Nerve Transfers for Brachial Plexus and Upper Extremity Nerve Injuries

Nerve transfer in the setting of both brachial plexus injury (BPI) and peripheral nerve injury (PNI) has become a valuable tool in the armamentarium of the hand and upper extremity surgeon. Depending on the level of injury, numerous donor nerves exist which can be utilized to re-animate deficient motor functions and/or restore sensation. Commonly after BPI, the patient is left with deficiencies in shoulder abduction, external rotation and/or elbow flexion/extension for which there are a host of available nerve transfer options. Unfortunately, we do not yet have many successful techniques to restore intrinsic hand function after complete BPI, however there are numerous techniques to improve hand function in the setting of PNI. Multiple donors are often available, and the decision for which to harvest is at the discretion of the surgeon, taking into consideration the presence of concomitant injury, regenerative distance and deficits which may result from donor harvest. For the best chance at an optimal outcome after nerve transfer, progressive rehabilitation programs for both motor and sensory re-education are critical. Multiple techniques for restoration of motor and sensory function after BPI and PNI are described below, as well as a description of typical rehabilitation protocol after nerve transfer.

Introduction

Brachial plexus injuries can be both devastating and life altering. Most are traumatic in nature resulting from penetrating trauma, falls, and motor vehicle collisions. Injuries involving a high velocity torque of the head away from the shoulder can result in preferential injury to the upper plexus, whereas violent overhead abduction of the arm with traction leads to lower plexus injury. It is difficult to quantify the specific number of brachial plexus injuries occurring each year, but we do know the incidence is increasing due to improvements in trauma related care, which in turn leads to better survivability of traumatic incidents like high velocity motor vehicle collisions. There are a wide range of surgical treatment modalities for the brachial plexus injury, including neurolysis, direct repair, nerve grafting and nerve transfer. In certain scenarios secondary soft tissue or bony procedures are considered as well, which include tendon transfer, free functioning muscle transfer and arthrodesis in a salvage situation. The choice of treatment hinges on a multitude of factors, but mainly which part of the plexus is involved, the mechanism of the injury, and timing from injury, as nerve grafting and transfer are ineffective past 12 months. The remainder of this chapter will focus mainly on techniques in nerve transfer.

Reconstruction of the brachial plexus injuries should aim to restore both motor and sensory function. Rather than trying to classify motor deficits by the specific nerve dysfunction (e.g., high median nerve deficit), it may be simpler to approach the reconstructive plan by noting the deficits that warrant restoration: shoulder abduction/external rotation, elbow flexion/extension, forearm pronation/supination, wrist flexion/extension, and finger flexion/extension. Surgical planning is then tailored to identify potential donors and match them to functional needs.

The pattern of injury should be considered when determining the timing of surgery. Open injury associated with neurological deficit should be explored once the patient is stable. Closed injuries may require additional workup such as computed tomography myelogram, magnetic resonance imaging, and electrodiagnostic testing, as well as a period of observation if neuropraxia or partial nerve injury is suspected. CT myelogram can aid in determining the presence of a preganglionic injury by demonstrating absent nerve rootlets or pseudomeningocele. MRI is also highly sensitive in detecting nerve root avulsion and has the advantage of being noninvasive, but image quality can be compromised in patients with prior neck or upper extremity surgery. Electromyography also aids in determining pre- or postganglionic injury. Fibrillation potentials in proximal musculature, preserved sensory nerve action potentials, and the absence of somatosensory (SSEP) and motor evoked potentials (MEP) are characteristic of preganglionic pathology. Postganglionic injuries will typically have preserved SSEP’s and MEP’s. Regardless of diagnostic modality, findings suggestive of preganglionic injury would lead the surgeon away from nerve reconstruction in favor of secondary reconstructive procedures. Associated injuries should also be considered and evaluated, as they may affect the availability of donor nerves (e.g., rib fracture) or the overall treatment strategy. This is especially true when a patient may have concomitant spinal cord and brachial plexus injuries.

Motor Restoration

Due to the rapid rate of muscle atrophy (5% per month) after denervation and the slow rate of nerve regeneration (1 mm/day), reinnervation of denervated muscle should be attempted as soon as possible, once the diagnosis has been confirmed by EMG/NCS testing and serial clinical examinations, and neuropraxia, if present, has been allowed to resolve. It is important to rule out multilevel injuries, such as concomitant spinal cord and peripheral nerve injuries.

Shoulder Abduction and External Rotation

Shoulder stability, which is crucial for elbow flexion, is largely maintained by the 4 rotator cuff muscles. Without a functioning rotator cuff, there is subluxation of the humeral head in the glenohumeral joint. During attempted elbow flexion, part of the force is spent on reducing the humeral head back into the glenohumeral joint, prior to being converted into elbow flexion. This should be considered when formulating a reconstructive plan for patients lacking both shoulder motion and elbow flexion.

