In a controlled experimental trial the induction of gonarthrosis following laser-assisted meniscectomy was assessed. A XeCl excimer laser (lambda = 308 nm, pulsewidth 20 ns, repetition rate 10-70 Hz, radiant exposure 10-40 mJ/mm2) and a continuous wave Nd:YAG laser (lambda = 1064 nm, energy density 21-93 W/mm2) were employed in connection with 600-micrometer and 800-micrometer quartz fibers, respectively. In an animal model, effects on the remaining meniscus and the corresponding cartilage surfaces were studied in vivo within an observation period of 6 months. For evaluation of the pathogenesis in laser induced arthrosis, morphological and biomechanical studies were performed on native human menisci. Compared to conventional meniscectomy, laser energy effectively prevents further fibrillation of the meniscal structure. A remodelling of the meniscus did not occur in any experimental group. The degree of reactive synovitis, assessed by macroscopic and histologic scoring, was significantly greater following Nd:YAG laser surgery than after excimer laser resection and conventional surgery (P < 0.05). On X-ray, more progression of degenerative changes was observed following laser procedures than after conventional meniscectomy. The proteoglycan content in the femoral cartilage corresponding to the zone of meniscus resection was significantly lower in the laser group than after conventional meniscectomy (P < 0.01), which substantiates macroscopic and radiographic findings indicating degenerative derangement of the hyaline cartilage. On light microscopy and scanning electron microscopy of meniscus specimens, excimer laser irradiation led to well-delineated resection borders with a mean transitional zone of 20 micrometers, whereas menisci exposed to Nd:YAG laser irradiation presented extensive vaporization zones with the surface covered by an amorphous structure. Menisci irradiated by excimer or Nd:YAG laser energy showed significantly increased rigidity (P < 0.05 and P < 0.01); the maximum value of radial strain at flexion was lower following Nd:YAG laser irradiation (mean 1.5 +/- 0.3%) and following excimer laser irradiation (mean 2.4 +/- 0.3%) than in non-irradiated menisci (mean 3.0 +/- 0.5%). These observations lead to the conclusion that laser-assisted meniscectomy promotes the early manifestation of gonarthrosis by virtue of a reduced femorotibial contact area and alterations in the biomechanical properties of the meniscus.