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4. Pediatrics MCQs

Practice Set 99 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 1961

Topic: Pediatric Hip

A 4-month-old infant with developmental dysplasia of the hip (DDH) has been treated with a Pavlik harness for the last three weeks. At the most recent clinical follow-up, the mother reports that the infant is no longer kicking the affected leg. On examination, the infant exhibits an inability to actively extend the knee, and there is a diminished patellar reflex on the affected side. What is the most likely cause of this complication?

. Sciatic nerve compression from hyperflexion
. Femoral nerve palsy from excessive hip flexion
. Obturator nerve palsy from excessive abduction
. Lateral femoral cutaneous nerve entrapment
. Common peroneal nerve compression at the fibular head

Correct Answer & Explanation

. Femoral nerve palsy from excessive hip flexion

Explanation

Femoral nerve palsy is a known complication of Pavlik harness treatment, usually caused by excessive hip flexion, which compresses the femoral nerve against the inguinal ligament. It presents as decreased active knee extension and a diminished patellar reflex. When this occurs, the harness must be adjusted to decrease flexion or temporarily discontinued until nerve function recovers.

Question 1962

Topic: Pediatric Hip

A 12-year-old male with a BMI in the 99th percentile undergoes urgent in-situ percutaneous pinning with a single cannulated screw for a stable Slipped Capital Femoral Epiphysis (SCFE).

Four months post-operatively, he returns to the clinic complaining of severe, worsening global hip stiffness and pain. Radiographs demonstrate marked, uniform joint space narrowing of the affected hip without segmental collapse of the femoral head. What is the most likely etiology of this complication?

. Avascular necrosis of the femoral head
. Unrecognized low-grade septic arthritis
. Chondrolysis secondary to unrecognized hardware penetration
. Iatrogenic femoral neck fracture
. Premature closure of the triradiate cartilage

Correct Answer & Explanation

. Chondrolysis secondary to unrecognized hardware penetration

Explanation

The clinical presentation of severe hip stiffness and uniform joint space narrowing on radiographs following SCFE pinning is classic for chondrolysis. A major known risk factor for chondrolysis in this setting is unrecognized penetration of the hardware (screw) into the joint space. Avascular necrosis typically presents with segmental subchondral sclerosis and collapse (crescent sign), rather than uniform joint space loss as the primary early radiographic finding.

Question 1963

Topic: Pediatric Hip

A 12-year-old obese male presents with 3 weeks of right thigh pain and a limp. He is diagnosed with a stable Slipped Capital Femoral Epiphysis (SCFE) and undergoes in situ single screw fixation. To avoid the most devastating vascular complication of this condition and its treatment, the surgeon must be mindful of the primary blood supply to the capital femoral epiphysis. Which vessel is this?

. Medial femoral circumflex artery
. Lateral epiphyseal artery
. Artery of the ligamentum teres
. Inferior gluteal artery
. Ascending branch of the lateral femoral circumflex artery

Correct Answer & Explanation

. Lateral epiphyseal artery

Explanation

The lateral epiphyseal artery, which is the terminal branch of the medial femoral circumflex artery (MFCA), provides the primary blood supply to the capital femoral epiphysis. During SCFE pinning, an exclusively anterior-superior pin placement risks penetrating the joint and damaging the blood supply. Proper placement is strictly center-center to avoid the superolateral extraosseous blood supply.

Question 1964

Topic: Pediatric Hip

A 3-month-old female is undergoing treatment with a Pavlik harness for developmental dysplasia of the hip (DDH). At the 3-week follow-up, the parents report that she is no longer kicking her right leg. On physical examination, she has absent active knee extension on the right, and the patellar reflex is absent. What is the most appropriate next step in management?

