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4. Pediatrics MCQs

Practice Set 291 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 5801

Topic: Pediatric Hip

A 6-week-old infant, who was a full-term vaginal delivery, presents with asymmetric thigh folds. Both Ortolani and Barlow tests are negative. What is the most appropriate next step in evaluation for developmental dysplasia of the hip (DDH)?

. Refer directly for hip spica casting
. Order a plain anteroposterior (AP) pelvis radiograph
. Perform a dynamic hip ultrasound
. Re-examine in 2 weeks to monitor for spontaneous resolution
. Initiate Pavlik harness treatment

Correct Answer & Explanation

. Perform a dynamic hip ultrasound

Explanation

For infants less than 4-6 months of age, especially with soft signs like asymmetric thigh folds and negative dynamic instability tests, a dynamic hip ultrasound is the imaging modality of choice. This allows for assessment of acetabular morphology and femoral head coverage, both statically and dynamically. Plain radiographs are unreliable due to the cartilaginous nature of the infant hip. Spica casting and Pavlik harness treatment are management options, not diagnostic steps, and should only follow a definitive diagnosis. Waiting for spontaneous resolution without imaging risks delayed diagnosis and worsened outcomes, especially with a positive clinical sign.

Question 5802

Topic: Pediatric Hip

Which of the following risk factors is considered the MOST significant for developmental dysplasia of the hip?

. Female sex
. First-born child
. Oligohydramnios
. Family history of DDH
. Breech presentation at term

Correct Answer & Explanation

. Breech presentation at term

Explanation

While all listed are risk factors, breech presentation (especially frank breech) at term carries the highest individual risk of DDH, increasing the likelihood by approximately 10-fold compared to cephalic presentation. Female sex, first-born status, and oligohydramnios also increase risk, but to a lesser degree than breech presentation. Family history is a significant risk factor as well, but breech presentation is often cited as the strongest modifiable or identifiable environmental factor.

Question 5803

Topic: Pediatric Hip
A 5-year-old child presents with a painless limp and a positive Trendelenburg sign on the right side. Radiographs show a right hip dislocation and a hypoplastic acetabulum. What is the most likely underlying condition?
. Transient synovitis
. Legg-Calvé-Perthes disease
. Septic arthritis
. Developmental dysplasia of the hip
. Slipped capital femoral epiphysis (SCFE)

Correct Answer & Explanation

. Developmental dysplasia of the hip

Explanation

The presentation of a painless limp, Trendelenburg sign, and radiographic evidence of hip dislocation with acetabular hypoplasia in a 5-year-old strongly points to undiagnosed developmental dysplasia of the hip. While DDH is typically diagnosed earlier, late presentations with these findings are common in cases that were missed or initially subtle. Transient synovitis and septic arthritis usually present with pain and often fever. Legg-Calvé-Perthes disease involves avascular necrosis of the femoral head and would show characteristic changes, but not typically a frank dislocation. SCFE usually occurs in pre-adolescent to adolescent children and involves a slipped epiphysis, not primary dislocation and acetabular hypoplasia.

Question 5804

Topic: Pediatric Hip

What is the critical age range when dynamic hip ultrasound is considered the most reliable imaging modality for DDH, before ossification significantly limits its utility?

. Birth to 2 weeks
. 2 weeks to 2 months
. Birth to 4-6 months
. 6 months to 1 year
. 1 year to 2 years

Correct Answer & Explanation

. Birth to 4-6 months

Explanation

Dynamic hip ultrasound is most reliable and preferred for assessing DDH from birth up to 4-6 months of age. Beyond this period, increasing ossification of the femoral head and acetabulum makes ultrasound less effective for detailed assessment, and plain radiographs become the standard imaging modality. Prior to 2 weeks, there's a higher rate of transient laxity that can resolve spontaneously.

