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4. Pediatrics MCQs

Practice Set 287 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 5721

Topic: 4. Pediatrics

What is the underlying pathophysiological mechanism of the genetic mutation seen in achondroplasia?

. Defect in intramembranous ossification leading to impaired flat bone formation
. Mutation in the COL1A1 gene affecting type I collagen synthesis
. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation
. Loss-of-function mutation in FGFR3 accelerating physeal growth
. Defect in the hypertrophic zone of the physis impairing apoptosis

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis, severely affecting endochondral ossification while intramembranous ossification remains normal.

Question 5722

Topic: 4. Pediatrics

A 14-month-old child with achondroplasia has a prominent thoracolumbar kyphosis. Neurological examination is completely normal. What is the recommended initial management?

. Posterior spinal fusion
. Anterior and posterior spinal fusion
. Extension bracing (TLSO)
. Avoidance of unsupported sitting
. Observation with only biannual radiographs

Correct Answer & Explanation

. Avoidance of unsupported sitting

Explanation

Thoracolumbar kyphosis in infants with achondroplasia is highly prevalent and typically resolves once the child begins walking and developing active lumbar lordosis. Initial management involves avoiding unsupported sitting; bracing is reserved for kyphosis that persists beyond walking age or is progressive.

Question 5723

Topic: 4. Pediatrics

An 8-year-old child with achondroplasia presents with progressive, symptomatic genu varum. Radiographs show significant mechanical axis deviation. What is the primary underlying skeletal cause of this specific deformity?

. Premature proximal tibial physeal arrest
. Asymmetric growth of the distal femoral physis
. Fibular overgrowth relative to the tibia
. Laxity of the lateral collateral ligament
. Underlying Vitamin D deficiency rickets

Correct Answer & Explanation

. Fibular overgrowth relative to the tibia

Explanation

Genu varum in achondroplasia is primarily caused by relative fibular overgrowth compared to the tibia, leading to a varus bending moment at the knee. Management often involves guided growth or corrective osteotomies depending on skeletal maturity and symptom severity.

Question 5724

Topic: 4. Pediatrics

The genetic defect in achondroplasia primarily affects which specific zone of the growth plate?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

The FGFR3 gain-of-function mutation in achondroplasia primarily inhibits the proliferation of chondrocytes. Therefore, the proliferative zone of the physis is the most directly affected area, resulting in defective endochondral ossification and short-limb dwarfism.

Question 5725

Topic: 4. Pediatrics



When evaluating an AP pelvis radiograph of a child with achondroplasia, which constellation of findings is most characteristic?

. Champagne glass pelvic inlet, squared iliac wings, and horizontal acetabular roofs
. Coxa valga, deep acetabula, and flared iliac wings
. Premature triradiate cartilage closure and severe coxa vara
. Increased acetabular angle, narrow sciatic notch, and tall iliac wings
. Dysplastic acetabula, coxa magna, and superior migration of the femoral head

Correct Answer & Explanation

. Champagne glass pelvic inlet, squared iliac wings, and horizontal acetabular roofs

Explanation

The classic pelvic radiographic findings in achondroplasia include a broad 'champagne glass' pelvic inlet, squared (elephant ear) iliac wings, and horizontal acetabular roofs. The greater sciatic notch is also typically narrow and small.

Question 5726

Topic: 4. Pediatrics

A 38-year-old healthy male and a 35-year-old healthy female have a newborn diagnosed with achondroplasia. What is the approximate recurrence risk for their future pregnancies?

. 0%
. <1%
. 25%
. 50%
. 100%

Correct Answer & Explanation

. <1%

Explanation

Approximately 80% of achondroplasia cases result from spontaneous de novo mutations, which are strongly associated with advanced paternal age. Since both parents are unaffected, the recurrence risk for future pregnancies is negligible (<1%), accounting only for rare instances of germline mosaicism.

