Reinnervation of skeletal muscle with a neuromuscular pedicle

Nerve-muscle-endplate band grafting: a new technique for muscle reinnervation

BACKGROUND

Because currently existing reinnervation methods result in poor functional recovery, there is a great need to develop new treatment strategies.

OBJECTIVE

To investigate the efficacy of our recently developed nerve-muscle-endplate band grafting (NMEG) technique for muscle reinnervation.

METHODS

Twenty-five adult rats were used. Sternohyoid (SH) and sternomastoid (SM) muscles served as donor and recipient muscle, respectively. Neural organization of the SH and SM muscles and surgical feasibility of the NMEG technique were determined. An NMEG contained a muscle block, a nerve branch with nerve terminals, and a motor endplate band with numerous neuromuscular junctions. After a 3-month recovery period, the degree of functional recovery was evaluated with a maximal tetanic force measurement. Retrograde horseradish peroxidase tracing was used to track the origin of the motor innervation of the reinnervated muscles. The reinnervated muscles were examined morphohistologically and immunohistochemically to assess the extent of axonal regeneration.

RESULTS

Nerve supply patterns and locations of the motor endplate bands in the SH and SM muscles were documented. The results demonstrated that the reinnervated SM muscles gained motor control from the SH motoneurons. The NMEG technique yielded extensive axonal regeneration and significant recovery of SM muscle force-generating capacity (67% of control). The mean wet weight of the NMEG-reinnervated muscles (87% of control) was greater than that of the denervated SM muscles (36% of control).

CONCLUSION

The NMEG technique resulted in successful muscle reinnervation and functional recovery. This technique holds promise in the treatment of muscle paralysis.

Locations of the motor endplate band and motoneurons innervating the sternomastoid muscle in the rat

Sternocleidomastoid (SCM) is a long muscle with two bellies, sternomastoid (SM) and cleidomastoid (CM) in the lateral side of the neck. It has been widely used as muscle and myocutaneous flap for reconstruction of oral cavity and facial defects and as a candidate for reinnervation studies. Therefore, exact neuroanatomy of the SCM is critical for guiding reinnervation procedures. In this study, SM in rats were investigated to document banding pattern of motor endplates (MEPs) using whole-mount acetylcholinesterase (AChE) staining and to determine locations of the motoneurons innervating the muscle using retrograde horseradish peroxidase (HRP) tracing technique. The results showed that the MEPs in the SM and CM were organized into a single band which was located in the middle portion of the muscle. After HRP injections into the MEP band of the SM, ipsilaterally labeled motoneurons were identified in the caudal medulla oblongata (MO), C1, and C2. The SM motoneurons were found to form a single column in lower MO and dorsomedial (DM) nucleus in C1. In contrast, the labeled SM motoneurons in C2 formed either one (DM nucleus), two [DM and ventrolateral (VL) nuclei], or three [DM, VL, and ventromedial (VM)] columns. These findings are important not only for understanding the neural control of the muscle but also for evaluating the success rate of a given reinnervation procedure when the SM is chosen as a target muscle.

Nerve-muscle pedicle implantation facilitates re-innervation of long-term denervated thyroarytenoid muscle in rats

CONCLUSIONS

Nerve-muscle pedicle (NMP) implantation was effective in the recovery from atrophic changes in long-term denervated thyroarytenoid (TA) muscle. Re-innervation occurred via the transferred nerve. However, the effectiveness of the NMP method may decline with increasing duration of denervation.

OBJECTIVES

To evaluate the effects of NMP implantation on long-term denervated rat TA muscle.

MATERIALS AND METHODS

Wistar rats (n=105) were divided into two groups in which the left recurrent laryngeal nerve (RLN) was transected without (DNV group) or with (NMP group) subsequent NMP implantation, and subgroups of each group were formed depending on the period after RLN transection (immediate to 48 weeks). In the DNV subgroups, we histologically assessed the area of muscle and the number of neuromuscular junctions. In the NMP subgroups, we performed electromyographic, videolaryngoscopic, and histologic assessments. The muscle area and muscle action potentials were evaluated by comparing the treated and untreated sides. The ratio of the number of nerve terminals to that of acetylcholine receptors was also assessed.

