Experimental Study On The Effect Of Adjacent Segment Intervertebral Disc After Anterior Lumbar Spinal Fusion With Internal Fixation

Objective:Through establishment of the experimental animal model of anterior lumbar spinal fusion with internal fixation,of which to observe the specific effects and change of biochemistry and enzymology, and then to investigate influencing factors and mechanism of adjacent segment intervertebral disc degeneration after lumbar spinal fusion with internal fixation. At the same time, the ultimate and real aim of the experiment is to expect to provide experimental evidence and reference for prevention and treatment of adjacent segment intervertebral disc degeneration and perfection of lumbar spinal fusion with internal fixation.Methods:32 New Zealand adult white rabbits were divided randomly into 4 groups, and each group had 8 rabbits. The 4 groups were as follows: A group: L4/5 intervertebral disc resection + interbody fusion cage replacement,no internal fixation; B group: L4/5 intervertebral disc resection + interbody fusion cage replacement + internal fixation with Ti-plate; C group: L4 vertebral body resection + L3/4 and L4/5 intervertebral disc resection + interbody fusion cage replacement, no internal fixation; D group: L4 vertebral body resection + L3/4 and L4/5 intervertebral disc resection + interbody fusion cage replacement + internal fixation with Ti-plate; Each group was divided randomly into 2 subgroups(3,6months subgroup) after surgery, and each subgroup had 4 rabbits. Standard anteroposterior and lateral lumbar radiographs were taken at 1 week,3 months and 6 months and the rabbits of each subgroup were killed by air embolism at 3 months and 6 months after surgery. After death, intact adjacent segment intervertebral discs were harvested for pathological examination,phloroglucinol spectrophotometric determination of the content change of proteoglycan in nucleus pulposus and determination of the expression of MMP-3 by immunohistochemical SABC method.Results:Single-level and double-level fusion with internal fixation((B,D group) obviously accelerated adjacent segment intervertebral disc degeneration in comparison with corresponding fusion without internal fixation(A,C group). Adjacent segment intervertebral disc degeneration of double-level fusion(C,D group) was more serious than corresponding single-level fusion(A,B group). In each group the cranial segment disc degeneration degree was higher than corresponding caudal segment'. Adjacent segment intervertebral disc degeneration at 6 months was more serious than at 3 months in each group. And all of the above results were significant in statistics by statistics analysis(P﹤0.05). There was significant correlation between the contents of proteoglycan in nucleus pulposus and the expression of MMP-3 in intervertebral disc and intervertebral disc degeneration(P﹤0.01), which was shown as: the contents of proteoglycan in nucleus pulposus decreased more obviously and the expression of MMP-3 in intervertebral disc was higher with the aggravation of intervertebral disc degeneration.Conclusion:Anterior lumbar spinal fusion with internal fixation can result in adjacent segment intervertebral disc degeneration, which is shown as: adjacent segment intervertebral disc degeneration is more serious with the increase of fusion segment,the use of internal fixation and the prolongation of fusion time with internal fixation, and the cranial segment disc degeneration degree is higher than corresponding caudal segment', moreover, it results in the change of the contents of proteoglycan in nucleus pulposus and the expression of MMP-3 in intervertebral disc correlated with the degree of intervertebral disc degeneration.