Effect of CO2-milliwatt laser on peripheral nerves: Part II. A histological and functional study

In order to further explore the role of laser for microneural repair, the e arly and late effects of CO2 laser irradiation on intact rat sciatic nerves were investigated. A total of 48 rat sciatic nerves were exposed to 100-mW laser power with a pulse duration of 1.0 s and a spot size of 320 mu m In one-half of the nerves, albumin solder was applied to the nerve followed by laser irradiation. The results were evaluated up to 94 days after surgery with functional toe-spreading test, and light and transmission electron mic roscopy. Irradiation of the nerve resulted in almost no deficit in the moto r function. A subperineurial degeneration of myelinated and unmyelinated ax ons is observed in the first 2 weeks after laser irradiation, while the cen tral part of the nerve remains undamaged, The degeneration is followed by a xonal regeneration with subsequent maturation of nerve fibres in time. No e xcessive intra-neural or extraneural scarring was seen, In the soldered ner ves, the solder elicits an inflammatory reaction upon the epineurium in the first week after irradiation. By week 1, the solder is completely absorbed . After 2 weeks, the inflammatory reaction ceases and by week 4, no residua l reaction is seen. At 12 weeks, only minimally disarranged epineurium is s een with otherwise normal neural architecture, In conclusion, CO2 laser irr adiation at 100 mW with pulses of 1.0 s has no long term negative effects o n nerve function and morphology, Therefore, these laser settings can be saf ely applied for laser-assisted nerve repair. (C) 2000 Wiley-Liss, Inc.