Thermal and chemical modification of collagenous tissues

Over the last decade, Sub-Ablative Thermotherapy has found ever-increasing application in orthopaedic (in the treatment of the instabilities of the knee, ankle, hip and shoulder joints and in the elimination of the discogenic pain in spine) and ophthalmologic surgery (for the correction of near/farsightedness). Utilizing sub-ablative levels of heating, the therapy aims at altering the configuration of the strain-damaged, pathological or congenitally anomalous collagenous tissue (such as tendon, ligament, skin, joint capsule, cornea, etc.) in order to re-establish stability and function.; This thesis describes research directed towards understanding, modeling and controlling the heat-induced responses of collagenous tissues. The main aim of the research was to establish the scientific basis and develop the tools to increase the safety and efficacy of Sub-Ablative Thermotherapy procedures.; In-vitro thermomechanical experimentation with a model collagenous tissue (New Zealand white rabbit patellar tendon) is performed in order to determine the constitutive relationships between the accumulated thermal damage and the resultant mechanical response and the stress-state of the collagenous tissues. Finite Element Analysis-based simulation tools are also developed in order to quantify the differences among clinically applied heating modalities such as, monopolar/bipolar radiofrequency and Ho:YAG laser.; It is shown that there is a trade-off between the kinematical stability established by altering the configuration of the collagenous tissue and the mechanical stability compromised by the heat-induced degradation of its mechanical properties. For a homogeneously heated tendon tissue, existence of different shrinkage regimes and a mechanical optimum state in the heat-induced response is shown. Through Finite Element Analysis, thermal damage fields created by clinically applied heating modalities are established and the effects of clinically important parameters such as probe sweep speed, radiofrequency power and saline circulation are examined. A computer-based simulation tool is also developed in order to simulate the heat-induced mechanical behavior of the collagenous tissues.; To accurately simulate the heat-induced mechanical response of a collagenous tissue, future studies should extend the analyses established here to multi-dimensions and should take into consideration the non-homogeneous nature of the tissues. After these studies are completed, the next challenge would be to apply the technology developed to the clinical setting.