Journal of Hand Therapy xxx (2014) 1e9

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Journal of Hand Therapy journal homepage: www.jhandtherapy.org

Special Issue

Advances in nerve transfer surgery Amy M. Moore MD a, Christine B. Novak PT, PhD b, * a b

Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St. Louis, MO, USA Hand & Upper Extremity Program, Division of Plastic & Reconstructive Surgery, University of Toronto, Toronto, ON, Canada

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 June 2013 Received in revised form 15 December 2013 Accepted 15 December 2013 Available online xxx

Peripheral nerve injuries are devastating injuries and can result in physical impairments, poor functional outcomes and high levels of disability. Advances in our understanding of peripheral nerve regeneration and nerve topography have lead to the development of nerve transfers to restore function. Over the past two decades, nerve transfers have been performed and modified. With the advancements in surgical management and recognition of importance of cortical plasticity, motor-reeducation and perioperative rehabilitation, nerve transfers are producing improved functional outcomes in patients with nerve injuries. This manuscript explores the recent literature as it relates to current nerve transfer techniques and advances in post-operative rehabilitation protocols, with a focus on indications, techniques and outcomes. Ó 2014 Hanley & Belfus, an imprint of Elsevier Inc. All rights reserved.

Introduction Improved understanding of nerve injury and regeneration has lead to increased surgical options for patients with peripheral nerve injuries. One such option is the restoration of muscle function by nerve transfer. A nerve transfer involves coapting a healthy, expendable donor nerve to a denervated recipient nerve to restore function to the recipient muscle.1 Over the past few decades, nerve transfers have been performed to restore upper extremity function after devastating brachial plexus injuries. Recently, the options for nerve transfers have expanded and include more distal nerve transfers in the forearm. These procedures as well as the therapy provided post-operatively have continued to evolve with successful functional outcomes.2e5 This manuscript will review commonly performed nerve transfers for restoring motor function in the upper extremity. Specifically, this review explores the recent literature as it relates to current nerve transfer techniques and advances in post-operative rehabilitation protocols, with a focus on indications, techniques and outcomes. Indications, principles, and considerations of nerve transfers As microsurgical techniques and understanding of internal nerve topography have improved, the indications for nerve transfers have * Corresponding author. Toronto Western Hospital, Hand Program, 399 Bathurst Street, 2EW-422, Toronto, ON, Canada M5T 2S8. Tel.: þ1 416 603 5800; fax: þ1 416 603 5392. E-mail address: [email protected] (C.B. Novak).

also expanded. Previously, nerve transfers were reserved for unsalvageable brachial plexus injuries and now are well integrated into clinical practice and treatment algorithms for peripheral nerve injuries. Nerve transfers are a viable treatment option for patients with a proximal nerve root avulsion, with delayed presentation of high peripheral nerve injuries, following trauma with significant scarring at the site of the nerve injury, with large neuromas-incontinuity and/or with multi-level nerve injuries.4,6e8 A nerve transfer involves transfer of an innervated nerve or specific nerve fascicles to an injured denervated nerve to provide the opportunity for regeneration and reinnervation to the target motor fibers or sensory end organs. There are many advantages to performing nerve transfers. Transferring a viable nerve closer to the target end organ (muscle or skin) allows for earlier reinnervation and function compared to nerve graft or repair at a more proximal injury site. Because nerve transfers are performed close to the target end organ, interpositional nerve grafts are not needed, thus potentially increasing the nerve fibers reinnervating the target muscle. Most importantly, nerve transfers avoid operating in previously injured and scarred fields and therefore decrease operative time and minimize the risk of downgrading function.4,7e10 Planning motor nerve transfers requires a thorough knowledge of motor function and redundancy of innervation to particular muscle groups to identify donor nerves and fascicles that may be used for transfer. The theory related to the selection of the donor nerves is similar to tendon transfer: synergistic muscle actions from the donor and recipient nerve are preferred to antagonistic motor function. While it is possible to recruit and reeducate an antagonistic muscle action, the motor learning postoperatively is more intuitive when a synergistic donor nerve/muscle is selected for

0894-1130/$ e see front matter Ó 2014 Hanley & Belfus, an imprint of Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jht.2013.12.007

