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4. Pediatrics MCQs

Practice Set 332 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 6621

Topic: 4. Pediatrics

According to the classic Ilizarov principles of distraction osteogenesis, what are the optimal latency period, distraction rate, and rhythm for a standard adult tibial diaphyseal lengthening?

. 7 to 10 days latency; 1.0 mm/day rate divided into 4 equal increments.
. 1 to 3 days latency; 0.5 mm/day rate divided into 2 equal increments.
. 14 to 21 days latency; 1.5 mm/day rate divided into 6 equal increments.
. 0 days latency; 1.0 mm/day continuous rate.
. 5 days latency; 2.0 mm/day rate divided into 4 equal increments.

Correct Answer & Explanation

. 7 to 10 days latency; 1.0 mm/day rate divided into 4 equal increments.

Explanation

Ilizarov established that optimal regenerate bone formation in adults occurs with a latency phase of 7-10 days followed by a distraction rate of 1 mm per day, divided into a rhythm of 0.25 mm every 6 hours.

Question 6622

Topic: 4. Pediatrics

In the principles of distraction osteogenesis (Ilizarov technique)

, what is the optimal rate and rhythm for distraction to promote robust bone regenerate without causing premature consolidation or nonunion?

. 1.0 mm per day divided into 1 adjustment of 1.0 mm
. 1.0 mm per day divided into 2 adjustments of 0.5 mm
. 1.0 mm per day divided into 4 adjustments of 0.25 mm
. 2.0 mm per day divided into 4 adjustments of 0.5 mm
. 0.5 mm per day divided into 2 adjustments of 0.25 mm

Correct Answer & Explanation

. 1.0 mm per day divided into 4 adjustments of 0.25 mm

Explanation

The classic Ilizarov principle of tension-stress dictates an optimal distraction rate of 1.0 mm per day, divided into a high-frequency rhythm of 0.25 mm four times a day, to optimize bone regeneration and soft tissue adaptation.

Question 6623

Topic: 4. Pediatrics



In severe adolescent Blount's disease, the complex multiplanar deformity of the proximal tibia classically includes varus angulation, internal tibial torsion, and which of the following sagittal plane abnormalities?

. Recurvatum (posterior bowing)
. Procurvatum (anterior bowing)
. Patella alta with distal femoral extension
. Anterior translation of the proximal fibula
. Fixed flexion contracture of the knee

Correct Answer & Explanation

. Procurvatum (anterior bowing)

Explanation

Adolescent Blount's disease is characterized by a three-dimensional deformity of the proximal tibia: varus angulation, internal tibial torsion, and procurvatum (apex anterior angulation). This occurs because the posterior aspect of the proximal tibial physis continues to grow faster than the anterior aspect.

Question 6624

Topic: 4. Pediatrics

When utilizing the Ilizarov method for lengthening a tibia following a corrective osteotomy, what is the optimal rate and rhythm of distraction to promote high-quality regenerate bone formation?

. 0.25 mm four times a day
. 1.0 mm once a day
. 1.5 mm twice a day
. 0.5 mm four times a day
. 2.0 mm once a day

Correct Answer & Explanation

. 0.25 mm four times a day

Explanation

The standard rate for distraction osteogenesis is 1 mm per day. The optimal rhythm breaks this daily distance into smaller, frequent increments, typically 0.25 mm four times a day. This minimizes soft tissue trauma and yields the best quality regenerate bone.

Question 6625

Topic: Pediatric Hip

Which of the following biomechanical changes is most characteristic of coxa vara?

. Decreased hip abductor moment arm
. Increased overall hip joint reaction force
. Decreased bending moment across the femoral neck
. Increased hip abductor moment arm
. Increased functional leg length

Correct Answer & Explanation

. Decreased bending moment across the femoral neck

Explanation

In coxa vara, the decreased neck-shaft angle moves the greater trochanter more laterally, which increases the abductor moment arm. While this decreases the joint reaction force, it pathologically increases the bending moment and shear force across the femoral neck.

Question 6626

Topic: Pediatric Hip

Which of the following describes the biomechanical effect of coxa vara (decreased neck-shaft angle) on the hip joint?

