Developmental Dysplasia of the Hip

Overview

Definitions

• Developmental dysplasia of the hip (DDH): a spectrum of developmental disorders of the acetabulum and proximal femur, characterized by instability of the hip joint (formerly known as congenital dysplasia of the hip)
• Subluxation: partial loss of contact between the head of the femur and the acetabulum
• Dislocation: total loss of contact

Classification

• Typical DDH: hip dysplasia in otherwise healthy children (this is the most common form)
• Teratologic DDH: hip dysplasia with an identifiable cause (e.g., arthrogryposis, genetic syndromes such as Down syndrome)
• Neuromuscular DDH: hip dysplasia due to weakness or spasticity in lower-extremity muscle groups (e.g., spina bifida or cerebral palsy)

Epidemiology

• Prevalence: 3–5 in 1,000 children
• More common in children of Caucasian descent
• 80% of cases are girls
• 63% of cases are unilateral, with the left hip most commonly affected.
• Mild hip instability is reported in up to 40% of neonates; these cases usually self-resolve.

Risk factors

• Single greatest risk factor: breech position, especially in late pregnancy (≥ 34 weeks gestation)
• Female sex
• Family history of DDH
• Tight lower-extremity swaddling

Etiology and Pathophysiology

Etiology

Developmental dysplasia of the hip is caused by an inadequate reduction of the femoral head in the acetabulum. This can occur due to several factors.

• Extrauterine factors:
  • Hypertrophy of the ligamentum teres
  • Fatty tissue within the socket
  • Thickening of the transverse acetabular ligament
  • Iliopsoas tendon interfering with access to the acetabulum
• Intrauterine factors:
  • Limited fetal motility in utero
  • Oligohydramnios

Pathophysiology

Normal development of the hip is dependent on contact between the acetabulum and femoral head. However, in DDH:

• There is interrupted contact between the femoral head and acetabulum.
• Because the femoral head gives depth to the acetabulum during normal fetal development, this interrupted contact causes the acetabulum to become shallow.
• A shallow acetabulum results in decreased coverage of the femoral head, which results in hip instability.

Clinical Presentation

• The clinical presentation of DDH depends on the child’s age and the severity of the pathology.
• For this reason, routine hip evaluation should be performed at all well-child exams until 9 months of age.
• DDH shows a progression through time, manifesting differently and more severely as time passes.

Diagnosis

The diagnosis of DDH is made clinically by demonstrating hip instability, asymmetry, and limited abduction of the hip.

Physical exam

Special tests have been devised to evaluate hip joint structure, range of motion, and strength. The choice of which to employ is age-based.

Neonates aged 0–2 months

• Ortolani maneuver (reduction of hips dislocated at rest)
  • High false-positive rate, especially in younger children
  • Remember that hip laxity may be present in up to 40% of newborns.
  • Steps:
    1. Child is placed in the supine position on a stable surface.
    2. Examiner grasps the child’s thigh with the thumb and index finger. 
    3. From an adducted position, the child’s hip is abducted while the trochanter is pushed anteriorly.
    4. Positive when a “hip clunk” is felt or if the maneuver reduces the hip. This hip clunk is the sound or sensation of the femoral head slipping back into the acetabulum.
• Barlow maneuver (dislocation of hips reduced at rest)
  1. Child is placed in the supine position on a stable surface.
  2. Examiner grasps the child’s thighs with the thumb and index finger. 
  3. The child’s hips are adducted.
  4. Examiner palpates the femoral head for movement out of the acetabulum.
  5. Positive when the femoral head is felt slipping, posteriorly, out of the acetabulum. Either a “palpable clunk” or subluxation may be felt on positive exams.

Children 2–3 months old

• Galeazzi test
  1. Child lays supine with hips flexed to 45° and knees flexed to 90°.
  2. Child’s feet are placed flat and level on a surface beside each other.
  3. Positive if one of the knees appears lower than the other knee. This occurs because the head of the femur is displaced posteriorly, shortening the length of the thigh. 
  4. Important: A positive test indicates a lower leg–length discrepancy and is not specific to DDH.
• Klisic test
  1. Examiner places a finger on the greater trochanter and a finger of the same hand on the anterior-superior iliac spine. 
  2. A line is drawn through the tips of both fingers.
  3. If the line passes through or above the umbilicus, the hip is adequately reduced (i.e., normal hip exam).
  4. If the line is below the umbilicus, the test is positive for a displaced hip.

Children who can walk

• Trendelenburg sign
  • Patient is unable to maintain their pelvis in line horizontally while standing on the ipsilateral leg 
  • Indicates hip abductor weakness

Imaging

Imaging can be used to confirm the diagnosis in children with risk factors and a normal physical examination, or in children with inconclusive physical examination findings.

• Hip ultrasound:
  • Useful as an adjunct to the physical exam until 4–6 months of age 
  • Specificity is low and usually operator-dependent.
• Hip X-ray: used from 4–6 months of age when the acetabulum and femoral head begin to ossify

Management

Main goals

• Obtaining and maintaining concentric reduction of the head of the femur in the acetabulum
• Achieving optimal growth and development
• Avoiding complications, notably avascular necrosis

Management by age group

Complications

• Most important complication: avascular necrosis of the femoral epiphysis (orthopedic emergency!) 
• Osteoarthritis (OA):
  • A form of arthritis caused by progressive wasting of articular cartilage and the surrounding joint structures
  • Patients with DDH are at an increased risk of developing OA.
• Pain
• Abnormal gait
• Reduced mobility
• Redislocation
• Residual subluxation
• Dysplasia of the acetabulum

Prognosis

• After reduction, the developmental potential of the acetabulum is excellent.
  • The earlier the treatment, the better the prognosis
  • 95% of cases treated with a Pavlik harness are successfully reduced.
• 90% of mild instability/dysplasia cases resolve spontaneously between months 2 and 6.

Differential Diagnosis

• Transient synovitis: transient inflammation of the hip joint characterized by limited mobility and pain. Magnetic resonance imaging (MRI) or ultrasound shows hip effusions. Management is conservative with rest and nonsteroidal anti-inflammatory drugs (NSAIDs) only. Unlike DDH, transient synovitis occurs later in childhood and generally has an infectious prodrome. 
• Septic arthritis: an infection of the joint causing acute, asymmetric arthritis. Most commonly caused by hematogenous spread, direct inoculation through medical procedures, or trauma. Infants present with high fevers and are unable to bear weight. Diagnosis is through ultrasound-guided needle aspiration, which is also the treatment of choice. 
• Slipped capital femoral epiphysis: an orthopedic disorder of childhood characterized by the pathological “slipping” of the femoral head. Risk factors include obesity, trauma, and genetic predisposition. Patients present with changes in gait and pain in the hip, knee, or groin that is worsened by activity. Plain radiographs confirm the diagnosis. Treatment is surgical.
• Legg-Calve-Perthes disease: a syndrome of unknown etiology characterized by idiopathic avascular necrosis of the femoral head.  Patients present with a gradual onset of hip pain and limp. Diagnosis involves imaging, including X-ray and MRI. Treatment is conservative with optional surgery in severe cases.