Developmental Dysplasia of the Hip DDH

Synonym: congenital dislocation of the hip

What is developmental dysplasia of the hip?

Developmental dysplasia of the hip (DDH) was formerly referred to as congenital dislocation of the hip (CDH). DDH is now the preferred term to reflect that DDH is an ongoing developmental process, which is variable in presentation and not always detectable at birth. DDH refers to a spectrum of severity ranging from mild acetabular dysplasia with a stable hip, through more severe forms of dysplasia with neonatal hip instability, to established hip dysplasia with or without later subluxation or dislocation.

Epidemiology

• DDH affects 1-3% of newborns and is responsible for 29% of primary hip replacements in people up to the age of 60 years.^[1]
• A systematic review of unscreened populations estimated the prevalence of clinically diagnosed, established hip dysplasia to be 1.3 per 1,000 but in populations screened clinically with Ortolani and Barlow tests, the prevalence is higher at 1.6-28.5 per 1,000 and it is higher still with ultrasound screening.^[1]
• The left hip is dislocated more often than the right, possibly due to the more common left occiput anterior position in utero, limiting abduction of the left hip. 20% of cases are bilateral.
• It is more common in cultures that use swaddling of babies, with lower extremities fully extended and wrapped together.^[2]
• In contrast, it is less common in cultures that carry their children in front of the mother with the hips widely abducted, the straddle or jockey position.^[3]

DDH risk factors

• Having a sibling with hip dysplasia increases risk by 5%.
• About 80% of cases are in girls, probably due to the effect of circulating maternal hormone relaxin on ligamentous laxity.^[4]
• About 60% of cases are firstborn.
• Vaginal delivery of babies with breech presentation is associated with a 17-fold increased risk of hip dysplasia; there is a 7-fold increase for breech babies delivered by elective caesarean section.^[1]
• Restriction of movement as with oligohydramnios increases the risk.
• The risk is also increased in multiple pregnancy and prematurity.
• It is more common with neuromuscular disorders, such as cerebral palsy, meningomyelocele and arthrogryposis.
• Those presenting with late DDH (presenting after 3 months of age) have fewer of the above risk factors: they are more likely to have been a cephalic delivery and more likely to have had a history of swaddling.^[5]

Screening for developmental dysplasia of the hip

Screening for DDH is part of the physical examination of newborn and 6- to 8-week-old babies. Ultrasound screening is not currently recommended as a screening tool for all babies.

• There is a suggestion that the national screening programme in the UK, which has operated since 1969, has not resulted in any fewer operations for late disease.
• However, studies have shown that clinical screening for neonatal instability of the hip by experienced orthopaedic examiners significantly reduces the incidence of late-presenting (walking) DDH.^[6]
• A Cochrane review found that there was insufficient evidence to give clear recommendations regarding screening for DDH. There was some inconsistent evidence that universal ultrasound results in a significant increase in treatment compared to the use of targeted ultrasound or clinical examination alone. The review concluded that ultrasound strategies have not been demonstrated to improve clinical outcomes including late-diagnosed DDH and surgery.^[7]
• A large long-term randomised controlled study of universal or selective ultrasound versus a well-done physical examination, showed higher treatment rates but no reduction in late cases of DDH.^[8] There was also no difference, at skeletal maturity, in acetabular dysplasia or degenerative change.

Ultrasound screening

Universal ultrasound examination is not recommended by Public Health England but selective ultrasound examination for babies with specific risk factors is recommended. An ultrasound examination of the hips should be performed within 6 weeks of age if:^[9]

• There is a first-degree family history of hip problems in early life, unless DDH has been definitely excluded in that relative.
• There is a breech presentation:
  • At or after 36 completed weeks of pregnancy, irrespective of presentation at delivery or mode of delivery; or
  • At delivery if this is earlier than 36 weeks.
  • In the case of a multiple birth, if any of the babies falls into either of these categories, all babies in this pregnancy should have an ultrasound examination.

Examination

The most important screening tool for DDH remains the physical examination^[3] . DDH is an evolving process; therefore, a normal physical examination in the neonatal period does not preclude a subsequent diagnosis of DDH.^[4] Asymmetrical skin folds are found in 25% of normal babies and are therefore not an important clinical finding in isolation.

Under 3 months old

• Observe for asymmetry:
• Asymmetrical gluteal or thigh skin folds.
• Limb length discrepancy (see Galeazzi sign below).
• Limitation and asymmetry of hip abduction when the hip is flexed to 90°.
• The Ortolani and Barlow tests are the most common clinical tests for newborn babies:
  • In the Ortolani test (screen for a dislocated hip), the examiner applies gentle forward pressure to each femoral head in turn, in an attempt to move a posteriorly dislocated femoral head forwards into the acetabulum. Palpable movement suggests that the hip is dislocated or subluxed, but reducible.
  • In the Barlow test (screen for a dislocatable hip), gentle backward pressure is applied to the head of each femur in turn, and a subluxable hip is suspected on the basis of palpable partial or complete displacement.
• Both Barlow and Ortolani tests detect an unstable hip but do not detect an irreducible dislocated hip, which is best detected by identifying limited abduction of the flexed hip. Nor do they detect a stable hip with abnormal anatomy - eg, acetabular dysplasia.
• Benign hip clicks, resulting from soft tissues snapping over bony prominences during hip movement, should be distinguished from the clunks produced during the Ortolani manoeuvre as the dislocated femoral head is reduced and from the subluxation felt during the Barlow test.
• The Barlow and Ortolani tests are useful in neonates but become difficult by 2-3 months of age.
• Stable hips may be dysplastic. Limited hip abduction (less than 60°) when the hip is flexed to 90° is the most important sign of a dislocated or dysplastic hip.^[1]

