Dissector Answers - Axilla & Arm

OBJECTIVES and EXPLANATIONS:

1. Describe the lymphatic drainage of the upper limb and the major lymphatic node groups of the axilla. (W&B 106-107, 123, N 184, 483)

As a general rule, the superficial lymphatic drainage of the upper limb follows the superficial venous drainage. Most of the lymph ends up in the lateral and central axillary lymph nodes, with some of it passing through the cubital lymph nodes along the way. Some of the lymph from the posterior surface of the upper limb travels in vessels that accompany the cephalic vein, piercing the clavipectoral fascia to end in the apical axillary lymph node. The deep lymphatic vessels of the upper limb accompany the major arteries to also end in the lateral and central axillary lymph nodes.

So what about these axillary lymph nodes? They are extremely important clinically, since they drain the major portion of the breast. These lymph nodes are carefully palpated during any thorough breast exam. There are five groups:

2. Recall the concept of the axilla as a space, its boundaries and its contents. (W&B 114-115, N 181)

The axillary space is shaped like a truncated pyramid. Its boundaries are:

3. Illustrate or describe the brachial plexus, including its parts, the nerves arising from it, and their specific origins and areas of distribution. (W&B 119-123, 708-714, N 429, 430)

Images from "Anatomy of the Human Body" by Henry Gray are provided by:

The brachial plexus consists of roots, trunks, divisions, cords, and branches. There is a classic mnemonic to help with this one: Robert Taylor Drinks Cold Beer. The roots are mostly derived from the ventral primary rami of C5 to T1. Three trunks, the superior, middle and inferior trunks, are derived from those roots (C5-C6, C7, and C8-T1 respectively). Each trunk divides into an anterior and posterior division. The posterior divisions of all three trunks unite to form the posterior cord. The anterior divisions of the superior and middle trunks unite to form the lateral cord. Finally, the anterior division of the inferior trunk forms the medial cord. (The medial aspect of your arm when it is in the anatomical position is also the inferior aspect when you stick your arm straight out, or, for that matter, when you are an embryo and your arm is 2mm long. In the same way, lateral is superior.) These cords then terminate as branches that supply the skin and muscles of the upper limb.

For the rest, we will rely on the tables:

Nerve Source Branches Motor Sensory
nerves from the roots:        
dorsal scapular brachial plexus (C5)   rhomboid major & minor; levator scapulae  
long thoracic brachial plexus (C5-C7)   serratus anterior  
nerves from the trunks:        
to subclavius superior trunk of brachial plexus   subclavius  
suprascapular superior trunk of brachial plexus (C5-C6)   supraspinatus, infraspinatus  
terminal branches (i.e., from the cords):        
lateral pectoral lateral cord of brachial plexus   pectoralis major  
musculocutaneous lateral cord of brachial plexus (C5,6) lateral antebrachial cutaneous coracobrachialis, biceps brachii, brachialis skin of lateral side of forearm
medial pectoral medial cord of the brachial plexus   pectoralis minor & major  
medial brachial cutaneous medial cord of brachial plexus     skin of the medial side of the arm
medial antebrachial cutaneous medial cord of brachial plexus     skin of medial side of forearm
median lateral & medial cords of brachial plexus anterior interosseous, palmar br., recurrent (motor) Br, common palmar digital ns. (1st-3rd) pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus (radial half), flexor pollicis longus, pronator quadratus, abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, radial 2 lumbricals skin of radial half of palm & palmar side of radial 3 1/2 digits (and nail bed for these digits)
ulnar medial cord of the brachial plexus palmar cutaneous Br, dorsal Br, superficial & deep Br flexor carpi ulnaris, flexor digitorum profundus (ulnar half), abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, ulnar 2 lumbricals, palmar & dorsal interossei skin of medial side of wrist & hand & ulnar 1 1/2 digits
upper subscapular posterior cord of brachial plexus   subscapularis  
thoracodorsal (middle subscapular) posterior cord of brachial plexus   latissimus dorsi  
lower subscapular posterior cord of brachial plexus   subscapularis, teres major  
radial posterior cord of brachial plexus posterior brachial cutaneous, inferior lateral brachial cutaneous, posterior antebrachial cutaneous, superficial & deep br triceps brachii, anconeus, brachioradialis, extensor carpi ulnaris, extensor carpi radialis longus & brevis, extensor digitorum, extensor digiti minimi, supinator, abductor pollicis longus, extensor pollicis longus & brevis, extensor indicis skin of posterior arm, forearm & hand
axillary posterior cord of brachial plexus superior lateral brachial cutaneous n. deltoid, teres minor skin of upper lateral arm
4. Predict the functional and cutaneous loss that might result in the back, posterior shoulder, pectoral region, or cutaneous upper limb, given an injury to a specific site in the brachial plexus. (W&B 185-186, N 430)

