# Laser Reconstruction of Spinal Discs Experiments and Clinic
## 3 Laser Reconstruction of the Intervertebral Disc in Animal Experiments
### Morphological Changes in Rabbit Discs as a Result of Ex Vivo and In Vivo Laser Irradiation
In the NP, the formed areas of necrosis gradually decreased in size due to the outgrowth of proliferating chondroblasts, which gradually matured into chondrocytes, the sources of which were both surviving chondrocyte-like cells and undifferentiated cells of the hyaline EP. As a result, areas of necrosis are replaced by tissue that is nonspecific for the NP: fibro-hyaline cartilage, which is a transitional form from more fibrous to more hyaline, and hyaline cartilage, which is associated with the nature of the source cells. In AF, the most significant necrotic and dystrophic changes occurred in the inner and transitional layers at the early stages. To a lesser extent, they are present in the middle layer of the AF. Changes began with the proliferation of active hypertrophic chondrocytes with many isogenic groups that replaced the affected tissues with fibrous cartilage with a non-lamellar structure or, which happened more often, with fibro-hyaline cartilage. The source of the cartilage formation was probably undifferentiated AF chondrocytes. Hyaline cartilage developed at the AF/NP border or near the hyaline layer of the EP. The laser irradiation dosimetry affected the rate of transformation of the disc tissue, as well as the volumetric and topical ratio of areas with different histological patterns. Since the above-described processes in NP and AF under different modes of laser irradiation occur at different rates, but in one direction (genetically predetermined by the staging of differentiation of cells of the chondrocyte series), than the difference between the biological effects of different modes was somewhat decreases three months after exposure. An important feature of laser-induced regeneration of cartilaginous tissue was that laser irradiation caused tissue transformation not only in areas directly in the irradiated zone, but also in zones located at a significant distance (several mm) from the affected zone. Under laser irradiation, the high activity of regeneration processes was apparently due to a regulatory thermomechanical response of poorly differentiated cells. The laser radiation activated the cells of the \"resource\" areas of the disc--the sources of the young cellular elements of the chondrocyte type--the inner and transition layers of the AF, the hyaline tissue of the EP and part of the cells of the NP. Young cells with a high proliferative and biosynthetic potential migrated from the listed zones to areas located near the damaged zones and provided acceleration and a qualitative advantage for the regeneration observed during pulsed-periodic laser exposure. There are two factors in DDD treatment: pain alleviation and the actual healing of the IVD. It is proposed that LLLT can regulate the inflammatory reactions, modulate the secondary damage, and reduce programmed cell death and edema in the primary phase of recovery [72]. High energy densities leading to damage of neuroreceptors also can lead to pain relief, but this effect is not long lasting and does not result in IVD restoration [32]. The thermomechanical effect of moderate power density laser radiation can positively influence the behavior of cells and neuroreceptors via PIEZO proteins, but this hypothesis requires future focused research. In addition, there is reason to believe that the reduction in disc instability after LRD gradually leads to a decrease in pain. Most animals do not walk upright, the load on the IVD is not so great, and the process of inactivation of IVD pain receptors in an in vivo animal experiment is difficult to objectify. We studied only the actual healing of IVD in rabbits. The combination of macroscopic and histological studies allowed us to conclude that Modes 1 and 2 are acceptable for the clinic, in which the NP and the inner layer of AF are most transformed into hyaline and fibrohyaline cartilage, which stabilizes the spine under conditions of degenerative destroyed IVD.