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Axilla and Arm


Atlas References

  • Netter: 405, 414, 419–424

  • McMinn: 138–145

  • Gray's Atlas: 384–419

Before You Begin

Axillary Borders

The pectoral region should have been dissected before the study of the axilla is begun. Refer to Chapter 4 for the regional anatomy of the pectoral region and breast. Review the following borders of the axilla:

  • Anterior wall: Pectoralis major and minor muscles and clavipectoral fascia

  • Posterior wall: Latissimus dorsi, teres major, and subscapularis muscles

  • Lateral wall: Humerus, short head of biceps brachii muscle, and coracobrachialis muscle

  • Medial wall: Upper five ribs, their intercostal muscles, and adjacent serratus anterior muscle

  • Base: Axillary fascia

  • Apex (cervicoaxillary canal): Superior border of scapula, 1st rib, and clavicle

Dissection Steps

  • o

    Make a skin incision from the shoulder distally to a point 2 to 3 inches (5 to 7.5 cm) above the elbow.

  • o

    An encircling incision around the midportion of the arm allows for medial retraction of the skin from the upper arm.

  • o

    Reflect the skin from the thorax, shoulders, axillae, and proximal portions of the arms medially to the axillary space (as shown previously in Fig. 4.4 ).

  • o

    See Chapter 8 for the incisions used in the forearm.

  • o

    Reflect the pectoralis muscles, better exposing the intercostobrachial and long thoracic nerves.

  • o

    Identify the long thoracic nerve running over the serratus anterior muscle.

  • o

    Note the intercostobrachial nerve emerging from the 2nd intercostal space.

Anatomy Note

The intercostobrachial nerve emerging from the 2nd intercostal space is the lateral cutaneous branch of the 2nd thoracic (T2) nerve crossing over the long thoracic nerve, to supply the skin of the proximal, medial aspect of the arm and axilla ( Fig. 7.1 ).

Fig. 7.1, Anterior region with skin removed and pectoralis muscles reflected, exposing intercostobrachial and long thoracic nerves.

  • o

    Preserve these two nerves.

Dissection Tip

Adipose tissue and lymphatics occupy most of the space in the axilla. Do not attempt to remove them at this stage. Push them away from the structures you identify, and remove them at a later stage.

  • o

    Identify the fascia that invests the axillary artery, axillary vein, and the brachial plexus, called the axillary sheath.

  • o

    Excise the axillary sheath between the axillary artery and the brachial plexus by gently pulling away the nerves ( Fig. 7.2 ).

    Fig. 7.2, Anterior axillary region with pectoralis muscles reflected, revealing excision of axillary sheath to expose terminal branches of brachial plexus.

  • o

    Remove the axillary sheath, and push the adipose tissue away from the brachial plexus ( Fig. 7.3 ).

    Fig. 7.3, Anterior axillary region with pectoralis muscles reflected and most of axillary sheath removed, revealing terminal branches of brachial plexus.

  • o

    Identify and clean the axillary artery and vein ( Fig. 7.4 ).

    Fig. 7.4, Anterior axillary view of deep dissection, revealing axillary vein and terminal branches of brachial plexus.

Anatomy Note

The axillary vein is formed at the base of the axilla by the confluence of the venae comitantes of the brachial artery with the basilic vein. (Large arteries, such as the axillary or femoral, are accompanied by a single vein. Medium and smaller arteries, such as the brachial, have two or more accompanying veins, which are found on either side of the artery and are called venae comitantes .)

Dissection Tip

Do not attempt to identify any lymph nodes associated with the axillary vein and its tributaries. Nodes are evident and easily dissected only in cadavers with cancer. Similarly, do not attempt to identify the central axillary nodes within the fat of the central portion of the axilla. Smaller tributaries to the axillary vein that obscure the dissecting field can be removed.

  • o

    Clean the adipose tissue between the pectoralis minor muscle and brachial plexus (see Fig. 7.4 ).

