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4. Pediatrics MCQs

Practice Set 260 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 5181

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying genetic pathophysiology involves an autosomal dominant gain-of-function mutation in FGFR3. Which specific zone of the physis is primarily inhibited as a result of this mutation?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Primary spongiosa
. Secondary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia results from a point mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. In normal physiology, FGFR3 limits chondrocyte proliferation. A gain-of-function mutation causes constitutive activation of the receptor, which severely inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to defective endochondral ossification.

Question 5182

Topic: 4. Pediatrics

A 6-month-old infant is evaluated for multiple fractures with minimal trauma and blue sclerae. Which of the following correctly pairs the most common mutation and its inheritance pattern for this condition?

. COL2A1, Autosomal Recessive
. COL1A1, Autosomal Dominant
. FGFR3, Autosomal Dominant
. COMP, Autosomal Dominant
. RUNX2, Autosomal Recessive

Correct Answer & Explanation

. COL1A1, Autosomal Dominant

Explanation

Osteogenesis imperfecta is most commonly caused by mutations in the COL1A1 or COL1A2 genes, which encode Type I collagen. The majority of clinical forms (such as Type I, the most common and mildest form) are inherited in an autosomal dominant pattern.

Question 5183

Topic: 4. Pediatrics

Osteogenesis Imperfecta (OI) is a genetic disorder characterized by bone fragility. At the molecular level, the most common mutation involves the substitution of which crucial amino acid in the collagen triple helix?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Glutamate

Correct Answer & Explanation

. Glycine

Explanation

OI is most commonly caused by a mutation in the COL1A1 or COL1A2 genes. This results in the substitution of glycine with a bulkier amino acid, disrupting the tight packing of the collagen triple helix.

Question 5184

Topic: 4. Pediatrics

A newborn is diagnosed with Spondyloepiphyseal Dysplasia Congenita (SEDC). This condition typically presents with a short trunk and involves abnormalities in a specific structural protein. Which genetic mutation is primarily responsible?

. COL1A1
. COL2A1
. COL10A1
. COMP
. FGFR3

Correct Answer & Explanation

. COL2A1

Explanation

SEDC is an autosomal dominant disorder caused by a mutation in the COL2A1 gene, leading to defective Type II collagen. This protein is essential for normal articular cartilage and the nucleus pulposus.

Question 5185

Topic: 4. Pediatrics

A 10-year-old boy presents with multiple extremity fractures and blue sclerae. A mutation in the COL1A1 gene is confirmed. What specific molecular defect in collagen synthesis does this mutation most commonly cause?

. Defective cross-linking by lysyl oxidase
. Impaired hydroxylation of proline residues
. Substitution of glycine with bulkier amino acids
. Inability to cleave procollagen terminals
. Defective secretion of tropocollagen from the fibroblast

Correct Answer & Explanation

. Substitution of glycine with bulkier amino acids

Explanation

Osteogenesis imperfecta is most commonly caused by point mutations that substitute glycine with bulkier amino acids in the COL1A1 or COL1A2 genes. Because glycine is the smallest amino acid and occupies every third position, its substitution disrupts the tight assembly of the collagen triple helix.

Question 5186

Topic: 4. Pediatrics

A 5-year-old boy presents with disproportionate short stature, frontal bossing, and rhizomelic limb shortening. Genetic testing reveals a gain-of-function mutation in the FGFR3 gene. In the physeal growth plate, this mutation primarily results in:

. Increased hypertrophy of chondrocytes
. Decreased proliferation of chondrocytes
. Premature apoptosis of resting zone chondrocytes
. Overproduction of type II collagen
. Inhibition of secondary ossification center formation

Correct Answer & Explanation

. Decreased proliferation of chondrocytes

Explanation

Achondroplasia is caused by an activating mutation in the FGFR3 gene, which normally acts as a negative regulator of bone growth. Its overactivation profoundly inhibits the proliferation of chondrocytes in the proliferative zone of the physis.

Question 5187

Topic: 4. Pediatrics

A 6-year-old girl is diagnosed with Klippel-Feil syndrome based on the classic clinical triad and cervical spine radiographs showing multiple congenitally fused segments. As part of her comprehensive evaluation, which of the following screening tests is most critical to perform?