RESULTS

The TA muscle area was significantly larger in most of the NMP subgroups compared with the DNV subgroups. Muscle action potentials were present in all NMP animals. All histologic and physiologic assessments revealed degradation as the denervation period in the five NMP subgroups.

Effects of a Nerve-Muscle Pedicle on the Denervated Rat Thyroarytenoid Muscle

OBJECTIVES

To evaluate the effects of the nerve-muscle pedicle (NMP) method on the rat thyroarytenoid (TA) muscle after transection of the recurrent laryngeal nerve (RLN).

STUDY DESIGN

Quantitative histologic assessment of the TA muscle after NMP implantation.

METHODS

Thirty-six Wistar rats were divided into two groups: animals subjected to transection of the left RLN alone (DNV group) and animals subjected to transection of the left RLN followed by immediate transplantation of a NMP flap containing the sternohyoid (SH) muscle and ansa cervicalis nerve branch (NMP group). Animals were killed 2, 4, and 10 weeks after the treatments. The TA muscle stained with hematoxylin-eosin was evaluated quantitatively. The pre- and postsynaptic structures of the neuromuscular junction (NMJ) in the TA muscle were analyzed histochemically. The myosin heavy chain (MyHC) isoforms were evaluated using immunohistochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR).

RESULTS

In the NMP group, the TA muscle fiber recovered to almost normal at 10 weeks, and the ratio of the number of synaptophysin-positive nerve terminals to that of alpha-bungarotoxin-positive acetylcholine receptors recovered to 79.8 +/- 11.8% (P < .05, compared with the control). Immunohistochemistry and the RT-PCR method after laser capture microdissection revealed the expression of MyHC isoforms type 2B and type 2A; the latter was detected in the SH muscle but not in the normal or denervated TA muscle.

CONCLUSION

The NMP method was effective for recovering from the atrophic changes of the TA muscle after transection of the RLN. This was attributed to successful reinnervation by reconstruction of the NMJ, which might change MyHC isoform expression.

Laryngeal reinnervation

Laryngeal reinnervation refers to any of a number of surgical procedures intended to restore neural connections to the larynx, which have usually been lost from some type of trauma (eg, surgical). The nerve function(s) to be restored may be those of the recurrent laryngeal nerve or its subdivisions, those of the superior laryngeal nerve, or both, and they may be motor or sensory. Several different donor nerves are available and have been described. The technique used may be direct end-to-end anastomosis (neurorrhaphy), direct implantation of a nerve ending into a muscle, the nerve-muscle pedicle technique, or muscle-nerve-muscle methods. These nerves and techniques may be combined in many ways. A number of new techniques have been reported in animal studies; however, the animal studies do not always predict the results of analogous surgeries in human patients. The historical and current perspectives on these techniques are discussed in this article.

Long-term excitability and fine tuning of nerve pedicles reinnervating strap muscles in the dog

Contraction of paralyzed striated muscles has been restored by stimulating reinnervating pedicles with currents of low intensity. In order to allow clinical application, stable, long-term excitability must emulate the parameters necessary for the stimulation of normal motor nerves. In 6 dogs, the ansa hypoglossi nerve was implanted into the contralateral denervated sternohyoid muscle and surrounded with a bipolar cuff electrode. Three of the reinnervating pedicles were chronically paced with a Medtronic Itrel II Multiprogrammable Pulse Generator (0.5 V, 0.2 second on [30 pulses per second, 0.21-millisecond pulse width], 2.9 seconds off). At reexploration after 8 months (6 months for 1 dog), frank contraction confirmed by electromyography tracings occurred in all animals with currents in the range of 0.1 to 0.5 mA. Muscle force was further manipulated by selective release of blocking currents (600 Hz, 1.7 to 0.4 mA) superimposed over regular stimulation (50 Hz, 0.3 to 1.7 mA). Nerve and muscle vitality were histologically confirmed. Long-term, low-intensity conduction capabilities, fine tuning, good tolerance of implanted electrodes, and lack of fatigue suggest that reinnervating pedicles may be successfully used for pacing when clinically indicated.

