Nerve transfers

33 Nerve transfers








Historical perspective


The classification of nerve injury is perhaps the single most important factor when determining management (Table 33.1). The six degrees of nerve injury have been well described.13 First- and second-degree injuries recover spontaneously, as do third-degree, albeit recovery is variable and less than normal, depending on scar tissue.4 Fourth- and fifth-degree injuries are significant and recovery is not expected. These injuries should be managed with prompt surgical intervention to prevent degeneration and fibrosis of the motor end plates.5 Sixth-degree injuries encompass a variety of nerve injuries within a single nerve, and the need to operate is determined on an individual basis.3,5




Once surgical intervention has been deemed necessary, there are a number of surgical options. Traditionally nerve repair or grafting was used with tendon transfers to augment poor recovery or delayed presentation. The difficulty with proximal nerve injuries is that the distance from the injury to the motor end plate is significant, and recovery is prolonged. In addition, delayed intervention may result in denervation and fibrosis prior to muscle reinnervation.5 Axonal regeneration has been shown to occur at the rate of approximately 1 inch (2.5 cm) per month and reinnervation of denervated muscle is not possible after 12–18 months; therefore nerve transfers offer a valuable means of providing regenerating axons in closer proximity to the motor end plate.6 Essentially, a nerve transfer converts a proximal nerve injury to a distal one, enabling faster recovery and quicker return to function.




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Nerve transfers were described very early; however they were traditionally reserved for otherwise unsalvageable root avulsions and proximal panplexus injuries.7 Approximately 20 years ago, nerve transfers were revisited and applied to a significantly broader patient population, with applications in partial plexus injuries to recreate specific essential functions in the upper extremity.3,8,9 As our understanding of internal nerve topography has broadened, techniques and equipment for performing microsurgery have improved, and our diagnostic ability for brachial plexus and peripheral nerve injury has progressed, the field of nerve transfers has exploded. Nerve transfers have become the standard of care for treatment of peripheral nerve injuries in the authors’ practice, and have largely replaced other modalities.



Basic science


There have been dramatic increases in our knowledge of nerve injury, healing, and regeneration. The majority will be touched on in Volume 1, Chapter 22 and Chapter 32 of this volume. The most relevant recent basic science advances pertaining to nerve transfers relate to end-to-side transfers (Fig. 33.1). End-to-side neurorrhaphy involves the coaptation of the distal end of an injured recipient nerve into the lateral aspect of an intact nerve, which serves as a proximal source of axons to regenerate into the injured nerve. Reports of end-to-side transfers occurred as early as the late 1800s and then made a resurgence in the 1990s.10 There has, however, been controversy regarding the success of these transfers, and sensory recovery has typically been more impressive than motor recovery.1115 The sprouting of axons in an end-to-side coaptation, thus eliminating the need for a proximal nerve stump, makes nerve transfers an option for proximal nerve injuries and has been well demonstrated in the literature.1619 While sensory nerves are able to sprout spontaneously (collateral sprouting), donor nerve axonotmetic injury is required for motor neuronal regeneration (regenerative sprouting) across the end-to-side repair (Fig. 33.2).15,17,17,20,21 An epineurotomy in the donor nerve is required, and partial axotomy will result in more significant regenerative sprouting into the recipient nerve, albeit at the potential expense of a measurable downgrade in donor nerve function.17




Reverse end-to-side nerve transfers involve the complete transection of the donor nerve, which is then coapted into the side of the intact recipient nerve. This maximizes the potential number of available motor axons from the donor nerve. This procedure does not interrupt any recovery in the injured recipient nerve because the nerve remains in continuity; however the additional axons recruited from the donor nerve improve distal target reinnervation, a concept known as “supercharging.”2224 In a proximal nerve injury, with a long distance required for reinnervation, this technique can protect target muscles from denervation atrophy and fibrosis.22




Diagnosis and patient presentation


The value of a complete history and physical examination in the patient with a potential brachial plexus or proximal nerve injury of the upper extremity cannot be overstated. Patients should be evaluated promptly after injury, both to provide a baseline for future serial examinations and to facilitate timing of surgical intervention where necessary.




