Comparison of Process Temperature during Laser and Mechanical Cutting of Compact Bone

Thermal side effects are the main problems concerning laser osteotomy. Data of the temperature increase in the vicinity of the laser cut for different irradiation conditions are important for understanding and optimisation of the laser ablation process. The first temperature measurements were done with an IR-camera (Flir SC 3000, spectral sensitivity 7.5 -- 10 textmum) from the back side of a bone plate (compact bone of bull femur) during drilling. The ablation is carried out with a TEA CO2 laser ($ = 10.6 textmum, pulse duration 1 textmus and focus diameter 230 textmum (1/e2 level)). In another series of experiments the temperature was monitored during multi-pass cutting with the same laser. The temperature was investigated depending on the laser pulse energy, pulse repetition rate and beam scanning velocity and the settings of the cooling spray. Room temperature was amounted to 23 textdegreeC. The temperature during the laser drilling (50 Hz, 30 mJ) grows up to 400textdegreeC (5 min, pressurised air jet cooling) respectively to 120 textdegreeC (3 min.) with a water spray cooling. During the laser multi-pass bone cutting with the use of a water spray and a scanning velocity of 2 mm/s the temperature reaches only 30 textdegreeC. These examinations emphasise that laser cutting is not dangerous for living bone cells under optimal conditions. The results of the temperature measurements during laser ablation are compared to the test results during mechanical abrasion. They underline that laser cutting of bones and mechanical abrasion show temperatures of an equal level. One strong advantage of laser cutting of bone is the nearly arbitrary cut geometry which could lead to an improvement in surgery.