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transfer. Given the availability of nerve donors, this may not always be feasible and successful function has been reported with antagonistic transfers.11 Unlike tendon transfers, nerve transfers do not rely on amplitude and excursion of the tendon muscle unit and do not require transection of the insertion and attachments of the muscle. By reinnervating the recipient muscle rather than transferring the muscle, scarring and disruption of ideal tension across the muscle are avoided.6,7 Donor nerves should be expendable and not result in downgrade of donor function. Ideally, the motor donor function should be at least Medical Research Council (MRC) grade 4.8 Nerve coaptations are performed without tension and a tensionless repair is confirmed by taking adjacent joints through a full range of motion before inset.7 The ideal timing of nerve transfers remains an evolving concept. Motor function after nerve transfer, as with nerve repair and graft, is dependent on time and the number of motor axons reinnervating the target muscle fibers.4,12 The absolute time at which reinnervation of a muscle must occur to avoid chronic axotomy and chronic denervation is not known. However, reinnervation of the muscle by 12e18 months after injury is the currently accepted duration.7,8 Axonal regeneration occurs at a rate of approximately a millimeter a day or an inch a month.13 A nerve transfer performed earlier and closer to the motor endplate will provide earlier muscle reinnervation and thus maximize functional outcomes. Peri-operative considerations Patient understanding of the nerve transfer procedures is important to ensure initial treatment strategies are correctly implemented. We begin pre-operatively with patient education and describe the nerve transfers that will be performed. We focus on providing realistic expectations with regards to return of function and timing. We describe the short and long term rehabilitation that will be necessary post-operatively. In some cases, patients are instructed preoperatively in the motor retraining exercises by utilizing the contralateral arm and normal movement patterns. This provides the initial instruction regarding the combined muscle contractions and movements required in the post-operative period. The early perioperative care is directed toward protection of the nerve coaptation site, edema, proximal and distal joint range of motion, and pain control. Postoperative pain following the surgical procedure may be controlled in most cases with analgesics, edema control, early range of motion and hand therapy. There are some patients who continue to experience ongoing neuropathic pain that will negatively impact therapy and outcome.14e16 In these cases, referral to a multi-disciplinary pain management team may be necessary. Nerve transfers are performed without tension at the coaptation site. The immobilization that is required after nerve transfer is variable and dependent upon the location of the nerve transfers and concomitant procedures that have been performed. Typically, the nerve transfer coaptation is protected for 7e10 days. Initially a bulky dressing is used for 2e3 days following surgery and then depending on the type of transfer, an orthosis, sling or other restrictive dressing may be used. Nerve transfers for elbow flexion and those of the forearm and hand are typically immobilized for comfort for 7e10 days. Further immobilization is not necessary following the initial time period as coaptations are performed with laxity allowing full range of joint motion. If tendon transfers are performed at the same time as the nerve transfer, then the rehabilitation paradigm including immobilization are related to the specific tendon transfer will take precedence. After nerve transfers for recovery of shoulder function, the shoulder is placed in an immobilizer for up to 4 weeks. Four weeks is preferred if the pectoralis major muscle has been detached and reinserted to enable the brachial plexus exposure. The patient is allowed and encouraged to

