DEVELOPMENTAL DISLOCATION OF
THE HIP
Methods for the early detection of developmental dislocation of the hip (DDH) have been reported for nearly 100 years. The first screening program in the United States was described and initiated in the 1930s. After World War II, extensive screening programs in the United States, Sweden, and England resulted in the early identification and, ultimately, the simple, effective, and safe treatment protocols.
In the United States, approximately 10 in 1000 infants are born with
DDH. As a result of screening programs, 96% of these children have normal hip
function. The longer the dislocation goes untreated, the more difficult it is
to obtain a satisfactory result. Routine screening for this entity should be an
integral part of newborn well-child care.
RECOGNITION OF DEVELOPMENTAL DISLOCATION OF THE HIP
ETIOLOGIC FACTORS
The etiology of DDH remains multifactorial. Mechanical and physiologic
properties of both the mother and infant have been implicated, combining to
produce instability and, ultimately, dislocation.
The time at onset of instability affects the severity of the condition.
The typical developmental dislocation develops just before delivery in an
otherwise normal infant. At birth, the clinical findings are often subtle and
radiographs are usually normal. In contrast, if the dislocation occurs early in
gestation, the clinical and radiographic findings are more severe with advanced
adaptive changes in the femoral head and pelvis. This is often termed teratologic
dislocation and is typically found in patients with underlying conditions
such as arthrogryposis, chromosomal abnormalities, and other severe congenital
anomalies such as spina bifida and lumbosacral agenesis. Teratologic
dislocations occur in less than 2% of patients with DDH.
MECHANICAL FACTORS
Mechanical factors most likely occur in the last trimester of pregnancy.
All have the effect of restricting intra-uterine space for the fetus, also
termed packaging. Roughly 60% of infants with DDH are firstborns,
suggesting that the tight unstretched uterus and abdominal wall inhibit fetal
movement. It is believed that the fetal pelvis becomes trapped within the
maternal pelvis, not allowing the normal flexion of the fetal hip and knee.
Breech presentation also plays a significant role in DDH. Thirty to 50
percent of affected children are delivered in breech presentation. When the
knees are extended in the frank breech position, excessive
hamstring stretch contributes further to hip laxity and instability. DDH is
seen more frequently in children with congenital knee dislocation or
recurvatum, as well as other packaging phenomena such as metatarsus adductus
and congenital muscular torticollis.
The left hip is more commonly involved than the right, in theory because
the left hip is trapped against the maternal sacrum in the most frequent
presenting position left occiput anterior. The maternal sacrum forces the
left hip into flexion and adduction, contributing to instability and,
ultimately, DDH. In this position, the femoral head is covered more by the
joint capsule than the acetabulum proper.
HORMONAL FACTORS
Maternal estrogens and other hormones that affect relaxation of the
pelvis right before delivery also affect the fetal hip. Their presence may lead
to temporary laxity in the hip joint in the fetus and newborn.
Studies suggest that the female infant is more affected by these hormones,
which may explain the higher incidence of DDH (6 : 1) in females.
Up to 20% of cases are deemed familial. This may be due to an inborn or
possibly an inherited error of estrogen metabolism and may explain the higher
rates of familial disease in Northern Italians, Scandinavians, and some Navajo
tribes.
POSTNATAL ENVIRONMENTAL FACTORS
In the first months of life, normal hip position is that of abduction
and flexion. In cultures in which swaddling of infants places the hips in
positions of extension and adduction, there is a 10-fold increase in DDH rates.
The practice of holding the child by the feet in the newborn period places the
hips in extension and should be avoided.
CLINICAL FINDINGS IN DEVELOPMENTAL DISLOCATION OF THE HIP
PATHOGENIC FACTORS
The pathogenesis of a typical developmentally dislocated hip is probably
quite simple. Near the time of delivery, the joint capsule is likely distended
and elastic. After delivery, the femoral head is free to move about the
distended lax capsule and can come in and out of the acetabulum freely. In
newborns, the femoral head can easily be returned to the normal position. At
this stage, the soft tissue structures and joint surfaces are essentially
normal and therefore the capacity to develop a normal hip exists. Therefore,
for a stable hip to develop, the femoral head needs to stay in contact with the
acetabulum as the joint capsule loses its laxity and returns to a normal
configuration. However, if the dislocation is allowed to persist, the
capsule, joint, and other soft tissue go through a series of adaptive changes.