Question 5727

Topic: 4. Pediatrics

A 3-year-old child presents with rhizomelic shortening, frontal bossing, and a trident hand. Genetic testing reveals a mutation in the FGFR3 gene. Which zone of the physis is primarily affected by this specific 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 the FGFR3 gene, which inhibits chondrocyte proliferation in the proliferative zone of the growth plate. This leads to defective endochondral ossification.

Question 5728

Topic: 4. Pediatrics

A 14-month-old boy with achondroplasia has a flexible thoracolumbar kyphosis of 35 degrees. He has not yet begun walking independently. Neurological examination is normal. What is the recommended orthopedic management?

. Immediate posterior spinal fusion
. Thoracolumbosacral orthosis (TLSO)
. Observation and avoidance of unsupported sitting
. Anterior release and posterior instrumented fusion
. Surgical decompression of the thoracolumbar junction

Correct Answer & Explanation

. Observation and avoidance of unsupported sitting

Explanation

Thoracolumbar kyphosis in infants with achondroplasia usually resolves once they begin walking and develop lumbar lordosis. Management consists of avoiding unsupported sitting; bracing is only considered if kyphosis persists or worsens after walking age.

Question 5729

Topic: 4. Pediatrics

Which of the following radiographic features of the pelvis is classic for a patient with achondroplasia?

. Deep and narrow greater sciatic notch
. Champagne glass-shaped pelvic inlet
. Vertical orientation of the acetabulum
. Coxa valga with elongated femoral necks
. Hypoplastic iliac wings with a narrow sacrum

Correct Answer & Explanation

. Champagne glass-shaped pelvic inlet

Explanation

The classic pelvic radiographic findings in achondroplasia include a "champagne glass" pelvic cavity (wider than deep), squared iliac wings, and horizontal acetabular roofs. The greater sciatic notch is typically small and narrow.

Question 5730

Topic: 4. Pediatrics

A 7-year-old girl with achondroplasia presents with progressive genu varum.

What is the primary underlying mechanical cause of genu varum in patients with this condition?

. Overgrowth of the fibula relative to the tibia
. Premature closure of the medial proximal tibial physis
. Ligamentous laxity of the lateral collateral ligament
. Medial meniscal hypoplasia
. Tibial torsion associated with early weight-bearing

Correct Answer & Explanation

. Overgrowth of the fibula relative to the tibia

Explanation

Genu varum in achondroplasia is largely driven by a length discrepancy between the tibia and fibula. The relatively longer fibula exerts a tethering and bowing effect on the tibia, leading to varus deformity.

Question 5731

Topic: 4. Pediatrics

A patient with achondroplasia presents to the clinic for a routine evaluation. Which of the following upper extremity abnormalities is most commonly associated with this condition?

. Radial head dislocation
. Cubitus valgus
. Limited elbow extension
. Ulnar nerve subluxation
. Congenital radioulnar synostosis

Correct Answer & Explanation

. Limited elbow extension

Explanation

Upper extremity anomalies in achondroplasia characteristically include rhizomelic shortening and limited elbow extension, often lacking up to 30 degrees. Radial head dislocation is more characteristic of conditions like multiple hereditary exostoses.

Question 5732

Topic: 4. Pediatrics

A male patient with achondroplasia marries a female of normal stature. What is the probability that their first child will inherit achondroplasia?

. 0%
. 25%
. 50%
. 75%
. 100%

Correct Answer & Explanation

. 50%

Explanation

Achondroplasia is inherited in an autosomal dominant pattern with essentially 100% penetrance. A heterozygous affected parent and an unaffected parent have a 50% chance of passing the mutant FGFR3 allele to each offspring.

Question 5733

Topic: 4. Pediatrics

Two individuals with achondroplasia are expecting a child and undergo genetic counseling. What is the chance of the fetus inheriting homozygous achondroplasia, and what is its expected clinical course?

. 25% chance; universally lethal in the perinatal period
. 25% chance; results in a mild phenotype
. 50% chance; universally lethal in the perinatal period
. 50% chance; results in severe intellectual disability
. 75% chance; compatible with normal lifespan

Correct Answer & Explanation

. 25% chance; universally lethal in the perinatal period

Explanation

When both parents have achondroplasia, there is a 25% risk of homozygous achondroplasia. This condition is universally lethal in the neonatal period, typically due to severe rib cage hypoplasia and subsequent respiratory failure.

