Ultrasound: Basic understanding and learning the language
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 Material Information
Title: Ultrasound: Basic understanding and learning the language
Series Title: International Journal of Shoulder Surgery
Physical Description: Journal Article
Language: English
Creator: Ihnatsenka, Barys ( Author, Primary )
Boezaart, Ander P, ( Author, Secondary )
Publisher: Medknow Publications
Publication Date: 2010
 Notes
Abstract: Ultrasound (US) use has rapidly entered the field of acute pain medicine and regional anesthesia and interventional pain medicine over the last decade, and it may even become the standard of practice. The advantages of US guidance over conventional techniques include the ability to both view the targeted structure and visualize, in real time, the distribution of the injected medication, and the capacity to control its distribution by readjusting the needle position, if needed. US guidance should plausibly improve the success rate of the procedures, their safety and speed. This article provides basic information on musculoskeletal US techniques, with an emphasis on the principles and practical aspects. We stress that for the best use of US, one should venture beyond the "pattern recognition" mode to the more advanced systematic approach and use US as a tool to visualize structures beyond the skin (sonoanatomy mode). We discuss the sonographic appearance of different tissues, introduce the reader to commonly used US-related terminology, cover basic machine "knobology" and fundamentals of US probe selection and manipulation. At the end, we discuss US-guided needle advancement. We only briefly touch on topics dealing with physics, artifacts, or sonopathology, which are available elsewhere in the medical literature.
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Full Text
ISSN 0973 - 6042


International Journal of

Shoulder Surgery


Volume 4 Issue 3 Jul-Sep 2010


Contents


> Shoulder sonography: Diagnostic and interventional utility

> Ultrasound: Basic understanding and learning the language

> Applied sonoanatomy of the posterior triangle of the neck

> Cytogenetic analysis of the pathology of frozen shoulder

> Axillary artery pseudoaneurysm after plate osteosynthesis for a clavicle nonunion:
A case report and literature review

> Irreducible anterior and posterior dislocation of the shoulder due to incarceration
of the biceps tendon


Online full text at
www.internationalshoulderjournal.org


Published by M wPublications










Review



Ultrasound: Basic understanding and

learning the language

Barys Ihnatsenka1, Andr6 Pierre Boezaart1,2


Website:
www intemationalshoulderjournal org
DOI:
10 4103/0973-6042 76960
Quick Response Code:


Ultrasound (US) use has rapidly entered the field of acute pain medicine and regional anesthesia
and interventional pain medicine over the last decade, and it may even become the standard of
practice. The advantages of US guidance over conventional techniques include the ability to both
view the targeted structure and visualize, in real time, the distribution of the injected medication,
and the capacity to control its distribution by readjusting the needle position, if needed. US
guidance should plausibly improve the success rate of the procedures, their safety and speed.
This article provides basic information on musculoskeletal US techniques, with an emphasis on
the principles and practical aspects. We stress that for the best use of US, one should venture
beyond the "pattern recognition" mode to the more advanced systematic approach and use US as
a tool to visualize structures beyond the skin (sonoanatomy mode). We discuss the sonographic
appearance of different tissues, introduce the reader to commonly used US-related terminology,
cover basic machine "knobology" and fundamentals of US probe selection and manipulation. At
the end, we discuss US-guided needle advancement. We only briefly touch on topics dealing
with physics, artifacts, or sonopathology, which are available elsewhere in the medical literature.

Key words: Hyperechoic, hypoechoic, anechoic, musculoskeletal, ultrasound, regional
anesthesia, ultrasound knobology, ultrasound probe selection and manipulation