Motor nerve transplantation

The motor nerve transplantation (MNT) technique is used to transfer an intact nerve into a denervated muscle by harvesting a neurovascular pedicle of muscle containing motor endplates from the motor endplate zone of a donor muscle and implanting it into a denervated muscle. Thirty-six adult New Zealand White rabbits underwent reinnervation of the left long peroneal (LP) muscle (fast twitch) with a motor nerve graft from the soleus muscle (slow twitch). The right LP muscle served as a control. Reinnervation was assessed using microstimulatory single-fiber electromyography (SFEMG), alterations in muscle fiber typing and grouping, and isometric response curves. Neurofilament antibody was used for axon staining. The neurofilament studies provided direct evidence of nerve growth from the motor nerve graft into the adjacent denervated muscle. Median motor endplate jitter was 13 microsec preoperatively, and 26 microsec at 2 months, 29.5 microsec at 4 months, and 14 microsec at 6 months postoperatively (p < 0.001). Isometric tetanic tension studies showed a progressive functional recovery in the reinnervated muscle over 6 months. There was no histological evidence of aberrant reinnervation from any source outside the nerve pedicle. Isometric twitch responses and adenosine triphosphatase studies confirmed the conversion of the reinnervated LP muscle to a slow-type muscle. Acetylcholinesterase studies confirmed the presence of functioning motor endplates beneath the insertion of the motor nerve graft. It is concluded that the MNT technique achieves motor reinnervation by growth of new nerve fibers across the pedicle graft into the recipient muscle.

Restoration of orbicularis oculi function by contralateral orbicularis oculi innervated muscle flap vs neuromuscular pedicle technique

In preliminary experiments with dogs and cats, unilateral paralysis of the orbicularis oculi muscle group was produced by a section of the seventh nerve that included the posterior auricular branch. Either one of two procedures was then employed in attempts to reinnervate the paralyzed eyelid. In one group of animals, a neuromuscular pedicle was employed and in another, a contralateral orbicularis innervated muscle flap was used. Both methods restored synchronous, reflex blinking to the denervated eyelid. Of the two procedures, neurotization appears to offer the greater promise because the use of a neuromuscular pedicle requires an expendable nerve that is functional, and no such suitable substitute is available in humans.

Does intralaryngeal motor nerve sprouting occur following unilateral recurrent laryngeal nerve paralysis?

Reinnervation of paralyzed intralaryngeal muscles by axonal sprouting from adjacent intact muscles (the phenomenon of muscular neurotization) has been observed, but the source is uncertain. The potential for laryngeal reinnervation of the posterior cricoarytenoid muscle (PCA) from contralateral PCA motor nerve sprouting in a rabbit model was investigated. Unilateral PCA denervation was produced by vagotomy. The rabbits were examined for signs of PCA recovery for up to 6 months, using fiberoptic endoscopy, electromyography (EMG), and histology. No return of vocal cord abduction, EMG activity, or any nerve sprouting across the midline from the intact PCA was found. We conclude that there is no significant spontaneous intralaryngeal muscular neurotization to the paralyzed PCA. The clinical ramifications of our data will be discussed.

Correlation between histology and nerve excitability after reinnervation of paralyzed strap muscles in the rabbit

We have recently shown that the mean muscle chronaxie for nerve pedicle implanted into denervated rabbit strap muscle is comparable to that of normal nerve. This study correlates excitability with histologic characteristics of muscles reinnervated via nerve-muscle pedicles (NMP) and direct nerve implants (DNI). Strength duration curves were measured in 13 rabbits 3.5 to 5 months after reinnervation by NMP (n = 6) and DNI (n = 7). Following this, control (n = 5) and reinnervated straps were harvested immediately before the animals were killed and frozen in liquid nitrogen. The material was submitted for hematoxylin-eosin stains as well as trichrome stains for general morphology, myofibrillar ATPase and NADH for fiber typing, and cholinesterase for determination of denervated fibers. In all animals with low chronaxie, expected type grouping from reinnervation was noted (n = 10). By contrast, the three animals in which chronaxie was abnormally elevated demonstrated fibrosis, inflammation, and absence of or poor type grouping. This suggests that type grouping is necessary for excitability after reinnervation of paralyzed striated muscles.