. Increases the joint reaction force and decreases the bending moment at the femoral neck.
. Decreases the abductor moment arm and increases the joint reaction force.
. Increases the abductor moment arm, decreases the total joint reaction force, and increases the bending moment across the femoral neck.
. Decreases the abductor moment arm, decreases the joint reaction force, and decreases the bending moment across the femoral neck.
. Increases both the joint reaction force and the bending moment across the femoral neck.

Correct Answer & Explanation

. Increases the abductor moment arm, decreases the total joint reaction force, and increases the bending moment across the femoral neck.

Explanation

Coxa vara lateralizes the greater trochanter, increasing the abductor lever arm and thereby reducing the required abductor force and total joint reaction force. However, the more horizontal femoral neck experiences an increased shear force and bending moment, predisposing it to fatigue failure.

Question 6627

Topic: 4. Pediatrics

A 10-year-old girl with a skeletal age of 10 sustains a distal femoral Salter-Harris IV fracture complicated by a complete premature physeal arrest of the distal femur. Using the Green-Anderson / Menelaus method, what is the expected leg length discrepancy at skeletal maturity?

. 2.4 cm
. 3.0 cm
. 3.8 cm
. 4.8 cm
. 6.0 cm

Correct Answer & Explanation

. 3.8 cm

Explanation

Using the Menelaus method, girls reach skeletal maturity at age 14, leaving 4 years of growth. The distal femur grows approximately 3/8 inch (9-10 mm) per year. 4 years x ~9.5 mm/year = ~3.8 cm (or 40 mm) of expected discrepancy.

Question 6628

Topic: Pediatric Lower Extremity

A patient with long-standing, severe Blount's disease undergoes lower extremity deformity planning. Analysis of a standing long-leg radiograph reveals a mechanical lateral distal femoral angle (mLDFA) of 88 degrees and a mechanical proximal tibial angle (MPTA) of 72 degrees. Where is the mechanical axis deviation (MAD)?

. MAD is significantly medial to the center of the knee joint.
. MAD is significantly lateral to the center of the knee joint.
. MAD passes directly through the center of the knee joint.
. MAD is normal, but the joint line obliquity is reversed.
. MAD cannot be determined without a lateral radiograph.

Correct Answer & Explanation

. MAD is significantly medial to the center of the knee joint.

Explanation

Blount's disease causes severe tibia vara (indicated by the abnormally low MPTA of 72 degrees; normal is ~87 degrees). This uncompensated varus deformity shifts the mechanical axis deviation (MAD) medially across the knee joint.

Question 6629

Topic: 4. Pediatrics

A 6-year-old child presents with a central physeal bar of the distal femur occupying 60% of the cross-sectional area of the physis following a traumatic injury. There is a 3 cm leg length discrepancy and progressive varus deformity. What is the most appropriate management regarding the physeal bar?

. Physeal bar resection and interposition with fat.
. Physeal bar resection and interposition with cranioplast (PMMA).
. Observation until skeletal maturity.
. Complete epiphysiodesis of the distal femur and planned limb lengthening.
. Medial opening wedge osteotomy without addressing the physis.

Correct Answer & Explanation

. Complete epiphysiodesis of the distal femur and planned limb lengthening.

Explanation

Physeal bar resection is generally contraindicated if the bar occupies more than 50% of the cross-sectional area, as the success rate for restoring growth is extremely low. The best management is complete epiphysiodesis to halt progressive angular deformity, combined with lengthening or contralateral epiphysiodesis.

Question 6630

Topic: Pediatric Hip

A patient presents with severe coxa vara (neck-shaft angle of 95 degrees). Compared to a normal neck-shaft angle (130 degrees), which of the following biomechanical profiles is characteristic of coxa vara?

. Increased hip joint reaction force and increased femoral neck bending moment
. Increased hip joint reaction force and decreased femoral neck bending moment
. Decreased hip joint reaction force and increased femoral neck bending moment
. Decreased hip joint reaction force and decreased femoral neck bending moment
. Unchanged hip joint reaction force and increased femoral neck bending moment

Correct Answer & Explanation

. Decreased hip joint reaction force and increased femoral neck bending moment

Explanation

Coxa vara increases the abductor moment arm, which decreases the required abductor force and therefore decreases the hip joint reaction force. However, the more horizontal femoral neck increases the shear force and bending moment across the femoral neck, increasing the risk of femoral neck fracture.

