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4. Pediatrics MCQs

Practice Set 320 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 6381

Topic: Pediatric Hip

Developmental dysplasia of the hip (DDH) has several known risk factors, including breech presentation. What is the primary biomechanical mechanism by which breech positioning in utero increases the risk of DDH?

. Increased maternal relaxin crossing the placenta
. Forced hip extension and adduction restricting normal acetabular development
. Direct trauma to the greater trochanter during delivery
. Decreased amniotic fluid volume causing generalized joint contractures
. Asymmetric tension on the iliopsoas tendon

Correct Answer & Explanation

. Forced hip extension and adduction restricting normal acetabular development

Explanation

Correct Answer: Forced hip extension and adduction restricting normal acetabular developmentBreech presentation forces the fetal hips into extreme flexion and limits abduction (often forcing adduction or extension depending on the exact breech type, but primarily restricting the normal flexed/abducted posture). This mechanical restriction prevents the femoral head from properly seating and stimulating the development of a deep, concentric acetabulum.

Question 6382

Topic: 4. Pediatrics

A Salter-Harris Type II fracture involves the physis and extends through the metaphysis. The characteristic metaphyseal bone fragment that remains attached to the epiphysis is known by which of the following eponyms?

. Codman's triangle
. Thurston-Holland fragment
. Barton's fragment
. Die-punch fragment
. Chaput tubercle

Correct Answer & Explanation

. Thurston-Holland fragment

Explanation

Correct Answer: Thurston-Holland fragmentIn a Salter-Harris Type II fracture, the fracture line travels through the physis and exits through the metaphysis. The triangular piece of metaphyseal bone that breaks off and remains attached to the epiphyseal fragment is classically referred to as the Thurston-Holland fragment.

Question 6383

Topic: Pediatric Hip

A 13-year-old obese boy complains of a 3-week history of right thigh and knee pain. He walks with an antalgic gait and has obligate external rotation of the right hip during passive flexion. Which of the following is the most appropriate initial management?

. Immediate physical therapy for hip range of motion
. Non-weight-bearing strictly and urgent in situ percutaneous pinning
. Closed reduction and spica cast application
. Open reduction and internal fixation through an anterior approach
. Observation with serial radiographs

Correct Answer & Explanation

. Non-weight-bearing strictly and urgent in situ percutaneous pinning

Explanation

The patient has a slipped capital femoral epiphysis (SCFE) characterized by obligate external rotation with hip flexion. Immediate non-weight-bearing and urgent in situ percutaneous pinning is required to prevent further slippage and minimize AVN risk.

Question 6384

Topic: Pediatric Hip

A 4-month-old female infant is diagnosed with developmental dysplasia of the hip (DDH) after an ultrasound shows an alpha angle of 45 degrees. The infant is placed in a Pavlik harness. Which nerve is most at risk of palsy if the harness causes excessive hip flexion?

. Sciatic nerve
. Femoral nerve
. Obturator nerve
. Superior gluteal nerve
. Lateral femoral cutaneous nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The Pavlik harness must be properly adjusted to avoid complications. Excessive hip flexion beyond 100-110 degrees places the infant at risk for femoral nerve palsy, while excessive abduction risks avascular necrosis of the femoral head.

Question 6385

Topic: Pediatric Hip

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

. The patient is male
. The patient has a body mass index greater than the 95th percentile
. The patient has underlying panhypopituitarism
. The patient is exactly 12 years of age
. The patient has radiographic retroversion of the acetabulum

Correct Answer & Explanation

. The patient has underlying panhypopituitarism

Explanation

Prophylactic pinning of the contralateral hip is strongly indicated in patients with endocrine disorders, such as panhypopituitarism, hypothyroidism, or renal osteodystrophy. These patients have a significantly higher risk of developing bilateral SCFE compared to the idiopathic population.

Question 6386

Topic: Pediatric Hip

A 6-month-old female with developmental dysplasia of the hip (DDH) fails to achieve stable reduction after 4 weeks of compliant Pavlik harness treatment. What is the most appropriate next step in management?