Physical examination


A complete physical examination of the upper extremity includes assessment of sensory and motor function, deep tendon reflexes, joint suppleness, and range of motion. Particularly in patients with late presentation, the presence of fixed joint contractures may preclude functional recovery. Perfusion, bony pathology, presence of edema, scar, previous incisions, and other soft-tissue trauma are factors that influence treatment choices.


Function should be graded at each joint. Shoulder function should be assessed by examining deltoid, supraspinatus, infraspinatus, trapezius, latissimus dorsi, serratus anterior, and pectoralis major. The patient’s ability to abduct/adduct, flex/extend, and internally/externally rotate must be assessed. The elbow should also be assessed for flexion and extension. Here it is important to differentiate between flexion secondary to biceps brachii and brachialis (musculocutaneous nerve) and brachioradialis (radial nerve). The forearm and wrist should be assessed for flexion/extension and pronation/supination. Palpation of the individual tendons with wrist flexion is essential to determine which nerves are involved, as well as the level and degree of injury. In the hand, a complete examination of extrinsic and intrinsic function again helps to delineate the level of injury.


Sensation should be examined by both dermatome and peripheral nerve distribution, and can be helpful in distinguishing these injuries. The authors advocate the use of both two-point discrimination and the ten-test to evaluate sensory loss in the hand.25 A Tinel’s sign, the tingling sensation elicited with percussion over a regenerating nerve, will help to localize the level of nerve injury, and may also be followed on serial clinical examination to check for signs of advancement, indicating spontaneous recovery. An advancing Tinel’s sign distal to the site of injury quite often precedes clinical motor recovery.


For completeness, the presence of Horner’s syndrome and dysfunction of nerve branches that come off the proximal brachial plexus (dorsal scapular nerve to rhomboids, long thoracic nerve to serratus anterior) indicate a very proximal level of injury.


image Video1


The scratch collapse test is useful primarily for patients with nerve compression pathology, but also has a role in evaluating the patient for potential nerve transfer procedures, as it can provide additional confirmation of the level of nerve injury (video 1). The test is performed by having the patient sit facing the examiner with the shoulders adducted, elbows held in 90° of flexion, neutral prosupination, and wrist and fingers extended. The examiner will then lightly scratch the area of the presumed nerve injury and exert force to the patient’s arms in the direction of internal shoulder rotation as the patient resists. Nerve injury at the test site is indicated by the inward collapse of the arm on the side ipsilateral to the injury.26,27


One of the most important components of the physical examination is the simple determination of what is functioning, and what function has been lost. Not only does this help to determine the level of injury, it can guide future surgical planning. In the presence of an injury requiring surgical intervention, it is important to examine the patient for putative nerve donors, both intraplexal and extraplexal (spinal accessory, medial pectoral, and thoracodorsal).





Electrodiagnostic testing


Electrodiagnostic testing, performed by an experienced person, can be a useful adjunct to physical examination for serial assessment of reinnervation in closed nerve injuries. Electromyography records the electrical activity of muscle fibers, tested both at rest and activity, by the insertion of needles into the muscle. Denervated muscles will demonstrated fibrillations and positive sharp waves on needle insertion; however the findings are not reliable until approximately 4 weeks after injury.29 Initial electrodiagnostic testing should be deferred until a minimum of 6–8 weeks postinjury to assess for signs of both axonal injury and root-level avulsion. Serial testing will reveal signs of reinnervation with nascent potential and motor unit potentials in the affected muscle groups, often prior to clinical evidence of recovery. Conduction velocity is used to measure the integrity of a peripheral nerve (sensory nerve action potentials (SNAP) or compound motor action potentials (CMAP)).29 A severed nerve will lose the ability to conduct a signal as wallerian degeneration occurs; however, if measured too early, the distal aspect of the nerve will still conduct, leading to an inaccurate assessment. This is another reason for delaying initial electrodiagnostic studies. Preganglionic injuries will be associated with a loss of sensation but an intact SNAP and an absent CMAP.29 Thus the level of injury can be confirmed with electrodiagnostic studies.


In patients with no evidence of recovery 3 months after a closed nerve injury, the balance should tilt towards consideration of surgical intervention.



