Developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) refers to hip instability, subluxation/dislocation of the femoral head, and/or acetabular dysplasia in a developing hip joint. The etiology is not yet fully understood but a breech presentation and family history of DDH are the most important risk factors. The clinical features depend on the age of the child. During the first 6 months, the child will be asymptomatic but the hip can be easily dislocated, and a clunk is felt during a hip examination. As the child grows older, contractures develop and abduction of the hip becomes limited. Deformities and leg length discrepancies also develop. A patient with DDH is at increased risk of accelerated osteoarthritis. Since DDH is a common congenital abnormality, all newborns must be screened by physical examination for DDH. Additional screening with imaging is recommended for children with a family history of DDH, a history of breech presentation, and/or clinical features of DDH. Ultrasonography is the imaging modality of choice for infants younger than 4 months, whereas x-rays are used for older children. The goal of treatment is to reduce and maintain the femoral head into the acetabulum as early as possible to allow the hip joint to develop normally. A rigid harness is used in children younger than 6 months. Children 6–18 months of age should be treated with closed reduction, while children older than 18 months should be treated with open reduction. Following either closed or open reduction, the hip should be immobilized in a hip spica cast. The prognosis is not good if treatment is initiated after 6 months.

• Incidence: most common congenital abnormality of skeletal development ^[1]
  • Hip instability: 1 in 100 births
  • Dislocation: 1 in 1000 births
• Sex: : ♀ > ♂ (4–5:1) ^[2]
• Racial/regional background ^[1]
  • High incidence in Native American, Eastern European, and Sami populations
  • Low incidence in Chinese and black populations

Epidemiological data refers to the US, unless otherwise specified.

• The exact etiology of DDH remains unknown.
• Several risk factors have been identified: ^[2]
  • Family history
  • Breech presentation
  • Inadequate intrauterine space for the fetus; (e.g., oligohydramnios, first born child, twins, large birth weight)
  • Diseases associated with ligamentous laxity
  • The left hip is more commonly affected. ^[2]
  • Secondary anatomic changes
    • Development of contractures around the hip
    • Problems associated with leg length discrepancy (e.g., abnormal gait, scoliosis, lordosis)

• Children with DDH have varying degrees of abnormal hip growth such as hip instability, hip subluxation, and/or hip dislocation which result in ^[3]
  • Hypertrophy of pulvinar fat in the acetabulum, transverse acetabular ligament, and/or ligamentum teres
  • Acetabular dysplasia

A positive Barlow sign shows that the reduced hip is subluxatable or dislocatable. A positive Ortolani sign shows that a dislocated hip is reducible.

Leg length discrepancy, Galeazzi sign, and/or asymmetrical gluteal folds may be absent in patients with bilateral DDH.

Screening ^[4]

• Physical examination must be performed at every well-baby visit for up to 6 months
• Screening with imaging is recommended up to 6 months of age only if one or more of the following risk factors are present
  • Breech presentation at birth
  • Positive family history of DDH
  • Clinical features of DDH

Imaging ^[4]

• Hip ultrasound: imaging of choice in all infants younger than 4 months
  • Alpha angle < 60°
  • Beta angle > 55°
• Pelvic x-ray (in AP and frog leg lateral view): imaging of choice in infants older than 4 months (when cartilage begins to ossify)
  • Findings of hip dislocation
    • Interrupted Shenton's line
    • The ossified nucleus of the femoral head lies at or above Hilgenreiner line
    • The ossified nucleus of the femoral head lies at or lateral to Perkin line
  • Findings of acetabular dysplasia
    • Acetabular angle > 30° after 4 months
    • Center-edge angle < 19° in the age group 6–13 years, or < 25° in children older than 14 years
• Arthrogram: indicated following closed reduction to ensure successful reduction (see “Treatment” below)
• Hip CT: imaging of choice to follow up patients with a hip spica (see “Treatment” below)
• Hip MRI: not used in the diagnosis of DDH

Ultrasound is the imaging technique of choice for diagnosis of DDH in infants less than 4 months while x-ray is the imaging modality of choice for infants older than 4 months.

• < 6 months
  • Pavlik harness (most commonly used splinting device) that maintains the hips in 90–100° of flexion and 50° of abduction ^[3]
  • Alternatives: rigid harnesses (e.g., von Rosen harness)
    • A rigid harness that is used to treat infants with developmental dysplasia of the hip (DDH) below the age of 6 months.
    • The harness keeps the hips abducted by 50° and flexed by 90–100° in order to achieve concentric reduction of the femoral head.
• 6–18 months; or failure of bracing: closed reduction followed by immobilization with a hip spica cast ^[5]
• > 18 months; or failure of closed reduction: surgical therapy (open reduction possibly with a pelvic/femoral osteotomy) followed by immobilization with a hip spica cast
• Older adolescents or adults: total hip arthroplasty

See “Differential diagnosis of pediatric hip pain.”

The differential diagnoses listed here are not exhaustive.

• Complications of DDH ^[3]
  • Residual acetabular dysplasia, subluxation, and/or redislocation despite treatment
  • Early osteoarthritis in the hip joint
  • Leg length discrepancy which may present with back pain, functional scoliosis, and/or knee pain
  • Genu valgum
• Complications of treatment ^[5]
  • Avascular necrosis (AVN) of the femoral epiphysis
  • Treatment-related transient femoral nerve palsy
  • Pavlik harness disease

We list the most important complications. The selection is not exhaustive.

• The outcomes of children with DDH who receive early treatment are generally good. ^[3]
• The reappearance of a U shaped acetabular teardrop shadow (Köhler's shadow) after reduction is an indicator of good hip function.
• Factors associated with a poor prognosis ^[5]
  • Late initiation of treatment (especially after 6 months)
  • Need for open reduction
  • Failure of a first-line treatment
  • Possibly, bilateral hip dislocation