1) DDH refers to a variety of conditions which describe an abnormal relationship between the acetabulum and the femoral head. DDH is now the preferred term for this condition which in the past was routinely described using the terms congenital and dislocated. The currently used language stresses the fact that this condition is not always present at birth and may develop postnatally during infancy and that maldevelopment without frank dislocation is often present. DDH is presumed to occur in otherwise healthy newborns and infants. Hip pathology associated with neuromuscular or syndromic conditions (teratologic dislocations i.e. spina bifida, arthrogryposis) are not considered characteristic of DDH.
This spectrum of DDH may include hips that are:
Dislocated the femoral head is entirely outside of the acetabulum. Dislocations may be reducible or irreducible.
Dislocatable The femoral head is within the acetabulum but may be displaced from its seat by physical maneuver
Subluxable The femoral head can be partially removed from the acetabulum
Dysplasia Condition not clinically apparent, but relates to radiographic findings that describe maldevelopment of the acetabulum
Although overall the disorder is uncommon, it is critical that screening is performed, so that diagnosis and treatment are started as early as possible for optimal results. Long-term complications of untreated dislocated hips include hip pain, impaired gait, and degenerative joint disease. Late detection has frequently been the cause of malpractice claims.
Brief epidemiologic review: Incidence has multifactoral influences - race increase in Lapp and Native Americans, decrease in Africans; sex girls > boys - but overall hip instability occurs in roughly 1:100 newborns with dislocation occurring in around 1-1.5:1,000. Regardless of screening method, at 18 months of age, DDH is detected in 1:5,000 infants.
The key element in terms of pathogenesis relates to the fact that, in utero, the femoral head develops at a rate that outstrips the rate of development of the acetabulum. During the late stages of gestation the acetabulum is at its shallowest with only approximately 50% coverage of the femoral head. This makes the hip vulnerable to mechanical forces that might push the femoral head away from the center of the acetabulum. During the last 4 weeks of gestation, acteabular development speeds up, outstrips femoral head development, and provides increased coverage.
2) The hip exam should always be performed on an undiapered infant who has been placed supine on the exam table. At no time should this exam be performed while an infant is supine on a caregivers lap.
The Ortolani and Barlow tests allow the examiner to detect hip instability. (See fig. 1) . The first part of the instability test is the Barlow maneuver. (*Remember B before O.) Examiners should flex the infant hip to 90? and place their thumbs on the inner thigh and index and middle fingers on the greater trochanter. Gently, the hip should be adducted and the knee directed posteriorly. A palpable clunk or sensation of hip movement represents the femoral head exiting the acetabulum and is a positive finding for a dislocatable hip. The second part of the instability test, the Ortolani maneuver begins with infant hip and examiner hands in the same position as the Barlow test. However, now the examiner gently abducts the hip while the femur is lifted anteriorly. If a palpable clunk is detected during this test, it is a sign of a dislocated hip being reduced the femoral head is clunking its way back into the acetabulum.
Following the instability test there are a number of tests for asymmetry that are critical for complete assessment of infant hips. The Galeazzi (or Allis or Perkins) test assesses for any leg length discrepancy. (See fig. 2) . Again the infant is placed supine on the examining table with the hips flexed to 90?. The knees are flexed and both feet are placed flat on the examining table. A normal exam yields both knees at the same level. If there is a unilateral hip dislocation, the posterior location of the affected hip will make the femur on that side appear shorter. A positive Galeazzi test shows the knee on the side of the affected hip to be at a lower level than the other knee.
An examination of inguinal, thigh, and gluteal skin folds should also be performed with attention to the presence of any asymmetry which might be a clue for DDH.
Inguinal folds normally do not extend beyond the anal aperture. Bilateral folds that extend beyond this point may be a clue for bilateral dislocated hips.
Anterior thigh creases and gluteal and popliteal creases should be symmetric. Asymmetry is a clue for dislocation. (See fig. 3) The affected side has creases that appear proximal when compared against the other side. It is recommended that hips be examined at all well visits until 1 year of age.
3) First, it is important to state that high-pitched hip clicks, alone and without any other findings, are commonly present during the newborn period and are considered to be of no urgent or emergent consequence. At this point we need to return to the history and assess for the risk status of this infant.
