Surgeons are quite adept at restoring the continuity of a disrupted peripheral nerve following a peripheral nerve injury. Although restoration of neural continuity may be enough to treat some patients with a peripheral nerve injury, many patients will require additional therapy. The surgeon must be prepared to treat the patient's dysfunction, not just the injured nerve. Here a reviews the available methods of restoring function to an extremity following nerve injury.

A variety of methods are available to enhance the patient's functional recovery. During the immediate postinjury period, physical therapy and splinting must be employed to avoid skin and muscle contractures and stiff joints. Contractures limit the maximum range of motion achieved by all other forms of therapy. Muscle transfers and orthotics may improve mobility in those patients who do not achieve a full functional recovery. The surgeon treating peripheral nerve injuries must be aware of the role that these techniques can play when planning a patient's therapy.

Here reviews the functional deficits incurred with upper extremity peripheral nerve injuries, as well as the potential for methods of therapy designed to restore lost function. A variety of treatment schemes are presented. The merits and disadvantages of each are discussed.

Physical Therapy

The need for maintaining joint mobility cannot be overlooked by the surgeon performing a peripheral nerve repair. A reinnervated muscle or tendon transfer cannot be expected to move a joint beyond what is allowed by the joint's intrinsic limitations of motion. Passive range of motion is preserved and joint contractions avoided with the help of a physical therapist. Most patients will not need daily supervised therapy once instructed regarding the appropriate therapy. The therapy often can be carried out at home. The therapist can then monitor the patient's progress at regular intervals. Even the most compliant patient, however, will need to be monitored for early contractures.

Orthotics

Orthotics can be used to help solve two fundamental problems encountered in patients with an upper extremity nerve injury. First, the orthotic can be used to prevent or correct soft tissue and joint contractures. The preservation of a normal range of motion will allow the patient to take full advantage of later reinnervation. Both static and dynamic splints are available for this purpose. The surgeon, working with the orthotist, must choose a splint that maximizes the patient's use of the injured extremity but that is not so cumbersome or unsightly as to discourage the patient's compliance. For instance, a splint with a dynamic finger extension assembly is ideal for a secretary with a radial nerve palsy, but it most likely would be too cumbersome for a salesperson who is self-conscious about appearance. It is emphasized that fixed orthoses must be used with caution since they can contribute to contracture formation.

Second, an orthotic device can be used to bolster weakened movement. This can be accomplished sometimes simply by stabilizing a joint. For instance, stabilizing the wrist of a patient with radial nerve palsy in a neutral or slightly extended position will tighten the finger flexion tendons, adding strength to the patient's grip. The patient thus may benefit from the transfer of power from a forceful movement to a weakened movement. In this case, the orthosis improves grasp by enhancing the normal tenodesis effect that causes the finger to flex when the wrist is extended. The patient with a severe, permanent hand paralysis may benefit from a mechanical device that is triggered by one of the patient's retained functions. These devices accomplish movement with the aid of electric motors or springs. In addition, a number of prosthetic devices are available to replace a lost portion of an upper extremity.

Neurotization

Despite reported success with regard to the treatment of brachial plexus lesions, the restoration of motor function following a brachial plexus avulsion remains a difficult problem. Although nerve grafts placed against the spinal cord could theoretically coax anterior horn cells to sprout viable axons, this technique has not been used to treat patients with brachial plexus avulsions. Function can be restored in this group of patients by either muscle transpositions or neurotization. Neurotization is a procedure whereby intact axons are rerouted to denervated neural elements (Figure 1). Neurotization is an established technique. The spinal accessory and hypoglossal nerves long have been used for neurotization of the facial nerve. In 1913 Tuttle reported his attempt at neurotization of the injured upper trunk of the brachial plexus using intact elements of the cervical plexus. The duration of follow-up, however, was too short to evaluate the results of his procedure adequately. Although Tuttle's case generally is considered to be the first reported case of neurotization, Cushing cited a report of the utilization of the radial nerve to innervate the median nerve. The first successful neurotization using intercostal nerves was reported by Yeoman, and the first successful neurotization using either the elements of the cervical plexus or intercostal nerve was reported by Kotani et al. Intercostal nerves and elements of the cervical plexus remain the most commonly used nerves for neurotization in the upper extremity.

