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4. Pediatrics MCQs

Practice Set 277 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 5521

Topic: Pediatric Hip
A 4-month-old infant with developmental dysplasia of the hip (DDH) is placed in a Pavlik harness. During follow-up, the parents report the infant is not kicking the affected leg. The physician notes the anterior straps are excessively tight, holding the hips in >120 degrees of flexion. This technical error most commonly results in which of the following complications?
. Avascular necrosis of the femoral head
. Femoral nerve palsy
. Obturator nerve palsy
. Inferior dislocation of the hip
. Sciatic nerve palsy

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Hyperflexion of the hips in a Pavlik harness (anterior straps too tight) causes compression of the femoral nerve against the inguinal ligament, leading to femoral nerve palsy (evident by a lack of active knee extension/kicking). Hyperabduction (posterior straps too tight) increases the risk of avascular necrosis.

Question 5522

Topic: 4. Pediatrics
A 4-year-old child presents with frequent fractures, short stature, and cranial nerve palsies. Radiographs demonstrate a generalized 'bone-within-bone' appearance and profound diffuse osteosclerosis. A mutation in which of the following is most likely responsible for the pathogenesis of this condition?
. Type I collagen (COL1A1/COL1A2)
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II (CA II) or TCIRG1
. Cathepsin K
. Tissue-nonspecific alkaline phosphatase (TNSALP)

Correct Answer & Explanation

. Carbonic anhydrase II (CA II) or TCIRG1

Explanation

The clinical and radiographic presentation is classic for malignant infantile osteopetrosis. This disease is characterized by a failure of osteoclastic bone resorption. Mutations in the TCIRG1 gene (a proton pump component) or Carbonic Anhydrase II (CA II) prevent osteoclasts from generating the acidic environment necessary to dissolve bone mineral in Howship's lacuna. The lack of resorption leads to dense, brittle bones and narrowed cranial foramina (causing nerve palsies).

Question 5523

Topic: 4. Pediatrics

An infant with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. During a follow-up visit, the infant is noted to have a new-onset lack of active knee extension on the treated side. Which of the following improper harness applications is the most likely cause of this complication?

. Excessive anterior strap tightening causing excessive hip flexion
. Excessive posterior strap tightening causing excessive hip abduction
. Inadequate anterior strap tightening allowing excessive hip extension
. Inadequate posterior strap tightening allowing excessive hip adduction
. Excessive tightening of the chest strap compressing the brachial plexus

Correct Answer & Explanation

. Excessive anterior strap tightening causing excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment and presents with decreased active knee extension and reduced patellar reflexes. It is caused by hyperflexion of the hip, which compresses the femoral nerve against the inguinal ligament. The anterior straps control hip flexion, and if adjusted too tightly, they cause this hyperflexion. Excessive abduction (from overly tight posterior straps) places the child at high risk for avascular necrosis (AVN) of the femoral head.

Question 5524

Topic: Pediatric Hip

In a patient presenting with an acute slipped capital femoral epiphysis (SCFE), prophylactic in situ pinning of the asymptomatic contralateral hip is most strongly indicated and routinely recommended in which of the following clinical scenarios?

. A 13-year-old obese male with an idiopathic slip
. A 12-year-old female with a severe slip angle (>60 degrees) on the affected side
. A 9-year-old male with confirmed renal osteodystrophy
. An 11-year-old male with a documented history of major pelvic trauma
. A 14-year-old male with a mild slip and a completely normal endocrine workup

Correct Answer & Explanation

. A 9-year-old male with confirmed renal osteodystrophy

Explanation

Prophylactic pinning of the asymptomatic contralateral hip in SCFE is controversial for typical idiopathic cases but is strongly recommended for patients at exceptionally high risk of a sequential slip. High-risk factors include age less than 10 years, widely open triradiate cartilage, and underlying endocrine or metabolic disorders (e.g., renal osteodystrophy, hypothyroidism, growth hormone deficiency). The 9-year-old with renal osteodystrophy possesses both a metabolic disorder and young age, putting him at near-certain risk for a contralateral SCFE.