. Echocardiography for aortic root dilation
. Renal ultrasound for genitourinary anomalies
. Ophthalmic examination for lens dislocation
. Pulmonary function tests for restrictive lung disease
. DEXA scan for bone mineral density

Correct Answer & Explanation

. Renal ultrasound for genitourinary anomalies

Explanation

Klippel-Feil syndrome is a congenital disorder characterized by the failure of segmentation of two or more cervical vertebrae. The classic triad includes a short neck, low posterior hairline, and limited neck range of motion. It is highly associated with other visceral and skeletal anomalies. Up to 30-40% of patients have congenital genitourinary anomalies (e.g., unilateral renal agenesis, horseshoe kidney). Therefore, a renal ultrasound is a critical screening tool. Other associated conditions include congenital heart defects (e.g., VSD, not specifically aortic root dilation), Sprengel deformity, and hearing loss.

Question 5188

Topic: 4. Pediatrics

A 3-year-old boy presents with a limp, refusal to walk, and low-grade fever for 4 days. Inflammatory markers (ESR, CRP) are elevated. An MRI reveals fluid and enhancement in the L4-L5 disc space with adjacent vertebral body endplate edema. Which of the following statements best explains the pathophysiology of this condition in this age group?

. Direct extension from an undiagnosed urinary tract infection via Batson's plexus
. Hematogenous seeding due to the persistence of vascular channels into the intervertebral disc
. Avascular necrosis of the vertebral endplate secondary to repetitive microtrauma
. Autoimmune destruction of the annulus fibrosus triggered by a viral infection
. Congenital deficiency of the posterior longitudinal ligament

Correct Answer & Explanation

. Hematogenous seeding due to the persistence of vascular channels into the intervertebral disc

Explanation

Pediatric discitis typically affects children under the age of 5. The primary pathophysiological mechanism is hematogenous seeding of bacteria (most commonly Staphylococcus aureus). Unlike adults, children have a rich vascular supply to the intervertebral disc via vessels that penetrate the cartilaginous endplates. These vascular channels typically obliterate by around age 7 or 8. Treatment involves blood cultures, immobilization, and appropriate intravenous antibiotics.

Question 5189

Topic: Pediatric Upper Extremity & Spine

A 14-year-old girl with Adolescent Idiopathic Scoliosis is evaluated for surgery. Her standing radiographs show a main thoracic curve of 55 degrees and a lumbar curve of 35 degrees. On side-bending radiographs, her lumbar curve reduces to 15 degrees, and her proximal thoracic curve reduces to 10 degrees. How is her curve pattern classified according to the Lenke system?

. Lenke Type 1
. Lenke Type 2
. Lenke Type 3
. Lenke Type 5
. Lenke Type 6

Correct Answer & Explanation

. Lenke Type 1

Explanation

A Lenke Type 1 curve involves a structural main thoracic curve with non-structural proximal thoracic and lumbar curves. Because the lumbar curve bends out to less than 25 degrees, it is considered non-structural.

Question 5190

Topic: Pediatric Upper Extremity & Spine

A 12-year-old pre-menarchal female presents for a routine scoliosis screening. Full-length standing radiographs demonstrate a right thoracic Cobb angle of 32 degrees. Her Risser stage is 0. According to current guidelines, what is the most appropriate primary management strategy?

. Observation with repeat radiographs in 6 months
. Full-time Thoracolumbosacral orthosis (TLSO) bracing
. Nighttime only bending brace
. Posterior spinal fusion with pedicle screws
. Anterior vertebral body tethering

Correct Answer & Explanation

. Full-time Thoracolumbosacral orthosis (TLSO) bracing

Explanation

Full-time TLSO bracing (at least 16-18 hours/day) is indicated for Adolescent Idiopathic Scoliosis in skeletally immature patients (Risser 0-2, pre-menarchal) with a Cobb angle between 25 and 44 degrees to prevent further curve progression.

Question 5191

Topic: Pediatric Hip

In the surgical treatment of a patient with Crowe Type IV developmental dysplasia of the hip (DDH), the surgeon decides to place the acetabular component in the true anatomical paleocenter. What additional surgical step is most frequently required to successfully reduce the hip and minimize the risk of sciatic nerve palsy?

