Biomechanical changes of the lumbar intervertebral disc after automated and nonautomated percutaneous discectomy: an in vitro investigation.

A total of 40 human lumbar motion segments were prepared and tested in an electromechanical materials testing machine to investigate the biomechanical changes, i.e., intradiscal pressure, radial extension, and height of the intervertebral disc, after percutaneous discectomy. In 20 discs (group A) the nuclear material was excised using the nonautomated percutaneous lumbar discectomy technique (NAPLD). In the other 20 (group B) the material was removed with the automated percutaneous lumbar discectomy method (APLD). The results of the two groups were analyzed statistically and compared to each other. In the NAPLD group the removal of 0.1 g freeze-dried nucleus pulposus material reduced the height of the disc an average of 0.32 mm, versus 0.47mm in the APLD group. The radial bulge increased in both groups after the removal of 0.1 g freeze-dried nucleus pulposus material, on average 0.10 mm versus 0.15 mm. The intradiscal pressure also decreased in both groups after the removal of 0.1 g freeze-dried nucleus pulposus material, on average 0.94 bar versus 1.88 bar. The differences between the biomechanical data of the two groups were statistically significant for all three parameters (P < 0.05). Our results show that the mechanism for improving radicular pain in patients with herniated disc after treatment with percutaneous discectomy is still in question. We postulate that loss of height of the disc and, as a consequence, reduction of tension in the affected nerve root, plays a major role with regard to this improvement.