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

Abstract

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. 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). 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. 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.