The timing of the neurotization procedure is critical. Two years after the injury, muscle cells are fragmented and the muscle atrophied, At this time, restoration of innervation will not result in meaningful contraction, Since innervation of the biceps brachialis or supraspinatus will not be evident until at least 7 months following the procedure, neurotization should be performed as soon as the diagnosis of a complete avulsion is established, If the patient is evaluated at more than 1 year following the injury, or if the recipient nerve is found to be fibrotic at the time of inspection, direct neurotization has little chance for success. Patients who have undergone a successful neurotization procedure can retrain the transposed nerves to serve a new function, Cushing noticed that as time passed, a patient with an accessory to facial nerve anastomosis could perform more and more intricate facial movements without concomitant shoulder movement. Vera et al. further documented this plasticity by serial electromyograms performed on a 4-year-old boy who had undergone an accessory to facial nerve anastomosis, Animal experiments performed to investigate the effects of cross-neurotization indicate the ability to re­educate the transposed nerves to subserve their new job. The Duke experience using intercostal nerves to reinnervate the biceps brachialis demonstrates the plasticity of the nervous system, Although initially the biceps brachialis only contracts with respiration, the patients soon learn to contract their biceps muscles independent of the respiratory cycle, Eventually biceps brachialis contraction is performed without a conscious effort, Available donor nerves contain a relatively small number of axons as compared to potential recipient targets. Therefore, attempts at neurotization of the trunks and cords of the brachial plexus have not been successful, as the regenerating axons diffuse out along disparate paths. It is best to direct available donor axons into a nerve just proximal to a single recipient muscle. Most procedures, therefore, are aimed at restoring elbow flexion or shoulder abduction.

Fig-1

Muscle and Tendon Transfers

Muscle transfers often are helpful in restoring function to a paretic upper extremity. A knowledge of this technique aids the surgeon in several ways, First, muscle transfers may enhance function in a patient with an irreparable nerve injury. Second, the literature on muscle transfers concentrates on the functional mechanical deficit caused by a nerve injury. It is important for the surgeon to know and document the functional evaluation of the injured nerve. A knowledge of muscle testing alone is inadequate. A knowledge of the patient's functional deficit is essential to the physician who must initiate physical therapy to avoid contractures and plan future operative procedures directed toward returning the patient to a productive life.

In this section, the general principles and the desired muscle transfers are outlined, The technical details and the merits of the variety of available procedures are not described, The interested physician therefore is directed to the literature detailing the technique of muscle transfers.

The art of tendon and muscle transfer has evolved over the last 130 years, A review of the rules guiding successful tendon transfers will lead to an understanding of the limitations of these techniques, Each time a tendon is removed for a transfer, a joint is made less stable or a movement weakened, Therefore, each tendon transfer has a price, The surgeon must decide which transfers will be most advantageous for the needs of the individual patient. For instance, in some patients, a powerful grasp is important in carrying out work. In these patients, tendon transfers to strengthen finger flexion are important. Other patients will do perfectly well with a weakened grasp. In those patients, such transfers are superfluous.

In planning a tendon transfer, the surgeon must take into account mechanical, tissue, and rehabilitation considerations. The mechanical considerations are straightforward. The muscle transferred must be of sufficient strength and have sufficient excursion to accomplish its new task. All forearm muscles do not have the same excursion. The laws of mechanical physics, especially those of vectors and levers, will determine the movement accomplished by the tendon transfer. For instance, if a tendon crosses two joints, its effect on the movement at each joint is determined by the direction of pull and length of the lever arm affecting that joint. Tissue factors must be taken into account when planning a tendon transfer and also in planning any surgery that precedes the transfer. Muscles and tendons must have an adequate blood supply in their new position. The tendon must be routed through virgin tissue. A tendon routed through scar tissue is likely to develop adhesions that impede its excursion. This principle must be kept in mind when planning operative procedures that precede the tendon transfers. Prior to the transfer, the target joint must have a full passive range of motion. Maintaining range of motion is accomplished by preoperative physical therapy, splinting, and occasionally the surgical release of adhesions. Finally, the most perfectly planned tendon transfer procedure will not be of benefit unless the brain can be reoriented to use the muscle in its new position. The patient must have a sufficient mental capacity and interest to participate in a re-education program. This program should be coordinated by a physical therapist who has the time and experience to help the patient use the new transfer effectively. The re­education process is said to be easiest when the donor muscle's former role was synergistic with the desired motor effect of the planned transfer.