This makes the dislocation more difficult to reduce, and the chance of
obtaining a satisfactory long-term result diminishes significantly.
It has been demonstrated that the stimulus for development of a normal
acetabulum is the presence of a normal femoral head within the acetabulum.
Conversely, a normal femoral head will develop if it is contained within a
normal acetabulum. Because the infant grows so rapidly in the first year of
life (tripling in size in the first 12 months), there is tremendous remodeling
potential in this period to convert pathologic changes to normal anatomy.
If the dislocation is not treated, the initially simple problem becomes
more complex. Persistent dislocation is met with normal muscle forces causing
proximal and lateral migration of the femoral head. The iliopsoas,
adductors, and hamstrings do not exist at their normal resting length and
become contracted. The acetabulum becomes dysplastic (more shallow) without the
stimulus of the femoral head. Fibrofatty tissue termed pulvinar develops
within the joint. The ligamentum teres becomes thickened, and the transverse
acetabular ligament becomes taught and migrates superiorly into the joint. The
joint capsule balloons anteriorly and becomes redundant. The
tight iliopsoas tendon compresses the joint capsule, trapping the femoral head
outside the acetabulum blocking reduction of the joint. This creates an
hourglass configuration of the joint space. Undue pressure on the labrum causes
it to enlarge and some- times invert into the joint, preventing reduction and
thus it is termed an inverted limbus.
The femoral head becomes misshapen and flattened as it
articulates with the outer table of the pelvis. The normal femoral
rotation is blocked, and the femoral head and neck stay in a position of
relative anteversion and valgus.
EXAMINATION OF THE NEONATE AND INFANT
The examination procedures described by Ortolani and Barlow are the most
reliable methods of making the diagnosis of DDH in the neonate (see Plate
2-25). The Ortolani test is a test of hip reduction. If the infant’s hip is
dislocated, then it can be reduced with this maneuver, which is also termed an
Ortolani positive hip. The Barlow test demonstrates the reverse. Gentle flexion
and adduction of the infant’s hip produces a painless clunk of dislocation,
indicating an unstable joint. Over time, if instability is allowed to persist,
these findings go away and the only reliable finding is limited abduction.
Based on the variability of the clinical findings, there exists a
spectrum of disease in DDH. The least severe form is simple dysplasia with
stable hip joints, followed by a Barlow positive hip (reduced but
dislocatable), then an Ortolani positive hip (dislocated but reducible), and
finally teratologic or unreducible hips. This spectrum is best illustrated
during the neonatal period.
RADIOLOGIC DIAGNOSIS OF DEVELOPMENTAL DISLOCATION OF THE HIP
CLINICAL MANIFESTATIONS IN OLDER CHILDREN
The findings of DDH become more obvious as children grow. The
surrounding soft tissue and bone gradually adapt to the abnormal position of
the femoral head. With time, it becomes increasingly difficult to reduce the
femoral head into the acetabulum, and the Ortolani test ultimately becomes
negative, with the femoral head remaining trapped outside the acetabulum. All
major muscle groups about the hip become contracted. Most apparent is the
adductors, which manifests clinically as decreased abduction of the affected
hip. The thigh is relatively shortened and the skin and subcutaneous tissue
bunch up, producing asymmetry in the thigh skin folds on occasion. With the
patient supine and the hips and knees flexed, the knees are not at the same
level (positive Allis or Galeazzi sign). The femur can be moved freely up and
down, which is described as pistoning or telescoping.
The child walks with a limp, owing to relative limb shortening and
pelvic tilt due to abductor weakness. The Trendelenburg test can be used to
assess abductor weakness. When both hips are dislocated, the perineal
space is widened and the trochanters appear more prominent than normal. There
is hyperlordosis of the lumbar spine, and the child walks with a waddling gait.
RADIOGRAPHIC EVALUATION
Selective screening imaging in children with suspected disease is the
most reliable and cost-effective measure to diagnose and treat DDH in an
efficient manner.
Ultrasound examination can provide an accurate assessment of the femoral
and acetabular anatomy and is superior to radiographs in the first 3 months of
life. Higher false-positive results are seen in ultrasound examinations earlier
than at 4 weeks of life due to immaturity. Ultrasound can also provide a
dynamic assessment of hip stability because the Ortolani and Barlow tests can
be applied while visualized with ultrasound. The true percentage of acetbular
coverage of the femoral head can be quantified.
