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4. Pediatrics MCQs

Practice Set 248 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 4941

Topic: 4. Pediatrics

Slipped capital femoral epiphysis (SCFE) typically occurs due to mechanical failure through which specific zone of the growth plate?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Mechanical failure in conditions like SCFE and most Salter-Harris fractures typically occurs through the zone of hypertrophy. This zone is mechanically the weakest due to the large cell volume and decreased structural extracellular matrix.

Question 4942

Topic: 4. Pediatrics

Type I collagen is the predominant organic structural macromolecule in bone. In its triple-helix structure, which amino acid is strictly required at every third position to allow the tight coiling of the alpha chains?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Glutamate

Correct Answer & Explanation

. Proline

Explanation

Glycine is the smallest amino acid and is required at every third position (Gly-X-Y repeating sequence) of the collagen polypeptide chain. Its small size allows the three alpha chains to pack tightly into a triple helix. Mutations substituting glycine with larger amino acids result in the structurally defective collagen seen in Osteogenesis Imperfecta.

Question 4943

Topic: 4. Pediatrics
Osteogenesis imperfecta (OI) type I is the most common form of the disease. It is typically caused by an autosomal dominant genetic mutation that results in which of the following collagen defects?
. A completely absent expression of the COL2A1 gene
. A quantitative defect producing decreased amounts of structurally normal type I collagen
. A qualitative defect resulting in a structurally abnormal type I collagen molecule
. A defect in the enzymatic degradation of glycosaminoglycans
. A mutation in the FGFR3 gene causing abnormal chondrocyte proliferation

Correct Answer & Explanation

. A quantitative defect producing decreased amounts of structurally normal type I collagen

Explanation

OI Type I is characterized by a quantitative defect (often a null allele mutation) resulting in decreased production of structurally normal type I collagen. This leads to a milder clinical phenotype. In contrast, OI Types II, III, and IV typically involve qualitative defects (e.g., missense mutations causing glycine substitution), leading to structurally abnormal collagen and much more severe clinical phenotypes.

Question 4944

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. His condition is primarily caused by a genetic mutation resulting in a gain of function in which of the following receptors?

. Fibroblast growth factor receptor 3 (FGFR3)
. Parathyroid hormone-related peptide (PTHrP) receptor
. Transforming growth factor-beta (TGF-beta) receptor
. Bone morphogenetic protein receptor 2 (BMPR2)
. Wnt-signaling frizzled receptor

Correct Answer & Explanation

. Fibroblast growth factor receptor 3 (FGFR3)

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This overactivity continuously inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to stunted endochondral ossification.

Question 4945

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. It is caused by an activating mutation in the FGFR3 gene. What is the normal physiological role of the FGFR3 receptor in the physis?

. Stimulates chondrocyte proliferation
. Inhibits chondrocyte proliferation
. Promotes osteoblast differentiation
. Delays vascular invasion
. Increases matrix metalloproteinase production

Correct Answer & Explanation

. Stimulates chondrocyte proliferation

Explanation

The normal function of Fibroblast Growth Factor Receptor 3 (FGFR3) is to inhibit chondrocyte proliferation in the proliferative zone of the physis. An activating (gain-of-function) mutation leads to excessive inhibition, resulting in shortened long bones.

Question 4946

Topic: 4. Pediatrics

Osteogenesis imperfecta (OI) type I is characterized by recurrent fractures, blue sclerae, and hearing loss. At the molecular level, this condition is most commonly caused by a mutation leading to which of the following defects in Type I collagen?

. Decreased quantity of structurally normal collagen
. Production of a structurally abnormal collagen molecule
. Inability to cross-link collagen fibrils
. Defective hydroxylation of lysine residues
. Failure of extracellular cleavage of procollagen

Correct Answer & Explanation

. Decreased quantity of structurally normal collagen

Explanation

OI Type I (the mildest and most common form) is typically caused by a null allele mutation resulting in a 50% reduction in the synthesis of structurally normal Type I collagen (quantitative defect). Other types (e.g., OI Type II) involve qualitative defects due to missense mutations.

Question 4947

Topic: 4. Pediatrics

A slipped capital femoral epiphysis (SCFE) is characterized by a biomechanical failure primarily propagating through which specific zone of the growth plate?

. Reserve (resting) zone
. Proliferative zone
. Hypertrophic zone
. Primary spongiosa
. Secondary spongiosa

Correct Answer & Explanation

. Reserve (resting) zone

Explanation

Epiphyseal separations, including SCFE and most Salter-Harris fractures, typically occur through the hypertrophic zone of the physis. This zone lacks substantial collagen matrix and represents the weakest link in shear and tension.

Question 4948

Topic: 4. Pediatrics

Achondroplasia is caused by an autosomal dominant mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. This mutation results in which of the following effects at the cellular level?

