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4. Pediatrics MCQs

Practice Set 280 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 5581

Topic: Pediatric Hip

A 12-year-old obese boy presents with an acute exacerbation of chronic left knee pain and an inability to bear weight. Radiographs demonstrate a severe slipped capital femoral epiphysis (SCFE). He undergoes in situ pinning. What is the most devastating complication associated with an acute-on-chronic SCFE treated with pinning?

. Chondrolysis
. Osteonecrosis of the femoral head
. Femoroacetabular impingement
. Slipped contralateral epiphysis
. Premature physeal closure

Correct Answer & Explanation

. Osteonecrosis of the femoral head

Explanation

Osteonecrosis (avascular necrosis) is the most devastating complication of SCFE. It is significantly more common in unstable slips (where the patient cannot bear weight) and its risk is exacerbated by forceful reduction or improper pin placement in the posterosuperior quadrant.

Question 5582

Topic: Pediatric Hip

When evaluating developmental dysplasia of the hip (DDH) via Graf's ultrasound method, the alpha angle is measured. What does the alpha angle represent, and what is the normal value for a 6-week-old infant?

. Measurement of the cartilaginous roof; normal is > 60 degrees
. Measurement of the bony roof; normal is > 60 degrees
. Measurement of the bony roof; normal is < 55 degrees
. Measurement of the cartilaginous roof; normal is < 55 degrees
. Measurement of the bony roof; normal is > 43 degrees

Correct Answer & Explanation

. Measurement of the cartilaginous roof; normal is > 60 degrees

Explanation

The alpha angle in Graf's ultrasound classification evaluates the concavity and depth of the bony acetabular roof. A normal alpha angle (Type I hip) is 60 degrees or greater. The beta angle measures the cartilaginous roof and normally is < 55 degrees.

Question 5583

Topic: Pediatric Lower Extremity

According to the Ponseti method for the treatment of idiopathic clubfoot, what is the correct sequence of deformity correction?

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

Correct Answer & Explanation

. Cavus, Adductus, Varus, Equinus

Explanation

The correct sequence of correction in the Ponseti method is remembered by the acronym CAVE: Cavus (elevate the first ray to supinate the forefoot), Adductus, Varus, and finally Equinus. The equinus correction often requires a percutaneous Achilles tenotomy as the final step.

Question 5584

Topic: Pediatric Hip

Which of the following endocrine disorders is most strongly associated with Slipped Capital Femoral Epiphysis (SCFE) in a patient presenting under the age of 10, frequently warranting prophylactic pinning of the contralateral hip?

. Hyperthyroidism
. Hypothyroidism
. Cushing's syndrome
. Addison's disease
. Hyperparathyroidism

Correct Answer & Explanation

. Hypothyroidism

Explanation

Hypothyroidism is the most common endocrine disorder associated with SCFE. Patients presenting with SCFE at an atypical age (< 10 years or > 16 years), or those with extreme short stature, should be evaluated for endocrine abnormalities, particularly hypothyroidism and growth hormone deficiency. Because the risk of bilateral involvement is very high in endocrine-associated SCFE, prophylactic pinning of the contralateral hip is generally indicated.

Question 5585

Topic: 4. Pediatrics

A researcher is evaluating the physeal growth plate of a pediatric animal model. Which specific zone is primarily characterized by the synthesis of Type X collagen and high levels of alkaline phosphatase?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of hypertrophy
. Primary spongiosa

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

The zone of hypertrophy in the physis prepares the matrix for calcification. The hypertrophic chondrocytes uniquely secrete Type X collagen and alkaline phosphatase, which are critical for matrix mineralization during endochondral ossification.

Question 5586

Topic: 4. Pediatrics

A pediatric patient presents with disproportionate short stature, frontal bossing, and rhizomelic shortening of the limbs. Which of the following describes the pathophysiology of the underlying genetic mutation?

. Defect in type 1 collagen synthesis
. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in the RUNX2 gene
. Defect in COMP (cartilage oligomeric matrix protein)
. Impaired osteoclast function due to TCIRG1 mutation

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This overactivity inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to decreased enchondral ossification.

Question 5587

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. The underlying autosomal dominant genetic mutation results in the abnormal function of which of the following physeal structures?

