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4. Pediatrics MCQs

Practice Set 30 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 581

Topic: 4. Pediatrics

Achondroplasia is characterized by disproportionate short stature. What is the underlying genetic and cellular mechanism responsible for this dysplasia?

. Autosomal recessive mutation in COL1A1 causing defective collagen synthesis
. Autosomal dominant mutation in FGFR3 causing inhibition of chondrocyte proliferation
. X-linked recessive mutation causing defective endochondral ossification
. Autosomal dominant mutation in FBN1 affecting microfibril formation
. Spontaneous mutation in the COMP gene leading to chondrocyte apoptosis

Correct Answer & Explanation

. Autosomal dominant mutation in FGFR3 causing inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the fibroblast growth factor receptor 3 (FGFR3) gene, inherited in an autosomal dominant pattern. This mutation constitutively activates the receptor, which paradoxically inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 582

Topic: Pediatric Lower Extremity

During the initial phase of the Ponseti casting technique for the treatment of idiopathic clubfoot, which component of the deformity must be addressed first?

. Cavus
. Adduction
. Varus
. Equinus
. Tibial torsion

Correct Answer & Explanation

. Cavus

Explanation

The Ponseti method corrects deformities in a specific order summarized by the acronym CAVE: Cavus, Adductus, Varus, then Equinus. The cavus is corrected first by elevating the first ray to align the forefoot with the hindfoot.

Question 583

Topic: Pediatric Lower Extremity

The Ponseti method of clubfoot cast treatment starts with which of the following steps:

. Pronation of the forefoot
. Dorsiflexion of the first ray
. Dorsiflexion of the ankle
. External rotation of the foot
. Internal rotation of the foot

Correct Answer & Explanation

. Dorsiflexion of the first ray

Explanation

Dorsiflexion of the first ray is the first step in the Ponseti method of cast treatment. Dorsiflexion decreases the cavus component. Pronation of the forefoot is the opposite of dorsiflexion and produces the opposite desired motion. Dorsiflexion of the ankle should be performed after the Achilles tenotomy. External rotation of the foot is performed later. Internal rotation of the clubfoot is never done.

Question 584

Topic: 4. Pediatrics
Meryon sign refers to which of the following physical phenomena in patients with muscular dystrophies:
. Wide-based gait
. Use of upper extremities in coming to stand
. Tendency to "slip through" when patient is suspended under the axillae
. Absence of facial expression
. Inability to fully flex the neck

Correct Answer & Explanation

. Tendency to "slip through" when patient is suspended under the axillae

Explanation

Meryon sign is the weakness of shoulder adduction when a child is lifted or suspended under the axillae. The examiner will feel that the child is slipping through his or her hands. It is due to weakness of the shoulder girdle muscles. Meryon sign is present in limb-girdle dystrophies and fascioscapulohumeral dystrophy.

Question 585

Topic: Pediatric Hip

The result of treatment of developmental dysplasia of the hip with Salter osteotomy is is worse with which of the following:

. A higher degree of the dislocation before treatment (Tonnis grade)
. Bilaterality
. Higher preoperative acetabular index
. Increased age at surgery
. Performing open reduction at a separate surgery than the osteotomy

Correct Answer & Explanation

. A higher degree of the dislocation before treatment (Tonnis grade)

Explanation

Salter osteotomy is effective in treating developmental dysplasia of the hip in young children. The result is worse with higher degrees of dislocation as assessed by the Tonnis system. It is better if the open reduction (if needed) is performed as a separate step than the osteotomy. The other factors have not been shown to be predictive.

Question 586

Topic: 4. Pediatrics
A 10-year-old boy with diplegic cerebral palsy walks with his knees turned in significantly. He has the appearance of severe valgus when walking. When examined in a supine position, there is no excessive valgus of the knees. His popliteal angle is 45°. An Ely test is negative. His hip internal rotation in the prone position is 80°, while his external rotation is 15°. The surgeon wishes to improve the patient's knee position during gait. The intervention most likely to accomplish this is:
. Botulinum toxin injection to the hamstrings
. Hamstring lengthening, medially
. Hamstring lengthening, medially and laterally
. Rectus transfer into the biceps
. Femoral derotation osteotomy

Correct Answer & Explanation

. Femoral derotation osteotomy

Explanation

The findings highlighted here are those of severe anteversion. Anteversion causes the appearance of valgus of the knees, and it does not resolve spontaneously in cerebral palsy. The procedure most likely to make a lasting improvement in the patient is derotational osteotomy of the femur.

