Experimental study of acute lengthening of sciatic nerve in rats

Objective To investigate the infusion volume and relevant lengthening value of acute expansion for peripheral nerve lengthening. Methods Tissue expander was applied in three groups of rats (8 rats each) to lenthen the sciatic nerve in one step by infusion of 3 ml, 5 ml, or 7 ml water respectively. Electromyographic testing was carried out before infusion, immediately after infusion, 5 minutes after infusion and 15 minutes after removal of the expander. Histological examination under light microscope and eletron microscope was also done. Results The lengthening value (the initial length was 1.5 cm) was 8.33 %, 14.7 %, and 20.4 % in three groups respectively. There was no significant difference of motor nerve conduction velocity and compound muscle action potential (CMAP) latent period before and after nerve expansion in groups of 3 ml infusion volume and 5 ml infusion volume. In the group of 7 ml infusion volume, however, motor nerve conduction velocity was slower and CMAP latent period was delayed after nerve expansion. In groups of 3 ml and 5 ml infusion volume, the axon density, the structure and ultrastructure of the lengthened nerve were almost normal, whilst decreased axon density, interfascicular vessel dilation, interstitial edema and hemorrhage, demyelination, and shrinkage of myelin sheath were observed in the nerves of the group of 7 ml infusion volume. Conclusion The optimal infusion volume for one stage rat sciatic nerve expansion was 5 ml. The nerve lengthenig value was 14.6 %.