5. Posterior triangle of neck, axilla, and brachial plexus

lecture 5 - Moon

what is the posterior cervical triangle (lateral cervical triangle)

associated with nerves and vessels that pass into and out of the upper limb. it is divided into an upper occipital triangle and lower supraclavicular triangle by the omohyoid muscle

the primary contents of the posterior cervical triangle are muscles, the spinal accessory nerve, the cervical plexus cutaneous branches, vessels, and the origins of the brachial plexus (roots and trunks)

boundaries of the posterior triangle of the neck

sternocleidomastoid (posterior)

clavicle

trapezius (anterior)

what is the sternocleidomastoid a landmark for

anterior vs posterior neck triangle

internal vs external jugular vein

sternocleidomastoid origin

manubrium of sternum and proximal clavicle

sternocleidomastoic insertion

mastoid process of the temporal bone

sternocleidomastoid innervation

spinal accessory nerve (CN XI)

sternocleidomastoid action

unilateral": tilts head to same side, rotates head to opposite side

bilateral: extends head, aids in respiration when head is fixed

scalene muscles blood supply

ascending cervical branch of inferior thyroid artery

scalene muscles innervation

cervical nerves

scalene muscles action

elevate ribs 1 and 2

scalene muscles origin

transverse processes of cervical vertebrae

scalene muscles insertion

1st and 2nd rib

scalene muscles importance

brachial plexus lies between the anterior and middle scalene muscles

small space so any increased pressure = compression = problem

cervical plexus

formed by the ventral rami of cervical nerves 1-4 that form a network of loops

provides general sensation to the neck and posterior head and motor innervation to hyoid muscles

spinal accessory nerve and the posterior cervical triangle

crosses over the superior aspect of the posterior cervical triangle on its route to innervate the trapezius muscle

Branches of the subclavian artery in the posterior triangle

the suprascapular artery (branch of thyrocervical trunk) passes into the scapular region to supply the supraspinatus and infraspinatus muscles

superficial and deep branches of the transverse cervical arteries supply the trapezius (superficial) and other back muscles (deep)

dorsal scapular artery supplies the rhomboids and levator scapulae

veins of the posterior cervical triangle

external jugular vein traveling superficial to the sternocleidomastoid to drain into the subclavian vein is a continuation of the axillary vein and ends by joining the internal jugular vein to form the brachiocephalic vein. it drains the entire upper limb

the superior thoracic artery

supplies the 1st and 2nd anterior intercostal spacest

the thoracoacromial artery (pectoral, clavicular, acromial, and deltoid branches)

branches supply the anterior axillary wall and related structures

the pectoral branch also contributes to the blood supply of the breast

lateral thoracic artery

supplies the anterior and medial walls of the axilla. it also contributes to blood supply to the breast

subscapular artery

the largest branch of the axillary artery and provides blood to the posterior wall fo the axilla

has 2 major terminal branches: thoracodorsal and circumflex scapular

thoracodorsal artery

travels with the thoracodorsal nerve to the latissimus dorsi

circumflex scapular artery

passes posteriorly to supply muscles and other structures on the lateral border of the scapula

anastomoses with branches of the dorsal scapular and suprascapular arteries to form the scapular anastomosis

anterior humeral circumflex artery

passes anterior to the surgical neck of the humerus

it anastomoses with the posterior branch

posterior humeral circumflex artery

runs posteriorly to exit the axilla with the axillary nerve through the quadrangular space

supplies surrounding structures and anastomoses with the anterior branch and an ascending branch of the deep brachial artery

where does the axillary artery change to crachial artery

the inferior border of teres major muscle

what is the brachial plexus

a network of nerves formed by the ventral rami of spinal nerves C5-T1

what is the function of the brachial plexus

supplies motor and sensory innervation to the shoulder, arm, forearm, and hand

why does the brachial plexus matter

it is essential for movement and sensation of the upper arm

it is also a common site of injury

understanding it helps correlate nerve injuries with clinical deficits

basic organization of brachial plexus

roots → trunks → divisions → cords → branches

(randy travis drinks cold beer)

ventral primary rami of C5 to T1

create the brachial plexus’

migrate with their respective myotomes into the developing upper limb (middle finger = C7)

