Optical properties of human articular tissue as implication for a selective laser application in arthroscopic surgery

Optical density of normal and pathological hyaline cartilage, meniscus, and synovium is determined using native and laser-irradiated tissue samples in order to examine potentials for a selective laser ablation.

One hundred forty-four autopsy specimens were irradiated in a direct contact mode using a XeCl excimer laser (lambda = 308 nm; 20 ns; 40 Hz; 40 +/- 2.1 J/mm2; 800 microns fused silica fiber) and a continuous-wave Nd:YAG laser (lambda = 1,064 nm; 1 s; 124 +/- 5.4 W/mm2; 600 microns fused silica fiber). Transmission spectra were obtained by microspectrophotometry in a spectral range from 250 to 770 nm.

In the ultraviolet spectrum analyzed, optical density (OD) is calculated to 0.81 +/- 0.05 for native hyaline cartilage, to 1.0 +/- 0.07 for meniscal tissue, and to 0.68 +/- 0.04 for synovium. With increasing wavelength the OD steadily decreases reaching mean values of 0.06 +/- 0.01, 0.13 +/- 0.03, and 0.15 +/- 0.04 at 750 nm. Compared to normal tissue degeneration of cartilage and meniscus lead to a significant increase in OD with a maximum relative OD of 4.39 and 1.26, respectively (P < .001 and P < .01). In synovitis the OD increases with a maximum ratio of 1.45:1 (P < .01). Following Nd:YAG laser exposition the OD of the coagulated zone exceeded the value of native tissue by a factor of 9.71 for cartilage, 4.71 for meniscus, and 3.04 for synovium (P < .001). Excimer irradiation leads to a 3.38-fold increase in OD for cartilage, 2.23-fold for meniscal tissue, and 1.6-fold for synovium (P < .01).

The results presented indicate that a preferential ablation of pathological tissue structures in articular surgery is possible by selecting laser systems with an appropriate spectral emission range. However, thermal laser tissue interaction may lead to severe alterations in optical properties reducing potentials of a preferential or selective laser application.