[Temperature and ablation measurements in laser therapy of intervertebral disk tissue]

We experimentally tested the effect of Laser light at wavelengths of 1064 nm, 1320 nm, 1440 nm and 2100 nm on intervertebral disc tissue. The tested parameters were tissue ablation, determined by weight reduction, and temperature change, measured with thermoelements. We used bovine nucleus pulposus tissue for ablation measurement and human spine segments for temperature measurement. We found that variation of single parameters such as power, frequency and energy per pulse had only a slight effect on ablation. The decisive factor for the mass of tissue ablated seems to be the total applied energy. One indispensable requirement is a suction unit; we procured a manifold increase in ablation rate using suction. In the investigations of tissue temperature, we found no risk to upper or lower plate when the fiber was centered correctly in the disc. Within a distance of 10 mm from the fiber tip, the temperature development was found to be radial, so no more tissue damage is to be expected in front of the tip than to the side of it. Although the various wavelengths tested are absorbed differently in water there were only small differences in temperature. Using a neodymium: YAG laser with a fiber of 400 micron diameter, we sometimes measured high cannula temperatures, showing that case one has to be exercised, especially with high energies. In conclusion, it can be said that both the Holmium:YAG laser and the neodymium:YAG laser are suitable for disc decompression with the parameters used currently in surgery.