PROCEDURE - ANTERIOR ARM

1. PRE-WORK (before lab) review the organization of the bony upper extremity from your atlas or on an articulated skeleton in the lab.
    (Netter402) (Netter409) (Netter410) (Netter426)

a) On the humerus, at the distal end identify the medial and lateral epicondyles with the olecranon fossa between. 

b) On the radius, at the proximal end examine the head and neck. Close to the proximal end is a bump called the radial tuberosity which is the attachment point for the biceps tendon.

c) On the ulna, at the proximal end examine the olecranon and coronoid processes.

2. Begin the examination of the upper limb by removing skin and superficial fascia from the anterior arm distally to the cubital fossa (pit of the elbow).
    (Figure615) (Netter405) (Photo6001)

While removing the superficial fascia, observe the major superficial veins of the arm if they are still present.

Cephalic vein - The cephalic vein courses in the superficial fascia distally along the lateral side.

Basilic vein - The basilic vein courses along the arm in the superficial fascia of the medial side.

Median cubital vein - The median cubital vein bridges between the cephalic and basilic veins at the cubital fossa. This provides a communicating vein between the two major superficial veins.

The median cubital vein is a common site for obtaining blood samples via venipuncture. Deeper structures of the cubital fossa are partly protected at this location by the aponeurosis of the biceps that lies deep to the median cubital vein.

3. Continue skin removal from the anterior forearm as far as the wrist.
    (Figure621) (Photo6001a)

Work medially and laterally as well as distally such that skin is reflected completely from the anterior forearm.

Do not dissect into the anterior compartment muscles at this time, we will examine them in detail in the next lab. The goal is to remove the forearm skin to expose the antebrachial fascia of the forearm in preparation for the next lab.

Numerous cutaneous nerves and superficial veins are present in the forearm, but we will not examine these in detail and they can be removed along with the skin.

4. Using scissors extend the longitudinal incision in the anterior surface of the brachial fascia distally to the cubital fossa.

This extends to the cubital fossa the prior incision made to access the brachial sheath.

5. Use your fingers to spread open the brachial fascia working laterally until your fingers are stopped by the lateral intermuscular septum.
    (Figure616) (Photo6071)

The intermuscular fascial septum separates the arm into an anterior compartment and a posterior compartment. As with the lower extremities, compartments are an important organizational principle to the upper limbs as muscles within generally share a nerve and vascular supply.

6. Repeat the process, separating the brachial fascia medial to the axillary sheath, until your fingers are stopped by the medial intermuscular septum.
    (Figure616)

The anterior compartment of the arm contains three muscles, the biceps brachii, brachialis, and coracobrachialis muscles, all of which are flexors.

These muscles are all innervated by the same nerve, the musculocutaneous nerve, and all receive blood from the brachial artery.

7. Use your fingers to separate the biceps brachii and trace the shape/connections of the muscle.
    (Figure617) (Netter421) (Photo6023)

The biceps brachii muscle typically has two proximal heads attached to the scapula. The long head attached to the supraglenoid tubercle (bump on the scapula just superior to the joint) and the short head to the coracoid process. (Photo6023a)

The tendon of the long head enters the glenohumeral joint capsule in a groove on the humerus. This makes the long head tendon appear visually 'shorter' than the short head, since most of the long head tendon is hidden inside the joint capsule itself.

Follow the biceps brachii muscle distally to the cubital fossa. The most anterior distal tendinous attachment of the biceps brachii is the bicipital aponeurosis. This is a broad flat extension of the biceps tendon blending into the antebrachial fascia of the forearm. (Photo6023b)

The bicipital aponeurosis can be quite variable, ranging from a distinct band through to nearly absent.

Deep to the bicipital aponeurosis is the second distal tendinous attachment of the biceps. This is a rounded tendon that courses deep to insert on the radial tuberosity (bump on the proximal radius). This tendon allows the biceps to be the strong supinator of the forearm when the elbow is flexed (i.e. motion of driving a screw with a screwdriver). (Photo6023b)

The biceps brachii muscle is one of the more variable muscles in the body. In approximately 10% of individuals there will be additional proximal heads (up to a record of seven supernumerary heads).

8. Lift and retract the biceps brachii muscle laterally so that you can examine the muscles deep to the biceps brachii muscle.
    (Figure617) (Netter421) (Photo6072)

As you reflect the muscle, take care to preserve the musculocutaneous nerve in the loose fascia deep to the muscle as it can sometimes be adherent to the deep surface of the biceps brachii muscle.

Brachialis muscle: The brachialis muscle attaches proximally to the humerus halfway down the arm and inserts distally on the coronoid process of the ulna.