Symptoms of brachial plexus injury may include a limp or paralyzed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand. Although injuries can occur at any time, many brachial plexus injuries happen during birth: the baby's shoulders may become impacted during the birth process causing the brachial plexus nerves to stretch or tear. There are four types of brachial plexus injuries: avulsion, the most severe type, in which the nerve is torn from the spine; rupture, in which the nerve is torn but not at the spinal attachment; neuroma, in which the nerve has tried to heal itself but scar tissue has grown around the injury, putting pressure on the injured nerve and preventing the nerve from conducting signals to the muscles; and neuropraxia or stretch, in which the nerve has been damaged but not torn. Neuropraxia is the most common type of brachial plexus injury.

These injuries usually occur at the roots. The upper roots of the brachial plexus supply the more proximal muscles, while the lower roots supply the more distal. The segmental innervation of the skin does not correlate with the supply of the muscles beneath.

Injury to the upper roots, C5 and C6, are the most common type. This results in Erb-Duchenne Palsy, or "Waiter's Tip". It affects the suprascapular nerve especially and frequently also involves the musculocutaneous and axillary nerves, which results in paralysis of the rotator cuff muscles, in addition to the biceps, brachialis, coracobrachialis, and deltoid muscles. Subscapularis may also be affected. The upper limb hangs limply, medially rotated by unopposed pectoralis major, latissimus dorsi, and teres major muscles and pronated due to loss of biceps.

Injury to the lower roots, C8 and T1, results in Klumpke's Palsy. The ulnar and median nerves are affected, paralyzing all of the intrinsic muscles of hand. Patients present with a "clawed hand" due to hyperextension of MP joints and flexion of digits by forearm flexors unopposed by interossei.

As for related cutaneous losses, check out a diagram of the cutaneous nerves of the upper limb.

5. Predict where the brachial plexus might be injured, given a functional or cutaneous loss in the back, posterior shoulder, pectoral region or cutaneous upper limb. (N 430)

If you know where the nerves go and what they innervate, then you will be able to work backwards:

The possibilities are numerous. See #3 and #4 above.

6. Identify or describe the axillary artery and vein, their major branches, and their relationships to each other, the brachial plexus, and the pectoralis minor muscle. (W&B 115-119, N 427, 429, 256)

Images from "Anatomy of the Human Body" by Henry Gray are provided by:

The axillary artery is the second portion of the upper limb's main arterial stem. (This arterial stem changes names regionally, even though it is all really the same vessel. It is like the external iliac, femoral, and popliteal arteries in the lower limb.) The axillary artery is defined to be the distal continuation of the subclavian artery, after that artery passes over the first rib. It continues to the inferior border of teres major where its name changes to the brachial artery.

The axillary artery is divided into three parts, numbered proximally to distally as parts 1, 2 and 3. Each part is defined in relation to the pectoralis minor muscle, which, by definition, covers the 2nd portion of the axillary artery. (The portion proximal to pectoralis minor is therefore the1st part of the axillary artery, while the portion distal to pectoralis minor is the 3rd portion of the axillary artery.

The 1st part has one branch, the superior thoracic artery, which supplies the intercostal muscles of the 1st and 2nd intercostal spaces and the upper portion of serratus anterior muscle.

The 2nd part has two branches, the thoracoacromial and lateral thoracic arteries. The thoracoacromial artery is a short trunk arising anteriorly and passing medial to the pectoralis minor muscle. It divides into four branches distributing according to their regional names: acromial, deltoid, pectoral and clavicular. The lateral thoracic artery is a variable artery that, in 65% of us, is a direct branch of the axillary artery, but can also arise from the thoracoacromial or subscapular arteries. It passes below the inferolateral border of pectoralis minor muscle to distribute most significantly to serratus anterior and the pectoral muscles.