The key risk factors are: sex, family history of DDH, and breech presentation. (See Table 1.) Girls are at 4-5x the risk for DDH at baseline. (The increased risk in girls vs. boys is thought to be an overabundance of the maternal hormone, relaxin, which may be a contributing factor in both ligamentous laxity and breech positioning.) Girls with a positive family history of DDH and girls with breech presentation at the time of parturition have the greatest risk. Female sex plus breech presentation increases the risk most drastically (120:1,000) and this risk is not affected by mode of delivery. Other conditions that might limit fetal mobility, such as oligohydramnios and firstborn status, have shown an association with DDH but these conditions are not absolute risk factors.
This infant, with only a hip click can be followed as per standard health supervision and seen in 2-4 weeks for reexamination. A soft click that persists after the newborn period (> 2 weeks-old) is cause for orthopedic referral. If Ortolani or Barlow were positive (a palpable clunk) urgent (not emergent) referral to an orthopedist is warranted. If this baby girl had either a positive FH or presented breech an ultrasound should be performed at 3-4 weeks.
4) By 2-3 months of age the Ortolani and Barlow maneuvers will no longer be positive and should not be relied on for assessing hip pathology. Beyond 3 months of age the most reliable indicator of DDH is limitation of abduction (<45?). A Galeazzi test should be performed as well looking for any leg length discrepancy. For this infant, limitation of abduction and asymmetric skin folds are indication for orthopedic referral. As far as imaging is concerned, many feel that an urgent referral is most important and that the specialist will order imaging tests as part of their evaluation. Others order initial images so that they are available to the specialist upon their initial eval. Important to stress that ultrasound is useful in infants younger than 5 months and that
x-rays are useful in infants older than 4 months. The poor utility of plain radiographs prior to this age has mainly to do with incomplete ossification of the femoral heads. Ultrasound is very useful in the early months as cartilage can be visualized and acteabular morphology can be assessed. The use of dynamic ultrasound allows for real-time image testing for instability.
5) If indeed this infant was found to have DDH, treatment goals are to provide and maintain reduction of the hip so that the femoral head and acetabulum may develop normally. This is achieved by ensuring contact between the cartilaginous surface of the femoral head and the cartilage of the floor of the acetabulum. Infants younger than 6 months can be treated to this end with a Pavlik harness. (See fig.4) The harness is essentially a splint that prevents adduction and extension and allows for flexion and abduction. Duration of use is variable and requires frequent monitoring until clinical, radiographic, and ultrasonographic evaluations are normal. Usually a minimum of 3 months is necessary. Frequent adjustments of the harness are necessary so that the rapid growth of the infant does not compromise ideal positioning for a successful result. Hip instability resolves in approximately 95% of cases and complete dislocations are cured in approximately 85% of cases.
In infants diagnosed after 6 months of age, splinting is successful less than 50% of the time. These infants usually can be managed by closed reduction while under general anesthesia and then placed in a spica cast for a minimum of 8 weeks. (See fig. 5) Unsuccessful reductions or patients who present older than 2 years of age require treatment with open reduction and +/- casting. Follow up is variable and based on the severity of disease. Usually radiographs are assessed yearly until 6 years old to assess for late complications such as AVN.
Readings:
American Academy of Pediatrics Clinical Practice Guideline:
Early Detection of Developmental Dysplasia of the Hip
Committee on Quality Improvement, Subcommittee on Developmental Dysplasia of the Hip, Pediatrics Vol. 105 No. 4 April 2000, pp. 896-905
Early Detection of Developmental Hip Dysplasia:
Synopsis of the AAP Clinical Practice Guideline
Goldberg, M J. Pediatr. Rev. 2001; 22; 131-5
Additional Reading:
Developmental dysplasia of the hip. Phillips, W. UpToDate. http://www.uptodateonline.com/utd/content/topic.do?topicKey=ped_orth/5564&selectedTitle=1~17&source=search_result
Ultrasonography in screening for developmental dysplasia of the hip in newborns: systematic review. Woolacott NF, Puhan MA, Steurer J, Kleijnen J. BMJ. 2005 Jun 18; 330(7505):1413.