Shoulder abduction is mainly powered by the axillary nerve, which innervates teres minor as well as the deltoid. Common donor nerves for axillary nerve neurotization include the medial pectoral nerve, a triceps branch of the radial nerve, and intercostal nerves. Using a triceps branch of the radial nerve allows the most distal neurotization, closest to the target muscle, and often results in the quickest recovery of function. It also is the easiest for cortical retraining since elbow extension is often synergistic with shoulder abduction. This procedure is performed by posteriorly utilizing the interval between the long and lateral heads of the triceps to expose the triangular and quadrilateral spaces. The radial nerve is identified in the triangular space, and the axillary nerve at the quadrilateral space ( Fig. 1 ). As it passes through the quadrilateral space, the axillary gives off a branch to the teres minor, then gives off anterior and posterior divisions. The anterior division is the main motor supply to the deltoid and has from 1 to 3 branches. These are then intraneurally dissected and transected as proximal as possible. The radial nerve branch to the medial of the triceps is then identified adjacent to the radial nerve distal to the origin of the branches to the lateral and long heads of the triceps ( Video 1 ). The donor nerve transected as distally as possible, and coapted to the anterior axillary branch(es). Unfortunately, a triceps branch of the radial nerve may not always be available, and other donors may need to be considered. The medial pectoral nerve and intercostal nerves are alternatives, but both have longer regeneration distances and are harder to rehabilitate.

Shoulder external rotation and forward flexion are achieved by the actions of the supraspinatus and infraspinatus muscles, which are both innervated by the suprascapular nerve. If the spinal accessory nerve is functional and available, it can be transferred to the suprascapular nerve to restore external rotation and forward flexion. Operative techniques involving both anterior (patient supine) and posterior (patient prone) approaches have been described. The posterior approach may have the advantage of technical ease in releasing the suprascapular ligament and thereby decompressing the suprascapular nerve. In addition, the nerve coaptation site is closer to the target muscles, which allows for decreased time to reinnervation. Furthermore, the posterior approach allows for more distal dissection and mobilization of the descending branch of the spinal accessory nerve, which may help to preserve innervation of the upper trapezius muscle. To carry out the procedure, the patient is placed in the lateral or prone position. The suprascapular notch is marked by bisecting a line from the medial upper border of the scapula to the lateral edge of the acromion. The location of the medial branch of the spinal accessory nerve is estimated using a line from the spinous processes of the thoracic spine to the lateral acromion. The branch is typically 40% distance from the midline. The incision lies parallel to and 2 cm proximal to the scapular spine, and is approximately 7 cm long. The trapezius muscle is split to identify the medial branch of the spinal accessory nerve, which is then tagged with a vessel loop ( Video 2 ). The suprascapular nerve is then identified after distal retraction of the supraspinatus, as it passes under the suprascapular ligament in the suprascapular notch ( Fig. 2 ). The insertion of the omohyoid is a landmark to the notch. The suprascapular artery lies superior to the ligament and must be dissected and mobilized prior to ligament release. Once release, the nerve is visualized, noting that it gives its branches to the supraspinatus just distal to the ligament. The medial branch of the spinal accessory nerve is then sectioned distally, and sutured to the suprascapular nerve which is sectioned proximally.

Alternatively, if the thoracodorsal nerve (posterior cord, contributions from C6, C7 and C8) is functional, it can serve as a donor to reinnervate the suprascapular nerve. When harvesting the thoracodorsal nerve, it can be harvested together with the accompanying vessels as a vascularized nerve, potentially improving the regeneration speed. Unfortunately, harvesting the thoracodorsal nerve will denervate the latissimus dorsi muscle, which helps with shoulder adduction and is often used as a backup option to restore elbow flexion. One must be aware of these consequences when considering utilization of the thoracodorsal nerve as a donor.

If axillary and suprascapular nerve function cannot be adequately restored, and shoulder subluxation cannot be corrected, shoulder arthrodesis may be a reasonable option for stabilization and pain control, the latter of which may result from instability. This may also improve volitional control of shoulder motion through motion at the scapulothoracic joint. The trapezius muscle, which is innervated by the spinal accessory nerve, plays an important role in scapular stabilization and scapulothoracic motion. If shoulder fusion is a consideration, one should preserve the trapezius muscle function in order to maximize scapulothoracic motion.

Elbow Flexion

In dealing with loss of elbow flexion due to injuries involving C5, C6, and C7 at the root or trunk level, or in the setting of isolated musculocutaneous nerve injury, the functioning motor fascicles from either the ulnar or median nerve may be used as a donor to neurotize the biceps and brachialis, which serve as the main elbow flexors. In some patients, if radial nerve function is intact, brachioradialis alone may be strong enough to provide elbow flexion.

Using a flexor carpi ulnaris (FCU) fascicle of the ulnar nerve to reinnervate the biceps muscle for elbow flexion restoration was first described by Oberlin in 1994. Subsequently, double fascicular transfer using a flexor carpi radialis (FCR) fascicle of the median nerve in addition to an FCU fascicle of ulnar nerve to reinnervate the brachialis and biceps respectively was reported to have improved results. ^, However, subsequent comparative studies investigating single versus double fascicular transfers have not demonstrated superiority. ^, The surgical technique for the double fascicular transfer begins with an incision over the bicipital sulcus on the anteromedial brachium, beginning 4 cm from the axilla and 4 cm from the medial epicondyle. The musculocutaneous nerve is identified between the biceps and brachialis, and the branches to each muscle are isolated. The median and ulnar nerves are then identified in the brachium. The motor fascicles are located medially in the substance of the nerve, and the expendable ulnar motor fascicles are located in the lateral or central part of the nerve ( Fig. 3 ). Internal neurolysis is performed of both nerves to identify fascicles of appropriate caliber and length for transfer. A handheld nerve stimulator is used to confirm innervation of the FCR and FCU prior to any nerve division ( Video 3 ). The brachialis branch is neurolysed and divided, then moved toward either the median or ulnar nerve to accommodate the best match in relation to caliber and length. A similar process is followed for the biceps branch. The donor nerves are then divided as distally as possible to facilitate a tension free coaptation.