[Changes in the lumbar intervertebral disk following use of the Holmium-Yag laser--a biomechanical study].

For a biomechanical study 10 specimen of the lumbar spine (L1-S1) were scanned with MRI. After that 18 normal motion segments were prepared for the experiments. The paraspinal musculature as well as the posterior elements were removed. Under an axial load of 500 N, in each disc 500 J and 1000 J of energy were applicated with a Holmium-Yag laser (2060 nm, fiber thickness 600 microns) into the nucleus pulposus. In nine of the 18 discs also 1500 J and 2000 J were applicated. At the beginning of every standardized experiment of a motion segment, as well as after every 500 J, the height of the disc, intradiscal pressure, the contour of the disc and the size of the transversal plane of the disc were determined with an axial load on the motion segment of 1000 N. The change in radial bulging of the disc was measured using the computer-assisted recordings of each disc contour. All the data were statistically analyzed using the Friedman-/Wilcoxon-test. After every application of 500 J energy, in the 18 discs as well as in the 9 discs, the height and the intradiscal pressure reduced. The differences per 500 J were for all measurements not significant (p < 0.05). Up till the application of 1500 J the radial bulge and the size of the transversal plane of the disc increased, although the differences per 500 J were not significant. From 1500 J to 2000 J the radial bulge and size of transversal plane of the disc decreased.(ABSTRACT TRUNCATED AT 250 WORDS)