Dissection of the Brachial Plexus to follow the Dissection of the Superficial Cutaneous
Nerves of the Neck and Arm
Dissection
1. The first thing to do is to remove the clavicle
a. Look at the skeleton and review the look of the clavicle
i. The medial end at the sternoclavicluar joint is deep and triangular
ii. The lateral end at the acromioclavicluar joint is thin and flat
b. Take a scalpel and cut the outline of the clavicle on top
i. Note that you will be incising the following muscles
ii. The lateral third will be the trapezius and deltoid
iii. The medial third will be the sternocleidomastoid and pectoralis
c. Stay close to the clavicle and then once removed save it so you can use it
to demonstrate the location of it later
2. Next you will begin digital dissection to find the paravertebral fascia and its
contents which are the
a. The anterior scalene
b. Interscalene nerves and subclavian artery
c. The middle scalene muscle
3. Make sure you are posterior to the sternocleidomastoid and use digital dissection
to go deeper than the level of the superficial cervical plexus
a. Recall that the superficial cervical plexus is under the superficial cervical
fascia which is a flat fascia that encases the sternocleidomastoid then
forms a fascial plane over the posterior triangle of the neck and then
encases the trapezius
i. The superficial cervical fascia is gone because of our dissection of
the superficial cervical plexus
ii. So there will be just adipose tissue to digitally dissect to get to the
interscalene groove and its contents
iii. Push you thumb down through this adipose
b. Use your thumb in a kind of downward motion with the thumb pointing
down the neck until you feel it slide over a bump that is the insertion of
the scalenes onto the first rib and the passage of the brachial plexus and
subclavian artery over the first rib
c. You should be able to get to the point where your digital dissection will
slide on under the tissue that was originally under the clavicle
d. Once you have done this you can now cut that tissue that was directly
under the clavicle away so you can open it all up and you can begin to see
things
4. Now take a look at the anatomy and you should be able to see an outline under the
fascia of the anterior scalene, the interscalene nerves and the middle scalene
a. This will look like three cylindrical cones going down to the first rib
b. Look at the skeleton again and familiarize yourself with the first rib and
try to see how these nerves and muscles are inserting on the first rib
5. Now take you Metz and forceps and begin to define the anatomy
a. Be careful as the muscles are friable so try to dissect with the Metz using
the poke and spread method along true anatomical planes and define the
anterior scalene, the interscalene nerves and the subclavian artery and the
middle scalene muscle
b. Note that as you slide your fingers down this fascia that towards the
bottom of these structures you may see a nerve leaving the brachial plexus
and going toward the scapula.
i. This is the suprascapular nerve
ii. Look at the skeleton again and note the coracoid process and
follow it posteriorly to the suprascapular notch.
iii. This is where the army goes over and the navy goes under
iv. The suprascapular nerve goes under the suprascapular ligament
and the artery goes over and they are joined in this area by the
omohyoid
v. The suprascapular nerve is blocked by orthopedic surgeons after a
shoulder scope for postop pain and can be used as one of the
blocks to help avoid diaphragmatic paralysis from an interscalene
or supraclavicular nerve block because of local finding its way to
the phrenic nerve
c. Go back to the cadaver and continue to dissect it and follow the
suprascapular nerve enough to define it so you won’t cut it later. Further
dissection of this nerve can be done later
6. Once you have found the interscalene nerves use your Metz to go deeper in
between the nerves and the anterior scalene muscle.
