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4. Pediatrics MCQs

Practice Set 152 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 3021

Topic: 4. Pediatrics
A 14-year-old female sustains an injury to her ankle while skateboarding. Radiographs reveal a Salter-Harris III fracture of the anterolateral distal tibia. Which ligament is responsible for the avulsion of this fracture fragment?
. Anterior talofibular ligament
. Calcaneofibular ligament
. Deltoid ligament
. Anterior inferior tibiofibular ligament
. Posterior inferior tibiofibular ligament

Correct Answer & Explanation

. Anterior inferior tibiofibular ligament

Explanation

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibia epiphysis. The avulsion is caused by the anterior inferior tibiofibular ligament (AITFL) as the distal tibial physis closes from central to anteromedial, leaving the anterolateral aspect open last.

Question 3022

Topic: 4. Pediatrics
A 13-year-old boy presents after an external rotation injury to his ankle. Radiographs show a Salter-Harris III fracture of the anterolateral distal tibia. The avulsed fragment in this injury is primarily pulled by which ligament?
. Anterior inferior tibiofibular ligament (AITFL)
. Posterior inferior tibiofibular ligament (PITFL)
. Anterior talofibular ligament (ATFL)
. Deltoid ligament
. Calcaneofibular ligament (CFL)

Correct Answer & Explanation

. Anterior inferior tibiofibular ligament (AITFL)

Explanation

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibia. The fragment is avulsed by the anterior inferior tibiofibular ligament (AITFL) due to the asymmetrical lateral-to-medial closure of the distal tibial physis.

Question 3023

Topic: Pediatric Upper Extremity & Spine

A 7-year-old boy presents with a Gartland Type II supracondylar humerus fracture. Radiographs show posterior displacement with an intact anterior humeral line. He has a strong radial pulse and good capillary refill. Sensory function is normal. What is the MOST appropriate management?

. Long arm cast immobilization in 90 degrees of flexion
. Closed reduction and percutaneous pinning (CRPP)
. Open reduction and internal fixation (ORIF)
. Observation with serial radiographs
. Skeletal traction

Correct Answer & Explanation

. Long arm cast immobilization in 90 degrees of flexion

Explanation

A Gartland Type II supracondylar humerus fracture is characterized by displacement with an intact posterior cortex and an intact anterior humeral line. While some sources might suggest closed reduction and casting for stable Type II fractures, the prevailing consensus for displaced Type II and all Type III fractures is closed reduction and percutaneous pinning (CRPP). This provides stable fixation, allowing for earlier mobilization and minimizing the risk of re-displacement, which is a common complication with casting alone. Cast immobilization in 90 degrees of flexion without pinning is generally reserved for non-displaced (Type I) or minimally displaced fractures. ORIF is usually reserved for open fractures, neurovascular compromise that doesn't resolve after reduction, or failed closed reduction. Observation is for Type I. Skeletal traction is largely historical for this injury.

Question 3024

Topic: 4. Pediatrics

A 10-year-old boy sustains a Salter-Harris Type II fracture of the distal radius with dorsal displacement. The fracture is moderately displaced. What is the MOST appropriate treatment?

. Open reduction and internal fixation (ORIF)
. Closed reduction and long arm cast immobilization for 4-6 weeks
. Observation and splinting
. Percutaneous pinning without reduction
. Short arm cast immobilization

Correct Answer & Explanation

. Open reduction and internal fixation (ORIF)

Explanation

A Salter-Harris Type II fracture involves the physis and a metaphyseal fragment (Thurston-Holland sign). In children, these fractures have a good prognosis for healing and remodeling. For moderately displaced fractures, closed reduction and long arm cast immobilization is the standard treatment. The long arm cast is crucial for controlling pronation/supination and maintaining reduction in the skeletally immature patient, especially for distal radius fractures. ORIF is rarely needed for Salter-Harris Type II fractures unless closed reduction fails or for very unstable reductions. Observation is for non-displaced fractures. Percutaneous pinning is typically for unstable reductions or Salter-Harris Type III/IV fractures requiring precise anatomical reduction. A short arm cast is often insufficient to maintain reduction in displaced pediatric forearm/wrist fractures.

