Chapter 2 The Brachial Plexus
Supraclavicular Brachial Plexus
Anatomy
• The surgeon must review the appropriate osteology. No matter how dense the scarring, the bony points are palpable at surgery and form welcome guides (Figures 2-1 and 2-2).
• The transverse processes of the lower cervical vertebrae should be studied in detail so that the surgeon understands the relationship of the intervertebral foramen to the transverse process, which forms a gutter supporting the spinal nerves, and the relationship of both to the vertebral artery, vein, and accompanying sympathetic fibers (Figures 2-3 and 2-4).
• The scalenus anterior is attached to the anterior tubercle and the scalenus medius to the posterior tubercle of the transverse process (Figure 2-5).
• The clavicle should be examined so that surgeon understands the points of attachment of the sternocleidomastoid (SCM), pectoralis major, deltoid, and subclavius (Figures 2-6 and 2-7). On rare occasions, the clavicle is divided at surgery, using a Gigli saw (Figure 2-8).
• The scapula should be reviewed so that the transverse scapular ligament can be located. This ligament is the point of attachment of the inferior belly of the omohyoid; the suprascapular nerve courses below it (Figure 2-9).
• The first rib should be mastered. The upper border is characteristically sharp. The stellate ganglion is anterior to the neck, and the vertebral artery ascends to the transverse process of C6, anterior to the ganglion. The point of attachment of the scalenus anterior should be clearly understood, because this separates the vein in front from the artery and lower trunk behind.
• The investing fascia of the neck splits to enclose the SCM, covers the posterior triangle, and splits to enclose the trapezius (Figure 2-10).
• The accessory nerve supplies the SCM and trapezius. Winding around the posterior border of the SCM are cutaneous branches of the cervical plexus. The transverse cervical and greater auricular nerves are excellent landmarks to both CN XI and C5 (Figures 2-11 and 2-12).
• There is a small triangular gap between the clavicular attachment of the SCM and the manubrial attachment. Immediately posterior to this interval is the termination of the internal jugular vein (Figure 2-13).
• The omohyoid consists of two bellies joined by an intermediate tendon. The tendon overlies the jugular vein, and the inferior belly runs parallel to the suprascapular nerve to the suprascapular notch (Figure 2-14).
• The root of the neck can be a difficult and frightening arena for the inexperienced surgeon. Any structure can be chosen by the surgeon as the key to understanding this region. We use the scalenus anterior for this purpose, because the surgeon can easily palpate the characteristic anterior surface of that muscle through fat and scar tissue (Figure 2-15).
• The scalenus anterior originates from the anterior tubercles and is inserted via a short tendon into the first rib. The phrenic nerve runs downward from lateral to medial on its anterior surface. Laterally, the spinal nerves and trunks of the brachial plexus are seen (Figure 2-16).
• The medial border of the scalenus anterior bounds a triangular space. The other borders are the subclavian artery and the lateral border of the longus colli. The contents of the space include the stellate ganglion, the vertebral artery, the thyrocervical vessels and their branches, the suprapleural membrane, and the pleura.
• The fascial planes should be clearly understood. The investing fascia, having split to enclose the SCM, roofs the posterior triangle and splits to enclose the trapezius. The prevertebral fascia covers the scalenus anterior, the subclavian artery, and the brachial plexus and continues into the axilla.
Figure 2-6 A lateral view depicts the relationship of the relevant fascia and musculature to each other.
Surgery
• The table is flexed at the patient’s waist so that the neck veins are not engorged. The chin is turned away from the operator. The neck is slightly extended. The surgeon may stand either on the side of the patient’s axilla or outside the deltoid. In either event, the patient’s shoulder must be free for shrugging or depressing during surgery, thus moving the clavicle if it is obstructing the surgeon’s view (Figure 2-17).
• The vertical limb of the skin incision follows the posterior border of the SCM. In the majority of cases, neither the cervical plexus nor CN XI is dissected, but the skin incision must be sufficiently high to view C5. The skin incision can be marked and draped for vertical extension, if more cephalad dissection is later required (Figure 2-11).
• The lower point of the vertical incision should be just above the clavicle. If it is anticipated that C8 and T1 will be dissected, the skin incision should be carried more medially before swinging laterally (Figure 2-11).
• The horizontal component of the incision is parallel to and above the clavicle and is then continued down over the cephalic vein (Figure 2-18).
• Once the skin and platysma have been incised, the fascia on the posterior border of the SCM is sharply incised, hard against the muscle (Figure 2-19).
• A fatty fibrous pad is then encountered. The surgeon palpates through this fat with the index finger, feeling the characteristic anterior surface of the scalenus anterior. This is an important step, because the novice tends to operate both too far laterally and too far superiorly and thus has difficulty finding the plexus (Figure 2-20).
• The surgeon knows that the phrenic nerve, in front of the scalenus anterior, is deep to the prevertebral fascia, so the fatty pad can be mobilized with dispatch, usually in an upward and lateral direction. Branches of the thyrocervical trunk will be encountered at several points in the dissection and should be divided if they get in the way (Figure 2-21).
• The external jugular vein may be retracted or divided if it is obstructive (Figure 2-22; see also Figure 2-21).
• The omohyoid is mobilized, and a sling is passed around the tendon. The muscle is drawn away from the field (usually upward).
• The phrenic nerve is accurately mobilized and gently tented forward as the surgeon dissects upward (throughout the operation, the surgeon must remain vigilant of the dissected phrenic nerve, so that inadvertent traction is not applied to this crucial structure while attention is focused elsewhere) (Figure 2-23). The phrenic nerve leads to the C5 spinal nerve (Figures 2-24 and 2-25).
• C5 enters the posterior triangle by running posterior to the scalenus anterior and anterior to the scalenus medius. No matter how dense the scar, the anterior tubercles can be palpated and C5 can be dissected at this point (Figure 2-26).
• On rare occasions, it may be necessary to nibble the anterior tubercle away and resect the slips of scalenus anterior, so as to completely dissect out the spinal nerve up to the intervertebral foramen. At this point, venous oozing is a nuisance and is controlled by judicious cautery and packing.
• The dorsal scapular nerve leaves C5 proximally. If stimulation of C5 results in levator scapulae contraction, the welcome inference is that axons are viable to at least that point and that grafts can be led from there, if necessary (see Figure 2-24).
