Anatomy of Axilla

Axilla: Pyramid shaped region.
Base formed by skin / fat / subcutaneous tissue.
Lateral wall = B icepetal groove
Posterior wall = scapula, subscapularis, teres major, latissimus dorsi. Latissimus dorsi / teres major form the posterior axillary fold.
Medial wall = ribs 1-4, intercostal muscles, serratus anteriot.
Anterior wall = pec minor / major. Pec major forms the anterior axillary fold in axilla.
Subclavian artery becomes axillary artery as it passes over the first rib.

Axillary sheath: Dense CT extension of the prevertebral fascia that contains the Brachial plexus, axillary artery and axillary vein. As the nerves of the brachial plexus emerge from the V column, they drag the fascia with them into the axilla to become axillary sheath. The axillary sheath disappears (thins out) as brachial plexus branches more.

Contents of the axilla:

Axillary artery = extension of subclavian
Axillary vein = continuation of the brachial veins, major tributaries are basillic and cephalic veins.
Axillary lymphatics and nodes = most common site of breast cancer metastasis.
Brachial plexus: Ventral rami from C5-T1.

Brachial plexus:

Starting at ventral rami from C5-T1, These are the roots→form larger trunks as C5/6 come together and C8/T1 come together to form trunks→divide and become “divisions”→divide again to become cords→divide again to become terminal branches.

“Robert Taylor Drinks Cold Beer”.

Find the roots in the posterior triangle in the neck.

These roots come together to form trunks above the clavicle (supraclavicular).

Divisions occur right behind the clavicle.

The Cords are wrapped around the axillary artery

Branches:

4 supraclavicular branches. Come from roots or trunks.
- Dorsal scapular (rhomboids, levator scapula) originates from roots
- Suprascapular (spinatus muscles)
- Long thoracic nerve (serratus anterior) originates from roots
- Nerve to subclavius
Infraclavicular branches (7)
- Pectoral nerves (lateral / medial)
- Medial cutaneous of arm
- Medial cutaneous of forearm
- Thoracodorsal nerve (latissimus dorsi)
- Lower subscapular
- Upper subscapular
Terminal nerves (with motor distributions)
- Musculocutaneous – C5-6 SC levels. Supply coracobrachialis, biceps brachii, brachialis (anterior portion of arm).
- Median – C5-T1 (entire plexus). Works much in forearm = ½ FD profundus, FP longus, pronators, FC radialis. In the hand = Thenar muscles.
- Ulnar C8-T1 spinal cord levels. Works in the forearm, innervates ½ of FD profundus, FC ulnaris in forearm. Also works in the hand = hypothenar muscles, ½ lumbaricals, adductor pollicis. Fine motor control of hand / fingers.
- Radial C5-T1. is the Extensor nerve→supplies all extensors, also supply Brachioradialis, supiator, snuff box mm (nonextensors).
- Axillary. C5/6. supply deltoid and Teres minor (shoulder only).

Cutaneous innervation of upper limb: important for assessing spinal cord injuries.

C5: Upper lateral arm
C6: Pad of thumb
C7: Pad of index finger
C8: Pad of little finger
T1: Medial elbow.
Axillary nerve: Skin over deltoid
Radial nerve: most of the back of the arm.
Musculocutaneous: lateral forearm. Innervates muscles of arm, skin of forearm.
Median nerve: palm of hand from ring finger to thumb.
Ulnar nerve: little finger / part of ring finger and portion of palm.

Arteries:

Axillary artery = begins at lateral border of Rib 1 and ends at teres major→ then known as the brachial artery. Has 3 parts:

First part = proximal to pec minor. Branch = superior thoracic artery (supplies pectoral muscles, upper thoracic wall, serratus anterior)
Second = posterior to pec minor. Branches = thoracoacromial artery (a trunk) which gives off many branches (clavicular, acromial, deltoid, and pectoral branches), lateral thoracic artery (supplies serratus anterior, pec minor, mammary glands).
Third = distal to pec minor. Branches = subscapular artery (largest branch of axillary artery) which branches into circumflex scapular artery which goes around onto back of scapula to supply teres minor and infraspinatus muscle. Another branch of third part = thoracodorsal artery which supplies latissimus dorsi. 3^rd branch = anterior humoral circumflex artery = supplies deloid and triceps. This branch meets with Posterior humeral circumflex artery (supplies deltoid and triceps as well) to form anastomoses as a form of collateral circulation.

Lateral thoracic artery and thoracodorsal artery are frequently connected and sometimes one will replace the other. May not find one of these arteries in some individuals.

Spaces and intervals:

Triangular space: contains circumflex scapular artery.
Quadrangular space: contains axillary nerve and the posterior circumflex humeral artery.
Triangular interval: contains profunda brachii artery (AKA deep artery of the arm) and the radial nerve. These two structures then pass into the radial (spiral) groove to be placed right on the shaft of the humerus.

Arterial Anastomoses:

Those around the shoulder are interconnected networks around the scapula:

Suprascapular artery
Posterior circumflex humeral artery
Circumflex scapular artery
Posterior intercostal arteries
Dorsal scapular artery

Dorsal Scapular Artery:

Can arise from 2 different sources:

75% of the time it is a branch off of the 3^rd part of the subclavian artery which then passes through the brachial plexus onto scapula to supply rhomboids and levator scapula.
25% of the time it is a branch of the transverse cervical artery. Thus, “transverse cervical artery” is usually not present.

Venous drainage:

Superficial veins are basilic and cephalic.

basilic continues as axillary. From back of the hand on dorsal side of forearmà passes elbow joint and then penetrates deep fascia→ passes into arm to become the axillary vein. Here, it is joined by the cephalic veinà becomes the subclavian.
cephalic joins axillary. Goes onto back of the hand.

Deep veins:

Paired brachial veins on either side of each major artery (brachial, radial, ulnar)
Axillary lymphatics: 20-30 lymph nodes. 5 groups. Drain 75% of the mammary glands.
Form the subclavian lymph trunk which dumps into venous system at junction of internal jugular vein and the subclavian vein.

Autonomics to upper extremity:

Preganglionic cells for sympathetics arise in the upper thoracic spinal cord (T2-6). They leave the spinal cord and enter the sympathetic chain via white ramià ascend to the cervicothoracic ganglion and junction of C and T vertebrae. Here, can find C8 and T1 nerve roots. Have synapse at this junction→ post ganglionic fibers leave via gray rami onto C8 and T1 roots of brachial plexus.These are vasoconstrictors to smooth muscles of blood vessels and innervate erector pili muscles to move hairs on the limb.

Parasympathetics: there are none. Thus, vasodilation is passive via blood pressure.
Costoclavicular syndrome:A type of thoracic outlet syndrome. Pallor and coldness of upper limb, diminished radial pulse, especially noted with increased angle between neck and shoulder.
Metastasis from Breast cancer:- largest portion of women will have axillary lymph node involvement.