Question 5805

Topic: 4. Pediatrics
A 2-month-old infant undergoes routine screening for DDH due to a family history. Both Ortolani and Barlow tests are negative. Ultrasound reveals an alpha angle of 55 degrees and a beta angle of 60 degrees. According to Graf's classification, what does this indicate?
. Type Ia (mature hip)
. Type Ib (mature hip with minor abnormality)
. Type IIa- (immature hip, not dysplastic)
. Type IIc (critical hip)
. Type III (decentered hip)

Correct Answer & Explanation

. Type IIc (critical hip)

Explanation

Graf's classification uses the alpha angle (measuring bony acetabular coverage) and beta angle (measuring cartilaginous coverage) to assess hip maturity and dysplasia. An alpha angle of 55 degrees (normal >60) and a beta angle of 60 degrees (normal <55) in an infant older than 6 weeks typically falls into the Type IIc category, indicating a critical or dysplastic hip that usually requires treatment. Type Ia and Ib are mature hips. Type IIa- (alpha 50-59, beta <77) is an immature hip but not considered dysplastic if <3 months. At 2 months, 55 degrees alpha is concerning. The specific values provided (alpha 55, beta 60) in a 2-month-old are consistent with a Type IIc hip, often requiring intervention.

Question 5806

Topic: Pediatric Hip

Which of the following conditions is LEAST likely to be considered in the differential diagnosis of a limping 18-month-old with asymmetric hip abduction?

. Septic arthritis
. Transient synovitis
. Juvenile idiopathic arthritis (JIA)
. Developmental dysplasia of the hip
. Slipped capital femoral epiphysis (SCFE)

Correct Answer & Explanation

. Slipped capital femoral epiphysis (SCFE)

Explanation

SCFE typically occurs in pre-adolescent to adolescent children (ages 10-16), rarely in a healthy 18-month-old. The other conditions are all relevant differential diagnoses for a limping toddler with asymmetric hip abduction: septic arthritis (acute, painful, febrile), transient synovitis (acute, painful, self-limiting), JIA (chronic, inflammatory), and developmental dysplasia of the hip (often presents with limping and abduction asymmetry in walking toddlers if previously undiagnosed or subluxed).

Question 5807

Topic: Pediatric Hip

A 4-month-old infant, previously identified as having an unstable left hip on newborn screening, has been managed in a Pavlik harness for 8 weeks. On follow-up examination, the left hip remains reducible but dislocates with adduction and posterior pressure. What is the most appropriate next step in management?

. Continue Pavlik harness for another 4 weeks
. Switch to a static abduction orthosis (e.g., abduction brace)
. Perform a closed reduction under anesthesia followed by spica casting
. Refer for open reduction and internal fixation
. Order a follow-up dynamic hip ultrasound

Correct Answer & Explanation

. Perform a closed reduction under anesthesia followed by spica casting

Explanation

If the Pavlik harness fails to stabilize the hip (hip remains unstable or dislocated after an adequate trial, typically 3-4 weeks to 6 weeks, but certainly 8 weeks for an unstable hip), then progression to more rigid immobilization or reduction is necessary. At 4 months, if the hip is still reducible but unstable, closed reduction under anesthesia followed by spica casting is generally the next step. Continuing the Pavlik harness for an additional 4 weeks on an already failed treatment is inappropriate. A static abduction orthosis is typically less effective than a Pavlik for dynamic instability and may be used as a step-down from a spica cast, not typically after Pavlik failure for an unstable hip. Open reduction is considered if closed reduction fails. A follow-up ultrasound is important for diagnosis and monitoring but not the immediate next step in management of a failed Pavlik for an unstable hip.

Question 5808

Topic: Pediatric Hip

In an infant with bilateral developmental dysplasia of the hip, which of the following clinical signs is least likely to be present?

. Limited hip abduction bilaterally
. Galeazzi sign
. Waddling gait (if ambulating)
. Increased lumbar lordosis
. Asymmetric skin folds

Correct Answer & Explanation

. Limited hip abduction bilaterally

Explanation

The Galeazzi sign relies on a unilateral discrepancy in limb length. In bilateral DDH, both hips are similarly affected, leading to comparable proximal migration of both femurs, making the Galeazzi sign unreliable or absent. Limited hip abduction, a waddling gait (due to bilateral abductor weakness and often increased lumbar lordosis), and increased lumbar lordosis (due to anterior pelvic tilt compensating for bilateral hip flexion contractures or hip dislocation) are all common findings in bilateral DDH. Asymmetric skin folds are also less reliable in bilateral cases, though subtle differences can still occur.

