INCISION OF THE ANULUS FIBROSUS INDUCES NERVE ROOT MORPHOLOGIC, VASCULAR, AND FUNCTIONAL-CHANGES - AN EXPERIMENTAL-STUDY

Study Design. The effects on nerve root structure, vasculature, and fu nction after incision of the adjacent disc was studied in a dog model. Objectives. To see if only incision of the disc per se is sufficient for inducing similar changes. Summary of Background Data. It is well k nown that nucleus pulposus will induce nerve root structural and funct ional changes in experimental situations. In these previous studies, r elatively large amounts of nucleus pulposus were applied. Methods. The left L7 nerve root was exposed and mobilized in 10 dogs. In five dogs , the adjacent L6-L7 disc was incised, and in five other dogs, the dis c was not incised. After 7 days, nerve conduction velocity was recorde d, and specimens were obtained for his histologic evaluation. Results. The nerve conduction velocity was significantly lower in the incision group (13 +/- 14 m/sec) compared with the nonincision group (73 +/- 5 m/sec). Structural changes of the axons were more pronounced in the i ncision group, however, the degree and distribution was too limited to fully account for the neurophysiologic reactions observed. There also were obvious signs of capillary stasis with an increased number and d iameter of the intraneural capillaries in the incision group. Conclusi ons. The present study indicated that incision of the anulus fibrosus is sufficient to induce significant morphologic and functional changes and that vascular mechanisms may be of importance for the observed ch anges. These experimental data suggest that leakage of nucleus pulposu s material from anular tears, with injury to adjacent nerve roots, mig ht be one pathophysiologic mechanism in patients with low back pain an d sciatica but with no radiologic or surgical evidence of disc herniat ion.