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

Background and Objective The purpose of this study was to compare the ablation of cortical bone at wavelengths across the near and midinfrared region. Study Design/Materials and Methods An free electron laser generating 4‐μs macropulses at specific wavelengths between 2.9 and 9.2 μm was used to ablate cortical bone. The same pulse intensity, repetition rate, radiant exposure, 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, and compared with the infrared absorption characteristics of cortical bone. Results Within the parameters used, bone ablation was found to be wavelength dependent. Incisions were deepest where protein has strong absorption, and were most shallow where mineral is a strong absorber. No char was observed on ablation surfaces where 3.0, and 5.9–6.45 μm wavelengths were used. Conclusions The use of wavelengths in the 6.1‐μm amide I to 6.45‐μm amide II region, with the pulse characteristics described, were the most efficient for cutting cortical bone and produced less collateral thermal injury than cutting with a surgical bone saw. This study confirms previous observations that the ablation mechanism below plasma threshold is consistent with an explosive process driven by internal vaporization of water in a confined space and demonstrates that ablation is enhanced by using wavelengths that target the protein matrix of cortical bone. Lasers Surg. Med. 25:421–434, 1999. © 1999 Wiley‐Liss, Inc.