Transfers to Restore Shoulder Function II—Medial Triceps Nerve to Axillary Nerve Transfer
Upper trunk brachial plexus injuries and other proximal injuries often cause loss of axillary nerve function and denervation of the deltoid, the major abductor of the shoulder. In patients with preservation of radial nerve function, abduction can be effectively restored via transfer of one of the triceps branches of the radial nerve to the axillary nerve.8,17–19 This transfer is commonly performed in conjunction with the accessory to SSN transfer, described previously. Use of the lateral and long triceps branches has been described, but the medial triceps branch is preferable, due to its independence, long reach, and ease of dissection.8 Exposure for this transfer is provided through an incision extending from the quadrilateral space distally along the posterior arm to the midhumerus. At the proximal end of the incision, the axillary nerve is identified within the quadrilateral space and dissected as far proximal as possible, to ensure inclusion of the branch to the teres minor. Often, the lateral brachial cutaneous nerve, a branch of the axillary nerve, is encountered first, coursing around the posterior edge of the deltoid. It can then be traced back to the main nerve trunk.
The medial triceps branch of the radial nerve is easily identified in the posterior arm, running alongside the main radial nerve, in the interval between the long and lateral heads of the triceps. As the medial triceps branch runs independently for a long distance, it can be readily dissected free, verified with nerve stimulation, and transposed superiorly, where a tension-free coaptation is made to the axillary nerve at the level of its emergence from the quadrilateral space8 (Fig. 2). Of course, the radial nerve is often involved in brachial plexus injuries, and intact radial nerve function is a prerequisite for this transfer.
Double Fascicular Transfer to Restore Elbow Flexion
The results of nerve transfers to restore elbow function can be dramatic. Early efforts in this area involved the use of intercostal or pectoral nerves, with some success.4 In 1994, Oberlin described the use of branches of the ulnar nerve as the donor, transferred to the biceps branch of the musculocutaneous nerve at the level of the distal brachium, thus greatly shortening the reinnervation distance. His initial series consisted of 4 patients, 3 of whom achieved M4 level elbow flexion.5 Humphreys and Mackinnon have subsequently demonstrated that the classic Oberlin transfer can be augmented by transfer of a redundant median nerve fascicle to the FCR or FDS to the brachialis branch, the so-called “double-transfer.”20–22
The procedure is performed with the patient in the supine position with the arm extended. An incision is made over the biceptal groove in the medial arm. The brachial artery, median, and ulnar nerves are exposed. The musculocutaneous nerve is identified lateral to these structures, deep to the biceps muscle. It is dissected out distally, exposing the branches to biceps and brachialis. The donor nerves are then prepared. By careful nerve stimulation, a median nerve fascicle can be identified with FCR or FDS function. There is a great deal of redundancy in these functionalities; therefore, one fascicle can usually be harvested without yielding a donor deficit. However, once the fascicle is identified and teased away, the remaining fascicles should be tested to ensure preservation of function. In a likewise fashion, an FCU fascicle of the ulnar nerve is identified, tested, and prepared for transfer. Again, the donor fascicles should be dissected out for sufficient length so that the nerve coaptations can be performed without tension and as close to the recipient muscles as possible8 (Fig. 3).
Several studies have been published reporting excellent long-term results from both the classic Oberlin transfer and the double transfer for elbow flexion.5,7,23–25 However, by including the brachialis muscle, the double transfer seems to confer additional functional benefit, especially in terms of increased flexion strength.20,26 In 2005, Mackinnon et al20 presented a series of 6 patients, all of whom regained M4 or M4+ elbow flexion function after the double transfer, at a mean follow-up of 20.5 months. As a further testament to the value of the double transfer, Oberlin and colleagues have adopted the technique, publishing in 2006 a series of 10 patients who had undergone the procedure. All 10 recovered elbow flexion to the M4 level and were able to lift between 1 and 4 kg of weight, at 12 months mean follow-up.26
Anterior Interosseous Transfer to Restore Ulnar Intrinsic Function
Recovery of ulnar intrinsic function is typically poor after a proximal ulnar nerve injury, even with prompt and appropriate nerve repair.27,28 Tendon transfers can be used to augment or reproduce ulnar intrinsic function, but with variable results.29 Where median nerve function is intact, the distal anterior interosseous nerve (AIN) can be effectively transferred to the ulnar deep motor branch to restore function.30,31 The transfer was initially described with an end-to-end coaptation; however, the terminal AIN can be transferred in a reverse end-to-side fashion to the ulnar nerve, to “supercharge” the motor fascicle of a recovering ulnar nerve after proximal repair.32 In our practice, we perform this transfer regularly for any ulnar nerve repair proximal to the elbow.
