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4. Pediatrics MCQs

Practice Set 272 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 5421

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism and is caused by an activating mutation in the FGFR3 gene. Which anatomical zone of the physis is primarily affected by this mutation?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

The activating mutation in FGFR3 heavily suppresses chondrocyte proliferation. This directly targets the proliferative zone of the physis, resulting in impaired endochondral ossification.

Question 5422

Topic: Pediatric Hip
A 6-year-old boy presents with a painless limp and restricted hip abduction. Radiographs show fragmentation of the femoral head consistent with Legg-Calvé-Perthes disease. According to the Herring lateral pillar classification, a hip maintaining exactly 60% of lateral pillar height falls into which group?
. Group A
. Group B
. Group B/C
. Group C
. Group D

Correct Answer & Explanation

. Group B

Explanation

In the Herring lateral pillar classification, Group A has no lateral pillar involvement, Group B maintains >50% of lateral pillar height, and Group C has <50% of the lateral pillar height maintained.

Question 5423

Topic: Pediatric Hip

A 6-week-old infant with developmental dysplasia of the hip (DDH) is being treated with a Pavlik harness. At the 1-week follow-up, the mother notes the infant has stopped kicking the affected leg. On examination, there is an absent patellar reflex on the affected side. What is the most appropriate next step in management?

. Continue the harness and observe for 1 week
. Discontinue the harness immediately
. Adjust the anterior strap to increase flexion
. Adjust the posterior strap to decrease abduction
. Switch to a rigid hip spica cast

Correct Answer & Explanation

. Discontinue the harness immediately

Explanation

The clinical presentation is classic for a femoral nerve palsy, a known complication of Pavlik harness treatment due to excessive hyperflexion of the hip. The immediate and most appropriate treatment is to discontinue the harness until motor function returns, after which an alternative bracing strategy or a modified harness application may be considered.

Question 5424

Topic: Pediatric Upper Extremity & Spine

A 45-year-old male is involved in a motor vehicle collision resulting in a spinal cord injury. Neurological examination reveals preserved motor function below the neurological level of injury, and more than half of the key muscles below the neurological level have a muscle grade of 3 or greater. Sensory function is preserved. Which ASIA Impairment Scale (AIS) grade does this represent?

. AIS A
. AIS B
. AIS C
. AIS D
. AIS E

Correct Answer & Explanation

. AIS D

Explanation

The ASIA Impairment Scale (AIS) D is defined as motor incomplete, with motor function preserved below the neurological level, and at least half of the key muscles below the neurological level of injury having a muscle grade of 3 or greater. AIS C has less than half with grade 3 or greater. AIS B is sensory incomplete (no motor function), and AIS A is complete (no motor or sensory in S4-S5).

Question 5425

Topic: Pediatric Hip

When performing in situ pinning for a severe Slipped Capital Femoral Epiphysis (SCFE), an unrecognized pin penetration into the anterosuperior quadrant of the joint space significantly increases the risk of which of the following complications?

. Femoral neck fracture
. Chondrolysis
. Avascular necrosis
. Cam-type femoroacetabular impingement
. Labral tear

Correct Answer & Explanation

. Chondrolysis

Explanation

Unrecognized pin penetration into the joint space during SCFE pinning is a primary and highly morbid cause of chondrolysis. Approaching the screw from the anterior femoral neck to the posterior epiphysis increases this risk. The 'approach-withdraw' technique under live fluoroscopy while ranging the hip helps prevent it.

Question 5426

Topic: 4. Pediatrics

A newborn is diagnosed with achondroplasia. This condition is caused by a genetic mutation that primarily results in which of the following cellular events?

. Defective synthesis of type I collagen
. Loss of function of the Runx2 transcription factor
. Gain-of-function in the fibroblast growth factor receptor 3 (FGFR3)
. Mutation in the cartilage oligomeric matrix protein (COMP) gene
. Impaired osteoclast carbonic anhydrase II activity

Correct Answer & Explanation

. Gain-of-function in the fibroblast growth factor receptor 3 (FGFR3)

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. FGFR3 normally functions to inhibit chondrocyte proliferation in the proliferative zone of the physis. The gain-of-function mutation constitutively activates this inhibition, leading to profoundly shortened long bones.

Question 5427

Topic: Pediatric Hip

A 12-year-old girl presents with an acute on chronic slipped capital femoral epiphysis (SCFE) of the left hip. Under which of the following circumstances is prophylactic in situ pinning of the contralateral right hip most strongly indicated?

. African American descent
. Obesity (BMI > 95th percentile)
. Male gender
. Underlying endocrinopathy
. Age greater than 14 years

Correct Answer & Explanation

. Underlying endocrinopathy

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly controversial in idiopathic cases but is generally recommended for patients with underlying endocrine disorders (such as hypothyroidism or growth hormone deficiency) or metabolic bone disease, as these patients have a much higher rate of bilateral involvement (up to 100%).

