Effects Of Laser Bone Ablation On Surrounding Tissue: An Experimental Study

【Objective】Using medical laser systems and drill as operating tools, New Zealand Rabbit's otic capsule and calvarial bone as the target tissue, to study the effects of laser bone ablation on surrounding tissue in vivo. Trying to obtain some evidence for safely application of laser in ear surgery.【Methods】Anatomized eight New Zealand Rabbits'middle ear, to study their anatomic structures and to locate the thinnest place between middle ear and brain. Compared the histological structure of the calvarial bone and the middle ear bone, in order to find the evidence for one of this study–using calvarial bone as a substitute for middle ear cavity wall, by using calvarial bone to study the effects of laser bone ablation on brain tissue. 4 rabbits chosen randomly from 28 healthy male New Zealand rabbits were used for determination in laser parameters,translation stage parameters, and laser dose. The rest rabbits were randomly divided into three groups, respectively named drill group,CO2 laser group and Er:YAG laser group. 6 hours after operation, to achieve bone and brain tissue samples around the place which were drilled or ablated. HE staining was used to assess the thermal damage in the peripheral bone tissue operated by laser ablation. Immunohistochemistry was used to detect the heat shock protein 70(HSP70) in brain tissue, to assess the effects on brain tissue operated by laser bone ablation.【Results】1. Calvarial bone and middle ear cavity wall bone have the similar thickness and structure, the former would be easier to expose in this experiment, in addition, calvarial bone surface is smooth to allow laser beam to irradiate it vertically. 2. Laser bone ablation could lead to harm to surrounding bone, the harmful degree were not the same. The drill group showed the most minor harm. Laser groups also showed different damage degree in different site, due to their different laser parameter,dose, operating mode applied.3. There were no damaged evidence in brain samples in HE staining sections in all three groups, there were no HSP70 expression either in whole brain samples. However, in the case in which the brain was irradiated by laser showed some slightly positive cells (HSP70 expression) in endochylema in brain sample.【Conclusion】1. Calvarial bone could be used as a substitute for middle ear cavity wall bone to study the effects of laser bone ablation on brain tissue.2. Laser bone ablation caused surrounding damage to the peripheral bone tissue, and the peripheral bone tissue damages by lasers were far seriously than bone cutting by drill.3. In this study, the selected laser systems with selected parameters and dose would not damaged to underneath brain tissue, while there was a thin layer of bone between ablation site and brain. Nevertheless, the further study to delayed or latent damage is still needed.