perform intermittent range of motion of the elbow and hand to prevent stiffness. After four weeks, shoulder and elbow active and passive range of motion may be resumed. Treatment to restore motor function following reinnervation depends on restoration of muscle balance and reestablishment of normal movement patterns. While sensory reeducation is frequently included in therapy programs following injury to a sensory nerve, motor reeducation is less commonly considered following motor nerve injury and repair. The alterations in motor cortex mapping are well documented, in addition to shifts in the motor cortex with nerve transfers.17e20 Muscle imbalances occur due to muscle weakness associated with denervation. This may persist due to the learned compensatory movement patterns and persistent weakness of the reinnervated muscles. Motor reeducation is instituted to relearn normal movement patterns and muscle recruitment and reestablish muscle balance. Coordination of the sensory and motor systems is necessary to achieve sensorimotor control in the upper extremity and should include use of activitybased sensorimotor retraining with controlled movements and appropriate feedback learning.21e23 Specifically for nerve transfers, optimal outcome depends not only on the number of motor axons reinnervating the muscle but also on appropriate cortical remapping. Collectively, studies which have evaluated cortical mapping following nerve transfers provide evidence of the changes in the motor cortex following transfers and importance of relearning.17,18,24 The established sensorimotor cortical maps and motor patterns are no longer pertinent because of the alteration in the new proximal nerve source. Effective therapy programs must include not only range of motion and strengthening exercises to restore muscle balance but also motor retraining to encourage appropriate cortical mapping and normal movement patterns.5 Because of the new proximal nerve source, initially, muscle contraction of the newly reinnervated muscle requires “contraction” of the muscle from the donor nerve. Until the motor pattern is established, the patient may require co-contraction of the newly innervated muscle and “contraction” of the muscle from the donor nerve to induce the intended action. These relearning strategies may be assisted by utilizing cortical input of the normal movement from the uninjured contralateral side by using bilateral actions and exercises. In general, the motor relearning associated with nerve transfers is similar to relearning following tendon transfers; the more synergistic the action and based on the original motor pattern, the more effortless the recruitment and establishment of the motor pattern. The inclusion of sensorimotor re-education and the inclusion of normal movement patterns for appropriate cortical remapping. Effective learning of any new task requires useful feedback to provide immediate responses and should be modified as muscle imbalances and motor patterns change.21 Bimanual tasks will increase utilization of the injured extremity in self-care activities and work and provide the opportunity for input of normal movement patterns and purposeful movements. Strengthening sessions should be planned in consideration of reinnervated muscle physiology and biomechanics; short duration exercise sessions (i.e. less than 5e10 min) with slow onset contractions and begin in mid-range (place and hold) or gravity eliminated positions. The initial focus is directed to the correct recruitment of the reinnervated muscle and restoration of muscle balance to minimize overuse of the stronger muscles and learned compensatory motor patterns. Upper limb actions require composite motor patterns of the glenohumeral and scapular muscles to position and stabilize the upper extremity. Weakness of the shoulder complex muscles can result from disuse and compensatory movement patterns. Typically this produces weakness of the middle and lower trapezius and serratus anterior muscles with

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Fig. 1. The double fascicular nerve transfer involves transfer using fascicles from the intact median and ulnar nerves to the injured musculocutaneous to provide innervation for elbow flexion. Reproduced with permission from: Boyd KU, Nimigan AS, Mackinnon SE: Nerve reconstruction in the hand and upper extremity. Clin Plast Surg 2011; 38:643e660.

overuse of the upper trapezius muscle. Exercises to address the muscle imbalances in the cervicoscapular region will help to maximize upper limb function. Patient education and inclusion of a home program are necessary to optimize learning of new motor/ sensory tasks and should be modified through ongoing assessment. Nerve transfers for restoration of upper extremity function Numerous nerve transfers have been described to restore function to the upper extremity. Time and experience have led to a number of nerve transfers that are associated with positive, reproducible clinical outcomes. In the following section, we have outlined the currently preferred options for reconstruction of elbow flexion, shoulder, forearm and hand function. As further studies and advances are performed, preferences are likely to be revised. The specific sections are organized as to the preference of restoration of function after a traumatic brachial plexus injury (elbow flexion, shoulder function) and isolated radial, median and ulnar nerve injury. Sensory nerve transfers are not discussed but can be reviewed in Boyd et al.7

Nerve transfers for restoration of elbow flexion Upper trunk injuries of the brachial plexus (C5, C6, C7) are one of the most common brachial plexus injury patterns in adult trauma.25 This injury affects the function of the suprascapular, axillary and musculocutaneous nerves leading to dysfunction of shoulder external rotation and abduction, shoulder flexion and extension, and elbow flexion. In these types of injuries, restoration of elbow flexion is the first priority, followed by shoulder function. A number of nerve transfers have been described to restore musculocutaneous nerve function including transfer of the intercostal nerves, spinal accessory nerves, medial pectoral nerves and fascicles from intact median and ulnar nerves.2,25e27 As with any nerve transfer, physical examination is used to determine the availability of the donor nerves and dictates the chosen donor nerves for transfer to restore function. If hand function is preserved, then our preferred nerve transfer for restoring elbow flexion is a double fascicular transfer which involves transfer of redundant nerve fascicles from the median and ulnar nerves to the biceps brachii and brachialis branches of the musculocutaneous nerve.

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Fig. 2. A posterior approach is used for the spinal accessory to suprascapular nerve transfer and provides innervation for shoulder abduction and external rotation (AeC). Reproduced with permission from: Boyd KU, Nimigan AS, Mackinnon SE: Nerve reconstruction in the hand and upper extremity. Clin Plast Surg 2011; 38:643e660.

