[Modifying the stapes footplate with various laser systems. II. The pulsed laser]

The object of the present study was to examine the tissue ablation capacity of various pulsed lasers at the stapes footplate. Isolated human stapes and bovine compact-bone platelets (thickness 90 microns) were used to determine effective laser parameters for achieving a perforation measuring 500 microns to 600 microns in diameter. Apart from achieving the perforation diameters, particular attention was given to the form and quality of the perforations, reproducibility of the perforation effect and the thermally altered border zones occurring at the footplate. Four pulsed laser systems were used: excimer, Ho:YAG, Er:YSGG and CO2 lasers. An adequately large perforation generally could only be achieved by several repeated shots at the same application site, since only a small amount of tissue was ablated per application. The mechanism of the photoablation caused the extent of the thermal side effects to be markedly 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 application time and the need to repeatedly irradiate the same application site, the higher pulse counts could prove to be disadvantageous in clinical practice. Among the pulsed laser systems, the Er:YSGG laser had the highest ablation rate at the stapes and was thus the most effective laser for interventions at the footplate. Although somewhat less effective 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 particularly effective at the footplate because of its low ablation rates.