The Comparative Study About Morphologic Change And Functional Recovery Of Rabbit's Orbicularis Oris After Denervation And Reinervation

Objective: Through facial nerve mutilation and denervation orbicu- laris oris to establish the animal experimental models ,to dynamicall, continuously and comparatively observe the morphologic change of nerve and muscle after denervation and reinervation with different methods at different times; research the regularity of change, discuss the influence of restoration time and method on the operation effect; to search the optimal operation time for restoration of facial nerve injury on early stage;to provide theoretic basis of selecting the time and method of clinic dynamic prosthesis on the later stage; meanwhile, discuss the feasible method for preventing the atrophy of mimic muscles after denervation.Methods: Divided 42 healthy adult New Zealand rabbits randomly and equally into group A and B. Bilateral mutilation of buccal branches was performed in each group after feeding for two weeks in order to produce the experimental models of denervated orbicularis oris. Two different methods of reinervation were performed at different times in two groups. A uses end-to-side anastomosis ,B uses end-to-end anastomosis. Each group was divided into 7 subgroups based on different reinnervation operation time (at once, 2 weeks, 3 weeks, 1 month, 3 months, 6months, 9months), each subgroup contained three rabbits and 6 samples .Observed and compared the histomorphological change of nerve and muscle under the light microscope before anastomosis and after the anastomosis for three months; The functional recovery degree of nerve and muscle was evaluated at three months after the reinervation through detected different index of electrophysiology data .Result: With the denervation time prolonging, the rabbits'orbicularis oris thinned and tarnished gradually. Under the light microscope, it can be seen that the muscle degenerated, swelled and became necrosis at two weeks after denervation; the muscular fibers atrophied more severely after one month; the regeneration phenomenon of muscle fiber was found apparently after three month; and the fibers atrophied in groups after nine months. The buccal branches of facial nerve became gloomy, hollow and inelastic after denervation for one month. Under the light microscope, the myelin sheath degenerated and swelled at two weeks after mutilation; axons dissolved and Schwann cell proliferated apparently after one month; the number of axons decreased severely from three to six months; partial myelin sheath restored after nine months, however, the integral nerve fibers were still rare. At three month after mutilation, the morphology structure and function of nerve and muscle got to recover with different degree by two different kinds of reinnervation methods. Through the comparison of the restoration effect of two method at the same time, the end-to-end anastomosis was better than end-to-side anastomosis. Through the comparison of the restoration effect of the same method at different time, the earlier operation performed, the better result got. In the subgroup that reinervation performed at once, the function and structure can recovered approximately normal. In nine month subgroup, the integral nerve fibers were less and muscles had no ability of contraction.Conclusion: The distal end of nerve occurred the Waller degeneration and regeneration after the mutilation of rabbit's buccal branches of facial nerve; orbicularis oris occurred degeneration, necrosis, regeneration and atrophy after denervation. At 9 months after denervation, the structure of nerve and muscle changed irreversibly. After the mutilation of facial nerve, the earlier operation performed, the better result got. The optimal opportunity for repairing nerve by end-to-end anastomosis is within two weeks. For the last group , The muscle cannot restore the ability of contraction. Whether the end-to-end anastomosis or end-to-side anasto- mosis is performed within three months, the morphology and function of nerve and muscle can recovered mostly. The end-to-side anastomosis can prevent muscular atrophy effectively. Compared the restoration effect of two method at the same time, the end-to-end anastomosis was better than end-to-side anastomosis. The end-to-end anastomosis is an ideal restoration method after nerve injury.