Facial nerve graft repair: suture versus laser-assisted anastomosis

Light-Activated Sealing of Nerve Graft Coaptation Sites Improves Outcome following Large Gap Peripheral Nerve Injury

BACKGROUND

Nerve repair using photochemically bonded human amnion nerve wraps can result in superior outcomes in comparison with standard suture. When applied to nerve grafts, efficacy has been limited by proteolytic degradation of bonded amnion during extended periods of recovery. Chemical cross-linking of amnion before bonding may improve wrap durability and efficacy.

METHODS

Three nerve wraps (amnion, cross-linked amnion, and cross-linked swine intestinal submucosa) and three fixation methods (suture, fibrin glue, and photochemical bonding) were investigated. One hundred ten Lewis rats had 15-mm left sciatic nerve gaps repaired with isografts. Nine groups (n = 10) had isografts secured by one of the aforementioned wrap/fixation combinations. Positive and negative control groups (n = 10) were repaired with graft and suture and no repair, respectively. Outcomes were assessed using sciatic function index, muscle mass retention, and histomorphometry. Statistical analysis was performed using analysis of variance and the post hoc Bonferroni test (p < 0.05).

RESULTS

Cross-linking improved amnion durability. Photochemically bonded cross-linked amnion recovered the greatest sciatic function index, although this was not significant in comparison with graft and suture. Photochemically bonded cross-linked amnion recovered significantly greater muscle mass (67.3 ± 4.4 percent versus 60.0 ± 5.2 percent; p = 0.02), fiber diameter, axon diameter, and myelin thickness (6.87 ± 2.23 μm versus 5.47 ± 1.70 μm; 4.51 ± 1.83 μm versus 3.50 ± 1.44 μm; and 2.35 ± 0.64 μm versus 1.96 ± 0.47 μm, respectively) in comparison with graft and suture.

CONCLUSION

Light-activated sealing of cross-linked human amnion results in superior outcomes when compared with conventional suture.

Effectiveness of fibrin adhesive in facial nerve anastomosis in dogs compared with standard microsuturing technique

PURPOSE

Epineural suturing is the most common technique used for peripheral nerve anastomosis. In addition to the foreign body reaction to the suture material, the surgical duration and difficulty of suturing in confined anatomic locations are major problems. We evaluated the effectiveness of fibrin glue as an acceptable alternative for nerve anastomosis in dogs.

METHODS

Eight adult female dogs weighing 18 to 24 kg were used in the present study. The facial nerve was transected bilaterally. On the right side, the facial nerve was subjected to epineural suturing; and on the left side, the nerve was anastomosed using fibrin adhesive. After 16 weeks, the nerve conduction velocity and proportion of the nerve fibers that crossed the anastomosis site were evaluated and compared for the epineural suture (right side) and fibrin glue (left side). The data were analyzed using the paired t test and univariate analysis of variance.

RESULTS

The mean postoperative nerve conduction velocity was 29.87 ± 7.65 m/s and 26.75 ± 3.97 m/s on the right and left side, respectively. No statistically significant difference was found in the postoperative nerve conduction velocity between the 2 techniques (P = .444). The proportion of nerve fibers that crossed the anastomotic site was 71.25% ± 7.59% and 72.25% ± 8.31% on the right and left side, respectively. The histologic evaluation showed no statistically significant difference in the proportion of the nerve fibers that crossed the anastomotic site between the 2 techniques (P = .598).

CONCLUSIONS

The results suggest that the efficacies of epineural suturing and fibrin gluing in peripheral nerve anastomosis are similar.

Photochemical Tissue Bonding: A Promising Technique for Peripheral Nerve Repair

BACKGROUND

Photochemical tissue bonding (PTB) is a novel tissue repair technique that uses visible light and a photosensitizing dye to crosslink proteins on tissue surfaces. This technique has been successfully demonstrated in a number of tissue repair models. An ideal nerve repair technique would be atraumatic and avoid placement of foreign bodies at the repair site. The epineurium is suited to photochemical repair as it is thin, translucent and has a relatively high collagen content. This study was designed to determine if PTB could be successfully applied in a peripheral nerve repair model.

MATERIAL AND METHODS

Forty Sprague Dawley rats underwent transection of the sciatic nerve. Animals were then randomized to four treatment groups; epineurial suture repair, epineurial cuff with PTB, epineurial cuff alone, and no repair. Functional recovery was assessed at 10 day intervals using walking track analysis and sciatic function index calculations. At 90 days postoperatively animals were sacrificed and sciatic nerves harvested for histology and histomorphometry.

