The influence of automated percutaneous lumbar discectomy (APLD) on the biomechanics of the lumbar intervertebral disc. An experimental study.

Twenty human lumbar motion segments were prepared and tested in an electromechanical materials testing machine in order to investigate the biomechanical changes, i.e. intradiscal pressure, radial extension and height of the intervertebral disc, after automated percutaneous lumbar discectomy (APLD) developed by Onik. The biomechanical data were statistically analyzed with the Friedman test (significance level p < 0.05). The APLD lasted 45 minutes in every segment. The mean weight of material removed was 4.6 g. The removal of 4.6 gram of nucleus pulposus material reduced the height of the disc by an average of 1.42 mm. The intradiscal pressure also decreased by an average of 5.7 bar. The radial bulge increased by an average of 0.45 mm. Our results show that the mechanism improving radicular pain in patients with herniated disc after treatment with percutaneous nucleotomy is still in question. While clinical studies show an improvement of 70% to 85% of patients treated with APLD for herniated disc, this in vitro study showed clearly that radial bulge increases after removal of nuclear material. 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.