Holmium:YAG laser ablation of human intervertebral disc: 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 microns 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 microseconds 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 microns and 590 microns in air and 80 microns and 730 microns in saline, respectively. At fluences between 200 and 700 mJ/mm2, the thermal necrosis ranged from 20 to 60 microns in air and from 10 to 50 microns in saline, the zone of denaturation also being less. The holes created with the 600 microns fiber were circular in shape, with a mean diameter of 500 microns (n = 3). The etch rates (penetration/pulse) appeared to increase with increasing fluences. In saline, the etch rate ranged from 7 to 53 microns/pulse (r = 0.57, P less than or equal to 0.10), and, in air, the values ranged from 7 to 65 microns/pulse (r = 0.79, P less than or equal to 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)