Menu

4. Pediatrics MCQs

Practice Set 273 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 5441

Topic: 4. Pediatrics

A 2-year-old boy presents with disproportionate short stature, frontal bossing, and rhizomelic shortening. What is the genetic mutation responsible for this condition?

. COL1A1
. FGFR3
. COMP
. RUNX2
. SOX9

Correct Answer & Explanation

. FGFR3

Explanation

Achondroplasia is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 5442

Topic: 4. Pediatrics
A patient with Osteogenesis Imperfecta suffers from frequent fractures. The underlying defect involves the predominant collagen type found in bone. Which collagen type is this?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen is the primary organic component of bone, tendons, and ligaments. Osteogenesis Imperfecta typically results from mutations in the COL1A1 or COL1A2 genes, affecting Type I collagen synthesis.

Question 5443

Topic: 4. Pediatrics

A 10-year-old child presents with bowed legs and a waddling gait. Laboratory studies reveal low serum calcium, low phosphorus, high alkaline phosphatase, and elevated parathyroid hormone. What is the primary cause of this condition?

. Vitamin C deficiency
. Genetic defect in FGFR3
. Vitamin D deficiency
. Overproduction of Growth Hormone
. Carbonic anhydrase II deficiency

Correct Answer & Explanation

. Vitamin D deficiency

Explanation

These laboratory findings are classic for nutritional Rickets resulting from Vitamin D deficiency, which leads to impaired mineralization of the physis. Secondary hyperparathyroidism occurs as a physiological response to the low serum calcium levels.

Question 5444

Topic: Pediatric Hip

Which of the following is the strongest clinical indication for prophylactic in situ pinning of the contralateral hip in a 12-year-old male presenting with a unilateral slipped capital femoral epiphysis (SCFE)?

. Age greater than 14 years
. Male sex
. African American descent
. Underlying endocrine disorder
. Body mass index > 95th percentile

Correct Answer & Explanation

. Underlying endocrine disorder

Explanation

Patients with underlying endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy) or prior radiation therapy have a significantly higher risk of bilateral SCFE. In these atypical presentations, prophylactic pinning of the contralateral hip is highly recommended.

Question 5445

Topic: Pediatric Hip

A 4-week-old female is diagnosed with developmental dysplasia of the hip (DDH) and placed in a Pavlik harness. Two weeks later, the parents report she has an inability to actively extend her knee on the treated side. What is the most likely cause?

. Hyperflexion of the hip in the harness
. Hyperextension of the hip in the harness
. Excessive abduction in the harness
. Inadequate abduction in the harness
. Avascular necrosis of the femoral head

Correct Answer & Explanation

. Hyperflexion of the hip in the harness

Explanation

An inability to extend the knee points to a femoral nerve palsy, a known complication of the Pavlik harness. It is caused by excessive hyperflexion of the hip, which stretches or compresses the femoral nerve. Excessive abduction in the harness, by contrast, is associated with avascular necrosis.

Question 5446

Topic: 4. Pediatrics

Which of the following describes the primary cellular defect in the physis of a patient with an activating mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene?

. Failure of provisional calcification in the hypertrophic zone
. Decreased chondrocyte proliferation in the proliferative zone
. Defective collagen type X synthesis in the hypertrophic zone
. Accelerated apoptosis in the resting zone
. Impaired osteoclast resorption at the primary spongiosa

Correct Answer & Explanation

. Decreased chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. In normal enchondral ossification, FGFR3 negatively regulates chondrocyte proliferation. The activating mutation leads to an exaggerated inhibitory signal, which severely diminishes chondrocyte proliferation in the proliferative zone of the physis, resulting in rhizomelic short stature.

Question 5447

Topic: Pediatric Hip

A 4-month-old female with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. Three weeks later, her mother notes the infant has decreased active extension of the left knee. What is the most likely iatrogenic cause?

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

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive hyperflexion of the hips. It presents with decreased active quadriceps function and usually resolves with temporary adjustment or removal of the harness.