Overall, the complete picture, including history, physical examination, and adjunct testing, should facilitate surgical decision-making. Appropriate treatment for open injuries with nerve dysfunction begs for timely management with surgery on an urgent or semiurgent basis. For these injuries, direct exploration and repair have historically been the treatment of choice, but in very proximal injuries, distal nerve transfer can allow for more timely and successful reinnervation. In closed nerve injuries or in gunshot wounds, appropriate management demands a more measured approach and surgery should be delayed to allow for spontaneous recovery, which is often superior to that seen in patients treated with hasty surgery. These patients in particular may benefit from “supercharging” with reverse end-to-side nerve transfer procedures, which can more quickly deliver regenerating axons to the appropriate end organ, while still allowing slower spontaneous recovery.22



Patient selection


Nerve transfers have become increasingly popular for a number of reasons, the most compelling of which is the “time is muscle” issue.24 The biggest challenge facing peripheral nerve surgeons is that with increasing time since injury, the ability to achieve good motor function becomes increasingly limited. In fact, for any nerve injury where there is complete discontinuity with the motor end organ, no reinnervation procedure will be able to restore muscle once denervation and fibrosis have occurred, a process which occurs as early as 1 year.24 Nerve transfers, by bringing the regenerating motor fibers closer to the target end organ more rapidly, essentially convert a more proximal-level injury to a more distal-level injury, thus increasing the chance of achieving meaningful muscle function.


Another advantage of nerve transfers is that they enable surgical reconstruction outside the zone of the original injury, avoiding complex dissections and limiting injury to critical neurovascular structures. In patients with brachial plexus trauma, the proximity of vital structures (great vessels, thoracic duct, lung) makes the occurrence of potentially life-threatening complications a real possibility. In other cases, such as concomitant vascular injury, previous blast injury, or soft-tissue deficits requiring flap reconstruction, the ability to avoid doing a complex nerve exploration in the setting of dense fibrotic scar is particularly advantageous.24


Nerve transfers allow for a very targeted intervention in cases of partial nerve injury such as in treatment of a sixth-degree or neuroma-in-continuity injury, where transfer can be done distal to the site of injury specifically to the nonfunctioning nerve branch. This allows for preservation of all intact function and restoration of only missing function. In addition, the ability to “supercharge” a recovering nerve is invaluable when it is unclear whether the nerve transfer or intrinsic recovery will be more beneficial.14,30


Unlike tendon transfers, nerve transfers require only minimal immobilization (7–10 days), which is especially valuable in patients presenting with significant baseline stiffness. Nerve transfers also preserve the biomechanical properties of the musculotendinous unit, such as end organ origin, insertion, excursion, and length–tension relationships. Finally, nerve transfers can restore unique function such as pronation, which is incredibly difficult to restore by traditional surgical techniques.31


Thus nerve transfers are indicated in a number of situations (Table 33.2), for example, in proximal brachial plexus injury where grafting is not possible or the required distance for reinnervation will not allow motor axons to reach the target motor before denervation and fibrosis have occurred. In situations of extreme scarring, or major upper extremity trauma, a nerve transfer is preferable to risking damage to critical structures within the scarred region. Nerve transfers are also indicated in segmental nerve loss, and in partial nerve transfers with functional loss. Patients presenting in a delayed manner with inadequate time to reinnervate the distal targets are good candidates for distal nerve transfers. Also, patients with sensory nerve deficits in critical regions should be considered for nerve transfer to restore sensation.


Table 33.2 Indications for nerve transfer







The main reason a nerve transfer should not be performed is similar to the contraindication for any other traditional nerve repair/graft intervention, namely end organ unresponsiveness. An old peripheral nerve injury will not respond to the new “magic” of nerve transfers. Muscle that is in complete discontinuity with the nerve for greater than 1 year will not be reinnervated no matter the elaborate reinnervation strategy employed.


More relative contraindications for nerve transfer include issues such as the time required for regeneration, challenges of the surgery, the anatomic knowledge required, and problems of postoperative retraining and therapy as these techniques are less familiar to hand therapists. There are some patients, such as the young manual laborer with a radial nerve injury, who may prefer the more rapid recovery associated with tendon transfer at the expense of the independent fine motor control that could be achieved through the use of nerve transfers. The surgery itself is challenging because of the detailed knowledge of internal nerve topography required. Most surgeons are not formally trained in the intraneural dissection techniques required to perform nerve transfers and the results are not apparent until months down the line. This requires a significant leap of faith for surgeons who are more used to immediate gratification and a clear result in weeks, not months or years!


