Thermal stress in cartilage under holmium laser irradiation

The ablation of joint cartilage by Holmium laser radiation is followed by the creation of an unexpected large avital cell area below of the irradiated spot. To examine the reasons for the tissue destruction the effect of shockwaves as well as the temporal development of temperature due to the laser absorption was investigated. The temperature raise was observed by an infrared-camera. The creation of cell destroying temperatures below the irradiated area is explained by the absorption of the Holmium laser light and the spread out of heat from the absorption area, whereby the effects due to shockwave seem to be neglible. To reduce the development of high temperatures a method is presented that allows a local coding of the irradiated area.