Question 6631

Topic: Pediatric Hip

A Bernese periacetabular osteotomy (PAO) is performed for symptomatic developmental dysplasia of the hip (DDH). What is the primary biomechanical alteration at the hip joint achieved by this procedure?

. Lateralization of the hip joint center, increasing the abductor moment arm
. Medialization of the hip joint center, decreasing the lever arm of body weight
. Distalization of the greater trochanter, increasing abductor tension
. Anterior translation of the femoral head, increasing the Wiberg center-edge angle
. Posterior displacement of the acetabulum, decreasing pelvic tilt

Correct Answer & Explanation

. Medialization of the hip joint center, decreasing the lever arm of body weight

Explanation

A PAO allows the acetabulum to be reoriented to increase femoral head coverage (improving the center-edge angle). It also medializes the hip joint center of rotation, which decreases the lever arm of the body weight and subsequently reduces the joint reaction force.

Question 6632

Topic: 4. Pediatrics

Using the Menelaus method for calculating limb length discrepancy, what are the accepted average growth rates of the distal femur and proximal tibia per year, respectively?

. 6 mm (1/4 inch) and 9 mm (3/8 inch)
. 9 mm (3/8 inch) and 6 mm (1/4 inch)
. 12 mm (1/2 inch) and 6 mm (1/4 inch)
. 10 mm (3/8 inch) and 10 mm (3/8 inch)
. 6 mm (1/4 inch) and 6 mm (1/4 inch)

Correct Answer & Explanation

. 9 mm (3/8 inch) and 6 mm (1/4 inch)

Explanation

The Menelaus rule of thumb estimates that the distal femoral physis grows approximately 9-10 mm (3/8 inch) per year, and the proximal tibial physis grows approximately 6 mm (1/4 inch) per year. Growth is estimated to cease at age 14 in girls and 16 in boys.

Question 6633

Topic: 4. Pediatrics

A 12-year-old boy presents with right lower limb length discrepancy and angular deformity due to a partial distal femoral physeal arrest following a Salter-Harris IV fracture. Imaging reveals a peripheral physeal bar. Under what conditions is physeal bar resection (epiphysiolysis) indicated?

. Bar < 50% of physeal area, > 2 years of growth remaining
. Bar > 50% of physeal area, > 2 years of growth remaining
. Bar < 50% of physeal area, < 1 year of growth remaining
. Bar > 50% of physeal area, regardless of remaining growth
. Central bars only, regardless of size or growth remaining

Correct Answer & Explanation

. Bar < 50% of physeal area, > 2 years of growth remaining

Explanation

Physeal bar resection is generally indicated if the bar involves less than 50% of the total physeal cross-sectional area and the child has at least 2 years of remaining skeletal growth. If the bar is larger or less growth remains, corrective osteotomy or epiphysiodesis is preferred.

Question 6634

Topic: 4. Pediatrics

During clinical evaluation of femoral anteversion in a child, the Craig's test is performed. The patient is placed prone with the knee flexed to 90 degrees. What specifically is being measured to determine the degree of anteversion?

. The angle of the tibia to the vertical when the greater trochanter is most prominent laterally
. The angle of the tibia to the horizontal when the hip is fully internally rotated
. The distance between the medial malleoli when the greater trochanter is neutralized
. The angle of the thigh relative to the table when the greater trochanter is felt maximally anterior
. The range of maximal internal rotation subtracted from maximal external rotation

Correct Answer & Explanation

. The angle of the tibia to the vertical when the greater trochanter is most prominent laterally

Explanation

In Craig's test (trochanteric prominence angle test), the examiner palpates the greater trochanter and rotates the hip until the trochanter is most prominent laterally (which parallels the femoral neck). The angle of the lower leg (tibia) relative to the true vertical represents the degree of femoral anteversion.

Question 6635

Topic: Pediatric Lower Extremity

A 2-year-old child is evaluated for bilateral genu varum. Which of the following radiographic parameters best differentiates infantile Blount's disease from physiologic bowing?