. Greater trochanteric advancement
. Subtrochanteric shortening osteotomy
. Extensive release of the gluteus medius
. Distal femoral lengthening osteotomy
. Placement of a jumbo acetabular component

Correct Answer & Explanation

. Subtrochanteric shortening osteotomy

Explanation

Crowe IV DDH is characterized by a high hip dislocation (>100% subluxation). Pulling the femur down to the true acetabulum stretches the surrounding neurovascular structures, particularly the sciatic nerve. To safely reduce the hip to the anatomical center without causing sciatic nerve palsy, a subtrochanteric shortening osteotomy of the femur is typically required.

Question 5192

Topic: Pediatric Hip

Metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) is occasionally considered for young, active patients. However, strict patient selection is required to prevent early failure. Which of the following patient profiles is universally considered a poor candidate (or absolute contraindication) for HRA due to high failure rates from adverse local tissue reaction and femoral neck fracture?

. A 45-year-old male with severe primary osteoarthritis and a large femoral head
. A 50-year-old male with a history of slipped capital femoral epiphysis (SCFE)
. A 38-year-old female with developmental dysplasia of the hip and a femoral head size of 42 mm
. A 55-year-old male with post-traumatic osteoarthritis and normal bone density
. A 40-year-old male with an isolated cam-type femoroacetabular impingement and cartilage loss

Correct Answer & Explanation

. A 38-year-old female with developmental dysplasia of the hip and a femoral head size of 42 mm

Explanation

Female gender, small femoral head component size (<48 mm), and underlying diagnoses of DDH or AVN (with large cystic changes) are major risk factors for failure in HRA. Small component sizes in MoM bearings lead to reduced fluid-film lubrication, higher wear rates, and increased metal ion release. Additionally, females have a higher rate of femoral neck fractures post-HRA.

Question 5193

Topic: Pediatric Hip

A 38-year-old female with Crowe Type IV developmental dysplasia of the hip (DDH) is undergoing a total hip arthroplasty. The femoral head is completely dislocated superior to the true acetabulum. To place the acetabular cup in the anatomic true acetabulum while preventing sciatic nerve stretch injury, what specific surgical adjunct is most frequently required?

. Adductor tenotomy and psoas release alone
. Subtrochanteric shortening osteotomy of the femur
. Greater trochanteric advancement
. High hip center cup placement
. Prophylactic sciatic nerve decompression

Correct Answer & Explanation

. Subtrochanteric shortening osteotomy of the femur

Explanation

In Crowe IV DDH, the hip is completely dislocated, and the soft tissues have contracted over many years. Bringing the femur down to an anatomic cup in the true acetabulum stretches the sciatic nerve, with a high risk of neuropraxia or permanent injury if the limb is lengthened more than 4 cm. A subtrochanteric shortening osteotomy of the femur is required to safely reduce the hip into the true acetabulum while protecting the sciatic nerve.

Question 5194

Topic: Pediatric Hip

A 13-year-old overweight boy presents with a 3-month history of vague left knee and thigh pain. On physical examination, as the left hip is passively flexed, it obligatorily moves into external rotation. Radiographs confirm a mild, stable slipped capital femoral epiphysis (SCFE). What is the most appropriate definitive management?

. Closed reduction and spica casting
. In situ pinning with a single cannulated screw
. Open reduction and internal fixation with multiple screws
. Subtrochanteric derotational osteotomy
. Observation and non-weight bearing with crutches

Correct Answer & Explanation

. In situ pinning with a single cannulated screw

Explanation

The patient has a stable Slipped Capital Femoral Epiphysis (SCFE). The standard of care for a mild, stable SCFE is in situ percutaneous fixation with a single cannulated screw placed in the center of the epiphysis to prevent further slippage. Closed reduction is contraindicated due to the high risk of osteonecrosis. Multiple screws do not significantly improve biomechanical stability for stable slips and increase the risk of joint penetration.

Question 5195

Topic: Pediatric Lower Extremity

In the treatment of infant clubfoot (talipes equinovarus) using the Ponseti method, serial casting follows a specific sequence to gradually correct the complex multiplanar deformity. What is the correct sequential order of deformity correction?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method requires sequential correction of the clubfoot deformity in the following order: Cavus, Adductus, Varus, and lastly Equinus (remembered by the mnemonic CAVE). The cavus is corrected first by elevating the first ray. The adductus and varus are corrected simultaneously by abducting the midfoot around the fixed head of the talus. Equinus is corrected last, often requiring a percutaneous Achilles tenotomy.