Question 5525

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic dwarfism, frontal bossing, and a trident hand. His condition is caused by an activating mutation in the FGFR3 gene. Which zone of the physis is primarily affected by this mutation?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which inhibits chondrocyte proliferation. This directly affects the proliferative zone of the physis, leading to impaired endochondral ossification.

Question 5526

Topic: 4. Pediatrics

A 9-year-old child with a highly restrictive diet presents with irritability, bone pain, and bleeding gums. Radiographs reveal a dense zone of provisional calcification and a radiolucent line adjacent to the physis. The patient's condition is caused by a deficiency in an enzymatic cofactor required for which process?

. Cleavage of procollagen to collagen
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Cross-linking of collagen via lysyl oxidase
. Mineralization of osteoid

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy due to Vitamin C deficiency. Vitamin C is an essential cofactor for prolyl and lysyl hydroxylases, which are responsible for the hydroxylation of proline and lysine residues necessary for stable collagen triple-helix formation.

Question 5527

Topic: 4. Pediatrics

A 4-year-old girl is evaluated for multiple fractures with minimal trauma, blue sclerae, and dentinogenesis imperfecta. This condition is most commonly caused by a genetic mutation affecting the synthesis of which of the following proteins?

. Type II collagen
. Type I collagen
. Fibrillin-1
. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the chains of Type I collagen. Because Type I collagen is the major structural protein of bone, sclera, and dentin, its defect leads to the classic clinical triad.

Question 5528

Topic: 4. Pediatrics

A 4-week-old female infant is placed in a Pavlik harness for a dislocated left hip (Graf Type IV). After 3 weeks of strict full-time wear, dynamic ultrasound demonstrates that the hip remains completely dislocated. What is the most appropriate next step in management?

. Continue the Pavlik harness for an additional 3 weeks and repeat ultrasound
. Transition to a static abduction orthosis (e.g., Ilfeld splint) and continue observation
. Discontinue the harness and proceed with closed reduction and spica casting
. Proceed directly to open reduction via an anterior approach and Pemberton osteotomy
. Switch to a rigid hip abduction brace for 6 weeks

Correct Answer & Explanation

. Discontinue the harness and proceed with closed reduction and spica casting

Explanation

If a dislocated hip fails to reduce after 3 to 4 weeks of proper Pavlik harness treatment, the harness must be discontinued. Continuing the harness in a persistently dislocated hip places the child at high risk for 'Pavlik harness disease' (erosion of the posterior rim of the acetabulum). The standard next step after failed Pavlik harness treatment for a dislocated hip is typically a closed reduction with spica casting under general anesthesia, utilizing an arthrogram.

Question 5529

Topic: Pediatric Hip

A 12-year-old boy presents with left knee pain and an obligate externally rotated gait.

Radiographs reveal a left slipped capital femoral epiphysis (SCFE). Which of the following is a recognized indication for prophylactic in situ pinning of the asymptomatic contralateral right hip?

. Male gender
. Age older than 14 years at initial presentation
. Presence of an underlying endocrinopathy (e.g., hypothyroidism)
. Obesity greater than the 95th percentile alone
. Mild slip severity on the symptomatic side

Correct Answer & Explanation

. Presence of an underlying endocrinopathy (e.g., hypothyroidism)

Explanation

Prophylactic pinning of the contralateral asymptomatic hip in SCFE is controversial but is strictly indicated in certain high-risk groups. These include patients with underlying endocrinopathies (such as hypothyroidism or growth hormone deficiency), renal osteodystrophy, prior pelvic radiation, or patients presenting at a very young age (e.g., <10 years for girls or <11 for boys) with an open triradiate cartilage. Obesity alone is a risk factor for SCFE but not an absolute indication for prophylactic pinning.

