What is Developmental Dysplasia of the Hip (DDH)?
Developmental dysplasia of the hip (DDH) is a spectrum of hip abnormalities ranging from mild acetabular immaturity and hip instability in newborns to frank hip dislocation, characterized by abnormal development of the acetabulum (hip socket) and femoral head relationship that can lead to early osteoarthritis if untreated 1.
Clinical Spectrum and Pathophysiology
DDH encompasses a wide range of anatomical abnormalities:
- Mild acetabular dysplasia: Shallow hip socket with maintained femoral head position
- Hip instability: Femoral head can be dislocated (Barlow test positive) or relocated (Ortolani test positive) 1
- Hip subluxation: Partial displacement of the femoral head from the acetabulum
- Complete hip dislocation: Femoral head completely displaced from the acetabulum 2
The acetabulum remains shallow and the femoral head develops in an abnormal position, leading to progressive structural changes 3. Untreated DDH results in chronic hip pain, early osteoarthritis (often before age 30), limb length discrepancy, altered gait, and joint contractures 4.
Epidemiology and Risk Factors
DDH is the most common congenital musculoskeletal disorder in newborns, with incidence ranging from 0.06 to 76.1 per 1,000 live births depending on population and screening methods 3.
Key risk factors include 5, 3:
- Female sex (significantly higher prevalence)
- Breech presentation (frank breech carries highest risk)
- Positive family history (first-degree relatives with DDH or early hip problems)
- Firstborn children
- Oligohydramnios
- Associated congenital deformities (torticollis, metatarsus adductus)
Higher prevalence occurs in Asian, Caucasian, Mediterranean, and American populations 6.
Diagnosis Approach by Age
Birth to 4 Weeks
Clinical examination only—imaging is NOT recommended 1. Physical examination includes:
- Barlow test: Attempts to dislocate an unstable hip
- Ortolani test: Attempts to relocate a dislocated hip
- Assessment for limited hip abduction, leg length discrepancy, and asymmetric thigh skin folds (though these lack specificity) 1
Critical pitfall: Ultrasound before 4 weeks has excessive false-positive rates (detecting physiologic immaturity that spontaneously resolves), leading to overtreatment 1.
4 Weeks to 4 Months
Hip ultrasound is the imaging modality of choice 1. The AAP recommends selective ultrasound screening at 4-6 weeks for:
- Girls with breech presentation (highest risk group)
- Girls with positive family history
- Boys with breech presentation
- Any infant with equivocal physical examination 1
Ultrasound advantages at this age:
- Visualizes cartilaginous structures (femoral head, acetabular cartilage)
- Graf classification system quantifies severity using alpha angle measurements
- Sensitivity 77%, specificity 99.8%, positive predictive value 49% 1
Important caveat: 41-58% of abnormal physical examinations are false-positives when correlated with ultrasound, and 84-95% of Graf type II hips normalize by 3 months without treatment 1.
4 to 6 Months (Transition Period)
Either ultrasound or pelvic radiograph is appropriate 1. Radiography becomes increasingly useful as the femoral head ossific nucleus appears (typically 4-6 months, range 1.5-8 months) 1.
Radiograph advantages: Normal radiograph at 4 months reliably excludes DDH and reduces unnecessary treatment in infants with positive ultrasound by 40% 1.
Beyond 6 Months
Pelvic radiograph is the preferred imaging modality 1. Assessment includes:
- Acetabular index measurement
- Femoral head position relative to Hilgenreiner and Perkin lines
- Shenton arc continuity
- Femoral head ossific nucleus position and development 1
Clinical examination becomes less reliable after 8-12 weeks as capsular laxity decreases and muscle tightness increases, making Barlow/Ortolani tests often negative even with persistent dislocation. Limited hip abduction becomes the most important screening finding, though it has only 40-55% positive predictive value 1.
Treatment Principles
Treatment success is inversely related to age at diagnosis—early detection is critical 5, 4.
Conservative Management (Birth to 6 Months)
Pavlik harness is first-line treatment for hip instability or dysplasia 1.
- Most effective when applied before 6 weeks of age
- Can be used up to 6 months of age
- Overall success rate 67-83% 1
- Ultrasound monitoring during treatment confirms concentric hip reduction and assesses treatment response 1
- Predictors of failure: low post-reduction alpha angle and <20% femoral head coverage 1
Surgical Intervention
Reserved for:
- Severe dysplasia or dislocation at presentation
- Late diagnosis (after 6 months)
- Failed conservative management 1
Late-presenting DDH (diagnosed after 3 months) occurs in only 0.22 per 1,000 births but represents a devastating missed diagnosis in walking-age children 1, 4.
Genetic Considerations
Multiple susceptibility genes have been identified (WISP3, PAPPA2, HOXB9, HOXD9, GDF5, TGF Beta 1, CX3CR1, UQCC, COL1A1, TbX4, ASPN), though both genetic and environmental factors contribute to DDH pathogenesis 6.