Circumferential measurement of anulus deviation after laser nucleotomy.

Background And Objective: Former studies investigated only the intradiscal pressure after laser nucleotomy. As the outer anulus causes compression of neural structures, the present in vitro study was performed to investigate the circumferential pressure conditions of the outer posterolateral anulus following laser nucleotomy.

Study Design, Materials And Methods: Laser nucleotomy was performed using a Hol:YAG laser (14 Watt, total energy applied 10kJ). Stiffness of the intervertebral disc and deviation of the posteriolateral portion of the disc under axial pressure were investigated. The forces observed during external deformation of the anulus were measured by stain gauges and recorded by a data logger. Measurements were taken at 4.8 and 10 kJ. The maximum axial load was 400 Newton.

Results: We found a preoperatively reduced external deviation within the punctured area after positioning the laser probe. Postoperatively, the posteriolateral parts of the disc showed a relatively increased external deviation due to reduced stiffness whereas the anterior parts remained unchanged. Stiffness of the disc decreased with increasing total energy applied.

Conclusions: Puncture of the intervertebral disc for laser nucleotomy should be performed on the side of the prolapse. Due to the reduced stiffness peak pressure loads on the protrusion site might be distributed over the whole disc. The linear negative correlation observed between energy and stiffness suggests a good therapeutic correlation with laser treatment.