a. Then try to separate the roots and trunks out
b. C5 C6 Superior
c. C7 Middle
d. C8 T1 lower
i. Note that the T1 is coming up from inside the chest and
ii. You must feel the first rib and its curve and
iii. Then kind of move your Metz in a way to snag it from underneath
the first rib
iv. And then put a tie on it so you can use it to show others
v. Leave the tie long enough so you can pull on it later with wet
gloves
e. Then begin to use your Metz along the axis of all the nerves to poke and
spread the scissor blades to help you remove the sheath around all these
nerves
f. By doing this your are in a way destroying the Axillary Sheath which is
the prevertebral fascia that covers the nerves as it goes into the axillary
area
7. As you move down the lateral cord you will note the following
a. The suprascapular nerve
b. The lateral pectoral nerve going to the pectoralis muscles
c. and then going down the arm as the musculocutaneous nerve and the
lateral contribution of the median nerve
8. Now pick up this lateral cord which is the outermost nerve and note that it is
bound to the other nerves below and underneath it by nerves that are actually the
divisions
a. I remember them with a 3-2-1 rule
i. Three posterior divisions make the posterior cord
ii. Two anterior divisions make the lateral cord
iii. One anterior division makes the medial cord
iv. 3-2-1 P:L:M
b. We need to come up with a mnemonic for this
i. If you start your hand as a fist and then start counting with your
thumb as one, your index as two and your middle finger as three it
reveals the palm PLM
ii. Paintings of Jesus made by Italians during the renaissance always
show him holding out his hand with the thumb and the index and
the middle finger extended out. This is to represent the Mystery of
the Three Persons of God
iii. That ‘s how Italians count and that is why pictures of Jesus show
his hand that way
iv. Maybe PaLM 3-2-1
v. You guys come up with something different if you want
9. If you have any trouble with this part of the dissection then move on down the
arm and find the terminal nerves
a. This will keep you moving and then help you discern the brachial plexus
later
b. Try to preserve the medial antebrachial nerves and basilic vein so it can be
demonstrated later
10. Typically if you follow the lateral cord it will help you find the musculocutaneous
nerve
a. Once you think you have this, verify it by looking under the bicep for the
nerve and use it to pull on it and make sure you have the right one.
b. Then the lateral cord contributes to the median nerve
11. Search for the median nerve
a. Once you see this nerve you can dissect on down the arm and note the
following
i. The median nerve begins on the lateral side of the artery and ends
up on the medial side of the artery in the cubital fossa
ii. In the cubital fossa, from medial to lateral, median nerve, brachial
artery, biceps tendon
iii. Remember TAN or NAT Nerve Artery Tendon
iv. With ultrasound you would place one side of the probe on the
tendon and then begin your search for the artery
12. Now find the ulnar nerve
a. It is common to run into the medial antebrachial nerve here while
searching for the ulnar because the medial brachial and medial
antebrachial cutaneous nerves are also branches of the medial cord as well
as the ulnar so you will have to follow it down to determine if it is really
the ulnar or the cutaneous nerves.
b. The ulnar splits from the brachial artery and goes under a tissue membrane
called the medial intermuscular septum
c. It descends to its typical location between the medial epicondyle and the
olecranon under this fascia
d. Once you find the ulnar nerve you can pull on it to help you strum it under
this fascia down near the medial epicondyle and then use your Metz to
poke through it and find the ulnar nerve
e. Tag it with a tie so it is easy to find later
f. If possible try to preserve some of the fascia overlying this nerve for
demonstration later
13. Find the radial nerve
a. In the axilla find the artery and search behind it for the radial
b. Once you find it you should be able to use the radial in its location
between the brachialis and brachioradialis muscles to make sure you have
the right nerve
c. Note the relationship of the nerve to the artery and note the relationship to
the latissimus dorsi tendon
d. Also make note of the fact that you pectoralis has been removed and that
you need to try to mentally reconstruct where the pectoralis muscle was so
you can then determine where you would normally be when doing an
axillary approach to the brachial plexus in the axilla
14. Now make your way back to the brachial plexus and use these nerves to help you
reveal the brachial plexus
15. Depending on time you can finish here as the next dissection will be further
dissection of the nerves to make sure you have it all figured out
a. As well as tracing the path of the suprascapular nerve
b. Following the path of the accessory nerve
c. Finding the phrenic nerve
d. Finding the dorsal scapular nerve
e. Defining the carotid artery and internal jugular vein and vagus
f. Alternate dissections can be done as well
i. Turning the cadaver prone to follow the
1. Axillary nerve
2. The suprascapular nerve
3. The greater occipital nerve
4. The accessory nerve
ii. Beginning a dissection of airway nerves