Axilla
The axilla is a pyramidal shaped space occupying the area between the upper part of the arm and upper part of the chest.The apex of the axilla is formed by the axillary inlet, a triangular space that extends into the neck bounded by the lateral border of the first rib medially, the posterior border of the clavicle anteriorly and the superior border of the scapula posteriorly. The axillary inlet is an important anatomical area because of all the structures passing between the upper limb and the neck .
The axilla has four sides (walls) and a base(floor).The anterior wall is made up of three muscles, pectoralis major, pectoralis minor and subclavius, in addition to the clavipectoral fascia. The posterior wall is made up of the anterior surface of the scapula and subscapularis, in addition to parts of latissimus dorsi, teres major and the long head of triceps brachii. The medial wall is formed by the thoracic wall, which includes the upper ribs and intercostal spaces, in addition to the upper part of serratus anterior. The lateral wall is formed by the upper medial part of the shaft of the humerus, and includes the bicipital groove (intertubercular sulcus) of the humerus and the attached muscles. The base of the axilla (floor) is made up of skin and axillary fascia.
Important structures passing through the axilla that provide the upper limbs with blood supply and nervous innervation include the axillary artery and its branches, the axillary vein and its tributaries and the cords of the brachial plexus .The axilla also contains groups of lymph nodes and the axillary tail of the breast.
The axilla has four sides (walls) and a base(floor).The anterior wall is made up of three muscles, pectoralis major, pectoralis minor and subclavius, in addition to the clavipectoral fascia. The posterior wall is made up of the anterior surface of the scapula and subscapularis, in addition to parts of latissimus dorsi, teres major and the long head of triceps brachii. The medial wall is formed by the thoracic wall, which includes the upper ribs and intercostal spaces, in addition to the upper part of serratus anterior. The lateral wall is formed by the upper medial part of the shaft of the humerus, and includes the bicipital groove (intertubercular sulcus) of the humerus and the attached muscles. The base of the axilla (floor) is made up of skin and axillary fascia.
Important structures passing through the axilla that provide the upper limbs with blood supply and nervous innervation include the axillary artery and its branches, the axillary vein and its tributaries and the cords of the brachial plexus .The axilla also contains groups of lymph nodes and the axillary tail of the breast.
Figure1: The axilla
The axillary artery
This is the major arterial supply of the upper limb. The subclavian artery is the main artery of the neck and continues as the axillary artery at the lateral border of the first rib. At the lower (inferior) border of teres major, the axillary artery becomes the brachial artery. Its course extends throughout the axilla, where it is in direct relation to the cords of the brachial plexus and its branches. Throughout its course in the axilla it is enclosed in connective tissue called the axillary sheath, which continues in the neck as the prevertebral fascia. The axillary artery is divided into three parts, according to its relation to pectoralis minor. The first part extends from the outer border of the first rib to the proximal border of pectoralis minor. The second part of the axillary artery extends behind pectoralis minor. The third part extends from the distal border of pectoralis minor to the distal border of teres major.
Figure2: Anterior & posterior circumflex humeral arteries
Relations of the axillary artery
Relation of the first part of the axillary artery
The anterior relation consists of skin, the superficial fascia, pectoralis major and its fascia and the cephalic vein. The posterior relation consists of the upper intercostal spaces with the intercostal muscles and the upper digitations of serratus anterior with its innervation (long thoracic nerve). The lateral relation consists of the cords of the brachial plexus. The medial relation consists of the axillary vein.
Relation of the second part of the axillary artery
The anterior relation consists of the skin, the superficial fascia, pectoralis major and minor muscles with their covering fascia. The posterior relation consists of the posterior cord of the brachial plexus, subscapularis and the shoulder joint. The lateral relations consist of the lateral cord of the brachial plexus. The medial relation consists of the medial cord of the brachial plexus and the axillary vein.
Relation of the third part of the axillary artery
The anterior relation consists of skin, the superficial fascia, pectoralis major and its fascia in the upper part and the medial root of the median nerve in the lower region. The posterior relation consists of subscapularis, latissimus dorsi and teres major muscles .The radial and axillary nerves lies in a posterior position. The lateral relation consists of coracobrachialis, biceps brachii and the upper part of the humerus. In addition, the musculocutaneous nerve and the lateral root of the median nerve lie laterally. Medial relations consist of the medial cutaneous nerve of the arm, the ulnar nerve and the axillary vein.
The anterior relation consists of skin, the superficial fascia, pectoralis major and its fascia and the cephalic vein. The posterior relation consists of the upper intercostal spaces with the intercostal muscles and the upper digitations of serratus anterior with its innervation (long thoracic nerve). The lateral relation consists of the cords of the brachial plexus. The medial relation consists of the axillary vein.
Relation of the second part of the axillary artery
The anterior relation consists of the skin, the superficial fascia, pectoralis major and minor muscles with their covering fascia. The posterior relation consists of the posterior cord of the brachial plexus, subscapularis and the shoulder joint. The lateral relations consist of the lateral cord of the brachial plexus. The medial relation consists of the medial cord of the brachial plexus and the axillary vein.