The commonly chosen redundant and expendable fascicles of the ulnar nerve innervate the flexor carpi ulnaris muscle and in the median nerve, the redundant fascicles innervate flexor carpi radialis, flexor digitorum superficialis and palmaris longus muscles (Fig. 1).7 In 1994, Oberlin et al described transfer of the ulnar nerve fascicle to the biceps branch of the musculocutaneous nerve.27 This group and others have reported their experience with this transfer with the majority of patients achieving Medical Research Council (MRC) strength 3 or better with no evidence of donor site morbidity.28e30 To increase the strength of elbow flexion, Mackinnon extended this idea by adding the reinnervation of the brachialis muscle with a fascicle from the median nerve.2 This combined nerve transfer has been shown to return elbow flexion strength, forearm supination with good results and minimal donor morbidity.2,31e34 Nerve transfers for restoration of shoulder function For upper brachial plexus injuries, shoulder recovery is secondary to elbow flexion in the hierarchy of restoration of function. Returning shoulder stability, abduction and external rotation is achieved by reinnervation of the suprascapular and axillary nerves, but reinnervation of both nerves is often dependent on the availability of donors. A recent meta-analysis demonstrated superior results with shoulder function and stability when both the suprascapular and axillary nerves were reinnervated as compared to single nerve reconstruction.34 Therefore, innervation of the

suprascapular and axillary nerves is preferable for optimal shoulder function. Many nerve donors have been described to innervate the suprascapular and axillary nerves; including the intercostal nerves, thoracodorsal nerve, medial pectoral nerve, long thoracic nerve, phrenic nerve, spinal accessory nerve, ipsilateral C7 root, contralateral C7 root, and hypoglossal nerve.35e39 Not all of these donor nerves have provided equal and consistent reinnervation of the target muscles with good shoulder function.25 Our current preference for restoring shoulder function is with transfer of the spinal accessory nerve to the suprascapular nerve and either a triceps branch or medial pectoral nerve to the axillary nerve. The transfer of the spinal accessory nerve to the suprascapular nerve can be performed from either an anterior approach or a posterior approach. The posterior approach provides adequate length of the spinal accessory nerve to avoid a nerve graft, allows coaptation distal to the suprascapular notch and closer to the muscle end-target thus decreasing the denervation time (Fig. 2).7,40,41 Although the approach was not specified, Merrell et al in their meta-analysis found that when the suprascapular nerve was reinnervated alone, shoulder abduction of MRC grade 3 or more was achieved in 92% of patients.34 The triceps branch to axillary nerve transfer is a common transfer to restore deltoid and teres minor muscle function. Our preference is to use the medial branch of the triceps as it is easily identified lying adjacent to the radial nerve and it has plenty of length to ensure a tensionless coaptation to the more proximal axillary nerve (Fig. 3).7 Others report use of the nerves to the long

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Fig. 3. For reinnervation of the deltoid muscle, a medial branch of the triceps to axillary nerve transfer is performed (A, B). Reproduced with permission from: Boyd KU, Nimigan AS, Mackinnon SE: Nerve reconstruction in the hand and upper extremity. Clin Plast Surg 2011; 38:643e660.).

head or lateral head of the triceps muscle.42e45 Importantly, reinnervation of the teres minor branch of the axillary nerve is included to allow for additional external rotation.25,40,45 Restoration of shoulder abduction and external rotation has been successfully reported with the dual combination of nerve transfers to the suprascapular nerve and axillary nerve by the spinal accessory nerve and triceps branch, respectively. In 2003, Leechavengvongs et al described their 7 patient case series results and reported MRC grade 4 deltoid muscle strength.43 Bertelli and Ghizoni later described their 10 patient series and reported return of MRC grade 3 or better strength in shoulder abduction in all patients and external rotation of MRC grade strength 3 or better in seven patients.45 Others have also reported successful recovery of shoulder stability, abduction and external rotation from this combination of transfers.10,46,47 When the triceps branches are not available for transfer, then the medial pectoral nerve may be transferred to the axillary nerve. The medial pectoral nerve is derived from the medial cord of the brachial plexus and has a high number of motor fibers. Ray et al recently published their outcomes in an eight patient case series.48 Postoperative function was graded according to MRC strength with 0e2 considered a “poor” outcome, 3 was a “fair” outcome, 4 was “good” and 4þ was considered “excellent.” They found that four patients had excellent recovery, two had good recovery, one patient had a fair recovery and one patient had poor functional recovery. Others have also reported good functional outcomes after this transfer.42,49 In their series of 13 patients who received this transfer, Samardzic et al report 83.3% recovery of shoulder abduction and 58.3% of shoulder external rotation.49