Ultrasound (US) use has rapidly entered the field of acute
pain medicine and regional anesthesia and interventional
pain medicine over the last decade, and it may even become
the standard of practice.['] US guidance for nerve blocks
and interventional pain management techniques may have
several potential advantages over conventional landmark-
based techniques that assume minimal anatomical variation
between persons, or nerve stimulation-assisted techniques that
are based on the premise that an appropriate motor response
is the perfect surrogate marker for needle proximity to the
sensory fibers of a nerve. These assumptions, of course, are not
entirely correct, and could potentially be responsible for block
failure or block placement difficulties when these conventional
techniques are used. The advantages of US guidance include
the ability to both view the targeted structure and visualize, in
real time, the distribution of the medication throughout and


relative to the tissue (e.g., nerve tissue), as well as the capacity
to control its distribution by readjusting the needle position,
capabilities which should plausibly improve the success rate of
the procedures. The ability to visualize the targeted structure
and other structures of importance, such as blood vessels, lung,
or other organs, should, logically, also improve the speed and
safety of the procedures.21

Compared to the use of fluoroscopy-guided procedures that
can only visualize bony tissue, US additionally allows the
visualization of soft tissues. US equipment is also more portable
and less expensive. Moreover, even regular use of US does not
place patients and practitioners at risk of harmful radiation
exposure, although this may be a matter of debate.b]

It should be clearly understood from the outset that the ability
to "see" the targeted structure with US does not preclude
a thorough knowledge of gross or micro-anatomy. Some


55 International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 +







Ihnatsenka and Boezaart: Understanding ultrasound


experts agree that proper utilization of US requires an even
better knowledge of applied anatomy than that required for
conventional techniques of nerve localization. For the best
use of US in acute pain medicine and regional anesthesia, one
should venture beyond the "pattern recognition" mode to the
more advanced systematic approach and use US as a tool to
visualize structures beyond the skin (advanced sonoanatomy
mode). 'Pattern recognition' refers to memorization of an US
image of a targeted structure (textbook picture) and learning
the maneuvers and techniques necessary to acquire the image.
This is, however, not sufficient in the presence of anatomical
variations or if US is used for diagnostic purposes. It also
implies the need for the continuous presence of a teacher to
confirm the image obtained and the required maneuver for
different block variations (personal observation). To advance
beyond the pattern recognition mode, a thorough knowledge
of applied anatomy combined with a basic understanding
of how a 2-dimensional (2-D) US image represents a
3-dimensional (3-D) anatomical structure is needed; the
latter is the goal we wish to accomplish in this paper for the
readership.

This article will provide basic information on musculoskeletal
US techniques, with an emphasis on the principles and
practical aspects. We discuss the sonographic appearance of
different tissues, introduce the reader to commonly used US
related terminology, cover basic machine "knobology" and
fundamentals of manipulation of the US probe and US-guided
needle advancement. We will only briefly touch on topics
dealing with physics, artifacts, or sonopathology, which are
available elsewhere in the medical literature. -61 We hope to,
in the future, publish an article that will provide an exhaustive
review concerning the use of sonoanatomy of the neck above
the clavicle.

US images in this paper were taken with a straight array 38-
mm, high frequency probe (6-13 MHz), although one image
was taken with a curved array 6o-mm, low frequency probe


(2-5 MHz) on an S-nerve US machine (S-Nerve, Sonosite,
Bothell, WA, USA). Use of other equipment, especially
curved probes, which have smaller "footprints," will produce
different images.






Echogenicity
Echogenicity of the tissue refers to the ability to reflect or
transmit US waves in the context of surrounding tissues.7-91
Whenever there is an interface of structures with different
echogenicities, a visible difference in contrast will be
apparent on the screen. Based on echogenicity, a structure
can be characterized as hyperechoic (white on the screen),
hypoechoic (gray on the screen) and anechoic (black on the
screen) [Figure 1].

Bone appears black or anechoic on US, with a bright
hyperechoic rim [Figures 1 and 2]. Because the US beam
cannot penetrate bone, it casts an acoustic shadow beyond
it. Cartilage appears hypoechoic, and is more penetrable by
US than bone. Blood vessels also appear black or anechoic
[Figure 1]. Veins are usually easily collapsible upon external
pressure by the transducer, while arteries are pulsatile and
do not collapse with moderate pressure. Blood vessels have a
distinct appearance on color Doppler mode: flow toward the
probe appears red, while flow away from the probe appears
blue. A useful mnemonic used by radiologists is BART, i.e.,
Blue Away, Red Toward. Muscles are hypoechoic with striate
structure; fat is almost anechoic, while fascia and other
connective tissue strands and fascicles appear as hyperechoic
lines [Figures i and 2]. Lymph nodes appear anechoic or
hypoechoic. The appearance of nerves is variable, depending
on the proximity to the neuraxium. Proximal nerves are hypo-
anechoic (approximately similar to blood vessels but neither


