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4. Pediatrics MCQs

Practice Set 270 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 5381

Topic: 4. Pediatrics

A child presents with disproportionate short stature, rhizomelic shortening, and frontal bossing. Genetic testing reveals a gain-of-function mutation in FGFR3. How does this mutation affect the physeal growth plate?

. Decreased apoptosis in the resting zone
. Constitutive activation inhibiting chondrocyte proliferation in the proliferative zone
. Decreased collagen type II production causing early closure
. Increased hypertrophic zone expansion leading to wide physes
. Lack of mineralization in the primary spongiosa

Correct Answer & Explanation

. Constitutive activation inhibiting chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia results from an FGFR3 mutation causing constitutive receptor activation. In the physis, this abnormal signaling inhibits chondrocyte proliferation and differentiation, ultimately restricting longitudinal bone growth.

Question 5382

Topic: 4. Pediatrics

A 6-year-old child presents with a history of multiple long bone fractures after minimal trauma, distinct blue sclerae, and progressive hearing loss. This genetic condition is caused by a defect in the synthesis of which structural protein?

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

Correct Answer & Explanation

. Type I collagen

Explanation

The clinical presentation is classic for osteogenesis imperfecta, an autosomal dominant disorder caused by mutations in COL1A1 or COL1A2. This leads to defective synthesis of Type I collagen, the major organic component of mature bone.

Question 5383

Topic: 4. Pediatrics

Osteogenesis imperfecta (OI) type I is a systemic connective tissue disorder most commonly caused by an autosomal dominant mutation affecting which of the following structural components?

. Type II collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Core binding factor alpha 1 (CBFA1)
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of type I collagen. This leads to quantitatively reduced or structurally defective type I collagen, resulting in brittle bones.

Question 5384

Topic: 4. Pediatrics

A 12-year-old obese boy presents with left thigh pain and an obligatory external rotation of the left hip with passive flexion. He is diagnosed with a stable Slipped Capital Femoral Epiphysis (SCFE). Prophylactic in situ pinning of the contralateral asymptomatic hip is most strongly indicated if the patient has which of the following concomitant conditions?

. Down syndrome
. Hypothyroidism
. Attention Deficit Hyperactivity Disorder (ADHD)
. Type 1 Diabetes Mellitus
. Blount's disease

Correct Answer & Explanation

. Hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but is generally recommended in patients with a high risk of bilateral involvement. Risk factors for bilaterality or future progression include endocrine disorders (e.g., hypothyroidism, renal osteodystrophy, panhypopituitarism), previous radiation therapy, and age less than 10 years at presentation.

Question 5385

Topic: 4. Pediatrics
A 4-year-old child presents with frequent fractures following minor trauma, blue sclerae, and hearing loss. Genetic testing is most likely to reveal a mutation affecting the synthesis of which of the following collagens?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis Imperfecta (OI) is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. Type I collagen is the major structural protein of bone, sclera, tendons, and ligaments.

Question 5386

Topic: Pediatric Lower Extremity

In the Ponseti method for treating idiopathic clubfoot (talipes equinovarus), correction of the deformity follows a specific sequence. Which component of the deformity is corrected first?

. Equinus
. Hindfoot Varus
. Midfoot Cavus
. Forefoot Adduction
. Tibial Torsion

Correct Answer & Explanation

. Midfoot Cavus

Explanation

The Ponseti method corrects clubfoot deformities in the mnemonic sequence CAVE: Cavus, Adductus, Varus, Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot. Next, the adduction and varus are corrected simultaneously by abducting the foot around the head of the talus.

Question 5387

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. What is the specific genetic defect and its primary effect on the physeal growth plate?

. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in FGFR3
. Defect in Type I collagen synthesis
. Defect in Type X collagen synthesis
. Mutation in the COMP gene

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the FGFR3 gene. This mutation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 5388

Topic: 4. Pediatrics

In the pediatric growth plate (physis), which zone is most susceptible to shear stress and is the typical site of failure in Salter-Harris fractures?

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

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 chondrocytes and minimal extracellular matrix. It is the most common site of failure in physeal injuries, such as Salter-Harris fractures.

