Diagnostic ultrasound ( PDFDrive )

1924 PART V Pediatric Sonography
by gently pushing and pulling the infant’s leg. his helps to
verify deformity of the acetabulum and to identify craniodorsal
movement of the femoral head under pressure. Zieger and colleagues
31 proposed a further adaptation of this view, advocating
lexion and adduction of the hip to identify lateral displacement
when instability is present. his is similar to the coronal/lexion
stress view.
In the normal coronal/neutral view, the femoral head is resting
against the bony acetabulum. he acetabular roof should have
a concave coniguration and cover at least half the femoral head.
he cartilage of the acetabular roof is hypoechoic and extends
lateral to the acetabular lip, terminating in the labrum, which
is composed of ibrocartilage and is echogenic (see Fig. 55.1C).
When a hip becomes subluxated or dislocated, the femoral head
gradually migrates laterally and superiorly, with progressively
decreased coverage of the femoral head (see Fig. 55.1E). In hip
dysplasia, the acetabular roof is irregular and angled, and the
labrum is delected superiorly and becomes echogenic and
thickened. When the hip is frankly dislocated, the labrum may
be deformed. Echogenic sot tissue is interposed between the
femoral head and the bony acetabulum. A combination of
deformed labrum, ibrofatty tissue (pulvinar), and thickened
ligamentum teres prevents the hip from being reduced.
he acetabulum can be assessed visually or with measurements,
noting the depth and angulation of the acetabular roof, as well
as the appearance of the labrum (see Fig. 55.1F). his can be
seen in both coronal/neutral and coronal/lexion views and should
be described in the report. Morin and colleagues 32,33 correlated
coverage of the femoral head by the bony acetabulum with
measurements of the acetabular angle. his assessment relates
acetabular depth (d) to the diameter of the femoral head (D)
and is expressed as percent (d/D × 100) coverage of the femoral
head. hese data showed that normal radiographic measurements
always had a femoral head coverage that exceeded 56%, and that
clearly abnormal radiographic measurements had coverage of
less than 40%. 33 his information should be used with caution
because there are intermediate values for which sonographic
and radiographic measurements do not correlate. We have also
noted cases in which sonography showed the acetabulum to be
better developed than it appeared radiographically, and vice
versa. 34 his discrepancy occurs because the radiograph is a
two-dimensional projection of the three-dimensional pelvis, and
selected sonographic images illustrate a single coronal slice that
may not match the projection.
Classiication of hip joints may also be based on the measurement
of the alpha and beta angles (see Fig. 55.1D-F). he alpha
angle measures the inclination of the osseous acetabular roof
with respect to the lateral margin of the iliac bone (baseline).
he beta angle is formed by the baseline iliac bone and the
inclination of the anterior cartilaginous acetabular roof, for which
the tip of the labrum is its key landmark. Ultrasound units may
contain sotware that facilitates measurement of these angles.
Four basic hip types have been proposed on the basis of alpha
and beta measurements. 30 Most of these subtypes have been
subdivided, and small changes in angular measurements can
result in a change in category. he reproducibility of angular
measurements and subtypes has been a point of considerable
discussion. In Europe, classiication by measurement has been
based on large numbers of infants examined. Some examiners
have experienced problems with the use of measurements, 31,32,34-36
but those who adhere strictly to the technique ind acceptable
reproducibility. 11,37,38
A
B
FIG. 55.1 Coronal/Neutral Hip View. (A) Linear array transducer is placed coronal and lateral with respect to the hip. The femur is in “physiologic
neutral” for the infant (slight hip lexion). (B) Scan area (dotted lines) on arthrogram.