Question 5809

Topic: 4. Pediatrics

A 7-month-old infant presents with a suspected left hip dysplasia. What is the most appropriate initial imaging study?

. Dynamic hip ultrasound
. AP pelvis radiograph
. CT scan of the hip
. MRI of the hip
. Arthrography

Correct Answer & Explanation

. AP pelvis radiograph

Explanation

For infants older than 4-6 months, when significant ossification of the femoral head and acetabulum has occurred, a plain anteroposterior (AP) pelvis radiograph becomes the primary imaging modality for DDH. Ultrasound is less effective after this age due to ossification. CT and MRI are generally reserved for pre-operative planning or complex cases where detailed soft tissue or bony anatomy is needed, not as an initial screening tool. Arthrography is an invasive procedure typically performed in conjunction with closed reduction attempts.

Question 5810

Topic: Pediatric Hip

Which of the following anatomical structures is most commonly interposed within the joint space, preventing successful closed reduction of a dislocated hip in DDH?

. Ligamentum teres
. Acetabular labrum
. Psoas tendon
. Capsule
. Inferior acetabular limbus

Correct Answer & Explanation

. Acetabular labrum

Explanation

The hypertrophied and inverted acetabular labrum is the most common obstruction to closed reduction in DDH, acting like a 'limbus' that prevents the femoral head from seating correctly. The psoas tendon can also become tight and anteriorly displaced, compressing the capsule and potentially obstructing reduction. The ligamentum teres is often elongated and hypertrophied, but less frequently the primary block. The inferior acetabular limbus is a part of the capsule and less commonly the primary block. The capsule itself can be constricted but the labrum often poses a more direct mechanical obstruction.

Question 5811

Topic: Pediatric Hip
What is the typical initial management for a stable but dysplastic hip (Graf Type IIa, alpha angle 50-59 degrees, <3 months old) in a newborn with no signs of instability?
. Immediate Pavlik harness application
. Watchful waiting with follow-up ultrasound in 3-6 weeks
. Referral for open reduction
. MRI to assess labral integrity
. Closed reduction and spica casting

Correct Answer & Explanation

. Watchful waiting with follow-up ultrasound in 3-6 weeks

Explanation

For a stable but immature/dysplastic hip (Type IIa) in an infant less than 3 months old, watchful waiting with a follow-up ultrasound is the recommended approach, as many of these hips will spontaneously mature. If the hip remains dysplastic after 3-6 weeks, then intervention like a Pavlik harness may be considered. Immediate Pavlik application is typically reserved for unstable or frankly dislocated hips. Open reduction, MRI, and closed reduction with spica casting are more aggressive interventions for more severe forms of DDH or failed conservative management.

Question 5812

Topic: Pediatric Hip
A 10-year-old female presents with chronic left hip pain, a Trendelenburg gait, and mild left limb-length discrepancy. Radiographs show a flattened acetabular roof, lateralization of the femoral head, and an increased acetabular index on the left. What is the most appropriate primary diagnosis?
. Legg-Calvé-Perthes disease
. Slipped capital femoral epiphysis
. Juvenile idiopathic arthritis
. Developmental dysplasia of the hip
. Femoroacetabular impingement (FAI)

Correct Answer & Explanation

. Developmental dysplasia of the hip

Explanation

The constellation of chronic hip pain, Trendelenburg gait, limb-length discrepancy, and specific radiographic findings (flattened acetabular roof, lateralization of femoral head, increased acetabular index) in a 10-year-old is highly characteristic of symptomatic, undiagnosed, or late-presenting developmental dysplasia of the hip. These radiographic signs point to acetabular hypoplasia and a suboptimal femoral head-acetabulum relationship. Perthes disease involves avascular necrosis and would show femoral head collapse. SCFE involves a slip of the physis. JIA is inflammatory, and while it can affect the hip, the radiographic findings are specific to dysplasia. FAI is a cause of hip pain due to abnormal contact but typically presents with different radiographic features, often related to cam or pincer deformities, and usually doesn't involve frank dysplasia to this extent.