The 3rd part has three branches. The subscapular artery is the largest branch of the axillary artery. It divides into the circumflex scapular and thoracodorsal branches three or four centimeters from its origin. The circumflex scapular artery passes through the triangular space and supplies the infraspinatous, subscapular, teres major, and teres minor muscles. It also anastomoses with the infraspinatous branch of the suprascapular artery in the infraspinatus fossa. The thoracodorsal artery is the principal supply to the latissimus dorsi muscle and is accompanied by the thoracodorsal nerve. The next branch of the 3rd part of the axillary artery is the anterior circumflex humeral artery. It runs anteriorly around the surgical neck of the humerus and anastomoses with the posterior circumflex humeral artery, which is the final branch of the 3rd part of the axillary artery. This is larger than its anterior partner, and passes through the quadrangular space with the axillary nerve.

As for the axillary vein, it begins as the union of the brachial veins with the basilic vein. It continues through the axilla, medial to the axillary artery, until it changes its name to the subclavian vein at the lateral border of the first rib. The axillary vein receives the cephalic vein and numerous other tributaries that roughly correspond to the branches of the axillary artery, though things are of course somewhat variable (See #15 below). (One thing to note is that the vein receives one or more thoracoepigastric veins, which represent anastomoses of veins from the superficial inguinal region with one or more axillary tributaries. This represents a possible route of collateral drainage if the inferior vena cava is obstructed for some reason.)

7. Identify prominent features of the humerus, cubital fossa and associated prominences of the scapula, radius and ulna as given in the lab manual. (N 420, 421, 436, 439)

The only prominent feature of the humerus that we are worried about here is the radial groove, which spirals around the posterior surface of the shaft of the humerus, containing the radial nerve and the deep brachial vessels. See the next session for prominent features of the bones of the forearm.

8. Identify the contents of each of the three compartments of the arm and the functional significance of the included muscles. (W&B 124-127, N 184, 420, 421, 426, 429, 431, 433, 434, 435, 447, 473, 474, 475, 476, 477, 479, 480)

The medial and lateral intermuscular septa divide the arm into an anterior (flexor) compartment and a posterior (extensor) compartment. Furthermore, the medial intermuscular septum consists of two laminae, and the space between them is the neurovascular compartment. The contents of each compartment are listed below:

anterior (flexor) compartment:

Muscle Origin Insertion Action Innervation
biceps brachii short head: tip of coracoid process; long head: supraglenoid tubercule of scapula tuberosity of radius flexes forearm, flexes arm (long head), supinates musculocutaneous nerve (C5,6)
brachialis anterior surface of lower one-half of humerus and intermuscular septa coronoid process of ulna flexes forearm musculocutaneous nerve (C5,6)
coracobrachialis coracoid process of scapula medial humerus at mid-shaft flexes and adducts arm musculocutaneous nerve (C5,6)

posterior (extensor) compartment:

Muscle Origin Insertion Action Innervation
triceps brachii long head: infraglenoid tubercle of scapula; lateral head: posterolateral humerus & lateral intermuscular septum; medial head: posteromedial surface of inferior 1/2 of humerus olecranon process of the ulna extends forearm; long head extends and adducts arm radial nerve
anconeus lateral epicondyle lateral side of olecranon and upper one-fourth of ulna extends forearm nerve to anconeus from radial nerve

Neurovascular structure Source Branches Supply to:
ulnar nerve medial cord of the brachial plexus palmar cutaneous Br, dorsal Br, superficial & deep Br motor: flexor carpi ulnaris, flexor digitorum profundus (ulnar half), abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi, ulnar 2 lumbricals, palmar & dorsal interossei
sensory: skin of medial side of wrist & hand & ulnar 1 1/2 digits

neurovascular compartment:

Neurovascular structure Source Branches Supply to:
brachial artery axillary (continuation distal to teres major m.) deep brachial, sup. ulnar collateral, nutrient, inf. ulnar collateral; terminal branches are the radial & ulnar arm, forearm & hand
median nerve lateral & medial cords of brachial plexus anterior interosseous, palmar br, recurrent (motor) br, common palmar digital nn (1st-3rd) motor: pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus (radial half), flexor pollicis longus, pronator quadratus, abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, radial 2 lumbricals
sensory: skin of radial half of palm & palmar side of radial 3 1/2 digits (and nail bed for these digits)

The compartment also contains the basilic vein and several brachial veins.