Relation of the third part of the axillary artery
The anterior relation consists of skin, the superficial fascia, pectoralis major and its fascia in the upper part and the medial root of the median nerve in the lower region. The posterior relation consists of subscapularis, latissimus dorsi and teres major muscles .The radial and axillary nerves lies in a posterior position. The lateral relation consists of coracobrachialis, biceps brachii and the upper part of the humerus. In addition, the musculocutaneous nerve and the lateral root of the median nerve lie laterally. Medial relations consist of the medial cutaneous nerve of the arm, the ulnar nerve and the axillary vein.
Figure3: The axillary artery & vein
Figure4: Pectoralis minor & thoracoacromial artery
Branches of the axillary artery
Branches of the first part of the axillary artery
Provides one branch, the superior thoracic artery (the highest thoracic artery), which is a small branch from the anterior surface. This artery runs along the upper border of pectoralis minor, and then passes inferomedially to supply the medial and anterior axillary walls. It also anastomoses with intercostal arteries.
Branches of the second part of the axillary artery
Provides two branches, as follows
1) The thoracoacromial artery, which is a short branch from the anterior surface that originates behind pectoralis minor and runs along its upper border. After piercing the clavipectoral fascia, it divides into four branches: deltoid, pectoral, acromial and clavicular.
2) The lateral thoracic artery arises behind pectoralis minor, from the anterior surface of the axillary artery, and runs along its lower border. It supplies the pectoral muscles and the lateral part of the breast. It may arise from the thoracoacromial, suprascapular or subscapular arteries.
Branches of the third part of the axillary artery
Provides three branches, as follows
1)The subscapular artery: this is the largest branch of the axillary artery originating from its posterior surface. This artery runs along the lower border of subscapularis and then divides into two branches.
A-The circumflex scapular artery which passes through a space formed by subscapularis, teres major and the long head of triceps (triangular space). It then enters the infraspinous fossa of the scapula .The circumflex scapular artery is an important part of the arterial anastomosis around the scapula.
B-The thoracodorsal artery takes a vertical course along the lateral border of the scapula. It shares in anastomosis around the scapula and supplies the adjacent muscles, which form the posterior and medial walls of the axilla.
2) The anterior circumflex humeral artery is a small branch arising from the lateral surface of the third part of the axillary artery. It takes a transverse course along the anterior surface of the surgical neck of the humerus and anastomoses with the posterior circumflex humeral artery around the neck. This artery supplies the surrounding area of the shoulder, including the joint itself.
3) The posterior circumflex humeral artery arises from the lateral wall of the third part .It passes posteriorly to the surgical neck through the quadrangular space. It supplies deltoid, teres major, teres minor and the long head of triceps.
Provides one branch, the superior thoracic artery (the highest thoracic artery), which is a small branch from the anterior surface. This artery runs along the upper border of pectoralis minor, and then passes inferomedially to supply the medial and anterior axillary walls. It also anastomoses with intercostal arteries.
Branches of the second part of the axillary artery
Provides two branches, as follows
1) The thoracoacromial artery, which is a short branch from the anterior surface that originates behind pectoralis minor and runs along its upper border. After piercing the clavipectoral fascia, it divides into four branches: deltoid, pectoral, acromial and clavicular.
2) The lateral thoracic artery arises behind pectoralis minor, from the anterior surface of the axillary artery, and runs along its lower border. It supplies the pectoral muscles and the lateral part of the breast. It may arise from the thoracoacromial, suprascapular or subscapular arteries.
Branches of the third part of the axillary artery
Provides three branches, as follows
1)The subscapular artery: this is the largest branch of the axillary artery originating from its posterior surface. This artery runs along the lower border of subscapularis and then divides into two branches.
A-The circumflex scapular artery which passes through a space formed by subscapularis, teres major and the long head of triceps (triangular space). It then enters the infraspinous fossa of the scapula .The circumflex scapular artery is an important part of the arterial anastomosis around the scapula.
B-The thoracodorsal artery takes a vertical course along the lateral border of the scapula. It shares in anastomosis around the scapula and supplies the adjacent muscles, which form the posterior and medial walls of the axilla.
2) The anterior circumflex humeral artery is a small branch arising from the lateral surface of the third part of the axillary artery. It takes a transverse course along the anterior surface of the surgical neck of the humerus and anastomoses with the posterior circumflex humeral artery around the neck. This artery supplies the surrounding area of the shoulder, including the joint itself.
3) The posterior circumflex humeral artery arises from the lateral wall of the third part .It passes posteriorly to the surgical neck through the quadrangular space. It supplies deltoid, teres major, teres minor and the long head of triceps.
Figure5: Axillary artery branches
The Axillary Vein
The axillary vein begins as a continuation of the basilic vein at the lower border of teres major muscle and runs upwards, where it related to the medial side of axillary artery and finally terminates as the subclavian vein at the outer border of the first rib.
Formation
Roots
Five roots formed by the anterior primary rami of C 5, 6, 7, 8 and T1.
