الفهرس 
Normal Hip Development and AnatomyOnly 14 pages are availabe for public view
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Abstract
The femoral head and acetabulum develop from the same
block of primitive mesenchymal cells. A cleft develops to separate them at 7 to 8 weeks’ gestation.
At birth, the femoral head and the acetabulum are primarily cartilaginous.
The characteristic shape of the hip is a result of reciprocal contact between the
acetabulum and the femur during growth. At birth, the acetabulum has a small bony component and
a larger cartilaginous component. During the first 6 postnatal weeks, the acetabulum is
particularly susceptible to modeling. If the femoral head is in the normal position in the
acetabulum, a normal hip results. If the femoral head is in an abnormal position that is not
corrected, the result may be a dysplastic hip.
Developmental dysplasia of the hip (DDH) refers to a spectrum of anatomical abnormalities of the
hip joint (dislocated, dislocatable, subluxed, subluxable and dysplasia) arising from a deviation
in normal hip development during embryonic, fetal and infantile growth periods.
The hip is at risk for dislocation during 4 periods:
(1)The 12th gestational week. (2)The 18th gestational week. (3)The final 4 weeks of gestation.
(4)During the 12th postnatal period
The hip is at risk as the fetal lower limb rotates medially. A dislocation at this time is termed
teratologic. All elements of the hip joint develop abnormally. The hip muscles develop around the
18th gestational week. Neuromuscular problems at this time, such as myelodysplasia and
arthrogryposis, also lead to teratologic dislocations. During the final 4 weeks of pregnancy,
mechanical forces have a role. Conditions such as oligohydramnios or breech position predispose to
DDH. Postnatally, infant positioning such as swaddling, combined with ligamentous laxity, also has
a role.
Before 1970, radiological examination of the hip was based on conventional radiography, and
scintigraphy. Later, computed tomography (CT) and magnetic resonance (MR) imaging were introduced,
but due to the deep location of the hip joint, ultrasound (US) examination has always had a
relatively limited role in the assessment of hip pathologies. However, many hip diseases are well
detectable at US provided that the US operator is familiar with the normal anatomy as well as the
US anatomy of this joint, and that the examination is performed accurately and compared to previous
diagnostic imaging results, if available. US study of the hip includes assessment of the soft
tissues, tendons, ligaments and muscles, and also of the bone structures and joint spaces.
Ultrasonographic techniques include static evaluation of the morphologic features of the hip, as
popularized in Europe by Graf and a dynamic evaluation, as developed by Harcke that assesses the
hip for stability of the femoral head in the socket,
as well as static anatomy. Dynamic ultrasonography yields more useful information.
In the Graf classification, a type I hip is considered normal, and developmental dysplasia is ruled
out. The type II hip, which has a slightly shallow acetabular cup and a rounded rim with the
femoral head in normal position, is considered to be developmentally immature in infants less than
three months of age. In infants older than three months, a type II hip is considered abnormal and
should be treated. A type III hip is subluxated, and a type IV hip is dislocated. A
dynamic approach, which consists of a multipositional evaluation using real-time ultrasonography to
visualize the hips during physical examination.
With both techniques, there is considerable inter observer variability, especially during the first
3 weeks of life. Experience with ultrasonography has documented its ability to detect abnormal
position, instability, and dysplasia not evident on clinical examination. Ultrasonography during
the first 4 weeks of life often reveals the presence of minor degrees of instability and acetabular
immaturity.
Studies indicate that nearly all these mild early findings, which will not be apparent on physical
examination, resolve spontaneously without treatment. Newborn screening with ultrasonography has
required a high frequency of reexamination and results in a large number of hips being
unnecessarily treated. One study demonstrates that a screening
process with higher false-positive results also yields increased
prevention of late cases.
Ultrasonographic screening of all infants at 4 to 6 weeks of age would be expensive, requiring
considerable resources. This practice is yet to be validated by clinical trial.
Consequently, the use of ultrasonography is recommended as an adjunct to the clinical evaluation.
It is the technique of choice for clarifying a physical finding, assessing a high-risk infant and
monitoring DDH as it is observed or treated. Used in this selective capacity, it can guide
treatment and may prevent overtreatment.