Diagnostic ultrasound ( PDFDrive )

CHAPTER 55 The Pediatric Hip and Other Musculoskeletal Ultrasound Applications 1927
positioned femoral head is not visualized (Videos 55.1
and 55.2).
In subluxation, the femoral head is displaced laterally,
posteriorly, or both, with respect to the acetabulum. Sot tissue
echoes are seen between the femoral head and the bony relections
from the medial acetabulum. In dislocation, the femoral head
is completely out of the acetabulum (see Fig. 55.2C). With superior
dislocations, the femoral head may rest against the iliac bone.
In posterior dislocations, the femoral head is seen lateral to the
posterior lip. he acetabulum is usually not visualized in a dislocation
because the bony shat of the femur blocks the view.
Dynamic examination in the coronal/lexion view has two
components. he irst is performed over the posterior lip using
a push-and-pull maneuver (see Fig. 55.2D-E). In the normal hip
the femoral head is never seen over the posterior lip of the acetabulum.
When there is instability, a portion of the femoral head
appears over the posterior lip of the triradiate cartilage as the
femur is pushed. With a pull, the head disappears from the plane.
In a dislocated hip, the femoral head may be located over the
posterior lip and may or may not move out of the plane with
traction. he second component of the dynamic examination is
performed over the midacetabulum. he Barlow-type maneuver
is performed with adduction and gentle pushing against the
knee. In the normal hip the femoral head will remain in place
against the acetabulum. With subluxation or dislocation, the
head will migrate laterally and posteriorly, and there will be
echogenic sot tissue between the femoral head and the acetabulum
(Videos 55.3, 55.4, and 55.5).
Transverse/Flexion View
Transition from the coronal/lexion view to the transverse/lexion
view is accomplished by rotating the transducer 90 degrees and
moving the transducer posteriorly so it is in a posterolateral
position over the hip joint. he orientation of the scan plane is
parallel to the lexed femoral shat (Fig. 55.3A). he plane of the
transducer and the landmarks are demonstrated on a computed
tomography (CT) scan of a patient in a spica cast with a normal
let and dislocated right hip (see Fig. 55.3B). Sonographically,
the bony shat and metaphysis of the femur give bright relected
echoes anteriorly, adjacent to the sonolucent femoral head. he
echoes from the bony acetabulum appear posterior to the femoral
head, and in the normal hip, a U-shaped coniguration is
produced by the metaphysis and the ischium (see Fig. 55.3C).
he relationship of the femoral head and acetabulum is observed
while the lexed hip is moved from maximum adduction to wide
abduction. he sonogram changes its appearance in abduction
and adduction. he deep, U-shaped coniguration is produced
with maximum abduction, whereas in adduction, a shallower,
V-shaped appearance is observed. It is important to have the
transducer positioned posterolaterally over the hip to see the
medial acetabulum. When the transducer is not posterior enough,
the view of the acetabulum is blocked by the femoral metaphysis,
and the hip can appear falsely displaced. In adduction, the hip
is stressed with a gentle posterior push (a Barlow test). In the
normal hip, the femoral head will remain deeply in the acetabulum
in contact with the ischium with stress. In subluxation, the hip
will be normally positioned or mildly displaced at rest, and there
will be increased lateral displacement from the medial acetabulum
with stress, but the femoral head will remain in contact with a
portion of the ischium. With frank dislocation, the hip will be
laterally and posteriorly displaced to the extent that the femoral
head has no contact with the acetabulum, and the normal
U-shaped coniguration cannot be obtained (see Fig. 55.3D).
he process of dislocation and reduction is able to be visualized
in unstable hips in the transverse/lexion view. With abduction,
the dislocated hip may be reduced, representing the sonographic
counterpart of the Ortolani maneuver. With adduction, the
subluxated hip may be dislocatable, corresponding to the Barlow
maneuver (Videos 55.6, 55.7, and 55.8).
Alternative Views
A transverse/neutral view is still used in our examination
protocol, but this view has not been included in published
guidelines. he transducer is directed horizontally into the
acetabulum from the lateral aspect of the hip; the leg is in physiologic
neutral position. he plane of interest is one that passes
through the femoral head into the acetabulum at the center of
the triradiate cartilage. 26 he position of the head with respect
to the triradiate cartilage is evident and can conirm indings
on the coronal/neutral view.
A number of anterior views have been described, and
sonographers experienced in their use have indicated success
with these views. 12,24 he anterior approach of Dahlstrom and
colleagues 13 is performed with the patient supine and the hips
lexed and abducted. he transducer is placed anterior to the
hip joint and is centered over the femoral head with the plane
of the sound beam parallel to the femoral neck (Fig. 55.4A-B).
A Barlow or push maneuver can be performed to detect instability.
Complete dislocation is considered to be present when femoral
head displacement exceeds 50% of its diameter (see Fig. 55.4C).
he image produced in a normal hip is an axial section through
the acetabulum and a longitudinal section through the femoral
head and neck. 11 he anterior view is particularly useful in rigid
abduction splints and casts in which the posterior aspect of the
hip is covered.
Evaluation of the Infant at Risk
We examine each hip in multiple views and report our indings
with an emphasis on position and stability. Femoral head position
is described as normal, subluxated, or dislocated. Dislocations
are easy to determine, and we have had no diiculty with their
identiication. Sometimes it can be problematic to decide whether
an abnormal hip that is widely displaced should be called “subluxated”
or “dislocated.” Stability testing is reported as normal, lax,
subluxatable, dislocatable (for subluxated hips), and reducible
or irreducible (for dislocated hips). When stress maneuvers are
performed, it is important that the infant be relaxed; otherwise,
inconsistency may be found between the sonographic and clinical
examination indings and in serial ultrasound studies.
he acetabulum is assessed visually and is described as normal,
immature, or dysplastic. More important are the development
of the cartilaginous labrum and its coverage of the femoral head.
Situations in which the bony component is steeply angled but
the cartilage is well developed and covers the femoral head should