Coracobrachialis muscle: The coracobrachialis muscle attaches proximally to the coracoid process of the scapula and distally to the shaft of the humerus. The musculocutaneous nerve typically pierces through the coracobrachialis muscle as the nerve courses distally into the arm.

The penetration of coracobrachialis by the musculocutaneous nerve is a characteristic feature of the muscle and helps identify both structures.

9. Return to the brachial plexus and trace the musculocutaneous nerve in the axilla and verify it penetrates into the coracobrachialis muscle. 
    (Netter465) (Netter421) (Netter463)
    (Photo6010) (Photo6072)

10. Find the continuation of the musculocutaneous nerve where it emerges from the coracobrachialis muscle and continues distally in the loose fascia between the biceps brachii and brachialis muscle.
    (Netter465) (Netter421) (Netter463) (Photo6072)

Branches from the musculocutaneous nerve innervate all three muscles in the anterior compartment of the arm.

After the last branch to the arm muscles, the continuation of the musculocutaneous nerve is a cutaneous nerve innervating the forearm (called the lateral cutaneous nerve of the forearm).

The lateral cutaneous nerve of the forearm passes into the cubital fossa and continues distally branching to innervate skin of the lateral forearm.

11. Return to the brachial plexus and trace the median nerve distally as it courses along the medial side of the biceps brachii muscle.
    (Netter419) (Netter423) (Netter463)
    (Photo6072) (Photo6073)

The initial segment of the median nerve is lateral to the brachial artery, but more distally it crosses to the medial side of the brachial artery to enter the cubital fossa.

12. Return to the brachial plexus and trace the ulnar nerve distally to where it penetrates through the intermuscular septum in the medial part of the distal arm.
    (Netter423) (Netter463) (Photo6010)
    (Photo6073) (Photo6074)

Separate the intermuscular septum at this point so you can follow the nerve continuation all the way to the medial epicondyle of the humerus.

The ulnar nerve passes into the forearm in contact with the posterior surface of the medial epicondyle.

This unfortunate arrangement of the ulnar nerve forms the 'funny-bone', susceptible to neurological symptoms when compressed ('bumped'). If you bend your elbow approximately half way you should be able to palpate the ulnar nerve's passage over the posterior aspect of the medial epicondyle of your humerus.

PROCEDURE - ARTERIES OF THE ARM

13. Replace the pectoralis minor muscle to its anatomical position and review the general artery organization before starting to dissect specific parts of the vessel in the following steps.
    (Figure610) (Netter418) (NetterBP100) (Photo6048)

The subclavian artery (and accompanying vein) course out of the thoracic cavity superior to the 1st rib, at which point the vessels change name to the axillary artery and vein.

For descriptive purposes the pectoralis minor muscle is a landmark for dividing the axillary artery into three regions. 

The branching pattern of the axillary artery can vary but usually there is one branch from part one, two branches from part two, and three branches from part three.

Part one of the axillary artery lies between the clavicle and the superior border of the pectoralis major muscle and gives rise to the superior thoracic artery.

The superior thoracic artery runs anteromedially and medial along the superior border of the pectoralis minor muscle. We will not be dissecting this artery.

Part two of the axillary artery is the region situated posterior to the pectoralis minor muscle and gives rise to the thoracoacromial and lateral thoracic arteries.

The lateral thoracic artery (also known as the long thoracic artery) courses inferior along the lateral side of the thorax and supplies breast with blood. We will not be dissecting this artery.

Part three of the axillary artery lies lateral to the pectoralis minor muscle and the inferior margin of teres major (distal to teres major the artery is renamed the brachial artery). The third part of the axillary artery gives rise to the subscapular, anterior humeral circumflex, and posterior humeral circumflex arteries.

14. Transect the axillary vein near the clavicle and again at the lower border of the teres major.

As required during examination of the arteries, remove this portion of the vein and any small venous branches. Removing the vein will make examination of the artery structures below easier, but appreciate that all the arteries are accompanied by similarly named veins.

15. Return to the region of the brachial plexus containing the 'M' pattern of terminal branches and identify the axillary artery surrounded by these nerve branches.
    (Netter419) (Photo6010)

16. Examine the axillary artery in this vicinity to find the three arteries arising from the third part of the axillary artery.
    (Figure610) (Netter419) (Netter418) (NetterBP100)
    (Photo6049) (Photo6050)

The anterior and posterior humeral circumflex arteries arise from the axillary artery adjacent to each other.

The posterior humeral circumflex artery is directed posteriorly around the humerus. The vessel disappears into the same fascia as the axillary nerve to pass through the quadrangular space.

The anterior humeral circumflex artery is usually smaller than the posterior humeral circumflex artery and is directed anteriorly around the humerus.