Question 5389

Topic: 4. Pediatrics

A 4-year-old child presents with multiple fractures from minimal trauma, blue sclerae, and early hearing loss. The genetic defect in this condition primarily affects the synthesis of which of the following molecules?

. Type I collagen
. Type II collagen
. Type X collagen
. Fibrillin-1
. Fibroblast growth factor receptor 3 (FGFR3)

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta (OI) is most commonly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. This leads to defective or decreased synthesis of Type I collagen, resulting in brittle bones, blue sclerae, and hearing loss.

Question 5390

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 note that the infant has stopped kicking with the affected leg. On examination, the hip is found to be in excessive flexion. Which of the following physical exam findings is most likely to be present?

. Inability to actively flex the hip
. Inability to actively extend the knee
. Inability to actively dorsiflex the ankle
. Inability to actively plantarflex the ankle
. Absent Achilles reflex

Correct Answer & Explanation

. Inability to actively extend the knee

Explanation

A known complication of treating DDH with a Pavlik harness in excessive hip flexion is femoral nerve palsy. This manifests as a loss of quadriceps function, leading to the inability to actively extend the knee. The treatment is temporary removal of the harness or adjustment to decrease the degree of hip flexion. Excessive abduction, conversely, increases the risk of avascular necrosis (AVN) of the femoral head.

Question 5391

Topic: Pediatric Hip

A 12-year-old girl with a history of severe hypothyroidism presents with a limp and left hip pain. Radiographs reveal a slipped capital femoral epiphysis (SCFE) of the left hip. What is the most appropriate definitive management?

. In situ pinning of the left hip only
. Open reduction and internal fixation of the left hip
. In situ pinning of the left hip and prophylactic pinning of the right hip
. Spica cast immobilization
. Proximal femoral osteotomy of the left hip

Correct Answer & Explanation

. In situ pinning of the left hip and prophylactic pinning of the right hip

Explanation

While unilateral SCFE is typically treated with single-screw in situ pinning, prophylactic pinning of the contralateral asymptomatic hip is strongly recommended in patients with specific risk factors. These high-risk factors include underlying endocrine disorders (such as hypothyroidism, panhypopituitarism), renal osteodystrophy, and a history of previous pelvic radiation. Given her severe hypothyroidism, prophylactic pinning of the right hip is indicated.

Question 5392

Topic: 4. Pediatrics

A 12-year-old obese male is diagnosed with a severe slipped capital femoral epiphysis (SCFE) of the left hip. Contralateral prophylactic pinning of the asymptomatic right hip is most strongly indicated if the patient has a history of which of the following conditions?

. Type 1 Diabetes Mellitus
. Hypothyroidism
. Asthma
. Achondroplasia
. Slipped capital femoral epiphysis in a second-degree relative

Correct Answer & Explanation

. Hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is debated for idiopathic cases but is highly recommended for patients with endocrine or metabolic disorders, as they have a significantly higher rate of bilateral involvement (approaching 100% in some cohorts). Hypothyroidism, renal osteodystrophy, and panhypopituitarism are major indications for prophylactic fixation.

Question 5393

Topic: Pediatric Lower Extremity

According to the Ponseti method for the conservative management of congenital talipes equinovarus (clubfoot), which component of the deformity must be addressed first during serial casting?

. Equinus
. Varus
. Adductus
. Cavus
. Internal tibial torsion

Correct Answer & Explanation

. Cavus

Explanation

The Ponseti method corrects the deformities of a clubfoot in a specific sequence, remembered by the acronym CAVE: Cavus, Adductus, Varus, Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot. Equinus is corrected last.

Question 5394

Topic: Pediatric Hip

A 13-year-old obese boy presents with knee pain and an antalgic gait. Examination reveals obligatory external rotation of the hip with passive flexion. What is the most appropriate initial treatment if radiographs confirm a stable Slipped Capital Femoral Epiphysis (SCFE)?

