Emerging techniques for nerve repair: nerve transfers and nerve guidance tubes.

Peripheral nerve injury is a serious health concern for society, affecting 2.8% of trauma patients, many of whom acquire life-long disability.52 For example, approximately 360,000 people in the United States experience upper extremity paralytic syndromes yearly, resulting in 8,648,000 and 4,916,000 restricted activity days and bed/disability days, respectively.23 Because peripheral neurons spontaneously sprout new axons after injury, patients with milder severity nerve injuries improve spontaneously, but many patients have more severe injuries that have a poor natural history to recover.16 Most severe injuries are associated with nerve injury gaps or lengthy scar within the nerve that prevents regenerating axons from effectively innervating the distal nerve stump.44 These are managed with a nerve repair of the divided nerve or, for the usual scenario of gaps longer than 1 cm or scar segments that need to be resected, placement of interposed nerve grafts.47 The nerve grafts provide a pathway for regenerating axons from the proximal nerve stump to innervate the distal one.45 However, recovery after nerve graft repair is limited by incomplete and non-specific regeneration and variable clinical results.27,43 Based on sound and solid experimental literature over the past half century, peripheral nerve surgeons in the past three decades have been increasingly using alternative techniques to interposed nerve autografts in an attempt to improve outcomes. For lengthy nerve injuries, or for those very proximal ones in which the spinal nerve root has been or are likely avulsed from the spinal cord, the use of nerve transfers has emerged.35 For short injury gaps, surgeons are using nerve guidance tubes in place of nerve grafts to perform the repair.6 This chapter reviews the rationale, principles, and theoretical advantages that these state-of-the-art techniques offer to the surgeon and their patient. Readers are encouraged to read other literature and reviews on each of these topics, which are provided in the references cited at the end of this chapter, for more detailed information as appropriate. NERVE TRANSFERS Nerve transfers, also referred to as “neurotization,” involve the repair of a distal denervated nerve element using a proximal foreign nerve as the donor of neurons and their axons, which will reinnervate the distal targets. The concept is to sacrifice the function of a (lesser valued) donor muscle to revive function in the recipient nerve and muscle that will undergo reinnervation.50 Since their first report by Tuttle64 in 1913 and popularization by Narakas49 three decades ago, nerve transfers have been used increasingly for the repair of brachial plexus injuries, especially in cases in which the proximal motor source of the denervated element is absent because of avulsion from the spinal cord.43 Increasingly advocated are the use of transfers in situations in which the proximal motor source is available, but the regeneration distance is so long that the outcome would be poor. A nerve transfer into the denervated distal nerve stump close to the motor end-organ would then restore function, which would not be possible otherwise.51 The use of nerve transfers has, therefore, been a major advance in the field of brachial plexus nerve reconstructive surgery, with many different ingenious transfers associated with improving results, as reported and reviewed recently.8,21,42,57,62 The anatomic and physiological principles that underlie nerve transfers are relatively straightforward. Because motor recovery has been the main goal, the choice of a donor nerve element that has a reasonable aliquot of motor fibers is required.50 The loss of the muscle denervated by transferring the donor nerve must not represent loss of important or critical function.31 Obviously, the value of the neuromuscular element to be reinnervated must greatly exceed the utility of the sacrificed one. An excellent compromise is achieved if some function of the donor muscle can be retained, by using only a portion of the nerve as the donor, exemplified by the use of only the distal terminal branch of accessory (transferred to suprascapular nerve), thereby sparing proximal branches to trapezius muscle.43 There are several important principles to adopt in order to maximize outcome in nerve transfers, the first of which is to reinnevate the recipient nerve as close to the target muscle as possible.51 An outstanding example of the latter is the Copyright © 2006 by Lippincott Williams & Wilkins 0148-703/06/5301-0185