Electrical control of gastric emptying in denervated and reinnervated canine stomach: a pilot study

Gastric emptying of solids is abnormally slow after vagotomy. To determine whether it was possible to accelerate emptying by electrical stimulation either of the gastric wall directly or of a "foreign" nerve brought in to reinnervate the stomach, eight dogs underwent truncal vagotomy (TV); five of the dogs received intercostal nerve muscle pedicle (NMP) implants. Gastric atony was demonstrated postoperatively in all animals up to 4 months later by means of radiological contrast studies. After allowing time for neurotization to occur (mean 78 days), the cervical vagi were stimulated to confirm that TV was complete. Gastric peristalsis, intraluminal pressures, and emptying were assessed during stimulation of the NMPs and of the gastric wall, followed by sacrifice for histologic study. Neither reinnervation alone nor stimulation of the NMPs improved emptying. Although viable somatic nerve was found in the gastric wall, nerve sprouting was not. By contrast, stimulation of the gastric wall with trains of pulses (20 Hz, 2-10 ms, 2-5 mA) evoked peristalsis in all animals. We conclude that somatic nerve tissue cannot produce functional reinnervation of a visceral organ; however, direct muscular stimulation can accelerate gastric emptying after TV.

The future of electronic pacing in laryngeal rehabilitation

Fascinating advances are ongoing in the rehabilitation of the incompetent larynx. The advent of microprocessor technology makes possible the construction of potentially implantable devices designed to allow the pacing of various functions of the reinnervated canine larynx. The history of electrical neurostimulation as a technique in laryngeal rehabilitation is reviewed and future human applications discussed in terms of technical feasibility and clinical needs.

An artificial myotatic reflex: a potential avenue to fine motor control

When a striated muscle becomes paralyzed, not only its motor function, but its sensory innervation may be impaired. Methods of rehabilitation have previously focused only on motor innervation, although striated muscles are submitted to self-regulation of length and tension. Indeed, reinnervated muscle may not contract appropriately unless sensory information is available, nor is it known whether sensory receptors are included in the reinnervation process. We hypothesized that the myotatic reflex (MR) would be absent in the event these sensory organs are not reinnervated, and that an artificial myotatic reflex (AMR) would be useful in reestablishing fine motor control. The strap muscles were exposed in six anesthetized rabbits. The MR was verified by stretching an intact sternohyoid muscle. Next, loss of the reflex was documented after the ipsilateral ansa hypoglossi was divided, and a crossover nerve-muscle pedicle (NMP) was brought in from the opposite sternothyroid. After 3 months, the MR was still absent; however, stretch of the contralateral sternohyoid produced a reflex response on the reinnervated side. A strain gauge sutured to the reinnervated muscle was linked to an electronic modulator so that stretch induced electric stimulation of the NMP and contraction (the AMR). We conclude that (1) proprioception is not reestablished in the reinnervated muscle; (2) by contrast, sensory information from the muscle of origin of the NMP is conveyed to the reinnervated side; and (3) the AMR offers promise toward more sophisticated control of paralyzed (i.e., facial, laryngeal) musculature.

Dynamic rehabilitation of the paralyzed face--II. Electronic control of the reinnervated facial musculature from the contralateral side in the rabbit

This work is the continuation of a previous pilot study in the rabbit in which motion originating on the face was picked up by miniature strain gages and channeled synchronously to strap muscles reinnervated via crossover nerve-muscle pedicles. In the current series of experiments, we modified the distal limb of the system to reinnervate the previously paralyzed opposite side of the face via an ansa hypoglossi nerve--thyrohyoid muscle pedicle in five animals. Muscular contraction was induced on the intact side by stimulating different branches of the facial nerve, and corresponding information was channeled to the reinnervated side through an upgraded electronic stimulator via monopolar electrodes placed around the nerve pedicle in the neck. In addition to demonstrating perfect synchrony between intact and reinnervated sides, this facial stimulator allowed the reinnervated side of the face to follow the intact side in a graded and sustained fashion, thus demonstrating that fine tuning of reinnervated facial musculature was possible.