. Resting zone of the physis
. Proliferative zone of the physis
. Hypertrophic zone of the physis
. Primary spongiosa
. Secondary center of ossification

Correct Answer & Explanation

. Proliferative zone of the physis

Explanation

Achondroplasia is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This continuously activated receptor inhibits chondrocyte proliferation in the proliferative zone of the physis, disrupting normal endochondral ossification.

Question 5588

Topic: 4. Pediatrics

A 10-year-old child presents with short stature, waddling gait, and hip pain. Radiographs reveal delayed, fragmented, and flattened capital femoral epiphyses, but the spine appears radiographically normal. A mutation in which of the following genes is the most common cause of this condition?

. COMP (Cartilage oligomeric matrix protein)
. COL2A1 (Type II collagen)
. FGFR3 (Fibroblast growth factor receptor 3)
. SLC26A2 (Sulfate transporter)
. RUNX2 (CBFA1)

Correct Answer & Explanation

. COMP (Cartilage oligomeric matrix protein)

Explanation

The presentation of abnormal epiphyses with a normal spine is classic for Multiple Epiphyseal Dysplasia (MED). MED is most commonly caused by an autosomal dominant mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene on chromosome 19.

Question 5589

Topic: 4. Pediatrics

Achondroplasia is an autosomal dominant condition characterized by a mutation in the FGFR3 gene. Which zone of the physis is primarily affected by this mutation?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which pathologically inhibits chondrocyte proliferation. Therefore, the proliferative zone of the physis is significantly narrowed and functionally impaired.

Question 5590

Topic: 4. Pediatrics

A 2-year-old child presents with bowing of the lower extremities and widening of the physes on radiographs. Laboratory studies reveal hypophosphatemia and elevated alkaline phosphatase. Which zone of the physis is abnormally widened in this condition?

. Resting zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Metaphysis

Correct Answer & Explanation

. Hypertrophic zone

Explanation

The patient has rickets, characterized by a failure of mineralization in the zone of provisional calcification. This failure leads to an accumulation of chondrocytes and profound widening of the hypertrophic zone.

Question 5591

Topic: 4. Pediatrics

In an acute slipped capital femoral epiphysis (SCFE), the mechanical failure and subsequent displacement primarily occur through which specific zone of the physis?

. Resting zone
. Proliferative zone
. Zone of hypertrophy
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

SCFE and most Salter-Harris fractures classically occur through the zone of hypertrophy of the physis. This zone is biomechanically the weakest due to the large size of chondrocytes and minimal extracellular matrix.

Question 5592

Topic: 4. Pediatrics

In the normal epiphyseal growth plate, which zone is the primary site of longitudinal bone growth and is structurally the weakest, making it the most common site for Salter-Harris fractures?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

The hypertrophic zone exhibits a massive increase in cell volume but lacks significant extracellular matrix and collagen. This makes it structurally the weakest point of the physis and the most common site of failure.

Question 5593

Topic: 4. Pediatrics

Achondroplasia is an autosomal dominant disorder characterized by rhizomelic dwarfism. It is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. What is the normal physiologic function of FGFR3 in the growth plate?

. Stimulates chondrocyte hypertrophy
. Promotes chondrocyte apoptosis
. Inhibits chondrocyte proliferation
. Stimulates vascular invasion
. Inhibits osteoclast activity

Correct Answer & Explanation

. Inhibits chondrocyte proliferation

Explanation

In the normal physis, FGFR3 acts as a negative regulator of bone growth by inhibiting chondrocyte proliferation and differentiation. A gain-of-function mutation results in excessive inhibition of these cells, leading to diminished endochondral ossification.

Question 5594

Topic: 4. Pediatrics

Which of the following describes the fundamental genetic defect in the most common form of short-limbed dwarfism?

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

Correct Answer & Explanation

. Gain-of-function mutation in the FGFR3 gene

Explanation

Achondroplasia is the most common short-limbed dwarfism. It 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 acts to inhibit chondrocyte proliferation in the proliferative zone of the physis.

Question 5595

Topic: 4. Pediatrics

An infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At follow-up, it is noted that the anterior straps have been overly tightened by the parents, holding the hips in excessive flexion. Which of the following complications is the child most at risk for developing?