Question 5196

Topic: Pediatric Lower Extremity

In the treatment of idiopathic clubfoot using the Ponseti method, the deformities must be sequentially addressed in a specific order. Which deformity is corrected first, and what is the specific maneuver used?

. Equinus, corrected by an Achilles tenotomy
. Varus, corrected by abducting the midfoot against the talus
. Adductus, corrected by applying lateral pressure on the cuboid
. Cavus, corrected by supinating the forefoot and elevating the first ray
. Cavus, corrected by depressing the first ray

Correct Answer & Explanation

. Cavus, corrected by supinating the forefoot and elevating the first ray

Explanation

The sequence of correction in the Ponseti method follows the acronym CAVE (Cavus, Adductus, Varus, Equinus). The cavus deformity is the first to be addressed. It is corrected by supinating the forefoot and elevating the first ray to align the forefoot with the already supinated hindfoot, thus unlocking the midtarsal joint for subsequent abduction.

Question 5197

Topic: Pediatric Hip

A 12-year-old obese male presents with a confirmed slipped capital femoral epiphysis (SCFE) of the left hip. During surgical planning, prophylactic pinning of the asymptomatic contralateral right hip is considered. Which of the following is an established strong indication for prophylactic pinning of the contralateral hip?

. Male sex alone
. Age older than 14 years at presentation
. Presence of an underlying endocrine disorder (e.g., hypothyroidism)
. BMI > 95th percentile alone
. Bilateral hip pain with strictly normal radiographs on the right

Correct Answer & Explanation

. Presence of an underlying endocrine disorder (e.g., hypothyroidism)

Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but is universally recommended in patients with an intrinsically high risk for a subsequent contralateral slip. Established high-risk factors include underlying endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy), prior radiation therapy to the pelvis, and a very young age at presentation (typically girls <10 years or boys <12 years).

Question 5198

Topic: 4. Pediatrics

A 6-year-old boy falls on an outstretched hand and presents with a displaced lateral condyle fracture of the humerus. Which of the following is the most compelling anatomical and clinical reason to perform an anatomic open reduction and internal fixation (ORIF) for this specific pediatric fracture?

. To prevent immediate acute radial nerve palsy
. To prevent a cosmetic cubitus varus deformity
. Because it is an intra-articular physeal fracture (Salter-Harris IV) heavily prone to nonunion
. To allow for immediate weight-bearing on the upper extremity
. Because closed reduction predictably causes immediate and total premature physeal closure

Correct Answer & Explanation

. Because it is an intra-articular physeal fracture (Salter-Harris IV) heavily prone to nonunion

Explanation

Pediatric lateral condyle fractures are typically Salter-Harris type IV injuries, meaning the fracture line crosses the physis and completely enters the articular joint space. The fracture fragment is subjected to constant pull by the extensor origin and is continuously bathed in synovial fluid (which inhibits primary bone healing). Consequently, non-anatomic reduction has an exceptionally high rate of nonunion, potentially leading to progressive cubitus valgus and tardy ulnar nerve palsy. Displaced fractures (>2mm) mandate ORIF.

Question 5199

Topic: Pediatric Hip

A 13-year-old obese male presents with acute-on-chronic left groin pain and an obligatory external rotation of the hip during flexion. Radiographs confirm a severe slipped capital femoral epiphysis (SCFE). What is the most devastating potential complication of treating this condition with in-situ single screw fixation?

. Chondrolysis
. Osteonecrosis (AVN)
. Femoral neck fracture
. Implant failure
. Infection

Correct Answer & Explanation

. Osteonecrosis (AVN)

Explanation

Osteonecrosis is the most devastating complication of SCFE and is associated with acute unstable slips, forceful reduction, and hardware penetration into the joint. In-situ fixation aims to minimize this risk, but AVN remains a primary concern in severe or unstable cases.

Question 5200

Topic: Pediatric Hip

A 4-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). The mother reports that the child has stopped kicking the affected leg. On examination, there is decreased active knee extension. What is the most likely cause?

. Obturator nerve palsy
. Sciatic nerve palsy
. Femoral nerve palsy
. Tibial nerve palsy
. Common peroneal nerve palsy

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Femoral nerve palsy is a known complication of the Pavlik harness, typically caused by excessive hyperflexion of the hip. Treatment involves temporary removal or adjustment of the harness until neurologic function returns.

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