Question 5448

Topic: Pediatric Hip

A 4-month-old female infant is diagnosed with developmental dysplasia of the hip (DDH). Ultrasound shows an alpha angle of 45 degrees. The infant is placed in a Pavlik harness. Which of the following positions is most likely to cause iatrogenic avascular necrosis (AVN) of the femoral head in this device?

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

Correct Answer & Explanation

. Excessive hip abduction

Explanation

The primary risk factor for avascular necrosis of the femoral head during Pavlik harness treatment is excessive hip abduction. Conversely, excessive hip flexion primarily causes femoral nerve palsy.

Question 5449

Topic: Pediatric Hip

A 4-week-old female is treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the two-week follow-up, she is noted to lack active knee extension on the affected side. What is the most likely cause?

. Avascular necrosis of the femoral head
. Excessive flexion of the anterior straps causing femoral nerve palsy
. Excessive abduction causing obturator nerve palsy
. Improper harness sizing leading to sciatic nerve palsy
. Development of a transient knee effusion

Correct Answer & Explanation

. Excessive flexion of the anterior straps causing femoral nerve palsy

Explanation

Hyperflexion of the hips in a Pavlik harness (>120 degrees) impinges the femoral nerve against the inguinal ligament, leading to an acute compressive neuropathy. It typically resolves with appropriate adjustment of the anterior straps.

Question 5450

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, cavus, varus, equinus
. Varus, cavus, adductus, equinus
. Cavus, equinus, varus, adductus

Correct Answer & Explanation

. Cavus, adductus, varus, equinus

Explanation

The Ponseti method corrects idiopathic clubfoot deformities sequentially based on the acronym CAVE: Cavus, Adductus, Varus, and finally Equinus. Equinus is corrected last, frequently requiring a percutaneous Achilles tenotomy.

Question 5451

Topic: 4. Pediatrics

A pediatric patient is diagnosed with achondroplasia. Which of the following best describes the genetic mutation and its effect on the epiphyseal plate?

. COL1A1 mutation causing defective type I collagen synthesis
. FGFR3 mutation causing constitutive activation and inhibition of chondrocyte proliferation
. COMP mutation causing abnormal cartilage oligomeric matrix protein
. Runx2 mutation causing defective osteoblast differentiation
. EXT1 mutation causing abnormal heparan sulfate synthesis

Correct Answer & Explanation

. FGFR3 mutation causing constitutive activation and inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This leads to constitutive activation of the receptor, which abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis, resulting in rhizomelic dwarfism.

Question 5452

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism. Which of the following best describes the underlying genetic mutation and its primary effect on bone growth?

. Activating mutation in FGFR3 inhibiting chondrocyte proliferation
. Inactivating mutation in FGFR3 stimulating chondrocyte proliferation
. Mutation in COL1A1 causing defective osteoid mineralization
. Mutation in COMP causing premature physeal closure
. Mutation in CBFA1 leading to absent clavicles

Correct Answer & Explanation

. Activating mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function (activating) mutation in the FGFR3 gene. This overactivity abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis, stunting endochondral ossification.

Question 5453

Topic: 4. Pediatrics

A pediatric patient is diagnosed with achondroplasia, the most common form of short-limb dwarfism. This condition is primarily driven by a gain-of-function mutation in the FGFR3 gene. Which specific anatomic zone of the physis is most severely inhibited by this mutation?

. Zone of resting cartilage
. Zone of proliferation
. Zone of hypertrophy
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Zone of proliferation

Explanation

The FGFR3 mutation in achondroplasia leads to constitutive activation of the receptor, which negatively regulates bone growth. This defect primarily impairs chondrocyte multiplication in the zone of proliferation.

Question 5454

Topic: 4. Pediatrics

Which type of collagen is most predominant in the hypertrophic zone of the physis and is essential for normal endochondral ossification?

. Type I
. Type II
. Type IX
. Type X
. Type XI

Correct Answer & Explanation

. Type X

Explanation

Type X collagen is specifically synthesized by hypertrophic chondrocytes in the growth plate. It facilitates matrix mineralization and is a critical structural component during endochondral ossification.