. Adjust the harness to increase hip flexion
. Adjust the harness to decrease hip flexion
. Remove the harness and apply a hip spica cast
. Remove the harness completely and observe
. Proceed immediately to closed reduction under anesthesia

Correct Answer & Explanation

. Remove the harness completely and observe

Explanation

The patient has developed a femoral nerve palsy, a known complication of Pavlik harness treatment caused by excessive hyperflexion of the hip which compresses the femoral nerve. The standard of care is to completely remove the harness to allow the nerve to recover. Once spontaneous recovery of the nerve occurs (usually within weeks), alternative treatment (like a rigid abduction orthosis or cast) can be instituted.

Question 1965

Topic: Pediatric Hip

A 12-year-old obese male presents with left thigh pain and an antalgic gait for 4 weeks. He has been entirely unable to bear weight on the left leg for the past 2 days. Radiographs show a slipped capital femoral epiphysis (SCFE) with a slip angle of 60 degrees.

What is the most significant risk factor for the development of avascular necrosis (AVN) in this patient?

. Severity of the slip angle
. Patient's weight
. Duration of symptoms prior to presentation
. Inability to bear weight
. Use of a single screw for fixation

Correct Answer & Explanation

. Inability to bear weight

Explanation

The clinical inability to bear weight, even with crutches, defines an unstable SCFE according to the Loder classification. Unstable SCFE carries a significantly higher risk of avascular necrosis (AVN), historically up to 50%, compared to stable SCFE where AVN is rare. While a severe slip angle increases the technical difficulty of fixation, stability is the primary predictor of AVN.

Question 1966

Topic: Pediatric Hip

An 8-week-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During the weekly clinical check, the orthopedic surgeon assesses the harness fit to prevent complications. Which of the following strap misadjustments most directly places the infant at risk for avascular necrosis (AVN) of the femoral head?

. Excessive flexion of the anterior straps
. Inadequate flexion of the anterior straps
. Excessive abduction of the posterior straps
. Excessive adduction of the posterior straps
. Over-tightening of the chest strap

Correct Answer & Explanation

. Excessive abduction of the posterior straps

Explanation

In the Pavlik harness, excessive abduction (too tight posterior straps) forces the femoral head into rigid abduction, creating high pressure that compresses the epiphyseal blood vessels (primarily branches of the medial circumflex femoral artery), leading to AVN of the femoral head. Conversely, excessive flexion (too tight anterior straps) puts the infant at risk for transient femoral nerve palsy.

Question 1967

Topic: 4. Pediatrics

An infant is born with idiopathic congenital talipes equinovarus (clubfoot) and is referred for Ponseti serial casting. According to the Ponseti method, what is the first step in the manual manipulation and casting sequence to correct the deformities?

. Dorsiflexion of the ankle to correct equinus
. Abduction of the midfoot with counter-pressure on the calcaneocuboid joint
. Supination of the forefoot with elevation of the first ray to correct cavus
. Pronation of the forefoot to correct adduction
. Eversion of the hindfoot to correct varus

Correct Answer & Explanation

. Supination of the forefoot with elevation of the first ray to correct cavus

Explanation

The Ponseti method corrects clubfoot deformities in a specific sequence remembered by the acronym CAVE: Cavus, Adductus, Varus, Equinus. The very first step is to correct the cavus deformity by supinating the forefoot and elevating the first metatarsal (first ray) to align the forefoot with the hindfoot. Abduction of the midfoot with counter-pressure on the head of the talus (not calcaneocuboid joint) then corrects the adductus and varus simultaneously.

Question 1968

Topic: Pediatric Hip

A 12-year-old boy with a BMI of 32 presents with a 4-week history of vague left knee pain and an antalgic gait. Radiographs reveal a mild, stable slipped capital femoral epiphysis (SCFE) of the left hip.

He is taken to the operating room for in situ pinning. To minimize the risk of joint penetration and adequately stabilize the epiphysis, the starting point for the screw should be located on the:

. Posterior aspect of the femoral neck
. Anterior aspect of the femoral neck
. Direct lateral aspect of the greater trochanter
. Inferior aspect of the femoral neck
. Superior aspect of the femoral neck

Correct Answer & Explanation

. Anterior aspect of the femoral neck

Explanation

In a slipped capital femoral epiphysis, the epiphysis displaces posteriorly and inferiorly relative to the femoral neck. To correctly trajectory a single screw perpendicular to the physis and into the center of the displaced epiphysis without violating the posterior cortex of the femoral neck, an anterior and superior starting point on the metaphysis/neck is required.

