Menu

4. Pediatrics MCQs

Practice Set 327 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 6521

Topic: 4. Pediatrics

A 12-year-old boy is undergoing tibial lengthening via distraction osteogenesis. Serial radiographs demonstrate premature consolidation of the regenerate bone. Which of the following parameters of the Ilizarov method was most likely applied incorrectly?

. Too short of a latency period
. Excessive rate of distraction
. Poor stability of the external fixator
. Inadequate nutritional supplementation
. Pin tract infection causing early fusion

Correct Answer & Explanation

. Too short of a latency period

Explanation

Premature consolidation typically occurs when the rate of distraction is too slow or the latency period (the time between osteotomy and the start of distraction) is too short. In robust healers like children, waiting too long before distracting allows the osteotomy to bridge completely.

Question 6522

Topic: Pediatric Hip
A patient is diagnosed with severe coxa vara (neck-shaft angle < 110 degrees). How does this proximal femoral morphology uniquely alter the biomechanics of the hip joint?
. Decreases the abductor moment arm and increases joint reaction force.
. Increases the abductor moment arm and decreases joint reaction force.
. Decreases both the abductor moment arm and joint reaction force.
. Increases both the abductor moment arm and joint reaction force.
. Has no effect on the abductor moment arm but increases shear forces.

Correct Answer & Explanation

. Increases the abductor moment arm and decreases joint reaction force.

Explanation

Coxa vara lateralizes the greater trochanter, which increases the abductor moment arm. This improved mechanical advantage decreases the required abductor force and the total joint reaction force, although it dramatically increases the bending moment across the femoral neck.

Question 6523

Topic: 4. Pediatrics

A 4-year-old girl presents with a congenital femoral deficiency resulting in a current leg length discrepancy (LLD) of 2.5 cm. Assuming the Paley multiplier for a 4-year-old girl is approximately 2.0, what is her predicted LLD at skeletal maturity?

. 2.5 cm
. 3.5 cm
. 5.0 cm
. 7.5 cm
. 10.0 cm

Correct Answer & Explanation

. 5.0 cm

Explanation

Congenital deformities typically maintain a constant ratio of shortening throughout growth. Using the multiplier method, the current discrepancy (2.5 cm) multiplied by the age- and sex-specific multiplier (2.0) predicts a 5.0 cm LLD at maturity.

Question 6524

Topic: 4. Pediatrics

A patient is undergoing tibial lengthening via distraction osteogenesis (Ilizarov method). Radiographs at week 4 reveal premature consolidation of the regenerate bone. Which of the following parameters is the most likely cause of this complication?

. Distraction rate of 1.0 mm/day
. Distraction rhythm of 0.25 mm four times daily
. Distraction rate of 0.5 mm/day
. Latency period of 7 days
. Use of a low-energy osteotome for the corticotomy

Correct Answer & Explanation

. Distraction rate of 0.5 mm/day

Explanation

A distraction rate of 0.5 mm/day is too slow and heavily predisposes the highly osteogenic regenerate to prematurely consolidate. The standard optimal rate is 1.0 mm/day, typically divided into four 0.25 mm increments.

Question 6525

Topic: 4. Pediatrics

A 10-year-old boy is scheduled for a percutaneous epiphysiodesis of the distal femur to address a predicted 3 cm leg length discrepancy. To reliably arrest growth and prevent iatrogenic angular deformity, what is the minimum required anatomical ablation of the physis?

. The peripheral 20% of the physis including the zone of Ranvier
. The central 25% of the physis
. At least the central 50% to 70% of the physis symmetrically
. Only the medial half of the physis
. Only the lateral half of the physis

Correct Answer & Explanation

. At least the central 50% to 70% of the physis symmetrically

Explanation

Successful epiphysiodesis requires complete and symmetric destruction of at least the central 50% to 70% of the growth plate. Unequal or insufficient ablation can lead to continued asymmetric growth, causing progressive varus or valgus deformities.

Question 6526

Topic: 4. Pediatrics

A 10-year-old girl with a right distal femoral physeal arrest presents with a 3 cm leg length discrepancy. Her bone age matches her chronological age. Assuming growth ceases at age 14, and using the rule of thumb for physeal growth, what is the most appropriate timing for a contralateral distal femoral epiphysiodesis?

. Immediately (Age 10)
. Age 10.5 to 11
. Age 11.5 to 12
. Age 12.5 to 13
. Age 13.5

Correct Answer & Explanation

. Age 10.5 to 11

Explanation

The contralateral distal femur grows at approximately 9 mm/year. To correct a 30 mm LLD, she needs 3.33 years of growth remaining (30 / 9). Subtracting 3.33 from skeletal maturity at age 14 yields an ideal surgical age of 10.67 years.

