Laser preconditioning on cranial bone site: analysis of morphological vascular parameters.

BACKGROUND AND OBJECTIVES: Bone vascularization is a key factor in the bone healing process following X-ray irradiation. Preserving the vascular network from X-ray-induced injury is a relevant approach in the promotion of bone healing. Previously, we developed a protocol of laser preconditioning (810 nm diode laser, 36 J/cm²) prior to X-ray radiation (18.75 Gy) which protects the bone vascular network from deleterious effects of X-ray radiation. The aim of this present work is to characterize the effects of laser preconditioning on the bone through a morphological analysis of vascular parameters. MATERIALS AND METHODS: Digital images of the vascular plexus were taken through an optical bone chamber which was implanted onto the calvaria of rabbits. Bespoke software was used for the quantification of the vessels (classified in four groups according to their diameter), vessel length, and number of nodes at weeks 0, 4, and 8. Twenty rabbits were divided into four groups: control group #1 (n = 5); laser group #2 (n = 5). X-ray radiation group #3 (n = 5), laser preconditioning 24 hours prior to X-ray radiation group #4 (n = 5). RESULTS: The bone vascular network was stable for groups #1 and #2. Statistical analysis showed a significant reduction of each observed vascular parameter for groups #3 and #4. In the laser preconditioned group #4 the loss was less marked than in the X-ray group #3, especially for large vessels (diameter >50 µm). DISCUSSION AND CONCLUSION: We provide in vivo microcirculatory evidence to support the concept of laser preconditioning of bone. A computer-based semi-automatic system is described to quantify superficial bone vascular network parameters that had been treated by laser preconditioning prior to X-ray radiation. Laser preconditioning significantly attenuates the deletion of the superficial bone vascular network irradiated by X-ray, especially concerning large diameter vessels.

Laser preconditioning of calvarial bone prior to an X-ray radiation injury: a preliminary in vivo study of the vascular response.

BACKGROUND AND OBJECTIVES: Thermal preconditioning prior to injury induces a cytoprotective effect on soft tissues and promotes their recovery. Lasers are an adequate tool to generate controlled and reproducible heat. X-ray irradiation induces a chronic antiangiogenic effect on bone, affecting its healing and remodeling processes. The aim of this study was to investigate the effect of laser preconditioning on the re-vascularization of X-ray irradiated bone. MATERIALS AND METHODS: A bone chamber was implanted onto the calvaria of rabbits to study the vascularization process. Digital pictures were taken of the vascular plexus at the target bone site using a modified digital camera. Vascular density (VD) was determined using image processing. It was defined as the ratio of blood vessel pixels to the total number of pixels to the region of interest. Laser preconditioning was performed with a diode laser (810 nm, 2 W, 3 seconds, 48 J/cm(2), 4 mm). A 12-week follow-up study was performed on 20 rabbits divided into four groups: #1: control group (n = 5); #2: laser irradiation alone (n = 5). #3: X-ray radiation (18.75 Gy) alone (n = 5), #4: laser preconditioning 24 hours prior to X-ray radiation (n = 5). RESULTS: VD remained stable during the 12-week follow up for group #1. No significant difference was observed between laser irradiation group (#2) and control group (#1) (P>0.5). The angiolytic action of X-ray radiation was confirmed in groups #3 and #4, which were statistically different from group #1 (P<0.001). However, the decrease of the vascularization was limited in group #4 highlighting a different evolution between group #3 and #4 (P<0.05). These results were confirmed by histological analysis. DISCUSSION AND CONCLUSION: The bone chamber is an effective reproducible method for the longitudinal analysis of the dynamics of vascularization. Our findings have shown that laser preconditioning is capable of preserving vascularization in an X-ray irradiated bone site, thus suggesting a novel approach for promoting the healing of bone tissue in which the vascular supply has been damaged.