Question 1969

Topic: Pediatric Hip

A 7-month-old female infant is evaluated for developmental dysplasia of the hip (DDH). She was initially treated with a Pavlik harness starting at 6 weeks of age, but the hip remained irreducible. Subsequent attempts at weaning and re-application have failed. Radiographs show a persistently dislocated left hip with acetabular dysplasia. What is the most appropriate next step in management?

. Re-application of the Pavlik harness for an additional 6 weeks
. Application of an abduction orthosis (e.g., Ilfeld splint)
. Closed reduction under general anesthesia and spica casting
. Open reduction, pelvic osteotomy, and femoral shortening osteotomy
. Observation until skeletal maturity, followed by total hip arthroplasty

Correct Answer & Explanation

. Closed reduction under general anesthesia and spica casting

Explanation

If Pavlik harness treatment fails to achieve or maintain a reduction in an infant with DDH, the harness should be discontinued to avoid 'Pavlik harness disease' (damage to the posterior acetabular wall) and AVN. The next definitive step in management for a child typically between 6 and 18 months of age is closed reduction under general anesthesia followed by spica casting.

Question 1970

Topic: Pediatric Hip

A 9-year-old boy presents with right hip pain and a limp. Radiographs confirm a slipped capital femoral epiphysis (SCFE). His weight is in the 40th percentile for his age. In addition to in situ pinning of the right hip, which of the following is the most appropriate next step in management?

. Prophylactic pinning of the contralateral hip
. Closed reduction and spica casting
. Endocrine evaluation including TSH, free T4, BUN, and creatinine
. MRI of the bilateral hips
. Open reduction and surgical subluxation

Correct Answer & Explanation

. Endocrine evaluation including TSH, free T4, BUN, and creatinine

Explanation

SCFE typically affects obese adolescents between the ages of 10 and 16. Atypical presentations include patients younger than 10 or older than 16, those with a weight less than the 50th percentile, and those with bilateral involvement at presentation. These atypical presentations strongly warrant an endocrine and metabolic workup to rule out underlying disorders such as hypothyroidism or renal osteodystrophy.

Question 1971

Topic: Pediatric Upper Extremity & Spine
A 5-year-old girl falls off monkey bars and presents with a Gartland type III extension-type supracondylar humerus fracture. The hand is pink, well-perfused, but she is unable to flex the interphalangeal joint of her thumb and the distal interphalangeal joint of her index finger. Which of the following nerve structures has most likely been injured?
. Radial nerve
. Ulnar nerve
. Anterior interosseous nerve
. Musculocutaneous nerve
. Recurrent motor branch of the median nerve

Correct Answer & Explanation

. Anterior interosseous nerve

Explanation

The anterior interosseous nerve (AIN), a motor branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures. It innervates the flexor pollicis longus, the lateral half of the flexor digitorum profundus (index and middle fingers), and the pronator quadratus. Clinically, AIN function is assessed by having the patient form an 'OK' sign. Failure to do so (resulting in a flattened pinch mechanism) indicates an AIN palsy.

Question 1972

Topic: Pediatric Hip

A 4-month-old female is being treated for developmental dysplasia of the hip (DDH) using a Pavlik harness.

What is the most common nerve palsy associated with excessive hyperflexion of the hips in this device?

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

Correct Answer & Explanation

. Femoral nerve

Explanation

Excessive flexion of the hips in a Pavlik harness can cause impingement of the femoral nerve against the inguinal ligament, leading to a femoral nerve palsy (typically presenting as decreased active knee extension). Excessive abduction, conversely, increases the risk of avascular necrosis of the femoral head.