Figure 1: US image of popliteal area. 1) Sciatic nerve (hyperechoic with stippled "honeycomb" structure); 2) Adipose tissue (hypoechoic);
3) Muscles (note the striations and hyperechoic fascial lines on muscle surfaces); 4) Vein (anechoic - partially collapsed under pressure to US
transducer); 5) Popliteal artery (anechoic - pulsating); 6) Bone (hyperechoic rim with hypoechoic shadow below it)


+ International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 56







Ihnatsenka and Boezaart: Understanding ultrasound


Figure 2: US image of thorax (ribs in short axis). 1) Rib (short-axis view, note the hyperechoic rim and intense acoustic shadow below it) 2)
Pleura with lung below (pleural sliding and shimmering, as well as comet tails artifact is seen only during live scan) 3) Neurovascular bundle 4)
Muscles 5) Fascia 6) Adipose tissue


collapsible nor pulsatile), and distal nerves are hyperechoic,
with a stippled ("honeycomb") structure (with hypo-anechoic
fascicles on the hyperechoic background of connective tissue
surrounding them) [Figure 1]. Ligaments and tendons have
a similar appearance to distal nerves (hyperechoic, but not
"honeycomb"). If in doubt, one can trace the "target structure"
proximally or distally in order to distinguish the nerve from
a tendon based on anatomy (the tendon will be traceable
to the muscle body). Tendons have characteristic striation
in the long-axis view, and are more anisotropic (discussed
later) than nerves. The lung has a very distinct appearance
[Figure 2]; one can usually visualize a "shimmering",
hyperechoic pleura sliding in rhythm with each breath, as well
as comet tail artifacts, if US is performed while the patient
is breathing; these are images that cannot be appreciated on
static pictures. Loss of sliding and shimmering pleura and
comet tail artifact may be due to pneumothorax.7-91

Scanning planes
Scanning planes are similar to the well-known anatomical
planes: axial (transverse), sagittal, parasagittal, and coronal.Elo
"Oblique" direction can be combined with any standard plane
to create, for example, a "parasagittal oblique" or "transverse
oblique" scanning plane.

Ultrasound views
All subjects, except cubes and spheres (that are absolutely
symmetrical in all directions), have a long axis and a short axis
when viewing them from a 2-D approach. Viewing a structure
in the long axis will provide a long-axis view, and vice versa;
an oblique view is also possible.

Anatomical structures, such as vessels or nerves, are more
commonly viewed in the short axis (round shape on the screen)
than long axis when the operator loses the lateral-medial
perspective. Rotating an US probe to go0 will change a short-
axis view into a long-axis view, and vice versa. An oblique view


can be appreciated during rotation of the probe between the
true short axis view and the long-axis view.

Angle of incidence
The angle at which the US waves encounter the surface of the
structure, termed, the angle of incidence, affects the way it is
presented on the screen. If the angle is perpendicular, or close
to perpendicular, more US waves will be reflected back to the
transducer and fewer will be "scattered" away, resulting in a
better image. If the US waves are more parallel to the surface
of the object (more than a 450 angle of incidence), the image
will have less definition. The operator can improve the image
of the target by tilting or rotating the probe, thus adjusting the
angle of incidence [Figure 3].

A close-to-perpendicular angle of incidence is also very
important for better needle visualization during US-guided
needle insertion, and can be achieved by changing the needle
approach such that it is advanced more perpendicular to the
US waves [Figure 4].

