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4. Pediatrics MCQs

Practice Set 276 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 5501

Topic: Pediatric Hip

A 14-year-old obese male presents with chronic left hip pain and an antalgic gait. Radiographs show a stable slipped capital femoral epiphysis (SCFE). Following in situ pinning, he continues to experience pain and limited range of motion, particularly internal rotation and flexion. What is the most likely long-term complication leading to his persistent symptoms, and what surgical intervention might be indicated?

. Avascular necrosis of the femoral head requiring core decompression
. Chondrolysis necessitating total hip arthroplasty
. Femoroacetabular impingement (FAI) requiring surgical dislocation and osteochondroplasty
. Nonunion of the physis requiring repeat pinning
. Contralateral SCFE requiring prophylactic pinning

Correct Answer & Explanation

. Femoroacetabular impingement (FAI) requiring surgical dislocation and osteochondroplasty

Explanation

SCFE results in a deformity of the proximal femur, specifically retroversion of the femoral head relative to the neck, creating a 'pistol grip' deformity or cam-type impingement. This altered morphology can lead to femoroacetabular impingement (FAI), causing persistent pain, restricted range of motion, and predisposing to premature osteoarthritis, even after successful in situ pinning. Surgical dislocation and osteochondroplasty aim to reshape the femoral head-neck junction to relieve impingement. Avascular necrosis is a significant complication, but persistent pain with specific motion restriction is more indicative of FAI. Chondrolysis and nonunion are less common and typically present differently. Contralateral SCFE is a risk but doesn't explain the persistent ipsilateral symptoms.

Question 5502

Topic: Pediatric Hip

A 9-month-old female is diagnosed with developmental dysplasia of the hip (DDH). She has a completely dislocated left hip that is reducible but unstable. Prior Pavlik harness treatment failed at 3 months of age. What is the most appropriate next step in management?

. Re-trial of Pavlik harness
. Rigid abduction bracing
. Closed reduction and spica casting under anesthesia
. Open reduction and Salter osteotomy
. Observation until age 2 followed by pelvic osteotomy

Correct Answer & Explanation

. Closed reduction and spica casting under anesthesia

Explanation

For infants aged 6 to 18 months with failed harness treatment or late-presenting DDH, closed reduction with spica casting under general anesthesia is the standard of care. Open reduction is reserved for failed closed reduction or older children.

Question 5503

Topic: Pediatric Upper Extremity & Spine
A 6-year-old boy has a Gartland type III supracondylar humerus fracture. After closed reduction and percutaneous pinning, the fracture is anatomically aligned, but the radial pulse remains absent while the hand remains pink and warm. What is the next best step?
. Immediate vascular exploration
. Perform a duplex ultrasound
. Observation and admission for close neurovascular checks
. Remove the pins and open the fracture
. Perform an intra-operative angiogram

Correct Answer & Explanation

. Observation and admission for close neurovascular checks

Explanation

In a "pink, pulseless" hand following anatomical reduction and pinning of a pediatric supracondylar humerus fracture, the standard of care is close observation. Vascular exploration is strictly indicated for a "white, pulseless" (ischemic) hand.

Question 5504

Topic: 4. Pediatrics

A 4-month-old female infant is brought in for a well-child check. Examination reveals a positive Ortolani sign on the left hip. Ultrasound shows a shallow acetabulum with an alpha angle of 40 degrees. What is the most appropriate initial management?

. Observation and repeat ultrasound in 4 weeks
. Pavlik harness application
. Closed reduction and spica casting
. Open reduction and spica casting
. Triple pelvic osteotomy

Correct Answer & Explanation

. Pavlik harness application

Explanation

An alpha angle of less than 60 degrees on ultrasound, combined with a positive Ortolani sign, confirms Developmental Dysplasia of the Hip (DDH). The Pavlik harness is the gold standard initial treatment for reducible DDH in infants under 6 months of age.

Question 5505

Topic: 4. Pediatrics
A 6-year-old boy presents with a 2-month history of a painless limp. Examination reveals limited internal rotation and abduction of the right hip. Radiographs show sclerosis and early fragmentation of the right capital femoral epiphysis. What is the primary goal of treatment in this condition?
. Stimulate immediate revascularization via core decompression
. Maintain the femoral head within the acetabulum to allow spherical remodeling
. Halt the disease progression using bisphosphonates
. Perform immediate prophylactic pinning to prevent slippage
. Eradicate infection using intravenous antibiotics

Correct Answer & Explanation

. Maintain the femoral head within the acetabulum to allow spherical remodeling

Explanation

Legg-Calvé-Perthes disease is an idiopathic avascular necrosis of the pediatric femoral head. The primary goal of treatment is "containment"—keeping the biologically plastic femoral head well-seated in the acetabulum to maintain a spherical shape as it heals and remodels.

Question 5506

Topic: Pediatric Hip

A 4-week-old female is treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During a follow-up visit, the parents report the infant is no longer actively extending the knee on the treated side. What is the most appropriate next step in management?

