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4. Pediatrics MCQs

Practice Set 275 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 5481

Topic: Pediatric Hip

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). The parents note that the infant has stopped kicking her right leg and appears unable to actively extend her right knee. What is the most likely cause?

. Avascular necrosis of the femoral head from excessive abduction
. Sciatic nerve palsy from excessive hip extension
. Femoral nerve palsy from excessive hip flexion
. Obturator nerve palsy from excessive adduction
. Hamstring spasm from inadequate harness sizing

Correct Answer & Explanation

. Femoral nerve palsy from excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by hyperflexion of the hips compressing the nerve against the rim of the pelvis. It presents with decreased active knee extension. Treatment involves adjusting the anterior straps to decrease hip flexion, which usually leads to spontaneous recovery.

Question 5482

Topic: 4. Pediatrics

In the Ponseti method for the treatment of congenital talipes equinovarus (clubfoot), what is the correct sequence of correction of the deformities?

. Cavus, Adductus, Varus, Equinus
. Equinus, Varus, Adductus, Cavus
. Cavus, Varus, Adductus, Equinus
. Adductus, Varus, Cavus, Equinus
. Varus, Cavus, Adductus, Equinus

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The mnemonic CAVE dictates the rigid sequence of correction in the Ponseti method: Cavus (corrected first by elevating the first ray), Adductus, Varus, and finally Equinus (which often requires a percutaneous Achilles tenotomy to fully correct).

Question 5483

Topic: Pediatric Hip

A 6-week-old female infant is brought in for a screening hip ultrasound due to breech presentation. Which of the following ultrasound findings indicates a normal, mature hip?

. Alpha angle < 50 degrees
. Beta angle > 77 degrees
. Alpha angle > 60 degrees
. Less than 50% femoral head coverage
. Dynamic instability on Barlow maneuver

Correct Answer & Explanation

. Alpha angle > 60 degrees

Explanation

According to Graf's classification of developmental dysplasia of the hip (DDH), a normal Type I hip has an alpha angle greater than 60 degrees and a beta angle less than 55 degrees.

Question 5484

Topic: Pediatric Hip

A 12-year-old boy with a BMI of 35 is diagnosed with a unilateral slipped capital femoral epiphysis (SCFE). Which of the following is an accepted indication for prophylactic in situ pinning of the contralateral, asymptomatic hip?

. Age > 14 years
. African American ethnicity
. Underlying renal osteodystrophy
. Anterior slippage of the affected hip
. High BMI alone

Correct Answer & Explanation

. Underlying renal osteodystrophy

Explanation

Prophylactic pinning of the contralateral hip in SCFE is indicated in patients with underlying metabolic or endocrine disorders (e.g., renal osteodystrophy, hypothyroidism, panhypopituitarism) due to the exceedingly high risk of bilateral progression.

Question 5485

Topic: 4. Pediatrics

A 2-week-old infant is brought to the clinic for management of congenital idiopathic clubfoot (talipes equinovarus) using the Ponseti method. What is the correct sequence of deformity correction during the casting process?

. Cavus, Adductus, Varus, Equinus
. Equinus, Varus, Adductus, Cavus
. Adductus, Varus, Cavus, Equinus
. Varus, Cavus, Adductus, Equinus
. Cavus, Varus, Adductus, Equinus

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method corrects clubfoot deformities in the specific order of the acronym CAVE: Cavus, Adductus, Varus, and finally Equinus. The cavus is corrected first by elevating the first ray.

Question 5486

Topic: Pediatric Hip

A 12-year-old overweight boy presents with groin pain and an obligatory external rotation of the hip during active flexion. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Which of the following is the most significant risk factor for the development of avascular necrosis (AVN) in this patient?

. Degree of chronicity (> 3 weeks duration)
. Patient obesity (> 95th percentile)
. Inability to bear weight on the affected limb
. Endocrine disorders (e.g., hypothyroidism)
. Prophylactic pinning of the contralateral hip

Correct Answer & Explanation

. Inability to bear weight on the affected limb

Explanation

The inability to bear weight defines an unstable SCFE. Unstable SCFE has a substantially higher risk of avascular necrosis (up to 47%) compared to stable SCFE, which has an AVN rate of less than 10%.

Question 5487

Topic: Pediatric Hip

During routine follow-up of a 12-year-old obese male who underwent in situ pinning for a stable Slipped Capital Femoral Epiphysis (SCFE) 6 months ago, he complains of severe global hip stiffness. Radiographs show joint space narrowing without femoral head collapse. What is the most likely complication?

. Avascular necrosis
. Chondrolysis
. Implant failure
. Femoroacetabular impingement
. Septic arthritis

Correct Answer & Explanation

. Chondrolysis

Explanation

Chondrolysis presents with severe stiffness and diffuse joint space narrowing on radiographs without initial head collapse. It is a known complication of SCFE, particularly associated with unrecognized pin penetration into the joint.

