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4. Pediatrics MCQs

Practice Set 281 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 5601

Topic: Pediatric Hip

A 6-week-old female infant is undergoing treatment for developmental dysplasia of the hip (DDH) utilizing a Pavlik harness. Ultrasound evaluation at 4 weeks into treatment demonstrates that the left hip remains persistently dislocated. What is the most appropriate next step in management?

. Add a hip abduction brace directly over the Pavlik harness
. Continue the Pavlik harness for an additional 4 weeks and re-evaluate
. Switch to double-diapering therapy
. Abandon the harness and plan for closed reduction and spica casting
. Proceed to immediate open reduction and femoral shortening osteotomy

Correct Answer & Explanation

. Abandon the harness and plan for closed reduction and spica casting

Explanation

If a dislocated hip fails to reduce after 3 to 4 weeks of proper Pavlik harness treatment, the harness should be abandoned to prevent "Pavlik harness disease" (damage to the posterior acetabular wall). The next step is a closed reduction and spica casting or a rigid orthosis.

Question 5602

Topic: Pediatric Hip

A 13-year-old overweight boy is diagnosed with an unstable slipped capital femoral epiphysis (SCFE). Which of the following factors most significantly increases his risk of developing avascular necrosis (AVN) following treatment?

. Preoperative slip angle greater than 50 degrees
. Inability to bear weight on the affected limb prior to surgery
. Use of two screws instead of a single screw for fixation
. Base of neck capsulotomy performed during the procedure
. Initiation of physical therapy within the first postoperative week

Correct Answer & Explanation

. Inability to bear weight on the affected limb prior to surgery

Explanation

An unstable SCFE, defined clinically by the inability to bear weight even with crutches, carries a significantly higher risk of AVN (up to 50%) compared to stable slips. Capsulotomy may actually reduce intracapsular pressure, potentially lowering AVN risk.

Question 5603

Topic: Pediatric Hip

A 4-month-old infant is being treated for developmental dysplasia of the hip (DDH) with a Pavlik harness. During a follow-up ultrasound, the hip remains dislocated, and the infant demonstrates decreased active knee extension on the affected side. What is the most likely cause of this neurologic finding?

. Obturator nerve palsy from excessive hip abduction
. Sciatic nerve palsy from excessive hip flexion
. Femoral nerve palsy from hyperflexion of the hip
. Peroneal nerve palsy from strap compression at the fibular head
. Tibial nerve palsy from tight foot straps

Correct Answer & Explanation

. Femoral nerve palsy from hyperflexion of the hip

Explanation

Femoral nerve palsy in a Pavlik harness is typically caused by excessive hip flexion pressing the nerve against the inguinal ligament. It presents with decreased active knee extension and requires immediate loosening or removal of the harness.

Question 5604

Topic: Pediatric Lower Extremity

During the Ponseti method for correcting idiopathic clubfoot, what is the correct order of deformity correction?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method follows the CAVE sequence: Cavus is corrected first by elevating the first ray. This is followed by correcting Adductus and Varus simultaneously via gradual abduction, with Equinus corrected last (often requiring a tenotomy).

Question 5605

Topic: Pediatric Hip

A 4-month-old infant with developmental dysplasia of the hip (DDH) is treated with a Pavlik harness. Two weeks later, the parents report the infant has stopped kicking the affected leg. Examination reveals absent active knee extension. What is the most likely cause?

. Sciatic nerve palsy from excessive hip flexion
. Femoral nerve palsy from excessive hip flexion
. Obturator nerve palsy from excessive abduction
. Avascular necrosis of the femoral head
. Inferior hip dislocation

Correct Answer & Explanation

. Femoral nerve palsy from excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment caused by excessive hip flexion. It typically resolves spontaneously when the hyperflexion is corrected or the harness is temporarily removed.

Question 5606

Topic: Pediatric Hip

A 6-year-old boy presents with a painless limp and limited hip internal rotation. Radiographs show fragmentation and sclerosis of the proximal femoral epiphysis. Which vascular structure's compromise is primarily implicated in the pathogenesis of this disease?

. Artery of the ligamentum teres
. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Inferior gluteal artery
. Superior gluteal artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The presentation is classic for Legg-Calve-Perthes disease. The blood supply to the femoral head at this age depends heavily on the lateral epiphyseal branches of the medial femoral circumflex artery.

Question 5607

Topic: Pediatric Hip

A 6-year-old boy presents with a persistent right leg limp and anterior thigh pain. Radiographs reveal a fragmented, sclerotic proximal femoral epiphysis consistent with Legg-Calve-Perthes disease. Which of the following is considered the most significant prognostic factor at the time of initial presentation?