Question 3025

Topic: Pediatric Upper Extremity & Spine

A 6-year-old boy falls from a playground structure and sustains a Gartland type III extension-type supracondylar humerus fracture. Radiographs demonstrate posterolateral displacement of the distal fracture fragment. Based on the displacement pattern of the proximal fragment, which neurovascular structure is at the HIGHEST risk of injury, and what corresponding clinical finding should the examiner specifically evaluate?

. Radial nerve; inability to actively extend the wrist and digits
. Anterior interosseous nerve; inability to actively flex the thumb IP joint and index finger DIP joint
. Ulnar nerve; inability to cross the index and middle fingers
. Posterior interosseous nerve; weak thumb extension with preserved wrist extension
. Musculocutaneous nerve; absent biceps reflex and paresthesia over the lateral forearm

Correct Answer & Explanation

. Radial nerve; inability to actively extend the wrist and digits

Explanation

In a Gartland type III extension-type supracondylar humerus fracture with posterolateral displacement of the distal fragment, the proximal shaft fragment is driven anteromedially. This anteromedial proximal spike places the structures in the anterior/medial aspect of the elbow—specifically the brachial artery, the median nerve, and its anterior interosseous nerve (AIN) branch—at the highest risk of injury. The AIN is the most commonly injured nerve in extension-type supracondylar humerus fractures overall, particularly with this posterolateral displacement pattern. An AIN palsy presents with loss of motor function to the flexor pollicis longus (FPL) and the flexor digitorum profundus (FDP) of the index finger, resulting in an inability to form the 'OK' sign. Conversely, posteromedial displacement of the distal fragment drives the proximal fragment anterolaterally, risking the radial nerve.

Question 3026

Topic: 4. Pediatrics

A 6-year-old child sustains a widely displaced, extension-type supracondylar humerus fracture.

On initial presentation in the emergency department, the child's hand is pink and well-perfused, but the radial pulse is non-palpable. The patient is taken to the operating room for closed reduction and percutaneous pinning. Post-reduction, the fracture is anatomically aligned, but the radial pulse remains absent. The hand remains warm and pink, with a capillary refill time of 2 seconds. What is the most appropriate next step?

. Immediate vascular surgery consultation for brachial artery bypass
. Exploration of the antecubital fossa
. Removal of the pins and immediate open reduction
. Observation and close neurovascular monitoring
. Emergent upper extremity angiography

Correct Answer & Explanation

. Immediate vascular surgery consultation for brachial artery bypass

Explanation

The management of a 'pulseless, pink' hand following reduction and pinning of a pediatric supracondylar humerus fracture is observation and close monitoring. Because the hand remains well-perfused (pink, brisk capillary refill), collateral circulation is sufficient. Vascular exploration or routine angiography is only indicated if the hand becomes 'pulseless and white' (poorly perfused) after closed reduction, which signifies inadequate collateral flow and impending ischemia.

Question 3027

Topic: Pediatric Upper Extremity & Spine



A 6-year-old boy presents with a completely displaced, extension-type supracondylar humerus fracture (Gartland Type III). On initial examination, the hand is pink but the radial pulse is non-palpable. The patient is taken emergently to the operating room. After closed reduction and percutaneous pinning, the fracture is anatomically aligned. The hand remains pink with brisk capillary refill, but the radial pulse remains absent. What is the most appropriate next step in management?

. Immediate open exploration of the brachial artery
. Angiography to identify the site of vascular occlusion
. Observation and admission for close neurovascular monitoring
. Removal of the percutaneous pins and open reduction
. Prophylactic fasciotomy of the forearm flexor compartments

Correct Answer & Explanation

. Immediate open exploration of the brachial artery

Explanation

The scenario describes a 'pink, pulseless' hand following reduction and pinning of a pediatric supracondylar humerus fracture. The current standard of care dictates that if the hand is well-perfused (pink, warm, brisk capillary refill <2 seconds, detectable pulse oximetry waveform) after fracture reduction, even in the absence of a palpable radial pulse, the appropriate management is close observation and monitoring. Open exploration is indicated only if the hand is 'white and pulseless' (ischemic) after reduction.