Question 5488

Topic: Pediatric Hip

A 7-year-old boy is diagnosed with Legg-Calve-Perthes disease. According to the Herring Lateral Pillar Classification, which of the following radiographic findings places the patient in Group C and carries a worse prognosis?

. No involvement of the lateral pillar
. >50% maintenance of lateral pillar height
. <50% maintenance of lateral pillar height
. Central pillar collapse only
. Subchondral fracture (Crescent sign)

Correct Answer & Explanation

. <50% maintenance of lateral pillar height

Explanation

In the Herring Lateral Pillar Classification, Group C is defined by greater than 50% loss of height of the lateral pillar of the femoral head. This indicates significant structural collapse and carries a poor prognosis, often leading to early osteoarthritis.

Question 5489

Topic: 4. Pediatrics

When treating an infant with congenital talipes equinovarus (clubfoot) using the Ponseti method, the initial casts specifically target the correction of which deformity?

. Equinus
. Varus of the hindfoot
. Cavus
. Adductus of the forefoot
. Internal tibial torsion

Correct Answer & Explanation

. Cavus

Explanation

The Ponseti method follows the CAVE sequence: Cavus, Adductus, Varus, and finally Equinus. The first cast addresses the cavus deformity by elevating the first ray to align the forefoot with the midfoot.

Question 5490

Topic: 4. Pediatrics

According to the Ponseti method for the treatment of idiopathic congenital talipes equinovarus (clubfoot), what is the first step in the sequence of deformity correction during serial casting?

. Correction of equinus by tenotomy of the Achilles tendon
. Correction of hindfoot varus by stretching the subtalar joint
. Correction of forefoot adductus by manipulating the midfoot against the talar head
. Correction of cavus by supinating the forefoot and elevating the first ray
. Derotation of the calcaneocuboid joint

Correct Answer & Explanation

. Correction of cavus by supinating the forefoot and elevating the first ray

Explanation

The Ponseti method follows a strict sequence of correction summarized by the mnemonic CAVE (Cavus, Adductus, Varus, Equinus). The very first step is the correction of the cavus deformity. This is achieved by supinating the forefoot and elevating the first metatarsal/ray to align the forefoot with the hindfoot, establishing a proper foundation for subsequent manipulations.

Question 5491

Topic: Pediatric Hip

An infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the infant is noted to have a lack of active knee extension on the affected side. This complication is most likely the result of which of the following?

. Hyperabduction causing avascular necrosis of the femoral head
. Excessive hip flexion causing femoral nerve palsy
. Excessive hip extension causing sciatic nerve palsy
. Tight posterior straps causing an obturator nerve palsy
. Inferior dislocation of the hip joint

Correct Answer & Explanation

. Excessive hip flexion causing femoral nerve palsy

Explanation

Femoral nerve palsy is a known complication of Pavlik harness use and manifests clinically as a loss of active knee extension (decreased quadriceps function). It is caused by excessive hip flexion, which stretches or compresses the femoral nerve as it passes under the inguinal ligament. Treatment involves loosening the anterior straps or temporarily removing the harness until function returns.

Question 5492

Topic: Pediatric Hip

While slipped capital femoral epiphysis (SCFE) typically occurs unilaterally, prophylactic in situ pinning of the asymptomatic contralateral hip is routinely recommended for specific patient populations due to a high risk of subsequent slip. Which of the following is a universally accepted indication for prophylactic contralateral pinning?

. Presentation with a severe (>60 degree) slip on the affected side
. Presence of an underlying endocrinopathy such as hypothyroidism
. Patient age greater than 14 years at the time of initial presentation
. An unstable slip on the initially affected side
. Body mass index (BMI) greater than the 95th percentile

Correct Answer & Explanation

. Presence of an underlying endocrinopathy such as hypothyroidism

Explanation

Contralateral prophylactic pinning in SCFE is indicated in patients with a high likelihood of developing a bilateral slip. Strong, universally accepted indications include the presence of an underlying endocrinopathy (e.g., hypothyroidism, panhypopituitarism), renal osteodystrophy, prior pelvic radiation, or a chronologic age less than 10 years at initial presentation. Severity or stability of the initial slip does not mandate prophylactic pinning of the normal side.

Question 5493

Topic: 4. Pediatrics

The genetic mutation responsible for achondroplasia primarily affects which zone of the physis?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in the FGFR3 gene. This mutation abnormally inhibits chondrocyte proliferation, thereby causing a primary defect in the proliferative zone of the physis and resulting in rhizomelic dwarfism.

Question 5494

Topic: 4. Pediatrics
Osteogenesis imperfecta (OI) type I is caused by a quantitative deficiency of structurally normal type I collagen. Which of the following clinical features is classically characteristic of OI type I but typically absent in OI type IV?
. Severe dentinogenesis imperfecta
. Blue sclerae that persist into adulthood
. Basilar invagination
. Severe long bone deformity at birth
. Hearing loss

Correct Answer & Explanation

. Blue sclerae that persist into adulthood

Explanation

According to the Sillence classification, OI Type I is the mildest and most common form, characterized by blue sclerae that remain distinctly blue throughout life. Patients with OI Type IV have normal or white sclerae. Dentinogenesis imperfecta is common in Types III and IV, but rare in Type I.

