BASIC INVESTIGATIONS ON HOLMIUM LASER EFF ECTS ON ARTICULAR-CARTILAGEAND THEIR IMPACT ON THE CLINICAL-APPLICATION TECHNIQUE

The in vitro study presented helps to clarify the biophysical mechanis ms and tissue interactions of the holmium laser at the point of impact on the surface of cartilage-bone specimens investigated in different experimental settings. A striking event is the creation of a vapor bub ble that opens up access for the laser beam through the fluid medium. This bubble shows a repoducible dynamic behavior function of the laser irradiance and the angle of incidence of the delivery fiber. These de termine directly the amplitude of the pressure waves induced when the bubble collapses. Apart from this acoustic effect, which is correlated with epicentric histological features that can hardly be considered b iologically relevant, a thermal effect is recognized that is finally r esponsible for the ablation and tissue damage. It induces typical hist ological alterations that can be observed along the laser beam axis, w ith a penetration function mainly of the irradiance but also of the an gle of incidence. Nevertheless, at a pulse energy of 1 J and an irradi ation angle of 30 degrees. the recorded overall depth of the immediate histological changes was down to 500-600 mu m. Thus, in realistic wor king conditions, the damage observed after cartilage sealing with the holmium laser remains within an absolutely acceptable range. This is i n agreement with the better results compared to mechanical cartilage d ebridement that have been reported in previous prospective clinical st udies.