Nerve transfers for isolated radial, median and ulnar nerve injuries Radial nerve injury e lack of wrist and finger extension The radial nerve is frequently injured with upper extremity trauma and isolated radial nerve injuries are commonly treated.50 Proximal radial nerve injuries result in lack of wrist and digit extension with diminished grip strength and hand function.51 Nerve transfers for restoration of radial nerve function optimize recovery by providing pure motor donors from a near-target axon source allowing for earlier reinnervation. We have expanded our indications to include patients who are willing to wait for reinnervation rather than an immediate intervention provided by tendon transfers as experience with nerve transfers for radial nerve palsy has increased and techniques refined. Nerve transfers are particularly useful for patients with hand stiffness and complex regional pain syndrome who may otherwise not be ideal candidates for tendon transfers. Hand therapy for reducing stiffness and for pain management may continue while waiting for muscle reinnervation to occur. A dual nerve transfer from the median nerve to the distal nerve branches of the radial nerve is our preferred procedure to restore radial nerve function (Fig. 4).6,52e54 The coaptation of the flexor digitorum superficialis (FDS) nerve to the extensor carpi radialis brevis (ECRB) nerve is performed to restore wrist extension. The flexor carpi radialis (FCR) nerve is transferred to the posterior interosseous nerve (PIN) to restore finger and thumb extension. This combination of transfers capitalizes on synergistic motion of

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Fig. 4. Median to radial transfer: (A) The radial nerve motor branches are transected and transposed toward the median nerve. (C) The branches of the median and radial nerves are shown. (B, D) The branches of the median nerve (green) are transected and coapted to the proximal cut end of the ECRB and PIN branches of the radial nerve. MN, median nerve; RN, radial nerve. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Reproduced with permission from: Brown JM, Mackinnon SE: Nerve transfers in the forearm and hand. Hand Clin 2008; 24:319e340.

the wrist and hand, and thus simplifies post-operative re-education. Further, the median to radial nerve transfers allow independent thumb and finger extension due to the reinnervation of each individual muscle innervated via the PIN.6,7,53 Outcomes from the median to radial dual nerve transfers were recently reported by Ray and Mackinnon.53 In 19 patients, at a mean follow-up of 20 months, recovery of wrist extension with MRC grade 4 strength was achieved in 18 patients. Fourteen patients recovered MRC grade 3 or better in finger and thumb extension, while five patients had MRC grade 0e2 recovery. In addition to the nerve transfer procedure, nine patients had a pronator teres to ECRB tendon transfer to allow for immediate wrist extension while waiting for muscle reinnervation. Median to radial nerve transfer is a viable option to restore wrist, thumb and finger extension. Surgical technique and motor re-education are critical for success. Others have also published their experience with nerve transfers to restore wrist and finger extension. Ukrit et al demonstrated the feasibility of the FDS to ECRB nerve transfer in an anatomical study and reported on two patients who regained MRC grade 4 strength in wrist extension at 24 months.55 Bertelli et al performed a transfer of the pronator quadratus motor branch to ECRB to restore wrist extension in four patients with brachial plexus injuries. At one year post-operatively, they report MRC grade 4 strength wrist extension.56 Bertelli and Ghizoni reported on four patients with C7-T1 brachial plexus palsy who received supinator motor branch nerve transfer to the PIN. At 12 months postoperatively, all patients recovered MRC grade 3 metacarpophalangeal joint extension and thumb extension.57 Dong et al also reported their results of the supinator branch to PIN nerve transfer in four patients who showed recovery of thumb and finger extension in 3 patients.58 Median nerve injury e lack of forearm pronation, finger flexion, and thumb opposition Critical hand function is provided by the median nerve. In addition to sensation of the radial three and a half digits of the hand,

