Effects of different methods of peripheral nerve repair on the number and distribution of muscle afferent neurons in rat dorsal root ganglion

Sensory nerve regeneration and reinnervation in muscle following peripheral nerve injury

Sensory afferent fibers are an important component of motor nerves and compose the majority of axons in many nerves traditionally thought of as "pure" motor nerves. These sensory afferent fibers innervate special sensory end organs in muscle, including muscle spindles that respond to changes in muscle length and Golgi tendons that detect muscle tension. Both play a major role in proprioception, sensorimotor extremity control feedback, and force regulation. After peripheral nerve injury, there is histological and electrophysiological evidence that sensory afferents can reinnervate muscle, including muscle that was not the nerve's original target. Reinnervation can occur after different nerve injury and muscle models, including muscle graft, crush, and transection injuries, and occurs in a nonspecific manner, allowing for cross-innervation to occur. Evidence of cross-innervation includes the following: muscle spindle and Golgi tendon afferent-receptor mismatch, vagal sensory fiber reinnervation of muscle, and cutaneous afferent reinnervation of muscle spindle or Golgi tendons. There are several notable clinical applications of sensory reinnervation and cross-reinnervation of muscle, including restoration of optimal motor control after peripheral nerve repair, flap sensation, sensory protection of denervated muscle, neuroma treatment and prevention, and facilitation of prosthetic sensorimotor control. This review focuses on sensory nerve regeneration and reinnervation in muscle, and the clinical applications of this phenomena. Understanding the physiology and limitations of sensory nerve regeneration and reinnervation in muscle may ultimately facilitate improvement of its clinical applications.

A novel conduit-based coaptation device for primary nerve repair

BACKGROUND

Conduit-based nerve repairs are commonly used for small nerve gaps, whereas primary repair may be performed if there is no tension on nerve endings. We hypothesize that a conduit-based nerve coaptation device will improve nerve repair outcomes by avoiding sutures at the nerve repair site and utilizing the advantages of a conduit-based repair.

METHODS

The left sciatic nerves of female Sprague-Dawley rats were transected and repaired using a novel conduit-based device. The conduit-based device group was compared to a control group of rats that underwent a standard end-to-end microsurgical repair of the sciatic nerve. Animals underwent behavioral assessments at weekly intervals post-operatively using the sciatic functional index (SFI) test. Animals were sacrificed at four weeks to obtain motor axon counts from immunohistochemistry. A sub-group of animals were sacrificed immediately post repair to obtain MRI images.

RESULTS

SFI scores were superior in rats which received conduit-based repairs compared to the control group. Motor axon counts distal to the injury in the device group at four weeks were statistically superior to the control group. MRI tractography was used to demonstrate repair of two nerves using the novel conduit device.

CONCLUSIONS

A conduit-based nerve coaptation device avoids sutures at the nerve repair site and leads to improved outcomes in a rat model. Conduit-based nerve repair devices have the potential to standardize nerve repairs while improving outcomes.

Fibrin glue repair leads to enhanced axonal elongation during early peripheral nerve regeneration in an in vivo mouse model

Microsurgical suturing is the gold standard of nerve coaptation. Although literature on the usefulness of fibrin glue as an alternative is becoming increasingly available, it remains contradictory. Furthermore, no data exist on how both repair methods might influence the morphological aspects (arborization; branching) of early peripheral nerve regeneration. We used the sciatic nerve transplantation model in thy-1 yellow fluorescent protein mice (YFP; n = 10). Pieces of nerve (1cm) were grafted from YFP-negative mice (n = 10) into those expressing YFP. We performed microsuture coaptations on one side and used fibrin glue for repair on the contralateral side. Seven days after grafting, the regeneration distance, the percentage of regenerating and arborizing axons, the number of branches per axon, the coaptation failure rate, the gap size at the repair site and the time needed for surgical repair were all investigated. Fibrin glue repair resulted in regenerating axons travelling further into the distal nerve. It also increased the percentage of arborizing axons. No coaptation failure was detected. Gap sizes were comparable in both groups. Fibrin glue significantly reduced surgical repair time. The increase in regeneration distance, even after the short period of time, is in line with the results of others that showed faster axonal regeneration after fibrin glue repair. The increase in arborizing axons could be another explanation for better functional and electrophysiological results after fibrin glue repair. Fibrin glue nerve coaptation seems to be a promising alternative to microsuture repair.

