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Difficulty: MediumPediatric Musculoskeletal Disorders

A 6-month-old female infant is brought to the clinic for a routine well-child examination. The parents have no concerns and report that the infant is feeding well, babbling, and rolling over from front to back. She was born at 39 weeks gestation via uncomplicated spontaneous vaginal delivery to a 28-year-old primigravid woman. Family history is significant for a maternal aunt who required treatment for a hip condition during infancy. On physical examination, the infant's vital signs are within normal limits. She is alert, active, and interactive. Examination of the lower extremities reveals asymmetric thigh and gluteal skin folds. When the infant is placed in the supine position with both hips and knees flexed and feet resting flat on the examining table, the right knee rests visibly lower than the left knee. The Ortolani and Barlow maneuvers do not elicit any clunk or instability. Which of the following is the most appropriate next step in management?

  1. Anteroposterior radiograph of the pelvisAnswer
  2. B
    Ultrasound of the bilateral hips
  3. C
    Computed tomography of the pelvis
  4. D
    Referral for pediatric neurology evaluation
  5. E
    Reassurance and routine follow-up in 2 months

Answer

Anteroposterior radiograph of the pelvis
The correct answer is an anteroposterior radiograph of the pelvis. This patient exhibits classic signs of developmental dysplasia of the hip (DDH), including asymmetric skin folds and a positive Galeazzi sign (unequal knee heights when the hips and knees are flexed in the supine position). While the Ortolani and Barlow maneuvers are negative, these tests become progressively less sensitive as infants age and the surrounding soft tissues tighten. Any infant with abnormal physical exam findings suggestive of DDH requires diagnostic imaging. The choice of imaging depends strictly on the patient's age. For infants younger than 4 months, ultrasound is the modality of choice because the femoral head is primarily cartilaginous and easily visualized. However, between 4 to 6 months of age, the capital femoral epiphysis begins to ossify. This ossified bone creates acoustic shadowing that obscures the deeper structures of the hip joint on ultrasound. Therefore, in a 6-month-old infant, an anteroposterior radiograph of the pelvis is the most reliable and appropriate next step to evaluate the hip joint.

Step-by-Step Solution

1
Evaluate the physical examination findings.
The patient has asymmetric skin folds and a positive Galeazzi sign (right knee lower than left).
These findings suggest a unilateral hip dislocation or leg length discrepancy indicative of Developmental Dysplasia of the Hip (DDH).
2
Determine the need for diagnostic imaging based on the patient's age.
The patient is 6 months old.
The algorithm for DDH imaging strictly depends on the age of the infant due to the timeline of skeletal maturation.
3
Select the appropriate imaging modality for a 6-month-old infant.
Anteroposterior radiograph of the pelvis is selected.
In infants older than 4 to 6 months, the capital femoral epiphysis begins to ossify, making plain radiographs the gold standard over ultrasound.

Key Concept

Age-appropriate diagnostic imaging for Developmental Dysplasia of the Hip (DDH)
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Topics

Pediatric Musculoskeletal Disorders

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