Prophylactic pinning of the contralateral hip is highly recommended in these cases.

Question 4538

Topic: Pediatric Hip
A 7-year-old boy is diagnosed with Legg-Calvรฉ-Perthes disease. According to the Herring Lateral Pillar Classification, which of the following radiographic criteria places the hip in Group B?
. No involvement of the lateral pillar
. Greater than 50% maintenance of lateral pillar height
. Less than 50% maintenance of lateral pillar height
. Complete collapse of the entire epiphysis including the medial pillar
. Extrusion of the lateral pillar without any loss of height

Correct Answer & Explanation

. Less than 50% maintenance of lateral pillar height

Explanation

In the Herring Lateral Pillar Classification for Perthes disease: Group A has no involvement of the lateral pillar. Group B has >50% maintenance of lateral pillar height. Group C has <50% maintenance of lateral pillar height. The classification strongly correlates with long-term sphericity of the femoral head.

Question 4539

Topic: Pediatric Hip

A 13-year-old obese male presents to the emergency department with severe right hip pain after a minor fall. He is completely unable to bear weight on the right leg. Radiographs reveal a slipped capital femoral epiphysis (SCFE). According to the Loder classification, what is the primary clinical significance of this presentation?

. It implies an acute-on-chronic slip.
. It indicates a high risk for subsequent chondrolysis.
. It designates an "unstable" SCFE, which carries a much higher risk of avascular necrosis (AVN).
. It mandates immediate open reduction via surgical dislocation.
. It suggests that contralateral prophylactic pinning is unnecessary.

Correct Answer & Explanation

. It designates an "unstable" SCFE, which carries a much higher risk of avascular necrosis (AVN).

Explanation

The Loder classification divides SCFE into stable (able to bear weight) and unstable (unable to bear weight, even with crutches). Unstable SCFE has a significantly higher risk of avascular necrosis (nearly 50%) compared to stable SCFE.

Question 4540

Topic: Pediatric Hip

A 12-year-old boy with a BMI in the 99th percentile presents to the emergency department with acute-on-chronic hip pain and is unable to bear weight on the affected limb. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following defines an 'unstable' SCFE according to the Loder classification, and what is its most devastating complication?

. Displacement > 50%; Chondrolysis
. Inability to bear weight; Avascular necrosis (AVN)
. Presence of an effusion; Degenerative joint disease
. Duration of symptoms < 3 weeks; Femoral neck fracture
. Inability to ambulate without crutches; Chondrolysis

Correct Answer & Explanation

. Inability to bear weight; Avascular necrosis (AVN)

Explanation

According to the Loder classification, an unstable SCFE is defined by the patient's inability to bear weight, even with assistive devices. Unstable slips carry a significantly higher risk (up to 50%) of developing avascular necrosis (AVN) of the femoral head compared to stable slips.

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