where is the brachial plexus located

the origin (roots and trunks) are located in the posterior cervical triangle and emerge between the anterior and middle scalene muscles

postaxial nerves

extensors (in the back of the limb)

come from the posterior cord

axillary - shoulder muscles

radial- arm and forearm muscles

preaxial nerves

flexors (in front of the limb)

come from the lateral and medial cords

musculocutaneous - arm

median- forearm except 1 ½ muscles

ulnar - hand except 1 ½ groups of muscles

brachial plexus contents in the posterior triangle

roots (interscalene)

trunks

dorsal scapular nerve

branches off roots

dorsal scapular (C5)

long thoracic (C5,6,7)

branches off trunk

suprascapular

nerve to subclavius

divisions of brachial plexus

anterior and posterior

anterior branches off cords

lateral pectoral n

medial pectoral n

medial brachial cutaneous n

medial antebrachial cutaneous n

posterior branches off cords

upper subscapular

middle subscapular (thoracodorsal)

lower subscapular

axillary n

radial n

“M” branch

musculocutaneous n (arm)

Median n (forearm)

Ulnar n (hand)

Postaxial nerves from the posterior cord and what they supply

axillary for the shoulder

radial for posterior arm and forearm

preaxial nerves come from the lateral and medial cords

cords of the brachial plexus supply the walls of the axilla directly

musculocutaneous - all anterior arm muscles

median - all anterior forearm muscles (except 1 1/2)

ulnar - all hand muscles (except 1 ½ groups)

terminal branches gross generalizations

musculocutaneous - anterior arm

median - anterior forearm

ulnar - hand

axillary - shoulder

radial - posterior arm and forearm

what is the axilla

roughly pyramidal in shape and is the transition zone between the neck and the arm

continuous with the neck at the axillary inlet and continuous with the arm through the lateral part of the floow of the axilla

the neurovascular contents of the axilla are significant

contains the proximal portions of the brachial plexus, the axillary artery and branches, axillary vein and tributaries, and axillary lymph nosed that drain the upper limb and chest wall

the axilla is

a 4 sided region - elongated

transition from the posterior triangle of the neck to the upper limb

all nerves and blood vessels of the upper limb travel through here

lots of fat to insulate and protect

axilla contents from anterior

axillary sheath, cords of the brachial plexus with branches supplying the walls, axillary artery and the main branches to the walls, deep veins of the upper limb

pectoralis major innervation

medial and lateral pectoral n

pectoralis mino innervation

medial pectoral n

subclavius innervation

n to subclavius

serratus anterior innervation and importance

innervated by long thoracic nerve

holds scapula against the thoracic wall

infraspinatus innervation

suprascapular n

teres minor innervation

axillary n

subscapularis innervation

upper and lower subscapular n

teres major innervation

lower subscapular n

latissimus dorsi innervation

thoracodorsal n

brachial plexus lesions - upper plexus injury

excessive widening of angle between neck and shoulder (C5-C6)

waiters tip hand - arm adducted and medially rotated

brachial plexus lesions - lower plexus injury

excessive angle between trunk and upper limb (C8-T1)

claw hand deformity - short intrinsic muscles of the hand are paralyzed, leaving the long extensors and flexors of the forearm unopposed

subclavian artery branches

thyrocervical trunk and suprascapular a.

axillary artery branches

superior thoracic a

thoracoacromial a (deltoid, pectoral, acromial, and clavicular branches)

lateral thoracic a.

posterior and anterior circumflex humeral aa.

subscapular a (thoracodorsal a. and circumflex scapular a.)

cephalic vein

superficial and lateral vein

drains to the axillary vein through the deltopectoral triangle (groove)

basilic vein

superficial and medial vein

drains to the medial intermuscular septum to join the brachial veins

superficial arm veins

cephalic and basilic veins communicate at the median cubital vein

superficial veins start in the dorsal venous arch of the hand

which vein pierces he clavipectoral fascia

the cephalic v

lymphatics of the axilla are arranged into 5 groups

pectoral (anterior)

subscapular (posterior)

humeral (lateral)

central

apical

efferent vessels unite to form

the subclavian lymphatic trunk