Children aged 3-6 months

• The physical signs are rather different and so are the requirements of examination.
• Unilateral limitation and asymmetry of hip abduction is the most reliable sign of DDH after eight weeks.^[10]
• If the hip is dislocated it is in a fixed position.
• The Galeazzi sign:
  • The child is examined lying supine with the hips and knees flexed to 90° and the height of each knee is compared.
  • Unilateral femoral shortening may signify hip dislocation or rarer abnormalities of the femur.
  • False negative results may occur with bilateral hip dysplasia or when the pelvis is not level.
  • A positive sign is that one leg appears shorter than the other.
  • This is usually due to dislocation of the hip; however, any discrepancy of limb length will produce a positive sign.
• Other physical signs for late dislocation include asymmetry of the gluteal thigh or labral skin folds, discrepancy in leg length, a widened perineum on the affected side, buttock flattening, asymmetrical thigh skin folds and standing or walking with external rotation of the affected leg.

Older children^[1]

• There is limited abduction when fully flexed.
• They may walk on toes on the affected side or present with a painless limp.

Bilateral dislocation of the hip

• DDH is bilateral in about 20% of cases.^[1]
• It can be quite difficult to diagnose, especially after the neonatal period.
• There is often a waddling gait with hyperlordosis.
• The Galeazzi sign for hip shortening is often absent, as are asymmetrical thigh and skin folds, or asymmetrically decreased abduction.
• Careful examination is needed with a high level of suspicion.

Investigations^[4]

• Dynamic ultrasound is used to assess hip stability and acetabular development in infants.
• Ultrasound helps diagnosis in children under 4.5 months but pelvic X-rays are more useful in older infants and children once the femoral head ossification centre has developed.
• CT and MRI scanning may also be needed but may require sedation.
• Arthrography is commonly used peri-operatively when deciding between closed and open reduction.

Developmental dysplasia of the hip treatment and management^[1]

Early diagnosis and treatment of those most severely affected are important for a good outcome. Most unstable hips stabilise spontaneously by 2-6 weeks of age and any hip that remains dislocatable or pathologically unstable after this time requires prompt treatment.

• Bracing is first-line treatment in children younger than 6 months. Surgery is an option for children in whom non-operative treatment has failed and in children diagnosed after 6 months of age.
• Early detection and treatment, although important, do not entirely avoid the need for subsequent surgery and surgery is needed by almost 6% of infants treated with abduction splinting.
• The indications for the various procedures and the most effective management interventions remain controversial.

Non-surgical management^[1]

• A dynamic flexion-abduction orthosis (Pavlik^® harness), left in place at all times, is used to maintain hip reduction. Treatment should start as soon as the diagnosis has been confirmed.^[11]
• The harness can be adjusted as the child grows and the hip stabilises.
• One study showed that when harness treatment was started by 90 days of age, only 5.7% of babies required further treatment.
• The main risks of splinting are avascular necrosis and a temporary femoral nerve palsy.
• Harness or splint treatment is much less successful if it is started after the age of 6-8 weeks.
• A Pavlik^® harness is contra-indicated in children older than 4.5-6 months and when the hip is irreducible.
• Several small studies have shown that stable hips with mild dysplasia can be observed safely for six weeks before a decision to treat is made.

Surgery^[1]

• Surgery is indicated for those who do not respond to early splint or harness treatment and for those who are diagnosed late and are not suitable for splint or harness treatment.
• The most common operation is closed reduction with adductor or psoas tenotomy (to decrease adduction contracture), followed by 3-4 months in a plaster cast or abduction brace.
• The older the child, the more likely an extensive procedure will be required with open reduction and soft tissue stabilisation of the joint, followed by a cast.
• Over the age of 18-24 months, an additional pelvic and/or femoral osteotomy is often required.
• Results worsen the older the child is at the time of surgery. Osteonecrosis and re-dislocation predict a poor functional result. A child aged over 3, with highly dysplastic acetabula, may have a better outcome if left untreated, as they may not have sufficient acetabular growth to remodel a surgically reduced hip.^[12]

Follow-up

• Follow-up is required at least until the hip is clinically stable and imaging shows a stable, centred, normal hip.
• The length of follow-up and the frequency of radiographic examinations are still debated.
• Follow-up may reveal acetabular dysplasia in the contralateral hip.^[12]

Complications

• Surgery can result in a number of complications, including re-dislocation, stiffness, blood loss and avascular necrosis of the capital femoral epiphysis (which occurs in 5-15% of cases).
• DDH is an important cause of childhood disability and accounts for up to 9% of all primary hip replacements (up to 29% of those in people aged 60 years or younger).^[13]
• Potential long-term complications include premature degenerative joint disease and low back pain.^[1]

Developmental dysplasia of the hip prevention^[3]

• Primary prevention of DDH through education about safe swaddling has been shown to be effective in communities who would otherwise use traditional swaddling techniques.
• The International Hip Dysplasia Institute and the Pediatric Orthopedic Society of North America advise that:
• Infant hips should be positioned in slight flexion and abduction during swaddling.
• The knees should also be maintained in slight flexion.
• Additional free movement in the direction of hip flexion and abduction may have some benefit.
• Avoidance of forced or sustained passive hip extension and adduction in the first few months of life is essential for proper hip development.