Question 5530

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism, caused by an activating mutation in FGFR3. This genetic anomaly primarily exerts its inhibitory effect on chondrocyte function within which specific zone of the physis?

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

Correct Answer & Explanation

. Proliferative zone

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 bone growth. When constitutively active, it severely inhibits chondrocyte proliferation and differentiation, predominantly affecting the proliferative zone of the physis, leading to diminished enchondral ossification.

Question 5531

Topic: 4. Pediatrics

A 5-year-old child is evaluated for severe kyphoscoliosis, knock-knees, and corneal clouding, but displays normal intelligence. Radiographs show universal platyspondyly with central anterior beaking. Urine analysis shows elevated levels of keratan sulfate. What is the deficient enzyme?

. Alpha-L-iduronidase
. Iduronate sulfatase
. Galactose-6-sulfatase
. Glucocerebrosidase
. Sphingomyelinase

Correct Answer & Explanation

. Galactose-6-sulfatase

Explanation

This is Morquio syndrome (Mucopolysaccharidosis Type IV). It is characterized by severe skeletal dysplasia (platyspondyly with central anterior beaking, atlantoaxial instability), normal intelligence, and corneal clouding. Type IVA is caused by a deficiency in N-acetylgalactosamine-6-sulfatase (galactose-6-sulfatase), leading to the accumulation of keratan sulfate. Alpha-L-iduronidase deficiency causes Hurler syndrome (MPS I).

Question 5532

Topic: 4. Pediatrics

A neonate is noted to have multiple fractures, blue sclerae, and profound hearing loss. A defect in the synthesis of type I collagen is suspected. At the molecular level, this defect most commonly involves the substitution of which essential amino acid in the collagen triple helix?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Glutamate

Correct Answer & Explanation

. Glycine

Explanation

Osteogenesis Imperfecta is typically caused by mutations in the COL1A1 or COL1A2 genes. The classic molecular defect is a single base pair mutation that results in the substitution of glycine by a bulkier amino acid. Glycine, being the smallest amino acid, is required at every third position (the Gly-X-Y repeating sequence) to allow the three alpha chains to pack tightly into a stable triple helix.

Question 5533

Topic: 4. Pediatrics

A 3-year-old child presents with a disproportionately short trunk, coxa vara, and severe myopia. Radiographs reveal delayed ossification of the pubic bones and flattened vertebral bodies (platyspondyly). The underlying pathophysiology involves a genetic defect in which of the following structural proteins?

. Type I collagen
. Type II collagen
. Type IV collagen
. Type X collagen
. Fibroblast growth factor receptor 3

Correct Answer & Explanation

. Type II collagen

Explanation

The clinical presentation is consistent with Spondyloepiphyseal Dysplasia Congenita (SEDC). SEDC is caused by a mutation in the COL2A1 gene, which results in defective Type II collagen. Because Type II collagen is the primary collagen in articular cartilage, the nucleus pulposus, and the vitreous humor of the eye, these patients typically present with severe spinal deformity (platyspondyly), epiphyseal dysplasia, and ocular complications like myopia and retinal detachment.

Question 5534

Topic: Pediatric Hip

A 12-year-old obese boy presents with acute on chronic left hip pain and inability to bear weight. Examination shows an obligatory external rotation of the hip with passive flexion. Slipped capital femoral epiphysis (SCFE) is diagnosed. What is the primary arterial supply to the femoral head that is at risk of disruption in this condition?

. Ligamentum teres artery
. Medial femoral circumflex artery (MFCA)
. Lateral femoral circumflex artery (LFCA)
. Inferior gluteal artery
. Superior gluteal artery

Correct Answer & Explanation

. Medial femoral circumflex artery (MFCA)

Explanation

In older children and adults, the predominant blood supply to the femoral head is the lateral epiphyseal branches of the Medial Femoral Circumflex Artery (MFCA). This precarious blood supply is at risk for disruption in a displaced or unstable SCFE, potentially leading to avascular necrosis (AVN).

