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Difficulty: MediumOrdering Imaging Studies

A pediatrician evaluates an infant in the outpatient clinic for a 4-week well-child visit. The patient was born full-term to a primigravid mother via scheduled cesarean delivery due to a frank breech presentation. The mother has no concerns today and reports the infant is feeding well. Vital signs are within normal limits. On physical examination, the physician notes asymmetry of the inguinal and gluteal creases. The Ortolani and Barlow maneuvers are performed; a soft, high-pitched click is heard on the left side, but there is no palpable clunk to suggest active dislocation. The infant demonstrates equal leg lengths and normal spontaneous movement of all extremities. What is the most appropriate next step in the radiologic evaluation of this patient?

  1. A
    Anteroposterior plain radiography of the pelvis
  2. B
    Computed tomography of the pelvis
  3. Ultrasonography of the hipsAnswer
  4. D
    Magnetic resonance imaging of the hips without contrast
  5. E
    Real-time fluoroscopy of the hip joints

Answer

The correct answer is ultrasonography of the hips.
The most appropriate imaging study for this patient is ultrasonography of the hips. This infant possesses significant risk factors for developmental dysplasia of the hip (DDH), including a breech presentation and female sex. Furthermore, her physical examination is equivocal, demonstrating asymmetric skin folds and a soft click, though lacking the diagnostic 'clunk' of a positive Ortolani or Barlow maneuver. According to evidence-based guidelines, infants with these risk factors or equivocal findings require formal imaging evaluation. Because the femoral head and acetabulum are entirely cartilaginous before 4 to 6 months of age, ultrasonography is the optimal modality. It clearly delineates the unossified cartilaginous anatomy and allows the clinician to perform dynamic stress testing of the joint in real-time.

Step-by-Step Solution

1
Analyze the patient's risk profile and physical examination findings.
The patient is a female infant with a history of breech presentation and asymmetric skin folds, placing her at high risk for developmental dysplasia of the hip (DDH). The physical exam is equivocal (click, but no clunk).
Identifying high-risk features determines the need for formal imaging rather than relying solely on clinical observation.
2
Correlate the patient's age with musculoskeletal developmental anatomy.
The patient is 4 weeks old, meaning her femoral heads and acetabula are predominantly composed of cartilage rather than ossified bone.
Anatomical development directly dictates which imaging modality will provide diagnostic utility.
3
Select the optimal imaging modality based on the anatomical constraints.
Ultrasonography is selected because sound waves easily penetrate and visualize cartilaginous structures, unlike X-rays which pass through them without creating a diagnostic image.
Ultrasound provides the safest, most accurate, and dynamic assessment of the neonatal hip prior to ossification.

Key Concept

In infants younger than 4 to 6 months with risk factors or equivocal exams for developmental dysplasia of the hip (DDH), ultrasonography is the preferred imaging modality because the femoral head is predominantly cartilaginous and not visible on plain radiographs.
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Ordering Imaging Studies

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