Long-term results of nerve-muscle pedicle reinnervation for laryngeal paralysis

Between 1976 and 1986, 214 patients with bilateral vocal fold paralysis and 73 patients with unilateral vocal fold paralysis were managed by the author using the nerve-muscle pedicle technique for reinnervation. Follow-up of at least 2 years has been obtained on 202 of the bilaterally and 70 of the unilaterally involved patients. Long-term success has been achieved in 74% of the bilateral group and 88% of the unilateral group. Successful reinnervation of unilateral paralyses usually maintains voice correction indefinitely, but there is late (2 to 5 years postsurgery) deterioration of successful airway restoration in approximately 17% of bilateral cases, which appears to be due to development of cricoarytenoid arthritis.

Selective reinnervation of the abductor and adductor muscles of the canine larynx after recurrent nerve paralysis

Functional rehabilitation of the larynx after unilateral vocal cord paralysis was attempted in the dog by selective reinnervation of the laryngeal muscles. The intralaryngeal branches of the right recurrent nerve were dissected. The adductor branch was anastomosed with the ansa cervicalis; the abductor branch was anastomosed with the trunk of the phrenic nerve either within the larynx or through the recurrent nerve, the adductor branch of which was sectioned. Results could be analyzed in seven dogs: mobility of the vocal cord was checked, and electromyography, stimulation of the nerves, and histologic studies were performed. Functional reinnervation of both the adductor and abductor muscles was obtained in only one case, with good abduction. Adduction was recorded in five cases. False-positive results emphasize the necessity of collecting several types of data before concluding that functional reinnervation has been accomplished. The reliability of the procedure can and must be improved.

Excitation thresholds for nerve pedicles: a preliminary report

Ongoing interest in the rehabilitation of paralyzed musculature in the head and neck has focused on the electronic stimulation of nerve-muscle pedicles that have been reimplanted into the incapacitated effector(s). Despite visual and histochemical evidence of reinnervation, it is still not known whether the excitability of a nerve-muscle pedicle (or for that matter a direct nerve implant) is equivalent to or better than that of reinnervated or normal muscle. Such information is necessary for the eventual construction of an implantable stimulator. Eighteen rabbits were anesthetized with intramuscular xylazine and ketamine and the ansa hypoglossi nerve was cut on one side. A crossover nerve-muscle pedicle was brought in from the opposite sternothyroid muscle to the sternohyoid in nine animals; the other nine received a direct nerve implant. After a minimum neurotization period of 3 months and reexploration, an electrical stimulator capable of delivering square wave pulses of variable amplitude and width was used to determine the thresholds of contraction of the nerve pedicles, an intact motor nerve of similar size, a normal muscle, and the reinnervated strap in 16 evaluable rabbits. Strength duration curves were established. The data indicate that thresholds for nerve pedicles are equivalent to those of normal nerves and are significantly lower than those of muscle.

Direct nerve implantation vs. nerve-muscle pedicle: a comparative study of reinnervation in the rabbit

To determine the optimal method for reinnervation of the paralyzed head and neck musculature, we compared direct muscular nerve implants (DNI) with nerve-muscle pedicles (NMP) in rabbits. In 25 anesthetized animals, one ansa hypoglossi nerve was cut. Five animals served as controls and two groups of 10 each received cross-over DNIs or NMP from one sternothyroid to the contralateral sternohyoid muscle. The transplanted nerves of animals that survived long enough for neurotization to occur (8 DNIs, 5 NMPs) were stimulated with 3 to 10 mA. 0.05 msec pulse trains to obtain force curves from corresponding straps. Fiber diameters and areas were calculated on muscles harvested before the animals were killed. There was a nonsignificant trend toward stronger contraction in the NMP group, but NMP fibers were significantly larger than those in DNI and control groups (p less than 0.001).

