Promotion of regenerative processes in injured peripheral nerve induced by low-level laser therapy

Objective: This study aimed to assess in vitro the influence of low-level laser therapy ( LLLT) on the regenerative processes of a peripheral nerve after trauma. Background Data: In peripheral nerve injury initiated after severing due to accident or by a surgeon during operation, photomodulation by light in the red to near-infrared range ( 530 - 1000 nm) using low-energy lasers has been shown to accelerate nerve regeneration. Method: Twenty-four New Zealand adult male rabbits were randomly assigned to two equal groupes ( control and laser-treated). General anesthesia was adminstered intramuscularly, and exploration of the peroneal nerve was done in the lateral aspect of the left leg. Complete section of the nerve was performed, which was followed by suturing of the neural sheath ( epineurium). Irradiation was carried out directly after the operation and for 10 consecutive days. The laser used was diode with wavelength of 901 nm ( impulsive) and power of 10 mW; it was a square-shaped window type ( 16 cm(2)), and its energy was applied by direct contact of the instrument's window to the site of the operation. Three rabbits from each group were sacrificed at the end of weeks 2, 4, 6, and 8, and specimens were collected from the site of nerve suturing and sent for histopathological examination. Results: Two important factors were examined via histopathology: diameter of the nerve fibers and individual internodal length. Compared to the control group, significant variations in regeneration were observed, including thicker nerve fibers, more regular myelin layers, clearer nodes of Ranvier with absence of short nodes in the treated group. Variations between the two groups for diameter were significant for the 2nd week ( p < 0.05), highly significant for the 4th and 6th weeks, respectively ( p < 0.01), and very highly significant for the 8th week ( p < 0.001). Variations between the two groups for internodal length were highly significant for the 2(nd) and 4(th) weeks ( p < 0.01), and very highly significant for the 6(th) and 8(th) weeks ( p < 0.001). Conclusion: This experiment affirms the beneficial effect of LLLT on nerve regeneration, since LLLT produced a significant amount of structural and cellular change. The results of the present study suggest that laser therapy may be a viable approach for nerve regeneration, which may be of clinical relevance in scheduled surgery or microsurgery.