Question 587

Topic: 4. Pediatrics

Which of the following procedures is most likely to increase recurvatum of the knee in patients with diplegic cerebral palsy:

. Medial hamstring lengthening
. Medial and lateral hamstring lengthening
. Rectus transfer to the hamstrings
. Tendoachilles lengthening
. Adductor lengthening

Correct Answer & Explanation

. Medial hamstring lengthening

Explanation

Lengthening of the medial and lateral hamstrings is more likely to overlengthen the posterior knee checkrein. Therefore, it should only be performed in selected cases with severe spasticity and no cospasticity of the rectus femoris. Lengthening of only the medial hamstrings carries less risk. The other procedures listed do not carry this risk.

Question 588

Topic: Pediatric Hip

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip. The parents report that the infant has stopped kicking the affected leg over the past two days. On examination, there is decreased active knee extension but normal foot and toe movement. Which of the following is the most appropriate next step in management?

. Switch to a rigid hip spica cast immediately
. Adjust the anterior straps to increase hip flexion
. Discontinue the Pavlik harness temporarily
. Order an urgent MRI of the lumbar spine
. Perform an immediate closed reduction in the operating room

Correct Answer & Explanation

. Discontinue the Pavlik harness temporarily

Explanation

The clinical presentation is highly suggestive of a femoral nerve palsy, a known complication of hyperflexion in a Pavlik harness. The most appropriate immediate management is to discontinue the harness or significantly loosen the anterior straps to allow the nerve to recover.

Question 589

Topic: Pediatric Hip

Which of the following conditions constitutes the strongest absolute indication for prophylactic in situ pinning of the contralateral asymptomatic hip in a 12-year-old patient presenting with a unilateral slipped capital femoral epiphysis (SCFE)?

. Obesity greater than 95th percentile
. Family history of SCFE
. Renal osteodystrophy
. Male gender
. African American ethnicity

Correct Answer & Explanation

. Renal osteodystrophy

Explanation

Endocrine and metabolic disorders, particularly renal osteodystrophy and hypothyroidism, significantly increase the risk of bilateral SCFE. Prophylactic pinning of the contralateral hip is highly recommended in these patients to prevent a subsequent slip.

Question 590

Topic: Pediatric Upper Extremity & Spine

A 6-year-old boy presents with a completely displaced, extension-type supracondylar fracture of the humerus. Which of the following neurologic deficits is most commonly associated with this specific injury pattern?

. Inability to abduct the fingers
. Inability to flex the interphalangeal joint of the thumb
. Inability to extend the metacarpophalangeal joints
. Decreased sensation over the volar aspect of the small finger
. Decreased sensation over the lateral aspect of the shoulder

Correct Answer & Explanation

. Inability to flex the interphalangeal joint of the thumb

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. AIN palsy presents with an inability to flex the IP joint of the thumb and the distal IP joint of the index finger, resulting in an abnormal "OK" sign.

Question 591

Topic: 4. Pediatrics

According to the Gross Motor Function Classification System (GMFCS), a 6-year-old child with cerebral palsy classified as GMFCS level V requires which of the following hip surveillance protocols?

. AP pelvis radiograph only if clinically symptomatic
. AP pelvis radiograph at age 2, then discharge if normal
. AP pelvis radiograph every 6 months
. Annual MRI of the hips to assess cartilage loss
. Biannual clinical examination with no radiographs required

Correct Answer & Explanation

. AP pelvis radiograph every 6 months

Explanation

Children with GMFCS level V cerebral palsy have the highest risk (up to 90%) of hip displacement. Surveillance guidelines recommend an AP pelvis radiograph every 6 months for these severely affected patients until skeletal maturity or stability is established.

Question 592

Topic: Pediatric Hip

In a patient presenting with Legg-Calve-Perthes disease, which of the following combinations of factors at the time of presentation portends the poorest prognosis?

. Age 5 years and greater than 50% lateral pillar involvement
. Age 9 years and greater than 50% lateral pillar involvement
. Age 4 years and Catterall group II
. Age 7 years and intact lateral pillar
. Age 6 years and Salter-Thompson group A

Correct Answer & Explanation

. Age 9 years and greater than 50% lateral pillar involvement

Explanation

The most significant prognostic factors in Legg-Calve-Perthes disease are the chronological age at onset and the extent of lateral pillar involvement (Herring classification). Onset after age 8 combined with greater than 50% lateral pillar collapse (Herring Group C) has the worst radiographic and clinical outcomes.

Question 593

Topic: 4. Pediatrics
A 2-year-old child is diagnosed with congenital scoliosis secondary to a fully segmented hemivertebra at T8. Which of the following routine screening evaluations is mandatory in the initial workup of this patient?
. Renal ultrasound
. Pulmonary function tests
. DEXA scan
. Genetic testing for the FBN1 mutation
. Ophthalmologic examination for lens dislocation

Correct Answer & Explanation

. Renal ultrasound

Explanation

Congenital scoliosis is frequently associated with VACTERL anomalies, with genitourinary abnormalities (such as unilateral renal agenesis) occurring in 20-30% of patients. A renal ultrasound and echocardiogram are mandatory components of the initial evaluation.