Most tendon transfers are carried out only when one is certain that there will be no further improvement in the patient's paralysis. Some authors advocate early transfers of a few tendons to help avoid contractures and to enhance function while awaiting reinnervation. The possibility of early transfers should be considered in the patient who is severely incapacitated by a peripheral nerve injury.

Sensory Retraining

The importance of sensation in the upper extremity often goes unrecognized. In fact, loss of sensation within the hand can be quite debilitating. Even if the patient recovers good motor function, the ability of the hand to carry out fine tasks will be limited by poor sensory perception.

In general, recovery of two-point discrimination in the hand is poor following the repair of an ulnar or median nerve injury. The recovery of sensation following peripheral nerve repair can be improved greatly by using sensory re-education techniques. Dellon et al. first re­ported near normal sensation in four adults who had undergone a median nerve repair followed by sensory education. Several other authors have corroborated these results. In sensory re-education, the patient stimulates the hypoesthetic area with progressively more intricate objects. At first, the patient looks at the object during stimulation to correlate the new sensory signal with the visual impression of the object. Then the patient blindly picks up and tries to identify the object. Using this technique, two-point discrimination is greatly improved. This improvement may persist for years.

When a nerve injury leaves a portion of the patient's palm or digit anesthetic, some sensation can be restored using neurocutaneous island pedicle flaps. With this technique, a flap of skin with a neurovascular pedicle is moved from a less vital area to a vital sensory surface. For instance, the ulnar volar surface of the ring finger can be transferred along with its neurovascular pedicle to the palmar surface of an insensitive thumb. Some patients will gradually reorient sensation in the graft from the donor site to the thumb. Unfortunately, the transferred pedicle may develop a cold sensation and hyperesthesia. Rarely, sensory nerve transpositions have been reported for restoration of sensation into the hand.

In the following section, specific nerve injuries will be discussed. The specific movements impaired and intrinsic mechanisms of compensation, or so called "trick movements" are reviewed. The more common methods used to restore lost function are outlined.

Axillary Nerve

An isolated axillary nerve injury denervates the deltoid muscle and thus greatly reduces the strength of shoulder abduction. Most patients still can raise the affected arm over the head using external rotation of the scapula as well as the supraspinatus, the long head of the biceps, and the clavicular fibers of the pectoralis major muscle. Unfortunately, the movement lacks power.

Because the axillary nerve subserves motor function primarily, repair of the nerve with or without a nerve graft offers an excellent chance of restoring function. This, therefore, is the preferred method of treatment.

Several ingenious muscle transfers using the trapezius, serratus anterior, levator scapulae, latissimus dorsi, and sternocleidomastoid muscles have been described to restore shoulder function. These transfers seldom are necessary for patients who have suffered an isolated axillary nerve injury but should be kept in mind for treating patients who have suffered concomitant paralysis of other shoulder muscles. Patients who have paralysis of most of their shoulder musculature from a C5-6 avulsion are best treated with a fusion of the scapula to the humerus. The transfer of one or two muscles will not benefit an unstable shoulder. Neurotization of the axillary nerve only has been attempted rarely in order to restore shoulder abduction. Neurotization procedures of the supraspinatus nerve using the distal branch of the spinal accessory nerve or intercostal nerves have been described. Because of its small sensory component, neurotization of the axillary nerve should produce results at least as good as similar procedures for the musculocutaneous nerve.