Anisotropy
Anisotropy in ultrasonography could be defined as a tissue
property that is responsible for changes in the US reflection
dramatically, even with mild changes in the angle of incidence.
It creates the phenomenon known as "now-you-see-me-now-
you-don't". Different tissues have varying degrees of anisotropy.
Nerves and tendons are notoriously anisotropic and could
make US-guided nerve blocks quite challenging. Tendons are
slightly more anisotropic than peripheral nerves, a factor that
occasionally can be used for differentiating structures that
may look similar on US, although tracing the structures more
proximally or distally to verify anatomical relationship is still a
better way of doing it. US probe maneuvers, such as pressure,
tilt, and rotation, are primarily performed to optimize the
angle of incidence in order to get the best reflection of the
targeted structure.

57 International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 *







Ihnatsenka and Boezaart: Understanding ultrasound


Figure 3: Schematic illustration of improving the angle of incidence
by tilting the probe. By tilting the probe from position 1 to position 2,
we obtained the true axial short-axis view of the artery and the nerve.
The shape of the image of the artery and the nerve got more rounded,
and the image of the nerve is much more defined in position 2 due to
a more favorable angle of incidence. Note the changes in Al and A2
distance as well


A,
57'I/
'9


Figure 4: Improving needle visualization during "in plane" needle
placement. To improve needle visualization, one can change the US
probe position (from 1 to 2) and the needle approach (from 1 to 2 to 3)
to optimize the angle of incidence between US waves and the needle


High frequency probes (10-15 MHz) and midrange frequency
probes (5-10 MHz) provide better resolution but have less
penetration. High frequency probes are, therefore, preferred for
US imaging of superficial structures (2-4 cm), while midrange
frequency probes are preferred for slightly deeper structures
(5-6 cm). However, when US imaging of deep structures (for
example, a proximal sciatic nerve that can be as much as 10
cm deep) is required, a low frequency probe (2-5 MHz) is
preferred, although the quality of the image will be substantially
poorer. When determining the correct choice between probes
with different US frequencies, choose the one that will provide

* International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 58


the best resolution for the required depth. Most practitioners
have several different probes for more flexibility.

T

Curvilinear probes generate a wedge-shaped US beam and a
corresponding image on the screen8 [Figure 5, left image]. The
curved image of the anatomical structures which, in reality, are
straight may initially look peculiar but, with time, the operator
becomes accustomed to the view. The curved probe can
easily roll on its scanning surface, thus affecting the direction
of the US beam. This ability to roll the probe is occasionally
advantageous in allowing us to "look around the corner", but
it can also have a disadvantage in that extra efforts are needed
to keep the US beam perpendicular to the skin surface while
looking straight down.

The curvilinear probe provides a broader view that could
be obtained via a smaller acoustic window; the image of
deeper structures is wider than the footprint of the probe.
This factor of widening of the image with the depth should
be also considered during distance measurement. In general,
determining the precise depth of the structure and width
assessment with a curved probe is tricky. It is necessary to
understand that the width of the image is equal to the probe
footprint size only at the uppermost part of the image, and
the depth marks on the side of the screen are pertinent only
for measurement of the depth on the line drawn through the
middle of the probe.

The curvilinear probe may be superior to the straight probe in its
ability to visualize the needle that advanced in plane at the steep
angle because it provides a more favorable angle of incidence.

Straight probes produce a straight US beam and an image with
a width equal to the size of the transducer footprint from the
surface to the deeper structures [Figure 5, right image].



The smaller footprint probe may be advantageous when
negotiating the small anatomical convexity and concavity of
the body surface, and may provide better contact between the
probe and skin, which is especially useful while using US in
uneven areas (supraclavicular or infraclavicular, for example),
especially for children. When the footprint of the probe is too
small, vision becomes "tunneled", although a larger footprint
will not only give a "wider picture" but also improve lateral
resolution. A small footprint of the probe is occasionally more
advantageous for in-plane needle advancement, allowing the
operator to place the needle entry closer to the target and thus
also shortening the distance to the target.



Color Doppler helps to distinguish structures with movement,







Ihnatsenka and Boezaart: Understanding ultrasound


for example, blood moving within vessels. Because proximal
nerves are usually hypo-anechoic and can be confused
with blood vessels, this function may be especially helpful
[Figure 6]. Color Doppler can also be used to determine the
direction of the blood flow when needed.

