Energy requirements for osteotomy of femora and tibiae with a moving CW CO2 laser.

This paper describes the laser cutting and the amount of laser energy needed to remove a unit mass of compact or cancellous human cadaveric bones ("heat-of-removal") by using a CO2 laser. Data are collected under different operating conditions, such as laser power, scanning speed, and lens focusing for fresh and fixed human bones from male and female femora and tibiae samples with ages varying between 28 and 73 years old. The aim of the present experiments was to demonstrate the feasibility of laser osteotomy, to find the energy requirements for given groove depths or bone removal rates, and to shed some light on optimum conditions for laser osteotomy. Only cadaveric bones were used in this study, since the present aim did not include the investigation of heating rates and the extent and effect of thermal necrosis adjacent to the cut. In vivo properties may be somewhat different from those of cadaveric material. While blood circulation within the living bone may contribute to the laser cutting characteristics, it cannot be addressed here. Experiments showed that very deep cuts are difficult to achieve with a CO2 laser, as at high-power/low-scan-speed the groove becomes rather wide, with unacceptable thermal damage adjacent to the cut, while multiple passes do not easily attain large depths. There was no significant difference for the laser heat-of-removal for different age groups and for male and female samples. The laser heat-of-removal was found to be higher for compact bone than for cancellous bone samples. Comparison of cross-sections of the cuts with an existing model gave good agreement.