On Long Term Effects of Low Power Laser Therapy on Bone Repair: A Demonstrative Study by Synchrotron Radiation-based Phase-Contrast Microtomography

Laser effects on fracture healing are still controversial and require further quantitative 3D measures of newly formed bone microstructural parameters. We performed a demonstrative investigation, by synchrotron radiation-based phase-contrast microtomography (SR-phc-microCT), on bone regeneration process in rats submitted to femoral osteotomy and treated with low power laser therapy (LPLT). Six Wistar rats were subjected to transverse osteotomy of the right and left femurs and randomly divided into four experimental groups: not grafted with biomaterials and not laser-treated (Group I, n = 3), not grafted with biomaterials but laser-treated (Group II, n = 3), grafted with biomaterials and not laser-treated (Group III, n = 3), grafted with biomaterials and laser-treated (Group IV, n = 3). LPLT was performed at dose of 16 J/cm2 per exposure, immediately after osteotomy, every 48 hours for the first week and every 72 hours for the next two weeks. Animals were sacrificed after 24 days. Bone regeneration and mineralization degree, with or without biomaterial’s grafts, were evaluated by SR-phc-microCT. We observed that, for regenerated bone struts in the dimensional ranges thicker than 200 mm and in absence of any biomaterial graft, the bone volume percentage in the LPLT-treated samples was almost two-fold greater vs. the controls. This effect is magnified in presence of Bioss grafts when the bone volume percentage in the LPLT-treated samples was found to be almost three-fold greater vs. not treated samples. Despite the reduced sample size, we demonstrated that SR-phc-microCT technique can play a fundamental role in the advanced characterization of laser-treated sites. In fact it allows, in a nondestructive way, a quantitative, statistically significant and high-resolution 3D analysis of newly formed bone microstructural parameters, keeping the sacrificed animals to the minimumin accordance with recent ethical standards.