Musculocutaneous Nerve

The musculocutaneous nerve rarely is injured in isolation. When such an injury occurs, some elbow flexion may be retained. The flexion in this case is carried out by the pronator teres and the brachioradialis muscles. More commonly, however, elbow flexion is lost as a part of a more extensive brachial plexus injury.

While awaiting return of elbow flexion, passive exercises should be initiated to maintain the full range of motion of the elbow. Several muscle transfers have been described to reconstitute elbow flexion. The original transfers described by Steindler called for a transposition of the origin of the finger flexor­pronator muscle group to a position more proximal on the humerus. Although this transfer produces only weak elbow flexion, still it is useful for treating patients who have suffered an upper brachial plexus avulsion. The latissimus dorsi, pectoralis muscle, and triceps all can be transposed to strengthen elbow flexion.

Because elbow flexion is the most vital function provided by the arm, the musculocutaneous nerve most frequently has been the target of neurotization procedures. In the Duke series, 16 patients had neurotization of the biceps brachialis by intercostal nerves and 4 additional patients had neurotization of a free gracilis muscle graft transposed into the position of the biceps. Nine of twenty patients (45%) obtained useful antigravity strength and a full range of elbow flexion following surgery. Several other authors have reported their experiences using intercostal nerves or elements of the cervical plexus to reinnervate the biceps brachialis (Table 1). 

Radial Nerve

Because the radial nerve primarily innervates muscle in the forearm and contains relatively few sensory fibers, a patient with a radial nerve injury has a good prognosis for recovery of some function following primary anastomosis or nerve grafting. A high radial nerve injury will result in weakness of the ulnar and radial wrist extensors, extension of all five digits of the metacarpophalangeal joint, abduction of the thumb, and extension of the thumb at the interphalangeal joint. Weak extension of the distal phalanx of the thumb is preserved in many patients by a slip of the abductor pollicis brevis that attaches to the extensor pollicis longus tendon. The inability to stabilize the wrist and the metacarpophalangeal joints greatly weakens the patient's grasp. This loss of wrist and finger stability is responsible for the greatest functional deficit. In some patients, sensory fibers to the dorsum of the hand travel along the antebrachial cutaneous nerve. In these patients, a radial nerve injury does not cause any loss of sensation. In any case, the sensory loss incurred by a radial nerve injury is of no functional significance unless it is accompanied by a painful neuroma.

Following radial nerve repair, the patient should be instructed in passive range of motion exercises to prevent joint adhesions and contractures of the web space between the thumb and index finger. Several types of orthoses have been described to improve the patient's function following a radial nerve palsy. A simple volar cock-up splint will hold the patient's wrist in extension, increasing the strength and accuracy of the patient's grip. The patient must be instructed to continue range of motion exercises or the splint can lead to joint contractions. Dynamic finger and thumb assemblies will hold the digits in extension while the patient is at rest but will still allow the patient to flex the digits. The dynamic assemblies make the splint more complicated and cumbersome. Some authors have advocated an early tendon transfer to serve as an internal splint while awaiting the return of motor function. The most common procedure uses an end-to-side anastomosis of the pronator teres and to the extensor carpi radialis brevis. This transfer will stabilize the patient's wrist and will not interfere with the normal musculature once nerve regeneration occurs. Muscle transfers are very successful at reducing the functional deficit that occurs following a radial nerve palsy. Because all of the ulnar and median innervated extrinsic muscles of the hand are available for transfer, a large number of different transfers have been described. Wrist extension is most commonly restored by a transfer of the pronator teres to the radial wrist extensor tendons. Finger extension is achieved by a transfer of the flexor carpi radialis or a single tendon of the flexor digitorum sublimis to the extensor digitorum common. Thumb extension and abduction can be achieved by transferring the palmaris longus, flexor carpi radialis, or one tendon of the flexor digitorum sublimis to the extensor pollicis longus tendon.

Ulnar Nerve

The repair of a disrupted ulnar nerve proximal to the elbow is unlikely to result in a good return of lost motor function. Such repair still should be performed in an attempt to restore sensation to the ulnar side of the hand. A complete proximal ulnar nerve lesion will result in weakness of the flexor carpi ulnaris, flexor digitorum profundus to the small and ring finger, adduction pollicis, and several intrinsic muscles in the fingers. Sensation will be lost over the ulnar one-and-a-half digits and adjacent hand.