. Continue Pavlik harness for an additional 4 weeks
. Transition to a rigid abduction orthosis (e.g., Ilfeld splint)
. Closed reduction and spica casting under general anesthesia
. Open reduction and spica casting
. Varus derotational osteotomy of the proximal femur

Correct Answer & Explanation

. Closed reduction and spica casting under general anesthesia

Explanation

If a Pavlik harness fails to reduce the hip after 3 to 4 weeks, it must be discontinued to prevent "Pavlik harness disease" (posterior acetabular wear and worsening dysplasia). The standard next step for a 6-month-old is a closed reduction and spica casting under anesthesia.

Question 6387

Topic: Pediatric Hip

A 13-year-old obese boy presents with acute on chronic groin pain and an inability to bear weight. Radiographs show a severe slipped capital femoral epiphysis. Following in situ pinning, he develops severe stiffness and pain with any hip motion. Radiographs now show symmetric joint space narrowing. What is the most likely complication?

. Avascular necrosis
. Chondrolysis
. Femoral neck fracture
. Deep space infection
. Screw cut-out

Correct Answer & Explanation

. Chondrolysis

Explanation

Chondrolysis is characterized by acute onset of severe stiffness and joint space narrowing after SCFE, particularly associated with unrecognized penetrating hardware. It leads to profound, rapid loss of articular cartilage and a painfully stiff hip.

Question 6388

Topic: 4. Pediatrics

A 12-year-old girl is diagnosed with multiple hereditary exostoses (MHE). Radiographs show multiple bony projections with cortico-medullary continuity.

The genetic mutation responsible for this condition primarily affects the synthesis of which of the following?

. Type I collagen
. Heparan sulfate
. Chondroitin sulfate
. Fibroblast growth factor receptor 3 (FGFR3)
. Runx2 transcription factor

Correct Answer & Explanation

. Heparan sulfate

Explanation

Multiple hereditary exostoses are caused by mutations in the EXT1 or EXT2 genes, which are tumor suppressors involved in the biosynthesis of heparan sulfate. This disruption affects Indian Hedgehog signaling and normal growth plate regulation.

Question 6389

Topic: 4. Pediatrics

A 15-year-old male presents with multiple painless, bony bumps around his knees and wrists. Radiographs reveal multiple pedunculated lesions growing away from the adjacent joints. Genetic testing is ordered. What is the underlying biochemical consequence of the most likely genetic mutation?

. Defect in type I collagen synthesis
. Defect in heparan sulfate proteoglycan synthesis
. Overactivation of the FGFR3 receptor
. Mutation in the GNAS1 gene
. Defect in the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Defect in heparan sulfate proteoglycan synthesis

Explanation

This patient has Multiple Hereditary Exostoses (MHE), an autosomal dominant condition caused by mutations in the EXT1 or EXT2 genes. These genes are responsible for the synthesis of heparan sulfate proteoglycans, which are essential for normal physeal signaling.

Question 6390

Topic: 4. Pediatrics

A 9-year-old child presents with short stature, fine sparse hair, and a bulbous, "pear-shaped" nasal tip. Hand radiographs are shown.

What genetic mutation is primarily associated with this syndrome?

. EXT1
. COMP
. FGFR3
. TRPS1
. COL2A1

Correct Answer & Explanation

. TRPS1

Explanation

The clinical presentation and cone-shaped epiphyses shown in the radiograph are classic for Trichorhinophalangeal Syndrome (TRPS) Type I. This condition is caused by mutations in the TRPS1 gene, which encodes a zinc finger transcription factor.

Question 6391

Topic: Pediatric Hip
Children with Trichorhinophalangeal Syndrome (TRPS) Type I are at an increased risk of developing which of the following hip pathologies, which frequently mimics a distinct pediatric orthopedic condition?
. Slipped capital femoral epiphysis
. Legg-Calvé-Perthes-like avascular necrosis of the femoral head
. Developmental dysplasia of the hip with frank dislocation
. Coxa vara due to a primary ossification defect
. Recurrent transient synovitis of the hip

Correct Answer & Explanation

. Legg-Calvé-Perthes-like avascular necrosis of the femoral head

Explanation

Patients with TRPS commonly develop early-onset degenerative changes and avascular necrosis-like fragmentation of the femoral head. These radiographic and clinical findings closely mimic Legg-Calvé-Perthes disease, necessitating routine clinical and radiographic hip screening.