Reinnervation of the trapezius muscle

The eleventh cranial nerve shoulder syndrome, which results from denervation of the trapezius muscle, contributes significantly to the postoperative morbidity of radical neck dissections. Multiple techniques exist for the reinnervation of muscles that have injured motor nerves. Reinnervation of denervated trapezius muscles was examined in the New Zealand white rabbit by use of three techniques of reinnervation: (1) neuromuscular pedicle transfer of the accessory nerve from the trapezius muscle, (2) direct accessory nerve implantation, and (3) neuromuscular pedicle transfer of the accessory nerve from the sternocleidomastoid muscle. The reinnervated trapezius muscles were examined grossly by direct nerve stimulation, electrophysiologically by evoked electromyography, and histologically by enzymatic muscle staining and silver-reducing nerve staining. The gross, electrophysiologic, and histologic results confirmed successful reinnervation of the trapezius muscle within 6 weeks of operation. No significant difference was observed between the various techniques of reinnervation.

Dynamic rehabilitation of the paralyzed face: I. Electronic control of reinnervated muscles from intact facial musculature in the rabbit

An entirely satisfactory solution to dynamic rehabilitation of the paralyzed facial musculature has not yet been found. Recent interest in selective reinnervation of the laryngeal musculature, synchronous with appropriate afferent information, has led us to propose that miniature strain gauges be placed on one or more muscles of facial expression on the intact side to channel electrical signals to the opposite corresponding facial musculature reinnervated via nerve-muscle pedicles. In order to avoid introducing extraneous factors related to facial motion, this principle was first studied on crossover ansa hypoglossi nerve-muscle pedicles in New Zealand white rabbits. Surgery was performed on a total of five animals that were under general anesthesia with xylazine and ketamine, through a midline neck incision. The animals were reexplored after 12 weeks, and after verification that reinnervation had taken place, a vertical incision was made under the external canthus, in order to expose the facial nerve. A miniature strain gauge was then sutured on the facial musculature and connected to a central modulating unit that was, in turn, linked to the nerve-muscle pedicle via a monopolar electrode. Facial wiggle that resulted from direct electrical facial nerve stimulation caused synchronous contraction of all reinnervated strap muscles under study; this was documented on film and through facial and strap muscle activity tracings. Our next step will be to extend this principle to paralyzed facial muscles. If successful, this system could be miniaturized for long-term implantation in human beings.

Histochemical study of posterior cricoarytenoid muscle reinnervation by a nerve-muscle pedicle in the cat

Reinnervation of the posterior cricoarytenoid (PCA) muscle with a nerve-muscle pedicle (NMP) has been proposed for patients with bilateral abductor vocal cord paralysis. Since its success has been controversial, a glycogen depletion histochemical technique was used to examine reinnervation. An ansa cervicalis NMP was implanted into the denervated PCA in nine cats. Eight months later, vocal cord activity was evaluated. The NMP nerve was stimulated extensively in seven cats (experimental group). Optical densities of NMP-supplied PCA muscle fibers from experimental and control groups were compared to detect differences in glycogen content. The results demonstrated quantitative evidence of reinnervation in two experimental animals. Electrical stimulation of the NMP produced abduction in one of these two animals, but was never observed during spontaneous respiration or airway occlusion. These observations indicate that reinnervation can occur but abduction requires electrical stimulation. The NMP technique may be more successful with an electrical pacer.

Reinnervation of skeletal muscle: a comparison of nerve implantation with neuromuscular pedicle transfer in an animal model

In recent years there has been increased interest in the possibility of reinnervating paralyzed muscles, particularly the muscles of the face and of the larynx. There has been dispute over the relative effectiveness of different approaches. This study was undertaken to compare direct nerve implantation with the transfer of a neuromuscular pedicle using denervated strap muscles in a rabbit model. Reinnervation was carried out both immediately after denervation and after a delay period. Evidence of return of function was obtained by a method of long-term electromyographic monitoring and was confirmed electrically by evoked electromyography and muscle tension measurement and histologically by brain stem uptake of horseradish peroxidase. Both methods of nerve transfer produced consistently functional neuromuscular units, with physiological activity and muscle strength comparable with those in normally innervated controls. Return of function was apparent within 6 weeks of both nerve implantation and neuromuscular transfer; with this model, neither method showed a clear advantage over the other.

