Diagnostic ultrasound ( PDFDrive )

CHAPTER 55 The Pediatric Hip and Other Musculoskeletal Ultrasound Applications 1921
In whites, overt dislocation is reported to be 1.5 to 1.7 per 1000
live births. 1,2 When lesser degrees of abnormality such as subluxation
are included, as many as 10 infants per 1000 live births
may show some features of the disorder. 3 Early detection of an
abnormality in the infant hip is the key to successful management.
If treatment is begun at a young age, most of the sequelae that
occur when DDH goes unrecognized until walking age can be
prevented. Clinical screening programs have been instituted,
and primary care physicians are taught to evaluate the hips as
part of the newborn physical examination. Historically, infants
with abnormal clinical examination indings were referred for
plain radiographic ilm examinations. Ultrasound has now become
the preferred technique for diagnosis and management of DDH
in the irst 6 months of life. 4 Hip sonography ofers clear advantages
over other imaging techniques in DDH. At the early age
of initial diagnosis in the irst 6 months of life, the femoral head
and acetabulum consist of cartilage components that are clearly
identiied by ultrasound. Real-time sonography allows assessment
of the hip in multiple planes, both at rest and with movement.
Ultrasound can replace radiographic studies and reduce radiation
exposure to the young infant.
he cause of DDH is multifactorial, with both physiologic
and mechanical factors playing a role. Maternal-fetal interaction
inluences the development of hip problems in both categories.
Maternal estrogens and hormones that afect pelvic relaxation
just before delivery are believed to lead to temporary laxity of
the hip capsule in the perinatal period. Most fetuses are exposed
to extrinsic forces in the later weeks of pregnancy because of
their increasing size and the diminishing volume of amniotic
luid. It is theorized that these forces, although gentle, can lead
to deformation if persistently applied. 5 An increased incidence
of DDH is reported in infants born in the breech position, in
infants with a positive family history of DDH, in irstborns, and
in pregnancy with oligohydramnios. Infants with skull-molding
deformities, congenital torticollis, and foot deformities are also
at increased risk for DDH. 6 Current reviews of risk have focused
on female breech delivery as the highest risk for DDH, and
imaging is recommended for these infants in published guidelines
from the major U.S. societies. 7-9 here is some evidence of familial
acetabular dysplasia, 10 although this is not considered a cause
in most cases.
Risk Factors for Development Dysplasia of
the Hip (DDH)
Family history of DDH
Firstborn child
Oligohydramnios
Breech delivery (female breech is the highest DDH risk
category)
Skull-molding deformities
Congenital torticollis
Foot deformities
he mechanism of a typical dislocation is thought to be a
gradual migration of the femoral head from the acetabulum
because of the loose, elastic joint capsule. In the newborn period,
the femoral head usually dislocates in a lateral and posterosuperior
position relative to the acetabulum. he displaced femoral head
can usually be reduced, and the joint components typically do
not have any major deformity. When dislocation is not recognized
in early infancy, the muscles tighten and limit movement. he
acetabulum becomes dysplastic because it lacks the stimulus of
the femoral head. Ligamentous structures stretch, and ibrofatty
tissue occupies the acetabulum. hus it becomes impossible to
return the femoral head to the acetabulum with simple manipulation;
a pseudoacetabulum may form along the inferior ilium
laterally where the dislocated femoral head rests.
Sonography is most oten used for evaluation of an infant
with an abnormal physical examination or a DDH risk factor,
such as positive family history, breech delivery, foot deformity,
or torticollis. Many reports attest to greater eicacy of
sonography compared with the clinical and radiographic
examination. 11-15
he routine screening of all newborn infant hips with ultrasound
has been a controversial issue. Based on a comparison
between clinical and sonographic screening with sonography,
Tonnis and colleagues 11 concluded that all newborns should be
screened for DDH with ultrasound because it detects more
pathologic joints than the clinical examination. In some European
countries, routine screening has been tried on a regional basis.
Critics of newborn screening programs note the high number
of infants undergoing treatment or requiring follow-up studies
(whether for minor instability or immaturity in acetabular
development), but it is also recognized that studying only infants
at risk will not eliminate late cases of DDH. 16,17
he current consensus in the United States is that the net
beneits of universal sonographic screening are not clearly established.
his opinion is based on the fact that there is a high rate
of spontaneous resolution of neonatal hip instability and dysplasia
and lack of evidence that intervention afects outcomes for the
population. 18 he American Academy of Pediatrics (AAP) has
published guidelines for pediatric examinations for the diagnosis
of DDH. 7 Screening by clinical examination is recommended,
and ultrasound is reserved for infants having abnormal examination
indings or risk factors. 19-22 If a frankly dislocated hip is
present, referral to orthopedic specialists is appropriate. When
the abnormal physical examination indings suggest less severe
hip instability shortly ater birth, sonography should not be done
until at least 3 to 4 weeks of age because hip instability may
resolve on its own. Experience has indicated that many infants
younger than 30 days have hip laxity that becomes normal ater
a few weeks without treatment. his is not a new observation;
the phenomenon was recognized clinically by Barlow. 1 It identiies,
however, a group of infants who need follow-up. Not all
infants’ hips become normal, and these patients require continued
observation. 11
Newborns with a risk factor for DDH should be checked at
4 to 6 weeks. his avoids multiple examinations in cases of
transient neonatal instability and immaturity related to maternal
hormones.