The Study Of The Compensation Ability Of Spit Nerve With Nerve Conduit

Bridging a long segment peripheral nerve defect is a major problem for surgeons. Autograft or allograft is a versatile solution by offering both mechanical guidance and accumulation and containment of trophic substances such as NGF supporting axonal sprouts growing. However, the limited availability, donor side morbidity, mismatch between nerve and graft size, mismatch of internal architecture between recipient and graft,neuroma and scar formation are obstacles of the autograft nerve transplantation. Allografts have been used for its better availability and variable size, but it requires permanent immunosuppression and often lead to poor nerve regeneration. Moreover, they are not suitable for long gap bridging because of the tune collapse, scar infiltration and early resorption.Thus, seeking a way to achieving one hundred percent nerve function recovery has been the hot area for decades. The use of conduits for bridging nerve defects has become one of the most promising way in researching nowadays. Many nerve conduits such as autologous blood vessels, muscle fibers, and silicone have been studied regarding their regeneration promoting properties.Recently, biodegradable materials(e.g. PLGA, poly(lactic-co-glycolic acid) were introduced showing to have variable success.However, almost all the experiment conducted in the lab on animals are under ideal situation, the nerve incision are neat. In clinic, however, most of the peripheral nerve injuries come after trauma, which the nerve injury situation is unpredictable. End-to-end suturing requires neat end, over-pruning the ends will lengthen the defect, making nerve regeneration more difficult. Thus, making the best use of the damaged nerve tissue could be a new breakthrough for peripheral nerve regeneration. In this study, we simulate the clinical complication by building a nerve split model with PLGA conduit bridging the nerve defect on sciatic nerve of SD rats, to explore the possibility and the compensation ability of the split nerve to a complete sciatic nerve. Objective:In this study, nerve splitting model is established to simulate clinical irregular nerve damage and to evaluate the compensatory abilility of the split nerve. Methods:After anesthetizing, right sciatic nerves were exposed, establishing the nerve split model by following methods;Group A: cut the right sciatic nerve with microsurgical scissors, incise the epineurium of the proximal for 5mm and expose the nerve tract, split the nerve tract into two half with microsurgical instruments, put one half of the split nerve tract on the PLGA scaffold and the distal of sciatic nerve, the defect between the proximal split nerve tract and the distal is 5mm. Suture the scaffold from both sides by 10-0 nylon suture to make the scaffold forming a conduit. Then sewing the needle thread the conduit from outer to inner, then threaded the epineurium and conduit from inner to outer for both proximal and the distal to immobilize the conduit.Group B: the method is same to group A, but split nerve tract to one quarter and three quarters, and put only a quarter of the nerve tract in the conduit.Control group: cut the right sciatic nerve, then suture the proximal and distal directly with 10-0 nylon suture directly. Result:1 General observations postoperation30 minutes after surgery, all three groups of rats shows the right limb paralyzed state such as foot droop, toes folding and dragging right limb while walking.No sigh of foot retraction after stinging were observed. Animals showed no complications after operations, and all suture sites healed without complications, no signs of discomfort were observed in the 12-week evaluation period. An increase in weight was observed in all groups postoperation(data not shown). At 12 th week, the knee flexion and extension and pain reflex was improved better in Group A and B, Group C shows less improvement.2 Observation with surgical microscopeSix weeks after surgery: the part sewed into piriformis was formed into neuroma in Group A and B, and the size of neuroma of Group A is smaller than Group B. Tissue adhesion was observed in suture part of Group C so as neuroma forming.Twelve weeks after surgery:the nerve conduit were nearly absorbed in Group A and B, after cutting off the nerve conduit, the regenerated nerve fiber all grew into the distal end.Neuroma was observed in Group C, making the nerve regeneration more difficult.3 Sciatic nerve function recovery(SFI)SFI was tested in 2nd,4th,6th,8th,10 th,12th week after surgery. No difference was observed in the 2nd and 4th week(P>0.05) between three groups. All three group showed an increase in 6th week, and Group A shows a better performance compared to other two groups(P<0.05) all the way to the 12 th week. However, no significance difference was observed between Group B and C(P<0.05).4 Muscle mass preservationBoth sides of gastrocnemius muscle(experimental muscles on the right and contralateral on the left) was harvested at the 12 th week after surgery,.We quantified this decrease by weighing the excised gastrocnemius muscle and calculating a ratio of muscle weight(referred to as R/L), using the weight of the experimental muscle(right) instead of the weight of the muscle on the control side(left). As the R/L ratio approached, a reduction in atrophy was observed. The lowest R/L ratio was found in Group C, which was significantly smaller than Group A and B(P<0.05). The nerve splitting with PLGA conduit on rats had a protective effect against muscle atrophy, with significantly higher muscle weight compared to the sham-treated rats.5 In vivo electrophysiological analysisTo quantify the functional recovery of regenerated nerves, electroph ysiological analysis was performed at 6 and 12 weeks post operation to determine the response in the hind limb gastrocnemius muscle to electr ical stimulation at the proximal end of the grafts. Group A and B show s a increasing trend between 6th and 12 th week while no data difference was shown in Group C. In 6th week, a difference was observed betwe en three groups compared to each other and so does in the 12 th week.6 Immunohistochemical staining12 weeks after operation, Group A showed a large number of regen erated myelinated nerve fibers mix with unmyelinated fibers. Schwann c ells with normal morphology wrap around the regenerated axons formin g myelinated fibers. Most myelinated nerve fibers are well developed wit h concentric circular plate layer structure, with less incompletely closed i mmature myelin. B group and C group, the regenerated nerve fibers were sparse, myelination is not complete. Conclusion:This study shows that the combine of split nerve with nerve conduit has positive effects on nerve healing. The use of PLGA nerve conduit, which has low immunity, can provide axonal regeneration by Schwann cell proliferation and preservation of neurotrophic factors. The split nerve tissue provide direct Schwann cell and neurotrophic factors that would help the regeneration. It was evident that the combination of nerve conduit and split nerve had positive effects on nerve regeneration that was analyzed. Further research on this topic may enable this method for clinical use.