Comparison of cortical bone ablations by using infrared laser wavelengths 2.9 to 9.2 mu m

Background and Objective: The purpose of this study was to compare the abla tion of cortical bone at wavelengths across the near and midinfrared region . Study Design/Materials and Methods: An free electron laser generating 4-mu s macropulses at specific wavelengths between 2.9 and 9.2 mu m was used to ablate cortical bone. The same pulse intensity, repetition rate, radiant ex posure, number of pulses, and delivery was used for each wavelength. Tissue removal, collateral thermal injury, and morphologic characteristics of the ablation sites were measured by light and scanning electron microscopy, an al compared with the infrared absorption characteristics of cortical bone. Results: Within the parameters used, bone ablation was found to be waveleng th dependent. Incisions were deepest where protein has strong absorption, a nd were most shallow where mineral is a strong absorber. No char was observ ed on ablation surfaces where 3.0, and 5.9-6.45 mu m wavelengths were used. Conclusions: The use of wavelengths: in the 6.1-mu m amide I to 6.45-mu m a mide II region, with the pulse characteristics described, were the most eff icient for cutting cortical bone and produced less collateral thermal injur y than cutting with a surgical bone saw. This study confirms previous obser vations that the ablation mechanism below plasma threshold is consistent wi th an explosive process driven by internal vaporization of water in a confi ned space and demonstrates that ablation is enhanced by using wavelengths t hat target the protein matrix of cortical bone. Lasers Surg. Med. 25:421-43 4, 1999. (C) 1999 Wiley-Liss, Inc.