Effect Of Cervical Internal Fixation And Fusion On Adjacent Segments In Rabbits

At present, spinal fusion has been widely applied in clinical practice, and plays an extremely important role in the treatment of spinal trauma, degenerative disease, congenital spinal deformity, spinal tumor and spinal tuberculosis. However, after spinal fixation and fusion, some patients were found to have radiographic adjacent segment degeneration (ASD). gradually, and even adjacent segment disease that required reoperation at the level above or below the fusion segment. In recent years, scholars have noticed that the spinal fusion can induce adjacent segment degeneration and there is an upsurge of investigating the retention of spinal motion segment. They used new surgical approaches and new methods of artificial nucleus replacement, artificial disc replacement, Minimally invasive surgery and spinal non fusion fixation technique. Meanwhile, many scholars carried out in-depth study on adjacent segment degeneration after fusion from follow-up ob-servation of clinical cases, biomechanical test of cadaver model, animal experimental study.By observing the effect of spinal fusion on adjacent segment degeneration, we can have a deeper understanding of its pathological process in order to further improve the surgical effect, and can plan the conditions before treatment. Current clinical observations are retrospective, and lack of prospective results. Cadaver sample study can simulate a fixed pattern, but cannot reproduce fusion, which is not convincing, the relationship between spinal fusion and adjacent segment degeneration is still contro-versial. Some people think that the ASD is likely to be the natural progression of vertebral degeneration. Animal experiment is a practical choice. But there is still a lack of systematic research in animal models. Currently, successful fixation and fusion is mostly performed on the thoracolumbar part in the animal models. Cervical spine models mostly come from large animals. Because perioperative management of large animals is complex, endotracheal intubation and monitoring may be required. Due to limited space and funding, it is inconvenient to raise a large number of large animals for research. Therefore, the sample size of large animals is not enough to demonstrate the issue. Small animals are easy to raise and affordable, from which large number of samples could be obtained, but whose spine, especially cervical spine is too small to fix and fuse. Thus, successful models with cervical fixation and fusion are rare. We found that the number of activities of rabbit’s cervical spine is much more than that of thoracolumbar part. When reared in the cages, most of the rabbits are in the supine or sitting position. Their cervical spine is in the vertical position, and can better reflect the human spine load than thoracolumbar part. Fixation and fusion should be performed on the cervical spine of models. Compared with cattle, sheep and dogs, rabbits should not be raised in too greater area, and can be reared in great number so that enough samples can be obtained in an economical and convenient way. The cervical spine of rats is too small to have anterior fixation and fusion, and also difficult to observe by X-ray. In this study, it was found that cervical spine surgery in rabbits is fast and minimally invasive, brings little interference to animals, does not require endotracheal intubation and monitoring, and has simple and convenient perioperative management and high survival rate, all of which has provided a strong guarantee for experimental success. So this study used New Zealand white rabbits, and achieved success. In the previous studies, the research group has successfully constructed the anterior cervical fusion fixation model of rabbits, and published a paper.The purpose of this study is on the basis of animal models of successful cervical spine fusion to further investigate the effect of anterior cervical discectomy and fusion (ACDF) of single segment at different levels on adjacent segments of cervical disc in rabbits and its laws, and to explore the mechanism of this change.As seen from the immunohistochemical statistical results of this study of the part one and part two, the difference was not statistically significant in the control group between 3 months and 6 months as well as between 6 months and 9 months, that is, the impact of 3-month aging would not cause the difference. The difference was statistically significant in the experimental groups between 3 months and 6 months as well as between 6 months and 9 months. The difference was statistically significant in 6 months and 9 months between the experimental groups and the control group. Therefore, we believed that fusion and internal fixation in this experiment caused and accelerated degeneration of adjacent segments of intervertebral disc in rabbits. The observations of the effect of anterior single segment fusion at different levels on adjacent segments of intervertebral disc showed:after fusion at the C3-4, C4-5 and C5-6 levels, degeneration occurred in adjacent upper and lower segments; after fusion at the C3-4 and C4-5 levels, the difference was not statistically significant between upper segment and lower segment; after fusion at the C5-6 levels, the difference was statistically significant between upper segment and lower segment, and degeneration was greater in the lower segment than in the upper segment. The results showed that motion compensation of flexion and extension after spinal fusion occurred in adjacent segments, motion compensation at C3-4 and C4-5 levels occurred in upper adjacent segment, motion compensation.PART I Changes of number of collagen type Ⅰ、Ⅱ on adjacent segments in rabbits after anterior cervical discectomy and fusionPurpose This study is to investigate the effect of anterior cervical discectomy with internal fixation and fusion on adjacent segments in rabbits.Methods Sixty New Zealand rabbits were randomly divided into four groups, one control group and three model groups, with 15 in each group. Each group underwent anterior cervical internal fixation and fusion at C3-4, C4-5, and C5-6 levels respectively. Three months after surgery, rabbits from each model group were examined by X-ray. Those with interbody fusion were included in the study while those without interbody fusion were excluded. Then New Zealand White rabbits under the same conditions were additionally taken to the surgery in order to ensure 15 in each group for research. Then five rabbits from each group were sentenced under anesthetic overdose at three, six and nine months after fusion. Immunohistochemistry was utilized to evaluate the effects of different fusion methods on adjacent segments of spine.Results As time went by, in model group, X-ray film can see the fusion of surgical segments. Immunohistochemical results of the intervertebral disc showed that the expression levels of collagen type Ⅱ fibrosus were increased. And collagen type Ⅰ tends to replace collagen type Ⅱ gradually in nucleus pulposus as time goes by. The change in collagen between upper and lower adjacent segments at C3-4 and C4-5 showed no statistical significance after fixation and fusion (p> 0.05). But for C5-6, the change showed statistical significance (p< 0.05). The difference was statistically significant (P<0.05) between the model group and the control group at 6 months and 9 months respectively.Conclusion Cervical internal fixation and fusion can induce intervertebral disc degeneration of adjacent segment in rabbits, and cervical internal fixation and fusion operated at different levels may result in different effects on adjacent segments of cervical intervertebral disc.PART Ⅱ Changes of number of collagen type Ⅰ、Ⅱ on adjacent segments in rabbits after anterior cervical discectomy and fusionPurpose This study is to investigate the effect of posterior cervical internal fixation and fusion on adjacent segments in rabbits.Methods Thirty New Zealand rabbits were randomly divided into two groups, one control group and one model groups, with 15 in each group. Model group underwent posterior cervical internal fixation and fusion at C4-5 levels.Three months after surgery, rabbits from model group were examined by X-ray. Those with interbody fusion were included in the study while those without interbody fusion were excluded. Then New Zealand White rabbits under the same conditions were additionally taken to the surgery in order to ensure 15 in each group for research. Then five rabbits from each group were sentenced under anesthetic overdose at three, six and nine months after fusion. Immunohistochemistry was utilized to evaluate the effects of posterior fusion methods on adjacent segments of spine.Results As time went by, in model group, X-ray film can see the fusion of surgical segments. Immunohistochemical results of the intervertebral disc showed that the expression levels of collagen type II fibrosus were increased. And collagen type I tends to replace collagen type II gradually in nucleus pulposus as time goes by. The change in collagen between upper and lower adjacent segments at C4-5 showed no statistical significance after fixation and fusion (p> 0.05). The difference was statistically significant (P<0.05) between the model group and the control group at 6 months and 9 months respectively.Conclusion Posterior cervical internal fixation and fusion can induce intervertebral disc degeneration of adjacent segment in rabbits.