Question 594

Topic: 4. Pediatrics

A 1-year-old child with achondroplasia presents with hypotonia, apneas, and delayed motor milestones. Which of the following pathologic mechanisms is the most likely cause of these symptoms and represents the leading cause of mortality in this age group?

. Thoracolumbar kyphosis
. Atlantoaxial instability
. Foramen magnum stenosis
. Severe progressive hydrocephalus
. Odontoid hypoplasia

Correct Answer & Explanation

. Foramen magnum stenosis

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis due to abnormal endochondral ossification of the skull base. This can cause cervicomedullary compression, leading to central sleep apnea, hypotonia, and sudden infant death if not decompressed surgically.

Question 595

Topic: Pediatric Lower Extremity
A 4-year-old boy, initially treated successfully for idiopathic clubfoot using the Ponseti method, presents with a relapse. He demonstrates dynamic supination of the foot during the swing phase of gait but passive range of motion is fully correctable. Which of the following is the most appropriate definitive management?
. Repeat serial casting followed by Achilles tendon lengthening
. Split anterior tibial tendon transfer (SPLATT)
. Tibialis anterior tendon transfer to the lateral cuneiform
. Triple arthrodesis
. Calcaneal sliding osteotomy

Correct Answer & Explanation

. Tibialis anterior tendon transfer to the lateral cuneiform

Explanation

Dynamic supination during the swing phase in a relapsed, previously corrected Ponseti clubfoot is caused by an overactive tibialis anterior tendon. The definitive treatment for a flexible foot in a child over age 2.5 is a whole tibialis anterior tendon transfer (TATT) to the lateral cuneiform.

Question 596

Topic: 4. Pediatrics

A 4-month-old infant is diagnosed with developmental dysplasia of the hip (DDH). Ultrasound confirms a dislocated hip. Which of the following is an absolute contraindication to the use of a Pavlik harness?

. Teratologic hip dislocation
. Alpha angle of 45 degrees
. Age greater than 3 months
. Bilateral hip dysplasia
. Breech presentation

Correct Answer & Explanation

. Teratologic hip dislocation

Explanation

Teratologic hip dislocations, often associated with arthrogryposis or myelomeningocele, are rigid and do not respond to Pavlik harness treatment. Closed or open reduction is typically required.

Question 597

Topic: Pediatric Hip

An 11-year-old boy with a BMI in the 99th percentile presents with a unilateral stable slipped capital femoral epiphysis (SCFE). Prophylactic pinning of the contralateral asymptomatic hip is most strongly indicated in patients with which of the following concomitant conditions?

. Type 1 diabetes mellitus
. Down syndrome
. Endocrine disorders such as hypothyroidism
. Legg-Calve-Perthes disease
. Achondroplasia

Correct Answer & Explanation

. Endocrine disorders such as hypothyroidism

Explanation

Endocrine disorders (e.g., hypothyroidism, renal osteodystrophy) significantly increase the risk of bilateral SCFE. This justifies prophylactic fixation of the contralateral hip.

Question 598

Topic: Pediatric Hip

Which of the following factors at the time of presentation confers the worst prognosis in a child with Legg-Calve-Perthes disease?

. Chronological age less than 6 years
. Bone age of 5 years
. Lateral pillar type C involvement
. Intact lateral pillar
. Decreased range of motion in abduction

Correct Answer & Explanation

. Lateral pillar type C involvement

Explanation

The Herring lateral pillar classification is highly prognostic. Lateral pillar type C (greater than 50% loss of lateral pillar height) predicts a poor radiographic and clinical outcome.

Question 599

Topic: 4. Pediatrics

A 6-year-old child with spastic quadriplegic cerebral palsy (GMFCS level V) is undergoing routine orthopedic surveillance. What is the most critical radiographic parameter to monitor for hip stability?

. Alpha angle
. Center-edge angle of Wiberg
. Reimer's migration percentage
. Acetabular index
. Neck-shaft angle

Correct Answer & Explanation

. Reimer's migration percentage

Explanation

Reimer's migration percentage is the standard measurement used in cerebral palsy hip surveillance. A migration percentage greater than 30% indicates subluxation and often warrants surgical intervention.

Question 600

Topic: Pediatric Hip

A 14-year-old boy undergoes in situ pinning for an unstable slipped capital femoral epiphysis (SCFE). Which of the following is the most common severe complication associated specifically with an unstable SCFE?

. Chondrolysis
. Osteonecrosis (avascular necrosis)
. Femoral neck fracture
. Implant failure
. Leg length discrepancy

Correct Answer & Explanation

. Osteonecrosis (avascular necrosis)

Explanation

Unstable SCFE, defined as the inability to bear weight even with crutches, carries a high risk of osteonecrosis (up to 47%). This is compared to a nearly 0% osteonecrosis rate in stable SCFE.

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