Question 5428

Topic: 4. Pediatrics

A 12-year-old obese male presents with a slipped capital femoral epiphysis (SCFE). The pathophysiology of this condition involves mechanical failure through which specific histologic zone of the physis?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

SCFE represents a type 1 Salter-Harris fracture where the epiphysis slips posteriorly and inferiorly. The mechanical failure occurs through the hypertrophic zone of the physis, which is structurally the weakest layer due to the large size of the chondrocytes and relatively sparse extracellular matrix.

Question 5429

Topic: 4. Pediatrics

An ultrasound of the hips is performed on a 6-week-old female infant. The Graf classification yields a Type IIa hip, characterized by an alpha angle of 55 degrees. What is the most appropriate management for this infant?

. Immediate application of a Pavlik harness
. Closed reduction and spica casting
. Open reduction via an anterior approach
. Observation and repeat ultrasound in 4 to 6 weeks
. Application of an abduction brace for 23 hours a day

Correct Answer & Explanation

. Observation and repeat ultrasound in 4 to 6 weeks

Explanation

A Graf Type IIa hip (alpha angle 50-59 degrees) in an infant under 3 months of age is considered physiologically immature rather than frankly dysplastic. The standard of care is observation and a repeat ultrasound at 10 to 12 weeks of age, as over 90% will normalize spontaneously.

Question 5430

Topic: Pediatric Lower Extremity

When utilizing the Ponseti method for the serial casting of idiopathic clubfoot (talipes equinovarus), correction of the deformities follows a strict sequential order (CAVE). What is the critical first step in the manipulation and casting process?

. Percutaneous Achilles tenotomy to correct equinus
. Abduction of the forefoot against counter-pressure on the calcaneocuboid joint
. Elevation of the first ray to correct the cavus deformity
. Derotation of the calcaneus to correct hindfoot varus
. Pronation of the forefoot to align with the hindfoot

Correct Answer & Explanation

. Elevation of the first ray to correct the cavus deformity

Explanation

The CAVE acronym outlines the order of correction: Cavus, Adductus, Varus, Equinus. The very first step is to supinate the forefoot by elevating the first ray, which aligns the forefoot with the hindfoot and corrects the cavus. Pronating the forefoot is a common error that actually worsens the cavus deformity.

Question 5431

Topic: 4. Pediatrics

A 2-month-old infant is evaluated for bilateral developmental dysplasia of the hip. Examination reveals bilateral knee extension contractures, clubfeet, and a flattened facial profile. What is the most likely underlying diagnosis and the expected response to Pavlik harness treatment?

. Arthrogryposis multiplex congenita; high success rate with Pavlik
. Larsen syndrome; high success rate with Pavlik
. Myelomeningocele; low success rate with Pavlik
. Arthrogryposis multiplex congenita; low success rate with Pavlik
. Amniotic band syndrome; high success rate with Pavlik

Correct Answer & Explanation

. Arthrogryposis multiplex congenita; low success rate with Pavlik

Explanation

Teratologic DDH is often seen in neuromuscular or syndromic conditions such as arthrogryposis multiplex congenita or myelomeningocele. These dislocations occur early in utero, are typically rigid, and are notoriously resistant to conservative management like the Pavlik harness, almost always requiring open surgical reduction.

Question 5432

Topic: Pediatric Hip

A 12-year-old obese male presents with left groin pain and a limp for 3 weeks. Examination reveals obligatory external rotation of the hip upon passive flexion. Radiographs confirm a mild slipped capital femoral epiphysis (SCFE). During in situ pinning, where should the screw be positioned within the epiphysis to minimize complications?

. Anterior-superior quadrant
. Anterior-inferior quadrant
. Posterior-superior quadrant
. Center of the epiphysis
. Posterior-inferior quadrant

Correct Answer & Explanation

. Center of the epiphysis

Explanation

In SCFE pinning, the goal is to place a single screw in the center-center position of the epiphysis on both AP and lateral radiographs. This maximizes biomechanical stability and minimizes the risk of joint penetration (which can lead to chondrolysis) or damage to the vulnerable posterior-superior retinacular vessels (which can cause avascular necrosis).

Question 5433

Topic: Pediatric Hip

A 13-year-old obese male presents to the emergency department complaining of left hip and knee pain for 2 weeks. Today, after a minor slip, he is completely unable to bear weight on the left leg, even with the assistance of crutches. Radiographs confirm a slipped capital femoral epiphysis (SCFE). Based on the Loder classification, what is the most significant prognostic risk for this specific type of slip?

. Chondrolysis
. Premature physeal closure
. Avascular necrosis (AVN) of the femoral head
. Cam-type femoroacetabular impingement
. Subtrochanteric femur fracture

Correct Answer & Explanation

. Avascular necrosis (AVN) of the femoral head

Explanation

The Loder classification defines a SCFE as 'unstable' if the patient is unable to bear weight, even with crutches. Unstable slips have a significantly higher risk of avascular necrosis (AVN) of the femoral head (approaching 20-50%) compared to stable slips, where the patient can bear weight and the AVN risk is nearly zero.