9. Correlate any fractures of the humerus with functional disruptions of associated muscular and neurovascular structures. (N 426, 434, 477)

The humerus can break just about anywhere along its length. The three most common places, due to relative weakness, are the surgical neck, the distal end of the middle 1/3 of the bone, and the supracondylar region. With surgical neck fractures, laceration of the axillary nerve and one or both circumflex humeral arteries could cause a significant problem. In the case of a fracture more distal along the shaft, the structure most in danger is the radial nerve, which is wrapping around the bone in the radial groove. According to Wheeless's Textbook of Orthopaedics, radial nerve palsy of some degree occurs with 18% of humeral shaft fractures.

10. Describe the movements of the shoulder and elbow joints.

The shoulder joint is a ball and socket joint. Movements there include flexion, extension, abduction, adduction, and circumduction, as well as medial and lateral rotation of the arm. The elbow joint is a hinge, permitting only flexion and extension.

11. Identify spatial relationships of all associated muscular and neurovascular structures within the cubital fossa. (W&B 132-134, N 447, 479)

The floor of the cubital fossa is the brachialis and supinator muscles, so all of the contents of the space lie superficial to those two structures. The tendon of the biceps brachii runs through the middle of the cubital fossa. Medial to it we find the brachial artery (which splits into radial and ulnar arteries near the inferior border of the cubital fossa). The median nerve lies medial to the brachial artery as they both enter the forearm. More superficially we find the median cubital vein, the lateral antebrachial cutaneous nerve, and branches of the medial antebrachial cutaneous nerve.

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Anterior Divisions (nerves) - The Veins of the Upper Extremity and Thorax - The Axillary Artery - The Brachial Artery - The Muscles and Fascia¾ of the Shoulder - The Muscles and Fascia of the Arm - Surface Anatomy of the Upper Extremity - Surface Markings of the Upper Extremity



QUESTIONS and ANSWERS:

12. Define the boundaries of the axillary space.
See #2 above. (N 181)
13. How is the axillary vein formed?

It's formed by the union of the brachial veins (which accompany the brachial artery) and the basilic vein at the inferior border of teres major. (N 184)

14. Is the axillary vein a single, paired or plexiform vein?

The axillary is normally a single vein.

15. Do the tributaries of the axillary vein correspond to the axillary arterial branches?

Yes, with the exception of the thoracoacromial vein, whose branches join the axillary vein independently and the cephalic vein which has no corresponding artery. (N 427, 256)

16. Are the axillary vein's tributaries paired?

Some, such as the brachial veins, are paired. Others, such as cephalic vein, are not. (N 184)

17. Can you see any valves in the veins?

There are valves within the axillary vein, and valves are also located in tributaries where they join the axillary vein.

18. Establish relationships of axillary artery and vein within the axilla.

At its source, the vein lies on the medial side of the artery, partly overlapping it. Thereafter, in the upper part of the axilla, the vein lies anterior and inferior to the artery. (N 429, 479)

19. Do you see a separate medial brachial cutaneous n.?

The medial brachial cutaneous nerve is much smaller than the medial antebrachial cutaneous nerve, and, once the skin of the axilla is removed, it may be difficult to find. It branches from the medial cord, just proximal to the medial antebrachial cutaneous nerve. It may make a nerve anastomosis with the intercostobrachial nerve.

20. What artery accompanies the axillary nerve?

The posterior circumflex humeral artery, a branch of the 3rd part of the axillary artery, accompanies the axillary nerve through the quadrangular space. (N 426, 432)

20a. What does lower subscapular nerve accompany?

Lower subscapular nerve accompanies circumflex scapular artery into the triangular space. (N 426)

21. Note how the three cords of the brachial plexus are derived from the trunks.

See #3 above. (N 430)

22. Note course, relations and parts of the axillary artery.

See #6 above. (N 427, 429)

23. Note the area of distribution of the axillary artery's branches as well as any accompanying nerves:

See #6 above. (N 427, 429, 430)

24. What is the source of the long thoracic nerve and what is "winged scapula"?

The long thoracic nerve arises from the anterior rami of C5-C7. Winged scapula is a condition in which the scapula protrudes from the back because it is not held in place by the counterbalancing forces of the serratus anterior and trapezius muscles. It results from injury to the long thoracic nerve. See #5 above. (N 191, 429)

25. Do muscles use the intermuscular septa as attachments?

The lateral and medial heads of triceps brachii and brachialis all use intermuscular septae as part of their origins.