the median nerve innervates muscles that control forearm pronation, wrist, finger and thumb flexion, and a significant component of thumb opposition. Reconstruction options for median nerve injuries are dependent on the location and severity of the nerve injury. In a high median nerve injury, forearm pronation, wrist, finger and thumb flexion, thumb opposition, and sensation are lost. To restore motor function, traditionally tendon transfers have been used for index finger and thumb flexion, and thumb opposition.59e61 More recently, nerve transfers to restore median nerve function have been described using the branches of the radial nerve, the brachialis branch of the musculocutaneous nerve and branches of the ulnar nerve.4,6,62 Pronation is a critical function provided by the median nerve and is necessary to perform many of the independent activities of daily living.63,64 Nerve transfers to restore pronation have been described. Boutros et al described transferring the flexor carpi ulnaris nerve branch to the pronator teres nerve.62 Tung and Mackinnon reported transfer of the branch to flexor digitorum superficialis (FDS) to the pronator teres branch in two patients with isolated pronation deficits.65 More recently, successful pronation has been restored using expendable branches from the radial nerve.63 Transfer of the nerve branch to the ECRB to the branch of the pronator teres is now our preferred choice given that many functions require simultaneous use of wrist extension and pronation. Motor re-education after this transfer can utilize synergistic movement patterns to incorporate motor actions of wrist extension and pronation.6,63 Nerve transfers can also be used to restore finger and thumb flexion innervated by the median nerve. Branches from the musculocutaneous, radial or ulnar nerves have been used to reinnervate the AIN.63,66e68 In high median nerve injuries, or in lower plexus injuries, the brachialis branch of the musculocutaneous nerve can be transferred directly to the AIN with successful return of thumb and finger flexion.67 This transfer is only performed in patients with an intact musculocutaneous nerve and normal elbow flexion to

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Fig. 5. For AIN function, a radial to median nerve transfers: (A) The median and radial nerve branches are identified. (B) Mobilization of the ECRB branch (green) to allow the nerve transfer to the AIN (pink). MN, median nerve; RN, radial nerve. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Reproduced with permission from: Brown JM, Mackinnon SE: Nerve transfers in the forearm and hand. Hand Clin 2008; 24:319e340.

avoid downgrading upper extremity function. In a series of four patients, Ray et al report MRC grade 3 strength or better in FPL and FDP function without weakness of elbow flexion.67 Zheng et al performed an anatomic feasibility study and report outcomes in 6 patients after reinnervating the posterior fascicular group of the median nerve (including the AIN and palmaris longus nerve fascicles) using the brachialis branch of the musculocutaneous nerve. Return of finger flexion with MRC grade four or greater strength was achieved in 5 of 6 patients.66 Transfer of the branches of the radial nerve has also been reported to obtain function of the AIN (Fig. 5).6 In a patient with an iatrogenic median nerve injury, Hsiao et al report reinnervation of the AIN using the supinator branch of the radial nerve with MRC grade 4 strength in FPL function and index finger FDP function.63 Garcia-Lopez et al reported successful return of AIN function after transfer of the brachioradialis nerve branch to the AIN.68 At 12 months postoperatively, the patient demonstrated MRC grade 3 strength of FPL and 2 in the FDP of the index and middle finger. Murphy et al presented a case of a median nerve injury treated with the radial nerve branches to ERCB and supinator transferred to the AIN.69 At one year follow up, the patient had return of MRC grade 3 finger flexion and at four years, the patient demonstrated increased pinch strength.69 Thumb opposition is the final critical motor function provided by the median nerve. In isolated low median nerve injuries that are not amenable to direct repair or short interpositional grafting, restoration of thumb opposition has been provided by nerve transfers from proximal branches of the median, specifically the terminal AIN supplying the pronator quadratus muscle.70 An interposition graft is usually needed for this transfer, but clinical studies have shown this transfer to be viable and effective.9,70,71 Ulnar nerve injury e lack of intrinsic muscle function Ulnar nerve injuries result in significant loss of power grip, pinch strength and hand dexterity.72,73 In high level injuries, recovery of intrinsic hand motor function is rare, even with immediate repair, due to the long distance from the site of injury to the target muscle fibers.73 Thus, nerve transfers are directed toward distal reinnervation of the intrinsic muscles of the hand. With an intact median nerve, the terminal branch of the AIN may be used as a donor and transferred to the deep motor branch of the ulnar nerve.71,74e76 Although this nerve transfer is not a synergistic donor, improvement in pinch and grip strength and decrease clawing can be expected.74,75 Most commonly this nerve transfer has been performed as an end-to-end repair.6 The feasibility and efficacy of the end-to-end transfer of the AIN to the ulnar motor branch have been reported by many.71,74e76 Recent experimental data have demonstrated the effectiveness of a reverse end-