Direct nerve repair and nerve grafting also remain valuable tools for the peripheral nerve surgeon and should continue to be the treatment of choice in a variety of scenarios. These include cases of multiple nerve injuries where there is a paucity of nerve donor material for nerve transfer. Also, in distal single-function nerve injuries, direct or graft repair is preferable to nerve transfer because one-to-one function is preserved, no retraining is necessary, no donor function is sacrificed, and the distance to the end target is short.


Patient general health, comorbidities, and associated injuries factor into the decision to perform nerve transfers. These procedures can be lengthy, and are not without significant risk from anesthesia in the fragile patient. In addition, patient compliance is an integral part of the recovery process, and patients require education preoperatively about the prolonged recovery and therapy times associated with nerve transfer.



Examples of nerve transfer procedures for specific injury patterns





Upper plexus injury



Specific patient exam findings


Upper plexus injuries involve injuries at the C5, C6, and/or C7 root or upper trunk level. Injuries of this type commonly include deficits of the dorsal scapular, the long thoracic, suprascapular, axillary, and musculocutaneous nerves. The dorsal scapular nerve innervates the rhomboid muscles and the levator scapulae muscles, which contribute to scapular adduction, retraction, and elevation. The long thoracic nerve innervates the serratus anterior muscle, which abducts the scapula, permitting the full range of shoulder flexion past 90°. The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. These muscles are rotator cuff muscles. The supraspinatus contributes to shoulder abduction with the deltoid muscle. The infraspinatus contributes to shoulder external rotation with the teres minor. The axillary nerve comes off the posterior cord, receiving innervation from C5 and C6. The axillary nerve supplies the deltoid and teres minor muscles, which provide shoulder abduction and external rotation respectively. It also provides cutaneous innervation over the lateral shoulder. The musculocutaneous nerve arises from the lateral cord and is primarily innervated by C5, C6, and occasionally C7. This nerve innervates coracobrachialis, biceps brachii, and brachialis, which power elbow flexion. The biceps is also the primary forearm supinator. The lateral antebrachial cutaneous (LABC) nerve is a terminal branch of the musculocutaneous nerve, and provides cutaneous innervation to the lateral forearm.


Patients with upper plexus injuries present with glenohumeral joint subluxation, loss of shoulder abduction and external rotation, and absent or weakened elbow flexion depending on the involvement of C7. Numbness over the lateral shoulder and forearm is noted.



Reconstruction techniques





Use of spinal accessory nerve (cranial nerve XI) to suprascapular nerve transfer (motor)


Restoration of shoulder stability and external rotation are facilitated by transferring the spinal accessory nerve (cranial nerve XI) to the suprascapular nerve. This transfer can be conducted by either an anterior or a posterior approach. In the posterior approach, the patient is positioned prone and surface landmarks are used to approximate the position of the nerves (Fig. 33.4). The spinal accessory nerve runs parallel to the border of the trapezius and is localized 44% of the way along a line connecting the acromion to the dorsal midline at the level of the superior border of the scapula (Fig. 33.5). The suprascapular nerve is located midway between the medial border of the scapula and the acromion as it runs through the suprascapular notch.32,33 These nerves are accessed through an incision located slightly obliquely just above the superior border of the spine of the scapula. Dissection is carried through the trapezius in a muscle-splitting fashion and an end-to-end coaptation, sparing the upper trapezius nerve branches, is performed.




For the anterior approach, an incision is designed 2 cm superior to and parallel to the clavicle extending laterally from the posterior border of the sternocleidomastoid (Fig. 33.6). The upper trunk is identified between the anterior and middle scalene muscles. The suprascapular nerve is a distinct branch of the upper trunk that sits on the superolateral aspect. The spinal accessory nerve is located in the posterior aspect of the incision on the deep surface of the trapezius muscle. Although an end-to-end transfer can be performed, the end-to-side approach with a partial neurectomy of the donor accessory nerve is preferred as this preserves some donor function. In the end-to-side transfer, a short interpositional graft from the recipient suprascapular nerve to the donor spinal accessory nerve is required to avoid tension. A proximal crush injury to the donor nerve encourages axonal sprouting such that regeneration into the recipient suprascapular nerve occurs without loss of significant donor nerve trapezius function.14



Feb 21, 2016 | Posted by in General Surgery | Comments Off on Nerve transfers

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