Effect of CO(2)-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 early and late effects of CO(2) 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 microm. 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 microscopy. Irradiation of the nerve resulted in almost no deficit in the motor function. A subperineurial degeneration of myelinated and unmyelinated axons is observed in the first 2 weeks after laser irradiation, while the central part of the nerve remains undamaged. The degeneration is followed by axonal regeneration with subsequent maturation of nerve fibres in time. No excessive intraneural or extraneural scarring was seen. In the soldered nerves, 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 residual reaction is seen. At 12 weeks, only minimally disarranged epineurium is seen with otherwise normal neural architecture. In conclusion, CO(2) laser irradiation at 100 mW with pulses of 1.0 s has no long term negative effects on nerve function and morphology. Therefore, these laser settings can be safely applied for laser-assisted nerve repair.