RESULTS

Functional recovery in the suture repair and epineural cuff with PTB groups were not significantly different (-70.6 +/- 17.8 versus -76.9 +/- 10.3, P = 0.64) at 90 days postrepair. Histology showed good axonal regeneration with all repair techniques. Histomorphometric analysis found no significant difference between the repair groups.

CONCLUSIONS

This study illustrates that peripheral nerves can be successfully repaired using a photochemical tissue bonding technique with results similar to those achieved with the current gold standard. With further development and refinement PTB may prove a useful tool in peripheral nerve repair.

Facial-Hypoglossal Nerve Anastomosis Using Laser Nerve Welding

The aim of this study is to compare laser nerve welding to microsurgical suturing of hypoglossal-facial nerve anastomosis (HFA), and a result of immediate to delayed repair, and to evaluate the effect of laser nerve welding on HFA for reanimation of facial palsy. The first group of five rats underwent immediate HFA by microsurgical suturing and the second group of five rats by CO2 laser welding. The third group of five rats underwent delayed HFA by microsurgical suturing, and the fourth group of five rats by laser nerve welding. The fifth group of five rats served as controls, with intact hypoglossal and facial nerve. In all rats of the four different treatment groups, cholera toxin B subunit (CTb) was injected in the epineurium distal to the anastomosis site on the postoperative 6th week and in the normal hypoglossal nerve in the five rats of the control group. Neurons labeled CTb of hypoglossal nuclei were positive immunohistochemically, and the numbers were counted. In the immediate HFA groups, CTb-positive neurons were 751 +/- 247 in the laser welding group (n = 5) and 888 +/- 60 in the microsurgical suturing group (n = 5). There was no significant difference (P = 0.117). In the delayed HFA groups, CTb-positive neurons were 749 +/- 54 in the laser welding group (n = 5) and 590 +/- 169 in the microsurgical suturing group (n = 5). The difference was not significant (P = 0.116). There was no significant difference between immediate and delayed anastomosis in the laser welding group (P = 0.600), but there was significance between immediate and delayed anastomosis in the microsurgical suturing group (P = 0.009). Injected CTb in intact hypoglossal neurons (n = 5) were labeled 1,003 +/- 52. No dehiscence in the laser welding site of nerve anastomosis was seen at the time of re-exploration for injection of CTb in all 10 rats. This study shows that the regeneration of anastomosed hypoglossal-facial nerve was affected similarly by laser welding and microsurgical suturing, and more effective, especially in delayed repair.

Laser Welding of Rat's Facial Nerve

The aim of this study is to compare regeneration of the severed nerves that were repaired by laser welding with those repaired by microsurgical suturing and evaluate the value in use of laser nerve welding in the head and neck area. In 12 rats the buccal branches of the facial nerves on the both sides were transected, and CO2 laser welding of the epineurium was performed on the right side and microsurgical suture technique was applied on the left side. In six rats Cholera Toxin B Subunit (CTb) was injected in the epineurium distal to the nerve anastomosis site at postoperative week 4. Another six rats were treated exactly in the same way in postoperative week 8. Six normal rats were used as controls. Intact facial nerve was observed after injection of CTb as well. Neurons of facial nuclei labeled positively by CTb were detected immunohistochemically, and the numbers were counted. CTb-positive neurons in the control group were 1311 +/- 258 (n = 6). CTb-positive neurons in the group (n = 6) with laser nerve welding were 1174 +/- 122 in postoperative week 4 and 1562 +/- 565 in postoperative week 8. CTb-positive neurons in the group (n = 6) with microsurgical suture were 1066 +/- 89 in postoperative week 4 and 1443 +/- 531 in postoperative week 8. CTb-positive neurons were seen significantly more in the group with laser welding than in the group with microsurgical suture in postoperative week (P = 0.028), but there was not much difference in postoperative week 8 (P = 0.463). None of 12 rats showed dehiscence at the nerve anastomosis done by laser welding. This study shows that nerve regeneration is more apparent in the nerve repaired by laser welding than in that repaired by microsurgical suture.