Question 5434

Topic: Pediatric Hip

A 12-year-old obese boy presents with left thigh pain and a limp for 3 weeks. Examination reveals an obligate external rotation of the left hip during flexion. Radiographs confirm a mild slipped capital femoral epiphysis (SCFE). Contralateral prophylactic in situ pinning is most strongly indicated in which of the following scenarios?

. The patient has a concurrent diagnosis of hypothyroidism
. The patient is male
. The slip angle on the affected side is greater than 50 degrees
. The patient has closed triradiate cartilages
. The patient is a competitive athlete

Correct Answer & Explanation

. The patient has a concurrent diagnosis of hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but is strongly recommended in patients with endocrine disorders (e.g., hypothyroidism, renal osteodystrophy, growth hormone deficiency) or those receiving radiation therapy, as they have a significantly higher risk of bilateral involvement.

Question 5435

Topic: Pediatric Hip

A 4-week-old female infant is diagnosed with developmental dysplasia of the hip (DDH) and placed in a Pavlik harness. Two weeks later, the parents notice she is not kicking her affected leg as much as the other. Examination reveals an inability to actively extend the knee on the affected side. This complication is most likely due to excessive:

. Hip flexion in the harness
. Hip extension in the harness
. Hip abduction in the harness
. Hip adduction in the harness
. Knee flexion in the harness

Correct Answer & Explanation

. Hip flexion in the harness

Explanation

The complication described is a femoral nerve palsy, which manifests as weakness of the quadriceps (inability to extend the knee). In a Pavlik harness, this is caused by excessive hip flexion, which stretches or compresses the femoral nerve. Excessive abduction can lead to avascular necrosis (AVN) of the femoral head.

Question 5436

Topic: 4. Pediatrics

A newborn sustains multiple fractures during an uncomplicated vaginal delivery. Examination reveals blue sclerae and joint hyperlaxity. This condition is primarily caused by a mutation affecting the synthesis of which of the following?

. Fibrillin-1
. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Type II collagen
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta (OI) is an autosomal dominant disorder characterized by bone fragility and blue sclerae. It is caused by mutations in the COL1A1 or COL1A2 genes, which lead to quantitative or qualitative defects in Type I collagen.

Question 5437

Topic: Pediatric Hip

A 13-year-old obese boy presents with knee pain and a limp. Examination reveals obligate external rotation of the hip during passive flexion. What is the typical displacement of the femoral neck relative to the capital femoral epiphysis in this condition?

. Anterior and superior
. Anterior and inferior
. Posterior and superior
. Posterior and inferior
. Medial and inferior

Correct Answer & Explanation

. Posterior and inferior

Explanation

In Slipped Capital Femoral Epiphysis (SCFE), the capital femoral epiphysis typically stays relatively stationary in the acetabulum, while the femoral neck displaces anteriorly and superiorly (externally rotating). This creates the radiographic appearance of the epiphysis 'slipping' posteriorly and inferiorly.

Question 5438

Topic: Pediatric Lower Extremity

In the Ponseti method for the treatment of idiopathic clubfoot (talipes equinovarus), which component of the deformity is corrected FIRST?

. Equinus
. Hindfoot varus
. Midfoot cavus
. Forefoot adductus
. Tibial torsion

Correct Answer & Explanation

. Midfoot cavus

Explanation

The Ponseti method corrects the deformities in a specific sequence remembered by the acronym CAVE: Cavus, Adductus, Varus, Equinus. The first step is to elevate the first ray to correct the midfoot cavus, which aligns the forefoot with the hindfoot.

Question 5439

Topic: 4. Pediatrics

A 3-year-old child presents with a limp, fever, and refusal to bear weight. Ultrasound shows a hip effusion. Which of the following parameters is NOT considered one of the classic four Kocher criteria for predicting pediatric septic arthritis?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate > 40 mm/hr
. Fever > 38.5°C (101.3°F)
. Serum white blood cell count > 12,000/mm3
. Joint fluid WBC > 50,000/mm3

Correct Answer & Explanation

. Joint fluid WBC > 50,000/mm3

Explanation

The Kocher criteria are clinical and serum laboratory parameters used to predict the likelihood of septic arthritisbeforeproceeding to joint aspiration. They include: fever > 38.5°C, inability to bear weight, ESR > 40 mm/hr, and serum WBC > 12,000/mm3. Joint fluid analysis (WBC > 50,000) is a definitive diagnostic test but is not one of the predictive Kocher criteria.

Question 5440

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. What is the underlying molecular pathophysiology of this autosomal dominant condition?

. Loss of function mutation in COL1A1 leading to fragile bone
. Gain of function mutation in FGFR3 inhibiting chondrocyte proliferation
. Loss of function in COMP altering cartilage extracellular matrix
. Mutation in Runx2 preventing osteoblast differentiation
. Mutation in SOX9 causing absent endochondral ossification

Correct Answer & Explanation

. Gain of function mutation in FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation causes constitutive activation of the receptor, which paradoxically inhibits chondrocyte proliferation in the proliferative zone of the physis.

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