. Increased chondrocyte proliferation
. Decreased chondrocyte apoptosis
. Inhibition of chondrocyte proliferation
. Excessive osteoclast activity
. Impaired collagen cross-linking

Correct Answer & Explanation

. Increased chondrocyte proliferation

Explanation

The FGFR3 mutation in achondroplasia is a gain-of-function mutation that constitutively activates the receptor. In the physis, this abnormal signaling strongly inhibits chondrocyte proliferation in the proliferative zone, stunting longitudinal bone growth.

Question 4949

Topic: 4. Pediatrics

Achondroplasia is caused by a mutation in the FGFR3 gene. What is the molecular consequence of this mutation on the growth plate?

. Decreased production of Type X collagen in the hypertrophic zone
. Constitutive activation leading to inhibition of chondrocyte proliferation
. Loss-of-function resulting in unregulated chondrocyte hypertrophy
. Defective formation of the secondary center of ossification
. Impaired osteoclast function leading to retained primary spongiosa

Correct Answer & Explanation

. Decreased production of Type X collagen in the hypertrophic zone

Explanation

Achondroplasia is an autosomal dominant disorder caused by an activating (gain-of-function) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 negatively regulates bone growth. The constitutive activation of FGFR3 profoundly inhibits chondrocyte proliferation and hypertrophy in the proliferative zone of the physis.

Question 4950

Topic: 4. Pediatrics

Salter-Harris type I and II fractures most commonly occur through which zone of the physis?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Physeal fractures (like Salter-Harris I and II) classically propagate through the hypertrophic zone, specifically the zone of provisional calcification (or junction of provisional calcification and degeneration). This is the mechanically weakest part of the physis due to its high cell-to-matrix ratio.

Question 4951

Topic: 4. Pediatrics

A 4-year-old boy is evaluated for short stature, frontal bossing, and rhizomelic shortening of the limbs. Genetic testing confirms a gain-of-function mutation in FGFR3. This genetic defect most directly impairs chondrocyte function in which zone of the epiphyseal growth plate?

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

Correct Answer & Explanation

. Reserve zone

Explanation

The patient has achondroplasia. FGFR3 normally acts as a negative regulator of bone growth. A gain-of-function mutation in FGFR3 excessively inhibits chondrocyte proliferation, directly affecting the proliferative zone of the physis, leading to decreased endochondral ossification.

Question 4952

Topic: 4. Pediatrics

The Hueter-Volkmann principle defines the response of the epiphyseal growth plate to mechanical loading. Which of the following statements accurately characterizes this biomechanical principle?

. Increased compression across the physis stimulates longitudinal bone growth.
. Increased tension across the physis inhibits longitudinal bone growth.
. Increased compression across the physis inhibits longitudinal bone growth.
. Cyclic shear forces are the primary stimulus for appositional bone growth.
. Static tensile loading drives intramembranous ossification via BMP-2.

Correct Answer & Explanation

. Increased compression across the physis stimulates longitudinal bone growth.

Explanation

The Hueter-Volkmann law states that increased mechanical compression across a physis retards or inhibits longitudinal growth, whereas increased tension (or decreased compression) accelerates growth. This principle helps explain the progression of deformities such as Blount's disease or adolescent idiopathic scoliosis.

Question 4953

Topic: 4. Pediatrics

Osteogenesis imperfecta is most commonly caused by an autosomal dominant mutation affecting which of the following processes?

. Defective cartilage template formation
. Impaired osteoclast ruffled border function
. Substitution of glycine in the procollagen triple helix
. Overactivation of the FGFR3 receptor
. Deficiency of carbonic anhydrase II

Correct Answer & Explanation

. Defective cartilage template formation

Explanation

Osteogenesis imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, typically involving the substitution of a bulky amino acid for glycine. This disrupts the formation and stability of the Type I collagen triple helix.

Question 4954

Topic: 4. Pediatrics

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. What is the primary effect of this mutation on the growth plate?

. Excessive proliferation of resting zone chondrocytes
. Inhibition of chondrocyte proliferation in the proliferative zone
. Premature apoptosis in the hypertrophic zone
. Failure of secondary ossification center formation
. Defective synthesis of Type II collagen

Correct Answer & Explanation

. Excessive proliferation of resting zone chondrocytes

Explanation

The FGFR3 gene normally acts as a negative regulator of bone growth. A gain-of-function mutation results in constitutive activation, which severely inhibits the proliferation of chondrocytes in the proliferative zone of the physis.

Question 4955

Topic: 4. Pediatrics
A 9-year-old boy has a history of multiple fractures. He presents with left leg pain following a minor fall. His anteroposterior and lateral plain radiographs are shown. The most likely genetic defect would be:
. FGF receptor 3
. Type I collagen
. Cartilage oligomeric matrix protein
. Fibrillin
. Type II collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The anteroposterior and lateral radiographs show thinned cortices and a gentle S-shaped curve of the tibia. The overall alignment of the tibia, as well as the physes, is normal. These are the radiographic features of osteogenesis imperfecta. In osteogenesis imperfecta, the genetic defect involves type I collagen. Type I collagen is made up of two alpha-1 chains and one alpha-2 chain in a triple helix. Glycine is the smallest amino acid and is crucial for coiling of the triple helix. Mutations in the glycine chain lead to severe forms of osteogenesis imperfecta.