Question 5734

Topic: 4. Pediatrics

Parents of a 5-year-old boy with achondroplasia inquire about growth hormone (GH) therapy to improve his adult height. According to current literature, what is the expected outcome of GH therapy in achondroplasia?

. Normalizes adult height to the 50th percentile
. Causes disproportionate lengthening of the trunk only
. May provide a mild increase in growth velocity but minimal impact on final adult height
. Cures the underlying chondrocyte defect
. Exacerbates genu varum requiring mandatory osteotomies

Correct Answer & Explanation

. May provide a mild increase in growth velocity but minimal impact on final adult height

Explanation

Growth hormone therapy in achondroplasia can initially increase growth velocity during the first few years of treatment. However, it does not correct the underlying skeletal dysplasia and has a negligible effect on final adult height.

Question 5735

Topic: 4. Pediatrics

A new targeted pharmacological therapy, Vosoritide, has been approved for pediatric patients with achondroplasia whose epiphyses are not yet closed. What is the mechanism of action of this medication?

. Direct inhibition of the FGFR3 receptor tyrosine kinase
. C-type natriuretic peptide (CNP) analog that antagonizes FGFR3 downstream signaling
. Recombinant human growth hormone
. Monoclonal antibody against bone morphogenetic protein 4 (BMP4)
. Osteoclast inhibitor to prevent bone resorption

Correct Answer & Explanation

. C-type natriuretic peptide (CNP) analog that antagonizes FGFR3 downstream signaling

Explanation

Vosoritide is a C-type natriuretic peptide (CNP) analog. It binds to the natriuretic peptide receptor-B (NPR-B), activating a signaling cascade that inhibits the overactive MEK/ERK pathway caused by the FGFR3 mutation, thereby promoting endochondral bone growth.

Question 5736

Topic: 4. Pediatrics

A 5-year-old boy falls from monkey bars and sustains an extension-type supracondylar humerus fracture. On presentation to the emergency department, his hand is pale and pulseless, but he has normal capillary refill and warm fingers. What is the most appropriate next step in management?

. Immediate open exploration of the brachial artery
. Closed reduction and percutaneous pinning, followed by vascular reassessment
. Application of a long arm cast in 120 degrees of flexion
. CT angiography of the upper extremity
. Observation with elevation and ice

Correct Answer & Explanation

. Closed reduction and percutaneous pinning, followed by vascular reassessment

Explanation

Correct Answer: B. Closed reduction and percutaneous pinning, followed by vascular reassessmentA pulseless hand in the setting of a pediatric supracondylar humerus fracture is a vascular emergency, often due to kinking, spasm, or entrapment of the brachial artery over the proximal fracture fragment. The immediate and most appropriate next step is urgent closed reduction and percutaneous pinning. In the majority of cases, anatomic reduction relieves the tension on the neurovascular bundle and restores perfusion. If the hand remains pulseless and poorly perfused (white/cold) after reduction, open exploration is indicated. CT angiography delays definitive treatment and is not indicated in the acute setting.

Question 5737

Topic: Pediatric Hip
A 13-year-old obese male presents with a 3-week history of left knee pain and a limp. He denies any recent trauma or systemic symptoms. On examination, as the left hip is passively flexed, it obligatorily deviates into external rotation. Radiographs of the knee are unremarkable. Which of the following is the most likely underlying pathophysiology of his condition?
. Avascular necrosis of the capital femoral epiphysis
. Shear failure through the hypertrophic zone of the physis
. Bacterial seeding of the hip joint
. Inflammation of the synovial lining of the hip
. Apophysitis of the tibial tubercle

Correct Answer & Explanation

. Shear failure through the hypertrophic zone of the physis

Explanation

The clinical vignette describes slipped capital femoral epiphysis (SCFE), which classically presents in obese adolescents with a painful limp, referred knee pain, and obligate external rotation of the hip during flexion. The underlying pathophysiology of SCFE involves mechanical shear failure through the hypertrophic zone of the physis (growth plate) due to increased mechanical stress (obesity) and hormonal changes during the adolescent growth spurt. Avascular necrosis of the epiphysis describes Legg-Calvé-Perthes disease, which typically affects younger children (ages 4-8).