The anterior and posterior humeral circumflex arteries arise from the axillary artery adjacent to each other. The anterior artery is usually the smaller of the two vessels.

The third, and normally largest, artery in this region of the axillary artery is the subscapular artery.

The subscapular artery arises at the lower border of the subscapularis muscle and is a major blood supply to the scapula.

17. Follow the axillary artery proximally examining the anterior surface in the region deep to the pectoralis minor muscle (i.e. part 2 of the axillary artery) and look for the thoracoacromial artery.
    (Figure610) (Netter419) (Netter418) (NetterBP100)
    (Photo6051) (Photo6052)

The thoracoacromial artery (or trunk) is typically a short vessel directed superomedially. The trunk almost immediately branches into smaller vessels. 

The thoracoacromial artery usually arises from the axillary artery just proximal to where the medial and lateral cord contributions to the median nerve span anterior to the artery.

The thoracoacromial artery branches into vessels directed to the pectoral, deltoid, clavicular, and acromial regions. We will not be dissecting these small divisions. 

18. Follow the axillary artery distally past the inferior border of the teres major muscle where the name changes to the brachial artery.
    (Netter423) (NetterBP100)

In the arm, the brachial artery gives a series of branches to the muscles of the anterior compartment supplying them with blood. 

Additionally, the brachial artery gives off a deep branch (the profunda brachii artery) which courses posteriorly to penetrate the intermuscular septum and enter the posterior compartment of the arm.  This supplies the triceps and posterior compartment tissues with blood.

20. Follow the brachial artery distally to where it enters the cubital fossa deep to the bicipital aponeurosis.

The cubital fossa is a triangular shaped transitional region between the arm and forearm.

Near the elbow, small branches arise from the brachial artery and wrap around the elbow joint.

Similar to the most joints, branches arise both proximal (called collateral arteries) and distal (called recurrent arteries) to the elbow joint. The proximal and distal branches anastomose to form a network surrounding the elbow joint. We won't examine these arteries in detail.

21. Cut the bicipital aponeurosis near the biceps tendon (take care not to cut the main biceps tendon) and reflect the aponeurosis to continue following the brachial artery.
    (Figure618) (NetterBP100)

The brachial artery ends in the cubital fossa near the neck of the radius by bifurcating into the radial and ulnar arteries.

22. Remove any fat within the cubital fossa so that you can observe the relationships within the fossa.
    (Figure618) (Netter423) (Netter463)

The cubital fossa is demarcated superiorly by an imaginary line between the humeral condyles, medially by the pronator teres muscle and laterally by the brachioradialis muscle. 

With the cubital fossa, the biceps brachii tendon is lateral, the brachial artery and vein is intermediate, and the median nerve is medial. However, due to partial pronation in donors, the relationships within the cubital fossa can be difficult to appreciate.

You may observe additional arterial branches arising distal to the elbow. These are part of the network of arteries/veins anastomosing around the elbow joint. We will not dissect these specifically.

23. Observe that the brachial vein accompanies the brachial artery, and also bifurcates into the radial vein and ulnar vein.

CLINICAL EXERCISE - Intraosseous Cannulation

24. In cases of severe blood loss it can be difficult to place an intravenous (IV) line into a patient. An alternative is to insert a needle into the marrow chamber of one of the long bones. The proximal humerus is a common site for insertion of such a needle. 

CAUTION: Needles are very sharp and must be handled with care following established safety procedures for minimizing needle-stick injury risk. Before using a needle you must review the safety videos if you have not already done so:
                                  Needle handling  --- Video --->

To view the intraosseous cannulation procedure performed on a donor:
   Intraosseous Cannulation (humerus)  --- Video --->

In this clinical exercise, you have the chance to perform an intraosseous cannulation by inserting a needle into the proximal humerus. For the steps to take:
                                 ------ click here ------

CHECKLIST

Skeletal Structures

Humerus
    Lateral epicondyle
    Medial epicondyle

Radius
    Head
    Neck
    Radial tuberosity

Ulna
    Olecranon process
    Coronoid process

Soft Structures

Superficial veins
    Cephalic vein
    Median cubital vein
    Basilic vein

Brachial fascia

Anterior arm
    Biceps brachii muscle & tendon
        Long & Short heads
    Brachialis muscle & tendon
    Coracobrachialis muscle & tendon

Musculocutaneous nerve

Median nerve

Radial nerve

Ulnar nerve

Subclavian artery (and vein)

Axillary artery (and vein)
    Part one
    Part two
        Thoracoacromial artery
    Part three
        Subscapular artery
        Posterior humeral circumflex artery
        Anterior humeral circumflex artery

Brachial artery (and vein)