Question 4956

Topic: 4. Pediatrics
A 12-year-old boy is brought to the clinic by his concerned parents. The boy's forearm is bowed, and his parents are confused as to the possible diagnosis and treatment options. You notice that the right forearm of the child is bowed ulnarwards and is shorter compared to the left forearm. The pronosupination is markedly decreased on the right side but is also limited on the left side. The patient has a good grip, pinch, and grasp. He is neurologically intact as well. The parents say that they first noticed the deformity around 6 or 7 years ago, and the mother informs you that she had noticed a hard bump on the forearm. She has recently noticed another bump on his right leg. The child does not complain of pain and is using both of his hands quite well. The parents were informed by a previous physician that the child has Madelung's deformity and are concerned that the disease is now involving other areas of his body. You order a radiograph of the forearm. The genetic pattern seen in patients with this type of presentation is:
. Autosomal recessive
. Autosomal dominant
. Sex-linked recessive
. Sex-linked dominant
. Sporadic

Correct Answer & Explanation

. Autosomal dominant

Explanation

Multiple hereditary exostoses is inherited in an autosomal-dominant manner with 90% penetrance.

Question 4957

Topic: 4. Pediatrics
Which of the following mutations occurs in patients with diastrophic dysplasia?
. Type II collagen mutation
. Type V collagen mutation
. Type I collagen mutation
. Sulfate transporter gene mutation
. Fibrillin gene mutation

Correct Answer & Explanation

. Sulfate transporter gene mutation

Explanation

Diastrophic dysplasia is caused by a mutation in the sulfate transporter gene (SLC26A2).

Question 4958

Topic: Pediatric Hip

A 12-year-old obese boy presents with a 3-week history of left knee pain and an antalgic gait. Examination reveals obligatory external rotation of the left hip upon flexion. Which of the following is considered an absolute indication for prophylactic in situ pinning of the asymptomatic contralateral hip in a patient with a Slipped Capital Femoral Epiphysis (SCFE)?

. Age greater than 14 years at initial presentation
. Initial presentation of a stable slip
. Presence of an underlying endocrine disorder
. Body Mass Index > 95th percentile
. Southwick slip angle greater than 50 degrees on the affected side

Correct Answer & Explanation

. Age greater than 14 years at initial presentation

Explanation

Prophylactic pinning of the contralateral asymptomatic hip in SCFE is controversial but is universally recommended in patients with a high risk of subsequent contralateral slippage. Absolute indications for prophylactic contralateral pinning include underlying endocrine disorders (such as hypothyroidism, renal osteodystrophy, or growth hormone deficiency), prior radiation therapy, or presentation at an abnormally young age (typically under 10 years). While obesity and severe slip angles increase the mechanical risk, they are considered relative indications.

Question 4959

Topic: Pediatric Hip

A 6-month-old infant is undergoing treatment with a Pavlik harness for developmental dysplasia of the hip (DDH). During a scheduled follow-up, the mother notes the child is no longer kicking the right leg. Physical examination confirms an absence of active knee extension on the right side. Which of the following specific positioning errors in the harness most likely caused this complication?

. Excessive hip flexion
. Inadequate hip flexion
. Excessive hip abduction
. Inadequate hip abduction
. Excessive hip external rotation

Correct Answer & Explanation

. Excessive hip flexion

Explanation

The patient is presenting with a femoral nerve palsy, a known complication of the Pavlik harness. It is classically caused by hyperflexion of the hip (excessive hip flexion), which compresses the femoral nerve against the inguinal ligament. Treatment involves temporary cessation of harness use or adjusting the anterior straps to decrease flexion until function returns. In contrast, excessive hip abduction in the harness significantly increases the risk of avascular necrosis (AVN) of the femoral head.

Question 4960

Topic: Pediatric Upper Extremity & Spine
A 6-year-old boy presents to the emergency department after falling from monkey bars. He has a visibly deformed left elbow. Radiographs confirm a displaced, posteromedial Gartland Type III supracondylar humerus fracture. On examination, the hand is pink and capillary refill is less than 2 seconds, but the radial pulse is completely non-palpable. What is the most appropriate next step in management?
. Immediate vascular surgery consultation for open brachial artery exploration
. Emergent closed reduction and percutaneous pinning
. CT angiography of the upper extremity to map the vascular injury
. Observation with strict elevation and cast application in 120 degrees of flexion
. Application of a warming blanket and repeated pulse checks every 4 hours

Correct Answer & Explanation

. Emergent closed reduction and percutaneous pinning

Explanation

The clinical presentation of a 'pink, pulseless hand' in the setting of a displaced pediatric supracondylar humerus fracture represents a vascular urgency. The brachial artery is often kinked or tethered over the proximal fracture fragment rather than transected. The standard of care is to proceed emergently to the operating room for closed reduction and percutaneous pinning (CRPP).

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