LASER THERAPY FOR TREATMENT OF TENDINOPATHY INDUCED IN WISTAR RATS: AN HISTOMORFOMETRIC STUDY/LASERTERAPIA PARA TRATAMENTO DE TENDINOPATIA INDUZIDA EM RATOS WISTAR: ESTUDO HISTOMORFOMETRICO/TERAPIA CON LASER PARA TRATAMIENTO DE TENDINOPATIA INDUCIDA EN RATAS WISTAR: ESTUDIO HISTOMORFOMETRICO

The aim of this study was to evaluate the effects of laser therapy in tendinopathy of Achilles tendon of Wistar rats. Thus, 12 adult male rats which were divided into two groups (L=laser and C=control) were used. All animals were submitted to unilateral tendinopathy (random selection) by transverse compression of the tendon (10 seconds) with Halsted forceps, as well as 10 scarifications (using a scalpel). After 24 hours of induction of lesion all animals of Group L received laser (904 nm/3 J/[cm.sup.2]/ 9 s) for 20 days, while Group C were handled as if they would receive radiation. After 3, 7, 14 and 21 days lesion induction, three rats from each group were euthanized, and the tendons obtained for histomorphometric analysis. The samples were processed as routine and the sections stained with hematoxylin-eosin, Masson's trichrome and Picrosirius Red. Data were analyzed by ANOVA, at 5% probability and regression analysis. No differences between groups neither between time for hemorrhage characteristics, angiogenesis, thickening of epitendon. Independently of the treatment there was a decrease (p=0.0129) of fibrinous adhesion (3rd to 21st day). On the other hand, morphometric analysis revealed higher (p=0.0120) amounts of fibroblasts cells in the group receiving laser therapy, with no effect of time. Semiquantitative assessment also showed higher (p=0.0000) amounts of fibroblasts cells in the treated group, but in this analysis, the number of fibroblasts increased with time (p=0.0001) in both group. In contrast, ANOVA revealed a reduction of the inflammatory cells from 3rd to 21st day in both groups (histology: p=0.0003; morphometry: p=0.0000). Although there was no difference between groups in the amount of collagen type I and III, morphometry revealed that the rats of group L showed higher (p=0.0096) amounts of collagen fibers than group C. For this characteristic, there was no effect of time, even though it was observed higher (p=0.0000) organization of collagen deposition on day 7. The amount of collagen fibers determined by histology revealed only the effect of time (p=0.0005), regardless of treatment, with an increase in this variable until the 14th day, with further reduction. Laser therapy initiated 24 hours after surgical induction of tendinopathy in the Achilles tendon of rats has the advantage of increasing quality and quantity collagen fibers, as well as the fibroblasts cells, which are fundamental on the synthesis of collagen.