Compared to 2-D US, Doppler works best when US waves
are almost parallel to the direction of the moving object (that
is, blood, as in the case of blood vessels). When the angle of
incidence is close to 90goo and flow is low, there may be no color
on the screen, possibly producing a false negative indication
of "no flow".151 To increase the sensitivity of vessel recognition,
the probe should be tilted out, off the perpendicular angle
of incidence. Power Doppler should also be used in these
situations because it is more sensitive in recognizing low flow
in small blood vessels despite an unfavorable angle of incidence
than regular Color Doppler.[51





Changing the gain will change the amount of white, black,
and gray on the monitor. Adjusting the gain of the image may
improve the operator's ability to distinguish structures on
the screen; the amount of gain to use depends on personal


preference. Most US machines have an auto-gain knob, which
is commonly used.

Modern US machines have useful "nerve", "angio" or "general"
modes. The "focus" function available on these machines may
help to improve visualization of the targeted structure, although
it is rarely needed for superficial structures if the depth is set
correctly.




It is wise to begin with a somewhat higher depth setting in
order to first get a "big picture", and then gradually decrease
the depth when the targeted structure is found. For US-guided
injection, the depth should be set about i cm deeper than the
target of interest. If another structure of importance, such as
a vessel or lung, is situated below the target, the depth should
be adjusted accordingly to produce a good view of the field
and improve safety.

By knowing the target depth and its position on the screen,
the initial angle of needle advancement can be estimated
even before visualizing the needle on the screen. (If one uses
a 4-cm-wide transducer and an in-plane approach, the initial
angle will be close to 450 if the targeted structure is situated


Figure 5: Curved low frequency US probe image versus straight high frequency probe image (subgluteal sciatic nerve). Note the difference in
the shape and the scope of the images, different depth and resolution. 1) Sciatic nerve; 2) Gluteus maximus; 3) Quadrates femoris; 4) Femur


US 2D picture


LOi LUOOXIe


Figure 6: Color Doppler over 2-D US of the anterolateral neck area at C6/C7 level. While looking only at the 2-D US image, one may confuse
vertebral artery (2) with a nerve root. Both may look the same on 2-D US. Color Doppler helps to distinguish nerve roots from blood vessels.
1) Carotid artery; 2) Vertebral artery; 3) Inferior thyroid vein


59 International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 +







Ihnatsenka and Boezaart: Understanding ultrasound


in the middle of the screen at the 2-cm depth and the needle
is inserted at the edge of the transducer.) This angle should be
adjusted as soon as the needle can be viewed on the screen and
its trajectory is clear.



Probe orientation is important because the US probe can
be easily rotated around (1800) while the position of the
monitor remains unchanged, which may create confusion in
the direction of probe manipulation and needle advancement
and placement. Therefore, it is always useful to confirm which
side of the probe corresponds to a particular side of the screen
in order to identify the correct orientation of the image. All
transducers have an orientation marker that corresponds to the
marker on the screen.



When dealing with US probe manipulation, the mnemonic
PART (Pressure, Alignment, Rotation and Tilt) is useful
[Figure 7]. It is important to understand that by manipulating
the US probe, we primarily manipulate the direction of the
beam, and, by changing the direction of the beam, slightly
different US images of the same structures can be obtained.

Pressure
Correct pressure application can considerably improve the
image quality. It affects the echogenicity of the tissue and
shortens the distance to the structure of interest. Ordinarily,
pressure must be applied evenly to get the correct direction of
the scan; however, occasionally, the operator may intentionally
need to apply more pressure on one side of the probe in order to
direct the US beam in the desired manner (angling the probe).
Pressure to the probe is also applied to compress a vein or to
push an anatomical structure out of the way of an intended
needle pass. Excessive pressure, however, can cause discomfort














K T


Figure 7: US probe manipulation maneuvers "PART" mnemonic
for Pressure, Alignment, Rotation and Tilt as fundamental probe
manipulation maneuvers

* International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 60


to the patient. Placing excessive pressure on the transducer may
also be responsible for significant depth underestimation to the
relatively deep structure if US is used solely for marking and
measuring, and if a procedure is done after that without US
on a patient who has significant amount of soft tissue, which
"springs back" when the probe is removed.