Question 5813

Topic: 4. Pediatrics

Which of the following 'packaging disorders' is most commonly associated with developmental dysplasia of the hip?

. Clubfoot (Talipes equinovarus)
. Congenital muscular torticollis
. Metatarsus adductus
. Congenital vertical talus
. Polydactyly

Correct Answer & Explanation

. Congenital muscular torticollis

Explanation

Congenital muscular torticollis and clubfoot (talipes equinovarus) are the two 'packaging disorders' most frequently associated with DDH. Metatarsus adductus is also a packaging disorder but less strongly associated than clubfoot. Congenital vertical talus and polydactyly are generally not considered packaging disorders directly related to in-utero constraint issues leading to DDH.

Question 5814

Topic: Pediatric Hip
A 2-year-old child presents with a new onset limp. On examination, there is limited internal rotation and abduction of the right hip, and a positive Trendelenburg sign on the right. Radiographs show flattening and fragmentation of the right femoral epiphysis. What is the most likely diagnosis?
. Developmental dysplasia of the hip (DDH)
. Septic arthritis
. Transient synovitis
. Legg-Calvé-Perthes disease
. Slipped capital femoral epiphysis (SCFE)

Correct Answer & Explanation

. Legg-Calvé-Perthes disease

Explanation

The presentation of a limp, limited hip motion (especially internal rotation and abduction), a positive Trendelenburg, and radiographic findings of flattening and fragmentation of the femoral epiphysis in a 2-year-old is classic for Legg-Calvé-Perthes disease (LCPD). DDH typically presents with different radiographic findings (acetabular hypoplasia, lateralization, dislocation). Septic arthritis and transient synovitis are acute, painful conditions. SCFE is typically seen in older children (adolescents).

Question 5815

Topic: 4. Pediatrics
A pediatric orthopedist is evaluating a 3-month-old with suspected DDH. The ultrasound shows an alpha angle of 48 degrees and a beta angle of 80 degrees. According to Graf's classification, this hip is best categorized as:
. Type Ia (mature hip)
. Type IIa+ (physiologically immature)
. Type IIb (dysplastic)
. Type III (decentered)
. Type IV (dislocated)

Correct Answer & Explanation

. Type III (decentered)

Explanation

An alpha angle less than 50 degrees (48 degrees) combined with a beta angle of 80 degrees (normal <55) in an infant over 3 months is indicative of a dysplastic hip, specifically Type III. Type III hips are decentered (often dislocated or severely subluxed) with a shallow, often deformed acetabulum. Type Ia and IIa are less severe or mature. Type IIb has an alpha angle between 43-49 degrees but usually a less severe beta angle than 80 degrees, and represents a dysplastic but still reducible hip. A Type IV hip is frankly dislocated, often with an everted labrum. An alpha angle of 48 at 3 months is severe.

Question 5816

Topic: 4. Pediatrics

Which finding on physical examination is most characteristic of a long-standing, irreducible hip dislocation in an older child with DDH?

. Positive Ortolani sign
. Positive Barlow sign
. Piston mobility
. Flexion contracture with limited hip extension
. Increased range of motion (ROM) in all planes

Correct Answer & Explanation

. Piston mobility

Explanation

Piston mobility refers to excessive superior-inferior movement of the femoral head (or its absence if dislocated) within the acetabulum. In a long-standing, irreducible dislocation, the femoral head is out of the acetabulum, and the hip may demonstrate piston mobility (telescoping) as the femoral head moves up and down relative to the pelvis. Ortolani and Barlow tests are for reducible instability in infants. Flexion contracture with limited hip extension can be present but is not as specific to irreducible dislocation as piston mobility. Increased ROM is unlikely in a dislocated hip; often, it's limited in certain planes or there's compensatory hypermobility.

