KEY NOTES CHAPTER 5: THE UPPER LIMB - Brachial Plexus Diagrams

Median nerve to radial nerve.

- An incision is made in the proximal volar forearm just below the antecubital crease. - The median nerve and its branches are identified by means of intraoperative stimulation of the flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), and palmaris longus (PL) muscles, the AIN, and the main median nerve. - Through the same incision, the radial sensory nerve can be identified and followed to identify the posterior interosseous nerve (PIN) and the branch to the extensor carpi radialis brevis (ECRB). - In preparation for nerve transfer, the radial nerve branches to the ECRB and the PIN should be separated as proximally as possible to maximize length for the transfer. - The nerve branch to the FDS and the FCR/PL branch of the median nerve should then be divided as distally as possible to allow a direct tension-free end-to end coaptation to the ECRB branch and the PIN.

Ulnar nerve ot AIN.

- An incision is made midway between the passage of the ulnar and median nerves at the elbow level. - The ulnar nerve is dissected at its entrance through the ulnar tunnel and then also distally. - The surgeon should then divide the flexor carpi ulnaris muscle (FCU) proximally, detach it from its proximal insertion at the medial epicondyle, and reflect it anteriorly and ventrally. - Nerve branches to the muscle are identified and carefully dissected. - The first and second branches to the FCU are measured, using a caliper, for their length from their emergence from the ulnar nerve and for their width in millimeters. Both branches are then separated with a scalpel. - The point of emergence of the AIN is dissected, just proximal to the arch of the flexor digitorum superficialis and 5 to 8 cm distal to the medial epicondyle. - Both branches to the FCU should then be sectioned as distally as possible, immediately proximal to their entry point into the muscle. - Both branches to the FCU are then brought into contact with the AIN.

AIN to ulnar nerve.

- An incision is made ulnar to the thenar crease in the hand. - It is then necessary to dissect the Guyon canal and to identify the deep motor branch of the ulnar nerve at the level of the hook of the hamate. - The deep motor branch of the ulnar nerve is traced from about 2 inches proximally from the distal wrist crease to the proximal border of the pronator quadratus. These fascicles must then be followed to the level of the anterior interosseous nerve (AIN). - The AIN begins to branch near the midportion of the pronator quadratus, and the nerve should be separated proximal to the split. - A direct repair of the AIN to the deep motor branch of the ulnar nerve is then completed.

Descending cervical plexus to upper and middle trunk.

- Some of the most important relationships in plexus surgery are those among the C5 and C6 spinal nerves, the phrenic nerve, and the descending cervical plexus. - The cervical plexus originates from C3 and C4. - The phrenic nerve has input from C3, C4, and C5. - The descending cervical plexus usually consists of several branches that then branch several more times to eventually innervate the strap muscles and skin of the neck

Median (Oberlin II / Mackinnon) and ulnar nerve (Oberlin I transfer) to musculocutaneous nerve.

- The biceps and brachialis nerve branches (musculocutaneous nerve branches) are dissected proximally and transferred to the donor median and ulnar nerves. - The flexor carpi radialis tendon is explored at the wrist level. - One fascicle of the flexor carpi ulnaris on the lateral border of the ulnar nerve and one fascicle of the flexor carpi radialis on the medial border of the median nerve are harvested. - Next, one fascicle from each of these nerves is partially cut out. - Donor nerve fascicles are separated and are sutured to musculocutaneous nerve branches.

Radial nerve to axillary nerve (Branch of long head of triceps to axillary: Leechavengvongs (Bangkok) procedure).

- The brachial plexus is dissected first at the level of the axilla. - Intraoperative nerve action potential examination is required to make a correct diagnosis and to repair the damaged nerve. - The posterior cord is divided into the axillary and radial nerves. The lateral cord is divided into the musculocutaneous and median nerves. The medial cord is divided into the median and ulnar nerves. - The radial nerve should be electrically tested after branching off the axillary nerve. - A fascicle from the radial nerve is harvested and assessed for viability using electrical nerve stimulation. - Viable nerves may possibly be transferred to the nerve branch of the triceps medial head. - The axillary nerve is cut after branching from the posterior cord and is sutured under the microscope to the partially cut radial nerve.

Pectoral branches (medial) to musculocutaneous nerve.

- The lateral cord is traced distally to the cord's contribution to the median nerve medially and the coracobrachialis branches and musculocutaneous nerve (MCN) laterally. - The MCN is encircled with a Penrose drain and is usually split away from the lateral cord contribution to the median nerve more proximally. Thus a suitable entry point for anastomosis with the shorter medial pectoral branches is created so that the juxtaposition can be done gracefully and without tension. - Medial pectoral branches, arising from the medial cord, are located by dissecting out the axillary artery. Usually the medial pectoral branches are found close to and somewhat beneath the largest pectoral arterial branches. - The medial pectoral nerve branches reach the pectoral muscles. - After the pectoral branches are cut close to the muscle, they are moved laterally, usually beneath the axillary artery, and sewn end-to-end with 7-0 Prolene to either a partially or a completely sectioned distal MCN.

