The Animal Experimental Study For Discogenic Low Back Pain

Disc is thought to be an significance source for a large number of severe low back pain cases.This type of pain originating from the disc is called discogenic pain. It is estimated that 40% of chronic low back pain cases are caused by internal disc disruption (IDD).Radial anular tear is the transection of the lamellar structure of annulus fibrosus, which starts from the fissure of nucleus pulposus and pains will be caused when the fissure reaches the posterior 1/3 part of annulus fibrosus with a high density of nerves fibers.The overall purpose of the present study was to establish a model of internal disc disruption (IDD) by injuring the inner layers of posterior annulus fibrosus of the goats via the anterior side of intervertebral disc with needles of defined gauges. Histologic, imageologic and immunohistochemistric studies were performed to observe the progress of disc degeneration.Objective(1) To establish the animal model of internal disc disruption (IDD) to observe acute, subacute and chronic pathological change and imaging change of the injured discs.(2 ) To study the association between internal disc disruption (IDD) and disc degeneration in animal model.(3 ) To study the possible pathogenesis of low back pain.Method15 half-a-year old goats, weight 15-25kg (average 18.5kg). Using puncture knife(1.2 mm diameter) in parallel with the adjacent upper and lower endplates , the inner side of posterior annulus fibrosus of L6,7 intervertebral discs was penetrated via the anterior side of intervertebral disc as the experimental intervertebral disc.L5,6 was treated as above, but the posterior annulus fibrosus cannot be penetrated as the positive control intervertebral disc. As the intact control intervertebral disc, the same operation as above was performed on the L4,5 intervertebral discs. MRI scan, discography were performed on the lumbar intervertebral discs of each experimental animal at each experimental time pointsafter operation (3 Weeks, 3 Months and 6 Months).HE and Masson stain was performed, and the morphological characteristics of intervertebral disc nucleus pulposus and posterior lateral annulus fibrosus were observed under light microscope.Nerves in intervertebral discs was examined using immunohistochemistry with SP (nerve transmitter) andPGP9.5 (nerve fibre) antibody.ResultsThe normal structure of posterior interior fibrous annual was kept at each time point for the L4,5 intervertebral discs with annulus fibrosus not injured and the L5,6 intervertebral discs with anterior annulus fibrosus injured. For all the L6,7 intervertebral discs, the posterior annulus fibrosus disruption did not healed. At 3 months and 6 months postoperatively, disruption developed to outer annulus fibrosus.Quantitative and qualitative MRI analysis were performed on the degenerative changes of intact and injured intervertebral discs through the median sagittal T2-weighted image using the methods in reference.All the L5,6 and L6,7 nucleus pulposus signal intensity were lower than the preoperative values, and constantly decreased with time. In all the L6,7 nucleus pulposus, MRI values at each time point were less than those of L5,6, and the difference of MRI index at 6 months was statistically significant (P<0.05).In all L4,5, L5,6, L6,7 discs, nerves were present to the outer one or three lamellae of the anulus fibrosus. Nerves were observed in the right posterior outer 1/4 regions of L6,7 discs easily, in addition, they also were observed further ingrowth into the disc along the puncture tract and periphery tissue, the im-munopositive cells were absent in the same of regions of L4,5 discs. Nerves were rarely seen in L5,6 discs at 3 weeks to 6 months postoperatively. SP^ PGP9.5 immunopositive cells were not observed in the nucleus pulposus of any disc examined.Conclusion(1) After the inner layers of posterior annulus fibrosus of the goats were injured via the anterior side of intervertebral disc, the disruption was diffculty to heal, the intervertebral disc degeneration occurred in the early stage.(2) After the inner layers of posterior annulus fibrosus of the goats wereinjured via the anterior side of intervertebral disc, there were a reliable animal model of intervertebral disc degeneration to be developed.(3) This finding suggests that discogenic low back pain was closely associated with nerve ingrowth.