Intraplexal or extraplexal nerve transfer (neurotization) procedures are being increasingly used as a management alternative for high-grade upper-extremity peripheral nerve injuries with outcomes that are either equivalent or improved compared with traditional exploration and grafting techniques. ¹ Preganglionic (i.e., spinal nerve root avulsion) injuries are particularly suited to treatment with nerve transfers because they transform a proximal-level injury to a far distal injury (placing regenerating axons closer to denervated motor end plates), and they allow for innervation of the target muscle without an interposition nerve graft. Moreover, nerve transfers obviate the need for exploration within the scarred traumatic area (where other bony or vascular injuries could be evident). ^{2,​ 3}

Upper trunk involvement is common in adult brachial plexus injuries and results in impaired elbow flexion, shoulder abduction, shoulder external rotation, as well as glenohumeral stability. Because elbow flexion and shoulder abduction and rotation are considered the most critical upper extremity functions, upper trunk brachial plexus injuries can have a devastating impact on a patient’s quality of life if function is not restored. Here we describe the management of upper trunk avulsion injuries after which spontaneous recovery is not possible. We focus on preoperative assessment of preganglionic lesions, the use of intraplexal and extraplexal nerve transfer procedures to reanimate shoulder and elbow movements and surgical outcomes.

72.2 Patient Selection

72.2.1 Physical Examination

Serial physical exaination assessments are critical in defining the pattern and severity of deficits after traumatic brachial plexus injuries. Evidence of an elevated hemidiaphragm and rhomboid or serratus anterior paralysis represent examination findings consistent with a preganglionic upper trunk avulsion. In contrast, the presence of Horner’s syndrome in this setting is suggestive of a T1 level preganglionic injury.

72.2.2 Electrodiagnostic Studies

Electrodiagnostic studies are generally first performed 4 to 6 weeks after injury to identify baseline values. Nerve conduction studies can be particularly valuable in determining a preganglionic versus a postganglionic root lesion. Denervation of posterior myotomes, absent motor action potentials, normal sensory nerve action potentials from clinically denervated skin, and absent somatosensory evoked potentials all represent findings consistent with preganglionic injuries. Nascent motor unit potentials, on the other hand, represent regeneration of injured axons and are good predictors of spontaneous recovery. ⁴

72.2.3 Imaging Studies

Imaging modalities may provide further confirmatory evidence of a preganglionic lesion. Plain film radiographs of the chest can be used to assess phrenic nerve function via diaphragmatic paralysis. Whereas root avulsion is often associated with pseudomeningocele formation, this imaging finding is not required for diagnosis. Although magnetic resonance (MR) imaging is often used to assess for avulsion-related pseudomeningoceles, computed tomography (CT)-myelography is the gold standard for identifying nerve root avulsions, in particular given its sensitivity in detecting small pseudomeningoceles. ⁴ Preganglionic injuries may also be associated with altered MR signal intensity in the spinal cord on the affected side, which can be due either to edema, hemorrhage, or myelomalacia. Further, changes in paraspinal muscle MR signal intensity suggest denervation and thus preganglionic injury. These changes potentially include edema and enhancement in the acute phase and volume loss in later stages. Finally, ongoing developments in MR neurography have allowed for overall improvements in the delineation of the anatomy and morphology of both proximal and distal plexal elements (e.g., the appearance of nerves and fascicles, including any abrupt changes in caliber or course) ⁵ (see ▶ Fig. 72.1).

72.2.4 Surgical Planning

Whereas a number of specific findings predominate in pure upper trunk (C5 and C6 nerve root) avulsion injuries, in practice, such injuries are associated with variable involvement of other plexal components, which in turn affects potential donor nerve options. For example, it is estimated that 15% of closed upper trunk injuries have subclinical C7 involvement. ⁶ In this instance, use of a donor nerve with a dominant C7 contribution (e.g., radial nerve) would be relatively contraindicated, depending on the combination of examination and electrodiagnostic findings. The main root contribution to the lateral and medial pectoral nerves is from C7 and C8, respectively. With pure upper trunk injuries, both lateral and medial pectoral nerve function may be maintained, allowing for sacrifice of the medial pectoral component (see later in this chapter) without the risk of compromising shoulder adduction.

72.2.5 Timing of Surgery

Taken together, the pattern and severity of brachial plexus involvement can be ascertained with high fidelity using serial assessments to help guide appropriate operative planning. The primary clinical dilemma is that early repair of nerve injuries yields the best surgical results, whereas spontaneous return of function, if it actually occurs, provides for vastly superior results than that observed after surgery. Given that adult motor end plates and muscle undergo irreversible fibrosis and atrophy approximately 12 to 18 months after denervation, it is critical to determine whether clinically significant motor improvement has occurred in the first 3 to 4 months after injury. Once it has been determined that clinically relevant motor improvement is not occurring (at 3 to 4 months after injury), surgical treatment should occur to allow for maximal nerve regeneration.

72.3 Preoperative Preparation

The patient is induced and general endotracheal anesthesia is administered. The patient’s involved upper extremity, in either the supine or prone position (as described below, depending on nerve transfer), is prepared and draped from the shoulder and axilla to the fingers and positioned on a swiveling side arm rest. Either short-acting or no neuromuscular blockade is ensured so that accurate intraoperative nerve stimulation trials can be performed. One of the lower extremities is prepared and draped in case harvest of a sural nerve graft is required. No local anesthesia should be used before assessment of the donor and recipient nerve status.

72.4 Operative Procedures

72.4.1 Reanimation of Shoulder Abduction

General Principles

Multiple nerve donor options can be used for reinnervation of the suprascapular (SSN) and axillary (AXN) nerves. As described here, the double transfer of the spinal accessory nerve (SAN) to SSN and radial nerve (RN) triceps branch to AXN has become a commonly used option in current practice. This double-transfer approach presents the potential functional advantage in that both shoulder abduction and external rotation are restored. A further advantage is noted given that triceps action is synergistic with shoulder abduction.

SAN to SSN Transfer

This nerve transfer is performed with the patient in either the supine or prone position. The prone position allows for mobilization of the SAN at a more distal portion, sparing further innervation to the trapezius muscle, but it still provides transfer of 1,500 to 3,000 myelinated axons. ^{7,​ 8} The prone position also obviates the need of repositioning when performing the RN to AXN transfer (described later herein) during the same anesthetic.

After positioning, the approximate locations of the donor SAN and recipient SSN are marked preoperatively in relation to the midline, medial scapular edge, and acromion ( ▶ Fig. 72.2). Accuracy with this step substantially facilitates operative identification of the nerves. The distal SAN and the SSN are marked at points 40% from the midline and 50% from the superior angle of the medial scapular edge, both in relation to the acromion, respectively. A surgical incision is then made as a transverse line spanning these two points lying above the spine of the scapula. The trapezius muscle fibers are split, and the superior transverse scapular ligament is palpated to identify the notch. The transverse scapular artery, which runs lateral to the SSN above the ligament, is protected during this dissection.

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