CUTANEOUS NERVES
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.
Shoulder
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.
Upper Arm
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.
Elbow
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.
