REACTIONS OF MENISCAL TISSUE AFTER ARTHROSCOPIC LASER APPLICATION - AN IN-VIVO STUDY USING 5 DIFFERENT LASER SYSTEMS

In many clinical and in vitro studies, the effect of laser radiation o n meniscal tissue was examined. Clinical studies referred to clinical criteria like swelling, effusion, and pain to evaluate laser effects. Invitro Studies showed the laser effect in the moment of cutting the t issue. But the effect of laser radiation on biological tissue also dep ends on the vital reaction of the tissue. So, the real extent of tissu e damage caused by laser irradiation can only be examind in long-term in vivo studies. This was the purpose of this study. Seventy-two knees of pigs underwent arthroscopic meniscal cuts in the anterior horn of the medial meniscus. The pigs were divided into 6 groups: The first 5 groups were operated with 5 different laser systems: Neodym:YAG 1,440- nm wavelength; Nd:YAG 1,064-nm wavelength, Excimer, Holmium:YAG, and C O2. The sixth group was operated with mechanical punches. From each gr oup, the menisci of the pigs were examined macroscopically and by ligh t-microscope after survival periods of 0, 2, 6, 12 weeks. Results were as follows. (1) All laser systems caused greater damage to the menisc al tissue than mechanical instruments. (2) This damage was a biologica l reaction of the tissue, characterized by a necrotic zone surrounding the meniscus cut. (3) This necrotic zone was not visible intraoperati vely but only 2, 6 and 12 weeks after operation. The diameter of the n ecrotic zone ranged between 1.5 mm and 9 mm. (4) Meniscus cuts with me chanical instruments showed no necrotic zone in the surrounding tissue . (5) Laser cuts in the meniscus caused more extensive healing reactio n than cuts with mechanical instruments. (6) The quality of this heali ng reaction varied with the different laser systems: the Nd:YAG 1,064- nm, Ho:YAG, and CO2 laser caused only an incomplete healing because th e tissue repair showed by tissue growing from the synovial edge into t he defect only. The Nd:YAG 1,440-nm wavelength and Excimer led to tiss ue growing from the synovial edge and to remodeling of original menisc al tissue, recognizable by reduction of the necrotic zone. Arthroscopi c surgeons should be aware that the damage to meniscus tissue caused b y a laser is much greater than can be seen intraoperatively and is muc h greater than the damage caused by mechanical punches. The healing re action of the tissue is more extensive after laser application than af ter use of mechanical instruments. Results of in vitro studies on the tissue damage caused by lasers are insufficient to describe the whole extent of laser effects on living tissue.