Sciatic nerve repair using adhesive bonding and a modified conduit

When repairing nerves with adhesives, most researchers place glue directly on the nerve stumps, but this method does not fix the nerve ends well and allows glue to easily invade the nerve ends. In this study, we established a rat model of completely transected sciatic nerve injury and repaired it using a modified 1 cm-length conduit with inner diameter of 1.5 mm. Each end of the cylindrical conduit contains a short linear channel, while the enclosed central tube protects the nerve ends well. Nerves were repaired with 2-octyl-cyanoacrylate and suture, which complement the function of the modified conduit. The results demonstrated that for the same conduit, the average operation time using the adhesive method was much shorter than with the suture method. No significant differences were found between the two groups in sciatic function index, motor evoked potential latency, motor evoked potential amplitude, muscular recovery rate, number of medullated nerve fibers, axon diameter, or medullary sheath thickness. Thus, the adhesive method for repairing nerves using a modified conduit is feasible and effective, and reduces the operation time while providing an equivalent repair effect.

A systematic review on the use of fibrin glue for peripheral nerve repair

BACKGROUND

Although Tisseel (Baxter, Deerfield, Ill.) was introduced over 30 years ago, the literature remains scant regarding its use and efficacy in peripheral nerve repairs. The goal of this systematic review was to summarize current literature on this topic and discuss differences in clinical outcome between the use of fibrin glue and conventional suturing methods for the repair of peripheral nerves.

METHODS

A comprehensive electronic literature search was run in the following databases: Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MEDLINE, CINAHL, and EMBASE. Articles were classified into three categories: animal, human, and cadaveric studies.

RESULTS

Sixteen articles were included in the final analysis (kappa = 0.78). The most consistent outcome measure of the studies assessed was histopathology, which was evaluated in nine of 16 studies. This was followed closely by biomechanics, which were evaluated in eight of 16 studies. Histopathological studies demonstrated less significant granulomatous inflammation in the fibrin groups as well as better overall axonal regeneration, fiber alignment, and recovery of nerve conduction velocities. Animal and cadaveric studies demonstrated no significant differences in stiffness and peak load at failure between microsuture and fibrin groups.

CONCLUSIONS

Although the majority of the reviewed studies employed animal models, most indicated that the performance of fibrin glue was equal, if not superior, to that of microsuturing when repairing peripheral nerves. Overall, many authors reported that fibrin glue was a quicker and easier modality to use than microsuture repair. There is, however, not a single well-controlled human trial assessing the efficacy of fibrin glue in relation to that of suturing techniques.

Pharmacological immunomodulation enhances peripheral nerve regeneration

To assess the effect of N-Acetylmuramyl-L-Alanyl-D-Isoglutamine MDP topically administrated on the regenerating peripheral neurons, twelve male C57BL/6J adult mice were equally distributed into three groups. Four mice underwent unilateral sciatic nerve transection and polyethylene tubulization, with a 4mm gap between the proximal and distal nerve stumps and were implanted with collagen + PBS (COL). Other four animals underwent the same surgical procedure but received collagen + MDP (COL/MDP) inside the prosthesis. Four animals were not operated and served as control group (NOR). After 4 weeks, the regenerated nerve cables were processed for total myelinated axon counting and myelinated fiber diameter measurement. The L5 dorsal root ganglion (DRG) was also removed and sectioned for sensory neurons counting and measurement. The results revealed significant difference (p<0.05) in axonal counting among the groups NOR (4,355±32), COL (1,869±289) and COL/MDP (2,430±223). There was a significant reduction in the axonal diameter in the operated groups (COL=3.38µm±1.16 and COL/MDP=3.54µm±1.16) compared to NOR (6.19µm±2.45). No difference was found in the number of DRG neurons between the experimental groups (COL=564±51; COL/MDP=514±56), which presented fewer sensory neurons compared to NOR (1,097±142). Data obtained indicate that locally applied MDP stimulates peripheral nerve regeneration in mice.