26. Where do branches of the musculocutaneous nerve enter anterior compartment muscles?

The musculocutaneous nerve is the continuation of the lateral cord of the brachial plexus after that cord's contribution to the median nerve. The musculocutaneous nerve gives off branches to the coracobrachialis as it pierces that muscle. It continues downward in the interval between the brachialis muscle and biceps brachii muscle, giving branches to each.

27. How does the musculocutaneous nerve terminate, where does it change its name, and does it have any accompanying arteries?

The musculocutaneous nerve terminates by piercing the brachial fascia lateral to the biceps tendon a short distance above the elbow. It continues as the lateral antebrachial cutaneous nerve. It has no accompanying arteries. (N 474)

28. How is the neurovascular compartment of the arm formed?

The medial intermuscular septum is divided into two laminae, which, with the overlying brachial fascia, form the neurovascular compartment. (N 435)

29. What are the relations and branches of the median nerve in the arm?

The median nerve has no muscular branches in the arm. Initially it rests atop the brachial artery in the neurovascular compartment, then comes to lie anterolateral to the brachial artery and is overlapped laterally by the coracobrachialis muscle. The nerve eventually becomes medial to the brachial artery, crossing over it at the midarm level. (N 435, 475)

30. Where does the ulnar nerve leave the neurovascular compartment?

At approximately mid-arm, the ulnar nerve pierces the posterior layer of the intermuscular septum to enter the posterior compartment. (N 433, 435, 473, 476)

31. Does the ulnar nerve have any branches in the arm?

No, it does not.

32. Is the ulnar nerve accompanied by any vessels in the arm? (N 434)

The superior ulnar collateral artery, one of the arteries of the elbow collateral circulation, accompanies ulnar nerve posterior to the medial epicondyle.

33. Is the brachial vein paired? How is it formed? What does it continue as? Where does the basilic vein join it?

The brachial vein is a paired set accompanying the brachial artery. It is formed at the elbow by the union of venae comitantes of the radial and ulnar arteries. It continues as the single axillary vein, after the two veins join at about the lower border of teres major muscle. (N 434, 256)

34. What are the collateral branches of the brachial artery around the elbow?

The brachial artery gives off two collateral branches for the elbow anastomosis: the superior ulnar collateral artery at mid-arm, that accompanies the ulnar nerve, and the inferior ulnar collateral artery, that passes anterior to the medial epicondyle. (N 434)

35. Locate the brachial artery and median nerve. What are their relative positions?

Remember TAN - in the cubital fossa, the biceps Tendon lies lateral, the brachial Artery is intermediate, and the median Nerve is most medial. (N 433)

36. Where does the brachial artery divide?

Within the cubital fossa, the brachial artery divides into the radial and ulnar arteries. (N 447)

37. What happens to the median nerve?

The median nerve passes into the forearm through the two heads of pronator teres. (N 448, 475)

38. Separate the brachialis from the brachioradialis muscle along the intermuscular septum between them and identify the radial nerve. Is it accompanied by vessels? What are they?

The radial nerve is accompanied above the elbow by the radial collateral artery, a terminal branch of the deep brachial artery. Below the elbow, radial nerve is accompanied by the radial recurrent artery, that anastomoses with the radial collateral. (N 447, 448)

39. What structures in the superficial fascia overlie the cubital fossa? What is their importance? Danger?

Branches of the medial antebrachial cutaneous nerve cross the medial portion of the cubital fossa, while the lateral antebrachial cutaneous nerve emerges from beneath the biceps on the lateral side of the cubital fossa. The median cubital vein also crosses the fossa obliquely, shunting blood from the cephalic vein up to join the basilic vein. This is a common site for phlebotomy, and cutaneous nerves may be in danger here. (N 480)

40. What nerve is given off to the forearm by the radial nerve as it enters the anterior compartment?

As the radial nerve pierces the lateral intermuscular septum it gives off the posterior antebrachial cutaneous nerve, which supplies the skin of the back of the forearm. (N 477)