Anatomy Note

The axillary artery extends from the lateral border of the 1st rib to the lower border of the teres major muscle. Just before it crosses the 1st rib, the artery is named the subclavian artery. Distal to the teres major, the name of the vessel changes to the brachial artery.

Dissection Tip

The arteries are named typically based on the structures they supply, not according to their origin.

  • o

    Identify the axillary artery and its three divisions, demarcated with its relationship to the pectoralis minor muscle ( Fig. 7.5 ).

    Fig. 7.5, Anterior axillary view revealing the second part of the axillary artery, thoracoacromial artery, and lateral cord. Red dashed lines represent the borders on the pectoralis minor muscle over the axillary artery, dividing its three portions.

  • o

    Identify the superior thoracic artery arising from the 1st part of the axillary artery. To identify this vessel, look for an artery penetrating the musculature of the 1st or 2nd intercostal space.

  • o

    From the 2nd part of the axillary artery (deep to pectoralis minor muscle), identify the thoracoacromial artery and the lateral thoracic artery (see Fig. 7.5 ).

  • o

    Look for the pectoral branches of the thoracoacromial artery supplying the pectoralis major and minor muscles. Do not look for the remaining branches of the thoracoacromial artery (deltoid, acromial, and clavicular).

Dissection Tip

The following anatomic landmarks may be helpful when identifying the branches of the axillary artery.

  • Superior thoracic artery: 1st or 2nd intercostal spaces

  • Lateral thoracic artery: Lateral border of pectoralis minor muscle. Often the lateral thoracic artery arises as a branch of the thoracoacromial artery.

  • Thoracoacromial artery: 2nd part of axillary artery

  • Pectoral branches: Look for these on the internal surface of the pectoralis major and minor muscles, and trace them backward to the axillary artery and thoracoacromial artery. The pectoral branches often originate directly from the 2nd part of the axillary artery.

  • Separate the axillary artery from the branches of the brachial plexus, and remove fat from the latissimus dorsi muscle ( Fig. 7.6 ).

    Fig. 7.6, Anterior view revealing removal of the fat from the latissimus dorsi muscle.

  • Do not remove fat deep to the axilla.

  • Continue removing the axillary sheath from the brachial artery and vein, and expose the median nerve distally to the midportion of the arm ( Fig. 7.7 ).

    Fig. 7.7, Removing the axillary sheath and soft tissue.

Dissection Tip

Exposing the branches of the brachial plexus to the midportion of the humerus allows greater mobility and facilitates the identification of structures deep in the axilla.

  • o

    Cut the axillary vein at the point where the 1st part of the axillary artery originates, and reflect the vein and its tributaries toward the forearm.

  • o

    Do not completely remove the vein from the cadaver.

  • o

    Distal to the pectoralis minor muscle, from the 3rd portion of the axillary artery, identify the anterior circumflex humeral, posterior circumflex humeral, and subscapular arteries ( Figs. 7.9 and 7.10 ).

Anatomy Note

The subscapular artery runs vertically toward the latissimus dorsi and branches into the thoracodorsal artery, supplying the latissimus dorsi muscle, and the circumflex scapular artery, traveling posteriorly to the muscles of the posterior scapula ( Figs. 7.8 and 7.9 ).

Fig. 7.8, Anterior axillary view with reflected pectoralis muscles, removed axillary vein, revealing the axillary artery and associated nerves.

Fig. 7.9, Axillary artery and ulnar and median nerves are pulled medially to expose radial nerve and anterior and posterior circumflex humeral arteries.

  • o

    Identify the subscapular artery and thoracodorsal arteries.

  • o

    I dentify and clean the branches of the medial cord: the medial pectoral nerve, ulnar nerve, medial root of median nerve, medial brachial cutaneous nerve, and medial antebrachial cutaneous nerve.

  • o

    Alongside the medial antebrachial cutaneous nerve, identify the basilic vein (formed at the medial aspect of the dorsal venous arch of the hand; see Chapters 8 and 9 for hand structures).

