Dynamic Observation On Adjacent Segments After Cervical Spinal Fusion

The spinal fusion was the vital way to treat clinically spinal tuberculosis, spinal trauma, congenital abnormality and degenerative diseases. A lot of national and international scholars had paid attention to the problem of adjacent segments after spinal fusion. They were becoming increasingly interested in studying how to remain the FSU and developing the new operations of the artificial nucleus pulposus and discus intervertebralis replacement. Meanwhile a few scholars did deep research to the degeneration after spinal fusion by a long time follow-up of many clinical cases and vitodynamics. However, at present there was not a kind of animal model to systematically study for us, moreover, the relationship between the spinal fusion and the adjacent degeneration segments was not clear. By studying why, how and what the process of degeneration was not only could we know the pathological and physiological process but also could do enough preparations before the spinal fusion operation. So in this experiment we tried our best to establish a sort of spinal fusion animal model. In the same condition we used the statistical methods to study the effects and rules of the adjacent segments after spinal fusion excluding effects of the natural degenerations and finally proposed the mechanism and preventive measures. Methods: Sixty clean Sprague-Dawley (SD) rats, which male and female number was equal and all they were 8 months old, were divided into 2 groups randomly which were named Control Group(C-G) and Experimental Group(E-G), 30 in each group. The 30 rats in the experimental group were surgically treated with the following procedures. The animals were anesthetized intraperitoneally with Ketamine (0.15g/kg.weight). Under sterile conditions, the slim bone rods acquired from caudal vertebrae were autograft around transverse process, articular process and vertebral plate of No. 4-5 cervical vertebrae (C4-5). The control groups were treated similarly without grafting bones. 20 SD-rats were choosed from C-G and E-G as the 2ⁿd-Group, the 4^th-group and the 6^th-group. 20 SD-rats were executed with depletion method after the 2 months, the 4 months and the 6 months respectively. From the base of skull to No. 1 thoracic (T₁) vertebra, the samples were obtained, labeled and finally fixed in 10% formaldehyde solution. Then the anteroposteriorand lateral cervical computer radiographs (CR) were taken and observed whether C4.5 was fused or not and what had changed in the adjacent segments. Pathologic histology slices were observed under an 01ympus-H2 light microscope after the samples were decalcified in 72 hours by EDTA, dewatered and transparent by gradient alcohol, steeped and embedded into wax ,cut 5 u m sheets, finally stained with hematoxylin and eosin. The judgement standard if C4.5 was fused or not was that, first, C4.5 was not clear and continuous osteotylus formed; Second, there were no any gross movement across the simulated fusion by manual force; finally, continuous bone trabecula were observed in pathological section. Except all those were not wholly fused every group was assessed according to Miyamoto' grade schema. Thereafter a P value of <0.05 was regarded as significant and two-sample t tests or Wilcoxon rank sum tests were done so as to analysis whether and which two groups were statistical significant.Results: SD-rats have seven cervical vertebras similar to human being. Normal vertebra of 8 month old SD-rats had no degeneration. But there were intervertebral slippage and osteophyma formation in abnormal ones. All C4.5 were fused fully except one in 2nd-group. The percent of fusion was 96.67%.There were not obvious narrow and osteophyma formation in 2nd group and 4th group but there were six cases which vertebral body slipped and osteophyma formed in Luschka joint .In pathological section obvious osteotylus combined C4-5 as one body except one in 2nd month group. Almost all intervertebral and vertebral were normal in 2nd month group and 4th month C-G which vacuolus central pulpy nucleus were surrounded by fibrocartilaginous ring clampped above and under endplates composed by cartilago hyalina. The front fibrocartilaginous ring disappeared and pulpy nucleus shrinked, even disappeared in 4th month E-G and 6th month C-G. The fibrocartilaginous ring broke, pulpy nucleus herniated and intervertebral space becomed narrow in 6th month E-G.Compared between the control-group and experimental-group at the same interval, the degeneration means of 2nd month and 4th month group had no statistical significance with t-test (P2=0.1174>0.05 and P4=0.1063>0.05),but the 6th month group had statistical significance (P6=0.0182<0.05).Meanwhile the degeneration of segments above and under the fusion had no statistical significance with Wilcoxon rank sum test( P=0.1875>0.05). Conclusion: ? The half-round fusion of cervical vertebrae, which reproducibility wasgood and the percentage of fusion was excellent, was successful and fit for the experiment. (2) Cervical intervertebral spinal fusion could accelerate the progression of degeneration of the adjacent segments in a long term but the changes were little in a short time, which required clinical doctors get the message of adjacent segments before spinal fusion operation and take good care and follow-up after operation. (3) The degeneration of segments above and under the fusion was not found different in 6th month experimental group. The result was not identical to other clinical ones which the degeneration segments were often below the fusion. The reasons were, one hand that the natural degeneration of C5.6, C6.7 and C4.5 in human being were often observed, on the other hand SD rats were reptile which required large samples and longer observation time to deep study.