Quantification of laser-induced cartilage injury by confocal microscopy inan ex vivo model

Background: The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur aft er laser meniscectomy. The objective of the present study was to evaluate t he effect of laser wavelength and energy on cartilage injury in an ex vivo model. Methods: Fresh bovine articular cartilage was exposed to either holmium:ytt rium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Bot h lasers were operated in a free-running mode and at a pulse-repetition rat e of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG a t 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by convention al histological analysis and by confocal microscopy. Thermal damage was ass essed by determining cell viability. Results: The extent of thermal damage demonstrated by confocal microscopy w as much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than tha t after Er:YAG-laser irradiation, which was associated with almost no damag e. In addition, the ablation depth was greater after treatment with the Er: YAG laser than after treatment with the Ho:YAG laser. Conclusions: In the present study, histological analysis underestimated the rmal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery. Clinical Relevance: Debridement and smoothing of cartilage in patients with osteoarthritis or cartilage defects should cause minimal injury to the sur rounding cartilage in order to avoid additional tissue destruction.