Dissection of the Brachial Plexus to follow the Dissection of the Superficial Cutaneous
Nerves of the Neck and Arm
Dissection
If there are four dissectors then divide the dissection so that two of you are on the right
and two on the left with one doing the neck and the other doing the arm
1. NECK
2. 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
3. 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
4. Omohyoid muscle
a. Crosses over the interscalene area
b. Suoperficial to it
c. Try to preserve this
5. Transverse cervical vein
a. Crosses this area too but lower
b. Yo can try to preserve this too but if it gets in the way it is okay to remove
it
6.
7. 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. The cervical fascia was a layer of fascia that forms a kind of
cylinder around the neck with sleeves for the sternocleidomastoid
and the trapezius
iii. The dissection down to the cervical plexus required you to dissect
through this layer to reach those nerves
iv. So there will be just adipose tissue to digitally dissect to get to the
interscalene groove and its contents
b.
c.
d.
e.
f.
g.
h.
v. Push you thumb down through this adipose until you get to what
appears to be a gray white tissue that is overlying the scalenes and
interscalene nerve bundles
vi. If you look closely you will see the scalenes and interscalene nerve
bundles underneath this fascia
Use your thumb in a kind of downward motion with the thumb pointing
down the neck until you feel it slide over a bump
i. This is the insertion of the scalenes onto the first rib and the
passage of the brachial plexus and subclavian artery over the first
rib
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. Above your
thumb will be the following:
i. Omohyoid
ii. Transcervical vein
iii. Fascia and muscle of the subclavius muscle
Omohyoid
i. Recall that this muscle goes from the hyoid down to a slip of fascia
under the SCM and then to the scapula near the notch
ii. Look at the skeleton to view the suprascapular notch
iii. This is where the omohyoid will insert and the notch is where the
suprascapular nerve will go through.
Once you have identified the omohyoid you can now cut that other tissue
that was directly under the clavicle away so you can open it all up and you
can begin to see things
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
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
More proximally, use the ties that are around the suprclavicular nerves and
the superficial cervical plexus to help move the tissue and adipose that
these nerves are going through to move it posteriorly
i. Dissecting the accessory away from the nerve to the trapezius is a
good idea
ii. The tissue that is still attached to the supraclavicular nerves distally
can be cut as long as there are ties on them to help you identify
them later and to use to help swing them out of the way
8. ARM
9. The basic concept is to find the terminal nerves in the arm so you can use them
later when you have the brachial plexus exposed to help identify the nerves and
cords in the plexus
10. Try to preserve the superficial cutaneous nerves
a. The medial antebrachial nerves and basilic vein so it can be demonstrated
later
b. The lateral antebrachial cutaneous nerve so you can follow the
musculocutaneous nerve later
c. The posterior antebrachial cutaneous nerves may have been cut or incises
but small twigs of them can still be se branching from the radial where it
rests on the humerus and distally to this
11. Search for the median nerve
a. Very close to the basilic vein but deeper in the intermuscular septum you
will find the brachial artery
i. There are two veins that accompany this artery called venae
comitantes
ii. They may be small or difficult to see or differentiate into two
because of the effects of the process of preservation of the cadaver
iii. Once you see the artery then at the elbow the nerve is medial to it
but you will see that it is on the medial side of the artery but lower
or more posterior to the artery. In other words, it is not on the same
plane as the artery if that plane is parallel to the table. The nerve is
lower or more posterior to that plane.
iv. This is important when viewing the median nerve at the elbow
b. From the brachial plexus
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. In the arm
b. Look for the ulnar nerve by feeling between your thumb and fingers just
above the medial epicondyle. You may feel something that feels like a
cord rolling between your fingers
c. This is the ulnar nerve
d. You can make an incision with your metz through the medial
intermuscular septum which is the fascia here
e. Try to preserve some of this fascia overlying the nerve so it can be
demonstrated later
f. This is the position used in ultrasound for finding the ulnar nerve on the
medial side of the arm. You would use the medial epicondyle as a
landmark then move the probe proximally to see the ulnar nerve under this
fascia or intermuscular septum
g. Now follow the nerve proximally and you will come to a point where the
ulnar nerve went under this intermuscular septum
13. Ulnar nerve from the brachial plexus
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
14. Find the radial nerve in the arm
a. Find the nerve in between the brachialis and the brachioradialis and follow
it up the arm until it begins to be near the humerus
b. It is at about this level that the cutaneous branches of this nerve to the
forearm leave the radial nerve on their way to become the posterior
antebrachial cutaneous nerve
c. This is about as far as you can go without cutting into the triceps
15. Find the radial nerve in the axilla
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
16. Intercostobrachial nerve
a. Find this nerve coming from in between the 2nd and 3rd intercostal space
b. This nerve will go posteriorly and cross over to the arm at the junction of
the tendon to the latissimus dorsi and the triceps
c. The medial brachial cutaneous is usually helping this nerve cover the
medial and posterior aspect of the arm and will join this nerve with a
branch in addition to continuing on with the main nerve to the arm in the
same path as the intercostobrachial
17. Pectoralis major and minor
a. The goal here is to incise the pectoralis major in such a way as to preserve
the underlying nerves and still be able to demonstrate its insertion into the
humerus and to show the relationships of the nerves to the muscle
i. Lateral pectoral nerve
ii. Medial pectoral nerve
b. This is done by incising it in a semicircle on the chest so it can be reflected
laterally
c. Once this is done you will see the pectoralis minor
d. Now look for the pectoral nerves. They will be associated with an artery
and vein so it may not appear like a distinct nerve.
