STAPES FOOTPLATE MANAGEMENT WITH VARIOUS LASER SYSTEMS .2. THE PULSED-LASER

The object of the present study was to examine the tissue ablation cap acity of various pulsed lasers at the stapes footplate. Isolated human stapes and bovine compact-bone platelets (thickness 90 mu m) were use d to determine effective laser parameters for achieving a perforation measuring 500 mu m to 600 mu m in diameter. Apart from achieving the p erforation diameters, particular attention was given to the form and q uality of the perforations, reproducibility of the perforation effect and the thermally altered border zones occurring at the footplate. Fou r pulsed laser systems were used: excimer, Ho:YAG, Er:YSGG and CO2 las ers. An adequately large perforation generally could only be achieved by several repeated shots at the same application site, since only a s mall amount of tissue was ablated per application. The mechanism of th e photoablation caused the extent of the thermal side effects to be ma rkedly lower than with the continuous wave (cw) and superpulse systems . For this reason and because of their highly reproducible perforation effect, they were basically better suited for stapedotomy than the cw systems. It was possible, however, that as a result of the longer app lication time and the need to repeatedly irradiate the same applicatio n site, the higher pulse counts could prove to be disadvantageous in c linical practice. Among the pulsed laser systems, the Er:YSGG laser ha d the highest ablation rate at the stapes and was thus the most effect ive laser for interventions at the footplate. Although somewhat less e ffective than the Er:YSGG laser in our studies, the Ho:YAG and pulsed CO2 lasers also appear to be suitable for stapes surgery. On the other hand, we did not consider the excimer laser (308 nm) to be particular ly effective at the footplate because of its low ablation rates.