Question 5817

Topic: Pediatric Hip

What is the primary mechanism by which oligohydramnios contributes to the development of DDH?

. Genetic predisposition
. Increased maternal estrogen levels
. Intrauterine mechanical constraint
. Reduced fetal calcium metabolism
. Decreased fetal movement

Correct Answer & Explanation

. Intrauterine mechanical constraint

Explanation

Oligohydramnios (low amniotic fluid volume) leads to decreased intrauterine space, resulting in increased mechanical constraint on the fetus. This constraint can impede normal hip development, predisposing to DDH, especially if the hips are held in an adducted and extended position. Genetic predisposition and maternal estrogen levels are also risk factors, but not directly linked to oligohydramnios. Reduced fetal calcium metabolism and decreased fetal movement are not the primary mechanisms for DDH in this context.

Question 5818

Topic: Pediatric Hip

A 1-month-old infant with a positive Ortolani sign on the right is placed in a Pavlik harness. What is the most common serious complication of improper Pavlik harness application or use?

. Femoral nerve palsy
. Avascular necrosis (AVN) of the femoral head
. Skin breakdown and irritation
. Ipsilateral genu valgum
. Contralateral hip subluxation

Correct Answer & Explanation

. Avascular necrosis (AVN) of the femoral head

Explanation

Avascular necrosis (AVN) of the femoral head is the most serious complication of Pavlik harness treatment for DDH. It is typically caused by excessive flexion and/or adduction, which places undue pressure on the blood supply to the femoral head. Femoral nerve palsy can occur but is less common than AVN. Skin breakdown is a common minor complication. Genu valgum and contralateral hip subluxation are not typical complications of Pavlik harness use.

Question 5819

Topic: 4. Pediatrics

Which of the following describes the 'classic' radiographic appearance of a dislocated hip in a 6-month-old infant?

. Decreased acetabular index, femoral head centered in the acetabulum
. Increased acetabular index, superior and lateral displacement of the femoral epiphysis
. Sclerotic and flattened femoral epiphysis with increased joint space
. Widened physis with metaphyseal irregularity
. Fragmented femoral head epiphysis with subchondral lucency

Correct Answer & Explanation

. Increased acetabular index, superior and lateral displacement of the femoral epiphysis

Explanation

In a dislocated hip in a 6-month-old, radiographs would typically show an increased acetabular index (indicating a shallow acetabulum), and the femoral epiphysis (which is still largely cartilaginous but its ossific nucleus is visible) would be displaced superiorly and laterally relative to the acetabulum. Decreased acetabular index and a centered femoral head indicate a normal hip. The other options describe Perthes disease (sclerotic, flattened, fragmented epiphysis), rickets (widened physis), or chronic conditions not directly related to the acute dislocated state of DDH.

Question 5820

Topic: Pediatric Hip

What is the primary purpose of drawing Hilgenreiner's line on an AP pelvis radiograph for DDH assessment?

. To assess the coverage of the femoral head by the acetabulum.
. To determine the vertical position of the femoral head relative to the pelvis.
. To measure the acetabular index (angle).
. To evaluate the integrity of Shenton's line.
. To identify the presence of a limbus in the joint.

Correct Answer & Explanation

. To determine the vertical position of the femoral head relative to the pelvis.

Explanation

Hilgenreiner's line is a horizontal line drawn between the inferior margins of the triradiate cartilages. Its primary purpose is to serve as a baseline for assessing the vertical position of the femoral head (or its ossific nucleus) relative to the pelvis. The femoral head's ossific nucleus should be below Hilgenreiner's line. It is also used in conjunction with a line drawn to the lateral acetabular margin to measure the acetabular index. While indirectly related to coverage, its direct purpose is positional assessment. Shenton's line is for continuity. A limbus is a soft-tissue finding, not directly assessed by Hilgenreiner's line.

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