The effect of low-level Nd:YAG laser energy on adult articular cartilage in vitro

Abstract

Reports of laser energy applied to soft tissues in vitro and in vivo suggest both stimulation and inhibition of specific metabolic processes, depending on the type of laser, the energy density (ED) used, the mode of delivery, and type of tissue studied. An earlier in vitro study of Nd:YAG laser irradiation of articular cartilage indicated stimulation of both matrix and DNA synthesis for 6 days following laser exposure. In vivo reports on the ability of Nd:YAG laser energy to stimulate the healing of partial-thickness cartilage defects are conflicting. In the present study, a noncontact continuous-wave Nd:YAG laser beam of varying EDs was applied to full-thickness adult articular cartilage explants maintained in organ culture; the metabolic processes of chondrocyte DNA synthesis and matrix synthesis were followed over 2 weeks. For both canine and bovine cartilage, low-levels of laser energy (ED 51–127 J/cm 2) stimulated matrix synthesis at 6–7 days following laser exposure, with a concomitant decrease in baseline DNA synthesis. By 12–14 days, however, these dose-dependent effects were no longer seen, with no significant differences from control noted for any of the laser energies studied. Histologic analysis of the cartilage explants following laser exposure showed no significant differences in cell number or morphology between sample and control groups; however, a decrease in matrix proteoglycan staining was seen in the highest laser energy group at all time points. These findings indicate that exposure to low-level noncontact Nd:YAG laser energy promotes a significant stimulation of cartilage matrix synthesis. However, a single exposure may not be sufficient to promote a sustained upregulation of cartilage metabolism. Based on the findings of this study, the potential for stimulating cartilage metabolism and repair via noncontact Nd:YAG laser energy applied arthroscopically warrants further study.