Question 6392

Topic: Pediatric Hip

A 12-year-old boy presents with short stature, a bulbous nose, and sparse scalp hair. Radiographs of his hands demonstrate cone-shaped epiphyses in the phalanges. Which of the following orthopedic hip conditions is strongly associated with this genetic syndrome?

. Protrusio acetabuli
. Slipped capital femoral epiphysis
. Coxa vara
. Legg-Calve-Perthes-like changes
. Femoroacetabular impingement

Correct Answer & Explanation

. Legg-Calve-Perthes-like changes

Explanation

This patient has Trichorhinophalangeal syndrome type 1 (TRPS1). Along with cone-shaped epiphyses of the phalanges, these patients frequently develop premature osteoarthritis of the hip secondary to Legg-Calve-Perthes-like avascular necrosis changes.

Question 6393

Topic: Pediatric Hip
Which of the following combinations of clinical and radiographic findings best distinguishes Trichorhinophalangeal syndrome (TRPS) Type I from Legg-Calvé-Perthes disease when evaluating a child with hip pain?
. Unilateral hip involvement with normal hand radiographs
. Bilateral severe coxarthrosis, sparse scalp hair, and cone-shaped epiphyses in the hands
. Slipped capital femoral epiphysis with associated generalized osteosclerosis
. Unilateral femoral head fragmentation with multiple osteochondromas
. Acetabular dysplasia with an absent clavicle

Correct Answer & Explanation

. Bilateral severe coxarthrosis, sparse scalp hair, and cone-shaped epiphyses in the hands

Explanation

TRPS Type I often presents with early, severe bilateral hip joint destruction that can mimic Legg-Calvé-Perthes. It is distinguished by syndromic features including sparse hair, a bulbous nose, and cone-shaped phalangeal epiphyses.

Question 6394

Topic: 4. Pediatrics

Review the clinical hand radiograph below.

The structural abnormality seen in the phalanges is highly characteristic of TRPS. What is the underlying molecular function of the TRPS1 gene?

. It encodes a structural collagen protein (Type II collagen).
. It functions as a zinc-finger transcription factor regulating chondrocyte maturation.
. It is a cell surface receptor for fibroblast growth factor (FGFR3).
. It acts as a chloride channel in the osteoclast ruffled border.
. It regulates the cleavage of type I procollagen.

Correct Answer & Explanation

. It functions as a zinc-finger transcription factor regulating chondrocyte maturation.

Explanation

The radiograph shows cone-shaped epiphyses typical of Trichorhinophalangeal syndrome (TRPS). The TRPS1 gene encodes a zinc-finger transcription factor that is essential for normal chondrocyte proliferation and apoptosis in the growth plate.

Question 6395

Topic: Pediatric Hip
A 12-year-old girl is diagnosed with TRPS1 based on facial features, sparse hair, and brachydactyly. She complains of persistent hip pain. Radiographs of her pelvis are most likely to demonstrate which of the following?
. Bilateral coxa vara with fragmented capital femoral epiphyses
. Protrusio acetabuli with severe osteopenia
. Ankylosis of the sacroiliac joints
. Coxa valga with subluxation of the femoral head
. Sclerotic 'rugger-jersey' appearance of the lumbar vertebrae

Correct Answer & Explanation

. Bilateral coxa vara with fragmented capital femoral epiphyses

Explanation

Patients with TRPS commonly develop severe, premature osteoarthritis of the hips. In childhood, this often manifests as bilateral epiphyseal fragmentation, flattening of the femoral head, and coxa vara, closely mimicking severe Legg-Calvé-Perthes disease.