. Age of the patient at clinical onset
. Patient sex
. Body mass index
. Duration of the limp
. Degree of internal rotation lost

Correct Answer & Explanation

. Age of the patient at clinical onset

Explanation

Age at clinical onset is the most critical prognostic factor in Legg-Calve-Perthes disease. Patients who develop the disease before the age of 6 generally have a better prognosis and greater potential for spherical remodeling of the femoral head.

Question 5608

Topic: Pediatric Hip

A 3-month-old infant is being treated in a Pavlik harness for developmental dysplasia of the hip (DDH). The mother brings the child in because she notices the baby is no longer actively kicking the affected leg, although the toes continue to move. What is the most likely complication occurring in this patient?

. Sciatic nerve palsy
. Femoral nerve palsy
. Obturator nerve palsy
. Avascular necrosis of the femoral head
. Inferior dislocation of the hip

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, typically caused by hyperflexion of the hip which compresses the nerve against the rim of the pelvis. Treatment requires immediate adjustment or removal of the harness until active quadriceps function returns.

Question 5609

Topic: Pediatric Lower Extremity

A 10-day-old infant is diagnosed with idiopathic clubfoot (talipes equinovarus). The orthopedic surgeon plans to initiate the Ponseti method of serial casting. What is the correct sequence of deformity correction in this method?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The Ponseti method systematically corrects clubfoot deformities using the 'CAVE' sequence: first Cavus (by elevating the first ray), then Adductus, then Varus, and finally Equinus (often requiring a percutaneous Achilles tenotomy).

Question 5610

Topic: 4. Pediatrics

Which of the following mutations is responsible for the development of achondroplasia?

. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in FGFR3
. Mutation in COL1A1 or COL1A2
. Mutation in CBFA1 (RUNX2)
. Mutation in the COMP gene

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3

Explanation

Achondroplasia is the most common form of short-limbed dwarfism and is caused by an autosomal dominant, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation leads to constitutive activation of the receptor, which severely inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 5611

Topic: 4. Pediatrics
A 4-year-old child with a history of multiple fractures following minor trauma is diagnosed with osteogenesis imperfecta type I. This condition is primarily characterized by a quantitative defect in which of the following collagens?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta (OI) type I is the most common and mildest form of OI, characterized by a quantitative defect (decreased production) of structurally normal Type I collagen, usually due to mutations in COL1A1 or COL1A2. Type I collagen is the primary structural protein found in bone, tendon, and skin.

Question 5612

Topic: 4. Pediatrics
A patient with chronic kidney disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies show hypocalcemia, hypophosphatemia, elevated parathyroid hormone (PTH), and elevated alkaline phosphatase. Radiographs reveal Looser zones. Which of the following is the primary pathophysiologic defect?
. Excessive production of unmineralized osteoid
. Increased osteoclastic bone resorption out of proportion to formation
. Defective collagen synthesis in bone matrix
. Constitutive activation of FGFR3
. Mutation in the tissue-nonspecific alkaline phosphatase (TNSALP) gene

Correct Answer & Explanation

. Excessive production of unmineralized osteoid

Explanation

The clinical picture and laboratory findings are consistent with osteomalacia. Osteomalacia is characterized by a defect in the mineralization of the newly formed bone matrix, leading to an accumulation of excessive, unmineralized osteoid. Looser zones (pseudofractures) are a radiographic hallmark.

Question 5613

Topic: 4. Pediatrics

In a child with spastic diplegic cerebral palsy, the crouch gait pattern is most commonly caused by contracture or spasticity of which muscle group?

. Hip adductors
. Gastrocnemius-soleus complex
. Hamstrings
. Quadriceps
. Tibialis anterior

Correct Answer & Explanation

. Hamstrings

Explanation

A crouch gait in cerebral palsy is characterized by excessive hip and knee flexion and ankle dorsiflexion during the stance phase. This is most commonly caused by overactivity or contracture of the hamstrings and hip flexors. Hamstring lengthening is often required to address crouch gait.

Question 5614

Topic: Pediatric Hip

In the evaluation of a 7-year-old boy with Legg-Calve-Perthes disease, the Herring lateral pillar classification is used on AP pelvis radiographs. A patient classified as Herring Group C has which of the following characteristics?

. No involvement of the lateral pillar
. >50% maintained lateral pillar height
. <50% maintained lateral pillar height
. Extrusion of the femoral head laterally
. Subchondral fracture line (crescent sign)

Correct Answer & Explanation

. <50% maintained lateral pillar height

Explanation

The Herring lateral pillar classification assesses the height of the lateral portion of the capital femoral epiphysis during the fragmentation stage. Group A has no involvement; Group B maintains >50% of the lateral pillar height; Group C maintains <50% of lateral pillar height. Group C portends the worst prognosis.

