New data obtained from treating polymethylmethacrylate (PMMA) with a non-moving cw- 10 watt-CO2 laser-beam focused at 2.5'', 5'', 7.5'' and 15.75'' are presented. . The final equations R(tc) and Z(tc) for each focal length are proposed. A very interesting correlation between the focal lengths in use and the integrated values of R and Z between 0 and 2 sec has been identified and discussed. This result has been used as basis to define a convenient operative protocol to follow during the planning phase of critical osteotomies or bone cement removal operations using a continuous-wave CO2 laser-beam set to any output power and focused by a set of most common, moving or non-moving focal lengths placed on the operating area. With a simple equation, it is possible to compare craters obtained with moving and non-moving laser-beams at different operative conditions between 0 and 2 sec, time interval which covers the majority of cases. A value of 2.3 +/- 0.1 between ablated volumes of PMMA and bone tissue has been identified. Several case studies regarding orthopaedic procedures from Literature are here reported and compared to the present LCA model. The computerized on-line flow of information for the laser-beam optimization and safety control is also described. Finally, a method for the simultaneous data collection from several operating rooms via a Local Area Network (LAN-Industry Standard IEEE) onto a central data base for later consultation is proposed in its general design.

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The minimal focal length value f(min)=0.013? for a TEM(22) laser beam profile can be used for reference in UCMIS procedures using commercially available pulsed CO2 lasers at the wavelength of 10.6??m. No laser thermoablation of compact PMMA samples is possible below f(min) while delivering I(min)=7.6?mW on its spot. Gaussian beams showing TEM00 profile need longer focal lengths for the same minimally ablated volume. Suggestions about the calibration requirements for such a lens are presented. More investigations are needed to validate the whole procedure before any preliminary surgical utilization can be considered.

A method for a controlled generation of primary damage craters in methacrylate ester samples (Vedril C, Montedison) induced by continuous and long-term exposure to CO2 laser radiation is proposed. The results are compared with the experimental values obtained 'in vitro' with 10 W continuous output power of a CO2 laser beam and fg = 7.5 in focal length of the laser's focusing head, and this shows that the proposed model can explain the phenomenon related to the generation of the limiting crater in typical biological tissue. It may have applications in clinical procedures where long-term exposure of the tissue to a laser beam must be considered. Also, the method may possibly be used to create and update a computer library automatically collecting data regarding different thermodynamic characteristics and values of various biological media.

The selection of the CO2 laser beam parameters and the irradiated media reported in this article have allowed identification of a critical set of ablative conditions to be further used in the operating room.