to-side or “supercharge” nerve transfer.77,78 This supercharge transfer has been used clinically79 to increase intrinsic function while allowing the native ulnar nerve to recover as well. More recently, Tung et al report a case of reinnervation of the motor branch of the ulnar nerve using branches from the PIN including the terminal branches of the extensor digiti minimi and the extensor carpi ulnaris branches in a patient with median and ulnar nerve injuries.80 Despite using a 10 cm nerve graft, they report, at four years post-operatively, MRC grade 4 strength in the first dorsal interosseous muscle. Conclusion Nerve transfers for restoration of upper extremity function are a viable option for patients with devastating nerve injuries. With ongoing success and encouraging functional outcomes, the indications and use nerve transfers are increasing. Techniques and surgical options continue to be advanced as our understanding of internal nerve topography, redundancy of motor function, and availability of expendable donor nerves is increased. Critical to the success of nerve transfers is the perioperative therapy and postoperative motor re-education. Early involvement of the hand therapist and development of individualized home exercise programs will continue to positively impact the functional outcomes in patients with nerve injuries. References 1. Mackinnon SE, Novak CB. Nerve transfers. New options for reconstruction following nerve injury. Hand Clin. Nov 1999;15(4):643e666. 2. Tung TH, Novak CB, Mackinnon SE. Nerve transfers to the biceps and brachialis branches to improve elbow flexion strength after brachial plexus injuries. J Neurosurg. Feb 2003;98(2):313e318. 3. Tung TH, Mackinnon SE. Brachial plexus injuries. Clin Plast Surg. Apr 2003;30(2):269e287. 4. Tung TH, Mackinnon SE. Nerve transfers: indications, techniques, and outcomes. J Hand Surg Am. Feb 2010;35(2):332e341. 5. Novak CB. Rehabilitation following motor nerve transfers. Hand Clin. Nov 2008;24(4):417e423. 6. Brown JM, Mackinnon SE. Nerve transfers in the forearm and hand. Hand Clin. Nov 2008;24(4):319e340. 7. Boyd KU, Nimigan AS, Mackinnon SE. Nerve reconstruction in the hand and upper extremity. Clin Plast Surg. Oct 2011;38(4):643e660. 8. Lee SK, Wolfe SW. Nerve transfers for the upper extremity: new horizons in nerve reconstruction. J Am Acad Orthop Surg. Aug 2012;20(8):506e517. 9. Mackinnon SE, Colbert SH. Nerve transfers in the hand and upper extremity surgery. Tech Hand Up Extrem Surg. Mar 2008;12(1):20e33. 10. Garg R, Merrell GA, Hillstrom HJ, Wolfe SW. Comparison of nerve transfers and nerve grafting for traumatic upper plexus palsy: a systematic review and analysis. J Bone Joint Surg Am. May 4 2011;93(9):819e829. 11. Pet MA, Ray WZ, Yee A, Mackinnon SE. Nerve transfer to the triceps after brachial plexus injury: report of four cases. J Hand Surg Am. Mar 2011;36(3): 398e405. 12. Lien SC, Cederna PS, Kuzon WM. Optimizing skeletal muscle reinnervation with nerve transfer. Hand Clin. 2008;24(4):445e454.

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Cortical plasticity following upper extremity injury and reconstruction. Clin Plast Surg. Oct 2005;32(4):617e634. 19. Davis KD, Taylor KS, Anastakis DJ. Nerve injury triggers changes in the brain. Neuroscientist. Aug 2011;17(4):407e422. 20. Taylor KS, Anastakis DJ, Davis KD. Cutting your nerve changes your brain. Brain. Nov 2009;132(Pt 11):3122e3133. 21. Duff SV. Impact of peripheral nerve injury on sensorimotor control. J Hand Ther. Apr-Jun 2005;18(2):277e291. 22. Muratori LM, Lamberg EM, Quinn L, Duff SV. Applying principles of motor learning and control to upper extremity rehabilitation. J Hand Ther. Apr-Jun 2013;26(2):94e103. 23. Westlake KP, Byl NN. Neural plasticity and implications for hand rehabilitation after neurological insult. J Hand Ther. Apr-Jun 2013;26(2):87e93. 24. Malessy MJ, de Ruiter GC, de Boer KS, Thomeer RT. Evaluation of suprascapular nerve neurotization after nerve graft or transfer in the treatment of brachial plexus traction lesions. J Neurosurg. 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