A 4-week-old female infant is brought to the pediatrician by her parents for a routine well-child examination. The infant was born at 39 weeks' gestation via cesarean section due to breech presentation. The mother reports that the infant is feeding well and meeting all early milestones. On physical examination, the skin folds on the posterior thighs are asymmetric. When the clinician flexes the infant's hips and knees to 90º and then gently abducts the hips, a palpable "clunk" is felt as the left femoral head relocates into the acetabulum. The right hip appears stable. There is no evidence of foot deformity or spinal abnormalities.
Which of the following is the most appropriate next step in the management of this patient?
The correct answer is:
E) Ultrasonography of the hips
The infant's presentation is highly suggestive of developmental dysplasia of the hip (DDH), a condition characterized by an abnormal relationship between the femoral head and the acetabulum. The "clunk" felt during the abduction maneuver is a positive Ortolani sign, which indicates that a dislocated femoral head is being reduced back into the acetabulum. The Barlow maneuver, conversely, involves adducting the hip while applying posterior pressure to see if the hip can be dislocated. In an infant younger than 4 to 6 months of age, the femoral head and acetabulum are primarily cartilaginous and are not well-visualized on plain radiographs. Therefore, ultrasonography is the gold standard for diagnosis in this age group, as it can assess the depth of the acetabulum and the stability of the femoral head.
Answer choice A: Immediate application of a Pavlik harness, is incorrect. While the Pavlik harness is the standard treatment for DDH in infants under 6 months of age, imaging confirmation is typically performed first to document the degree of dysplasia or dislocation before initiating treatment.
Answer choice B: Observation and reassessment at the 2-month visit, is incorrect. While mild hip laxity can sometimes resolve spontaneously in the first two weeks of life, a persistent positive Ortolani or Barlow sign at 4 weeks requires prompt diagnostic imaging and intervention to prevent permanent joint deformity and gait abnormalities.
Answer choice C: Open reduction with pelvic osteotomy, is incorrect. Surgical intervention is generally reserved for older children (usually >18 months) or those who have failed closed reduction and bracing. It is not an appropriate initial step for a 4-week-old infant.
Answer choice D: Radiography of the pelvis and hips, is incorrect. Plain X-rays are unreliable in infants under 4–6 months because the femoral epiphysis has not yet ossified. X-rays become the preferred diagnostic modality only after the secondary ossification centers appear.
Key Learning Point
Developmental dysplasia of the hip (DDH) is most commonly found in first-born females with a history of breech positioning. Screening is performed via the Barlow (dislocatable) and Ortolani (reducible) maneuvers. Ultrasonography is the diagnostic study of choice for infants <4 to 6 months, while radiographs are used for older infants. The primary treatment for children <6 months is the Pavlik harness, which maintains the hips in flexion and abduction.