Preliminary observations after facial rehabilitation with the ansa hypoglossi pedicle transfer

Facial paralysis is a very disabling condition, both functionally and cosmetically. Despite the different methods of facial reanimation that have been described, there is no single method that will restore normal facial tone and motion. Of the methods available, primary neurorrhaphy is probably the most effective. The recovery period, however, is prolonged and, as a result, muscle tone and bulk may be lost. The hypoglossal-facial anastomosis is also a very reliable and effective technique but requires necessary interruption of both major cranial nerve trunks. Transfer of a neuromuscular pedicle (based on the ansa hypoglossi) has been offered as a method of facial reanimation that involves neither prolonged recovery nor interruption of the major cranial nerve functions. The application of this technique for reinnervation of a paralyzed larynx was first described by Tucker in 1970, and the technique was applied to facial muscle (in animal models) in 1977. The effectiveness of this technique--and its application in the management of facial paralysis in the human patient--remains controversial. We report our experience with a series of six patients who underwent neuromuscular pedicle transfer in conjunction with other more conventional methods of facial reanimation. The function of the pedicle and its contribution to the overall facial rehabilitation were assessed clinically and electromyographically. Factors influencing the success of the procedure and clinical and experimental evidence to support its application are discussed. While our experience with this technique is limited, it would appear that the neuromuscular pedicle transfer may play a useful adjunctive role in reanimation of the face in selective cases of facial paralysis.

Assessment of facial reinnervation by use of chronic electromyographic monitoring

The study of muscle reinnervation has been difficult because of lack of an accurate, reproducible method to monitor return of function. Visual assessment relies on subjective interpretation. Histology provides anatomic, not functional, information. Electromyography and anatomic tracing have been most effective in evaluating physiologic return of muscle function. It has been difficult to assess the timing of functional return electromyographically because measurements are intermittent and electrode placement varies. A method was designed to allow long-term monitoring of electromyographic (EMG) activity in the facial musculature of the rabbit. Sixteen rabbits were monitored for at least 1 month or until return of normal EMG activity was identified. Various levels of injury (nerve crush, transection without repair, and transection with immediate end-to-end anastomosis) were evaluated. EMG evidence of reinnervation was seen in all animals with nerve crush injuries as well as those with anastomoses. Physiologic continuity of the nerves was then evaluated by retrograde transport of horseradish peroxidase. All muscles showing return of EMG activity had uptake of HRP into the appropriate brain stem motor neurons. The denervated muscles showed no HRP uptake. The information gained in this study shows potential for use of this technique in comparing functional return of muscle activity between different reinnervation methods.

Laryngeal pacemaker. Part I. Electronic pacing of reinnervated strap muscles in the dog

The best approach to management of bilateral vocal cord paralysis, with its resultant airway compromise, has not yet been universally agreed upon. Recently proposed methods have included direct stimulation of the laryngeal dilators by the modulation of rhythmic information from the chest wall, diaphragm, phrenic nerve, or accessory muscles of respiration. In such an approach, the information obtained is not necessarily related to inspiration only, and direct implantation of a stimulating electrode into the laryngeal musculature may not be fully efficient and tolerated over time. To obviate such difficulties, the authors propose to broaden the concept of electrical pacing by (1) developing a better source for the triggering of electrical activity during inspiration and (2) devising a reliable means of long-term physiologic stimulation of denervated striated muscle not subject to deterioration over time. Such an experimental unit was constructed in the canine. It is based on afferent information that originates from the mechanical lengthening of the trachea during inspiration and is detected through a linear strain gauge sutured to the tracheal rings. The signal obtained is modulated through an impedance detector and is amplified. An efferent limb consisting of a monopolar cuffed electrode placed around a crossover nerve-muscle pedicle from one sternohyoid muscle to the other was used successfully. Such a preliminary experiment with a strap muscle avoids the extraneous factors related to function of the paralyzed larynx. Successful nerve-muscle pedicle pacing, synchronous with respiration, was verified through electromyographic recordings and direct observation in all animals studied.