Die Knochenzemententfernung mit dem Laser - Bone Cement Removal with the Laser

Abstract

In operations requiring replacement of cemented endoprothesis, the removal of both the prosthesis and the cement is often difficult as the cement adheres strongly to the bone. Mechanical removal frequently results in fenestration or traumatisation of the bone. The aim of non-contact removal of polymethylmethacrylate (PMMA) with the laser, is to access normally inaccessible regions while inflicting a minimum amount of damage to the bone substance. The much cited cw or superpulsed CO2-laser cannot be used clinically, due to the thermal stressing of the bone. The paper shows spectra of PMMA with and without dopants, e.g. Tinuvin as UV absorber, optical staining with a high-pressure mercury lamp at lambda = 275 +/- 25 nm, lambda = 350 +/- 25 nm and various radiation times, as well as with an excimer laser lambda = 248 nm, FWHM 20 ns, and ablation measurements were made with the following lasers: excimer laser, Lambda Physics, EMG 102, FWHM 25 ns, lambda = 351 nm, excimer laser, Technolas, MAX 10, FWHM 60 ns, lambda = 308 nm, and a pulsed CO2 laser from PSI, lambda = 9.2 and 10.6 microns, FWHM 130 and 65 microseconds, pulse peak power 3.8 and 7.7 kW. The excimer laser, pulse length less than 100 ns, is unsuitable for clinical use because the required removal rate cannot be achieved either with doped PMMA or with pure PMMA. More promising results have been obtained with the pulsed (microseconds range) CO2 laser which has a removal rate of up to 30 times that of the above-mentioned excimer laser, with significantly lower thermal stressing of the bone than with the cw or super pulsed CO2 laser.

Optical Absorption Coefficient, Time of Thermal Relaxation, Time of Surface Threshold, and Time of Heat Incubation for PMMA Samples at the CO2Laser-Beam Wavelength of 10.6 µm

“…This paper therefore proves that it could indeed be suggested 12 to reduce or completely abolish the utilization of colorant dopants in the preparation of the bone cement mixture, since the mathematical calculation proves that ␣ > 500 cm Ϫ1 . This decision would reduce or avoid the deterioration of mechanical characteristics of bone cement itself, which can cause bone deterioration during the bone cement removal procedure.…”

“…For example, Scholz et al 12 consider the fact that colorant dopants of bone cement strongly bind to PMMA, and if the absorption coefficient of the PMMA would be larger than 500 cm Ϫ1 , the dopants themselves could be reduced or abolished completely in the preparation of the mixture of bone cement. This would reduce trauma to the bone caused by a high percentage of colorants, which occurs during the removal procedure of the cement using laser techniques.…”

Experimental in-vitro bone cements disintegration with ultrasonic pulsating water jet for revision arthroplasty

“…Braren et al [27] demonstrated the use of excimer laser for the material removal of bone cement, but in experiments this tool was very slow. Scholz et al [28] found that carbon dioxide laser showed the best effect, but is currently used rarely. Caillouette et al [29], deSteiger et al [31] and Smith et al [32] described a new ultrasonically-driven tool for the removal of bone cement.…”