Effects of anulus fibrosus and experimentally degenerated nucleus pulposuson nerve root conduction velocity - Relevance of previous experimental investigations using normal nucleus pulposus

Study Design. Nerve conduction velocity was measured in the pig cauda equin a after local application of anulus fibrosus or in vitro/postmortem degener ated nucleus pulposus from the same pig. Objectives. To analyze the effects of anulus fibrosus and degenerated nucle us pulposus on nerve conduction velocity. Summary of Background Data. Previous studies on nucleus pulposus-induced ef fects on nerve roots have used normal, nondegenerated nucleus pulposus. Bec ause both anulus fibrosus and degenerated nucleus pulposus are commonly see n in the clinical situation of disc herniation, the value of the previous w ork could be questioned. Methods. Anulus fibrosus and nucleus pulposus were harvested using a retrop eritoneal approach. The nucleus pulposus was degenerated artificially eithe r by addition of sodium lactate with HCl added to form a pH of either 6.0 o r 3.5 (in vitro degeneration), or by storing the nucleus pulposus at 4 C un til a pH of 6.0 (postmortem degeneration) was reached. After epidural appli cation, the nerve conduction velocity was determined at 7 days (anulus fibr osus) or 3 days (degenerated nucleus pulposus). Results. Application of anulus fibrosus did not induce any reduction of ner ve conduction velocity. In vitro and postmortem degenerated nucleus pulposu s induced a reduction of nerve conduction velocity similar to that of norma l nucleus pulposus. Conclusions. Although only nerve function and not pain was assessed, it see ms likely that previous experiments using normal nucleus pulposus may be re levant for evaluating the pathophysiologic mechanisms behind the nucleus pu lposus-induced nerve root injury, also in a clinical perspective.