[Changes in the lumbar disk following use of non-automated percutaneous discectomy. A biomechanical study].

For a biomechanical study 8 specimens of the lumbar spine (L1-S1) were scanned with MRI. After that 21 motion segments were prepared for the experiments. The paraspinal musculature as well as the posterior elements were removed. From each disc 1,0 g, 2,0 g, and 3,0 g of nuclear material were consecutively removed under an axial load of 500 N. At the beginning of every standardized experiment of a motion segment, as well as after the excision of every gram of nuclear material, intradiscal pressure, the height of the disc and the contour 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-test. The nuclear material removed from the discs ('in-vitro nuclear material') was placed in isotonic saline over 45 minutes and again weighted ('wet weight'). Af that the nuclear material was freeze-dried ('dry weight'). The results of this study showed that after the excision of every gram of nuclear material the height of the disc decreased in average 0,77 mm. Also intradiscal pressure reduces significantly: from the initial stage, on average, 9, 19 bar to the endstage (= after the removal of 3,0 g), on average, 2, 58 bar. Radial bulge increases with every gram removed, on average 0,23 mm. The weight of the wet nuclear material is 2,6 times as much as that of the in-vitro nuclear material and 11 times as much as that of the freeze-dried material.