Question 5738

Topic: Pediatric Upper Extremity & Spine
A 5-year-old boy falls from monkey bars and sustains a Gartland type III supracondylar humerus fracture. On presentation to the emergency department, his hand is pale and pulseless, but he has brisk capillary refill and normal motor function of the hand. What is the most appropriate next step in management?
. Immediate open exploration of the brachial artery
. Closed reduction and percutaneous pinning, followed by reassessment of the pulse
. CT angiography of the upper extremity
. Application of a long arm cast in 120 degrees of flexion
. Observation and elevation for 24 hours

Correct Answer & Explanation

. Closed reduction and percutaneous pinning, followed by reassessment of the pulse

Explanation

In a pulseless but well-perfused (pink, brisk capillary refill) hand following a displaced supracondylar humerus fracture, the initial step is urgent closed reduction and percutaneous pinning. Often, the brachial artery is kinked, tethered over the proximal fracture fragment, or in spasm, and anatomic reduction restores the pulse. If the hand remains pulseless and becomes poorly perfused (white/ischemic) after reduction, open exploration of the brachial artery is indicated. CT angiography delays definitive treatment and is not indicated in the acute setting of a pulseless, pink hand.

Question 5739

Topic: 4. Pediatrics

A 13-year-old overweight boy presents with a 3-week history of left knee pain and a limp. On examination, as his left hip is passively flexed, it obligatorily goes into external rotation. Radiographs reveal a widening of the left proximal femoral physis. Which of the following is the most appropriate definitive management?

. Immediate non-weight bearing and bracing
. In situ single screw fixation of the proximal femoral epiphysis
. Closed reduction and spica casting
. Proximal femoral osteotomy
. Core decompression of the femoral head

Correct Answer & Explanation

. In situ single screw fixation of the proximal femoral epiphysis

Explanation

Correct Answer: In situ single screw fixation of the proximal femoral epiphysisThe patient's presentation is classic for a Slipped Capital Femoral Epiphysis (SCFE). The obligate external rotation with passive hip flexion is a hallmark clinical sign. The standard of care for a stable SCFE is in situ fixation, typically with a single cannulated screw placed centrally into the epiphysis. This prevents further slippage and promotes premature physeal closure. Closed reduction is contraindicated as it significantly increases the risk of avascular necrosis.

Question 5740

Topic: Pediatric Hip

A 13-year-old obese male presents with a 2-week history of left groin pain and a limp. He is currently unable to bear weight on the affected limb. Radiographs reveal a slipped capital femoral epiphysis (SCFE). He undergoes urgent in situ percutaneous pinning. Which of the following factors is most strongly associated with the development of avascular necrosis (AVN) of the femoral head in this patient?

. The degree of posterior slip angle greater than 30 degrees.
. The patient's body mass index (BMI) greater than the 95th percentile.
. The inability to bear weight prior to surgical intervention.
. The presence of bilateral SCFE involvement.
. The use of a single screw rather than two screws for fixation.

Correct Answer & Explanation

. The inability to bear weight prior to surgical intervention.

Explanation

Correct Answer: CThe Loder classification categorizes Slipped Capital Femoral Epiphysis (SCFE) into stable and unstable based on the patient's ability to bear weight (with or without crutches). An "unstable" SCFE is defined by the inability to bear weight and carries a significantly higher risk of avascular necrosis (AVN) of the femoral head (up to 47%) compared to stable SCFE, where the AVN rate is typically less than 10%. While slip angle and BMI are important factors in the disease process, stability is the primary prognosticator for AVN.

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