Question 6396

Topic: 4. Pediatrics

A bone biopsy is obtained from a child with frequent fractures and hepatosplenomegaly.

Histological evaluation shows islands of calcified cartilage matrix persisting within mature trabecular bone. What is the diagnosis?

. Osteogenesis imperfecta
. Osteopetrosis
. Achondroplasia
. Paget's disease
. Fibrous dysplasia

Correct Answer & Explanation

. Osteopetrosis

Explanation

The persistence of primary spongiosa (calcified cartilage cores) within mature bone trabeculae is the pathognomonic histological finding of osteopetrosis. It results from fundamentally defective osteoclastic resorption during endochondral ossification.

Question 6397

Topic: 4. Pediatrics

In addition to characteristic hand deformities, patients with Trichorhinophalangeal Syndrome Type 1 (TRPS1) are most likely to develop which of the following orthopedic conditions in the lower extremities?

. Slipped capital femoral epiphysis (SCFE)
. Bilateral clubfeet
. Legg-Calve-Perthes-like avascular necrosis of the femoral head
. Congenital pseudoarthrosis of the tibia
. Blount's disease

Correct Answer & Explanation

. Legg-Calve-Perthes-like avascular necrosis of the femoral head

Explanation

TRPS1 is frequently associated with hip pathology that closely mimics Legg-Calve-Perthes disease. This avascular necrosis-like process in the femoral head can lead to premature and severe osteoarthritis.

Question 6398

Topic: Pediatric Hip
A 10-year-old male with known Trichorhinophalangeal syndrome (TRPS) presents with a painless limp and restricted hip abduction. Which of the following hip pathologies is frequently associated with TRPS type I and most likely explains his symptoms?
. Slipped capital femoral epiphysis
. Legg-Calvé-Perthes-like avascular necrosis
. Developmental dysplasia of the hip
. Femoroacetabular impingement (cam type)
. Coxa vara from subtrochanteric pseudofractures

Correct Answer & Explanation

. Legg-Calvé-Perthes-like avascular necrosis

Explanation

Patients with Trichorhinophalangeal syndrome (TRPS) frequently develop hip abnormalities that closely mimic Legg-Calvé-Perthes disease. This includes avascular necrosis-like changes and subsequent flattening of the femoral head (coxa plana).

Question 6399

Topic: 4. Pediatrics

A 45-year-old woman complains of chronic right knee pain and locking. Imaging reveals multiple intra-articular calcified loose bodies of uniform size. What is the classic pathophysiologic mechanism of this condition?

. Fragmentation of osteophytes due to advanced osteoarthritis
. Metaplasia of the synovial membrane into cartilage
. Defective endochondral ossification of the physis
. Autoimmune destruction of articular cartilage
. Chondrocyte hypertrophy induced by trauma

Correct Answer & Explanation

. Metaplasia of the synovial membrane into cartilage

Explanation

Primary synovial chondromatosis involves benign cartilaginous metaplasia of the synovial membrane, producing uniform loose bodies. This contrasts with secondary synovial chondromatosis, which results from mechanical fragmentation in degenerative joint disease and produces loose bodies of varying sizes.

Question 6400

Topic: 4. Pediatrics

Which of the following genetic mechanisms is fundamentally responsible for the pathogenesis of multiple hereditary exostoses (MHE)?

. Gain-of-function mutation in the FGFR3 gene
. Loss-of-function mutation in EXT1 or EXT2 genes resulting in defective heparan sulfate synthesis
. Translocation t(11;22) affecting the EWSR1 gene
. MDM2 gene amplification promoting cell cycle progression
. GNAS1 mutation leading to increased cyclic AMP

Correct Answer & Explanation

. Loss-of-function mutation in EXT1 or EXT2 genes resulting in defective heparan sulfate synthesis

Explanation

MHE is an autosomal dominant disorder caused by loss-of-function mutations in EXT1 or EXT2. These genes encode glycosyltransferases essential for heparan sulfate chain elongation, disrupting normal chondrocyte proliferation and differentiation.

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