What are the characteristics of Developmental Dysplasia of the Hip (DDH) in newborns?

Characteristics of Developmental Dysplasia of the Hip (DDH) in Newborns

DDH in newborns represents a spectrum of hip abnormalities ranging from mild hip laxity and dysplasia to complete dislocation, characterized by abnormal acetabular shape and malposition of the femoral head that requires early detection through physical examination at every well-baby visit. 1, 2

Definition and Clinical Spectrum

DDH encompasses various anatomical abnormalities where the femoral head has an abnormal relationship with the acetabulum, ranging from:

• Hip instability and capsular laxity 1, 2
• Mild subluxation with partial displacement 1
• Complete fixed dislocation 1, 2
• Isolated acetabular dysplasia (abnormal socket shape) 1

Epidemiology and Incidence

• Affects approximately 1.5 per 1,000 Caucasian American births 2
• Occurs less frequently in African Americans 1
• Female infants are affected 4 to 8 times more commonly than males 1, 2
• Left hip involvement is three times more frequent than right hip 1

Key Risk Factors (in Order of Importance)

The three most critical risk factors are:

1. Breech positioning in utero (relative risk 3.8) - causes extreme hip flexion with knee extension, leading to iliopsoas muscle shortening and contracture that promotes femoral head dislocation 1, 2
2. Female gender (relative risk 2.5) - attributed to higher estrogen receptor concentration and increased sensitivity to maternal relaxin hormone 1, 2
3. Positive family history (relative risk 1.4) - genetic predisposition demonstrated by increased prevalence in monozygotic versus dizygotic twins 1, 2

Additional risk factors include:

• Infant swaddling practices 1, 2
• Oligohydramnios (reduced amniotic fluid causing restricted hip mobility) 1
• Firstborn status (though not definitively proven in recent meta-analyses) 1

Important caveat: Preterm infants are NOT at increased risk for DDH 1

Pathophysiology

The etiology is multifactorial with two primary mechanisms:

Hormonal factors:

• Maternal hormone relaxin causes abnormal laxity of hip capsule and surrounding ligaments 1, 2
• Infants with DDH have higher concentrations of estrogen receptors 1

Mechanical factors:

• Limited in utero hip mobility from breech position, oligohydramnios, or being firstborn 1
• Left occiput anterior fetal position places left hip against maternal spine, limiting abduction and explaining higher left-sided involvement 1

Clinical Presentation in Newborns

Physical examination findings indicating DDH:

Positive provocative tests (most reliable in first 2-3 months):

• Ortolani test positive - palpable or audible "clunk" when abducting and lifting the flexed thigh, indicating the femoral head reducing back into the acetabulum from a dislocated position 1, 3
• Barlow test positive - hip can be dislocated posteriorly with gentle adduction, then relocated with abduction, identifying unstable hips missed by Ortolani test 1, 3

Other physical findings:

• Asymmetric skin folds (thigh or gluteal) 1, 3
• Apparent leg length discrepancy with shortening on affected side 1, 3
• Limited hip abduction (becomes more prominent after 3 months of age) 1, 3

Critical distinction: A stable "clicking" hip with no laxity is benign and should not be confused with a positive Ortolani or Barlow test 1, 3

Natural History and Prognosis

Most newborn hip abnormalities resolve spontaneously:

• 60-80% of abnormalities identified by physical examination normalize without intervention 1, 2
• Greater than 90% of abnormalities identified by ultrasound resolve spontaneously 1, 2
• Most borderline "abnormal" hips in the neonatal period represent physiologic immaturity rather than true pathology 1, 2

Consequences of untreated DDH:

• Untreated subluxation and dislocation inevitably lead to early degenerative joint disease 1, 2
• DDH causes up to one-third of all total hip arthroplasties in patients under 60 years of age 1, 2
• Late presentation is a major negative prognostic factor, requiring more complex treatment and surgical intervention 1, 2

Screening Recommendations

The American Academy of Pediatrics recommends selective screening rather than universal ultrasound screening 1, 2

Clinical examination schedule:

• Perform hip examination at every well-baby visit: 2-4 days for newborns, then at 1,2,4,6,9, and 12 months of age 1, 3

Imaging indications:

• Positive Ortolani or Barlow test 3
• Breech presentation in utero 1, 2
• Family history of DDH 1, 2
• Inconclusive physical examination findings 1, 2

Timing of ultrasound:

• Should be performed after 2 weeks of age, as physiologic laxity is common immediately after birth and often resolves spontaneously 2
• For infants with risk factors, ultrasound screening is recommended at 6 weeks of age 4
• Ultrasound is the preferred imaging modality for infants under 4-6 months of age 2, 3

Common pitfall: Universal ultrasound screening increases detection of "abnormal" hips but does not significantly decrease late diagnosis of DDH and carries risk of overtreatment with iatrogenic avascular necrosis 1, 2

Age-Specific Examination Considerations

In newborns and infants under 3 months:

• Ortolani and Barlow tests are most reliable 1, 3
• Focus on detecting hip instability and capsular laxity 1, 3

After 3 months of age:

• Ortolani and Barlow tests become less reliable as hip capsule tightens 1, 3
• Limitation of hip abduction and asymmetric thigh folds become more useful clinical signs 1, 3

Treatment Implications

Most serious complication of treatment is avascular necrosis, which is a predictor of poor prognosis 1, 2, 3

Treatment approach depends on age:

• Pavlik harness is not typically instituted in neonates because many unstable hips stabilize without intervention 4
• Treatment with Pavlik harness is indicated in children older than 2 weeks with persistent hip instability 4
• Early diagnosis and treatment (particularly during first 6 months of life) results in less invasive interventions and minimized long-term effects 4, 5