Plain radiographs (anteroposterior and frog-leg views)
become more useful after 3 months of life. Char-acteristic findings of DDH
include (1) proximal and lateral migration of the femoral head/neck on the
ilium, (2) a shallow, incompletely developed acetabulum, (3) development of a
false acetabulum, and (4) delayed ossification of the proximal femoral ossific
nucleus. A useful method of assessing infantile hips involves a system of lines
on the anteroposterior pelvis radiograph. Accurate positioning of the child for
the radiograph is critical. The legs must be extended and the hips in neutral
rotation. These are most helpful when unilateral disease is present because
there is a normal comparison on the same film.
In the older child, contrast arthrography may be helpful to visualize
articular changes. It is seldom indicated as a sole imaging modality but rather
used in conjunction with treatments such as closed reduction and assessing the
adequacy of reduction.
The goal of treatment remains to return the femoral head to its normal
position within the acetabulum and to keep it there to allow further
development. In the infant younger than the age of 6 months, closed reduction
can usually be accomplished and is almost always accompanied by an adductor
tenotomy to maintain reduction in a cast. In older children, gentle closed
reduction becomes more difficult, and more invasive measures are needed to
achieve the goal of a stable reduction.
ADAPTIVE CHANGES IN DISLOCATED HIP THAT INTERFERE WITH REDUCTION
TREATMENT OF CLINICALLY REDUCIBLE HIP
Closed Reduction
Reduction of the hip is typically achieved with the patient under
general anesthesia. Gentle flexion and abduction of the hip is applied. The
reduced hip must be maintained in a comfortable and normal physiologic position
of flexion and abduction. This position is critical. It must avoid excessive
stress to the joint yet also keep the femoral head from redislocating. Ninety
degrees of flexion and moderate abduction is the ideal position, referred to by
Salter as the “human position.” The femoral head and neck should point toward
the triradiate cartilage on a plain radiograph. Tension on the hip can be
lessened with a percutaneous adductor tenotomy, which is utilized in a majority
of such cases. In a large number of children, hip instability noted at birth
spontaneously resolves in a few weeks. Simple positioning and close clinical
and radiographic follow-up are all that is typically needed in these cases. The newborn with
documented more severe instability (Ortolani-positive hips) should be placed in
some type of restraint device, typically a Pavlik harness. The reduction should
be maintained for several weeks.
Although there are many devices that have historically been employed to
maintain reduction of the un-stable newborn hip (e.g., double diapers, Ilfeld
splint, Von Rosen splint, Frejka pillow), the current choice remains the Pavlik
harness. It provides the proper re-straints with a shoulder harness, foot
cuffs, and straps that tether the limbs at customizable degrees of
flexion and abduction. Velcro closures make the harness simple to apply and
remove for bathing.
The harness is applied loosely with the straps maintaining reduction of
the hip in a position of around (no greater than) 100 degrees of flexion and
limiting adduction such that the knees cannot touch when brought to midline.
This zone can be adjusted based on the stability of the hip. Care must be taken
to avoid excessive flexion or abduction, because they can result in femoral nerve
neurapraxia and avascular necrosis, respectively. Once the device is properly
applied, ultrasonography is used to confirm reduction. Follow-up ultrasound
examinations in the harness can also be used for monitoring as well as
radiographs after 3 months of age.
The advantages of the Pavlik harness are several. It allows for
spontaneous hip motion within the limits of stability. It also prevents
extension of the hip and knee, which predisposes hips to instability. The
infant can remain in the harness for essentially all care except bathing, and
the risk of avascular necrosis remains very low because there is no forced
abduction. The duration of treatment is typically related to patient age at
onset of treatment.
Treatment of the Clinically Unreducible Hip
The clinically unreducible hip is typically seen in a child older than 6
months of age. The soft tissue contractures and adaptive changes make it such
that the hip cannot spontaneously reduce. If more than the simple force needed
for an Ortolani examination is required to reduce the hip, then closed
reduction under anesthesia is indicated. Preoperative traction has been used
historically to stretch the soft tissues before closed reduction. This has
largely been replaced with percutaneous adductor tenotomy at the time of closed
reduction. This lessens the tension on the reduction, allowing the femoral head
to rest within the acetabulum without undue tension or force.
Once a closed reduction under anesthesia is accomplished, the hip is
immobilized in a spica cast. Radiographs with or without an arthrogram should
demonstrate the femoral head and neck directed toward the triradiate cartilage.
