Knee

A popliteal sciatic nerve block done with the Sonosite SII ultrasound machine is a clinically valuable technique that results in anesthesia of the calf, tibia, fibula, ankle, and foot. Anesthesiologist Dr. David Auyong MD of Seattle, Washington here reviews scanning techniques and sonographic landmarks for the procedure, discussing important structures, techniques to visualize the popliteal vein, types of probe used, and needle/injection choices. The Sonosite II allows precise placement of local anesthetic, much reducing patient discomfort, providing superior visualization of the nerve and the needle during block placement.

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- The Popliteal Sciatic Nerve Block
is a good block to do for the sciatic nerve
because this is where the sciatic nerve
is found most shallow.
This block can be performed for post year knee pain
after knee surgery, as well as, calf, foot
and ankle surgery.
This is the main nerve that supplies the lower leg.
I find a lateral position gives you good control
of the patients airways if you sedate them
as well as good ergo-dynamics to do the block.
Here we have our patient positioned laterally
with a pillow between the legs for comfort.
To do the Popliteal Sciatic Nerve Block
we use a linear probe.
The linear probe allows us to see structures well
in the shallow plane,
but gives us a wide field of view
to see our needle approaching the nerve.
To perform the Politeal Sciatic Nerve Block
we put the probe directly in the back of the knee.
Placement of the probe in the back of the knee
reveals a structure of the nerve, the vein, the artery.
I call this structure, the snowman in the back of the knee.
You have three circles on top of each other.
The upper most circle represented by the tibial
component of the sciatic nerve.
The middle structure represented by the vein
and the deep structure represented by the popliteal artery.
If we put color Doppler on the screen
we are able to see the pulsating artery
in this area.
Sometimes it's difficult to see the popliteal vein
because this is a low-flow state,
such as we see here.
To visualize the popliteal vein better
we can squeeze the back of the calf,
increasing venous flow through the popliteal vein,
such as this.
There we can see increased venous flow
through the popliteal vein represented better
by color Doppler.
Now, as I mentioned, this is only the tibial component
of the sciatic nerve.
We wanna get the nerve where it comes together
and has both components, the peroneal
and the tibial component.
As we scan up the leg, here we now see
the peroneal component laterally,
the tibial component medially,
the popliteal vein and popliteal artery.
On the medial side we see the semitendinosus
and semimembranosus muscles.
On the lateral side we see
the biceps femoris, long and short heads.
As we keep going up the leg
the tibial and peroneal components join into one nerve.
Sometimes we block the nerve at this level
where the two components are joining.
This allows us to get both components
with a single injection at the nerve.
My needle approach for these blocks
are gonna be from lateral to medial.
What I typically do is measure the depth
of the sciatic nerve in this setting.
Here the sciatic nerve is approximately
one-and-a-half to two centimeters deep to the probe.
So if I measure one-and-a-half to two centimeters deep,
my needle is gonna come in completely perpendicular
and have a very bright view of the needle
and needle shaft as it advances to the nerve.
Now, I typically like to inject deep to the nerve
as well as superficial to the nerve
in order to get complete surrounding
of the popliteal sciatic nerve
for the most rapid onset for this block.
Typical volumes used are 20 to 30 milliliters
of local anesthetic.
This block takes some time to onset
and studies have shown even with complete surrounding
of the nerve, it takes up to 30 minutes
for the nerve block to onset in most patients.
Here we see the popliteal sciatic nerve
surrounded by the biceps femoris laterally
and the semitendinosis/semimembranosis medially.
Our needle is advanced directly above the nerve
and the local anesthetic is injected,
pushing the nerve deeper.
We then withdraw the needle
and readvance the needle again close to the nerve
so we can get local anesthetic spreading
to the medial side of the nerve,
which is more of the tibial component.
Now you can visualize both the peroneal and tibial component
with a local anesthetic completely surrounding the nerves.

Brightcove ID

5508136021001

https://youtube.com/watch?v=X0wqmWXEcTg

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How to: Femoral Nerve Block

Read more about How to: Femoral Nerve Block

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Dr. David Auyong reviews scanning techniques and sonographic landmarks for an ultrasound guided nerve block .

Clinical Specialties

Anesthesiology (Regional)

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The femoral nerve block is used
for many different surgeries.
The femoral nerve block can be used for knee surgery,
hip surgery, femur surgery,
or even medial ankle surgery to get the saphenous nerve.
To perform the femoral nerve block,
there's a few key positioning tips.
We want to put the patient completely supine.
Many of our patients are larger and have larger abdomens,
so putting the patient supine allows us to get
high enough in the femoral region.
Also, if their adipose tissue hangs over the femoral region,
we want to put tape here and tape their abdomen away
out of the way, so you can put your probe
comfortably in the femoral region.
To do an ultrasound guided femoral nerve block,
we use a linear high frequency probe.
To start the femoral nerve block,
we usually put the probe right in the femoral crease.
On our screen now, we see several important features.
From medial to lateral, we see the Iliacus muscle,
we see the nerve sitting right on the Iliacus muscle,
and we also see the femoral artery,
and then to the right we see the femoral vein.
There are a few fascia coverings in this area
that are important.
The Facia Iliaca runs above the femoral nerve
and below the artery.
The Fascia Lata runs above all of this,
above the artery and vein as well.
Now for the femoral nerve, we want to see a hyperechoic
or bright nerve sitting on the Iliacus muscle.
The true femoral nerve is a wide, flat nerve
laying directly on the muscle.
If you inject above the Facia Iliaca,
this will create a barrier to your nerve
and allow a block that is not complete.
So as we move up and down the leg,
we're gonna see some key that will help you find
the femoral nerve in all patients.
More medially, you see the pulsating femoral artery,
and medial to that you see the femoral vein.
Here the vein collapses with pressure.
Now some keys to find the femoral nerve
in every patient are as follows.
If the probe is placed too cranially,
your femoral artery and vein and nerve
drop deep on the screen.
The femoral vein, artery, and nerve
are too deep, then you need to move the probe caudally.
If you probe is placed too distally,
that femoral artery is going to split
into two femoral arteries.
Here you can see a pulsating Profunda femoral deep
as well as a true femoral artery superficial.
Now I'm gonna put some color flow on that,
and you can see a pulsating artery deeper,
and a superficial femoral artery as well.
Now the vein is on the left,
represented in red in this picture.
As we move cranially, those two arteries come together.
When we look laterally from there,
the nerve has also come together from
many branches, forming one femoral nerve.
This way we can see the femoral nerve the best
when the artery also comes together as well.
Now our needle approach to the femoral nerve
is going to be from lateral to medial.
Typically, we use a 10-centimeter needle
because we use these in-plane approaches
to the femoral nerve.
I like to put my target on the further side of the screen
so I can see my needle coming in from the lateral side.
So I'll put my first injection lateral to the nerve
just above the Iliacus muscle
to ensure injection below the Fascia Iliaca
but not within the Iliacus muscle.
By using typical volume, such as 20 to 30 milliliters,
we'll get spread above the nerve
or below the nerve, without poking into
the nerve, and damaging the nerve.
In this femoral nerve block, you can see a single
injection needle being advanced lateral to the nerve
which is lying right on the Iliacus muscle.
You can see the pulsating femoral artery medially,
and the local anesthetic now spreading over
the wide, flat femoral nerve.
Our needle tracks in with the local anesthetic
so we can get local anesthetic spreading
all the way medial around the femoral nerve here.

Brightcove ID

5765925239001

https://youtube.com/watch?v=Z-O_EaAE_rg

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Dr. David Auyong reviews scanning techniques and sonographic landmarks for an ultrasound guided nerve block .