The cutaneous nerves of the upper limb and elbow are for the most part derived from the brachial plexus, although the uppermost nerves to the shoulder are derived from the cervical plexus. Some of the cutaneous nerves arise directly from the medial, lateral, or posterior cord of the brachial plexus, whereas others are terminal branches of the peripheral nerves of the upper extremity.
The supraclavicular nerves (C3, C4) become superficial at the posterior border of the sternocleidomastoid muscle within the posterior triangle of the neck. They pierce the superficial layer of the cervical fascia and the platysma muscle, radiating in three lines: (1) the medial supraclavicular nerves cross over the clavicle anteriorly to cover the shoulder more medially; (2) the intermediate supraclavicular nerves also run anteriorly and go toward the acromion laterally; and (3) the lateral or posterior supraclavicular nerves cross over the scapula to cover the shoulder posteriorly.
The superior lateral brachial cutaneous nerve (C5, C6) is the termination of the lower branch of the axillary nerve of the brachial plexus. Leaving the axillary nerve, it turns superficially around the posterior border of the lower third of the deltoid muscle to pierce the brachial fascia. Its cutaneous distribution is the lower half of the deltoid muscle and the long head of the triceps brachii in the most proximal aspect of the upper arm, both anteriorly and posteriorly.
The inferior lateral brachial cutaneous nerve (C5, C6) is derived from the posterior antebrachial cutaneous nerve shortly after this nerve branches from the radial nerve. The inferior lateral brachial cutaneous nerve becomes superficial in line with the lateral intermuscular septum a little below the insertion of the deltoid muscle. It accompanies the lower part of the cephalic vein and distributes in the lower lateral surface of the arm, below the area covered by the superior lateral brachial cutaneous nerve and extending both anteriorly and posteriorly.
The posterior brachial cutaneous nerve arises within the axilla as a branch of the radial nerve (C5 to C8). Traversing the medial side of the long head of the triceps brachii muscle, the nerve penetrates the brachial fascia to distribute in the middle third of the back of the arm, below the area covered by the superior lateral brachial cutaneous nerve, and lateral to the distribution of the medial brachial cutaneous nerve and the inter-costobrachial nerve.
The medial brachial cutaneous nerve (C8, T1) arises from the medial cord of the brachial plexus in the lower axilla. It descends along the medial side of the brachial artery to the middle of the arm, where it pierces the brachial fascia and supplies the skin of the posteromedial surface of the lower third of the arm as far as the olecranon.
The intercostobrachial nerve is the larger part of the lateral cutaneous branch of the second thoracic nerve (T2). In the second intercostal space at the axillary line, it pierces the serratus anterior muscle to enter the axilla. Here, it usually anastomoses with the medial brachial cutaneous nerve and then pierces the brachial fascia just beyond the posterior axillary fold. Its cutaneous distribution is along the medial and posterior surfaces of the arm from the axilla to the elbow.
The medial antebrachial cutaneous nerve arises from the medial cord of the brachial plexus. A small branch pierces the axillary fascia and supplies the skin over the medial anterior area of the arm.
Cutaneous innervation about the elbow can be more variable and includes coverage by the inferior lateral brachial cutaneous nerve laterally and posteriorly, the medial brachial cutaneous nerve medially and posteriorly, and the medial antebrachial cutaneous nerve anteriorly. As the elbow continues into the proximal forearm, coverage is taken over by the antebrachial cutaneous nerves (medial, lateral, posterior). The medial antebrachial cutaneous nerve (C8, T1) is a continuation of the medial cord of the brachial plexus after the medial brachial cutaneous nerve, whereas the lateral antebrachial cutaneous nerve (C5, C6) is the terminal branch of the musculocutaneous nerve, running along next to the cephalic vein. The posterior antebrachial cutaneous nerve (C5 to C8) is another cutaneous branch of the radial nerve after the posterior brachial cutaneous nerve has branched off more proximally. All three of the antebrachial cutaneous nerves continue along distally to provide cutaneous innervation for the entire forearm, down to the level of the wrist.