Before cast immobilization, the safe zone of Ramsey is determined. This is
defined as the range of motion within which the hip remains reduced. The safe
zone can, and in most cases should, be increased with a percutaneous adductor
tenotomy.
DEVICE FOR TREATMENT OF CLINICALLY REDUCIBLE DISLOCATION OF HIP
SURGICAL PROCEDURES
If an adequate closed reduction is unable to be achieved and maintained,
then open reduction should be considered.
Medial (Adductor) Approach
This approach is typically used in patients younger than the age of 12
months. Although age is an important consideration for this approach, perhaps
more important is patient size. The larger the child, the farther away the femoral
head is from the medial-based incision and hence the more difficult it becomes
to accomplish reduction through this approach.
The medial approach allows direct access to the contracted portion of
the capsule but does not permit visualization or access to the redundant
capsule for plication to prevent redislocation. The medial femoral circumflex
artery is at risk in this approach and lies in close proximity to the psoas
tendon.
Once the capsule is encountered, it is opened and the femoral head is
reduced. Anatomic obstacles to reduction such as the pulvinar may need to be
excised to permit reduction. An inverted limbus can be mobilized if necessary,
and a taught transverse acetabular ligament can be incised if necessary to
permit reduction. Once the hip is reduced, capsular closure is not necessary.
After wound closure, the child is immobilized in a bilateral hip spica
cast. The cast is carefully molded about the
trochanter to maintain reduction and prevent redislocation into the redundant
capsule. Excessive abduction force should not be used.
Anterolateral Approach
In older and larger children, the femoral head cannot be adequately
accessed via a medial approach. The anterolateral approach is utilized for
these cases. An oblique incision just distal to and along the course of the
iliac crest allows access and provides a better cosmetic result. As with the
medial approach, the intra-articular obstacles to reduction are removed and
the hip is reduced. The redundant portion of the capsule is excised and
plicated to add stability to the reduction. A postoperative case is applied to
support the reduction. If the position of the hip alone does not provide enough
stability, then the quality of the reduction/capsulorrhaphy should be
reassessed.
After open reduction, children younger than the age of 2 can wear a
postoperative hip abduction orthosis until acetabular remodeling has occurred.
In older children with less remodeling potential, innominate osteotomy can be
performed to improve the acetabular anatomy. The Salter innominate osteotomy
provides additional anterior and lateral coverage, which is deficient in DDH
patients. Derotational osteotomies of the proximal femur can also be performed
to better position the femoral head in the acetabulum. Femoral shortening
osteotomy is frequently used to decrease tension on the reduction. These bony
procedures can be used at the time of open reduction if deemed necessary by the
surgeon.
BLOOD SUPPLY TO FEMORAL HEAD IN INFANCY (AFTER OGDEN)
COMPLICATIONS OF TREATMENT
Avascular Necrosis of the Femoral Head Forcing the
hip into severe and unusual positions can have severe consequences, the most
devastating of which is avascular necrosis of the femoral head.
Compromise of the blood supply to the femoral head for even a short time can
produce complete death of the femoral head. Redislocation of the hip can be
problematic but can ultimately be corrected. Although it can be tempting to
keep the hip in certain positions to maintain reduction, extreme positions must
be avoided.
Several points regarding the femoral head blood supply and reduction of
the femoral head have been described by Ogden. In the newborn, both the lateral
and medial circumflex femoral arteries supply the femoral head. Contributions
from the lateral circumflex regress by age 5 to 6
months. The medial femoral circumflex artery residing on the posterior femoral
neck becomes the predominant blood supply to the femoral head. Interruption of
the medial circumflex in the newborn may have little effect on the femoral
head, but in the child older than 6 months, it can produce devastating necrosis
of the entire femoral head. This has a profound effect on the developing
proximal femur.
Earlier rates of avascular necrosis after closed reduction of the hip
were unacceptably high. It is postulated that forced
wide abduction places pressure on the medial femoral circumflex artery with
contact from the limbus and other posterior structures, occluding the primary
vessel to the femoral head. The vessel can also be compressed along its
tortuous course by the iliopsoas tendon against the inferior pubic ramus as
well as the pectineus-adductor group. Surgical release of these muscles lessens
the tension on the reduction as well as tension on the critical blood supply to
the femoral head, reducing the rate of avascular necrosis.