Question 6527

Topic: 4. Pediatrics

A pediatric patient with developmental coxa vara presents with a neck-shaft angle of 100 degrees. Compared to a normal hip biomechanical model, which of the following describes the altered forces across the proximal femur?

. Increased abductor mechanical advantage and increased femoral neck bending moment
. Decreased abductor mechanical advantage and increased femoral neck bending moment
. Increased abductor mechanical advantage and decreased femoral neck bending moment
. Decreased abductor mechanical advantage and decreased femoral neck bending moment
. No change in mechanical advantage but increased joint reaction force

Correct Answer & Explanation

. Increased abductor mechanical advantage and increased femoral neck bending moment

Explanation

In coxa vara, the elevated greater trochanter lengthens the abductor moment arm, which increases the abductor mechanical advantage and lowers the overall joint reaction force. However, the horizontal orientation of the femoral neck significantly increases the bending and shear forces across the neck, predisposing to pseudarthrosis.

Question 6528

Topic: 4. Pediatrics

An infant is evaluated for limb deformity and diagnosed with fibular hemimelia. Which of the following is the most characteristic clinical and radiographic presentation associated with this condition?

. Anteromedial tibial bowing with absent lateral foot rays and a ball-and-socket ankle
. Posteromedial tibial bowing with a calcaneovalgus foot deformity
. Anterolateral tibial bowing with pseudarthrosis and absent medial rays
. Posterolateral tibial bowing with syndactyly and a rigid equinus contracture
. Anteromedial tibial bowing with intact foot rays but a hypoplastic lateral collateral ligament

Correct Answer & Explanation

. Anteromedial tibial bowing with absent lateral foot rays and a ball-and-socket ankle

Explanation

Fibular hemimelia is the most common congenital long bone deficiency and classically presents with anteromedial bowing of the tibia. It is strongly associated with absent lateral rays of the foot, tarsal coalition, an absent ACL, and a ball-and-socket ankle joint.

Question 6529

Topic: 4. Pediatrics

According to the Aitken classification of Proximal Focal Femoral Deficiency (PFFD), a Class A deficiency is characterized by which of the following radiographic findings at skeletal maturity?

. Absence of the femoral head and acetabulum
. A pseudarthrosis at the subtrochanteric level that fails to ossify
. A bony connection between the femoral head and shaft with a severe coxa vara deformity
. Complete absence of the proximal femur with a tufted proximal end
. An osseous defect between the femoral head and shaft that does not resolve

Correct Answer & Explanation

. A bony connection between the femoral head and shaft with a severe coxa vara deformity

Explanation

In Aitken Class A PFFD, the femoral head is present in the acetabulum, and the initial cartilaginous connection between the head and the shaft eventually ossifies. This ultimately results in an intact bony connection, albeit with a severely shortened femur and significant coxa vara.

Question 6530

Topic: 4. Pediatrics

When evaluating a child with an abnormally short femur, which of the following clinical features most reliably differentiates a simple congenital short femur from Proximal Focal Femoral Deficiency (PFFD)?

. The presence of anterolateral tibial bowing
. The severity of the leg length discrepancy at birth
. The presence of normal proximal femoral anatomy without subtrochanteric pseudarthrosis
. The absence of the lateral rays of the foot
. The presence of a ball-and-socket ankle joint

Correct Answer & Explanation

. The presence of normal proximal femoral anatomy without subtrochanteric pseudarthrosis

Explanation

A simple congenital short femur is a miniature but morphologically normal bone, maintaining normal proximal femoral integrity and hip joint stability. In contrast, PFFD involves focal structural deficits in the proximal femur, typically presenting with severe coxa vara or pseudarthroses.

Question 6531

Topic: 4. Pediatrics

A 10-year-old girl is predicted to have a 3.5 cm leg length discrepancy at skeletal maturity secondary to a prior physeal arrest of the distal femur. Using the Green-Anderson growth remaining rules, how much longitudinal growth per year is typically expected from the distal femoral physis?

. 6 mm/year
. 10 mm/year
. 14 mm/year
. 18 mm/year
. 22 mm/year

Correct Answer & Explanation

. 10 mm/year

Explanation

The distal femur contributes approximately 3/8 inch or 9-10 mm of growth per year. In comparison, the proximal tibia contributes roughly 1/4 inch or 6 mm of longitudinal growth per year.