. Adjust the anterior straps to increase hip flexion
. Discontinue the harness immediately and switch to a rigid spica cast
. Loosen the anterior straps to reduce hip flexion
. Perform an immediate ultrasound to rule out avascular necrosis
. Continue the current harness settings and reassure the parents

Correct Answer & Explanation

. Loosen the anterior straps to reduce hip flexion

Explanation

The infant has developed a femoral nerve palsy, which is caused by excessive hip flexion in the Pavlik harness. The anterior straps should be loosened or the harness temporarily discontinued to allow nerve recovery.

Question 5507

Topic: Pediatric Hip

A 6-month-old female is diagnosed with developmental dysplasia of the hip (DDH) after an unsuccessful 6-week trial of a Pavlik harness. Radiographs confirm a persistently dislocated right hip. What is the most appropriate next step in management?

. Continue Pavlik harness for 4 more weeks
. Transition to an abduction orthosis (e.g., Ilfeld splint)
. Closed reduction and spica casting under general anesthesia
. Open reduction with pelvic osteotomy
. Wait until walking age for spontaneous resolution

Correct Answer & Explanation

. Closed reduction and spica casting under general anesthesia

Explanation

Following the failure of a Pavlik harness in an infant, closed reduction and spica casting under general anesthesia is the standard next step. Open reduction is indicated if closed reduction is unsuccessful or in older children.

Question 5508

Topic: Pediatric Hip

A 6-year-old boy presents with a painless limp, and radiographs show sclerosis and fragmentation of the capital femoral epiphysis. According to the Herring lateral pillar classification for Legg-Calve-Perthes disease, a patient with 60% maintenance 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 classification, Group B is characterized by radiolucency and loss of height of the lateral pillar, but greater than 50% of the normal height is maintained. Group C indicates less than 50% of the lateral pillar height remains.

Question 5509

Topic: Pediatric Upper Extremity & Spine
A 5-year-old boy presents with a displaced Gartland type III supracondylar humerus fracture. His hand is pink and well-perfused, but the radial pulse is absent by palpation and Doppler. Following closed reduction and percutaneous pinning, the fracture is perfectly aligned; however, the radial pulse remains absent while the hand stays pink. What is the most appropriate next step in management?
. Immediate exploration and repair of the brachial artery
. Performance of a brachial arterioventricular bypass graft
. Admission for 24 to 48 hours of observation with serial neurovascular checks
. Urgent CT angiogram of the upper extremity to map the vascular injury
. Immediate administration of weight-based intravenous heparin

Correct Answer & Explanation

. Admission for 24 to 48 hours of observation with serial neurovascular checks

Explanation

A "pulseless, pink hand" following anatomical reduction of a supracondylar humerus fracture indicates robust collateral circulation maintaining adequate distal perfusion. The standard of care is close inpatient observation with serial neurovascular exams, avoiding the morbidity of unnecessary vascular exploration.

Question 5510

Topic: 4. Pediatrics

In which zone of the physis do Salter-Harris type I fractures most commonly occur?

. Reserve zone
. Proliferative zone
. Hypertrophic zone (specifically the zone of provisional calcification)
. Hypertrophic zone (specifically the zone of cell maturation/degeneration)
. Metaphysis

Correct Answer & Explanation

. Hypertrophic zone (specifically the zone of cell maturation/degeneration)

Explanation

Salter-Harris fractures typically propagate through the mechanically weakest zone of the physis, which is the zone of cell hypertrophy (specifically the zone of cell maturation and degeneration) because it lacks abundant collagen and calcified matrix.

Question 5511

Topic: 4. Pediatrics
A 2-year-old girl with blue sclerae, dentinogenesis imperfecta, and multiple prior fractures is diagnosed with Osteogenesis Imperfecta (OI). According to the Sillence classification, which type of OI is typically lethal in the perinatal period?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Sillence Classification of OI: Type I is the most common and mildest form. Type II is lethal in the perinatal period due to severe pulmonary complications and in utero fractures. Type III is the most severe non-lethal form, leading to progressive deformity. Type IV is intermediate in severity.

Question 5512

Topic: Pediatric Hip

A 3-month-old female with developmental dysplasia of the hip (DDH) has been treated in a Pavlik harness for two weeks. During a follow-up exam, she demonstrates an absent patellar reflex and lacks active knee extension on the treated side. What is the most appropriate next step in management?

. Loosen the anterior straps to decrease hip flexion
. Loosen the posterior straps to decrease hip abduction
. Discontinue the harness and proceed to closed reduction and spica casting
. Obtain an MRI of the lumbar spine to rule out dysraphism
. Continue the current harness settings as this is a transient normal finding

Correct Answer & Explanation

. Loosen the anterior straps to decrease hip flexion

Explanation

The patient has developed a femoral nerve palsy, a known complication of excessive hip flexion in a Pavlik harness. The appropriate management is to loosen the anterior straps (decreasing flexion) or temporarily remove the harness if the palsy does not quickly resolve. Excessive abduction (tight posterior straps) can lead to avascular necrosis of the femoral head.

Question 5513

Topic: 4. Pediatrics

Osteogenesis imperfecta (OI) is a genetic connective tissue disorder characterized by bone fragility. The majority of OI cases are caused by mutations in the COL1A1 or COL1A2 genes. At the molecular level, what is the primary consequence of these mutations?

