The autotomy relief effect of a silicone tube covering the proximal nerve stump.

A technique of covering the proximal nerve stump (PNS) has been reported as a preventative method or treatment for neuroma. However, its detailed pain relief mechanism remains unknown. We created a silicone tube model in which the PNS of the rat sciatic nerve was introduced into the tube, whereas the controls had no tube. The score of autotomy observed in the tube group was lower than that in the control group at 3 days to 2 weeks after surgery, which suggested that the silicone tube had pain-like behavior inhibitory action. To elucidate the mechanism of autotomy inhibition, immunohistochemistry and Toluidine blue staining were performed in the PNS. The increase in S-100-immunoreactivity (IR) including Schwann cells was inhibited at 1 week after surgery in the tube group, and the increase in the number of macrophages shown by ED-1-IR at 1, 2, and 4 weeks after surgery was similarly inhibited. Toluidine blue staining showed that the increase in the number of mast cells was inhibited at 1, 2, and 4 weeks after surgery and in the number of lymphocytes at 1 and 2 weeks after surgery in the tube group. Therefore, blocking of the infiltration of inflammatory cells into the PNS by the silicone tube was thought to be the mechanism of autotomy inhibition. To further explore details of this mechanism, the expression of nerve growth factor (NGF), production of which is induced by inflammatory cells and of the NGF receptor TrkA was examined in the PNS and the dorsal root ganglion using immunohistochemistry and a ribonuclease protection assay. In the PNS, the increase in NGF-IR was inhibited at 1, 2, and 4 weeks after surgery in the tube group, suggesting that this could be one of the pain-like behavior inhibitory effects. Copyright (c) 2006 Orthopaedic Research Society.