  • o

    Trace and expose the median nerve to the elbow (see Fig. 7.9 ).

Dissection Tip

Anatomic Landmarks

  • Subscapular artery: Arises from the 3rd part of the axillary artery (pull the medial cord upward to expose it) and runs vertically down between the latissimus dorsi and subscapularis muscles.

  • Thoracodorsal artery: Arises from the subscapular artery and continues to run downward to supply the latissimus dorsi muscle. This artery is found on the surface of the latissimus dorsi accompanied by the middle subscapular nerve (trace the artery backward to its origin).

Anatomy Note

The brachial plexus is divided into rami, trunks, divisions, cords, and terminal branches. The rami, trunks, and divisions are identified later in the root of the neck dissection. In this dissection, you will be able to identify the cords and terminal branches of the brachial plexus. The cords are named in respect to their positions in relationship to the axillary artery. As a result, the lateral cord is situated lateral to the axillary artery, the medial cord medial to the axillary artery, and the posterior cord posterior (deep) to the axillary artery. The lateral cord gives off two branches: the lateral pectoral nerve supplies the pectoralis major muscle, and the musculocutaneous nerve supplies the biceps brachii, coracobrachialis, and brachialis muscles (see Fig. 7.8 ) ( Plate 7.1 ).

Plate 7.1, Lateral and medial cords of the brachial plexus.

Dissection Tip

A landmark for identifying the musculocutaneous nerve is that the nerve pierces the proximal portion of the coracobrachialis muscle.

Dissection Tip

Anatomic Landmarks

  • Ulnar nerve : Look for the nerve traveling along the medial aspect of the arm, not providing any branches to the arm, and crossing posterior to the medial epicondyle.

  • Median nerve: Look for the nerve traveling along the medial aspect of the arm without giving off any branches to the arm. It is found easily as it travels underneath the bicipital aponeurosis.

  • Medial brachial cutaneous nerve: Runs parallel for a short distance in the arm with the medial antebrachial cutaneous nerve and is distributed to the skin of the arm. This nerve is often cut when the skin of the arm is reflected.

  • Medial antebrachial cutaneous nerve: Runs parallel and superficial to the ulnar nerve and is distributed to the skin of the forearm. The basilic vein runs together with this nerve.

Dissection Tip

The medial brachial cutaneous nerve (medial cutaneous nerve to the arm) often is severed during the removal of the skin over the brachium. The medial antebrachial cutaneous nerve (medial cutaneous nerve to the forearm) runs parallel to the ulnar nerve. The landmark for identifying the ulnar nerve is to trace it as it crosses posterior to the medial epicondyle of the humerus. In contrast, the medial antebrachial cutaneous nerve runs more superficially and terminates in the skin of the forearm (see Fig. 7.14 ).

Anatomy Note

The posterior cord gives rise to the following branches: upper, middle thoracodorsal, and lower subscapular nerves; axillary nerve; and radial nerve.

Dissection Tip

To identify the posterior cord, pull the medial cord and the axillary artery, laterally, away from the coracobrachialis muscle ( Figs. 7.8 to 7.10 ). Look posteriorly and deep to it for the posterior cord.

Fig. 7.10, Anterior axillary view with reflected pectoralis muscles, traction from axillary artery, revealing lateral cord, posterior cord, and musculocutaneous nerve. Red dashed line shows level of the surgical neck of the humerus.

  • o

    Deep to the axillary artery, identify the posterior cord.

  • o

    Identify and trace the radial nerve as it penetrates the triceps brachii.

  • o

    At the level of the surgical neck of the humerus, dissect and expose the anterior and posterior circumflex humeral arteries (see Fig. 7.10 ).

Dissection Tip

Anatomic Landmarks

Radial nerve: Look at the medial surface of the arm for the nerve innervating the triceps brachii muscle (see Fig. 7.15 ). Trace the nerve backward to the axilla and posterior cord.

Dissection Tip

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