Question 1973

Topic: 4. Pediatrics

Osteogenesis imperfecta (OI) type I is a connective tissue disorder characterized by brittle bones and blue sclerae. It is most commonly caused by a mutation in which of the following genes?

. FGFR3
. COMP
. COL1A1 or COL1A2
. COL2A1
. RUNX2

Correct Answer & Explanation

. COL1A1 or COL1A2

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of type I collagen. FGFR3 mutations cause achondroplasia. COMP mutations are seen in pseudoachondroplasia and multiple epiphyseal dysplasia. COL2A1 mutations cause type II collagenopathies (e.g., Kniest dysplasia). RUNX2 mutations cause cleidocranial dysplasia.

Question 1974

Topic: Pediatric Hip

A 12-year-old boy with a BMI in the 98th percentile presents with 3 weeks of vague left groin and knee pain. He walks with an antalgic, externally rotated gait. Radiographs confirm a stable left slipped capital femoral epiphysis (SCFE).

Which of the following is the strongest indication for prophylactic in situ pinning of his asymptomatic right hip?

. Age greater than 14 years at initial presentation
. Posterior sloping angle of 40 degrees on the affected side
. Concomitant diagnosis of hypothyroidism
. Unilateral slip angle greater than 60 degrees
. BMI greater than the 95th percentile

Correct Answer & Explanation

. Concomitant diagnosis of hypothyroidism

Explanation

Endocrine disorders (such as hypothyroidism, panhypopituitarism, or renal osteodystrophy) and previous radiation therapy are strong indications for prophylactic contralateral pinning in SCFE due to the exceptionally high risk of a subsequent contralateral slip. While young age (e.g., < 10 years) and open triradiate cartilage are also considered risk factors for contralateral disease, a high BMI alone or the severity of the unilateral slip does not represent an absolute indication for prophylactic pinning.

Question 1975

Topic: Pediatric Hip

A 4-month-old female is diagnosed with Developmental Dysplasia of the Hip (DDH). She is placed in a Pavlik harness. To successfully maintain hip reduction while preventing iatrogenic avascular necrosis, the Pavlik harness safely restricts which of the following combined movements?

. Flexion and abduction
. Extension and adduction
. Flexion and internal rotation
. Extension and abduction
. Flexion and external rotation

Correct Answer & Explanation

. Flexion and abduction

Explanation

The Pavlik harness is a dynamic flexion-abduction orthosis used to treat DDH. It maintains the hip in flexion and limits adduction and extension, thereby stabilizing the reduction. It does not rigidly lock the hip in position but acts as a tether to prevent extension and adduction (the positions that favor dislocation). Excessive forced abduction is avoided as it significantly increases the risk of iatrogenic avascular necrosis of the femoral head.

Question 1976

Topic: Pediatric Hip

A 12-year-old obese male presents with left knee pain and an antalgic gait. Physical examination reveals an obligate external rotation of the left hip as it is passively flexed. Radiographs confirm a displaced Slipped Capital Femoral Epiphysis (SCFE) on the left.

Prophylactic percutaneous pinning of the contralateral (asymptomatic) hip is most strongly indicated if the patient has a history of which of the following conditions?

. Hyperthyroidism
. Type 1 Diabetes Mellitus
. Hypothyroidism
. Addison's disease
. Hyperparathyroidism

Correct Answer & Explanation

. Hypothyroidism

Explanation

Prophylactic pinning of the contralateral hip in SCFE is controversial but is generally strongly recommended in patients with an underlying endocrinopathy or metabolic bone disease (e.g., hypothyroidism, renal osteodystrophy, growth hormone deficiency), as well as in patients presenting at an unusually young age (often defined as <10 years old). These patients have an extremely high risk (up to 100% in some metabolic conditions) of developing a contralateral slip.