Carbon dioxide laser-assisted nerve repair: effect of solder and suture material on nerve regeneration in rat sciatic nerve

In order to further improve and explore the role of lasers for nerve reconstruction, this study was designed to investigate regeneration of sharply transected peripheral nerves repaired with a CO(2) milliwatt laser in combination with three different suture materials and a bovine albumin protein solder as an adjunct to the welding process. Unilateral sciatic nerve repair was performed in 44 rats. In the laser group, nerves were gently apposed, and two stay sutures (10-0 nylon, 10-0 polyglycolic acid, or 25 microm stainless steel) were placed epi/perineurially. Thereafter, the repair site was fused at 100 mW with pulses of 1.0 s. In the subgroup of laser-assisted nerve repair (LANR), albumen was used as a soldering agent to further reinforce the repair site. The control group consisted of nerves repaired by conventional microsurgical suture repair (CMSR), using 4-6 10-0 nylon sutures. Evaluation was performed at 1 and 6 weeks after surgery, and included qualitative and semiquantitative light microscopy. LANR performed with a protein solder results in a good early peripheral nerve regeneration, with an optimal alignment of nerve fibers and minimal connective tissue proliferation at the repair site. All three suture materials produced a foreign body reaction; the least severe was with polyglycolic acid sutures. CMSR resulted in more pronounced foreign-body granulomas at the repair site, with more connective-tissue proliferation and axonal misalignment. Furthermore, axonal regeneration in the distal nerve segment was better in the laser groups. Based on these results, CO(2) laser-assisted nerve repair with soldering in combination with absorbable sutures has the potential of allowing healing to occur with the least foreign-body reaction at the repair site. Further experiments using this combination are in progress.

Laser, fibrin glue, or suture repair of peripheral nerves: a comparative functional, histological, and morphometric study in the rat sciatic nerve

OBJECT

This study was undertaken to evaluate CO2 laser-assisted nerve repair and compare it with nerve repair performed with fibrin glue or absorbable sutures.

METHODS

In eight rats, the sciatic nerve was sharply transected and approximated using two 10-0 absorbable sutures and then fused by means of CO2 milliwatt laser welding (power 100 mW, exposure time 1 second per pulse, spot size 320 microm), with the addition of a protein solder (bovine albumin) to reinforce the repair site. The control groups consisted of eight rats in which the nerves were approximated with two 10-0 absorbable sutures and subsequently glued using a fibrin sealant (Tissucol), and eight rats in which the nerves were repaired using conventional microsurgical sutures (four to six 10-0 sutures in the perineurium or epineurium). Evaluation was performed 16 weeks postsurgery and included the toe-spreading test and light microscopy and morphometric assessment. The motor function of the nerves in all groups showed gradual improvement with time. At 16 weeks, the motor function was approximately 60% of the normal function, and there were no significant differences among the groups. On histological studies, all nerves revealed various degrees of axonal regeneration, with myelinated fibers in the distal nerve segments. There were slight differences in favor of the group treated with laser repair, in terms of wound healing at the repair site. In all groups, the number of axons distal to the repair site was higher compared with those proximal, but the axon diameter was significantly less than that in control nerves (p < 0.05). There were no significant differences in the number, density, or diameter of the axons in the proximal or distal nerve segments among the three nerve repair groups (p < 0.05), although there was a trend toward more and thicker myelinated axons in the distal segments of the laser-repaired nerves.

CONCLUSIONS

It was found that CO2 laser-assisted nerve repair with soldering is at least equal to fibrin glue and suture repair in effectiveness in a rodent model of sciatic nerve repair.

Novel solid protein solder designs for laser-assisted tissue repair

BACKGROUND AND OBJECTIVES

Previous studies have shown that the application of chromophore-enhanced albumin protein solders to augment laser tissue repairs significantly improves repair strength, enhances edge co-optation, and reduces thermal tissue injury. These investigations are furthered with this in vitro study conducted to assess a new range of specially designed chromophore-enhanced solid protein solders manufactured and tested for application during laser-assisted tissue repair.

STUDY DESIGN/MATERIALS AND METHODS

The experimental study was divided into three parts. In the first part of the study, the creation of a chromophore concentration gradient across the thickness of the solid protein solder was investigated as a means to improve control of the heat source gradient through the solder during laser irradiation. In the second part of the study, predenaturation of the solid protein solder was investigated as a means for enhancing the stability of the solder in physiological fluids before irradiation. Finally, in the third part of the study, the feasibility of using synthetic polymers as a scaffold for traditional albumin protein solder mixes was investigated as a means of improving the flexibility of the solder.

RESULTS

Uniform denaturation across the thickness of the solder was achieved by controlling the chromophore concentration gradient, thus ensuring stable solder-tissue fusion when the specimen was submerged in a hydrated environment. Predenaturation of the solid protein solder significantly reduced the solubility of the solder, and consequently, improved the handling characteristics of the solder. The solder-doped polymer membranes were flexible enough to be wrapped around tissue, whereas their solid nature avoided problems associated with "runaway" of the less viscous liquid solders currently used by researchers. In addition, the solder-doped polymer membranes could be easily tailored to a wide range of geometries suitable to many clinical applications.

