Nerve Transfers (Neurotizations)

Specifically, nerve transfers involve re-assigning an “expendable” or redundant working nerve, part of a nerve (fascicle), or a nerve branch (donor) to a more important, nonfunctioning nerve (recipient).

The use of and enthusiasm for nerve transfers have increased dramatically in the past two decades largely due to the creative contributions of innovators such as Drs. Christophe Oberlin and Susan Mackinnon. The introduction of a fascicular transfer by Oberlin et al. (1994)³ for upper trunk injuries catalyzed the transformation. This procedure introduced the concept of fascicular transfer by using functioning ulnar nerve fascicles supplying the flexor carpi ulnaris to be selectively transferred onto the nerve to biceps with excellent results.^3–5

The new era of nerve transfer has created a major controversy in brachial plexus surgery now—the role of nerve grafts versus nerve transfers in postganglionic injuries. This issue remains largely unresolved. The advantages and disadvantages of performing nerve transfers over nerve grafts are listed in Tables 198-1 and 198-2. As can be seen, the advantages of performing nerve transfers may outweigh those of brachial plexus nerve grafting. In fact, in the event of patients sustaining panplexal nerve injuries secondary to multiple root avulsions, nerve transfers may be the only viable form of repair.

TABLE 198-1 Advantages of Performing Nerve Transfer versus Nerve Graft

TABLE 198-2 Disadvantages of Performing Nerve Transfer versus Nerve Graft

Surgical Anatomy

The brachial plexus is formed by the ventral rami of the fifth to eighth cervical and the first thoracic nerve roots. It is essential to remember that the nerves emerge between the scalenus anterior and medius (interscalene triangle) to form trunks in the supraclavicular fossa. The divisions of the brachial plexus are retroclavicular while the cords are infraclavicular and named as such in relation to the axillary artery.

Supraclavicular Exploration

The key muscles for the supraclavicular exploration of the brachial plexus are the omohyoid (deep to which lies the fat pad covering the plexus) and the scalenus anterior (deep to which lie the nerves). The latter is often difficult to identify especially when there is extensive scarring. They are then identified indirectly as the structures that lie beneath the phrenic nerve. The phrenic nerve may be identified visually as the only neural structure (other than the nerve to subclavius) that passes from lateral to medial in the root of the neck (Fig. 198-1). If scarring is extensive, blind neural stimulation using 0.1–2 mA of current may provoke capnographic changes if not frank diaphragmatic contraction that may guide the surgeon to the approximate location of this key structure before sharp dissection is commenced.⁸ The phrenic nerve can then be traced back to the C5 nerve via its contribution to the former. From here, the C5 nerve can then be traced to the upper trunk. Proximal and distal dissection allows identification of C6 and the divisions of the upper trunk. The suprascapular nerve is the key target in this exploration and can be found superior, lateral, and posterior to the upper trunk. Its direction confirms its identity. It parallels the omohyoid and runs posteriorly obliquely to the scapular notch. In the event of a complete rupture of the C5 and C6 nerves, the distal components of the plexus can be found near, behind, or even below the clavicle.

FIGURE 198-1 Intraoperative photograph. The phrenic nerve (black arrows) can be seen crossing from lateral to medial over the scalenus anterior (SA). The C5, C6 nerves and the upper trunk (asterisk) pass behind and lateral to this muscle but anterior to the scalenus medius (SM). The nerve to subclavius (black arrowheads) and the accessory phrenic nerve (white arrowhead) are also depicted.

The spinal accessory nerve can be identified by exposing the lateral aspect of the supraclavicular incision. The nerve can be identified reliably a few centimeters above the clavicle on the anterior surface of the trapezius at its medial border. Other smaller, mostly sensory nerves frequently seen in this location represent neural elements of the cervical plexus. These may produce weak contractions of the trapezius. In contrast, direct stimulation of the spinal accessory nerve produces powerful trapezius contraction.

Care has to be taken, during dissection, not to injure the lymphatic duct on the right and the chyle carrying thoracic duct on the left side. These elements are at risk during medial dissection such as with exposure of the lower trunk elements.

Infraclavicular Exploration

The key muscle in the infraclavicular exploration of the brachial plexus is the pectoralis minor. This may be approached either through the preferred corridor offered by the deltopectoral groove or a transpectoralis major (muscle splitting) exposure. The pectoralis minor is identified as the musculotendinous structure passing inferomedially from the coracoid process of the scapula to the third–fifth costochondral junctions. This anatomy also helps the surgeon to define ribs and the underlying intercostal nerves with a number. Division of the pectoralis minor muscle reveals the cords, terminal branches, and axillary vessels within the axillary sheath. Fat can treacherously encase these structures, especially the axillary and cephalic veins. Due care must be taken while retracting the pectoralis minor as the medial and lateral pectoral nerves arborize in the adjacent fat planes when penetrating this muscle.

The key neural structure to be identified here is the median nerve, which is characterized by a Y-shape at its take-off from both the lateral and medial cords. The median nerve helps navigation. The lateral root of the median nerve enters the lateral cord. The lateral cord can then be followed distally into the musculocutaneous nerve. Its medial root can be traced proximally into the medial cord and the medial cord can be traced to the ulnar nerve in the arm which lies in the biceps–triceps groove. The proximal median nerve is at first lateral to the brachial artery and crosses it ventrally in the mid-arm to gain its medial relation. At this point, the ulnar nerve, which lies medial to the brachial artery in the upper arm, begins descending posteriorly to eventually penetrate the medial intermuscular septum and pass behind the medial epicondyle.

It is important to realize that the musculocutaneous nerve provides its first branch to the coracobrachialis muscle and then penetrates this muscle. This must not be mistaken for the nerve to the biceps which is given off its lateral aspect in the mid-arm (typically 12 cm distal to the acromion). The nerve to the brachialis is given off further distally (approximately 17 cm distal to the acromion) and typically lies lateral to the terminal branch, the lateral antebrachial cutaneous nerve.⁹ The former is a pure motor branch, while the latter is a sensory nerve. The authors verify the nature of both these terminal divisions by tracing the brachialis branch until it arborizes on the muscle surface. A variation that has to be considered is the low take-off of the musculocutaneous nerve from the median nerve. This is important to consider especially when the median nerve is being considered as a donor for a simultaneous nerve transfer.

General Principles: Surgical Technique