Diagnostic ultrasound ( PDFDrive )

CHAPTER 55 The Pediatric Hip and Other Musculoskeletal Ultrasound Applications 1923
two-word combination that indicates the plane of the transducer
with respect to the body (coronal or transverse) and the position
of the hips (neutral or lexed).
It is the objective of the dynamic hip assessment to determine
the position and stability of the femoral head, as well as the
development of the acetabulum. With a normally positioned
hip, the femoral head is congruently positioned within the acetabulum.
Mild displacement, such as when the head is in contact
with part of the acetabulum or is displaced but partly covered,
is referred to as subluxation. he dislocated hip has no contact
with or coverage by the acetabulum. A change in position of the
femur may change the relationship of the femoral head and
acetabulum. A hip that is subluxated in the neutral or rest position
may seat itself with lexion and abduction. A dislocated hip may
improve its position and partially reduce to a subluxated position.
his is, in fact, a principle of treatment.
he stability of the hip is determined through motion and
the application of stress. he stress maneuvers are the imaging
counterparts of the clinical Barlow and Ortolani maneuvers,
which are the basis for the clinical detection of a hip abnormality.
he Barlow test determines whether the hip can be dislocated.
he hip is lexed and the thigh brought into the adducted
position. he gentle push posteriorly can demonstrate instability
by causing the femoral head to move out of the acetabulum. 1
he Ortolani test determines whether the dislocated hip can be
reduced. As the lexed, dislocated hip is abducted into a frog-leg
position, the examiner feels a vibration or “clunk” that results
when the femoral head returns to the acetabulum. 28 he normal
hip is always seated at rest, with motion, and during the application
of stress. he lax hip is normally positioned at rest and
shows mild subluxation with stress. It must, however, invariably
remain within the conines of the acetabulum. he subluxated
hip is displaced laterally at rest and is loose; it may be dislocatable
with stress and reducible with lexion and abduction. he dislocated
hip may be able to be returned to the acetabulum with
traction and abduction. his hip is distinguished from the most
severe form of DDH, in which the femoral head is dislocated
and cannot be reduced.
At birth, the proximal femur and much of the acetabulum
are composed of cartilage. On sonographic examination, cartilage
is hypoechoic compared with sot tissue, so it is easy to distinguish.
A few scattered specular echoes can be visualized within the
cartilage when high-frequency transducers are used and technique
adjustments are optimally set. he acetabulum is composed of
both bone and cartilage. At birth, the bony ossiication centers
in the ilium, ischium, and pubis are separated by the triradiate
cartilage, which has a Y coniguration. A cartilaginous acetabular
rim (the labrum) extends outward from the acetabulum to form
the cup that normally contains the femoral head. Most of the
acetabular cartilage has an echogenicity similar to the femoral
head. It is still possible to determine the joint line, which distinguishes
the cartilaginous acetabulum from the femoral head,
by simply rotating the femur. More pronounced movement of
the hip oten creates echoes within the joint space, probably as
a result of the formation of microbubbles. At the lateral margin
of the labrum, the hyaline cartilage changes to ibrocartilage,
and this shows increased echogenicity. he echogenic hip capsule,
composed of ibrous tissue, borders the femoral head laterally.
he bony components of the hip relect all of the sound beam
from their surface. his creates a bright linear or curvilinear
appearance on the sonogram, indicating the contour of the osseous
surfaces in that plane.
Radiographically, the ossiication center of the femoral head
is recognized between the second and eighth months of life. It
is typically seen earlier in females than in males, and there is a
wide normal variation for the time of appearance. Although
some asymmetry between the let and right hips can be normal,
both in time of appearance and in size, delayed appearance and
development are associated with DDH. Hip sonograms relect
the development of the ossiication center and can be used to
document the development of the center. 29 he ossiication center
can be found with ultrasound several weeks before it is visible
radiographically. Initially, a conluence of blood vessels produces
increased echoes within the cartilage. his precedes actual
ossiication. As ossiication begins, the calcium content is insuficient
to produce a visible radiographic density; however, the
sound waves are relected. With maturation, the size of the
ossiication center increases. In early development, the echoes
from the center have a punctate appearance, whereas later in
the irst year of life, the growth in size gives it a curvilinear
margin. As the normal infant approaches 1 year of age, the size
of the ossiication center precludes accurate determination of
medial acetabular landmarks.
Sonography of the hip is practical only up to 8 months of
age, unless there is delayed ossiication of the femoral head.
Between 4 months and 6 months, radiography becomes more
reliable. Usually by 1 year of age, the femoral ossiication center
is large enough to prevent good sonographic visualization of the
acetabulum. 9 he presence and size of the ossiic nucleus can be
evaluated in all views.
Coronal/Neutral View
he coronal/neutral view, which forms the basis for the
morphologic technique, is performed from the lateral aspect
of the joint with the plane of the ultrasound beam oriented
coronally with respect to the hip joint. he femur is maintained
with a physiologic amount of lexion. he coronal/neutral view
is performed with the patient supine. he transducer is placed
on the lateral aspect of the hip, and the hip is scanned until a
standard plane of section is obtained (Fig. 55.1). he plane must
precisely demonstrate the midportion of the acetabulum, with the
straight iliac line superiorly and the inferior tip of the os ilium
seen medially within the acetabulum. he echogenic tip of the
labrum should also be visualized. he alpha and beta angles, if
measured, relate to ixed points on the bony and cartilaginous
components of the acetabulum 30 (see Fig. 55.1), and the exact
plane must be obtained for the measurements to be reliable. he
similarity can be noted between the appearance of the acetabulum
in this coronal/neutral view and in the coronal/lexion view (Fig.
55.2). he diference is that the bony shat (metaphysis) of the
femoral neck is visualized below the femoral head in the coronal/
neutral projection. In the coronal/lexion view, the femoral shat
is not in the plane of examination because the femur is lexed.
A stability test can be performed in the coronal/neutral view