Question 5455

Topic: 4. Pediatrics

A newborn is evaluated for short-limbed dwarfism, frontal bossing, and midface hypoplasia. Radiographs reveal rhizomelic shortening. The underlying genetic mutation results in which of the following cellular effects?

. Decreased osteoclast activity
. Inhibition of chondrocyte proliferation
. Defective cross-linking of collagen
. Abnormal mineralization of osteoid
. Overproduction of fibroblast growth factor

Correct Answer & Explanation

. Inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which leads to constitutive inhibition of chondrocyte proliferation in the proliferative zone of the physis.

Question 5456

Topic: 4. Pediatrics

In a growing child with nutritional rickets, which zone of the physis is most significantly widened and disorganized?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

In rickets, failure of mineralization in the zone of provisional calcification leads to a massive accumulation of unmineralized cartilage. This specifically widens the hypertrophic zone of the physis.

Question 5457

Topic: Pediatric Hip

A 12-year-old obese male presents with acute, severe left hip pain and inability to bear weight after a minor fall. He reports a 3-month history of mild, intermittent left groin pain. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following factors most significantly increases the risk of avascular necrosis (AVN) in this patient?

. Chronicity of the slip prior to the fall
. Inability to bear weight on the affected limb
. Degree of posterior slip angle on the lateral radiograph
. Patient's BMI percentile
. Concomitant hypothyroidism

Correct Answer & Explanation

. Inability to bear weight on the affected limb

Explanation

According to the Loder classification, an unstable SCFE is defined by the inability to bear weight, even with crutches. Unstable SCFE carries a significantly higher risk of avascular necrosis (up to 47%) compared to stable SCFE.

Question 5458

Topic: Pediatric Hip

A 4-month-old female is being treated with a Pavlik harness for developmental dysplasia of the hip. At the two-week follow-up, the parents report the infant is no longer actively kicking her left leg, and physical exam reveals absent active knee extension on that side. What is the most appropriate management?

. Continue harness and observe
. Adjust the anterior straps to increase hip flexion
. Discontinue the harness immediately
. Switch to a rigid hip spica cast
. Perform an emergent ultrasound

Correct Answer & Explanation

. Discontinue the harness immediately

Explanation

The clinical picture describes a femoral nerve palsy, a known complication of hyperflexion in a Pavlik harness. The harness must be discontinued immediately to prevent permanent nerve injury and allow for neurological recovery.

Question 5459

Topic: Pediatric Hip

A 13-year-old obese boy presents with right groin and knee pain, and an obligatory external rotation of the hip during passive flexion. He is diagnosed with a slipped capital femoral epiphysis (SCFE). Which of the following is a generally accepted indication for prophylactic in situ pinning of the contralateral asymptomatic hip?

. Male gender
. Age greater than 14 years
. Underlying endocrine disorder
. Body Mass Index > 30
. Bilateral knee pain

Correct Answer & Explanation

. Underlying endocrine disorder

Explanation

Prophylactic pinning of the contralateral hip in SCFE is generally recommended for patients with underlying metabolic or endocrine disorders (e.g., hypothyroidism, renal osteodystrophy) due to the high risk of bilateral involvement. It may also be considered in patients who are highly unlikely to follow up.

Question 5460

Topic: 4. Pediatrics

A 13-year-old obese boy presents with right thigh pain and a limp. Examination reveals obligate external rotation of the right hip during flexion. Radiographs show a widened right proximal femoral physis. What is the most appropriate definitive management?

. Spica cast immobilization
. In situ pinning with a single cannulated screw
. Closed reduction and internal fixation
. Open reduction and femoral neck osteotomy
. Proximal femoral epiphysiodesis using bone graft

Correct Answer & Explanation

. In situ pinning with a single cannulated screw

Explanation

This patient has a Slipped Capital Femoral Epiphysis (SCFE), characterized by obligate external rotation upon hip flexion. The gold standard treatment is in situ pinning with a single cannulated screw to stabilize the physis and prevent further slippage.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page