Alignment (sliding)
The main goal of this maneuver is to find the structure of
interest and position it optimally on the screen for needle
advancement (usually in the middle of the screen for an out-
of-plane approach and somewhat on the opposite side of the
screen for an in-plane approach). Sliding is also very useful
for tracing the potential structure proximally and distally for
better verification of pertinent anatomy during a "scout scan".

Rotation
With rotation, one can achieve several goals. First, one can
attain a true axial view of the target with its long axis parallel
to the surface but not perpendicular to the current US plane.
For example, if you image a blood vessel (that is parallel to the
surface) in the short-axis view and slide a US probe along the
vessel's long axis, you must slightly rotate the probe when the
vessel makes a turn in order to maintain true short axis view.
Second, one can align the target into a more favorable trajectory
for a safe needle pass (away from vessels or pleura, for example).

Rotation will affect the image if it brings the object out of the
true axial view. If the long axis of the object remains parallel to
the surface and the US probe is gradually rotated relative to the
long axis of the structure, the round cross section of the true
axial cut (of the normally round vessel or nerve, for example)
will be replaced by a more oval shape. By continuous rotation
of the probe of goo from the initial probe position, one can
change the view of the structure from its short axis to its long
axis, and vice versa.

Tilt
There is no particular recognized terminology to define the
direction of the tilt, and confusion can arise from the fact that
when the probe is tilted in one direction, the US plane, in fact,
sweeps to the opposite direction.

Several goals can be achieved by tilting the probe. First, by
sweeping the US beam in the particular direction desired by
tilting the probe, one can "preview" the image by sliding the
probe in the opposite direction of the tilt [Figure 8]. Second,
by tilting the probe, a true short-axis view of the object can
be obtained, the long axis of which is not perpendicular to the
initial US beam plane [Figure 3, position 2].

As with rotation, if the US plane cuts the long axis of the
target at the angle that is not perpendicular, it will distort the
2-D image [Figure 3, position i]. By tilting the probe out of the
true axial view of the target, the image will change as follows:







Ihnatsenka and Boezaart: Understanding ultrasound


a. The distance from the surface to the target will increase
and
b. The shape of the target on the screen will be untrue (oval
instead of round, for example).




US artifacts are responsible for untrue images when we see on
the monitor something that does not exist in reality or we do
not see something that is in fact true. Many artifacts from US
have been described; some are well understood and related
to the physics of US, such as reverberation, mirror image,
or acoustic enhancement artifacts, while others are not fully
understood. These are outside of the scope of our paper; if
detailed information is desired on these topics, the reader is
referred to specialized texts.[b]




A general description of sonopathology can be found in other
articles.EJ1 As a rule of thumb, factors that negatively affect
the echogenicity of tissues include the accumulation of extra
water in soft tissue, as occurs with edema; loss of muscle mass,
as happens with hypotrophy; and accumulation of micro-
droplets of fat in the muscle, thereby producing an US image
with less sharpness and contrast. Fluid collections could be
readily seen by US and this has been used by radiologists for
years. Air bubbles in the soft tissue can significantly affect the
image to the point that it renders US unproductive. It stands
to reason that a great deal of experience in imaging of normal
sonoanatomy is needed before an operator can reliably visualize
any pathology. Pure anatomical variations, such as unusual
location of the nerve or presence of additional nerve or vessel,
for example, are not considered pathological, provided these
variations are not affecting normal function. Some anatomical
variations that are missed on the exam before the nerve block,
nevertheless, could be responsible for block failure.

T


In-plane needle placement occurs when the needle can be
seen on the US monitor in the long-axis view (long axis of the
needle is situated within the US scanning plane). Out-of-plane
needle placement occurs when the long axis of the needle is
directed across the scanning plane so the needle can be seen in
the short-axis view [Figure 9]. Although other approaches can
be employed, in-plane needling is commonly used for single
injections, while out-of-plane is used for catheter placement.

