Definition
Congenital Dislocation of the Hip, the terminology has
been replaced by: DDH: generic term encompassing
the many variations of congenital hip dysplasia, subluxation, and
dislocation
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Radiographic Appearance
Xrays taken before four months old - before the head of
the thigh bone (femur) starts to convert from invisible-on-xray
cartilage to visible bone (ossification) - are unreliable to rule
out hip dysplasia. They must be repeated after ossification has
begun to be trusted.
On plain radiographs, after the femoral head has started to ossify
features to note are, delayed appearance of the ossifying nucleus, a
shallow acetabulum with displacement of the femoral head upwards and
laterally from its normal position. (Image 1)Ultrasonography
serves as an excellent method for diagnostic imaging of the immature
hip. Sonography affords direct visualization of the cartilaginous
components of the hip joint. The value of ultrasonography diminishes
as development of the ossification center occurs. Between six months
and a year of age, radiography becomes more reliable. Usually by one
year of age the center is sufficiently developed to prevent good
visualization of the acetabulum with ultrasound. he ultrasound test
of the hip is the best under four months.
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Pathology
Developmental dysplasia of the hip (DDH) was formerly referred to as
congenital dislocation of hip. Now that the condition is better
understood, the former term is preferred to reflect the facts that
DDH is a developmental (ongoing) process, variable in manifestation
and not always detectable at birth
DDH involves a dysplasia, or abnormal formation of the hip joint
occurring between fetal life and maturity as a result of instability
The hips are not dislocated at birth, but if a dislocation occurs,
then the complications of the dislocation - malformation of the hip
socket, twisting of the thigh bone (femoral anteversion), and hip
muscle shortening (contractures) will develop.
Hips that are found to be normal at birth (and even in the first few
months of life) can subsequently be found to be abnormal later. This
cannot be overemphasized! The best orthopedist in the world can be
fooled by the initial hip exam. We cannot be complacent about your
child's hip stability and development.
The cause of DDH is both physiologic - having to do with the child's
basic makeup as well as the child's response to the maternal
hormones
mechanical - a result of positional influences in utero
The majority of children with DDH have ligamentous laxity -
looseness of the fibrous bands connecting bones together in joints.
This predisposes to hip instability; instability allows the hip to
slip out of position; and certain mechanical factors such as breech
presentation can aggravate the problem. Maternal hormones associated
with pelvic relaxation around the time of birth also aggravate the
instability of the newborn hip joint by allowing softening and
stretching of the baby's hip ligaments.
It has been estimated that only 1 in 100 newborn infants have
clinically unstable hips (subluxatable - the ball of the hip is able
to be moved around loosely in the hip joint - or dislocatable - the
ball of the hip is able to be actually slid in and out of joint with
a "clunk" that can be felt), whereas only one in 800 to 1,000 of
newborn infants eventually experience a true dislocation whereby the
ball of the hip lies outside the socket.
There is a 9:1 female predominance; apparently the baby's own female
hormones must aggravate the abnormal looseness of the hip ligaments.
Of children with DDH, approximately 60% are firstborn
30-50% develop in the breech position; 2% to 3% of all babies are
breech presentations, but about 20% of DDH patients are born breech.
The breech position tends to force the ball of the hip out of the
socket, predisposing to dislocation after birth. Highest risk is the
frank breech position with the hips flexed and the knees extended -
basically feet up by the shoulders. There is also an association of
congenital muscular torticollis ("wry neck"), metatarsus adductus
(toes bent inward) or talipes equinovarus (club foot) with DDH. A
child with any condition caused by intrauterine cramping deserves
very careful attention to rule out DDH.
If an abnormal hip remains untreated, the child will develop the
long-term complications, including:
osteoarthritis
pain
abnormal gait
unequal leg length
decreased agility
Diagnosis
The Barlow test is the most important manoeuvre in examining the
newborn hip. The examiner attempts to push the ball of the hip
rearward out of the socket.
The Ortolani test is a manoeuvre to reduce a recently dislocated
hip. If positive, the examiner feels a "clunk" as it pops back into
place. It is most likely to be positive in infants who are 1-2 month
old because adequate time must have passed for the true dislocation
to have occurred. After 2 mo of age, this test is no longer useful
because of the development of soft tissue contractures which prevent
the hip from being relocated.
The thigh creases should be symmetrical from side to side; if they
are not, possible hip dislocation has to be considered carefully.
Leg length inequality is another tip-off to dislocation, as is
uneven knee position from side to side.
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Treatment:
If an unstable hip is recognized at birth, treatment consists of
maintaining the position of the hip in flexion (knee up towards the
head) and abduction (knee away from the centreline) for about 1-2
months. The Pavlik harness is the most widely used device, but the
Frejka splint and some other devices are also used. The device
chosen for treatment maintains proper position of the femoral head
and allows for "tightening up" of the ligamentous structures as well
as for stimulation of normal formation of the hip socket. The
treatment must be continued until the hip is stable and xrays or
ultrasound examinations are normal.
From 1-6 months, true dislocations may develop. As a consequence,
treatment is directed toward reduction of the femoral head into the
socket (acetabulum), usually with the Pavlik harness or similar
device. The harness pushes the femoral head toward the socket, and
usually, relocation of the femoral head will occur within 3-4 wk.
The Pavlik harness is approximately 95% successful in dysplastic or
subluxated hips and 80% successful in true dislocations. Triple
diapering is frowned upon now because it promotes hip extension,
which is not a good position for normal hip development. If a
spontaneous reduction does not occur by splinting, then a surgical
closed reduction (manipulation under anaesthesia) is done.
In the older infant from 6-18 Mo, surgical closed reduction
(manipulation under general anaesthesia) is the major method of
treatment.
After 18 months of age, the progressive deformities become so severe
that major open surgical intervention is necessary to realign the
hip.
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Image 1
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Useful Link
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