The Impact of Intervertebral Disc Hydration on the Photothermal Responses and Carbonization Properties in Low-Energy Laser Therapy

Purpose Percutaneous Laser Disc Decompression (PLDD) is a minimally invasive treatment for lumbar disc herniation (LDH), but its effectiveness can be influenced by factors like laser power and treatment time, which vary with the degree of disc degeneration. Reduced water content in degenerated discs may affect treatment outcomes. This study examines how low-energy laser treatment impacts intervertebral discs with different water content, focusing on photothermal and carbonization effects. Methods Fresh intervertebral discs from adult pig spines (L2-L5) were used. Discs with poor and rich water content were prepared by vacuum freeze-drying and saline soaking, respectively, with untreated discs serving as controls. Three groups—poor, normal, and rich water content—were exposed to laser irradiation at 1W, 2W, and 3W. Images of the discs were captured, and the irradiated and carbonized areas were measured to evaluate photothermal effects. Results After 5 minutes of irradiation, the poor water content group showed the largest irradiated area at low power (112,894 ± 18,664 pixels), compared to the normal (75,644 ± 11,298 pixels) and rich (51,641 ± 7,348 pixels) groups. As power increased, the poor water content group continued to show a larger irradiated area. For carbonization, the poor water content group exhibited the largest carbonized area (64,759 ± 9,876 pixels) at low power, and this trend continued at higher powers. Conclusion The water content of intervertebral discs significantly affects laser irradiation and carbonization. Discs with poor water content show larger irradiated areas and earlier, more extensive carbonization. Careful control of treatment time is necessary when treating severely degenerated discs to avoid excessive carbonization and potential negative effects.