When performing out-of-plane needle advancement, dynamic
tilting or sliding of the transducer when advancing the needle
may help track the tip of the needle [Figure lo]. Visualizing
the tip of the needle can be challenging, yet is essential. For this
purpose, it is common to use tissue movement, or injections


Figure 8: Schematic illustration of tilting and sliding during image
acquisition in the neck. Position 1: The probe is perpendicular to the
skin at the level between C6 and C7. Tilting the probe (position 2) allows
us to see C7 transverse process and C7 nerve root. Sliding the probe
more caudad (position 3) allows us to see an image similar to the image
obtained from position 2 but with the probe perpendicular to the skin


In plane needling Out of plane needling
Figure 9: In- and out-of-plane needle placement


target


Figure 10: Improving tip of the needle visualization during out-of-
plane needle placement. Gradual tilting of the probe during needle
advancement allows the operator to follow the tip of the needle.
Sliding a probe without tilting could be an alternative way of keeping
the needle tip in the view

61 International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 *







Ihnatsenka and Boezaart: Understanding ultrasound


of small volumes of dextrose (if nerve stimulation is planned)
or normal saline as an indicator (hydrolocation). Use of US,
in combination with nerve stimulation, may be especially
beneficial for the out-of-plane approach in some instances.

The in-plane mode is usually the preferred approach because
it allows one to visualize the entire needle, including its tip.
Visualization can be enhanced if a larger or specially designed
echogenic needle is used and a more favorable angle of incidence
is employed.[12]





An US machine should be positioned on the contralateral side
of the patient, with the operator standing on the ipsilateral
side that needs to be blocked or examined. The transducer
is usually held in the operator's nondominant hand, with the
needle in the dominant hand. The transducer should gently
be held quite low on the probe, close to the scanning surface,
rather than harshly gripped on the top of the handle. When
planning to use the in-plane approach, it is preferable to place
the probe directly perpendicular to the skin. (If it is possible to
do without sacrificing image quality, try not to tilt the probe,
as this will add difficulty with in-plane needle advancement;
personal observation).



T

It is important to stabilize the US probe position after obtaining
the desired image. This can be facilitated by gently bracing the
hand holding the probe on the patient's body. Subsequently,
we recommend taking the operator's attention off the screen
and focusing on attaining correct needle alignment with the
US probe. Only after some advancement of the needle through
the skin has occurred should the probe operator shift his/her
attention back to the screen. At that point, if the needle can be
visualized on the screen, further advancement and trajectory
changes can be made based on feedback from the US screen
without averting attention to the probe position and needle.
Eye-hand coordination is required for this maneuver, and
phantom exercises are very helpful to enhance this particular
skill.1'3

Operators, particularly at the beginning of training, commonly
lose sight of the tip of the needle or the entire needle from
view. In these instances, it is perfectly proper to look back at
the probe and find the best possible way to realign the needle
with the US plane. If only the tip of the needle is "moving
out" of view, one can slightly withdraw the needle back and
try again with slight trajectory adjustment. Visualization of
the needle can also be regained by slight probe manipulations


(tilt, rotation, or sliding). It is important to develop a "feel of
depth" for needle advancement and have accurate expectations
for corresponding changes on the US screen should they occur.
The US beam is very thin (about 1 mm wide), so even subtle
movements can bring the needle in and out of the viewing
field. If the operator does not have this "feel of depth" and
corresponding expectation for the tip of the needle position
on the screen, and tip of the needle accidently moves out of
the US plane, the operator may advance the needle deep,
before realizing it.




Knowledge of the fundamentals of US that were mentioned in
this article, combined with understanding of the clinical 3-D
anatomy of the area of the interest, will allow practitioners to
use musculoskeletal US and US-guided procedures effectively
and safely. We hope to publish an article dedicated to
sonoanatomy of the neck above the clavicle in the near future.



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Source of Support: Nil, Conflict of Interest: None declared.


* International Journal of Shoulder Surgery - Jul-Sep 2010 / Vol 4 / Issue 3 62




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