. Metaphyseal-diaphyseal angle (MDA) greater than 11 degrees
. Mechanical axis deviation lateral to the knee center
. Tibiofemoral angle of 10 degrees varus
. Symmetrical flaring of the femoral metaphyses

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle (MDA) greater than 11 degrees

Explanation

The metaphyseal-diaphyseal angle (MDA) of Drennan is used to differentiate physiologic bowing from infantile Blount's disease. An MDA > 11-16 degrees is highly predictive of progression to Blount's disease.

Question 6636

Topic: 4. Pediatrics

When predicting a pediatric limb length discrepancy at maturity using the Paley multiplier method, the calculation is fundamentally based on which of the following biological assumptions?

. The short limb grows at an exponentially slower rate over time.
. The discrepancy arises only during the pubertal growth spurt.
. The short limb grows at a constant proportion (constant inhibition) relative to the normal limb.
. The short limb ceases longitudinal growth precisely 2 years prior to the normal limb.

Correct Answer & Explanation

. The short limb grows at a constant proportion (constant inhibition) relative to the normal limb.

Explanation

The multiplier method assumes the principle of constant inhibition, meaning the short limb grows at a constant, proportional rate relative to the normal limb throughout childhood.

Question 6637

Topic: Pediatric Hip

A patient with developmental dysplasia of the hip is found to have a center-edge (CE) angle of Wiberg of 12 degrees. How does this anatomic variation pathologically alter hip biomechanics?

. It increases the abductor moment arm, increasing joint forces.
. It decreases the articular contact area, resulting in increased superior joint contact stress.
. It lateralizes the center of rotation, permanently decreasing the body weight moment arm.
. It induces a functional shortening of the rectus femoris.

Correct Answer & Explanation

. It decreases the articular contact area, resulting in increased superior joint contact stress.

Explanation

A decreased CE angle (<20 degrees) indicates poor lateral acetabular coverage. This significantly decreases the contact area between the femoral head and acetabulum, leading to concentrated, elevated contact stresses superiorly and accelerating osteoarthritis.

Question 6638

Topic: 4. Pediatrics

Based on the Ilizarov principle of tension-stress, optimal bone regeneration and soft tissue histogenesis during distraction osteogenesis are achieved using which distraction rate and rhythm?

. 1 mm per day, divided into 4 increments of 0.25 mm
. 2 mm per day, divided into 2 increments of 1.0 mm
. 0.5 mm per day, performed in a single adjustment
. 3 mm per day, divided into 6 increments of 0.5 mm

Correct Answer & Explanation

. 1 mm per day, divided into 4 increments of 0.25 mm

Explanation

Ilizarov's fundamental research established that a distraction rate of 1 mm/day, divided into four separate increments of 0.25 mm (QID), optimizes the local mechanical environment for regenerate bone formation.

Question 6639

Topic: Pediatric Hip

In a patient with untreated developmental dysplasia of the hip characterized by proximal migration of the femur, how is the biomechanical function of the gluteus medius primarily compromised?

. The resting muscle length is stretched, increasing passive tension.
. The abductor moment arm is decreased and the resting muscle length is shortened.
. The center of rotation is medialized, increasing the mechanical advantage.
. The line of action is shifted anteriorly, acting as a primary flexor.

Correct Answer & Explanation

. The abductor moment arm is decreased and the resting muscle length is shortened.

Explanation

Proximal migration of the greater trochanter decreases the horizontal distance between the hip center and the abductor insertion (decreased moment arm) and reduces the resting length of the muscle, resulting in a severe biomechanical disadvantage and weakness.

Question 6640

Topic: 4. Pediatrics

A pediatric orthopedic surgeon applies a tension band plate (guided growth) to the medial aspect of the distal femoral physis to correct genu valgum. The gradual correction of this deformity relies on which of the following biological principles?

. Wolff's law
. Hueter-Volkmann principle
. Heuter-Volkmann reversed
. Tension-stress effect

Correct Answer & Explanation

. Hueter-Volkmann principle

Explanation

The Hueter-Volkmann principle states that increased mechanical compression across a physis inhibits longitudinal growth, while decreased compression stimulates it. Plating the medial side slows medial growth, allowing the lateral side to 'catch up'.

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