e. Once you can see the nerves or at least are aware of their probable location
you can then remove incise the pectoralis major from its insertion on the
humerus in such a way that will allow you to demonstrate it later
18. Pectoralis Minor
a. Note the insertion into the coracoid process
b. You may now incise the origin of this muscle off of the chest wall
c. You may also incise it from its insertion into the coracoid process
d. Now you will be able to see under the pectoralis major and minor during
your dissection of the brachial plexus from the neck to the axilla
19. The PEC Block
a. PEC I is a block that involves injecting local in between the pectoralis
major and minor and
b. PEC II is a block under the pectoralis minor
c. PEC III is a block done under the serratus anterior in the area of the 3rd or
4th rib
d. These blocks are all done like an infraclavicular block by placing the
probe in the deltopectoral groove
20. Brachial Plexus in the neck
a. Now take a look at the anatomy in the neck and you should be able to see
an outline under the prevertebral fascia of the anterior scalene, the
interscalene nerves and the middle scalene
b. This will look like three cylindrical cones going down to the first rib
c. 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
d. The posterior scalene inserts onto the 2nd rib
21. 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
22. Once you have found the interscalene nerves use your Metz to go deeper in
between the nerves and the anterior scalene muscle.
a.
b. The roots of the brachial plexus are in a straight line but the orientation of
this line will become apparent as you separate the scalenes from the nerve
roots
c. Then try to separate the roots and trunks out
d. C5 C6 Superior
e. C7 Middle
f. 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 to demonstrate it
g. 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
h. By doing this you are in a way destroying the Axillary Sheath which is the
prevertebral fascia that covers the nerves as it goes into the axillary area
23. 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. The musculocutaneous nerve going down the arm
d. The lateral contribution of the median nerve
24. Lateral cord
a. Now pick up this lateral cord which is the outermost group of nerves
b. Note that it is bound to the other nerves below and underneath it by nerves
that are actually the divisions
c. Note too that this is commonly seen on ultrasound as what appears to be
an independent bundle of nerves on the supraclavicular approach
25. 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. My mnemonic for this is PaLM 3-2-1
i. The logic behind it is based on the following:
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 Trinity or the Three Persons of God, The Father The Son and
The Holy Spirit
iii. When visiting Italy you’ll will notice that Italians count by holding
out their thumb and calling that one, then their index is two and the
middle is three. That is why pictures of Jesus show his hand that
way
iv. If you start with your hand as a fist in the supinated position and
then start counting with your thumb as one, your index as two and
your middle finger as three it begins to reveals the palm.
v. So look at your hand and count starting with your thumb then spell
palm starting with the middle finger
vi. PaLM 3-2-1
c. The posterior cord, formed by three divisions, can be tough to see but keep
in mind that the division from the inferior root is the smallest.
d. The lateral cord and its formation by two divisions is usually easy to see.
e. The medial cord just appears to be a continuation of the inferior root as its
contribution to the posterior cord is small and behind it.
f. Occasionally you will see a division split in two
26. Lateral Cord
a. Typically if you follow the lateral cord it will help you find the
musculocutaneous nerve
b. 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.
c. Then the lateral cord contributes to the median nerve
d. Now find the contribution to the lateral pectoral nerve
27. Medial Card
a. The contribution to the medial pectoral nerve is usually wrapped around
the artery and vein underneath so it will take some effort to follow
b. Use the nerve that is attached to the pectoralis muscles to help find it
c. There is usually a bringing between these two nerves as well
28. Posterior cord
a. Find the axillary nerve
b. It is easy to confuse it with the MCN but that nerve is more distal down
the arm
c. The axillary goes around the surgical neck of the humerus
29. 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