. Closed reduction and spica casting
. In situ pinning with a single cannulated screw
. Open reduction and internal fixation
. Proximal femoral osteotomy
. Observation and non-weight bearing

Correct Answer & Explanation

. In situ pinning with a single cannulated screw

Explanation

The standard of care for a stable SCFE is in situ pinning with a single, partially threaded cannulated screw placed centrally in the epiphysis. Closed reduction is contraindicated due to the high risk of disrupting the blood supply and causing osteonecrosis.

Question 5395

Topic: Pediatric Hip

A 13-year-old obese boy presents with progressive left knee pain and an antalgic gait. Examination reveals obligatory external rotation of the hip during passive flexion. Which of the following is the most appropriate initial management?

. Physical therapy for hip abductor strengthening
. Non-weight bearing and immediate orthopedic referral for in situ pinning
. Closed reduction and spica casting
. Open reduction and internal fixation
. Proximal femoral osteotomy

Correct Answer & Explanation

. Non-weight bearing and immediate orthopedic referral for in situ pinning

Explanation

The clinical presentation is classic for a Slipped Capital Femoral Epiphysis (SCFE). The standard of care is immediate non-weight bearing to prevent further slippage, followed by in situ percutaneous screw fixation.

Question 5396

Topic: Pediatric Hip

A 4-month-old female infant is diagnosed with developmental dysplasia of the hip (DDH) that is reducible. A Pavlik harness is prescribed. Which of the following represents the most serious complication of excessive hyperflexion of the hips in the harness?

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

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Excessive hyperflexion in a Pavlik harness can lead to femoral nerve palsy. Avascular necrosis is typically a complication of excessive rigid abduction, while femoral nerve palsy is the classic risk of excessive flexion.

Question 5397

Topic: 4. Pediatrics

In the context of Slipped Capital Femoral Epiphysis (SCFE), prophylactic pinning of the contralateral asymptomatic hip is most strongly indicated for a patient with which of the following underlying conditions?

. Down syndrome
. Hypothyroidism
. Achondroplasia
. Neurofibromatosis type 1
. Marfan syndrome

Correct Answer & Explanation

. Hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip is recommended in patients with endocrine disorders (like hypothyroidism) or renal osteodystrophy. These conditions significantly increase the risk of bilateral and sequential slips compared to idiopathic cases.

Question 5398

Topic: Pediatric Hip

A 4-week-old infant is being treated with a Pavlik harness for Developmental Dysplasia of the Hip (DDH). Excessive hyperflexion of the hips in the harness most commonly risks injury to which of the following nerves?

. Sciatic nerve
. Obturator nerve
. Superior gluteal nerve
. Femoral nerve
. Lateral femoral cutaneous nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

Excessive flexion in a Pavlik harness (greater than 100-120 degrees) can compress the femoral nerve against the inguinal ligament, leading to transient femoral nerve palsy. Excessive abduction, on the other hand, risks avascular necrosis.

Question 5399

Topic: 4. Pediatrics

A 24-year-old man presents with a short forearm and a hand deformity. The patient is otherwise healthy with no other congenital defects. The clinical appearance of his forearm is shown (). Your diagnosis is:

. Ulnar club hand
. Preaxial longitudinal deficiency
. Postaxial longitudinal deficiency
. Thumb aplasia
. Hypoplastic hand syndrome

Correct Answer & Explanation

. Preaxial longitudinal deficiency

Explanation

This is a classic appearance of a radial club hand, which is often referred to as preaxial longitudinal deficiency. Ulnar club hand and postaxial longitudinal deficiency are synonymous.

Question 5400

Topic: 4. Pediatrics
A 24-year-old man presents with a short forearm and a hand deformity. The patient is otherwise healthy with no other congenital defects. The patient has an elbow flexion contracture of 70° and desires lengthening. Which of the following statements is not true regarding lengthening:
. Nerve palsies may occur during lengthening.
. Lengthening must be done gradually.
. Lengthening usually equalizes limb length.
. Lengthening helps improve function by extending the reach.
. Lengthening leads to recurrence of the deformity.

Correct Answer & Explanation

. Lengthening usually equalizes limb length.

Explanation

In most cases of radial club hand, excluding a hypoplastic radius, full correction cannot be achieved.

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