Thermal diffusion of low-energy semiconductor laser disc repair in adult porcine spine

English Keywords:Low-energy semiconductor laser  Thermal radiation effects  Animal experiments  Photothermal  Disc degeneration

English Abstract:

  【Abstract】 Objectives: To observe the dynamic thermal diffusion patterns and local histological changes in disc and surrounding area during low-energy semiconductor laser disc repair(LESL-DR). Methods: Three adult pigs weighing approximately 40kg were used in this study. Intact vertebra-intervertebral disc structure units from L1 to L5 in vitro were collected and nine intact intervertebral disc samples were selected and randomly divided into three groups of a low-power group(n=3), a medium-power group(n=3), and a high-power group(n=3), which were continuously irradiated for 5min using a low-energy semiconductor laser at power settings of 1W, 2W, and 3W, respectively. During irradiation, real-time temperature changes were monitored using a high-precision infrared thermographic imaging system at three predefined sites: the disc center(P1), the center of the annulus fibrosus(P2), and the anterior wall of the spinal canal(P3). Histological changes were assessed using hematoxylin and eosin staining after irradiation. Results: After 5 minutes of continuous irradiation, the temperature at point P1 did not reach statistical significance(P=0.064); At point P2, the temperatures were (50.62±2.44)℃, (65.51±2.46)℃, and (68.12±3.30)℃ in the low-, medium-, and high-power groups(P<0.01); Similarly, at point P3, the temperatures were (32.30±2.51)℃, (42.77±2.17)℃, and (48.93±3.03)℃(P<0.01). During laser irradiation, temperatures at P1, P2 and P3 increased over time. The temperature at P1 exhibited a rapid increase during the initial phase(0-40s), followed by a plateau and a secondary rise between 210s and 240s. Peak temperatures at P1 exceeded 100℃ in all groups and surpassed 110℃ in the high-power group. The temperature pattern at P2 was similar to that observed at P1, although the magnitude of increase was lower in the low-power group. Temperature changes at P3 were most strongly dependent on laser power, with maximal temperatures approaching 50℃ in the high-power group, approximately 40℃ in the medium-power group, and consistently remaining below 35℃ in the low-power group. Histological analysis revealed a clear power-dependent increase in intervertebral disc tissue damage after laser irradiation, characterized by progressive expansion of carbonized areas and increasing disruption of the annulus fibrosus matrix architecture.Conclusions: LESL-DR produces a three-stage characteristic of "rapid temperature rise - plateau period - secondary temperature rise" thermal diffusion patterns in ex vivo porcine intervertebral discs. As laser power increases, the peak temperature and degree of tissue damage at different temperature measurement points of the intervertebral disc also increase.