. Defective cross-linking of mature collagen fibrils outside the cell by lysyl oxidase
. Replacement of a critical glycine residue by a bulkier amino acid, disrupting the collagen triple helix
. Inability to hydroxylate proline and lysine residues due to Vitamin C deficiency
. Overproduction of Type II collagen in the bone extracellular matrix
. Defective cleavage of procollagen C- and N-terminal propeptides by peptidases

Correct Answer & Explanation

. Replacement of a critical glycine residue by a bulkier amino acid, disrupting the collagen triple helix

Explanation

OI is primarily caused by mutations in COL1A1 or COL1A2. The most common pathogenic mechanism is a single-base substitution that replaces a crucial glycine residue (the smallest amino acid, which fits inside the helix core) with a bulkier amino acid. This disrupts the tight coiling of the Type I collagen triple helix, leading to structurally abnormal or severely depleted Type I collagen.

Question 5514

Topic: 4. Pediatrics

A 5-year-old child with a history of multiple low-energy fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with osteogenesis imperfecta. This condition is most commonly caused by a genetic mutation leading to the substitution of which specific amino acid in the collagen triple helix?

. Proline
. Hydroxyproline
. Glycine
. Lysine
. Hydroxylysine

Correct Answer & Explanation

. Glycine

Explanation

Osteogenesis imperfecta is typically caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. The most common defect is a missense mutation that substitutes a bulky amino acid for glycine in the repeating Gly-X-Y sequence of the type I collagen triple helix, destabilizing the entire structure.

Question 5515

Topic: 4. Pediatrics

In the process of normal endochondral ossification at the physis, which specific cellular zone is primarily affected and functionally impaired in patients with achondroplasia?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally functions as a negative regulator of bone growth. Its constitutive activation leads to marked inhibition of chondrocyte proliferation. Therefore, the primary functional defect manifests in the proliferative zone of the physis, leading to decreased cartilage production and stunted endochondral bone growth (rhizomelic dwarfism).

Question 5516

Topic: 4. Pediatrics

In pediatric orthopedics, a Slipped Capital Femoral Epiphysis (SCFE) anatomically occurs predominantly through which specific zone of the proximal femoral physis?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

A Slipped Capital Femoral Epiphysis (SCFE), like most Salter-Harris type fractures, typically propagates through the hypertrophic zone of the physis. This zone is the weakest portion of the growth plate biomechanically because the chondrocytes are markedly swollen (hypertrophic) and the structural intercellular matrix is minimal, right before it gains structural integrity in the calcifying zone of provisional calcification.

Question 5517

Topic: 4. Pediatrics

A neonate is diagnosed with achondroplasia. Both parents are of average stature. Which of the following best describes the pathogenesis of this skeletal dysplasia?

. Defect in type I collagen synthesis
. Loss-of-function mutation in the Runx2 gene
. Gain-of-function mutation in the fibroblast growth factor receptor 3 (FGFR3) gene
. Deficiency of the enzyme arylsulfatase E
. Mutation in the SOX9 transcription factor

Correct Answer & Explanation

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

Explanation

Achondroplasia is the most common form of short-limb dwarfism and is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This overactive receptor inappropriately inhibits chondrocyte proliferation in the proliferative zone of the physis. Up to 80% of cases are new mutations, strongly associated with advanced paternal age.

Question 5518

Topic: 4. Pediatrics

A 4-year-old child presents with rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs show a narrowing of the interpedicular distances from L1 to L5. This condition is most commonly caused by a mutation in which gene?

. COL1A1
. FGFR3
. COMP
. RUNX2
. SOX9

Correct Answer & Explanation

. FGFR3

Explanation

The clinical presentation is classic for achondroplasia. Achondroplasia is caused by an activating (gain-of-function) mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene, leading to inhibition of chondrocyte proliferation in the growth plate.

Question 5519

Topic: Pediatric Hip

An obese 12-year-old boy presents with a stable slipped capital femoral epiphysis (SCFE) of the left hip. Under which of the following conditions is prophylactic in situ pinning of the contralateral, asymptomatic right hip most strongly indicated?

. Presentation during the summer months
. Associated primary hypothyroidism
. BMI greater than the 95th percentile
. Presence of a positive Drehmann sign on the left
. Male gender

Correct Answer & Explanation

. Associated primary hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is highly recommended for patients with underlying endocrine disorders (such as hypothyroidism) or renal osteodystrophy. These conditions carry a significantly higher risk for bilateral involvement.

Question 5520

Topic: 4. Pediatrics

A 7-year-old child sustains a Salter-Harris Type II fracture of the distal radius. The fracture line propagating transversely through the physis typically traverses which of the following histologic zones of the growth plate?

. Reserve (resting) zone
. Proliferative zone
. Zone of hypertrophy
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

Fractures through the physis typically occur in the zone of hypertrophy. This zone is mechanically the weakest because of a high cell-to-matrix ratio, large chondrocyte volume, and a relative lack of collagen.

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