Weakness of the flexor carpi ulnaris and ulnar portion of the flexor digitorum profundus muscles does not pose a significant problem to most patients. Wrist flexion is still carried out by the flexor carpi radialis and palmaris longus muscles, although there is some loss of strength and radial deviation of the wrist. Strong lateral pinch of the thumb is weakened by the loss of the adductor pollicis and the deep head of the flexor pollicis brevis muscles. Some weakened thumb adduction can be carried out by the abductor pollicis brevis muscle if the thumb is held in front of the palm. If the thumb is held in the plane of the palm, weak adduction is achieved by combined actions of the extensor pollicis longus and the flexor pollicis longus muscles The telltale flexion of the distal phalanx of the thumb with lateral pinch performed by the extensor pollicis longus results in Froment's sign. This weakened adduction diminishes the thumb's effectiveness as a stabilizer during a power grip. Interossei weakness causes loss of finger abduction and adduction. This manifests as an instability of the index finger during fine pinch. Some finger abduction is performed by the finger extensors when the fingers are allowed to flex forward away from the palm. Loss of the interossei muscles also weakens flexion of the metacarpophalangeal joint and results in a weakened "power grip" (Figure 2).

Fig-2

This loss of coordinated metacarpophalangeal flexion decreases the patient's ability to wrap his or her fingers around an object. With the additional loss of the lumbricale muscles to the ring and small fingers, hyperextension of the metacarpophalangeal joints results. This hyperextension in turn decreases the patient's ability to straighten the interphalangeal joints, leading to clawing of the ulnar two fingers. Loss of the intrinsic muscles to the small finger results in flattening of the hand, which further weakens grip. A chronically abducted small finger will inhibit the patient's ability to quickly put the hand into a contained space such as a pocket or shirt sleeve. In summary, the motor deficits that occur with an ulnar nerve injury greatly weaken the patient's "power grip," i.e., the prehensile position in which the object is clamped by the flexed fingers and stabilized by the thumb. Precision grip is much less impaired (Figure 2).

Exercise and splinting may be necessary to avoid flexion contractions of the ring and little fingers' interphalangeal joints. A splint with a metacarpophalangeal extension stop assembly will prevent metacarpophalangeal joint hyperextension and finger clawing. Some authors have advocated internal splints to coordinate the residual motor function of the hand while nerve regeneration is taking place. To this end, a single tendon from the flexor digitorum sublimis is used to stabilize the metacarpophalangeal joints of the ring and little fingers and to improve adduction of the thumb.

It is not possible to transfer enough tendons to restore each muscle lost following the loss of the ulnar nerve, so the surgeon must concentrate on restoring functions that are important to each individual patient. Weakness of the flexor digitorum profundus and flexor carpi ulnaris is only of consequence if the patient's occupation requires a strong, accurate grasp across the entire palm. Grasp can be improved by attaching the flexor digitorum profundus tendons of the ring and small fingers to that of the middle finger or by attaching the extensor carpi radialis tendon to the two weakened tendons.

A number of transfers have been devised to improve flexion of metacarpophalangeal joints. If the metacarpophalangeal joints can be kept from hyperextending, the extensor digitorum communis will adequately extend the interphalangeal joints. Most often, the extensor carpi radialis longus or flexor carpi radialis tendon is used to flex the ulnar metacarpophalangeal joints.

Thumb adduction is strengthened most often using the brachioradialis muscles, a single tendon from the flexor digitorum sublimis, or less commonly, the extensor digit proprius. A pulley is established with a fascial sling, or by passage of a tendon around the metacarpal of the long finger so that the thumb is pulled horizontally in the plane of the palm.

The strengthened thumb adductor will still pinch against the weakened index finger abductor. If the patient's occupation requires a strong lateral pinch, index finger abduction can be strengthened by a transfer from the extensor pollicis brevis and fusion of the metacarpophalangeal joint of the thumb. Cupping of the metacarpal arch and little finger adduction are accomplished by a transfer from the extensor digiti minimi or less commonly from the flexor digitorum superficialis.