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

Correct Answer & Explanation

. Femoral nerve palsy

Explanation

Hyperflexion of the hips in a Pavlik harness (typically >120 degrees) can compress the femoral nerve against the inguinal ligament, leading to an iatrogenic femoral nerve palsy. Excessive abduction, on the other hand, puts the child at risk for avascular necrosis (AVN) of the femoral head.

Question 5596

Topic: Pediatric Hip

Following in-situ pinning of a severe slipped capital femoral epiphysis (SCFE), a 15-year-old patient develops symptomatic femoroacetabular impingement (FAI). Which of the following anatomic abnormalities is the primary cause of this impingement?

. Pincer-type impingement from acetabular retroversion
. Cam-type impingement from anterolateral metaphyseal prominence
. Subspinous impingement from AIIS hypertrophy
. Ischiofemoral impingement from residual coxa vara
. Pincer-type impingement from coxa magna

Correct Answer & Explanation

. Cam-type impingement from anterolateral metaphyseal prominence

Explanation

In a severe SCFE, the femoral epiphysis slips posteriorly and medially relative to the metaphysis. This leaves the anterolateral metaphysis prominent. During hip flexion and internal rotation, this bony prominence abuts the anterior acetabular rim, causing classic cam-type femoroacetabular impingement.

Question 5597

Topic: 4. Pediatrics

Achondroplasia is an autosomal dominant skeletal dysplasia caused by a gain-of-function mutation in the FGFR3 gene. This mutation directly impairs enchondral ossification primarily in which zone of the physis?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

The activating mutation in FGFR3 leads to abnormal inhibition of chondrocyte proliferation. This primary defect manifests in the proliferative zone of the growth plate, resulting in short-limb dwarfism.

Question 5598

Topic: Pediatric Hip

A 10-year-old girl presents with a unilateral slipped capital femoral epiphysis (SCFE). She is at the 15th percentile for weight and 10th percentile for height. Considering her atypical presentation for SCFE, she undergoes an endocrine workup. Which of the following underlying conditions is the strongest indication for prophylactic pinning of the contralateral asymptomatic hip?

. Hyperthyroidism
. Hypothyroidism
. Type 1 Diabetes Mellitus
. Hyperparathyroidism
. Achondroplasia

Correct Answer & Explanation

. Hypothyroidism

Explanation

Patients with SCFE who present outside the typical age range (girls 11-13, boys 13-15) or who are not overweight should be evaluated for endocrine disorders. Hypothyroidism is the most common endocrine disorder associated with SCFE. Bilateral involvement is significantly higher in patients with endocrine disorders, and prophylactic pinning of the contralateral hip is highly recommended in this population to prevent a future slip.

Question 5599

Topic: Pediatric Hip

A 4-month-old female infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the mother notes the child is no longer kicking her right leg. Examination reveals decreased quadriceps tone and an absent patellar reflex on the right. What positioning error in the Pavlik harness typically leads to this complication?

. Excessive flexion of the hip
. Excessive extension of the hip
. Excessive abduction of the hip
. Excessive adduction of the hip
. Excessive internal rotation of the hip

Correct Answer & Explanation

. Excessive flexion of the hip

Explanation

The clinical picture describes a femoral nerve palsy, a known complication of Pavlik harness treatment. This is caused by excessive flexion of the hip, which can compress the femoral nerve against the inguinal ligament. Excessive abduction, on the other hand, is associated with a different severe complication: avascular necrosis (AVN) of the femoral head due to compression of the posterior circumflex femoral artery.

Question 5600

Topic: Pediatric Upper Extremity & Spine
A 6-year-old boy sustains a severe Gartland Type III supracondylar humerus fracture. Radiographs show the distal fragment is displaced posteromedially. Based on this displacement pattern, which neurovascular structure is at the greatest risk of injury?
. Median nerve
. Radial nerve
. Ulnar nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Radial nerve

Explanation

In a posteromedial displacement of a supracondylar humerus fracture, the proximal fragment is pushed anterolaterally, impaling the radial nerve. Conversely, posterolateral displacement puts the median nerve and brachial artery at greatest risk.

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