Question 6532

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and a trident hand. A mutation in the FGFR3 gene is confirmed. Which zone of the physis is primarily affected by this genetic 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.

Question 6533

Topic: 4. Pediatrics

A newborn presents with severe micromelia, bilateral clubfeet, hitchhiker thumbs, and cystic swelling of the pinnae. A mutation in which of the following genes is most likely responsible for this condition?

. SLC26A2
. COL2A1
. COMP
. FGFR3
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

Diastrophic dysplasia is characterized by hitchhiker thumbs and cauliflower ears. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter.

Question 6534

Topic: 4. Pediatrics

A newborn presents with a cleft palate, "hitchhiker" thumbs, and cystic swelling of the external ears. Radiographs reveal shortened limbs and a severe kyphoscoliosis. Which of the following genes is mutated in this condition?

. SLC26A2 (DTDST)
. COL2A1
. FGFR3
. COMP
. SOX9

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia is caused by an autosomal recessive mutation in the SLC26A2 gene, which encodes a sulfate transporter. Clinical hallmarks include hitchhiker thumbs, cauliflower ears, cleft palate, and severe spinal deformities.

Question 6535

Topic: 4. Pediatrics

In pediatric acute hematogenous osteomyelitis, which anatomical region of the long bone is most frequently affected and why?

. Diaphysis due to nutrient artery entry
. Epiphysis due to highly fenestrated capillaries
. Metaphysis due to sluggish blood flow in venous sinusoids
. Physis due to rapid cellular division
. Apophysis due to traction microtrauma

Correct Answer & Explanation

. Metaphysis due to sluggish blood flow in venous sinusoids

Explanation

The metaphysis is the most common site for pediatric acute hematogenous osteomyelitis. As the nutrient artery branches into the metaphysis, it forms sharp hairpin loops into large venous sinusoids, causing sluggish blood flow that favors bacterial deposition.

Question 6536

Topic: 4. Pediatrics

A 4-year-old child presents with a short trunk, severe coxa vara, cleft palate, and high myopia. Notably, the child's hands and feet are of normal length. Which collagen type is primarily affected in this disorder?

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

Correct Answer & Explanation

. Type II

Explanation

Spondyloepiphyseal dysplasia congenita (SEDc) is an autosomal dominant disorder caused by a mutation in the COL2A1 gene affecting Type II collagen. It affects articular cartilage and the nucleus pulposus, presenting with short trunk dwarfism, coxa vara, myopia, and normal-sized hands and feet.

Question 6537

Topic: 4. Pediatrics

A 4-month-old infant presents with rhizomelic shortening, frontal bossing, and a trident hand. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Which of the following describes the underlying pathophysiology of this condition?

. Defect in type I collagen synthesis
. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in COMP
. Deficient sulfation of glycosaminoglycans
. Defect in the RANKL-OPG signaling pathway

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation leads to constitutive activation of the receptor, which severely inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 6538

Topic: 4. Pediatrics

A newborn is evaluated for severe shortening of the limbs. Physical examination reveals "hitchhiker" thumbs, bilateral clubfeet, and cystic swelling of the pinnae. Mutations in which of the following genes are responsible for this condition?

. COL1A1
. FGFR3
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

The clinical features describe diastrophic dysplasia, which is an autosomal recessive disorder. It is caused by mutations in the SLC26A2 gene, resulting in a defect in the diastrophic dysplasia sulfate transporter (DTDST) and impaired sulfation of cartilage proteoglycans.

Question 6539

Topic: 4. Pediatrics

A 5-year-old girl presents with short stature, waddling gait, and joint laxity. Unlike classic achondroplasia, her facial features and head circumference are completely normal. Radiographs demonstrate delayed epiphyseal ossification and irregular, widened metaphyses. A mutation in which of the following genes is the most likely cause?

. FGFR3
. COMP
. COL2A1
. RUNX2
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia classically presents with normal facies and normal intelligence, distinguishing it from true achondroplasia. It is caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 6540

Topic: 4. Pediatrics

A 14-month-old child presents with a limp and low-grade fever. Laboratory tests show a normal WBC count and mildly elevated CRP. Blood cultures are negative, but synovial fluid PCR from the knee is positive for a fastidious gram-negative coccobacillus. Which organism is most likely?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Kingella kingae
. Haemophilus influenzae
. Salmonella typhi

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a leading cause of osteoarticular infections in children aged 6 to 36 months. It is notoriously difficult to culture but is readily identified using nucleic acid amplification techniques like PCR.

Test Yourself

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

On this Page