Thermal side effects of fiber-guided XeCl excimer laser drilling of cartilage

We examined thermal effects during ablation of human joint cartilage using two XeCl excimer lasers with pulse durations of approximately 20 ns and 60 ns. An increase in radiant exposure or repetition rate caused a rise in tissue temperature up to 82 degrees C at a 100-microns distance. With increasing distance from the crater edge, the temperature dropped exponentially. Radiant exposures higher than 1.8 J/cm2 and repetition rates above 20 Hz lead to a formation of hot gaseous products escaping from the laser crater. When osteoarthritic cartilage is irradiated, these gases spread inside the tissue causing a temperature rise of > 50 degrees C at a distance of 1 mm from the crater edge. In the contact mode, we found a linear rise of ablation rate with increasing repetition rate both in air or saline. But ablation rates in saline were only half the rates achieved in air. Both phenomenons can be explained by additional thermal effects of excimer lasers working in the range of higher repetition rates and pulse energies.