Question 3028

Topic: Pediatric Upper Extremity & Spine

A 6-year-old boy presents with a completely displaced, extension-type supracondylar humerus fracture (Gartland Type III). He exhibits weakness with active flexion of the thumb interphalangeal joint and the distal interphalangeal joint of the index finger. Which of the following nerve injuries is most likely present?

. Radial nerve
. Ulnar nerve
. Anterior interosseous nerve
. Main trunk of the median nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Radial nerve

Explanation

The anterior interosseous nerve (AIN), a motor branch of the median nerve, is the most commonly injured nerve in extension-type pediatric supracondylar humerus fractures. The AIN innervates the flexor pollicis longus (FPL), the lateral half of the flexor digitorum profundus (FDP), and the pronator quadratus. An AIN neuropraxia results in the inability to actively flex the thumb interphalangeal (IP) joint and the index finger distal interphalangeal (DIP) joint, classically leading to an abnormal 'OK' sign (creating a pinch rather than an O). The radial nerve is the second most commonly injured nerve, often seen with posteromedial fracture displacement.

Question 3029

Topic: 4. Pediatrics

Regarding the Mendelian inheritance patterns in orthopedics, which condition is typically inherited in an autosomal dominant manner?

. Spinal Muscular Atrophy
. Osteogenesis Imperfecta
. Duchenne Muscular Dystrophy
. Cystic Fibrosis
. Spina Bifida

Correct Answer & Explanation

. Spinal Muscular Atrophy

Explanation

Osteogenesis Imperfecta (OI), particularly types I, II, III, and IV, is predominantly inherited in an autosomal dominant fashion, often due to mutations in the COL1A1 or COL1A2 genes, affecting Type I collagen synthesis. Spinal Muscular Atrophy and Cystic Fibrosis are autosomal recessive. Duchenne Muscular Dystrophy is X-linked recessive. Spina Bifida is a multifactorial condition.

Question 3030

Topic: 4. Pediatrics

A 4-year-old child presents with multiple fractures after minor trauma, blue sclerae, and hearing loss. Genetic testing reveals a mutation resulting in a defect in the folding of the collagen triple helix. Which of the following best describes the underlying genetic anomaly in the most severe, non-lethal form of this disease?

. Quantitative defect in type I collagen production
. Substitution of a bulky amino acid for glycine in the pro-alpha chain
. Mutation in the FGFR3 gene resulting in a gain of function
. Defect in osteoclast carbonic anhydrase II
. Defect in the CBFA1 (RUNX2) transcription factor

Correct Answer & Explanation

. Quantitative defect in type I collagen production

Explanation

The patient has Osteogenesis Imperfecta (OI). Type I OI (mildest) is a quantitative defect resulting in decreased production of normal type I collagen. Types II, III, and IV are qualitative defects, typically caused by a point mutation replacing glycine with a bulkier amino acid. This substitution disrupts the stable packing of the collagen triple helix. Type III is the most severe non-lethal form.

Question 3031

Topic: 4. Pediatrics

In the physial growth plate, a gain-of-function mutation in the FGFR3 gene predominantly affects which of the following zones, resulting in achondroplasia?

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

Correct Answer & Explanation

. Reserve zone

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. FGFR3 normally acts as a negative regulator of endochondral bone growth. When overactive, it prematurely inhibits chondrocyte proliferation. This primary defect localizes to the proliferative zone of the physis, leading to the characteristic short-limbed (rhizomelic) dwarfism.

Question 3032

Topic: 4. Pediatrics

A 4-year-old boy is evaluated for frequent fractures and progressive hearing loss. Radiographs demonstrate a diffuse, symmetric skeletal sclerosis with a 'bone within bone' appearance. The underlying pathogenesis of his disease most likely involves a defect in the function of which of the following?

