Brachial Plexus

If not previously accomplished, carry out the following:

Reflect the pectoralis major to its attachment on the humerus and separate the deltoid from the clavicle and reflect laterally.

Divide the pectoralis minor at the coracoid process reflect medially.

Divide and reflect the conjoined tendon (tendons of the short head of the biceps and the coracobrachialis). Locate the musculocutaneous nerve entering the coracobrachialis. Identify the axillary sheath in relation to the clavicle, acromion and coracoid process.

Open the axillary sheath proximal to the coracoid process. Identify the axillary vein and artery as well as a portion of the brachial plexus. Recall the axillary vessels become the subclavian artery and vein as they pass beneath the clavicle.

Open the axillary sheath distal to the coracoid process.

Identify the axillary artery. The cords of the brachial plexus are named for their relationship to the artery. Identify the medial and lateral cords. Reflect the axillary artery medially to locate the posterior cord.

Follow the lateral cord distally.  Reidentify the musculocutaneous nerve to the biceps, coracobrachialis and brachialis muscles. Locate its distal branch, the lateral cutaneous nerve of the forearm.

Note the contribution of the lateral cord to the median nerve.

Locate the medial cord and identify the ulnar nerve by following its course distally. Also identify the medial cutaneous nerves of the arm and forearm as the remaining branches of the medial cord.

Note the contribution of medial cord to the median nerve.

Reflect the axillary vessels along with the medial and lateral cords medially.

Identify the posterior cord and its major branches, the radial and axillary nerves.

The axillary nerve will course around the neck of humerus and the radial nerve around the shaft of humerus.

If the medial wall of the axilla is intact, identify the long thoracic nerve to the serratus anterior. This nerve arises from the roots of the brachial plexus and travels medially along the chest wall.

Similarly, identify the thoracodorsal nerve arising from the posterior cord and passing to the deep surface of the latissimus dorsi.

These two nerves are vulnerable with axillary node dissection.

Follow the brachial plexus medially. Identify the anterior and middle scalene muscles, which provide anatomic landmarks for the phrenic nerve, subclavian vessels and brachial plexus.

The phrenic nerve lies on the anterior surface of the anterior scalene.

The trunks of the brachial plexus pass between the anterior and middle scalene muscles. Identify the upper, middle and lower trunks.

Note the relationship of the subclavian vessels to the anterior scalene. The subclavian vein lies above the anterior scalene and the subclavian artery lies beneath it.

Look for the suprascapular nerve arising from the upper trunk. Follow this nerve posteriorly to the suprascapular notch. This nerve continues on the posterior surface of the scapula to the supraspinatus and infraspinatus.

Detach the anterior scalene to reveal the C5, C6, C7, C8 and T1 spinal nerves (roots of brachial plexus).

With inferior retraction of the subclavian artery, the vertebral artery may come into view. The vertebral artery is a proximal branch of the subclavian that provides posterior circulation to the brain. At C6, the vertebral artery enters the transverse foramina of the cervical spine.

Re-identify the medial and lateral cord and their contributions to the median nerve. Follow the median nerve to the cubital fossa (antecubital fossa).

Follow the lateral cord and reidentify the musculocutaneous nerve and the lateral cutaneous nerve of the forearm.

Follow the ulnar nerve from the medial cord to to the cubital tunnel, posterior to the medial epicondyle of the humerus.

Follow the axillary nerve around the neck of the humerus.

Examine the cubital fossa and locate the:

• Lateral cutaneous nerve of the forearm
• Biceps tendon
• Median nerve
• Brachial artery

Incise the bicipital aponeurosis between the pronator teres and biceps tendon to follow the the brachial artery and median nerve into the forearm.

Identify the radial and ulnar branches of the brachial artery.

Follow the median nerve as it passes deep to the humeral head of the pronator teres.

From a medial approach, separate the biceps and triceps to expose the humeral shaft. Follow the radial nerve from the posterior cord around the radial (spiral) groove in the humerus.

Lateral to the biceps tendon, identify the brachialis and brachioradialis muscles. Identify the superficial (sensory) and deep (motor) branches of the radial nerve emerging between brachialis and brachioradialis.