CONCLUSION

The novel solid protein solder designs presented here add a new dimension to tissue repair as their flexible, moldable, and absorption controllable nature, greatly improves the clinical applicability of laser-assisted tissue repair.

Photothermal effects of laser tissue soldering

Low-strength anastomoses and thermal damage of tissue are major concerns in laser tissue welding techniques where laser energy is used to induce thermal changes in the molecular structure of the tissues being joined, hence allowing them to bond together. Laser tissue soldering, on the other hand, is a bonding technique in which a protein solder is applied to the tissue surfaces to be joined, and laser energy is used to bond the solder to the tissue surfaces. The addition of protein solders to augment tissue repair procedures significantly reduces the problems of low strength and thermal damage associated with laser tissue welding techniques. Investigations were conducted to determine optimal solder and laser parameters for tissue repair in terms of tensile strength, temperature rise and damage and the microscopic nature of the bonds formed. An in vitro study was performed using an 808 nm diode laser in conjunction with indocyanine green (ICG)-doped albumin protein solders to repair bovine aorta specimens. Liquid and solid protein solders prepared from 25% and 60% bovine serum albumin (BSA), respectively, were compared. The efficacy of temperature feedback control in enhancing the soldering process was also investigated. Increasing the BSA concentration from 25% to 60% greatly increased the tensile strength of the repairs. A reduction in dye concentration from 2.5 mg ml(-1) to 0.25 mg ml(-1) was also found to result in an increase in tensile strength. Increasing the laser irradiance and thus surface temperature resulted in an increased severity of histological injury. Thermal denaturation of tissue collagen and necrosis of the intimal layer smooth muscle cells increased laterally and in depth with higher temperatures. The strongest repairs were produced with an irradiance of 6.4 W cm(-2) using a solid protein solder composed of 60% BSA and 0.25 mg ml(-1) ICG. Using this combination of laser and solder parameters, surface temperatures were observed to reach 85+/-5 degrees C with a maximum temperature difference through the 150 microm thick solder strips of about 15 degrees C. Histological examination of the repairs formed using these parameters showed negligible evidence of collateral thermal damage to the underlying tissue. Scanning electron microscopy suggested albumin intertwining within the tissue collagen matrix and subsequent fusion with the collagen as the mechanism for laser tissue soldering. The laser tissue soldering technique is shown to be an effective method for producing repairs with improved tensile strength and minimal collateral thermal damage over conventional laser tissue welding techniques.

Effect of the CO2 milliwatt laser on neuroma formation in rats

BACKGROUND AND OBJECTIVE

The purpose of this study was to determine whether the milliwatt laser can suppress neuroma formation at the end of a divided nerve.

STUDY DESIGN/MATERIALS AND METHODS

The peripheral nerves of eight rats were transected with microscissors and the cross-sectional area of their proximal ends was irradiated using the CO2 milliwatt laser. The power ranges used were similar to those applied to weld neural tissue.

RESULTS

None of the eight irradiated nerve ends formed a neuromatous bulb and only one of them regenerated into the surrounding tissues. Histologically, these nerve ends did not show the disorganized picture of classic neuromas. On morphometric measurements, they contained less connective tissue than the control nerve ends (P < 0.001) and their nerve fibers were larger in diameter (P < 0.001) and better myelinated (P < 0.001).

CONCLUSION

These findings in rats show that the CO2 milliwatt laser has the ability to suppress neuroma formation at the end of a divided nerve.

Prevention of pharyngocutaneous fistulas by means of laser-weld techniques

Although much has been written on methods of dealing with pharyngocutaneous fistulas once they have formed, there are few reports of methods of preventing fistula formation from occurring. We examined the use of laser-weld techniques with the neodymium:yttrium aluminum garnet (Nd:YAG) and diode lasers to seal pharyngotomy closures. Laser-weld techniques have been used successfully in many other tissues, but reports documenting use in the upper aerodigestive tract are minimal. Indocyanine-green dye-enhanced collagen and fibrinogen were studied as laser solder materials for the diode laser. Twenty-nine experimental animals were studied. Neither the Nd:YAG nor the diode laser was successful in preventing fistula formation. Tensiometric studies documented significant strength of the laser welds ex vivo, but this finding was not clinically significant.

