[Effect of surgical laser on collagen-rich tissue]

The goal of this ex-vivo study was a controlled macroscopical and microscopical comparison of the immediate effects of surgical lasers on dense collagenous tissues. The investigation of the exact denaturizing effects following tissue interaction between lasers and collagenous fibers are of importance for a better understanding of the observed and described healing process. Partial tenotomies were performed ex vivo on sixty tendons of the flexor digitorum profundus muscle of New Zealand White Rabbits using four surgical lasers (Holmium:YAG-, Erbium:YAG-, Neodym:YAG-, and CO2-Laser). The tendons were evaluated macroscopically, histologically and observations were made on the surgical handling of the lasers during the procedure. The choice of lasers allowed the comparison of a wide spectrum of wavelengths (gamma = 1.0 to 10.6 microns). In addition, beam delivery modalities were compared to each other (focus vs. contact). The pulse (frequency and power) was varied within each laser. Other parameters including focus size, absorption, dispersion, and thermal tissue conductivity were maintained constant in this test arrangement in order to allow a later comparison between the observed areas of denaturated collagen. The macroscopical and histological results showed great differences in the effects of the four lasers. Even within each single laser group, the results varied greatly with the choice of variable parameters. Holmium:YAG- and CO2-Laser can produce similar areas of collagen denaturation. When comparing specimens with similar areas of collagen denaturation induced by different laser types, different amounts of charring were observed. Erbium:YAG-Laser tenotomies showed generally inhomogeneous denaturation areas, while tenotomies with Neodym: YAG-Laser used in continuous mode resulted in significant charring and tissue retraction in the area of interaction. These observations help in defining the combination of parameters with which Holmium:YAG-, Erbium:YAG-, and CO2-Lasers can be used for transsection of dense collagenous tissues. In addition, these histological results as well as already published observations on healing patterns following laser surgery allow for the formulation of a hypothesis on the effects of laser in the wound healing process.