These transfers are designed to increase the strength and accuracy of the patient's grip and pinch. Some sensibility can be re-established by using a neurovascular cutaneous island graft.

Median Nerve

A high median nerve Injury is a disabling condition. Denervation of the long flexors to the distal interphalangeal joint of the thumb, index, and long fingers, and the primary flexors of the proximal interphalangeal joint of all four fingers weakens the patient's power grip. Some paralysis is partially compensated for by intact muscles. The distal phalanx of the long finger usually flexes synchronously with the distal phalanx of the ring finger, as the two tendons of the flexor digitorum longus muscle share a common, ulnar innervated muscle belly. Although loss of the flexor digitorum sublimis decreases the strength of the grasp and independent finger flexion, the intact flexor digitorum profundus to the ulnar digits flexes the proximal interphalangeal joint along with the distal interphalangeal joint. Precision pinch is impaired by loss of thenar palmar abduction (abduction perpendicular to the palm) and opposition (internal rotation) movements initiated by the opponens pollicis, abductor pollicis, and to a lesser extent, flexor pollicis brevis (Figure 2))· The flexor pollicis brevis and longus muscles add strength to the pinch. Some palmar abduction and internal rotation of the thumb occur in approximately one-third of patients with a medial nerve injury as a result of a dominant ulnar innervation of the flexor pollicis brevis muscle.

An injury to the median nerve proximal to the elbow weakens wrist pronation and flexion. Wrist flexion is still carried out in the absence of the flexor carpi radialis and digitorum flexors by the intact flexor carpi ulnaris and abductor pollicis longus muscles. This compensated motion usually occurs with concomitant ulnar wrist deviation.

It must be remembered that median nerve injury robs the patient of critical sensory perception in the tips of the thumb and index finger. Without this sensation, fine pinch is of little value. While awaiting reinnervation of the thenar eminence following a median nerve repair, the surgeon must guard against contracture of the dorsal skin of the thenar web. This common contracture limits opposition of the thumb and, if it occurs, should be treated by splinting or even surgical release. Mobility of the interphalangeal joints of the thumb and index fingers also must be maintained. Some surgeons advocate early muscle transfers to act as internal splints.

Several orthotic devices have been developed to oppose the thumb and index fingers, stabilize the thumb, and prevent web space contractures. Accessories may be added to prevent wrist dorsiflexion. Following an irreparable injury to the hand, spring- or electrically driven devices can oppose the thumb and index fingers providing the patient has retained a useful pinch mechanism.

Several muscle transfers have been described to restore opposition of the thumb following an injury of the median nerve. The flexor digitorum sublimis muscle is the most commonly used motor for an opponensplasty following a low median nerve injury. Following a high median nerve injury that has paralyzed the long finger and wrist flexors, thumb opposition can be partially restored by a tendon graft attached to a transposed extensor muscle such as the extensor carpi ulnaris, extensor indicis proprius, or ex­tensor digiti minimus.

Because the ulnar portion of the flexor digitorum longus is innervated by the ulnar nerve, simultaneous flexion of all of the fingers can be provided by tenodising (suturing together) the long flexor tendons of the small and ring fingers to those of the long and index fingers. This only will allow the fingers to flex in mass and may result in a "swan neck" deformity of some or all of the digits. Independent flexion of the index finger is important to the patient who depends on a precision pinch. This can be accomplished by a transfer of the extensor carpi radialis longus tendon to the flexor digitorum longus tendon of the index finger. Flexion of the thumb is accomplished by attaching the brachioradialis muscle to the tendon of the flexor pollicis longus. The ulnar deviation frequently observed in wrist flexion carried out solely by the flexor carpi ulnaris can be corrected by splitting that muscle's tendon and attaching one slip of the split tendon to the insertion of the flexor carpi radialis insertion.

Sensation can be partially restored to the ulnar volar surface of the thumb and opposing surface of the index finger by rotating a double cutaneous island with neurovascular pedicle from the opposing surfaces of the ring and small fingers.