BACKGROUND: Ultrasound is a kind of mechanical wave and characterized by mechanical effect,heat affect and physical and chemical effect.Ultrasound can promote regeneration of peripheral nerves after a slight injury based on its mechanical effect.However,whether it can promote regeneration of peripheral nerves after a severe injury or not is still unclear.OBJECTIVE: To study the effect of low-intensity ultrasound(LIU)on regeneration of injured peripheral nerve,throgh examining sciatic nerve function index,the sensory nerve conduction velocity and the thickness of myelin sheath.DESIGN: Single factor design of contrast observation.SETTING: Institute of Ultrasound Engineering,Chongqing Medical University.MATERIALS:A total of 64 female Wistar rats,of clean grade,age 3 moths,weighing 200-250g ,were provided by Experimental Animal Center of Chongqing Medical University. All rats were randomly divided into treatment group and control group with 32 in each group. In addition rats were observed at 4 time points, including 2,4,6 and 8 weeks,with 8 at each time point.The main equipments were detailed as follows:forceps (Medical Treatment Apparatus Company,Chongqing),low-intensity ultrasound treatment instrument(Institute of Ulrasound Engineering in Medicine),the analysis instrument of diagram resembles and arithmetic figure(the United States Bio-RAD Company),ultrasound coupling agent(Xunde Image material factory,Hangzhou),Osmium Tetraoxide(Next Chimicam,South Africa).METHODS:The experiment was carried out in Institute of Ultrasound Engineering of Chongqing Medical University from December 2003 to May 2004.The right sciatic nerves of 64 rats were crushed with forceps for 30 s to form the experimental animal models.Then they were treated at 3 days after operation.Rats in the treatment group received the LIU exposure.LIU was applied every other day to the crush site of rats,which had a spatial peak,time-averaged intensity of 0.25 W/cm2 operated at 1 MHz for 1 minute per application for total 8 weeks.At various stages after operation,the sciatic nerve function index(SFI).the sensory nerve conduction velocity and its histology were detected.Rats in the control received a sham exposure.MAIN OUTCOME MEASURES:SFI;sensory nerve conduction velocity;density of myelinated nerve fiber;velocity of nerve regeneration;histological examination.RESULTS: Among 64 Wistar rats, 2 were lost during the experiment and another 2 were supplied. ①Histological examination:Two weeks after treatment,degeneration of axis-cylinder and myelin sheath was obvious in treatment group as compared with that in control group. Within 4-8 weeks after treatment.regeneration of axis-cylinder and myelin sheath of nerve fiber was superior in treatment group to that in control group.At 8 weeks after treatment,axis-cylinder and myelin sheath in treatment group were closed to normal value.Quantity of nerve fiber was less in control group than that in treatment group and the arrangement was disorder.At 2,4 and 6 weeks after treatment,proliferation of Schwann cells was superior in treatment group to that in control group.At 6 and 8 weeks after treatment,proliferation of fiber tissue in nerve was severer in control group than that in treatment group.②SFI:At 4.6 and 8 weeks after treatment.SFI was higher in treatment group than that in control group(t=8.00,12.41m15.13,P＜0.01).③Sensory nerve conduction velocity:At 2,4,6 and 8 weeks after treatment,sensory nerve conduction velocity was faster in treatment group than that in control group(t=11.74,10.81,3.51,P＜0.01).④Density of myelinated nerve fiber:At 2,4,6 and 8 weeks after treatment,density of myelinated nerve fiber was higher in treatment group than that in control group(t=2.16,P＜0.05;t=3.29,3.52,3.23,P＜0.01).⑤Velocity of nerve regeneration:Velocity of nerve regeneration was(1.50+0.08)mm/d and(1.22±0.10)mm/d of treatment group and control group.respectively. This suggested that velocity of nerve regeneration was faster in treatment group than that in control group(t=2.708,P＜0.05).CONCLUSION:LIU can promote the regeneration of injured peripheral nerve from the appearance,construction,function aspect and functional recovery.Its mechanism may be through the modulation and effect of many links of nerve regeneration process.