Question 5615

Topic: Pediatric Hip

A 12-year-old obese boy presents with acute on chronic left hip pain and inability to bear weight. He is diagnosed with an unstable Slipped Capital Femoral Epiphysis (SCFE). In addition to urgent in situ fixation, which of the following statements regarding the risk of avascular necrosis (AVN) in this condition is true?

. Unstable SCFE carries a >40% risk of AVN, whereas stable SCFE carries <5% risk
. The risk of AVN is lower in unstable SCFE compared to stable SCFE
. Capsulotomy has been definitively proven in all large prospective trials to eliminate AVN risk
. Prophylactic pinning of the contralateral hip decreases the AVN risk of the affected hip
. The primary blood supply compromised in SCFE AVN is the anterior retinacular artery

Correct Answer & Explanation

. Unstable SCFE carries a >40% risk of AVN, whereas stable SCFE carries <5% risk

Explanation

An unstable SCFE (defined by Loder as the inability to bear weight even with crutches) is a surgical emergency with a high risk of avascular necrosis, reported to be up to 40-50%. In contrast, stable SCFE has a very low AVN risk (<5%). The lateral epiphyseal vessels (branches of the medial femoral circumflex artery) are the primary compromised vessels.

Question 5616

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. Which of the following best describes the genetic inheritance and molecular pathogenesis of this condition?

. Autosomal recessive, loss of function in FGFR3
. Autosomal dominant, gain of function in FGFR3
. X-linked recessive, loss of function in FGFR3
. Autosomal dominant, loss of function in COMP
. Autosomal recessive, gain of function in SOX9

Correct Answer & Explanation

. Autosomal dominant, gain of function in FGFR3

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation aberrantly inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 5617

Topic: 4. Pediatrics
A newborn presents with multiple fractures, blue sclerae, and profound osteopenia. Osteogenesis imperfecta (OI) is suspected. The classic forms of this disease are caused by mutations in COL1A1 or COL1A2 genes, which primarily result in defects of which structural protein?
. Type II collagen
. Type III collagen
. Type I collagen
. Elastin
. Fibrillin-1

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is a genetic disorder of connective tissue primarily caused by quantitative or qualitative defects in Type I collagen, the major organic component of bone matrix.

Question 5618

Topic: Pediatric Hip

A 12-year-old obese boy presents with acute-on-chronic left hip pain. He is brought in via wheelchair and is completely unable to bear weight. Radiographs show a slipped capital femoral epiphysis (SCFE). He is scheduled for in situ pinning. What is the most significant complication risk associated with his specific presentation?

. Chondrolysis
. Osteoarthritis
. Avascular necrosis of the femoral head
. Leg length discrepancy
. Femoral shaft fracture

Correct Answer & Explanation

. Avascular necrosis of the femoral head

Explanation

The patient has an unstable SCFE, clinically defined by the inability to bear weight even with crutches. Unstable SCFE carries a dramatically higher risk of avascular necrosis of the femoral head (up to 47%) compared to stable SCFE.

Question 5619

Topic: Pediatric Hip

A 13-year-old obese male presents with knee pain and a limp. Examination shows obligatory external rotation of the hip during passive flexion. He is diagnosed with a stable Slipped Capital Femoral Epiphysis (SCFE). What is the primary blood supply at risk during in situ pinning of this condition?

. Anterior retinacular artery
. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Artery of the ligamentum teres
. Inferior gluteal artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the femoral head in adolescents and adults. Its deep branch gives rise to the lateral epiphyseal (retinacular) vessels, which are critically vulnerable during both the natural progression of SCFE and its surgical fixation, risking avascular necrosis (AVN).

Question 5620

Topic: Pediatric Hip

A 4-month-old female is diagnosed with Developmental Dysplasia of the Hip (DDH). During an ultrasound evaluation, the alpha angle is measured. In the Graf classification, what does the alpha angle represent, and what is the normal value in a mature infant hip?

. Measures the cartilaginous roof; normal > 50 degrees
. Measures the cartilaginous roof; normal > 60 degrees
. Measures the bony roof (acetabular concavity); normal > 60 degrees
. Measures the bony roof (acetabular concavity); normal < 50 degrees
. Measures femoral head coverage; normal > 50%

Correct Answer & Explanation

. Measures the bony roof (acetabular concavity); normal > 60 degrees

Explanation

In Graf's ultrasound classification for DDH, the alpha angle measures the osseous (bony) roof of the acetabulum (the concavity of the iliac bone). A normal alpha angle (representing a Type I hip) is 60 degrees or greater. The beta angle measures the cartilaginous roof.

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