Question 5495

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic mutation occurs in the FGFR3 gene. This mutation primarily affects which specific zone of the epiphyseal growth plate?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by an activating mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene, which normally acts as a negative regulator of bone growth. The mutation leads to suppression of chondrocyte proliferation, primarily affecting the proliferative zone of the physis, resulting in decreased enchondral ossification.

Question 5496

Topic: 4. Pediatrics

A 12-year-old child presents with a swollen, painful knee and a history of a large, expanding erythematous rash with a central clearing on the thigh two months ago. Lyme arthritis is suspected. Which of the following pairs correctly identifies the causative organism and its primary vector?

. Borrelia burgdorferi; Ixodes scapularis tick
. Rickettsia rickettsii; Dermacentor variabilis tick
. Neisseria gonorrhoeae; Human-to-human transmission
. Treponema pallidum; Ixodes pacificus tick
. Ehrlichia chaffeensis; Amblyomma americanum tick

Correct Answer & Explanation

. Borrelia burgdorferi; Ixodes scapularis tick

Explanation

Lyme disease is caused by the spirochete Borrelia burgdorferi and is transmitted by the bite of infected blacklegged ticks (Ixodes scapularis in the eastern/midwestern US, and Ixodes pacificus in the western US). The history describes erythema migrans, classic for early localized Lyme disease, which can progress to late-stage Lyme arthritis if untreated.

Question 5497

Topic: 4. Pediatrics
Osteogenesis Imperfecta (OI) Type I is the most common and mildest form of the disease, classically presenting with blue sclerae and recurrent fractures. What is the fundamental defect at the molecular level in OI Type I?
. Production of structurally abnormal Type I collagen (qualitative defect)
. Decreased production of structurally normal Type I collagen (quantitative defect)
. Defect in the hydroxylation of proline residues
. Mutation in the COMP gene affecting cartilage oligomeric matrix protein
. Defect in Type II collagen leading to secondary bone fragility

Correct Answer & Explanation

. Decreased production of structurally normal Type I collagen (quantitative defect)

Explanation

OI Type I is characterized by an autosomal dominant null allele mutation in COL1A1. This results in a decreased amount (approximately half) of structurally normal Type I collagen (a quantitative defect). More severe forms of OI (Types II, III, IV) involve missense mutations (often glycine substitutions) resulting in structurally abnormal collagen (a qualitative defect).

Question 5498

Topic: 4. Pediatrics

A 16-year-old male with a tall, thin habitus, pectus excavatum, and joint hyperlaxity presents with a sudden onset of chest pain. He is diagnosed with an aortic root dissection. The underlying connective tissue disorder is associated with a mutation in which of the following genes?

. COL1A1
. COL2A1
. FBN1 (Fibrillin-1)
. FGFR3
. COMP

Correct Answer & Explanation

. FBN1 (Fibrillin-1)

Explanation

The clinical presentation is classic for Marfan syndrome, an autosomal dominant disorder caused by a mutation in the FBN1 gene, which encodes the glycoprotein fibrillin-1. Fibrillin-1 is a major component of microfibrils in the extracellular matrix. Mutations lead to defective connective tissue and dysregulation of TGF-beta signaling.

Question 5499

Topic: Pediatric Hip

A 12-year-old obese male presents with left knee pain and a limp. Pelvic radiographs demonstrate a slipped capital femoral epiphysis (SCFE). According to the Loder classification, which finding definitively characterizes this SCFE as 'unstable'?

. Slip angle > 50 degrees on the lateral radiograph
. Presence of a joint effusion on ultrasound
. Inability to bear weight with or without crutches
. Duration of symptoms less than 3 weeks
. Disruption of Klein's line on the AP radiograph

Correct Answer & Explanation

. Inability to bear weight with or without crutches

Explanation

The Loder classification divides Slipped Capital Femoral Epiphysis (SCFE) into stable and unstable based purely on the patient's clinical ability to bear weight. An unstable SCFE is defined by the inability to bear weight, even with the use of crutches. Unstable SCFEs have a significantly higher risk of developing avascular necrosis (up to nearly 50%).

Question 5500

Topic: Pediatric Hip
The Herring Lateral Pillar classification is highly prognostic for the final functional and radiographic outcome in Legg-Calvé-Perthes disease. During which radiographic stage of the disease should this classification be applied?
. Initial/Ischemia stage
. Fragmentation stage
. Reossification stage
. Healing stage
. Residual stage

Correct Answer & Explanation

. Fragmentation stage

Explanation

The Herring Lateral Pillar classification for Legg-Calvé-Perthes disease is properly assessed during the fragmentation stage of the disease, when the extent of epiphyseal collapse is maximally apparent. It evaluates the height of the lateral pillar of the femoral head (Group A: >100%, Group B: >50%, Group C: <50% height maintained).

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