Prognostic Factors for the Surgical Management of Peripheral Nerve Lesions

Although the evaluation and treatment of patients with peripheral nerve injuries has evolved and improved over the years, there are still some arguments on the methods and results of surgery. We reviewed retrospectively the clinical, electrophysiological and surgical characteristics of peripheral nerve lesions for 1,636 nerves in 1,565 patients who had been managed in our department in a 10-year period. The most common cause of injuries was gunshot wound in 56.3% of all patients, followed by sharp lacerations (20.6%), fractures (10.6%) and tractions (5.1%). Among 1,636 cases of nerve injuries, the most frequently wounded nerve was median nerve (32.3%), followed by ulnar (24.1%), radial (12.1%), sciatic (10.7%) and peroneal nerves (7.7%), and brachial plexus (7.7%). Simple decompression was the most preferred technique for nerve repair in 27.8%. The electrophysiological improvement was observed in 66.8%, as assessed by electromyography. Clinical improvement was found in 58.4%, as judged by muscle strength grading. If the nerve is compressed or contused, but remains intact, the improvement is satisfactory after surgery. The type of injury, its time of occurrence, initial deficit, and degree of recovery expected are important issues in establishing the treatment plan, which may range from skilled observation to extensive surgical intervention.

Long-term functional outcome in facial nerve graft by fibrin glue in the temporal bone and cerebellopontine angle

The aim of this study was to evaluate the functional outcome of facial nerve repair with fibrin glue in end-to-end anastomosis and intermediate nerve graft. Thirty-six patients undergoing facial nerve repair by end-to-end anastomosis or facial nerve grafting using exclusively fibrin glue between 1986 and 1999 were included in this retrospective study. The population comprised ten vestibular schwannomas (28%), nine temporal bone fractures (25%), seven facial nerve schwannomas (19%), four facial nerve hemangiomas (11%), two iatrogenic facial nerve interruptions (6%) and four miscellaneous facial nerve lesions (11%). Data were reviewed concerning etiology, location of the nerve interruption, type of repair and postoperative facial function according to the repaired facial nerve recovery scale (A: normal; B: independent movements of eyelid and mouth; C: strong closure of eyelids and mouth; D: incomplete eyelid closure; E: minimal movement; F: no movement). Eleven patients (31%) underwent end-to-end nerve anastomosis and 25 (69%) underwent intermediate facial nerve grafting. The mean follow-up period was 50 months (range: 3-95). Among patients followed-up more than 18 months (n = 20), a score of B or C was obtained in 16 patients (80%), a score D in 2 cases (10%) and a score E in 2 cases (10%). The type of repair and the site of interruption did not influence the results. Fibrin glue is a simple, rapid and efficient means of facial nerve repair. In case of intraoperative facial nerve interruption, this type of repair can be attempted in any location at the time of the tumor removal.

Assessment of the method and timing of repair of a brachial plexus traction injury in an animal model for obstetric brachial plexus palsy

A Sunderland type IV traction injury to the C6 root of adult sheep or newborn lamb brachial plexus was used as a model for obstetric traction injury to the C5 root in humans. In one experimental cohort the injury was created and repaired using interfascicular nerve autografts or coaxially aligned freeze-thawed skeletal muscle autografts in a group of adult sheep and in a group of newborn lambs. In a second cohort a similar injury was created and repaired either immediately or after a delay of 30 days, using either interfascicular nerve autografts or coaxially aligned freeze-thawed skeletal muscle autografts in four groups of six newborn lambs. In all cases both functional and morphometric indices of nerve regeneration were poorer in the injured and repaired nerves than in normal nerves. In lambs the method of repair made no difference and no significant differences were found for any of the indices of nerve function or morphology. In sheep the use of muscle grafts was associated with a poorer outcome than the use of nerve autografts. Where a delay of 30 days had elapsed between injury and repair, the results using nerve autografts were not significantly different. Where freeze-thawed muscle autografts had been used, the maturation of the regenerated nerve fibres after delay was significantly poorer than after immediate repair. The electrophysiological variables CV(max) and jitter, which may be applied clinically, were found to be good discriminators of recovery in all of the animals and in respect of all procedures.

Changes in muscle cytoarchitecture after peripheral nerve injury and repair. A quantitative and qualitative study

The aim of this study was to assess the changes which occurred in the rat in target muscles after the injury and repair of a specific peripheral nerve, using several clinically-appropriate surgical techniques. There were alterations in the size, shape, morphology and cytochemical architecture of the fibres of the target muscles. These changes were marked when transection and repair of the nerve was compared with the less-severe crush injury. The method of repair did not correlate significantly with the occurrence of changes in muscle cytoarchitecture. The results suggest that the extent of cell loss and the changes in muscle fibre architecture were influenced by the type of injury, rather than by the method of repair.