Laser(-assisted) nerve repair. A review

Over the last decade low power laser irradiation has been used to repair nerves by photothermal welding. Nineteen animal and clinical experimental studies of laser tissue welding of nerves are reviewed. Possible mechanisms of tissue welding are presented, together with the benefits, limitations, and possible future implications of several techniques used in laser nerve repair. The consensus of these studies is that nerve welding has some advantages over standard suture repair. These advantages include less neuroma- und scar formation and shorter repair time. The major disadvantage of laser nerve repair is the initial inferior tensile strength. In the future, use of dyes or proteins could enhance the welding process by reinforcing the union strength, thus may improve the results of this promising technique.

Laser tissue welding: a comprehensive review of current and future clinical applications

Laser techniques for joining tissue, in combination with other surgical technologies, will be a hallmark of surgery in the next century. At present, there are many clinical applications of tissue welding and soldering which are beginning to achieve wide spread acceptance. These exciting clinical developments are the result of many advances which have been made in the past few years in our understanding of the mechanism of laser tissue welding. Also contributing to this progress are many important technical refinements such as tissue solders and feedback control of the laser device. In this article, we describe in depth the history and development of laser tissue welding including key theoretical concepts as well as crucial experiments which have added to our insight into this phenomenon. We also review the evolving concepts of its clinical application and indicate clinical applications which are likely to become more important in the future.

CO2 laser repair of the facial nerve: an experimental study in the rat

The facial nerve is often injured by trauma, infection or during the course of tumour resection. Many techniques of nerve anastomosis have been described with the current standard nerve repair using the microscope and monofilament suture. The purpose of this study was to evaluate the CO2 surgical laser as a tool for facial nerve anastomosis. Following preliminary electrical measurements 36 nerves were anastomosed using either laser or conventional monofilament suture. Laser anastomosis had neither beneficial nor detrimental effects on nerve regeneration. This method of anastomosis may be advantageous when surgical access is limited. In addition this study found that the use of CO2 laser as a dissecting or vapourizing tool in proximity to intact facial nerves results in degenerative changes.

CO2 laser nerve welding: optimal laser parameters and the use of solders in vitro

To improve the welding strength, an in vitro study was performed to investigate the bonding strength of CO2 laser nerve welding (LNW), with and without the use of human albumin solution, dried albumin solution, egg white, fibrinogen solution, fibrin glue, and red blood cells as a solder. Fifteen different combinations of laser power (50, 100, and 150 mW) and pulse duration (0.1 to 3 s) were used with a spot size of 320 microns. The results have been compared to suture, fibrin glue, and laser-assisted nerve repair (LANR). The strongest welds (associated with whitening and caramelization of tissue) were produced at 100 mW with pulses of 1.0 s and at 50 mW with pulses of 3 s. The use of a dried albumin solution as a solder at 100 mW with pulses of 1 s increased the bonding strength 9-fold as compared to LNW (bonding strength 21.0 +/- 8.6 g and 2.4 +/- 0.9 g, respectively). However, positioning the nerves between cottons soaked in saline for 20 minutes resulted in a decrease of the bonding strength (9.8 +/- 4.5 g). The use of a 20% albumin solution and egg white, both at 50 mW with pulses of 3 s, resulted in a bonding strength of, respectively, 5.7 +/- 2.1 g and 7.7 +/- 2.4 g. Other solders did not increase the bonding strength in comparison to LNW. The substantial increase in bonding strength for some solders suggests that it is worthwhile to investigate the dehiscence rate and nerve regeneration of solder enhanced LNW in an in vivo study.

An investigation of the potential for laser nerve welding

Suture repair of a severed peripheral nerve is cumbersome, presents a focus for infection and neuroma formation, and does not always produce adequate stump alignment. An alternative form of repair is laser nerve welding, which is attractive because it does not introduce foreign material into the anastomotic site, it forms a circumferential seal, and it can be performed in difficult-to-reach areas. Laser repair has not been widely accepted both because the effect of laser irradiation on intact nerves is not well documented, and the anastomotic strength of the weld has been inferior to suture repair. In the first part of the present study, rat sciatic nerves were exposed and irradiated with increasing intensities from a Sharplan CO2 and KTP laser to document nerve damage as recorded by decreases in the peak compound action potential. A new technique of laser repair (S-Q weld) was then developed that involved harvesting subcutaneous tissue from the adjacent dermis, wrapping it around the two opposed nerve stumps, and lasering it to the epineurium to effect a weld. The strength of the S-Q weld (6.1 grams) was considerably greater than that produced by laser welding alone. The third phase of the study compared regeneration at 2 months in severed rat sciatic nerves repaired by either microsuture or S-Q weld. Analysis of the compound action potential values indicated that the number of regenerating fibers after laser repair was greater than that after suture repair, although a significant difference could not be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)