CIRCUMFERENTIAL MEASUREMENT OF ANULUS DEVIATION AFTER LASER NUCLEOTOMY

Background and Objective: Former studies investigated only the intradi scal pressure after laser nucleotomy. As the outer anulus causes compr ession of neural structures, the present in vitro study was performed to investigate the circumferential pressure conditions of the outer po sterolateral anulus following laser nucleotomy. Study Design, Material and Methods: Laser nucleotomy was performed using a Hol:YAG laser (14 Watt, total energy applied 10kJ). Stiffness of the intervertebral dis c and deviation of the posteriolateral portion of the disc under axial pressure were investigated. The forces observed during external defor mation of the anulus were measured by stain gauges and recorded by a d ata logger. Measurements were taken at 4.8 and 10 kJ. The maximum axia l load was 400 Newton. Results: We found a preoperatively reduced exte rnal deviation within the punctured area after positioning the laser p robe. Postoperatively, the posteriolateral parts of the disc showed a relatively increased external deviation due to reduced stiffness where as the anterior parts remained unchanged. Stiffness of the disc decrea sed with increasing total energy applied. Conclusions: Puncture of the intervertebral disc for laser nucleotomy should be performed on the s ide of the prolapse. Due to the reduced stiffness peak pressure loads on the protrusion site might be distributed over the whole disc. The l inear negative correlation observed between energy and stiffness sugge sts a good therapeutic correlation with laser treatment. (C) 1997 Wile y-Liss, Inc.