Question 5535

Topic: 4. Pediatrics

The Ponseti method is the gold standard for the treatment of idiopathic congenital talipes equinovarus (clubfoot). What is the correct sequence of deformity correction using serial casting?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The sequence of correction in the Ponseti method follows the mnemonic C-A-V-E: Cavus (corrected first by supinating the forefoot to align with the hindfoot), Adductus, Varus, and finally Equinus (which often requires a percutaneous Achilles tenotomy).

Question 5536

Topic: Pediatric Hip

A 13-year-old obese male presents to the emergency department with acute-onset right hip pain. He is entirely unable to bear weight on the right leg, even with crutches. Radiographs demonstrate a Slipped Capital Femoral Epiphysis (SCFE). What is the most significant prognostic factor for the development of avascular necrosis (AVN) in this patient?

. The anatomical degree of the epiphyseal slip angle
. The patient's Body Mass Index (BMI)
. The clinical instability of the slip (inability to bear weight)
. Delay in surgical treatment beyond 24 hours
. Use of a single central screw for fixation

Correct Answer & Explanation

. The clinical instability of the slip (inability to bear weight)

Explanation

The most important prognostic factor for the development of AVN in SCFE is the stability of the slip. An unstable SCFE (defined by Loder as the inability to bear weight, even with crutches) has a high rate of AVN (up to 47%), whereas stable slips have an AVN rate approaching zero.

Question 5537

Topic: Pediatric Hip

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the two-week follow-up, the parents report the infant is not kicking her left leg as much. On examination, there is decreased active extension of the left knee, but normal ankle movements. What is the most likely cause of this complication?

. Hyperflexion of the hip causing femoral nerve compression
. Excessive abduction of the hip causing obturator nerve compression
. Avascular necrosis of the femoral head
. Inadequate flexion of the hip leading to hip subluxation
. Ischemic contracture of the quadriceps

Correct Answer & Explanation

. Hyperflexion of the hip causing femoral nerve compression

Explanation

The most common nerve injury associated with Pavlik harness use is a transient femoral nerve palsy, typically caused by hyperflexion of the hip. This presents with decreased active extension of the knee (quadriceps weakness). Treatment involves adjusting the harness to reduce flexion; the palsy typically resolves spontaneously.

Question 5538

Topic: 4. Pediatrics
Pediatric physeal fractures (Salter-Harris type I-III) typically propagate through the structurally weakest layer of the growth plate. Which histologic zone does this represent?
. Reserve zone
. Proliferative zone
. Zone of hypertrophy
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

The zone of hypertrophy is structurally the weakest area of the physis due to the large volume of swollen chondrocytes and comparatively sparse extracellular matrix. Most physeal fractures propagate through this specific layer.

Question 5539

Topic: Pediatric Hip

In the pathogenesis of Slipped Capital Femoral Epiphysis (SCFE), the classic displacement of the capital femoral epiphysis relative to the femoral neck is in which direction?

. Anterior and superior
. Posterior and inferior
. Anterior and inferior
. Posterior and superior
. Directly medial and un-rotated

Correct Answer & Explanation

. Posterior and inferior

Explanation

In SCFE, the capital femoral epiphysis is held within the acetabulum while the femoral neck displaces anteriorly and superiorly. Thus, relative to the neck, the epiphysis "slips" posteriorly and inferiorly.

Question 5540

Topic: Pediatric Lower Extremity

What is the correct sequence of deformity correction in the Ponseti method for idiopathic clubfoot?

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

Correct Answer & Explanation

. Cavus, Varus, Adductus, Equinus

Explanation

The mnemonic CAVE dictates the order of correction: Cavus (elevating the first ray to align the forefoot with the hindfoot), Adductus, Varus, and finally Equinus (often requiring a percutaneous Achilles tenotomy as the final step).

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