. Type I collagen synthesis
. Carbonic anhydrase II
. Fibroblast growth factor receptor 3
. Core binding factor alpha-1 (Cbfa1/Runx2)
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type I collagen synthesis

Explanation

The patient's clinical and radiographic presentation is classic for malignant infantile osteopetrosis, a condition characterized by severely impaired osteoclast function. The autosomal recessive form is most often caused by mutations in genes necessary for acidifying the Howship's lacuna, such as TCIRG1, ClCN7, and Carbonic Anhydrase II (CAII). Defective Type I collagen is seen in osteogenesis imperfecta; FGFR3 mutations cause achondroplasia; Cbfa1 mutations lead to cleidocranial dysplasia; and COMP mutations cause pseudoachondroplasia.

Question 3033

Topic: 4. Pediatrics

A 14-year-old boy with multiple painless bony protuberances around his knees and ankles presents with a new onset of pain and rapid growth of a lesion on his proximal humerus over the last 3 months. His father has a similar history. Genetic testing of this patient is most likely to reveal a mutation in a gene responsible for which of the following cellular processes?

. Fibroblast growth factor receptor 3 (FGFR3) signaling
. Alpha subunit of the stimulatory G protein (Gs-alpha)
. Synthesis of heparan sulfate proteoglycans
. Cleavage of type I collagen
. Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Fibroblast growth factor receptor 3 (FGFR3) signaling

Explanation

The patient has Multiple Hereditary Exostoses (MHE), an autosomal dominant condition characterized by multiple osteochondromas. MHE is primarily caused by mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases that are essential for the biosynthesis of heparan sulfate proteoglycans. Disruption of this pathway leads to abnormal chondrocyte proliferation and bone growth. FGFR3 mutations cause achondroplasia, while Gs-alpha mutations are associated with fibrous dysplasia.

Question 3034

Topic: 4. Pediatrics

Physeal fractures and specific pediatric orthopedic conditions tend to preferentially involve distinct histologic zones of the physis. Through which zone of the physis does the failure typically occur in a slipped capital femoral epiphysis (SCFE)?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of provisional calcification
. Zone of hypertrophy

Correct Answer & Explanation

. Reserve zone

Explanation

Slipped capital femoral epiphysis (SCFE) and most Salter-Harris physeal fractures typically occur through the zone of hypertrophy (specifically the primary spongiosa region). In this zone, the chondrocytes swell and undergo apoptosis, and the extracellular matrix is sparse and lacks structural collagen, making it the mechanically weakest point of the physis. The reserve zone is affected in Gaucher disease; the proliferative zone in achondroplasia; and the zone of provisional calcification in rickets.

Question 3035

Topic: 4. Pediatrics

A 14-year-old boy presents with multiple firm, painless bony prominences around his knees and ankles. Radiographs demonstrate multiple sessile and pedunculated lesions projecting away from the adjacent joints, with continuous medullary cavities.

This condition is most commonly associated with a genetic mutation leading to a deficiency in which of the following?

. Heparan sulfate
. Chondroitin sulfate
. Fibroblast growth factor receptor 3 (FGFR3)
. Transforming growth factor beta (TGF-b)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Heparan sulfate

Explanation

The patient has Multiple Hereditary Exostoses (MHE), an autosomal dominant condition characterized by multiple osteochondromas. It is caused by mutations in the tumor suppressor genes EXT1 or EXT2. These genes encode glycosyltransferases essential for the synthesis of heparan sulfate. The deficiency in heparan sulfate disrupts the regulation of Indian hedgehog (Ihh) signaling at the growth plate, leading to abnormal physeal growth and osteochondroma formation. FGFR3 mutations are seen in achondroplasia.

Question 3036

Topic: 4. Pediatrics

A 12-year-old boy sustains a Salter-Harris Type II fracture of the distal femur. Fracture propagation typically occurs through which specific zone of the physis, and what is the primary extracellular matrix characteristic responsible for the structural weakness in this zone?

. Reserve zone; high concentration of Type II collagen
. Proliferative zone; high concentration of aggrecan
. Hypertrophic zone; decreased ratio of extracellular matrix to cell volume
. Calcified zone; high concentration of Type X collagen
. Primary spongiosa; high concentration of Type I collagen

Correct Answer & Explanation

. Reserve zone; high concentration of Type II collagen

Explanation

Physeal fractures typically propagate through the zone of hypertrophy (specifically the provisional calcification region). The hypertrophic zone is structurally the weakest part of the physis because the chondrocytes undergo massive enlargement, resulting in a significantly decreased ratio of extracellular matrix (collagen) to cell volume. This relative lack of supportive matrix makes it highly susceptible to mechanical failure under shear or tension.

