# 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 most cases, the NP tissue was partially or completely replaced by fibrohyaline or hyaline cartilage (Figure 4B). In the 90 days after the operation, fibrohyaline and hyaline cartilages predominated in the NP of all animals (Figure 4C). Signs of necrosis in this mode were minor. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Laser Mode** & **1** & **2** & **3** \\ \hline Pulse duration, ms & 1000 & 100 & 10 \\ Pulse repetition rate, Hz & 0.5 & 1 & 1 \\ Power, W & 0.7 & 1.5 & 3 \\ Number of the series of pulses & 3 & 3 & 1 \\ The duration of the pause & & 15 & 10 & - \\ between the series of pulses, s & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Laser mode selection for clinic. Wavelength 1560 nm, number of pulses in a series 10. Figure 4: Histological examination of the in vivo laser restoration of damaged discs in rabbits: (**A**) simulation of DDD (control): NP in 2 months after needle insertion. Necrotic acellular tissue, \(\times\)400; (**B**) laser-irradiated disc, mode 1. In 30 days in the upper left corner is a fragment of fibrohyaline cartilage in the NP. Area of necrosis (top right) and growing hyaline cartilage tissue (bottom), \(\times\)100; (**C**) irradiated disc, mode 1. In 90 days. Transitional fibrohyaline cartilage in the NP. Numerous isogenic groups, fibrosis and hyaline-like (below) matrix, \(\times\)200; (**D**) irradiated disc, mode 2. 30 days. Development of hyaline cartilage in two months after laser irradiation, \(\times\)400; (**E**) irradiated disc, mode 2. 30 days. Osteophyte, consisting of bone tissue (right), fibro-hyaline cartilage (left), \(\times\)200; (**F**) irradiated disc, mode 2. 90 days. Fibrous-hyaline cartilage in the NP, \(\times\)400. Hematoxylin and Eosin (H&E). Mode 2: After 30 days, the formation of hyaline or fibro-hyaline cartilage (Figure 4D) was observed in the NP, while, in the outer third of the AF, osteophytes formed consisting of cancellous bone tissue and fibro-hyaline cartilage (Figure 4E). The hyaline layer between the bone part of the EP and IVD was thickened. In the middle and inner layers of the AF, the structure slightly changed in some of the discs. After 90 days, the inner layer of AF was largely replaced by fibro-hyaline or hyaline cartilage, and in the middle layer, manifestations of tissue remodeling were observed, associated with the gradual formation of fibro-hyaline cartilage. Signs of gradual tissue transformation into fibro-hyaline and hyaline cartilage were revealed in the NP. After 30 days, diffuse compaction of the NP matrix occurred, the size of cell clusters decreased, a change in the dominant cell type was noted--instead of notochondral cells, chondrocyte-like cells began to prevail in the NP. A total of 90 days after surgery, most of the NP (up to 90% of the volume) had already been replaced by fibro-hyaline cartilage, in which signs of hyaline cartilage were more pronounced in some areas (Figure 4F), and signs of fibrous cartilage were in others. The border between the NP and AF was hardly identifiable. In AF, foci of hyaline or fibro-hyaline cartilage with pronounced proliferation of chondrocytes and the formation of large isogenic groups were observed. Mode 3: In the 30 days after irradiation, large fields of fibro-hyaline and hyaline cartilage with isogenic groups were formed in the middle and inner layers of the AF, as well as at the site of the NP. In several cases, foci formed by the tissue of the NP appeared in the AF, possibly due to the \"throwing\" of the NP particles under irradiation with a short laser pulse. After 90 days, there was a pronounced expansion of the EP and a widespread transformation of tissue into fibro-hyaline and hyaline cartilage, which had a more diffuse character than at 30 days. Thus, the histological and histochemical study of IVD under all modes of laser irradiation showed that after 30 and 90 days, similar morphological changes occurred, which lead to the replacement regeneration of tissue damage in the NP and AF.