Intercostal nerves to musculocutaneous nerve

- The procedure provides useful biceps and brachialis function in about 40% to 50% of cases, depending on the series and the nature of the patients selected for the procedure. -Some controversy exists over which intercostal nerves to use to maximize motor axon outflow, as well as over the level at which they should be sectioned. - We prefer to use the third, fourth, fifth, and sometimes sixth intercostal nerves and usually section them at the anterior axillary line. - The incision needs to be combined with one made to expose the plexus at the cord-to-nerve level in the axilla. - The intercostal nerves are found under the inferior surface of their respective ribs, below the intercostal vessels, in the neurovascular plane. With upward retraction on the rib, the nerve can be identified, encircled by a Vasaloop, and then dissected away from the intercostal artery and vein. - In women, the superficial branch of the T4 intercostal nerve can be spared and only the deep (motor or muscular) branch used. This preserves sensation on and around the nipple. - We dissect out lengths of 4 or 5 inches, extending from the posterior axillary line. - The intercostal nerves are sectioned anteriorly at the level of the anterior axillary line and brought back to be tunneled through axillary fat to reach the axillary level of the plexus. - They are then sewn together directly to the MCN, which has been split away from the lateral cord contribution to the median nerve, or to the axillary nerve. - Care must be taken not to lacerate the pleura. If this is done, it is repaired with 4-0 silk on a fine needle. - It is sometimes useful to harvest a small piece of pectoral or intercostal muscle to be sewn in place as a stent or stamp for closure of the hole.

What incisions are used to access the brachial plexus?

1. Supraclavicular ∘ Parallel to clavicle or posterior border of sternocleidomastoid, +/- osteotomy of clavicle. ∘ Gives access to roots, trunks and suprascapular nerve. 2. Infraclavicular ∘ Incision in deltopectoral groove. ∘ Gives access to cords and branches. ∘ Pectoralis minor is detached from coracoid process to improve exposure. 3. Combined ∘ Incisions joined / kept separate across clavicle.

What are the common patterns of injury?

C5-6 injury (15% - upper trunk). • Erb's palsy. • Affects shoulder stability, elbow flexion, forearm supination, sensation. C5-7 injury (35% - upper and middle trunks) • In addition to above, elbow, wrist and finger extension may be affected (contribution of C7 is variable). C8-T1 injury (10% - lower trunk). • Klumpke's palsy. • Affects hand intrinsics, +/- extrinsics, sensation (variable contribution of C7). • Involvement of lower roots → Horner's syndrome. C5-T1 injury (75% - pan-plexus). • Insensate flail arm.

Accessory nerve to suprascapular nerve

The distal accessory nerve can be utilized when (1) useful lead-outs from C5 or C6 are not available for neurotization of the suprascapular nerve (SCN), or (2) the surgeon wishes to use such lead-outs for other destinations in the plexus. - The distal accessory nerve can be mobilized and sewn either end-to-end or by means of an interpositional graft to the SCN. - Stimulation of CN XI produces muscular contraction of the trapezius and sternocleidomastoid. - The SCN is dissected back into the upper trunk and is divided through viable tissue. - The mobilized accessory nerve is divided so that it can be tunneled beneath some of the supraclavicular fat pad and sewn by 7-0 Prolene to the mobilized suprascapular nerve.

Summarise the nerves arising from the roots 2.

• Dorsal scapular (C5) - rhomboids, levator scapulae. • Long thoracic (C567) - serratus anterior.

Summarise the nerves arising from the lateral cord 3.

• Lateral pectoral (C567) - clavicular pectoralis major, pectoralis minor. • Musculocutaneous (C567) - coracobrachialis, biceps, brachialis. • Median (C5678, T1) - formed by medial and lateral cords.

Summarise the nerves arising from the medial cord 5.

• Medial pectoral (C8, T1) - sternocostal pectoralis major, pectoralis minor. • Medial cutaneous nerve of the arm (C8, T1). • Medial cutaneous nerve of the forearm (C8, T1). • Ulnar (C8, T1) - some forearm flexors, hand intrinsics. • Median (C5678, T1) - formed by medial and lateral cords.

Summarise the nerves arising from the upper trunk 2.

• Suprascapular (C56) - supraspinatus, infraspinatus. • Nerve to subclavius (C56) - subclavius.

Summarise the nerves arising from the posterior cord 5.

• Upper subscapular (C56) - subscapularis. • Thoracodorsal (C678) - latissimus dorsi. • Lower subscapular (C56) - subscapularis, teres major. • Axillary (C56) - deltoid, teres minor. • Radial (C5678, T1) - triceps, anconeus, brachioradialis, forearm extensor muscles.