HOLMIUM - YAG LASER ABLATION OF HUMAN INTERVERTEBRAL-DISK - PRELIMINARY EVALUATION

Percutaneous discetomy has become a viable alternative in the treatment of herniated intervertebral disc. This study determined the effectiveness of holmium:YAG laser for ablation of human disc tissue. Human cadaveric intervertebral disc was harvested and stored in cold saline-soaked gauze for evaluation within 24 hr of removal. Using a specially designed apparatus, a 600-mu-m diameter fiber was advanced perpendicular through the annulus fibrosis at a controlled force of 0.098 Newtons (10 g). Samples were lased in air (n = 17) and in room temperature saline (n = 32). The laser energy was delivered at 5 Hz, 250-mu-sec pulsewidth, and from 50 mJ/mm2 to 1,100 mJ/mm2 fluence. Three to six holes were lased using identical parameters in each tissue specimen and were evaluated histologically and by morphometric analysis. The maximum zone of thermal necrosis and thermal denaturation occurred at 700-1,100 mJ/mm2; 140-mu-m and 590-mu-m in air and 80-mu-m and 730-mu-m in saline, respectively. At fluences between 200 and 700 mJ/mm2, the thermal necrosis ranged from 20 to 60-mu-m in air and from 10 to 50-mu-m in saline, the zone of denaturation also being less. The holes created with the 600-mu-m fiber were circular in shape, with a mean diameter of 500-mu-m (n = 3). The etch rates (penetration/pulse) appeared to increase with increasing fluences. In saline, the etch rate ranged from 7 to 53-mu-m/pulse (r = 0.57, P less-than-or-equal-to 0.10), and, in air, the values ranged from 7 to 65-mu-m/pulse (r = 0.79, P less-than-or-equal-to 0.03). No tissue ablation occurred at 50 mJ/mm2, suggesting that the ablation threshold lies between 50 and 200 mJ/mm2. This study demonstrates that controlled ablation of human disc tissue can be accomplished with the holmium: YAG laser, the degree of thermal injury being related to the amount of energy delivered.