Modeling the thermal histories of collagenous tissues subjected to different heating modalities

Application of sub-ablative levels of heat to collagenous tissues causes helix-to-coil transformation in the collagen microstructure resulting in overall tissue shrinkage. This phenomenon has important therapeutic applications in medicine, such as thermokeratoplasty, treatment of shoulder, knee and ankle instabilities and treatment of chronic discogenic lumbar pain associated with hemiated discs. During the therapy, heat is applied arthroscopically by a laser or a radio-frequency probe (bipolar or monopolar). The amount and permanence of shrinkage established in the tissue is a function of the maximum temperature reached and the exposure time as well as the mechanical stress applied on the tissue during heating. Therefore, the thermal and mechanical history that the tissue experiences is a major factor determining its response and long-term mechanical stability. These are the defining factors for the success of the therapy. It is hypothesized in this study that there are significant differences between the thermal histories created in the tissue by different heating modalities owing to the differences between their modes of action. The solutions to the temperature distributions created by these different heating modalities -laser and radiofrequency applied with a bipolar and a monopolar probeare compared and parameters of clinical significance are discussed.