Trunks
There are three trunks: the upper, middle and lower at the following points:
a) C5 and C6 join to form the upper trunk.
b) C7 forms the middle trunk.
c) C8 and T1 join to form the lower trunk.
Divisions
Each trunk divides into anterior and posterior divisions.
Cords
a) The lateral cord is formed by the union of the anterior divisions of the upper and middle trunks.
b) The medial cord is formed by the anterior division of the lower trunk.
c) The posterior cord is formed by the union of the posterior divisions of all the three trunks (described above).
Five roots formed by the anterior primary rami of C 5, 6, 7, 8 and T1.
Trunks
There are three trunks: the upper, middle and lower at the following points:
a) C5 and C6 join to form the upper trunk.
b) C7 forms the middle trunk.
c) C8 and T1 join to form the lower trunk.
Divisions
Each trunk divides into anterior and posterior divisions.
Cords
a) The lateral cord is formed by the union of the anterior divisions of the upper and middle trunks.
b) The medial cord is formed by the anterior division of the lower trunk.
c) The posterior cord is formed by the union of the posterior divisions of all the three trunks (described above).
The Brachial Plexus
The brachial plexus is formed by the anterior rami of the C5, C6, C7, C8, & T1 spinal nerves, which are the main nerve supply of the upper limb. The brachial plexus is divided into the following parts: roots, trunks, divisions and cords.
Branches of the plexus for the upper limb
A) Branches from the roots, including:
1) Long thoracic nerve from C 5, 6, 7, and
2) Dorsal scapular nerve from the C 5.
B) Branches of the trunks: Only the upper trunk gives two branches:
1) Suprascapular nerve (C5, 6), and
2) Nerve to subclavius (C5, 6).
C) Branches of the cords:
a) Lateral cord:
1) Lateral pectoral (C5, 6, 7),
2) Musculocutaneous (C5, 6, 7), and
3) The lateral root of median nerve (C5, 6, 7).
b) Medial cord:
1) Medial pectoral (C8, T1),
2) Medial cutaneous nerve of the arm (C8, T1),
3) Medial cutaneous nerve of the forearm (C8 ,T1),
4) The medial root of the median nerve (C8, T1), and
5) Ulnar nerve (C7, 8, T1).
c) Posterior cord:
1) Upper subscapular (C5, 6),
2) Lower subscapular (C5, 6),
3) Axillary (Circumflex) (C5, 6),
4) Thoracodorsal (C6, 7, 8), and
5) Radial (C5, 6, 7, 8, T1).
1) Long thoracic nerve from C 5, 6, 7, and
2) Dorsal scapular nerve from the C 5.
B) Branches of the trunks: Only the upper trunk gives two branches:
1) Suprascapular nerve (C5, 6), and
2) Nerve to subclavius (C5, 6).
C) Branches of the cords:
a) Lateral cord:
1) Lateral pectoral (C5, 6, 7),
2) Musculocutaneous (C5, 6, 7), and
3) The lateral root of median nerve (C5, 6, 7).
b) Medial cord:
1) Medial pectoral (C8, T1),
2) Medial cutaneous nerve of the arm (C8, T1),
3) Medial cutaneous nerve of the forearm (C8 ,T1),
4) The medial root of the median nerve (C8, T1), and
5) Ulnar nerve (C7, 8, T1).
c) Posterior cord:
1) Upper subscapular (C5, 6),
2) Lower subscapular (C5, 6),
3) Axillary (Circumflex) (C5, 6),
4) Thoracodorsal (C6, 7, 8), and
5) Radial (C5, 6, 7, 8, T1).
Figure6: Brachial plexus branches
The Axillary Lymph Nodes
There are five groups of lymph nodes, as follows:
a) The anterior (pectoral) group, which is located along the lateral thoracic vessels at the lower border of pectoralis minor. It receives afferent lymphatics from the lateral part of the breast,
b) The posterior (subscapular) group, which is located along the subscapular vessels on the subscapularis. It receives afferent lymphatics from the upper half of the trunk posteriorly to the level of the iliac crest,
c) The lateral group, which is located along the upper part of the humerus medial to the axillary vein. It receives afferent lymphatics from the upper limb,
d) The central group located in the centeral part of the axilla. It receives lymphatics from the anterior, posterior and lateral groups, and
e) Apical group located at the apex of the axilla. It receives afferents lymphatics from the anterior, posterior, lateral and central groups.
a) The anterior (pectoral) group, which is located along the lateral thoracic vessels at the lower border of pectoralis minor. It receives afferent lymphatics from the lateral part of the breast,
b) The posterior (subscapular) group, which is located along the subscapular vessels on the subscapularis. It receives afferent lymphatics from the upper half of the trunk posteriorly to the level of the iliac crest,
c) The lateral group, which is located along the upper part of the humerus medial to the axillary vein. It receives afferent lymphatics from the upper limb,
d) The central group located in the centeral part of the axilla. It receives lymphatics from the anterior, posterior and lateral groups, and
e) Apical group located at the apex of the axilla. It receives afferents lymphatics from the anterior, posterior, lateral and central groups.