Question 1977

Topic: Pediatric Lower Extremity

A 2-year-old girl is evaluated for severe bowing of her lower extremities. You suspect infantile Blount's disease rather than physiologic bowing. Which of the following radiographic parameters is the most reliable predictor that the deformity will progress to clinical Blount's disease and likely require intervention?

. Tibiofemoral angle > 10 degrees
. Metaphyseal-diaphyseal angle (Drennan angle) > 16 degrees
. Mechanical axis deviation > 2 cm
. Epiphyseal-metaphyseal angle > 20 degrees
. Neck-shaft angle < 120 degrees

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle (Drennan angle) > 16 degrees

Explanation

The metaphyseal-diaphyseal angle (Drennan's angle) is used to differentiate physiologic genu varum from infantile Blount's disease. An angle > 16 degrees is highly predictive of progressive infantile Blount's disease. An angle < 10 degrees is typical for physiologic bowing, which usually resolves spontaneously. Angles between 10 and 16 degrees represent a gray area requiring close clinical and radiographic observation.

Question 1978

Topic: 4. Pediatrics

A 13-year-old obese boy presents with a 3-month history of vague left knee pain and a limp. Physical examination demonstrates an obligate external rotation of the left hip during flexion. Radiographs demonstrate a posterior and inferior displacement of the proximal femoral epiphysis. Through which physeal zone does the primary failure occur in this condition?

. Zone of resting cartilage
. Zone of proliferation
. Zone of hypertrophy
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Zone of hypertrophy

Explanation

Slipped Capital Femoral Epiphysis (SCFE) characteristically involves a structural failure through the zone of hypertrophy of the physis. This zone is the weakest biomechanically because the chondrocytes are enlarged, lacking substantial extracellular matrix. This is in contrast to Salter-Harris fractures, which typically propagate through the zone of provisional calcification or the zone of hypertrophy depending on the vector, but SCFE specifically involves pathologic widening and slipping through the hypertrophic zone.

Question 1979

Topic: Pediatric Hip
A 6-year-old boy presents with a painless limp of 3 months' duration. His mother notes restricted hip motion, particularly in abduction and internal rotation. Radiographs reveal sclerosis, flattening, and early fragmentation of the proximal femoral epiphysis. In the natural history of Legg-Calvé-Perthes disease, which of the following represents the correct sequence of radiographic stages?
. Fragmentation, Initial (necrosis), Reossification, Healed
. Initial (necrosis), Fragmentation, Reossification, Healed
. Reossification, Fragmentation, Initial (necrosis), Healed
. Initial (necrosis), Reossification, Fragmentation, Healed
. Fragmentation, Reossification, Initial (necrosis), Healed

Correct Answer & Explanation

. Initial (necrosis), Fragmentation, Reossification, Healed

Explanation

The classic radiographic progression of Legg-Calvé-Perthes disease (Waldenström stages) follows four distinct phases: 1) Initial stage (avascular necrosis, sclerosis, and growth arrest), 2) Fragmentation stage (subchondral radiolucent crescent sign, epiphysis fragmenting), 3) Reossification stage (new woven bone formation), and 4) Healed or residual stage (final shape of the femoral head).

Question 1980

Topic: 4. Pediatrics

A 4-month-old infant is treated with a Pavlik harness for developmental dysplasia of the hip. At a follow-up visit, the infant is noted to have decreased active extension of the knee on the treated side. Which of the following positioning errors is the most likely cause of this complication?

. Excessive flexion of the hip
. Excessive extension of the hip
. Excessive abduction of the hip
. Excessive adduction of the hip
. Inadequate stabilization of the chest strap

Correct Answer & Explanation

. Excessive flexion of the hip

Explanation

Decreased active extension of the knee in an infant treated with a Pavlik harness is indicative of a femoral nerve palsy. The femoral nerve can become compressed against the pelvis if the hip is positioned in excessive hyperflexion (typically >120 degrees). If this occurs, the anterior straps should be loosened or the harness temporarily discontinued to allow neurological recovery. Excessive abduction is associated with avascular necrosis of the femoral head.

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