Question 3037

Topic: Pediatric Hip

A 6-year-old boy presents with a painless limp and restricted hip abduction and internal rotation. Radiographs demonstrate sclerosis and fragmentation of the capital femoral epiphysis, confirming a diagnosis of Legg-Calvé-Perthes disease (LCPD). Which of the following is the most critical prognostic factor for the long-term anatomic outcome of his hip?

. Age of the patient at the time of presentation
. Duration of symptoms prior to diagnosis
. Range of motion at initial presentation
. Presence of a metaphyseal cyst
. Gender of the patient

Correct Answer & Explanation

. Age of the patient at the time of presentation

Explanation

Age at clinical onset is the single most important prognostic factor in Legg-Calvé-Perthes disease (LCPD). Children who develop the disease before the age of 6 to 8 years generally have a much better prognosis and a higher potential for sphericity and remodeling than older children. The extent of epiphyseal involvement (e.g., the Lateral Pillar or Herring classification) is the second most important prognostic factor.

Question 3038

Topic: 4. Pediatrics

A newborn presents with multiple rib and long bone fractures, blue sclerae, and generalized osteopenia. Genetic testing reveals a mutation in the COL1A1 gene. The defective synthesis of the corresponding collagen type in this patient primarily affects which of the following structural entities?

. Articular cartilage
. Nucleus pulposus
. Basal lamina
. Bone matrix
. Hyaline cartilage

Correct Answer & Explanation

. Articular cartilage

Explanation

The clinical presentation is classic for Osteogenesis Imperfecta (OI), predominantly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, leading to defective type I collagen synthesis. Type I collagen constitutes 90% of the organic matrix of bone, providing tensile strength. It is also the major structural protein in tendons, ligaments, skin, and sclerae. Articular cartilage and the nucleus pulposus primarily contain type II collagen.

Question 3039

Topic: 4. Pediatrics

A 4-year-old boy presents with progressive bowing of his legs and short stature. Laboratory studies reveal a normal serum calcium level, significantly decreased serum phosphate, an elevated alkaline phosphatase, and normal parathyroid hormone levels. Genetic testing is most likely to reveal a loss-of-function mutation in which of the following genes?

. COL1A1
. FGFR3
. PHEX
. TNFRS11B
. ALPL

Correct Answer & Explanation

. COL1A1

Explanation

The clinical presentation and laboratory findings (normal calcium, low phosphate, normal PTH) are classic for X-linked hypophosphatemic rickets (XLH). XLH is caused by a loss-of-function mutation in the PHEX gene. This leads to an overproduction of FGF23, which results in renal phosphate wasting and decreased 1,25-dihydroxyvitamin D synthesis. COL1A1 is associated with osteogenesis imperfecta. FGFR3 is associated with achondroplasia. TNFRS11B encodes osteoprotegerin (associated with juvenile Paget's disease). ALPL encodes tissue-nonspecific alkaline phosphatase, which is mutated in hypophosphatasia.

Question 3040

Topic: Pediatric Hip

A 12-year-old obese boy presents with acute-on-chronic hip pain and an externally rotated lower extremity, consistent with a slipped capital femoral epiphysis (SCFE). In situ pinning is planned. The surgeon must employ careful technique to avoid injury to the primary blood supply of the capital femoral epiphysis, which is a terminal branch derived mainly from the:

. Ligamentum teres artery
. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Inferior gluteal artery
. Superior gluteal artery

Correct Answer & Explanation

. Ligamentum teres artery

Explanation

The medial femoral circumflex artery (MFCA) provides the predominant blood supply to the femoral head and capital femoral epiphysis in children (after age 3-4) and adults. Specifically, the lateral epiphyseal artery, a terminal branch of the deep branch of the MFCA, is the most critical vessel, and injury to it significantly increases the risk of avascular necrosis.

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