Comparison of microsuturing to the use of tissue adhesives in anastomosing sciatic nerve cuts in rats

The purpose of this study was to investigate and to compare the effects of microsuturing to that of tissue adhesives (Tisseel) on the healing of anastomosing peripheral nerve incisions. Forty-five Wistar-Albino rats were placed in special cages and separated into three groups (n = 15). In the control group, biliteral sciatic nerves were explored but no incision was made. In the first experimental group, bilateral sciatic nerves were incised and end-to-end anastomosing was performed by microsuturing the epineurium. In the second experimental group, tissue adhesive (Tisseel) was used alone in anastomosing the sciatic nerve cuts. Assessments of the healing processes were demonstrated by 1.electromyography (EMG), 2. measuring the electrical responses of the anastomosed nerves after electrical stimuli, 3. histopathological examination. Statistical analysis of the EMG findings showed that the Tisseel group was the closest in the healing process to the control group. After applying electrical stimuli to the dissected nerves, the resistance value of the Tisseel group was nearest to those of the control group. The histopathological examinations showed highly degenerative nerve bundles and prominent foreign body granuloma at the anastomosed sites of the microsutured group. The granulomatous inflammation was observed to be much less in the Tisseel group. We conclude that the healing effect of Tisseel was found to be superior to that of microsuturing as demonstrated by the findings of EMG, electrical responses of the anastomosed nerves, and histopathological examination.

The fate of motoneurons in the spinal cord after peripheral nerve repair: a quantitative study using the neural tracer horseradish peroxidase

This study assessed the changes that occurred in the spinal motoneuron pool after the repair of a specific peripheral nerve by means of several clinically appropriate surgical techniques: nerve graft, muscle graft, and epineurial suture. The motoneuron pool relating to a single muscle was assessed at 50, 100, 200, and 300 days after repair via retrograde axonal transport of the neural tracer horseradish peroxidase. The results indicate that although a small portion of the motoneuron population dies following peripheral nerve surgery, this is not a significant number. The majority of the anterior horn cells appear to have the ability to both survive nerve transection and form new functional connections with the regenerated nerve after repair. The degree of cell loss is influenced by the nature of the injury and the method of repair implemented. Injuries involving neurotmesis result in the loss of a greater proportion of the cell population than less severe injuries involving axonotmesis. A greater proportion of the motoneuron population is preserved when the severed nerve has been repaired using a direct epineurial suture than when repair is achieved by means of a graft. The two methods of grafting produced comparable results, although the muscle graft tended to result in the preservation of a greater number of cells than the nerve graft, making it an acceptable alternative method for the surgical repair of short gaps in peripheral nerves.

A rostrocaudal somatotopic organization in the brachial dorsal root ganglia of neonatal rats

A rostrocaudal somatotopic organization in the rat lumbar dorsal root ganglia (DRGs) during development has been demonstrated. The present study shows that such a rostrocaudal somatotopic organization also exists in the brachial DRGs of neonatal rats. WGA-HRP or WGA-HRP/HRP injections into the forepaw of neonatal rats gave rise to completely and partially labeled DRGs. Partial labeling always concerned the caudal or rostral halves of the rostral-most or caudal-most labeled DRGs, respectively. Labeling of forelimb nerves (cutaneous branch of the musculocutaneous nerve, median and ulnar nerve) in neonatal rats also resulted in whole labeled DRGs and labeled rostral or caudal halves of DRGs. Accordingly, just as was found for the hind limb nerves, the position of the somata of the sensory neurons of forelimb nerves can be restricted to the rostral or caudal half of a DRG. Moreover, it was observed that the rostrocaudal organization in the brachial DRGs is maintained in the spinal nerves. Application of tracer to the cut end of intercostal nerves in neonatal rats produced labeling of one whole thoracic DRG. It is therefore possible that the rostrocaudal organization in the brachial and lumbar DRGs is a consequence of the formation of the plexuses. In one instance a subdivision in the labeling pattern of a midthoracic DRG was noticed after a WGA-HRP injection into the thoracic wall of a neonatal rat. The whole thoracic DRG was labeled except the dorsorostral corner. This indicates that during development, some kind of somatotopic organization may exist also in the thoracic DRG.