A longitudinal palmar incision is used to expose the contents of Guyon canal, and it is extended proximally in a zigzag fashion across the wrist crease and into the distal forearm to provide exposure of the AIN.33 The ulnar motor branch is identified as it dives deep to the origin of the flexor digiti minimi muscle at the hamate hook. Under operative microscopy, the motor fascicle is readily separable from the remainder of the nerve into the distal forearm. The AIN is identified at the proximal border of the pronator quadratus muscle. The nerve is traced into the muscle a short distance and divided just before its terminal branches. Proximal dissection is performed to gain adequate length for a tension-free coaptation, either end-to-end or reverse end-to-side, as the clinical situation dictates33 (Fig. 4).
Anatomic studies have shown that there are more than 1200 motor axons in the ulnar motor branch at the wrist, compared to approximately 900 axons in the AIN, some of which are afferent sensory fibers.34 Despite this axonal mismatch, excellent results have been reported. In 1999, Battiston and Lanzetta reported the results of 7 cases of proximal ulnar nerve injury treated with an AIN to ulnar motor branch transfer. At a mean follow-up of 2.5 years, 5 patients experienced recovery to the M4 level, and 1 patient, an 11-year-old boy, had M5 level function.35 Three years later, Novak and Mackinnon reported a series of 8 patients, with a mean follow-up of 18 months. All patients experienced significant improvements in lateral pinch and gripping strength. Only 1 patient required subsequent tendon transfer, to restore small finger adduction.30
Numerous sensory transfers have been described, to restore sensation after ulnar, median, or radial nerve injuries, or to restore critical sensation after brachial plexus injuries.8,33,36–40 All of these transfers are based on the principle of sacrificing nerves that provide noncritical sensation to restore essential hand or digital sensation. For less critical sensory nerves, an end-to-side nerve transfer can be performed, thus preserving sensation in the donor dermatome. Experimental studies have shown that in the absence of injury to the donor nerve, only sensory axons will traverse such a repair.41–43 Most authors agree that the end-to-side technique can provide protective sensibility to noncritical areas, but higher levels of sensory recovery are not typical.33
Median nerve sensation is critical for fine manipulation and tip-to-tip pinch. Restoring sensation to the radial aspect of the thumb and ulnar side of the index finger are of utmost priority after median nerve injury, and in the past neurovascular island flaps have been used to restore sensibility to these areas. The fourth webspace and dorsum of the hand are less critical sensory distributions, and the nerves which provide sensation to these areas are potential donors for nerve transfers. Brown and Mackinnon describe a trio of nerve transfers designed to restore critical sensation after median nerve injury.33 In this procedure, the dorsal cutaneous branch of the ulnar nerve is transferred end-to-end to the branch of the median nerve to the thumb, first, and second webspaces. The ulnar nerve branch to the fourth webspace is transferred in an end-to-side fashion to the third webspace branch of median nerve. The ulnar sensory branch is also transferred in an end-to-side fashion to the distal cut end of the dorsal sensory branch of ulnar nerve, with an autograft, to preserve protective sensation in the donor site44 (Fig. 5).
The early phase of rehabilitation after nerve transfer is similar to any nerve injury, with a focus on range of motion and edema control. As function improves in the recipient muscle units, a program of reeducation is initiated, with intensive practice and repetition.45 Retraining is more easily achieved when a synergistic transfer is used. For sensory transfers, early behavioral reinforcement is of proven benefit, with patients who undergo early sensory reeducation having less severe paresthesias and better 2-point discrimination than those who do not.46 The process of cortical reorganization continues long after injury, so motor unit retraining with a certified therapist may be of benefit for many months, or even years, after injury.47
There is a large and rapidly growing body of literature regarding nerve transfers in the upper extremity. Despite this fact, and possibly because of it, there has been a slow adoption of these techniques by hand surgeons. A wide array of nerve transfers have been described, but there are a few for which the clinical evidence is very strong. These include the accessory to SSN and medial triceps to axillary nerve for shoulder abduction, the double fascicular transfer for elbow flexion, and the distal AIN to ulnar motor branch transfer for ulnar intrinsic function. These transfers are not technically challenging, require no extraordinary equipment or expertise, and have the potential to provide dramatic improvements in function for injuries which have been traditionally discouraging to treat. For complex injury patterns, such as brachial plexus avulsion injuries or multiple nerve injuries, nerve transfers form a therapeutic triad with tendon transfers and motor unit reeducation to achieve the fullest possible functional recovery (Fig. 6). The future will certainly bring the development of new nerve transfer procedures, as well as additional clarity regarding the value and indications for the transfers already described. The possible applications of nerve transfers are limited only by human anatomy and human imagination.
The author thanks Tom Dolan, MS, and Matt Hazard, Bio-Medical Illustrators with the University of Kentucky Academic Technology Group, for the preparation of illustrations.
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Keywords:Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
nerve transfers; nerve injury; nerve regeneration; brachial plexus