In order to improve complications associated with conventional methods of neurotomy, a new method was proposed. In this method, nerve fiber is degenerated with a local heat generated by an irradiation of high power infra red light to a nerve fiber through an optical fiber with a needle in which the optical fiber is involved. As a basic study of this new method, tissue reaction with a light generated heat in nerve fiber was investigated pathologically, and the blockage of impulse in nerve fiber was investigated with somato-spinal evoked potential (SSEP) method, by using rabbits. A semiconductor laser with 810nm of wave length and 850mw of maximum power was used as a high power infra red light source. Total or partial thermal degeneration in nerve fiber were observed with all the nerve irradiated with 400-800mW of laser power and 2-10 seconds of irradiation. As the magnitude of degeneration in nerve fiber was higher in thin fiber, so it was considered that the selective blockage of pain would be possible by controlling the irradiate condition of laser. In the experiment of SSEP, the evoked potential was reduced with the procedure of laser irradiation. However, reduced potential was still remain by the irradiation with 400mw of laser power and 30 seconds of irradiation. It was considered that the magnitude of neurotomy could be controllable by controlling the irradiate condition of laser.
